Partial denervation of the whiskerpad in adult mice: altered patterns of metabolic activity in barrel cortex

One hundred days after unilateral C-row nerve transection in the adult mous e whiskerpad, the caudal follicles of row C are reinnervated with approxima te to 80 % of the original number of axons [Corthesy, M.-E., Bronchti, G. & Welker, E. (1999) Eur. J. Neurosci., 11, 2835-2846]. To what extent is thi s reinnervation functional, and how does it interact with the enlargement o f the functional representation of neighbouring rows subsequent to the dene rvation? Using the autoradiographic deoxyglucose method, we studied the whi sker representation at the level of the barrel cortex 100 days post lesione m. We stimulated whiskers belonging to the denervated row C, the neighbouri ng rows B and D, or to all five rows A-E. The deoxyglucose uptake was measu red in tangential sections through layer IV. The results indicate that, 100 days post lesionem, whiskers of row C reactivate their cortical barrels. H owever, (i) the magnitude of this cortical response was reduced; (ii) row C barrels were equivalently activated by the stimulation of the neighbouring rows; and (iii) when all whiskers were stimulated, we observed a significa ntly reduced deoxyglucose uptake over the representation of nonlesioned whi skers of rows D and E. Therefore, 100 days after the peripheral nerve lesio n the reinnervation of the whiskerpad had not restored a normal pattern of activation at the level of the barrel cortex. We propose that this is due t o a modified interaction between the representations of the various rows of follicles at the cortical level that does not return to normal.