EFFECTS OF d-TUBOCURARINE ON THE FROG SYMPATHETIC GANGLION CELL AND ON SYNAPTIC FUNCTION

Sympathetic ganglion cells of Rana pipiens exposed to d -tubocurarine (curare), 0.3 to 3.0 mM, displayed decreases in resting potentials, spike amplitudes and rates of rise and fall and in current thresholds for direct stimulation. The magnitudes of the effects were related to drug concentration, although cells varied considerably in sensitivity to curare. Curare was also the most potent transmission-blocking agent we have examined (4-24 µM), and the block was temporarily reversed after preganglionic tetanic stimulation. Synaptic excitability, determined with paired preganglionic stimuli at varying intervals, was slightly enhanced by concentrations of curare both supra- and subthreshold for transmission block. Such subthreshold concentrations also suppressed physostigmine-induced orthodromic stimulus-bound repetitive spiking in Rana catesbiana . Thus, the composite data afford a series of concentration-effect interrelationships for curare actions on the ganglion cell membrane and on synaptic function. The interrelationships, and the kinds and sites of action, provide the basis for discussing: 1) the uniform potency and efficacy of curare action on various neural tissues; 2) the question of site of action for curare transmission block; 3) the mechanistic contrasts between curare and another effective ganglion-blocking agent, tetraethylammonium; and 4) the failure of curare depolarization to generate spike discharge in sympathetic ganglion cells and in nerve.