Cardiac inotropic, chronotropic, and dromotropic actions of subretrofacial neurons of cat RVLM

Abstract

The cardiac actions of microinjecting sodium glutamate (0.5–2 nmol) among sympathetic premotor neurons of the subretrofacial nucleus in the rostral ventrolateral medulla (RVLM) were studied in chloralose-anesthetized cats after bilateral vagotomy, sinoaortic denervation, adrenalectomy, and α1-receptor blockade. Glutamate microinjections increased heart rate by 25.9 ± 1.8 beats/min (17.5%), systolic rate of rise in left ventricular pressure (LVdP/d t) by 1,443 ± 110 mmHg/s (119%), and arterial blood pressure by 26.9 ± 1.7 mmHg (50%), whereas they shortened the electrocardiogram P–R interval in 85 of 103 cases by 7.5 ± 1.2 ms (11.4%), triggering junctional rhythms on five occasions. The increase in LVdP/d tusually led the rise in blood pressure, and its magnitude greatly exceeded any increase attributable to changes in heart rate, diastolic filling, or afterload. Right-sided microinjections caused significantly greater tachycardias than did left-sided microinjections, but only left-sided microinjections triggered junctional rhythms (5 of 52 vs. 0 of 51; P < 0.05), whereas microinjections on either side raised LVdP/d tequally. Subretrofacial neurons thus drive positive chronotropic, inotropic, and dromotropic actions via the cardiac sympathetic nerves, whereas subsets among them preferentially control different aspects of cardiac function.