Relative effects of different spinal autonomic nuclei on cardiac sympathoexcitatory function

Abstract

Mean arterial pressure and heart rate were monitored in immobilized and artificially ventilated male Wistar rats either anesthetized with pentobarbital or decerebrated at midcollicular level. The rate of increase in the left ventricular pressure was also monitored in order to compute contractility index. L-glutamate (1.77 nmole) was microinjected (10 nl) into the following autonomic nuclei of the spinal cord at C 8 to T 4 levels: 1) intermediolateral column (IML), 2) n. intercalates spinalis (IC) and 3) n. intercalates pars paraependymalis (ICpe); this region is commonly known as the central autonomic area (CA). The site of microinjection was marked by injection of a dye; these studies suggested that microinjections of glutamate into the IML are likely to encompass the neurons in the nucleus (n.) intermediolateralis thoracolumbalis pars principalis (ILp) and n. intermediolateralis thoracolumbalis pars funicularis (ILf). Sympathoexcitatory cardiac responses to glutamate microinjections were elicited from T 1 to T 3 levels; these responses could not be evoked at C 8 and T 4 levels. In each of these segments, maximum responses were obtained from the IML while the responses evoked from the IC and the CA were minimal. These results suggest that at T 1 to T 3 levels of the spinal cord, IML is the main cell group regulating sympathetic cardiac function; CA and IC may play a relatively minor role in this function.