The effects of axotomy on bullfrog sympathetic neurones.

1. The effects of axotomy on the electrical properties of B cells in paravertebral sympathetic ganglia were studied using standard intracellular recording techniques. The effects were apparent after 1 week and persisted throughout the 47 days of study. 2. Action potential duration (spike width) and amplitude (spike height) were significantly increased in axotomized neurones. 3. The duration of the after-hyperpolarization which followed the action potential showed considerable scatter in control neurones (mean +/- S.E. of mean, 159.0 +/- 5.8 ms for 100 cells). Following axotomy, the duration was significantly reduced (50.9 +/- 2.3 ms for 97 cells). The amplitude of the after-hyperpolarization was also significantly smaller in axotomized neurones. 4. Changes in the characteristics of the action potential and the after-hyperpolarization in axotomized neurones were not due to alteration in resting membrane potential or input resistance which were unchanged after axotomy. Rheobase current was significantly increased. 5. There was neither a significant depression of the rate of rise or the amplitude of orthodromically evoked nicotinic e.p.s.p.s nor any obvious ultrastructural alteration following axotomy. 6. Despite the decrease in the duration of the after-hyperpolarization, the rate of discharge in response to constant current injection was little changed in axotomized neurones. 7. Although axotomy produces significant changes in several measurable electrophysiological parameters in bullfrog sympathetic ganglion cells, the present results imply that mature neurones are able to maintain relatively normal electrical activity despite injury.