Presynaptic actions of 4-aminopyridine and gamma-aminobutyric acid on rat sympathetic ganglia in vitro.
Responses to bath-applications of 4-aminopyridine(4-AP) and gamma-aminobutyric acid (GABA) were recorded intracellularly from neurones in the rat isolated superior cervical ganglion. 4-aminopyridine (0.1-1.0 mmol/l) usually induced spontaneous action potentials and excitatory postsynaptic potentials (EPSPs), which were blocked by hexamethonium. Membrane potential was unchanged; spike duration was slightly increased. Vagus nerve B- and C-fibre potentials were prolonged. In 4-AP solution (0.2-0.3 mmol/l), GABA (0.1 mmol/l), 3-aminopropanesulphonic acid or muscimol evoked "bursts" of spikes and EPSPs in addition to a neuronal depolarization. These "bursts", which were not elicited by glycine, glutamate, taurine or (+/-)-baclofen, were completely antagonised by hexamethonium, tetrodotoxin or bicuculline methochloride. It is concluded that: (a) 4-AP has a potent presynaptic action on sympathetic ganglia; (b) presynaptic actions of GABA can be recorded postsynaptically in the presence of 4-AP; and (c) the presynaptic GABA-receptors revealed in this condition are similar to those on the postsynaptic membrane.
D000200:Action Potentials / Q000187:drug effects; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D005260:Female; D005728:Ganglia, Sympathetic / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D011956:Receptors, Cell Surface; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology*
D000631:Aminopyridines; D011956:Receptors, Cell Surface; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline