Reduction in acetylcholine sensitivity of axotomized ciliary ganglion cells.

Abstract

Isolated cell clusters from ciliary ganglia of 3-4 day old chickens were used to examine the electrical characteristics and sensitivity to iontophoretically applied acetylcholine (ACh) of normal cells and cells that had been axotomized on the day of hatching. Resting potentials, input resistances and capacitances were the same in axotomized cells as in normal cells. These averaged about 70 mV, 165 M.OMEGA. and 35 pF [Farads], respectively. Sensitivity to iontophoretically applied ACh was lower in axotomized cells than in normal cells by a factor of about 8. The rise times of the ACh potentials were the same in the 2 groups; indicating that the reduced sensitivity was not due to a diffusion barrier. The slopes of the dose-response curves, plotted on a double-logarithmic scale, suggested that the cooperative action of 2 ACh molecules was involved in activating a post-synaptic conductance channel. This relation was unaltered by axotomy. The estimated reversal potential for the action of ACh was unchanged after axotomy. Cells in isolated clusters were similar to those in intact ganglia with respect to threshold depolarization, amplitude and time course of action potentials and ability to generate repetitive action potentials. There were no differences in these characteristics between normal and axotomized cells. Cells in the isolated clusters had input resistances which were larger by a factor of 2-3 and capacitances that were smaller by a factor of about 2 than those of cells in intact ganglia. These differences may be due to loss of initial segments of axons from the isolated cells. Normal cells in the isolated clusters displayed spontaneous miniature synaptic potentials, indicating that synaptic integrity was maintained during the isolation procedure. As in intact ganglia, no spontaneous activity was observed in axotomized cells.