Alterations in brainstem and cortical organization of rats sustaining prenatal vibrissa follicle lesions.

Vibrissa follicles were cauterized in late fetal or newborn rats to determine whether the relationships between brainstem and cortical changes observed after neonatal peripheral damage would also be obtained when vibrissa follicles were cauterized earlier in development. Vibrissa follicles were cauterized between embryonic day 15 (E-15) and the day of birth (P-0). The vibrissa-related representation in the brainstem was examined with cytochrome oxidase histochemistry, and that in the cortex was evaluated with either serotonin immunocytochemistry or anterograde labeling with Di-I when animals reached 6-8 days of age. There was a significant relationship between the ages at which lesions were carried out and the extent to which the representations of undamaged vibrissa follicles were altered in the brainstem and cortex. Peripheral lesions carried out between E-15 and E-18 resulted in significant increases in the cross-sectional areas of the patches corresponding to the undamaged vibrissa follicles in both the brainstem and cortex. Lesions at later ages resulted in significant increases only in the cortex. In some animals that sustained peripheral damage on E-20 and all of those that received lesions on P-0, there were aggregates of labeling in cortex that had no counterpart in the brainstem. Prenatal, but not postnatal, vibrissa follicle damage also reduced the overall dimensions of the cortical region devoted to the representation of these receptor organelles. Finally, there was a strong negative correlation between the magnitude of peripheral lesions (i.e., the number of vibrissa follicles ablated) and the extent of the reorganization in the brainstem and cortex.