Blockade of bicuculline-induced pressor and tachycardic responses by forebrain administration of muscimol.

To determine whether i.v. administered bicuculline acts in the forebrain to increase arterial blood pressure and heart rate, this agent was administered i.v. to chloralose anesthetized cats that had muscimol injected into and restricted to the forebrain ventricles. Bicuculline (0.5 mg/kg i.v.) given alone increased arterial pressure by 56 +/- 8 mm Hg and heart rate by 45 +/- 11 beats/min. Bicuculline given to animals exposed to muscimol exhibited no increase in either of these parameters. Muscimol localized to the forebrain did not alter the pressor response to a non-GABA antagonist agent, strychnine, indicating a specific interaction of the drugs with GABA receptors in the forebrain.