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NIDA Home > Publications > Director's Reports > May, 2010 Index    

Director's Report to the National Advisory Council on Drug Abuse - May, 2010

Research Findings - Intramural Research

Chemistry and Drug Metabolism

Is There a Better Biological Matrix for Drug Monitoring in Drug Treatment, Drug Court, Workplace and Criminal Justice Drug Testing than Urine?
Oral fluid (saliva) is an important new biological matrix for drug monitoring in drug treatment, research trials, workplace, and criminal justice (drug court) programs. This technology was proposed by the Substance Abuse Mental Health Services Administration for approval for drug testing in 2004, but it was never finalized because of the possibility of false positive results from passive inhalation of cannabis smoke. IRP researchers developed and fully validated a new analytical method to monitor the inactive metabolite 11-nor-9-carboxy-Ć9-tetrahydrocannabinol (THCCOOH) in oral fluid in the pg/mL concentration range, as well as the parent THC. THCCOOH is not present in cannabis smoke, documenting that the individual actually metabolized the drug. This could pave the way for approval of this important new matrix that will be highly useful for monitoring drug relapse in treatment programs. In clinical trials of cannabis dependence and evaluation of treatment modalities, drug testing to identify drug relapse is one of the most important objective outcome measures. Unfortunately, following chronic daily cannabis, urinary excretion can be extended for more than 30 days. This makes differentiation of new cannabis use from residual drug excretion highly difficult. Oral fluid testing may be a more effective means of identifying new drug use due to its shorter detection window. Identification of THCCOOH in oral fluid provides a solution to the problem of passive exposure. The authors are now evaluating this method in clinical studies of chronic cannabis users and in controlled drug administration studies, none of which could have been possible without this new analytical method. This paper has important public health consequences. Milman G, Barnes AW, Lowe RW, Huestis MA. Simultaneous quantification of cannabinoids and metabolites in oral fluid by two-dimensional gas chromatography mass spectrometry. Journal of Chromatography A 2010 Feb 26; 1217(9): 1513-1521. Epub 2010 Jan 4.

Clinical Pharmacology and Therapeutics

Nicotine Psychopharmacology Section/Clinical Pharmacology and Therapeutics Branch

Breath Carbon Monoxide and Saliva Cotinine as Biomarkers for Smoking
As a biomarker of smoking, semiquantitative analysis of cotinine (NicAlert¨) offers several advantages over breath carbon monoxide (CO) and quantitative analysis of cotinine. Recent studies have used urine NicAlert¨ and breath CO in combination to verify abstinence. However, no studies have evaluated the performance of saliva NicAlert¨ against or in combination with breath CO. Breath CO, saliva NicAlert¨, and smoking history were compared in an urban population of daily smokers (n = 24) and nonsmokers (n = 25). Saliva NicAlert¨ predicted self-reported smoking with 100% sensitivity and 96% specificity. At a cutoff of > 5 ppm, breath CO had 100% sensitivity and 100% specificity in predicting self-reported smoking. Breath CO was positively correlated with saliva NicAlert¨ and negatively correlated with minutes since last cigarette. Saliva NicAlert¨ had high sensitivity and specificity in identifying daily smokers. Compared to saliva NicAlert¨, breath CO level was more indicative of recent smoking. Future treatment studies should evaluate the performance of saliva NicAlert¨ as an alternative to the urine test. Marrone GF, Paulpillai M, Evans RJ, Singleton EG, Heishman SJ. Breath carbon monoxide and semiquantitative saliva cotinine as biomarkers for smoking. Hum Psychopharmacol Clin Exp. 2010; 25: 80-83.

Puffing Behavior During the Smoking of a Single Cigarette in Tobacco-dependent Adolescents
Adult and adolescent smokers regulate their nicotine and smoke intake by smoking low-yield cigarettes more intensely than high-yield cigarettes. One likely mechanism of nicotine regulation is altered puffing topography, which has been demonstrated in adult smokers. The purpose of this study was to examine the pattern of puffing behavior during the smoking of a single cigarette in adolescents. Tobacco-dependent adolescents (n = 89) were enrolled in a treatment trial testing the efficacy of nicotine replacement therapy. About 1 week before their quit date, participants smoked ad libitum one of their usual brand of cigarettes during a laboratory session. Smoking topography measures included puff volume, puff duration, puff velocity, and interpuff interval. Controlling for sex, race, and number of puffs, puff volume and puff duration decreased 12.8% and 24.5%, respectively, from the first three to the last three puffs. Puff velocity and interpuff interval increased 14.8% and 13.5%, respectively. Puff volume was positively correlated with puff duration and puff velocity, whereas puff duration and puff velocity were negatively correlated. However, none of the topography measures were correlated with smoking history variables. These results suggest that adolescent smokers, like adults, are able to regulate smoke and nicotine intake on a puff-by-puff basis, therefore indicating that this aspect of smoking control is acquired early in the tobacco-dependence process. Collins, CC, Epstein DH, Parzynski CS, Zimmerman D, Moolchan ET, Heishman SJ. Puffing behavior during the smoking of a single cigarette in tobacco-dependent adolescents. Nicotine Tob Res. 2010; 12: 164-167.

Behavioral Neuroscience Research Branch

Amphetamine Administration Into the Ventral Striatum Facilitates Behavioral Interaction With Unconditioned Visual Signals In Rats
Administration of psychomotor stimulants like amphetamine facilitates behavior in the presence of incentive distal stimuli, which have acquired the motivational properties of primary rewards through associative learning. This facilitation appears to be mediated by the mesolimbic dopamine system, which may also be involved in facilitating behavior in the presence of distal stimuli that have not been previously paired with primary rewards. However, it is unclear whether psychomotor stimulants facilitate behavioral interaction with unconditioned distal stimuli. IRP researchers found that noncontingent administration of amphetamine into subregions of the rat ventral striatum, particularly in the vicinity of the medial olfactory tubercle, facilitates lever pressing followed by visual signals that had not been paired with primary rewards. Noncontingent administration of amphetamine failed to facilitate lever pressing when it was followed by either tones or delayed presentation or absence of visual signals, suggesting that visual signals are key for enhanced behavioral interaction. Systemic administration of amphetamine markedly increased locomotor activity, but did not necessarily increase lever pressing rewarded by visual signals, suggesting that lever pressing is not a byproduct of heightened locomotor activity. Lever pressing facilitated by amphetamine was reduced by co-administration of the dopamine receptor antagonists SCH 23390 (D1 selective) or sulpiride (D2 selective). These results suggest that amphetamine administration into the ventral striatum, particularly in the vicinity of the medial olfactory tubercle, activates dopaminergic mechanisms that strongly enhance behavioral interaction with unconditioned visual stimuli. Shin R, Cao J, Webb SM, Ikemoto S. Amphetamine administration into the ventral striatum facilitates behavioral interaction with unconditioned visual signals in rats PLoS One, 2010 Jan 15: 5(1): e8741.

Integrative Neuroscience Section

Signal-Averaged Electrocardiogram In Physically Healthy, Recently Abstinent Chronic Cocaine Users
Cocaine use is associated with cardiac arrhythmias, but predicting who is at risk is difficult. Signal-averaged electrocardiography (SA-ECG), unlike standard ECG, can detect markers of ventricular late potentials (VLP), which may be a precursor to malignant ventricular arrhythmias. IRP scientists evaluated SA-ECG parameters in 60 medically screened, physically healthy, recently abstinent, chronic cocaine users and in 54 non-drug-using controls. SA-ECGs were done periodically for up to 12 weeks of monitored abstinence in 25 of the cocaine users. Cocaine users differed significantly from controls in only one of three SA-ECG parameters considered markers of VLPs. The proportion of subjects with abnormal SA-ECG parameters did not differ significantly between male cocaine users and male controls. There were no significant changes over time in either the mean values or proportion of subjects with abnormal values for any SA-ECG parameter. There were significant gender differences among controls, but not among cocaine users. These findings suggest that chronic cocaine use is not associated with a higher prevalence of abnormal SA-ECG parameters in physically healthy users. Kanneganti P, Copersino ML, Nelson RA, et al. Signal-averaged electrocardiogram in physically healthy, recently abstinent chronic cocaine users. Journal of Addiction Medicine. 2009;3(3):128-133.

Interest In Marijuana Treatment Programs Among Teenage Smokers and Nonsmokers
Many adolescents smoke marijuana, but little is known about adolescents' interest in marijuana treatment programs. IRP scientists evaluated this question by telephone interview in a convenience sample of 575 adolescents (13-17 years old) responding to advertisements for tobacco research studies at the NIDA IRP. 81% of respondents endorsed the need for marijuana treatment programs for adolescents. These adolescents were younger and less likely to smoke tobacco, smoke marijuana, or use alcohol than those not endorsing such a need. Among the 192 marijuana smokers, the 58.8% who endorsed the need for marijuana treatment programs took their first puff of marijuana at a younger age than those who did not endorse the need. Those who were willing to participate in a marijuana treatment program were more likely African-American and took their first marijuana puff at a younger age than those not interested in treatment. These findings suggest that a majority of adolescent marijuana smokers endorse the need for and are willing to attend marijuana treatment programs. Sheer AJ, Gorelick DA, Collins CC, et al. Interest in marijuana treatment programs among teenage smokers and nonsmokers. Journal of Substance Abuse Treatment. 2009; 37(4):421-425.

Behavioral Neuroscience Research Branch

Mu Opioid Receptors in the Ventral Tegmental Area Regulate Somatodendritic Dopamine Release By Affecting GABA and Glutamate Transmission
The rewarding effect of opiates and other drugs of abuse has been attributed to increased dopamine transmission within the mesolimbic system which originates in the ventral tegmental area (VTA) and projects to the nucleus accumbens and prefrontal cortex. The activity of VTA dopamine neurons is controlled by their intrinsic properties, as well as inhibitory and excitatory inputs from local neurons and from other brain areas. Mu opioid receptors are enriched in the VTA and their activation increases dopamine release. Although this effect has been attributed to the activation of opioid receptors on GABA neurons and the resulting disinhibition of dopamine neurons, evidence in support of this hypothesis was obtained in anesthetized animals and slice preparations. Importantly, however, the functional connectivity of these preparations differs from that in the intact or awake animal. Furthermore, the role of mu opioid receptors in modulating glutamate input to the VTA is unclear. The use of in-vivo microdialysis has provided direct neurochemical evidence that activation of mu opioid receptors in the VTA of the freely moving animal produces a concentration-dependent decrease in local GABA levels and an augmentation of somatodendritic dopamine levels. Constitutive deletion of the mu opioid receptor led to an elevation of basal GABA overflow and a reduction in glutamate levels in the VTA. Although, gene deletion did not alter basal somatodendritic dopamine overflow, a significant correlation between basal dopamine levels and the glutamate/GABA ratio in wildtype but not knock out mice was seen. Mu opioid receptors have been implicated in modulating the rewarding effects of various drugs of abuse. Mu opioid receptor knock out mice demonstrate reduced sensitivity to the reinforcing properties of various drugs of abuse, including morphine, heroin, alcohol, δ9-tetrahydrocannabinol, nicotine, and cocaine. The present findings suggest that this reduction may result from loss of the intricate balance between glutamatergic and GABAergic neurotransmission in the VTA. This in turn leads to an increase in the frequency of spontaneous inhibitory postsynaptic currents, a decrease in the firing activity of dopaminergic neurons and inhibition of dopamine release in the nucleus accumbens. Furthermore, they provide new evidence that VTA mu opioid receptors may contribute to addiction vulnerability by modulating GABAergic and glutamatergic inputs to dopaminergic neurons. Chefer VI, Denoroy L, Zapata A, Shippenberg TS. Eur J Neurosci 2009; 30: 272-278.

Delta Opioid Receptor Antagonism Prevents Sensitization to the Conditioned Reinforcing Effects of Morphine
Functional interactions between mu and delta opioid receptors are implicated in the development of morphine tolerance and dependence. Antisense oligonucleotides to the delta opioid receptor attenuate the development of morphine dependence. Similarly, pharmacological antagonism or genetic deletion of this opioid receptor type reduces opiate dependence and analgesic tolerance. Other studies have shown that repeated mu opioid receptor agonist administration increases delta opioid receptor cell surface expression in brain and spinal cord. These data demonstrate that delta opioid receptor function is altered following chronic morphine exposure and suggest that aberrant activity of this opioid receptor system may contribute to the dysregulation of behavior that occurs following repeated administration of morphine and other mu opioid receptor agonists. The contribution of delta opioid receptors to the conditioned rewarding effects of morphine and the enhanced conditioned response that occurs after repeated morphine administration is unknown. This information, however, is important in view of the documented role of environmental stimuli previously associated with opiate administration in drug-craving and relapse to addiction. The present study addressed this issue using the conditioned place preference procedure in rats. Subjects received home cage injections of saline or morphine (5.0 mg/kg/day x 5 days) before conditioning. For sensitization studies, the delta opioid receptor antagonists (DOPr1/2: naltrindole, DOPr2: naltriben, DOPr1: 7-benzylidenenaltrexone) were administered before morphine injections. Conditioning sessions (2 morphine; 2 saline) commenced 3 days later. To assess the influence of acute delta opioid receptor blockade on the conditioning of morphine reward in na•ve animals, 3 morphine and 3 saline conditioning sessions were employed. Antagonists were administered before morphine conditioning sessions. Morphine was ineffective as a conditioning stimulus after two conditioning sessions in na•ve rats. However, doses of 3.0 mg/kg and greater produced significant conditioned place preferences in morphine pre-exposed rats, confirming that sensitization develops to the conditioned rewarding effects of morphine. In animals that received morphine pre-exposure with naltrindole or naltriben but not 7-benzylidenenaltrexone, sensitization was prevented. No attenuation of morphine place conditioning was observed in animals that received delta opioid receptor antagonists acutely, before conditioning sessions. These data indicate a critical role of delta opioid receptor systems in mediating sensitization to the conditioned rewarding effects of morphine. The efficacy of naltrindole and naltriben in preventing the enhanced response to morphine suggest the specific involvement of the delta opioid receptor-2 subtype in the sensitization process. Shippenberg TS, Thompson A, Chefer VI. Biological Psychiatry 2009; 65(2): 169-174.

The Endogenous Cannabinoid, Anandamide, Modulates Dopamine Transporter Function and Cell Surface Expression By a Receptor-Independent Mechanism
Systemic administration of the endocannabinoid, anandamide (AEA), increases extracellular dopamine (DA) concentrations in the nucleus accumbens, a brain region implicated in mediating the abuse liability of various psychoactive drugs. Increased DA concentrations are also observed in response to synthetic cannabinoid agonists. Although these effects have been attributed to alterations in DA release, AEA and other cannabinoids inhibit dopamine uptake in native tissue and heterologous expression systems suggesting that AEA may modulate DA transmission by regulating the DA transporter. The cellular mechanisms mediating the functional interaction of AEA with the dopamine transporter are unclear. The present studies used live cell confocal microsopy and the fluorescent high affinity DA transporter substrate, ASP+ to address this issue. AEA addition to EM4 cells expressing yellow fluorescent protein-tagged human DAT (hDAT) produced a concentration-dependent inhibition of ASP+ accumulation (IC50: 3.2 ± 0.8 μM). This effect occurred within 1 min after AEA addition and persisted for 10 min thereafter. Pertussis toxin did not attenuate the effects of AEA suggesting a mechanism independent of Gi/Go coupled receptors. Amidohydrolase inhibiton failed to alter the AEA-evoked inhibition of ASP+ accumulation. Methanandamide, a metabolically stable analogue of AEA inhibited accumulation whereas arachidonic acid was without effect suggesting that the effects of AEA are not mediated by its metabolic products. The extent of AEA inhibition of ASP+ accumulation was not altered in cells pre-treated with a specific and potent fatty acid amide hydrolase inhibitor or with the cyclooxygenase inhibitor, indomethacin. Live cell imaging revealed a significant redistribution of the transporter from the membrane to the cytosol in response to AEA treatment consistent with transporter internalization. Similarly biotinylation experiments revealed that the decrease in DA transporter function was associated with a reduction in transporter cell surface expression. These results demonstrate that AEA modulates dopamine transporter function via a cannabinoid receptor-independent mechanism and suggest that AEA may produces this effect, in part, by modulating transporter trafficking. These findings add to a growing body of evidence indicating cannabinoid receptor-independent actions of AEA. Additional studies examining the role of transporter regulation to AEA-evoked alteration in of DA transmission function observed in-vivo are warranted. Oz M, Jaligam V, Galadari S, Petroianu G, Shuba YM, Shippenberg TS. J Neurochem 2010; 112: 1454 - 1464. Preclinical Pharmacology Section

Animal Models
This book chapter provides an overview of animal models used to study drug addiction, focusing on two important elements of these models: reinforcement and the effects of environmental cues. The reinforcing effects of drugs are believed to be responsible for the development of drug abuse. Features of the environment that are associated with the drug's reinforcing effects are believed to guide and maintain the long chains of behavior required to ingest the drug, and they may also induce relapse to drug use after a period of abstinence. Drug self-administration is the gold standard among the available models. The chapter describes how the schedule of reinforcement (which stipulates the relationship between behavior, environmental cues, and drug delivery within the self-administration procedure) can be manipulated to focus on specific aspects of addiction. Other models are also described and compared, including conditioned place preference, drug discrimination, intracranial electrical self-stimulation, and locomotor sensitization. When combined with neuroscience techniques, these animal models allow researchers to study the relationships between behavior and the underlying brain mechanisms involved in all stages of addiction. Panlilio LV, Schindler CW, Goldberg SR. Animal Models. In PG Miller, J Strang, PM Miller (Eds), Addiction Research Methods, pp. 269-284. Oxford, England: Blackwell Publishing Ltd., 2010.

Dopaminergic Augmentation of Delta-9-tetrahydrocannabinol (THC) Discrimination: Possible Involvement of D(2)-induced Formation of Anandamide
Although delta-9-tetrahydrocannabinol (THC)-induced elevations in accumbal dopamine levels are believed to play an important role in the abuse-related effects of cannabis, little direct evidence has been provided that the dopaminergic system is involved in the psychotropic effects of THC. The objective of this study is to investigate whether drugs activating or blocking the dopaminergic system modulate the discriminative effects of THC. In rats that had learned to discriminate 3 mg/kg of THC from vehicle injections, the indirect dopaminergic agonists cocaine and amphetamine, the D(1)-receptor agonist SKF-38393, and the D(2)-receptor agonists quinpirole and apomorphine did not produce significant THC-like discriminative effects. However, both cocaine and amphetamine and D(2)-, but not the D(1)-, receptor agonists, augmented THC discrimination. Neither the D(1)-receptor antagonist SCH-23390 nor the D(2)-receptor antagonist raclopride reduced the discriminative effects of THC, even at doses that significantly depressed baseline operant responding. However, the D(2)-, but not the D(1)-, antagonist counteracted the augmentation of THC's discriminative effects produced by cocaine and amphetamine. The authors hypothesized that release of anandamide by activation of D(2) receptors was responsible for the observed augmentation of THC discrimination. This hypothesis was supported by two findings. First, the cannabinoid CB(1)-receptor antagonist rimonabant blocked quinpirole-induced augmentation of THC discrimination. Second, inhibition of anandamide degradation by blockade of fatty acid amide hydrolase augmented the THC-like effects of quinpirole. The authors conclude that dopamine does not play a major role in THC discrimination. However, activation of the dopaminergic system positively modulates the discriminative effects of THC, possibly through D(2)-induced elevations in brain levels of anandamide. Solinas M, Tanda G, Wertheim CE, Goldberg SR. Psychopharmacology, 2010, 209(2): 191-202.

Effects Of Cannabinoid Receptor Antagonists On Maintenance and Reinstatement Of Methamphetamine Self-Administration In Rhesus Monkeys
Cannabinoid receptor antagonists have shown some promise as treatments capable of reducing abuse and relapse to a number of abused drugs. In rodents, such effects have been observed with methamphetamine self-administration. However, the effects of cannabinoid receptor antagonists on methamphetamine self-administration and relapse have not been studied in primates. In the present study, rhesus monkeys were trained to respond on a three-component operant schedule. During the first 5-min component, fixed-ratio responses were reinforced by food, during the second 90- or 180-min component fixed-ratio responses were reinforced by i.v. methamphetamine. The third component was identical to the first. There was a 5-min timeout between each component. The effects of the cannabinoid receptor antagonists AM 251 and rimonabant were tested at various doses against self-administration of 3microg/kg/injection methamphetamine, and 1mg/kg AM 251 and 0.3mg/kg rimonabant were tested against the methamphetamine dose-effect function. The 1mg/kg dose of AM 251 was also tested for its ability to alter reinstatement of extinguished self-administration responding. The cannabinoid receptor antagonist AM 251 was found to reduce methamphetamine self-administration at doses that did not affect food-reinforced responding. The cannabinoid receptor antagonist rimonabant had similar, but less robust effects. AM 251 also prevented reinstatement of extinguished methamphetamine seeking that was induced by re-exposure to a combination of methamphetamine and methamphetamine-associated cues. These results indicate that cannabinoid receptor antagonists might have therapeutic effects for the treatment of methamphetamine dependence. Schindler CW, Panlilio LV, Gilman JP, Justinova Z, Vemuri VK, Makriyannis A, Goldberg SR. European Journal of Pharmacology, 2010, 633: 44-49.

Methamphetamine Self-Administration Is Associated With Persistent Biochemical Alterations In Striatal and Cortical Dopaminergic Terminals In the Rat
Methamphetamine (meth) is an illicit psychostimulant that is abused throughout the world. Repeated passive injections of the drug given in a single day or over a few days cause significant and long-term depletion of dopamine and serotonin in the mammalian brain. Because meth self-administration may better mimic some aspects of human drug-taking behaviors, IRP researchers examined to what extent this pattern of drug treatment might also result in damage to monoaminergic systems in the brain. Rats were allowed to intravenously self-administer meth (yoked control rats received vehicle) 15 hours per day for 8 days before being euthanized at either 24 hours or at 7 and 14 days after cessation of drug taking. Meth self-administration by the rats was associated with a progressive escalation of daily drug intake to 14 mg/kg per day. Animals that self-administered meth exhibited dose-dependent decreases in striatal dopamine levels during the period of observation. In addition, there were significant reductions in the levels of striatal dopamine transporter and tyrosine hydroxylase proteins. There were also significant decreases in the levels of dopamine, dopamine transporter, and tyrosine hydroxylase in the cortex. In contrast, meth self-administration caused only transient decreases in norepinephrine and serotonin levels in the two brain regions, with these values returning to normal at seven days after cessation of drug taking. Importantly, meth self-administration was associated with significant dose-dependent increases in glial fibrillary acidic protein in both striatum and cortex, with these changes being of greater magnitude in the striatum. These results suggest that meth self-administration by rats is associated with long-term biochemical changes that are reminiscent of those observed in post-mortem brain tissues of chronic meth abusers. Krasnova IN, Justinova Z, Ladenheim B, Jayanthi S, McCoy MT, Barnes C, Warner JE, Goldberg SR, Cadet JL. PLoS One, 2010, 5(1): e8790.

Role of the Central Ascending Neurotransmitter Systems in the Psychostimulant Effects of Caffeine
Caffeine is the most consumed psychoactive drug in the world. It is a non-selective adenosine receptor antagonist that in the brain targets mainly adenosine A_{1} and A_{2A} receptors. The same as classical psychostimulants, caffeine produces motor-activating, reinforcing and arousing effects. This depends on the ability of caffeine to counteract multiple effects of adenosine in the central ascending neurotransmitter systems. Motor and reinforcing effects depend on the ability of caffeine to release pre- and postsynaptic brakes that adenosine imposes on the ascending dopaminergic system. By targeting A_{1}-A_{2A} receptor heteromers in striatal glutamatergic terminals and A_{1} receptors in striatal dopaminergic terminals (presynaptic brake), caffeine induces glutamate-dependent and glutamate-independent release of dopamine. These presynaptic effects of caffeine are potentiated by the release of the postsynaptic brake imposed by antagonistic interactions in the striatal A_{2A}-D_{2} and A_{1}-D_{1} receptor heteromers. Arousing effects of caffeine depend on the blockade of multiple inhibitory mechanisms that adenosine, as an endogenous sleep-promoting substance, exerts on the multiply interconnected ascending arousal systems. Those mechanisms include a direct A_{1}-receptor mediated modulation of the corticopetal basal forebrain system and an indirect A_{2A}-receptor mediated modulation of the hypothalamic histaminergic and orexinergic systems. FerrŽ S. J Alzheimers Dis. 2010 Feb 24. [Epub ahead of print]

Oligomerization of G-protein-coupled Receptors: A Reality
G-protein-coupled receptors (GPCRs) have been classically perceived as receptors that do not Ôneed' to oligomerize to be functional, to execute their basic function of transducing a signal from ligand binding to G-protein activation. In fact, recent studies have shown that monomers of class A GPCRs (adrenergic beta2, rhodopsin, and opioid mu receptors) reconstituted in lipid vesicles couple and activate their respective G proteins upon agonist binding. Also monomeric rhodopsin in solution can activate its G-protein transducin. Nevertheless, the authors have now an important amount of experimental evidence that indicates that GPCR oligomerization, including homomerization and heteromerization, is a general phenomenon and it still needs to be determined if GPCR monomers are functionally present in the cellular plasma membrane. Ferre S, Franco R. Current Opinion in Pharmacology, 2010, 10(1): 105.

Chemical Biology Research Branch

Evidence That Intrathecal Morphine-3-Glucuronide May Cause Pain Enhancement
Via Toll-Like Receptor 4/MD-2 and Interleukin-1β Morphine-3-glucoronide (M3G) is a major morphine metabolite detected in cerebrospinal fluid of humans receiving systemic morphine. M3G has little-to-no affinity for opioid receptors and induces pain by unknown mechanisms. The pain enhancing effects of M3G have been proposed to significantly and progressively oppose morphine analgesia as metabolism ensues. IRP scientists have recently documented that morphine activates toll-like receptor 4 (TLR4), beyond its classical actions on mu-opioid receptors. This suggests that M3G may similarly activate TLR4. This activation could provide a novel mechanism for M3G-mediated pain enhancement, as (a) TLR4 is predominantly expressed by microglia in spinal cord and (b) TLR4 activation releases pain-enhancing substances, including interleukin-1 (IL-1). IRP scientists present in vitro evidence that M3G activates TLR4, an effect blocked by TLR4 inhibitors, and that M3G activates microglia to produce IL-1. In vivo, intrathecal M3G (0.75 microg) induced potent allodynia and hyperalgesia, blocked or reversed by interleukin-1 receptor antagonist, minocycline (microglial inhibitor), and (+)-and (-)-naloxone. This latter study extends the authors' prior demonstrations that TLR4 signaling is inhibited by naloxone nonstereoselectively. These results with (+)-and (-)-naloxone also demonstrate that the effects cannot be accounted for by actions at classical, stereoselective opioid receptors. Hyperalgesia (allodynia was not tested) and in vitro M3G-induced TLR4 signaling were both blocked by 17-DMAG, an inhibitor of heat shock protein 90 (HSP90) that can contribute to TLR4 signaling. Providing further evidence of proinflammatory activation, M3G upregulated TLR4 and CD11b (microglial/macrophage activation marker) mRNAs in dorsal spinal cord as well as IL-1 protein in the lumbosacral cerebrospinal fluid. Finally, in silico and in vivo data support that the glucuronic acid moiety is capable of inducing TLR4/MD-2 activation and enhanced pain. These data provide the first evidence for a TLR4 and IL-1 mediated component to M3G-induced effects, likely of at least microglial origin. Lewis SS, Hutchinson MR, Rezvani N, Zhang Y, Maier SF, Rice KC, Watkins LR. Neuroscience. 2010 Jan 20; 165(2): 569-583.

Possible Involvement Of Toll-Like Receptor 4/Myeloid Differentiation Factor-2 Activity Of Opioid Inactive Isomers Causes Spinal Proinflammation and Related Behavioral Consequences
Opioid-induced glial activation and its proinflammatory consequences have been associated with both reduced acute opioid analgesia and the enhanced development of tolerance, hyperalgesia and allodynia following chronic opioid administration. Intriguingly, recent evidence demonstrates that these effects can result independently from the activation of classical, stereoselective opioid receptors. Here, a structurally disparate range of opioids cause activation of signaling by the innate immune receptor toll like receptor 4 (TLR4), resulting in proinflammatory glial activation. In the present series of studies, IRP investigators demonstrate that the (+)-isomers of methadone and morphine, which bind with negligible affinity to classical opioid receptors, induced upregulation of proinflammatory cytokine and chemokine production in rat isolated dorsal spinal cord. Chronic intrathecal (+)-methadone produced hyperalgesia and allodynia, which were associated with significantly increased spinal glial activation (TLR4 mRNA and protein) and the expression of multiple chemokines and cytokines. Statistical analysis suggests that a cluster of cytokines and chemokines may contribute to these nociceptive behavioral changes. Acute intrathecal (+)-methadone and (+)-morphine were also found to induce microglial, interleukin-1 and TLR4/myeloid differentiation factor-2 (MD-2) dependent enhancement of pain responsivity. In silico docking analysis demonstrated (+)-naloxone sensitive docking of (+)-methadone and (+)-morphine to human MD-2. Collectively, these data provide the first evidence of the pro-nociceptive consequences of small molecule xenobiotic activation of spinal TLR4 signaling independent of classical opioid receptor involvement. Hutchinson MR, Lewis SS, Coats BD, Rezvani N, Zhang Y, Wieseler JL, Somogyi AA, Yin H, Maier SF, Rice KC, Watkins LR. Neuroscience. 2010 Feb 21. [Epub ahead of print]

Effects Of Kappa Opioids In An Assay Of Pain-Depressed Intracranial Self-Stimulation In Rats
Selective, centrally acting kappa opioid agonists produce antinociception in a wide range of preclinical assays, but these compounds perform poorly as analgesics in humans. This discrepancy may be related to the behavioral depressant effects of kappa agonists. Kappa antagonists do not typically produce antinociception, but they produce antidepressant-like effects in some preclinical assays. The objective of this study was to test the hypothesis that the kappa agonist U69,593 and the kappa antagonist norbinaltorphimine would produce pronociceptive and antinociceptive effects, respectively, in an assay of pain-depressed behavior. Effects of U69,593 (0.056-0.56 mg/kg), norbinaltorphimine (10-32 mg/kg), and morphine (3.2 mg/kg) were evaluated on the stimulation of a stretching response and the depression of intracranial self-stimulation (ICSS) of the medial forebrain bundle produced in rats by a common noxious stimulus (intraperitoneal administration of dilute lactic acid). U69,593 produced a dose-dependent blockade of acid-stimulated stretching but only exacerbated acid-induced depression of ICSS. Thus, U69,593 produced antinociception in the assay of pain-stimulated behavior but pronociceptive effects in the assay of pain-depressed behavior. Norbinaltorphimine did not alter acid-stimulated stretching or acid-induced depression of ICSS. The mu opioid agonist morphine blocked both acid-stimulated stretching and acid-induced depression of ICSS. These results support the hypothesis that prodepressant effects of kappa agonists may limit their clinical utility as analgesics. These results do not support the use of kappa antagonists to treat depressant effects of pain. These findings illustrate the potential value of using complementary assays of pain-stimulated and pain-depressed behaviors for preclinical evaluation of candidate analgesics. Negus SS, Morrissey EM, Rosenberg M, Cheng K, Rice KC. Psychopharmacology (Berl). 2010 Jan 26. [Epub ahead of print]

Modulation Of Delta Opioid Agonist-Induced Antinociception By Repeated Morphine Pretreatment In Rhesus Monkeys
Repeated treatment with morphine increases antinociceptive effects of delta opioid agonists in rodents by a mechanism that may involve increased cell-surface expression of delta receptors. The present study evaluated effects of repeated morphine treatment on behavioral effects of the delta agonist SNC80 and the mu agonist fentanyl in rhesus monkeys. In an assay of schedule-controlled responding, three monkeys responded for food reinforcement under a fixed-ratio 30 schedule. In an assay of thermal nociception, tail-withdrawal latencies were evaluated in three monkeys using thermal stimulus intensities of 48 and 54 degrees C. In both assays, the effects of SNC80 (0.032-3.2mg/kg) and fentanyl (0.001-0.056 mg/kg) were evaluated after repeated treatment with saline or a regimen of morphine doses modeled on the regimen that enhanced delta agonist antinociception and apparent delta receptor availability in previous rodent studies. Both SNC80 and fentanyl dose-dependently decreased rates of schedule-controlled responding, and repeated morphine treatment did not significantly alter these effects. In the assay of thermal nociception, SNC80 had little effect on tail-withdrawal latencies from water heated to 48 or 54 degrees C, whereas fentanyl increased tail-withdrawal latencies at both temperatures. Repeated morphine tended to increase the antinociceptive effects of SNC80 and to decrease the antinociceptive effects of fentanyl, but these effects of repeated morphine were small and were significant only at the higher stimulus intensity (54 degrees C). These results provide limited support for the proposition that prior stimulation of mu receptors selectively increases the antinociceptive effects of delta agonists in rhesus monkeys. Negus SS, Banks ML, Folk JE, Rice KC. Life Sci. 2010 Mar 13; 86(11-12):385-392. Epub 2010 Jan 21.

Differential Effects of Serotonin 5-HT1A Receptor Agonists on the Discriminative Stimulus Effects of the 5-HT2A Receptor Agonist 1-(2,5-Dimethoxy-4-methylphenyl)-2-aminopropane in Rats and Rhesus Monkeys
Although many drugs act by indirectly stimulating multiple receptors (e.g., reuptake inhibitors), relatively little is known about interactions between agonism at different receptors. This study compared the effect of serotonin (5-HT)(1A) receptor agonists with the discriminative stimulus effects of the 5-HT(2A) receptor agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) in rats and rhesus monkeys. Eight rats discriminated 0.56 mg/kg i.p. DOM and responded under a fixed ratio (FR) 10 schedule of food presentation, whereas three rhesus monkeys discriminated 0.32 mg/kg s.c. DOM and responded under an FR 5 schedule of stimulus shock termination. DOM and the 5-HT(2A) receptor agonists 2,5-dimethoxy-4-n-propylthiophenethylamine (2C-T-7) and dipropyltryptamine (DPT), but not the 5-HT(1A) receptor agonists 8-hydroxy-2-(di-npropylamino) tetralin hydrochloride (8-OH-DPAT) and 3-chloro-4-fluorophenyl-(4-fluoro-4-([(5-methyl-6-methylaminopyridin-2-ylmethyl) amino) methyl] piperidin-1-yl) methanone (F13714), occasioned responding on the DOM-associated lever in rats and monkeys. Both 8-OH-DPAT and F13714 attenuated the discriminative stimulus effects of DOM in monkeys but not in rats; these effects of 8-OH-DPAT and F13714 were prevented by the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide (WAY 100635). DPT and 2C-T-7 enhanced the discriminative stimulus effects of DOM in rats and monkeys in an additive manner. Taken together, the results suggest that the DOM discriminative stimulus is pharmacologically similar and mediated by 5-HT(2A) receptors in rats and monkeys; however, the ability of 5-HT(1A) receptor agonists to modify the effects of DOM is markedly different between these species. These results indicate possible differences in the neurobiology of 5-HT systems that could be important for studying drugs that have multiple mechanisms of action (e.g., reuptake inhibitors that indirectly stimulate multiple receptors). Li JX, Koek W, Rice KC, France CP. J Pharmacol Exp Ther. 2010 Apr; 333(1): 244-252. Epub 2010 Jan 6.

Synthesis and Preliminary Biochemical Evaluation of Novel Derivatives of PCP
(±)-Trans-Ph/Et and (±)-cis-Ph/Et 1-(2-ethyl-1-phenylcyclohexyl)piperidine were synthesized from 2-ethylcyclohexanone. In contrast to the corresponding trans-substituted 2-methyl compound which is 5x more potent than PCP, the trans-2-ethyl derivative has a 75x lower affinity for the PCP binding site. The cis-2-ethyl isomer is inactive like the cis-2-methyl derivative. (±)-1-(1- Phenylcyclohexyl)-2-methylpiperidine is almost as active as the parent PCP. Reduction of the aromatic ring or quaternization of the piperidine in PCP reduces the affinity for the PCP site. Linders JTM, Furlano DC, Mattson MV, Jacobson AE, Rice KC. Letters In Drug Design and Discovery 2010; 7: 79-87.

Cellular Neurobiology Research Branch

Development and Plasticity Section, Cellular Neurobiology Research Branch

Prenatal Exposure To Cocaine Causes Cytoarchitectural Alterations In The Developing Neocortex
Previously, IRP scientists reported that cocaine inhibits neural progenitor cell proliferation through oxidative endoplasmic reticulum stress and consequent down-regulation of cyclin A, whereas cyclin A expression was increased in astrocytes. In the present study, cell type-specific responses to cocaine were further explored. Gene expression profiles were examined in 5 types of cells obtained from the human fetal cerebral cortex at 20 weeks gestation. Cells were treated with 100 μM cocaine in vitro for 24 hours, followed by gene expression analysis using a human neural/stem cell/drug abuse-focused cDNA array, with verification by quantitative real-time reverse-transcriptase polymerase chain reaction. Cocaine influenced transcription of distinct categories of genes in a cell type-specific manner. Cocaine down-regulated cytoskeleton-related genes including ezrin, γ2 actin, α3d tubulin, and α8 tubulin in neural and/or A2B5+ progenitor cells. In contrast, cocaine modulated immune and cell death-related genes in microglia and astrocytes. In microglia, cocaine up-regulated the immunoregulatory and proapoptotic genes interleukin-1β and BCL2-associated X protein. In astrocytes, cocaine down-regulated the immune response gene glucocorticoid receptor and up-regulated the antiapoptotic genes 14-3-3 ε and HVEM. Therefore, cell types comprising the developing neocortex show differential responses to cocaine. These data suggest that cocaine causes cytoskeletal abnormalities leading to disturbances in neural differentiation and migration in progenitor cells, while altering immune and apoptotic responses in glia. Understanding the mechanisms of cocaine's effects on human central nervous system cells may help in the development of therapeutic strategies to prevent or ameliorate cocaine-induced impairments in fetal brain development. Gene expression profiling reveals distinct cocaine-responsive genes in human fetal CNS cell types. Lee CT, Lehrmann E, Hayashi T, Amable R, Tsai SY, Chen J, Sanchez J, Shen J, Becker KG, Freed WJ. J Addict Med 2010; 3(4): 218-226.

Pathobiology Research Section, Cellular Neurobiology Research Branch

Opioids Have Been Demonstrated To Play An Important Role In CNS Development By Affecting Proliferation and Differentiation In Various Types Of Neural Cells
This study examined the effect of a stable delta opioid peptide [D-Ala(2), D-Leu(5)]-enkephalin (DADLE) on proliferation and differentiation in an AF5 CNS neural progenitor cell line derived from rat mesencephalic cells. DADLE (1 pM, 0.1 nM, or 10 nM) caused a significant growth inhibition on AF5 cells. The opioid antagonist naltrexone at 0.1 nM also caused growth inhibition in the same cells. When DADLE and naltrexone were both added to the AF5 cells, the resultant growth inhibition was apparently additive. DADLE alone or DADLE in combination with naltrexone did not cause apoptosis as evidenced by negative TUNEL staining. The cell-cycle progression analysis indicated that both DADLE (0.1 nM) and naltrexone (0.1 nM) caused an arrest of AF5 cell cycle progression at the G1 checkpoint. Neuronal marker indicated that DADLE- or naltrexone-treated AF5 cells tend to differentiate more when compared to controls. Results demonstrate the nonopioid action of both DADLE and naltrexone on cell cycle arrest and differentiation in a CNS neural progenitor cell line. Results also suggest some potential utilization of DADLE and/or naltrexone in stem cell research. Tsai SY, Lee CT, Hayashi T, Freed WJ, Su TP. Delta opioid peptide DADLE and naltrexone cause cell cycle arrest and differentiation in a CNS neural progenitor cell line. Synapse 2010; 64(4):267-273.

Cholesterol At the Endoplasmic Reticulum: Roles Of the Sigma-1 Receptor Chaperone and Implications Thereof In Human Diseases
Despite substantial data elucidating the roles of cholesterol in lipid rafts at the plasma membrane, the roles of cholesterol and related lipids in lipid raft microdomains at the level of subcellular membrane, such as the endoplasmic reticulum (ER) membrane, remain less understood. Growing evidence, however, begins to unveil the importance of cholesterol and lipids on the lipid raft at the ER membrane. A few ER proteins including the sigma-1 receptor chaperone were identified at lipid raft-like microdomains of the ER membrane. The sigma-1 receptor, which is highly expressed at a subdomain of ER membrane directly apposing mitochondria and known as the mitochondria-associated ER membrane or MAM, has been shown to associate with steroids as well as cholesterol. The sigma-1 receptor has been implicated in ER lipid metabolisms/transports, lipid raft reconstitution at the plasma membrane, trophic factor signalling, cellular differentiation, and cellular protection against beta-amyloid-induced neurotoxicity. Recent studies on sigma-1 receptor chaperones and other ER proteins clearly suggest that cholesterol, in concert with those ER proteins, may regulate several important functions of the ER including folding, degradation, compartmentalization, and segregation of ER proteins, and the biosynthesis of sphingolipids. Hayashi T, Su TP. Cholesterol at the endoplasmic reticulum: Roles of the sigma-1 receptor chaperone and implications thereof in human diseases. Subcell Biochem. 2010; 51: 381-398.

Sigma-1 Receptors Regulate Hippocampal Dendritic Spine Formation Via A Free Radical-Sensitive Mechanism Involving Rac1xGTP Pathway
Sigma-1 receptors (Sig-1Rs) are endoplasmic reticulum (ER)-resident proteins known to be involved in learning and memory. Dendritic spines in hippocampal neurons play important roles in neuroplasticity and learning and memory. This study tested the hypothesis that Sig-1Rs might regulate denritic spine formation in hippocampal neurons and examined potential mechanisms therein. In rat hippocampal primary neurons, the knockdown of Sig-1Rs by siRNAs causes a deficit in the formation of dendritic spines that is unrelated to ER Ca(2+) signaling or apoptosis, but correlates with the mitochondrial permeability transition and cytochrome c release, followed by caspase-3 activation, Tiam1 cleavage, and a reduction in Rac1. GTP. Sig-1R-knockdown neurons contain higher levels of free radicals when compared to control neurons. The activation of superoxide dismutase or the application of the hydroxyl-free radical scavenger N-acetyl cysteine (NAC) to the Sig-1R-knockdown neurons rescues dendritic spines and mitochondria from the deficits caused by Sig-1R siRNA. Further, the caspase-3-resistant TIAM1 construct C1199DN, a stable guanine exchange factor able to constitutively activate Rac1 in the form of Rac1.GTP, also reverses the siRNA-induced dendritic spine deficits. In addition, constitutively active Rac1.GTP reverses this deficit. These results implicate Sig-1Rs as endogenous regulators of hippopcampal dendritic spine formation and suggest a free radical-sensitive ER-mitochondrion-Rac1.GTP pathway in the regulation of dendritic spine formation in the hippocampus. Tsai SY, Hayashi T, Harvey BK, Wang Y, Wu WW, Shen RF, Zhang Y, Becker KG, Hoffer BJ, Su TP. Sigma-1 receptors regulate hippocampal dendritic spine formation via a free radical-sensitive mechanism involving Rac1xGTP pathway. Proc Natl Acad Sci USA. 2009; 106(52): 22468-22473.

Proteomics Unit, Cellular Neurophysiology Section, Cellular Neurobiology Research Branch

Localization and Imaging of Sialylated Glycosphingolipids in Brain Tissue Sections by MALDI Mass Spectrometry
In this study, IRP researchers describe a simple and efficient method for mapping the distribution and localization of all sialylated sphingoglycolipids present in coronal mouse brain sections using a conventional axial MALDI-TOF. A single scan of a histological tissue section gives a complete profile of ganglioside species, without derivatization or labeling. IRP researchers have developed and tested a new matrix preparation (2,6-dihydroxyacetophenone (DHA)/ammonium sulfate/ heptafluorobutyric acid (HFBA)) to maximize the detection of all ganglioside species, the ammonium sulfate limits the formation of salt adducts while the addition of HFBA increases the stability of DHA in vacuum thus facilitating imaging applications. These results, in both extracted samples and whole tissue sections using negative ion reflectron and linear mode, show differences in localization in several brain regions depending on the sialic acids and the ceramide associated core gangliosides. Colsch B, Woods AS. Localization and imaging of sialylated glycosphingolipids in brain tissue sections by MALDI Mass Spectrometry. Glycobiology. 2010 Feb 28. [Epub ahead of print]

Simultaneous Imaging Of Small Metabolites and Lipids In Rat Brain Tissues At Atmospheric Pressure By Laser Ablation Electrospray Ionization Mass Spectrometry
Atmospheric pressure imaging mass spectrometry is a rapidly expanding field that offers advantages in the ability to study biological systems in their native condition, simplified sample preparation, and high-throughput experiments. In laser ablation electrospray ionization (LAESI), the native water molecules in biological tissues facilitate sampling by a focused mid-infrared laser beam. The ionization of the ablated material is accomplished by electrospray postionization. In this work, IRP scientists demonstrate that the imaging variant of LAESI simultaneously provides lateral distributions for small metabolites and lipids directly in rat brain sections. To cope with the fragile nature and potential dehydration of the brain tissue due to drying in the ambient environment as well as to minimize analyte redistribution, a Peltier cooling stage is integrated into the LAESI imaging system. The authors demonstrate the utility of high-resolution (m/Deltam > 6000) time-of-flight mass spectrometry with LAESI to deconvolute spatial distributions of different chemical species with identical nominal mass. To help with the evaluation of the massive data sets, Pearson colocalization maps are calculated for selected small metabolites and lipids. The authors show that this approach reveals biologically meaningful correlations between these two classes of biomolecules. Nemes P, Woods AS, Vertes A. Simultaneous imaging of small metabolites and lipids in rat brain tissues at atmospheric pressure by laser ablation electrospray ionization mass spectrometry. Anal Chem. 2010; 82(3): 982-988.

Molecular Neurobiology Research Branch

Editor, Addiction Reviews 2 Annals of the New York Academy of Sciences, v 1187, 2010 appeared online February, 2010
This volume provides 19 state of the art reviews relevant to addictions from US, EU and Asian authors in this series, for which Dr Uhl is the founding editor. It initiates a new section "places in the addictions" for which the inagural article describes the Office of National Drug Control Policy.

David SP, Mezuk B, Zandi PP, Strong D, Anthony JC, Niaura R, Uhl GR, Eaton WW. Sex differences in TTC12/ANKK1 haplotype associations with daily tobacco smoking in Black and White Americans. Nicotine Tob Res. 2010 Mar;12(3):251-62. Epub 2010 Feb 4.

This paper describes gender differences in effects of DRD2 locus haplotypes on smoking in ECA study participants from Baltimore.

Drgon T, Zhang PW, Johnson C, Walther D, Hess J, Nino M, Uhl GR. Genome wide association for addiction: replicated results and comparisons of two analytic approaches. PLoS One. 2010 Jan 21;5(1):e8832.

This paper describes 1M SNP genome wide association studies in MNB subjects who were dependent on at least one illegal substance vs controls, as well as the convergence of these results using two distinct analytic approaches to this "nontemplate" genome wide association method. This extensive work provides the first report of genome wide association results with this density of SNPs, validates the pooling method as used herein, and confirms many other modest sized effects on individual differences in vulnerability to developing dependence on an addictive substance. While there is no large effect at any specific locus, this work provides the most up to date and densest information on molecular genetics of illicit substance dependence.

Jones JD, Hall FS, Uhl GR, Riley AL. Dopamine, norepinephrine and serotonin transporter gene deletions differentially alter cocaine-induced taste aversion. Pharmacol Biochem Behav. 2010 Feb;94(4):580-587. Epub 2009 Dec 4. Stimulants produce aversive effects, which can be identified in conditioned taste aversion assays, as well as rewarding effects. This paper describes, for the first time, differences in the aversive effects of stimulants when NET, DAT or SERT are deleted.

Li B, Arime Y, Hall FS, Uhl GR, Sora I. Impaired spatial working memory and decreased frontal cortex BDNF protein level in dopamine transporter knockout mice. Eur J Pharmacol. 2010 Feb 25;628(1-3):104-107. Epub 2009 Nov 22. Neurotrophins including BDNF are associated with altered mnemonic processes. This work with Japanese collaborators studies a possible contribution of BDNF to the altered mnemonic processes that we and others have identified in DAT KO mice.

Drgonova J, Zimonjic DB, Hall FS, Uhl GR. Effect of KEPI (Ppp1r14c) deletion on morphine analgesia and tolerance in mice of different genetic backgrounds: when a knockout is near a relevant quantitative trait locus. Neuroscience. 2010 Feb 3;165(3):882-895. Epub 2009 Oct 9.

This paper describes contributions of deletion of a morphine-regulated protein phosphatase 1 inhibitor (KEPI) that was discovered in MNB to behavioral adaptations to morphine, as well as other behaviors. In addition, it identifies and provides a novel method for eliminating the effects of nearby genetic background (since the KEPI gene is close to that for the mu opiate receptor whose variants do provide a major quantitative trait locus for morphine effects in mice strains).

Psychobiology Section, Medications Discovery Research Branch

Reinforcing Effects of σ-receptor Agonists in Rats Trained to Self-administer Cocaine
Sigma receptor (σR) antagonists have been reported to block certain effects of psychostimulant drugs. IRP investigators found that these same σR antagonists did not affect cocaine self-administration. Interestingly, these drugs block conditioned place preference induced by cocaine indicating that the two procedures used to assess abuse liability of drugs tap different aspects of the activity of drugs of abuse. In contrast to the inactivity of σR antagonists against cocaine self administration, σR agonists were effective reinforcers in subjects trained to self administer cocaine. In addition, σR agonists, like dopamine uptake inhibitors, potentiated the reinforcing effects of cocaine in the self-administration procedure. The σR antagonists antagonized the self administration of σR agonists, despite their inactivity against cocaine. Response rates maintained by maximally effective doses of σR agonists were selectively decreased by σR antagonists (effective doses did not alter response rates maintained by food reinforcement). Although σR antagonists block some cocaine-induced effects, the lack of effect on cocaine self-administration suggests that the primary reinforcing effects of cocaine do not involve direct effects at σRs. However, the self-administration of σR agonists in cocaine-trained subjects, potentiation of cocaine self-administration by σR-agonists suggest enhanced abuse-related effects resulting from concomitant dopaminergically-mediated actions and σR-mediated actions of the drugs.Hiranita T, Soto PL, Tanda G, Katz JL. Reinforcing effects of σ-receptor agonists in rats trained to self-administer cocaine. Journal of Pharmacology and Experimental Therapeutics 2010; 332: 515-524.

Cognitive Safety of a Benztropine Analog with Preclinical Efficacy for ADHD
The evidence for efficacy of atypical dopamine transport inhibitors was reviewed along with techniques for examining cognitive effects of drugs in a symposium entitled "Cognitive safety - a new framework for the safety of drugs" at the 83rd Annual Meeting of the Japanese Pharmacological Society. March 16-18, 2010, Osaka, Japan. Katz JL, Soto PL, Koffarnus M. Cognitive safety of a benztropine analog with preclinical efficacy for ADHD. Journal of Pharmacological Sciences 2010; 112, Suppl. 1, 17P.


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