Muscarinic postsynaptic events in the cat superior cervical ganglion in situ.

Abstract

In the cat superior cervical ganglion in situ volleys in the preganglionic nerve are capable to evoke hyperpolarizing (P-waves) and depolarizing synaptic responses (LN-waves) which are mediated by muscarinic receptors. In the unblocked and unconditioned ganglion a repetitive stimulation by brief trains of shocks is required to produce a LN-wave; a discharge of ganglionic action potentials is only exceptionally seen during this slow synaptic potential. Single shocks evoked no detectable muscarinic effect. After various procedures (tetanic conditioning, anticholinesterases, slight depolarization by nicotinic agents, KCl and isoprenaline), all known to enhance the responsiveness to exogenous muscarinic agents, a ganglionic transmission of impulses through muscarinic receptors was demonstrated both in the presence and absence of an intact nicotinic transmission. The LN-wave is the postsynaptic event mediating the muscarinic pathway. It is best seen during desensitization of nicotinic receptors by high doses of nicotine.