Injection of muscimol into posterior hypothalamus blocks stress-induced tachycardia.

Article date: 1989/7/11

PubMed ID: 2750964

Journal name: The American journal of physiology (ISSN: 0002-9513)


We have previously shown that the physiological and behavioral manifestations of emotional stress are produced when drugs impairing gamma-aminobutyric acid (GABA)-mediated synaptic inhibition are injected into the posterior hypothalamic nucleus in rats [Wible, J.H., Jr., F.C. Luft, and J.A. DiMicco. Am. J. Physiol. 254 (Regulatory Integrative Comp. Physiol. 23): R680-R687, 1988]. The purpose of this study was to assess further the potential role of GABA receptors in this region in the response to stress using muscimol, a GABAA receptor agonist. In six chronically instrumented conscious rats, air stress after vehicle treatment evoked marked and sustained tachycardia (+130 +/- 14 beats/min at +10 min) accompanied by a less dramatic increase in arterial pressure (+14 +/- 3 mmHg). Microinjection of muscimol (10 ng; 88 pmol) at the same posterior hypothalamic site in which GABA blockade causes cardiovascular changes similar to those seen in stress produced a modest depression of cardiovascular function in unstressed animals (-28 +/- 5 beats/min and -6 +/- 3 mmHg). However, similar treatment with muscimol virtually abolished the stress-induced tachycardia in the same rats (+9 +/- 8 beats/min), while having no significant effect on baroreflex-evoked increases in heart rate caused by intravenous infusion of sodium nitroprusside (4 micrograms). These findings support a role for activation of neurons in the posterior nucleus of the hypothalamus in the generation of stress-induced cardiovascular changes and for control of this mechanism by local GABA receptors.

Author List: Lisa M, Marmo E, Wible J H, DiMicco J A

Publication Types: Journal Article; Research Support, U.S. Gov't, P.H.S.

Substances mentioned in the article: Muscimol; bicuculline methiodide; gamma-Aminobutyric Acid; Bicuculline;

Mesh terms: Animals; Bicuculline/analogs & derivatives; Blood Pressure/drug effects; Heart Rate/drug effects; Hypothalamus/physiology; Hypothalamus, Posterior/drug effects; Male; Muscimol/pharmacology; Rats; Rats, Inbred Strains; Stress, Physiological/physiopathology; gamma-Aminobutyric Acid/physiology;

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