Facilitation of ganglionic response to bethanechol by repetitive stimulation of the preganglionic nerve

Repetitive stimulation of the preganglionic nerve of the rat superior cervical sympathetic ganglion potentiates the amplitude of asynchronous firing elicited by the muscarinic agonist, bethanechol. The amplitude of stimulus-induced facilitation is not related to frequency of stimulation and occurs with a stimulation frequency of 10 Hz or greater. Facilitation, but not the asynchronous firing is reduced by lowering the temperature of the bathing solution. Dibutryl cyclic adenosine monophosphate and theophylline had no effect on asynchronous firing but reduced stimulus-induced facilitation. Neither dibutryl cyclic guanosine monophosphate up to 1 mM nor nitroprusside had any significant effect on bethanechol-induced asynchronous firing or stimulus-induced facilitation. Tetraethylammonium caused a 200% increase in stimulus-induced facilitation. Acetylcholine, in a concentration that elicited maximum nicotinic firing, had no effect on the magnitude of bethanechol-induced asynchronous firing. Increased Ca++, Mg++ or Mn++ reduced both asynchronous firing and stimulus-induced facilitation. It is concluded that facilitation is a result of transmitter release, possibly not acetylcholine.