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 mouse whiskerpad, the caudal follicles of row C are reinnervated with approximately 80 % of the original number of axons [Corthésy, M.-E., Bronchti, G. & Welker, E. (1999) Eur. J. Neurosci. , 11, 2835-2846]. To what extent is this reinnervation functional, and how does it interact with the enlargement of the functional representation of neighbouring rows subsequent to the denervation? Using the autoradiographic deoxyglucose method, we studied the whisker representation at the level of the barrel cortex 100 days post lesionem. We stimulated whiskers belonging to the denervated row C, the neighbouring rows B and D, or to all five rows A-E. The deoxyglucose uptake was measured in tangential sections through layer IV. The results indicate that, 100 days post lesionem, whiskers of row C reactivate their cortical barrels. However, (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 significantly reduced deoxyglucose uptake over the representation of nonlesioned whiskers of rows D and E. Therefore, 100 days after the peripheral nerve lesion 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 to a modified interaction between the representations of the various rows of follicles at the cortical level that does not return to normal.