title: Hyperpolarizing action of enkephalin on neurons in the dorsal motor nucleus of the vagus, in vitro.
abstract: Intracellular recordings were made from neurons of the dorsomotor vagal nucleus (DMV) in slices of rat medulla oblongata. [D-Ala2, D-Leu5]-enkephalin (DADLE), applied by perfusion (0.01-3 microM) or droplets, dose-dependently hyperpolarized 85% of the DMV neurons tested. The hyperpolarization, associated with a decrease in membrane resistance, persisted after elimination of synaptic activity by perfusion with Ca2(+)-free/high-Mg2+ solution or with 1 microM TTX solution. The opioid antagonist, naloxone, reversibly inhibited DADLE-induced hyperpolarization. The hyperpolarization depended on extracellular K+ concentration and reversed at about -90 mV. DADLE also decreased Ca2(+)-dependent spike duration and after-hyperpolarization (AHP). DAGO (a selective mu-receptor agonist), but not DPLPE (a selective delta-receptor agonist), mimicked DADLE's effects on membrane potential, Ca2(+)-dependent spike duration, and AHP. It is concluded that DADLE, through postsynaptic mu-type opioid receptors, hyperpolarized DMV neurons by increasing K+ conductance, which may have an inhibitory effect on DMV output. DADLE-induced decrease of spike duration and AHP was also mediated by mu-receptors and could have additional effects on functions of the DMV neuron by virtue of reduction in Ca2+ entry.
authors.affiliation: Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
authors.forename: S M
authors.initials: SM
authors.lastname: Duan
authors.forename: N
authors.initials: N
authors.lastname: Shimizu
authors.forename: A
authors.initials: A
authors.lastname: Fukuda
authors.forename: T
authors.initials: T
authors.lastname: Hori
authors.forename: Y
authors.initials: Y
authors.lastname: Oomura
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D016308:Enkephalin, Leucine-2-Alanine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D011188:Potassium / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D014630:Vagus Nerve / Q000187:drug effects
chemical_list: D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D016308:Enkephalin, Leucine-2-Alanine; D020881:Enkephalin, D-Penicillamine (2,5)-; D011188:Potassium; D002118:Calcium