title: Activation of brainstem endorphinergic neurons causes cardiovascular depression and facilitates baroreflex bradycardia.
abstract: The effects of electrical stimulation of the arcuate nucleus on blood pressure, heart rate and baroreflex sensitivity were studied in urethane-anesthetized Sprague-Dawley rats. Stimulation of the mid-anterior parts of the arcuate nucleus at 80 Hz, 0.8 ms and 50-200 microA caused a biphasic, depressor/pressor, response and moderate bradycardia. Intravenous administration of a vasopressin V1-receptor antagonist eliminated the pressor component and unmasked a pure depressor response. This depressor response could be inhibited by naltrexone, 2 mg/kg i.v., by an antiserum against beta-endorphin, 100 nl injected directly into the ipsilateral nucleus tractus solitarii, or by deafferentation of the dorsal vagal complex (nucleus tractus solitarii and dorsal vagal nucleus) by an ipsilateral, dorsolateral knife-cut of the medulla oblongata. Stimulation of the arcuate nucleus at currents of 20-40 microA did not influence basal blood pressure or heart rate but potentiated the reflex bradycardia induced by phenylephrine, and this effect was completely blocked by naltrexone. It is concluded that a beta-endorphin-containing pathway projecting from the arcuate nucleus to the ipsilateral dorsal vagal complex is involved in depressor cardiovascular regulation and in the facilitation of baroreflex bradycardia.
authors.affiliation: Laboratory of Physiologic and Pharmacologic Studies, National Institute on Alcohol Abuse and Alcoholism, Bethesda, MD 20892.
authors.forename: J A
authors.initials: JA
authors.lastname: Mastrianni
authors.forename: M
authors.initials: M
authors.lastname: Palkovits
authors.forename: G
authors.initials: G
authors.lastname: Kunos
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D001919:Bradycardia / Q000503:physiopathology*; D002320:Cardiovascular Physiological Phenomena; D002319:Cardiovascular System / Q000187:drug effects; D004558:Electric Stimulation; D004723:Endorphins / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004723:Endorphins; D009271:Naltrexone