Interactions between GABA and 5-hydroxytryptamine in the guinea-pig ileum.
In isolated segments of the guinea-pig ileum, there was: (a) an early, short-lived (less than 20 s) depression by gamma-aminobutyric acid (GABA) of contractile responses to 5-hydroxytryptamine (5-HT), acetylcholine(ACh), or nicotine, also seen with 3-amino-1-propanesulphonic acid (3APS) or muscimol in place of GABA, and sensitive to bicuculline, picrotoxinin or piretanide, and (b) a delayed, longer-lasting (30 s-1 min) depression of responses to 5-HT and nicotine, but not exogenously applied ACh, also seen with baclofen and only antagonised by delta-aminovaleric acid (DAVA). At 25 degrees C, all these effects were still observed but slowed, whilst at 37 degrees C after cold storage (6 degrees C) overnight, the early, short-lived depression was reduced or eliminated, yet the delayed depression was enhanced. It is concluded that the early, short-lived depression is mediated through GABAA-receptor sites, and the delayed, longer-lasting depression through GABAB-receptor sites on neurones of the myenteric plexus; effects consistent with GABA being a neurotransmitter in the enteric nervous system.
D000109:Acetylcholine / Q000037:antagonists & inhibitors; D000818:Animals; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology; D011963:Receptors, GABA-A; D012701:Serotonin / Q000494:pharmacology / Q000502:physiology*; D013696:Temperature; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology / Q000502:physiology*
D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D000109:Acetylcholine