Serotonin blocks the facilitatory action of muscarinic and nicotinic agents in the hippocampus in vivo.
The inhibitory effect of serotonin, released iontophoretically, on acetylcholine-induced facilitation of population spikes evoked by fimbria-commissural stimulation was studied in the CA1 region of rat hippocampus in vivo. After serotonin was applied for 2.6 +/- 0.8 min, acetylcholine's action was inhibited in 39 cases out of 57 (68.4%), by 68.9 +/- 23.1%, irrespective of whether serotonin alone increased or reduced the population spike. Spiperone, used as a 5-hydroxytryptamine1A (5-HT1A) antagonist, suppressed the inhibitory action of serotonin in 14 of 21 tests. Serotonin had similar effects on population spike facilitations induced by acetyl-beta-methylcholine and dimethylphenylpiperazinium. Thus serotonin, probably acting on 5-HT1A receptors, blocks effectively but indiscriminately all cholinergic facilitations, whether mediated by nicotinic or muscarinic receptors.
Hong
Y
Y
Anaesthesia Research Department, McGill University, Montréal, Qué., Canada.
Krnjević
K
K
D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists; D013134:Spiperone / Q000494:pharmacology
D008688:Methacholine Compounds; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D012702:Serotonin Antagonists; D016210:Methacholine Chloride; D012701:Serotonin; D013134:Spiperone; D000109:Acetylcholine