title: Presynaptic gamma-aminobutyric acid receptors in the rat anococcygeus muscle and their antagonism by 5-aminovaleric acid.
abstract: 1 The effects of gamma-aminobutyric acid (GABA) and related drugs on the isolated anococcygeus muscle of the rat were determined. 2 GABA caused a dose-related inhibition of the electrically-evoked twitch response. 3 The maximum response to GABA was a 56.8% depression of twitch response, with an EC50 of 0.68 microM. 4 (+/-)-Baclofen mimicked the effect of GABA (EC50 0.9 microM). (+)-Baclofen was more than 100 times less active than (--)-baclofen. 5 The response to GABA was unaffected by picrotoxin or bicuculline but was antagonized by 5-aminovaleric acid (0.5) mM). 6 Our results suggest that GABAB receptors are present on motor nerve terminals in the rat anococcygeus muscle and that 5-aminovaleric acid is an antagonist of these receptors.
mesh_terms: D000596:Amino Acids / Q000494:pharmacology*; D021542:Amino Acids, Neutral; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000378:metabolism*; D009411:Nerve Endings / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D021542:Amino Acids, Neutral; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; C013809:5-aminovaleric acid