Facilitatory effect of some drugs on transmission in the frog sympathetic ganglion.

Effects of 3,4-diaminopyridine and dimethylsulfoxide on transmission in frog sympathetic ganglion were analyzed. In the presence of either drug repetitive waves appeared in the compound action potential. Intracellular recording revealed a repetitive firing of certain populations of ganglionic neurons following each orthodromic stimulus. Antidromic stimulation did not evoke any repetitive response. Dependence of the repetitive response on drug concentration and stimulation rate is described. An enhancement and prolongation of fast EPSP was observed in the presence of both drugs. It is assumed that by interference with changes in membrane potassium permeability the drugs prolong the action potential in presynaptic terminals with a resulting increase in synaptic output of transmitter. The repetitive firing of the postsynaptic membrane subsequent to activation of the synapse is a consequence of its prolonged and more profound depolarization. Presumably, this is one of several mechanisms of drug-induced increase in efficacy of synaptic transmission in frog sympathetic ganglion known as stimulus-bound repetition.