Responses of adrenal sympathetic preganglionic neurons to stimulation of cardiopulmonary receptors

Abstract

The current study examined whether or not the activation of Bezold-Jarisch reflex with administration of phenylbiguanide (PBG, 100 μg/kg) into right atrium elicits differential responses in the two populations of adrenal sympathetic preganglionic neurons (SPNs) regulating the release of epinephrine (EPI ADR SPNs) and norepinephrine (NE ADR SPNs), respectively, from adrenal medullary chromaffin cells. Extracellular activity of 48 adrenal SPNs in the intermediolateral cell column (IML) were recorded in urethane/chloralose-anesthetized rats. Twenty-three EPI ADR SPNs and 25 NE ADR SPNs were antidromically activated by stimulation of left adrenal nerve and orthodromically activated by rostral ventrolateral medulla (RVLM) stimulation. At a mean arterial pressure (MAP) of 99.6±2.8 mmHg, the mean spontaneous discharge rates of EPI ADR SPNs and NE ADR SPNs were 6.2±0.5 and 4.3±0.5 spikes/s, respectively. Intra-atrial PBG markedly inhibited 96% of EPI ADR SPNs (by 3.8±0.4 spikes/s; n=22) and 76% of NE ADR SPNs (by 2.9±0.5 spikes/s; n=19) with hypotensive responses ( ΔMAP=33.2±5.3 and 26.4±5.0 mmHg, respectively). The remaining SPNs were weakly excited or unaffected. We conclude that both groups of SPNs regulating catecholamine release are primarily inhibited by stimulation of cardiopulmonary receptors and that these responses parallel the sympathoinhibitory and hypotensive components of the Bezold-Jarisch reflex.