AREGU Apr. 45/4

Campos, R. R., and R. M. McAllen. Cardiac inotropic, chronotropic, and dromotropic actions of subretrofacial neurons of cat RVLM. Am. J. Physiol. 276 (Regulatory Integrative Comp. Physiol. 45): R1102–R1111, 1999.—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 a1-receptor blockade. Glutamate microinjections increased heart rate by 25.9 6 1.8 beats/min (17.5%), systolic rate of rise in left ventricular pressure (LVdP/dt) by 1,443 6 110 mmHg/s (119%), and arterial blood pressure by 26.9 6 1.7 mmHg (50%), whereas they shortened the electrocardiogram P–R interval in 85 of 103 cases by 7.5 6 1.2 ms (11.4%), triggering junctional rhythms on five occasions. The increase in LVdP/dt usually 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/dt equally. 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.