EARLY PATTERNING OF PRELIMBIC CORTICAL AXONE TO THE STRIATAL PATCH COMPARTMENT IN THE NEONATAL MOUSE

The striatum receives excitatory input from virtually the entire cereb ral cortex. In the adult, this input is segregated into two functional ly distinct compartments of the striatum, the patch (striosome) and ma trix regions. This study determined whether the patterning of corticos triatal afferents from the prelimbic cortex to the striatal patch comp artment develops during the early period of collateral formation or in stead at the time of peak synaptogenesis. Initial formation of cortico striatal axon collaterals was observed by embryonic day (E) 19. Quanti fication of corticostriatal collaterals revealed a significant increas e in the number and complexity of collateral branches at postnatal day 6 as compared to E19. Concomitant with the increase in collateral bra nching, a heterogeneous pattern of collateralization consisting of par allel rows of corticostriatal collaterals was observed in the medial s triatum. In addition to the rows, clusters of corticostriatal axons oc curred more laterally. These clusters colocalized with patches of dens e tyrosine hydroxylase-positive fibers, a marker for the striatal patc h compartment in the neonatal mouse. Together, these data indicate tha t corticostriatal patterning occurs during the period of early axon co llateralization resulting in a segregation of corticostriatal axon col laterals from the prelimbic cortex to the striatal patch compartment.