Fig. 3. Autonomic components of 1 minimum alveolar concentration (MAC) isoflurane (ISO) actions on mean arterial pressure (MAP)–heart rate (HR) baroreflex curves for brain-intact/sham (A  and C ) and decerebrate (Dec;B  and D ) rats. Antagonism of cardiac β-adrenergic receptors with atenolol (ATN; 1 mg/kg) depressed the tachycardia portion of the baroreceptor reflex during isoflurane similarly to isoflurane alone in intact (A ) and decerebrate (B ) rats. Antagonism of cardiac muscarinic receptors with methyl atropine (MAT; 0.5 mg/kg) eliminated the bradycardic baroreceptor reflex responses present during isoflurane in intact (C ) and decerebrate (D ) rats. Each panel shows curves for the following conditions: (1) zero isoflurane; (2) during 1 MAC isoflurane; and (3) 1 MAC isoflurane plus antagonist. Parentheses indicate the number of animals. Zero isoflurane curves represent pooled averages from other series. Closed circles indicate resting levels of MAP and HR for each curve. bpm = beats/min.