Modulated intra-train spike responses in the cat superior cervical ganglion in vivo.

The known two-stage facilitation/depression pattern of postganglionic responses was found at high (24 Hz) frequency stimulation of the preganglionic nerves. We found that the depression stage was exaggerated under partial hexamethonium blockade but it was not affected by partial transection of the preganglionic trunk. At low frequency (8 Hz) normal recruitment turned into the familiar two-stage pattern under moderated hexamethonium doses. The depression course under the competitive nicotinic antagonist dihydro-beta-erythroidine was markedly slower than under hexamethonium. These observations are accountable to the known use-dependence effect of hexamethonium.