Synaptic potentials induced by postganglionic stimulations in cat bladder parasympathetic neurones

Abstract

Intracellular recording techniques were used to examine and compare synaptic potentials evoked by stimulating pre- and postganglionic nerve trunks in cat bladder parasympathetic ganglia. In the 76 ganglion cells examined, two types of responses were recorded on stimulating the postganglionic nerve: an antidromic action potential (type PostNS1; n = 30) or a fast excitatory postsynaptic potential (f-EPSP; type PostNS2; n = 46) which resulted in an orthodromic-like action potential. In some of the cells exhibiting a PostNS1 response (n = 19), a fast depolarization was superimposed on the antidromic spike. This depolarization was due to the synaptic activation of nicotinic receptors. In many of the cells exhibiting either PostNS1 or PostNS2 responses, repetitive stimulation of the postganglionic nerve induced a slow hyperpolarization. Applying nicotinic (hexamethonium, 0.5-1 mM) receptor muscarinic (atropine, 1 microM), alpha-adrenergic (phentolamine, 1 microM) and purinergic (caffeine, 0.5-1 mM) receptor antagonists completely inhibited the tetanus-induced slow hyperpolarization in some cells (n = 5). In other cells (n = 15), a slow hyperpolarization persisted in the presence of these antagonists. These results indicate that stimulation of the postganglionic nerve trunk of cat bladder parasympathetic ganglia can elicit not only an antidromic action potential, but also synaptic potentials which are mediated by the activation of cholinergic (nicotinic and muscarinic), noradrenergic and purinergic receptors, as well as non-cholinergic, non-alpha-adrenergic and non-purinergic synaptic potential.