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Cortical Circuits SPECIFICATION OF LIMBIC CORTICAL CIRCUITS. Jurgen Bolz1, Fanny Mann1, Pat Levitt2, 1INSERM Unite’ 371 Cerveau et Vision, 18 ave du Doyen Lepine, 69500 Bron, France; 2University of Pittsburgh School of Medicine, Pittsburgh, USA.

One of the basic features distinguishing cortical areas is the pattern of specific afferent and efferent projection that define functional circuits. For example, during development thalamocortical afferents select their appropriate cortical region in a highly specific manner. This raises the possibility that there are regional specific cues with the cortex that guide thalamic afferents to select their cortical target area. The idea is supported by the expression patterns of the limbic system-associated membrane protein (LAMP) found primarily in the developing limbic areas of the cortex which was identified by Pat Levitt and colleagues. Transplantation studies of this group have show that the origin of cortical thalamic afferent innervating a cortical graft depends on its LAMP phenotype. To elucidate the role LAMP in the establishment of cortical connections, we analyzed the outgrowth of thalamic and cortical explants prepared from presumptive limbic and non-limbic regions on membrane substrates of either LAMP-expressing CHO cells or on membranes of non-transfected CHO cells (control). We found that length and sprouting of limbic thalamic and limbic cortical axons was enhanced on the LAMP substrate. Non-limbic thalamic fibers, however, responded by exhibiting reduce outgrowth compared to control. The length and branching behavior of neocortical fibers was not affected by LAMP. In a second set of experiments, explants were cultured on native postnatal membranes prepared from limbic or neocortical areas. Limbic thalamic and limbic cortical axons branched significantly more on membranes from limbic cortex, their target membranes, than on neocortical membranes. In contrast, non-limbic thalamic axons emitted more collaterals on membranes of neocortex. These branching preferences could be abolished by blocking LAMP on the membranes with a monoclonal antibody. Our results indicate that LAMP contributes to target recognition during cortical development through both attractive and repulsive mechanisms. Moreover, these experiments suggest the existence of membrane-bound molecules that specify neocortical areas as target for appropriate thalamic and cortical afferents.

[Abstract Titles] [Anderson] [Chugani] [Levitt] [Olson] [Zhou]

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