Cardiorespiratory effects produced by injecting drugs that affect GABA receptors into nuclei associated with the ventral surface of the medulla.
It has recently been shown that L-glutamic acid induced stimulation of cell bodies in a circumscribed area of the rostral ventrolateral medulla (RVLM) in the cat, produced increases in arterial pressure (AP), decreases in heart rate (HR) and transient apnea (Gatti, Norman, DaSilva and Gillis, 1986). The purpose of the present study was to determine if this same area was sensitive to GABA receptor agonists and antagonists. Injection of the GABA agonist muscimol (200 ng), into the rostral ventrolateral medulla of cats anesthetized with chloralose produced a precipitous and immediate fall in arterial pressure (-95 +/- 4.6) and heart rate (-31 +/- 5.9; n = 4, P less than 0.05). Maximal cardiovascular effects could only be achieved if muscimol was injected bilaterally. These effects of muscimol on arterial pressure were dose-dependent. Time-action curves for the effects of muscimol on arterial pressure and respiration were different. Hypotension occurred first and was followed later in time by a decrease in minute ventilation. Within 30 min all animals were apneic after the 200 ng dose. The cardiovascular effects of muscimol were reversed by the injection of the GABA receptor antagonist bicuculline. These data indicate that stimulation of GABA receptors in the rostral ventrolateral medulla produced selective cardiovascular effects and that respiratory neurons sensitive to GABA are apparently not localized with these cardiovascular neurons.
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001931:Brain Mapping; D002320:Cardiovascular Physiological Phenomena; D002415:Cats; D005260:Female; D007555:Isoxazoles / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D012119:Respiration; D009435:Synaptic Transmission; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D007555:Isoxazoles; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; C015542:gaboxadol; D001640:Bicuculline