Altered spatial patterns of functional thalamocortical connections in the barrel cortex after neonatal infraorbital nerve cut revealed by optical recording

In rodents, the somatosensory cortex has a cell aggregation cluster termed the barrel, reflecting a whisker vibrissa, and this barrel formation is dis rupted by infraorbital nerve cut at birth. In the present study, we prepare d thalamocortical slice preparations from rats that received infpaorbital n erve cut either at birth or at postnatal day (P) 7 and those from normal ra ts, recorded the optical response reflecting neural excitation in the somat osensory cortex with a voltage-sensitive dye (RH482) and compared the optic al responses from lesioned rats with those from normal rats. In normal rats at P10, the optical response elicited electrically by thalamic stimulation propagated to the cortex, and then several patchy clusters appeared in lay er IV. The size and location of these patchy responses precisely matched ei ther barrels identified by cytochrome oxidase staining or terminal arbors o f thalamocortial axons stained with biotinylated dextran amine. In contrast , at P10 in P0-lesioned rats, clusters having a wider horizontal width but smaller amplitude than those seen in normal rats appeared in layer IV. Corr espondingly, neither cytochrome oxidase staining nor biotinylated dextran a mine labeling of thalamocortical axons showed any barrel-like clusters or g lomerular axon terminals. Likewise, at P5-P6, the tangential width of clust ers in layer IV were larger than that in normal rats. At P10 in P7-1esioned rats, small cluster-matched barrels were seen in the optical response as w ell as in normal rats. These results suggest that P0 infraorbital nerve cut interrupted segregatio n of functional synapses into the barrels and retarded the maturation of th alamocortical transmission. (C) 1999 IBRO. Published by Elsevier Science Lt d.