Research Findings - Basic Neuroscience Research
RGS9-2 Signaling Partners
Regulators of G protein signaling (RGS) are known to bind to G alpha proteins, speeding the process of GTP hydrolysis and terminating the signaling pathway in which the GPCR participates. Based on immunoblotting and immunoprecipitation results, the RGS9-2 protein, highly expressed in the striatum and nucleus accumbens, forms a tertiary complex with the G protein Gbeta5, and with R7BP (R7 binding protein) at distinct binding regions of RGS9-2. Certain details about the stoichiometry of this complex are understood: Gbeta5 is necessary for the constitutive expression of RGS9-2, and these two partners are expressed in direct proportion, i.e., both their expression levels increase, or decrease together, as in the case of R7BP being absent in a R7BP knockout mouse species. The binding of R7BP may aid in targeting RGS9-2 to post-synaptic neuronal regions, and may also contribute to the stability of the RGS9-2/Gbeta5 complex. RGS9-2 has been studied as a regulator of dopamine and opioid (mu receptor) signaling in the animal brain. RGS9-2 levels are decreased in rats chronically self-administering cocaine, and RGS9-2 knockout mice have increased sensitivity to the rewards of morphine (lower doses) in place conditioning experiments, compared to wild type mice. RGS9-2 knockout mice show enhanced withdrawal symptoms following morphine administration. Dr. Martemyanov and his associates at the University of Minnesota have carried out a quantitative proteomics study to detect changes in the proteins that complex to RGS9-2 when R7BP is absent, using the R7BP knockout mouse. Three striatal brain samples were used: a wild type, an R7BP knockout sample, and, for control purposes, an RGS9-2 knockout sample to detect non-specific interactions in the absence of RGS9-2. Following immunoprecipitation to obtain proteins from the samples, each sample was treated with trypsin to produce fragment peptides, which were derivatized with three different isotopically-labeled tags, samples were combined, separated by LC, and analyzed by mass spectrometry. RGS9-2 interaction with Gbeta5 was confirmed, and, in the absence of R7BP in the complex, twenty-one new binding partners of RGS9-2 were identified as being upregulated, including the heat shock chaperone protein Hsc70. Hsc70 was absent (no immunoprecipitation) in RGS9-2 knockout samples, and in R7BP knockout striatal tissue, increasing in amount when R7BP was absent. The binding of Hsc70 protein was found to take place at a C-terminus peptide fragment of RGS9-2. When Hsc70 was "silenced" by siRNA for Hsc70, the RGS9-2 expression increased 17%, based on Western blotting analysis. Therefore, Hsc70 negatively regulated the RGS9-2 expression. Although the mechanism of Hsc70 action is not known presently, Hsc70 may serve to regulate RGS9-2 by targeting a RGS9-2 complex into lysosomes, where it can be degraded. Posokhova E, Uversky V, Martemyanov KA. Proteomic identification of Hsc70 as a mediator of RGS9-2 degradation by in vivo interactome analysis. J Proteome Res 2010; 9(3): 1510-1521.
Negative Allosteric Modulators that Target Human α4β2 Neuronal Nicotinic Receptors
Allosteric modulation of nicotinic acetylcholine receptors (nAChRs) is considered to be one of the most promising approaches for therapeutics. The present authors previously reported on the pharmacological activity of several compounds that acted as negative allosteric modulators (NAMs) of nAChRs. In this publication the effects of 30 NAMs from the authors' small chemical library on both human α4β2 (Hα4β2) nAChRs and human α3β4 (Hα3β4) nAChRs expressed in HEK ts201 cells were investigated. Using calcium accumulation assays, these NAMs inhibited nAChRs activation with IC50 values ranging from 2.4 ÁM to greater than 100 ÁM. Several NAMs showed relative selectivity for Hα4β2 nAChRs with IC50 values in the low micromolar range. A lead molecule, KAB-18 was identified that showed relative selectivity for Hα4β2 nAChRs. This molecule contains 3-phenyl rings, 1 piperidine ring, and 1 ester bond linkage. Structure-activity relationship (SAR) analyses revealed 3 regions of KAB-18 that contributed to its relative selectivity. Predictive 3D-QSAR (comparative molecular field analysis and comparative molecular similarity indices analysis) models were generated from these data and a pharmacophore model was constructed to determine the chemical features that were important for biological activity. Using docking approaches and molecular dynamics on Hα4β2 nAChR homology model, a binding mode for KAB-18 at the α/β sub-unit interface that corresponded to the predicted pharmacophore was described. This binding study was supported by mutagenesis studies. In summary, these studies highlight the importance of SAR, computational, and molecular biology approaches for the design and synthesis of potent and selective antagonists targeting specific nAChR sub-types. Henderson BJ, Pavlovicz RE, Allen JD, Gonzalez-Cestari TF, Orac CM, Bonnell AB, Zhu MX, Thomas Boyd R, Li C, Bergmeier SC, McKay DB. Negative Allosteric Modulators that Target Human α4β2 Neuronal Nicotinic Receptors, J Pharmacol Exp Ther. 2010, Jun 15. [Epub ahead of print].
Molecular Mechanisms Involving Cocaine/Sigma Receptor-Mediated Induction of MCP-1: Implication For Increased Monocyte Transmigration
Cocaine abuse hastens the neurodegeneration often associated with advanced HIV-1infection. The mechanisms, in part, revolve around the neuroinflammatory processes mediated by the chemokine monocyte chemotactic protein-1 (MCP-1/CCL2). Understanding factors that modulate MCP-1 and, in turn, facilitate monocyte extravasation in the brain is thus of paramount importance. These researchers demonstrate that cocaine induces MCP-1 in rodent microglia through translocation of the sigma receptor to the lipid raft microdomains of the plasma membrane. Sequential activation of Src kinase, mitogen-activated protein kinases (MAPKs), and phosphatidylinositol-3' kinase (PI3K)/Akt and nuclear factor kappaB (NF-kappaB) pathways resulted in increased MCP-1 expression. Furthermore, conditioned media from cocaine-exposed microglia increased monocyte transmigration, and this was blocked by antagonists for CCR2 (MCP-1 receptor) or sigma receptor. These findings were corroborated by demonstrating increased monocyte transmigration in mice exposed to cocaine, which was attenuated by pretreatment of mice with the sigma receptor antagonist. Consistently, cocaine-mediated transmigratory effects were not observed in CCR2 knockout mice. It was concluded that cocaine-mediated induction of MCP-1 accelerates monocyte extravasation across the endothelium. Understanding the regulation of MCP-1 expression and functional changes by cocaine/sigma receptor system may provide insights into the development of potential therapeutic targets for HIV-1-associated neurocognitive disorders. These findings have implications for cocaine abusers with HIV-1 who are known to have increased risk of stroke and CNS-associated inflammation. These findings suggest that sigma receptor antagonists could be considered as adjunct therapeutic agents for the treatment of cocaine addicts infected with HIV. Yao H, Yang Y, Kim KJ, Bethel-Brown C, Gong N, Funa K, Gendelman HE, Su TP, Wang JQ, Buch S. Molecular mechanisms involving sigma receptor-mediated induction of MCP-1: implication for increased monocyte transmigration. Blood 2010; Jun 10; 115: 4951-4962.
A Programmable Transdermal Patch for Delivering Nicotine Via Carbon Nanotubes (CNT) Membranes
Dr. Bruce Hinds and his colleagues at the University of Kentucky have developed a small skin patch that is cable of delivering nicotine in a controllable manner by turning on or off a minute electrical current across a permeable membrane. The heart of this device is based completely on new nanotechnological approaches. CNTs crossing a solid polymer film are the active layer that can be switched with the voltage. The CNTs are a truly unique material system with atomically flat and chemically inert graphite planes rolled into tubes 1.5-7 nanometers in diameter. Work in the Hinds' group showed that this allowed fluid flow 10,000 times faster than in pores of similar size. In addition, the nanotubes are electrically conductive and a single layer of charged chemistry can be placed at the pore entrance. This closely mimics the principles of ion channel proteins that regulate the flow of ions into and out of cell walls. Constructing robust human-made platforms over large areas with each pore having the same performance as natural protein channels is a grand challenge of nanotechnology with far-reaching impact wherever the control of selective chemical transport is needed (i.e. pharmaceutical synthesis, sensing, drug delivery, energy storage). When connected to a nicotine reservoir, these CNT patches were shown by Dr. Hinds to successfully switch between high and low concentrations on human skin consistent for effective nicotine cessation treatment. These controllable CNT patches have the potential to be developed to deliver other compounds for drug abuse treatments as well as nicotine. Wu J, Paudel KS, Strasinger C, Hammell D, Stinchcomb AL, Hinds BJ. Programmable transdermal drug delivery of nicotine using carbon nanotube membranes. PNAS 2010; 107(26): 11698-11702.
Heroin Use or Heroin Use Plus HCV Infection Impairs CD56+ Cell-Mediated Innate Immune Function
Ho and colleagues examined 37 heroin users with (17) or without (20) HCV infection. In addition, 17 healthy subjects were included in the study. Although there was no significant difference in CD56+ T cell frequency in PBMCs among three study groups, CD56+ T cells isolated from the heroin users had significantly lower levels of constitutive interferon-gamma (IFN-c) expression than those from the normal subjects. In addition, when stimulated by interleukin (IL)-12, CD56+ natural T cells from HCV-infected heroin users produced significantly lower levels of IFN-c than those from the normal subjects. This diminished ability to produce IFN-c by CD56+ T cells was associated with the increased plasma HCV viral loads in the HCV-infected heroin users. Investigation of the mechanisms showed that heroin use or heroin use plus HCV infection induced the expression of suppressor of cytokine signaling protein-3 (SOCS-3) and protein inhibitors of activated STAT-3 (PIAS-3), two key inhibitors of IL-12 pathway. These findings provide in vivo evidence that heroin use or heroin use plus HCV infection impairs CD56+ T cell-mediated innate immune function, which may account for HCV infection and persistence in liver. Ye L, Wang X, Metzger DS, Riedel E, Montaner LJ, Ho W. Upregulation of SOCS-3 and PIAS-3 Impairs IL-12-Mediated Interferon-Gamma Response in CD56+ T Cells in HCV-Infected Heroin Users. PLoS ONE. 2010 March; 5(3): 1-10.
Dopamine Modulates the Action of Endocannabinoids In the Brain (Prefrontal Cortex) Which May Contribute to the Change In Neuronal Activity That Underlies Cannabinoid (THC)-Produced Neuropsychiatric Disorders
Dopamine (DA) and cannabinoids strongly influence prefrontal cortical functions, such as working memory, emotional learning, and sensory perception. Although endogenous cannabinoid receptors (CB(1)Rs) are abundantly expressed in the prefrontal cortex (PFC), very little is known about endocannabinoid (eCB) signaling in this brain region. Recent behavioral and electrophysiological evidence has suggested a functional interplay between the dopamine and cannabinoid receptor systems in mid-brain areas, but it is unknown whether a functional interaction also occurs in the PFC. This paper provides data to support a functional interaction. Using immunoelectron microscopy, it was shown that CB(1)Rs and dopamine type 2 receptors (D(2)Rs) colocalize at terminals of symmetrical, presumably GABAergic, synapses in the PFC. Furthermore, activation of either receptor suppresses GABA release onto layer 5 pyramidal cells. Co-activation of both receptors triggers eCB-mediated long-term depression of inhibitory transmission (I-LTD). D(2)Rs most likely facilitate eCB signaling at a presynaptic site because disrupting postsynaptic D(2)R signaling does not diminish I-LTD. Therefore, facilitation of eCB-LTD may be one mechanism by which DA alters the balance between excitatory and inhibitory neuronal activity in the PFC to produce PFC-mediated behavioral deficits and cannabinoid-induced neuropsychiatric disorders. Chiu CQ, Puente N, Grandes P, Castillo PE. Dopaminergic modulation of endocannabinoid-mediated plasticity at GABAergic synapses in the prefrontal cortex. J Neurosci. 2010 May 26;30(21): 7236-7248.
Repeated Stress Differentially Alters the Signaling of Two Endocannabinoids: Anandamide (AEA) and 2-Arachidonoylglycerol (2-AG) Ligands In the Brain to Regulate the Neuroendocrine Response to Stress
Secretion of glucocorticoid hormones during stress produces an array of physiological changes that are adaptive and beneficial in the short term. In the face of repeated stress exposure, however, habituation of the glucocorticoid response is essential as prolonged glucocorticoid secretion can produce deleterious effects on metabolic, immune, cardiovascular, and neurobiological function. Endocannabinoid signaling responds to and regulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis that governs the secretion of glucocorticoids; however, the role this system plays in adaptation of the neuroendocrine response to repeated stress is not well characterized. Herein, the PIs demonstrate a divergent regulation of the two endocannabinoid ligands, N-arachidonylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG), following repeated stress such that AEA content is persistently decreased throughout the corticolimbic stress circuit, whereas 2-AG is exclusively elevated within the amygdala in a stress-dependent manner. Pharmacological studies demonstrate that this divergent regulation of AEA and 2-AG contribute to distinct forms of HPA axis habituation. Inhibition of AEA hydrolysis prevented the development of basal hypersecretion of corticosterone following repeated stress. In contrast, systemic or intra-amygdalar administration of a CB(1) receptor antagonist before the final stress exposure prevented the repeated stress-induced decline in corticosterone responses. The present findings demonstrate an important role for endocannabinoid signaling in the process of stress HPA habituation, and suggest that AEA and 2-AG modulate different components of the adrenocortical response to repeated stressor exposure. Hill MN, McLaughlin RJ, Bingham B, Shrestha L, Lee TT, Gray JM, Hillard CJ, Gorzalka BB, Viau V. Endogenous cannabinoid signaling is essential for stress adaptation. Proc Natl Acad Sci U S A. 2010 May 18;107(20): 9406-9411.
Extinction Training After Cocaine Self-Administration Alters Glutamate Receptor Trafficking In the Nucleus Accumbens Core To Inhibit Cocaine Seeking
Learning to inhibit drug seeking can be an important strategy for inhibiting relapse, and this can be modeled by extinguishing drug seeking in response to a drug-paired context. Rats were either extinguished or withdrawn without extinction training (abstinence) from cocaine self-administration, and measurements of postsynaptic density proteins in the core and shell subcompartments of the nucleus accumbens (NAc) were compared with yoked-saline controls. Extinguished, but not abstinent, rats had elevations of several proteins, including Homer1b/c that regulates trafficking of the glutamate receptor, mGluR5, in the postsynaptic density of the NAc core. No differences in protein levels were measured in the postsynaptic density of the NAc shell in either extinguished or abstinent rats. Additionally, it was found that surface expression of mGluR5 was reduced only in the core of extinguished animals. Blunted long-term depression (LTD) was also observed only in extinguished rats. These data indicate that the elevation in Homer1b/c in the NAc core may have sequestered mGluR5 away from the membrane surface and that the loss of surface mGluR5 alters neuronal activity. Accordingly, when Homer1c was over expressed in the NAc core of cocaine-naive rats with an adeno-associated virus, long-term depression was inhibited. This mechanism may contribute to the inhibition of cocaine seeking by extinction training because over expression of Homer1c in the NAc core also inhibited cue-induced reinstatement of cocaine seeking. These data identify a cellular mechanism that may contribute to extinction-induced inhibition of cocaine seeking. Knackstedt LA, Moussawi K, Lalumiere R, Schwendt M, Klugmann M, Kalivas PW. Extinction training after cocaine self-administration induces glutamatergic plasticity to inhibit cocaine seeking. J Neurosci. 2010 Jun 9;30(23): 7984-7992.
Functional Impact of a Single-Nucleotide Polymorphism in the OPRD1 Promoter Region
The delta-opioid receptor mediates the rewarding effects of many substances of abuse. Dr. Zhang and colleagues reported an increased frequency of the minor G-allele of single-nucleotide polymorphism (SNP) rs569356 (the only variant identified so far in the promoter region of the delta-opioid receptor gene (OPRD1)) in European American subjects with opioid dependence compared with European American controls. Functional genetic variation in promoter regions may alter the affinity of transcription factors and other modulatory proteins that bind to the DNA sequence and thus influence the specificity and kinetics of the transcription process. In this study, Dr. Zhang and colleagues examined the functional significance of this variant through luciferase reporter and electrophoretic mobility shift assays (EMSA). The minor G-allele was associated with significantly greater expression levels of firefly luciferase than the major A-allele of SNP rs569356 (P=0.003). EMSA also showed specific gel shift bands, suggesting that SNP rs569356 is situated in the binding site of potential transcription factors. These results suggest that the minor G-allele of SNP rs569356 may enhance transcription factor binding and increase OPRD1 expression. Zhang H, Gelernter J, Gruen JR, Kranzler HR, Herman AI, Simen AA. Functional Impact of a Single-Nucleotide Polymorphism in the OPRD1 Promoter Region. J Hum Genet. 2010 May; 55(5): 278-284.
A Novel MicroRNA Regulates Cocaine Intake Through CREB Signalling
Non-coding RNAs are emerging as important regulators of biological processes; however their role in regulation of addictive processes remains poorly characterized. Dr. Kenny and co-workers have identified a 21 nucleotide microRNA , miR-212, that is found at higher levels in the dorsal striatal brain region of animals that self-administer cocaine. In rats with extended access to cocaine, reduction of miR-212 levels in the striatum leads to increased cocaine intake, while overexpression of miR-212 leads to decreased cocaine intake. Further molecular experiments revealed that miR-212 achieves it effects via simultaneous reduction in expression of several messenger RNAs which encode regulatory proteins that impinge upon the Raf1 protein kinase signaling pathway (including the SPRED1 repressor of Raf1). Overall these gene expression changes lead to increased levels of Raf1 protein kinase activity, increased expression of the CREB regulatory protein TORC , and ultimately increased activity of the transcription factor CREB. The identification of a novel miR-212 pathway that regulates cocaine intake provides a new and unexpected target for the development of potential therapeutic agents to treat cocaine addiction. Hollander JA, Im HI, Amelio AL, Kocerha J, Bali P, Lu Q, Willoughby D, Wahlestedt C, Conkright MD, Kenny PJ. Striatal microRNA controls cocaine intake through CREB signalling. Nature. 2010; Jul 8; 466(7303): 197-202.
Cortical DNA Methylation Maintains Remote Memory
Contextual fear conditioning, in which rodents receive a foot shock in a particular environmental milieu, leads to memories of the environmental milieu that last for several months. During this time period "the memory transitions from 'recent' to 'remote'". It is believed that during memory consolidation the control of the memory shifts from the hippocampal brain region to dependence upon the anterior cingulated (ACC) or cortical brain region. Previously DNA methylation of specific genes in the hippocampus had been shown to be important for memory formation; however the molecular basis of memory maintenance remains mysterious. Dr. Miller and co-workers found that a single associative learning experience led to DNA methylation of the memory-associated gene calcineurin in the cortex. This DNA methylation lasted at least 30 days after the initial associative learning event. Interestingly, inhibitors of the DNA methyltransferase enzyme that methylates DNA disrupted the memory. Overall these experiments suggest that maintenance of long lasting memory requires DNA methylation in the prefrontal cortex. Future investigations in this area may shed light on the role of DNA methylation in memory-related addictive processes and suggest ways in which this epigenetic pathway could be manipulated therapeutically. Miller CA, Gavin CF, White JA, Parrish RR, Honasoge A, Yancey CR, Rivera IM, Rubio MD, Rumbaugh G, Sweatt JD. Cortical DNA methylation maintains remote memory. Nat Neurosci. 2010; Jun 13(6): 664-666.
Additional Loci Associated with the Genetics of Smoking Behavior
Nicotine dependence is determined by an interplay of neurobiological, environmental, developmental and genetic factors. Environmental influences are important in the initiation of smoking, but the heritability of smoking persistence, smoking quantity and nicotine dependence is strongly influenced by genetic factors. Genetic variants within a cluster of nicotinic acetylcholine receptor genes on chromosome 15q25 are associated with nicotine dependence, as well as smoking-related diseases such as lung cancer, peripheral artery disease, and chronic obstructive pulmonary disease. Due to many replication studies, there is high confidence in the15q25 genetic variants, but they account for a small portion of the genetic variance for nicotine dependence. To search for additional variants associated with smoking behavior, Dr. Kari Stefansson and colleagues performed meta-analyses of genome-wide association studies focusing on cigarettes smoked per day (CPD) and smoking initiation. There were 30,431 ever smokers and 16,050 never-smokers for smoking initiation and 31,266 subjects. For each subject, 2,500,000 imputed and genotyped SNPs were combined and analyzed. In addition to the 15q25 locus, two new loci (8p11, and 19q13) were found to be genome-wide significant for CPD, and passed further quality control metrics. No significant loci were observed for smoking initiation. The SNPs on chromosome 8p11 are in close proximity to another cluster of nicotinic acetylcholine receptor subunit genes, CHRNB3 and CHRNA6. The SNPs on chromosome 19q13 are located in a genomic region harboring CYP2A6, which plays a major role in the oxidation of nicotine. Other SNPs on 19q13 are in the RAB4B gene and the CYP2B6 gene. Overall, this work provides additional genetic loci with strong associations to nicotine dependence and CPD. The dissection of the causal variants and pathways to nicotine dependence and smoking related diseases is underway. Thorgeirsson T, et al. Sequence variants at CHRNB3-CHRNA6 and CYP2A6 affect smoking behavior. Nat Genet. 2010; May 42(5): 448-453.
Argonaute 2 in Dopamine 2 Receptor Expressing Neurons Regulates Cocaine Addiction
Cocaine regulates gene expression and the expression of proteins within a region of the brain called the striatum. The changes in gene expression occur through the release of the neurotransmitter, dopamine from the nerve terminals of VTA neurons that form synapses with neurons in the striatum Dopamine acts on the dopamine receptor 2 (DRD2) located on striatal neurons to produce changes in electrical excitability and changes in the expression of mRNAs (messenger RNA). mRNA is translated into proteins that carry out the functions of the cell. It has recently been discovered that microRNAs (miRNAs), a non coding RNA, binds to mRNAs to regulate the amount of the translation of protein from mRNA. Levels of translation are regulated by the RISC (the RNA-induced silencing complex). This complex consists of DICER that generates the miRNA and Argonaut that binds the miRNA and regulates mRNA decay or suppression of translation. Dr. Anne Schafer together with Noble Laureate, Paul Greengard examined the role that Ago2 plays in regulating miRNA expression induced by cocaine in DRD2 expressing neurons to identify which miRNA among the 300 miRNAs play a role in regulating gene expression altered by cocaine. Schafer and her colleagues show that abolishing the function of the Ago2 protein selectively in DRD2 neurons of the striatum significantly reduces the motivation of mice to self-administer cocaine without affecting the number, morphology, or distribution of neurons in the striatum or their dopaminergic innervation. This is associated with a reduction of 94/376 miRNAs expressed in DRD2 striatal neurons with 15 showing a 3 to 17 fold reduction in expression. 23 of the 63 miRNA induced by cocaine are Ago2 dependent. Among these 23 miRNAs are miRNAs that regulate CREB, FosB, Mef2, BDNF, and Cdk5r1, all genes that have been implicated in mediating addiction to cocaine. These results show that Ago2 through its regulation of miRNAs plays a significant role in cocaine addiction. Future experiments will determine the role that the 23 miRNAs play in mediating changes in stable gene expression following cocaine self-administration. Schaefer A, Im HI, Veno MT, Fowler CD, Min A, Intrator A, Kjems J, Kenny P, O'Carroll D, Greengard P. Journal of Experimental Medicine, July 19, 2010 Cite by DOI: 10.1084/jem.20100451.
Cortical Laminar Development Is Coordinated at Bottom through Gap Junctions
During cortical embryonic development, the nuclei of the dividing neural precursor cells in the ventricular zone and subventricular zone translocate back and forth between the ventricular surface and basal surface. This phenomenon is known as interkinetic nuclear translocation. During this process the nuclei of the dividing neural precursors move away from the ventricular surface basally to divide, then move back to the surface to either migrate radially with the rest of the committed cell bodies to the cortical surface or prepare for another round of translocation basally for another division. The timing and coordination of nuclear translocation for these precursors are very important, since normal cortical layers can only emerge by precisely timed cell migration from ventricular zones into the right cortical layers at the right time. How this precisely timed nuclear translocation is coordinated has not been well known. A group of NIDA funded researchers at Yale University, led by Dr. Pasko Rakic, report that the neural precursor cells generate spontaneous transient Ca2+ waves in the ventricular zones. The Ca2+ wave signals the precursor cells' timing and location of interkinetic movement through gap junctions on the cell membrane. Blocking the gap junctions using a chemical MFA, or through gap junction subunit gene knockdown, delays or blocks the nuclear migration. This delay also changes the nuclear length/width ratio, with consequences in neural cell differentiation and migration, and may lead to abnormal corticogenesis and dysfunction of the cerebral cortex in adult organisms. Liu X, Hashimoto-Torii K, Torii M, Ding C, Rakic P. Gap Junctions/Hemichannels Modulate Interkinetic Nuclear Migration in the Forebrain Precursors. Journal of Neuroscience 2010: 30: 4197-4209.