Selective antagonism of muscarinic potentials on the superior cervical ganglion of the rat

Abstract

Selective antagonists have been used to classify the muscarinic receptors involved in the slow excitatory postsynaptic potential and slow inhibitory postsynaptic potential of the superior cervical ganglia of the rat, as recorded in 1 μM neostigmine, using a grease-gap method. Cardioselective M 2 antagonists, e.g. AF-DX 116, depressed the slow inhibitory postsynaptic potential and enhanced the slow excitatory postsynaptic potential. The M 1 selective antagonist pirenzepine depressed both potentials equally. The high potency of pirenzepine against the slow excitatory postsynaptic potential, however, indicates that it is mediated by M 1 receptors. The slow excitatory and inhibitory postsynaptic potentials were found to be pharmacologically similar to the muscarinic agonist-induced depolarisation and hyperpolarisation of this preparation, respectively. The actions of two muscarinic agonists on the postsynaptic potentials were also studied. It is concluded that the slow excitatory postsynaptic potential is mediated by M 1 receptors and the slow inhibitory postsynaptic potential by cardiac-like M 2 receptors.