DIFFERENTIAL EXPRESSION OF THE ELECTROPHYSIOLOGICAL RESPONSES TO AXOTOMY IN BULLFROG SYMPATHETIC NEURONS FOLLOWING NERVE INJURY AT 15-DEGREES-C

In frogs maintained at 15 degrees C, there is a partial failure of the cell body reaction (CBR) to axotomy. We investigated, in the sympathe tic B-cells of the bullfrog, the effects of axotomy at 15 degrees C on the changes in electrophysiological properties which we found previou sly to follow axotomy at 21 degrees C. While the increase in action po tential (AP) duration was delayed by about 14 days, it increased by th e normal amount. In contrast, the reduction in after-hyperpolarization (AHP) duration was both delayed and attenuated. These results show th at there is a differential expression of these two components of the C BR, with changes in AHP duration more sensitive to lowered temperature . In attempts to determine if the effect of reduced temperature was on the signalling of axotomy or on the cell body response to the signal, we performed experiments where the 15 degrees C frogs were maintained at 21 degrees C for 7 days, immediately after axotomy, or after vario us delays. These results suggest that at 15 degrees C, there is an inc reased delay in signalling that the injury has occurred, but we were n ot able to show conclusively that maintained expression of the CBR req uires an ambient temperature of 21 degrees C. This study emphasizes th at the CBR to axotomy is not a unitary response to a single signal, bu t can be dissected, by lowered ambient temperature, into differentiall y regulated components.