Inhibition of neuronal firing by opiates: evidence against the involvement of cyclic nucleotides.
1. Extracellular recordings were made in vitro from single neurones of the myenteric plexus of the guinea-pig ileum. 2. Neuronal firing was inhibited by morphine and normorphine (10 nM to 1 micrometer). Cyclic adenosine 3',5'-monophosphate (cyclic AMP) (100 micrometer to 1 mM) also inhibited the firing of the majority of the neurones. Prostaglandin E2 usually caused a short-lasting excitation of myenteric neurones and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine was usually without effect on firing rate. 3. The inhibition of neuronal firing by normorphine was unaffected by prior and/or concurrent administration of cyclic AMP, dibutyryl cyclic adenosine 3',5'-monophosphate, prostaglandin E2 or 3-isobutyl-1-methylxanthine. As these four treatments might be expected to elevate intracellular levels of cyclic AMP, the results lend no support to the notion that a reduction in intracellular cyclic AMP is essential to the inhibition of firing produced by morphine.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects*; D011458:Prostaglandins E / Q000494:pharmacology; D013997:Time Factors
D009294:Narcotics; D011458:Prostaglandins E; D009270:Naloxone; D003994:Bucladesine; D000242:Cyclic AMP; D000109:Acetylcholine; D015056:1-Methyl-3-isobutylxanthine