Lack of evidence of an interaction between leu-enkephalin and muscarinic-like responses in the frog semicircular canal.
Using multiunit recording of action potentials from the whole vestibular nerve, we studied whether opioid peptide leu-enkephalin (Enk) may modulate muscarinic-like responses in semicircular organs of the frog. When acetylcholine (ACh) (0.1-1 mM) was applied with 1 nM Enk, the maximal frequency increase induced by ACh was reduced.However,the frequency decrease of ACh responses under Enk did not differ from the frequency decline in basal spike discharge induced by Enk alone. Administration of atropine (1 microM) left the response to Enk intact and blocked the excitatory effect of ACh. No modification of the ACh response under Enk was observed in the presence of the non-selective opioid receptor antagonist naloxone (10 microM). This study suggests that no interaction exists between the ACh-mediated excitatory action on resting activity in the isolated semicircular canal preparation and the suppressive action of Enk.
Andrianov
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Pavlov Institute of Physiology of the Russian Academy of Sciences, St Petersburg, Russia. andryu@infran.ru
Ryzhova
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D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D066298:In Vitro Techniques; D009116:Muscarine / Q000494:pharmacology*; D018721:Muscarinic Agonists / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011896:Rana temporaria; D012665:Semicircular Canals / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D009292:Narcotic Antagonists; D014665:Vasodilator Agents; D009270:Naloxone; D004743:Enkephalin, Leucine; D001285:Atropine; D009116:Muscarine; D000109:Acetylcholine