Modulation of synaptic transmission in autonomic ganglia mediated via the activation of postganglionic muscarinic M1 receptors.

The facilitatory actions of muscarine on synaptic transmission were measured in rat superior cervical ganglia in vitro. Muscarine (300 nmol/l) induced increases in submaximal population action potentials, which were mimicked by the M1 receptor agonist McN-A-343 (1 mumol/l) and antagonized by the M1 receptor antagonist pirenzepine (100 nmol/l) and telenzepine (100 nmol/l), but not by the M2 receptor antagonist AF-DX 116 (1 mumol/l). Slow excitatory postsynaptic potentials recorded from curarized rabbit isolated superior cervical ganglia were also blocked by telenzepine (300 nmol/l) but not by AF-DX 116 (3 mumol/l). It is concluded that M1 receptors mediate the excitatory actions of muscarinic agonists in these sympathetic ganglia.