Differential expression of the electrophysiological responses to axotomy in bullfrog sympathetic neurons following nerve injury at 15°C

In frogs maintained at 15°C, there is a partial failure of the cell body reaction (CBR) to axotomy. We investigated, in the sympathetic B-cells of the bullfrog, the effects of axotomy at 15°C on the changes in electrophysiological properties which we found previously to follow axotomy at 21°C. While the increase in action potential (AP) duration was delayed by about 14 days, it increased by the normal amount. In contrast, the reduction in after-hyperpolarization (AHP) duration was both delayed and attenuated. These results show that there is a differential expression of these two components of the CBR, 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°C frogs were maintained at 21°C for 7 days, immediately after axotomy, or after various delays. These results suggest that at 15°C, there is an increased delay in signalling that the injury has occurred, but we were not able to show conclusively that maintained expression of the CBR requires an ambient temperature of 21°C. This study emphasizes that the CBR to axotomy is not a unitary response to a single signal, but can be dissected, by lowered ambient temperature, into differentially regulated components.