Propranolol blocks recurrent synaptic activation in paravertebral sympathetic ganglia of bullfrogs

Intracellular recordings were made from neurons in bullfrog sympathetic ganglia. Orthodromic, intracellular and antidromic stimulations evoked recurrent depolarizing responses accompanied by a spontaneous firing of the action potential in type 2 neurons. The depolarizing response elicited by intracellular and antidromic stimulations was selectively blocked by propranolol (1 microM), but not by yohimbine and phenoxybenzamine. Propranolol did not block the 'nicotinic' fast excitatory postsynaptic potential evoked by orthodromic stimulation. These results suggest that excitatory beta-adrenoceptors mediate the recurrent synaptic facilitation of nicotinic transmission in type 2 neurons of bullfrog sympathetic ganglia.