Expression of R-cadherin and N-cadherin by cell groups and fiber tracts inthe developing mouse forebrain: Relation to the formation of functional circuits

The expression of R-cadherin and N-cadherin was mapped in the postnatal for ebrain of the mouse by immunohistochemistry and in situ hybridization. Resu lts show that the two molecules are expressed in specific and restricted pa tterns in numerous brain nuclei, gray matter areas and cortical layers that are widely distributed throughout the mouse forebrain at postnatal day 1. The expression pattern of R-cadherin is clearly distinct from that of N-cad herin, but overlap is observed in many areas. In many cortical areas, the t wo cadherins have a laminar-specific distribution that varies from region t o region. In addition, immunohistochemical data revealed expression of R-ca dherin protein and N-cadherin protein in the neuropil of many brain regions as well as in the axons that travel in fiber tracts such as the olfactory tract, the anterior commissure, the corpus callosum, the stria terminalis a nd the fornix. Often, subsets of axons within the same fiber tract differen tially express R-cadherin and N-cadherin, with partial overlap of expressio n. The targets of the cadherin-immunoreactive fiber bundles often contain n europil as well as cell bodies of neurons that also express the same type(s ) of cadherin, suggesting that R-cadherin and N-cadherin may be involved in target recognition and the establishment of connections. Specifically, the expression of R-cadherin and N-cadherin is related to the maturation of th alamocortical sensory pathways, corticofugal pathways, and pathways associa ted with the hippocampal complex, the piriform cortex, and the amygdala. It is also relate to the development of the cell groups associated with these pathways. Together, the results from the present study indicate the possibility that the selective adhesion of neural structures that express the same type(s) o f cadherin contributes to the formation of gray matter areas, neural circui ts and functional connections in the postnatal forebrain of the mouse. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.