On the involvement of GABA in the analgesia produced by baclofen, muscimol and morphine.
In the mouse hot-plate test (50 degrees C), muscimol produced analgesia which was blocked by bicuculline but not by picrotoxin. Analgesia produced by baclofen was dose-dependent and stereoselective, but was not blocked by bicuculline, picrotoxin or naloxone. Morphine-induced analgesia was not altered by bicuculline. The inhibitors of GABA-transaminase, amino-oxyacetic acid, gamma-acetylenic GABA and gamma-vinyl GABA, produced analgesia which was much more prolonged than that observed with muscimol, baclofen or morphine. The analgesic action of these agents was not significantly altered by bicuculline. At a higher plate temperature (55 degrees C), GABA-transaminase inhibitors produced minimal analgesia but significantly enhanced the analgesic action of baclofen. gamma-Vinyl GABA markedly increased both the peak effect and the duration of analgesia but gamma-acetylenic GABA and amino-oxyacetic acid caused smaller increases. In the mouse hot-plate test, bicuculline-sensitive GABA receptors appear to mediate the analgesic action fo muscimol. Analgesia produced by baclofen, morphine and inhibitors of GABA-transaminase may involve another class of GABA receptors which are insensitive to bicuculline.
D000612:4-Aminobutyrate Transaminase / Q000378:metabolism*; D000698:Analgesia; D000700:Analgesics; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D008297:Male; D051379:Mice; D009118:Muscimol / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology; D000637:Transaminases / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D000612:4-Aminobutyrate Transaminase; D000700:Analgesics; D001418:Baclofen; D001640:Bicuculline; D009118:Muscimol; D009270:Naloxone; D010852:Picrotoxin; D000637:Transaminases; D005680:gamma-Aminobutyric Acid