Unilateral induced neocortical malformation and the formation of ipsilateral and contralateral barrel fields

Freezing lesions to the developing cortical plate of rodents results in a f ocal malformation resembling human 4-layered microgyria, and this malformat ion has been shown to result in local and widespread disruptions of neurona l architecture, connectivity, and physiology. Because we had previously dem onstrated that microgyria caused disruptions in callosal connections, we hy pothesized that freeze lesions to the postero-medial barrel sub-field (PMBS F) in one hemisphere would affect the organization of this barrel field con tralaterally. We placed freeze lesions in the presumptive PMBSF of neonatal rats and, in adulthood, assessed the architecture of the ipsilateral and c ontralateral barrel fields. Malformations in the PMBSF resulted in a substa ntial decrease in the number of barrels as identified by cytochrome oxidase activity. More importantly, we found an increase in the total area of the contralateral PMBSF, although there was no difference in individual barrel cross-sectional areas, indicating an increase in the area of inter-barrel s eptae. This increase in the septal area of the contralateral PMBSF is consistent w ith changes in callosal and/or thalamic connectivity in the contralateral h emisphere. These results are another example of both local and widespread d isruption of connectional architecture following induction of focal microgy ria. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.