A neurophysiological study of the medullary sympathetic pathway to the adrenal gland (1131.7)

Abstract

Neurons in the rostral ventrolateral medulla (RVLM) control adrenaline secretion from the adrenal gland and participate in glucose homeostasis. Here, we examined sympathetic evoked responses recorded from the adrenal sympathetic nerve in response to intermittent stimulation of the RVLM. All experiments were performed using isoflurane/urethane‐anaesthetised, artificially‐ventilated, paralysed, male Sprague‐Dawley rats. The RVLM was first identified by extracellular single unit recording combined with field potential mapping of the facial nucleus. We compared the latencies of the evoked adrenal sympathetic nerve (ASNA) response to the lumbar sympathetic nerve (LSNA) response upon electrical stimulation of RVLM (0.5 Hz, 1 ms pulse width, 50‐300 μA) after conversion to urethane (1.4 g/kg, i.v.). RVLM stimulation elicited an evoked ASNA response that depended on whether the recording was primarily pre‐ or post‐ganglionic activity as judged by the effect of the ganglion blocker hexamethonium (Hex; 20‐40 mg/kg, i.v.). Pre‐ganglionic ASNA consisted of an early peak (latency ‐ 79±9 ms, n=4) and a late peak (latency ‐ 149±6 ms). Lumbar sympathetic nerve activity exhibited a prominent early peak (latency ‐ 87±7 ms; n = 5) that was eliminated by Hex. Pre‐ganglionic ASNA was reduced by 62 % after intrathecal kynurenate (0.5 μmole/10 μl; P<0.01, late peak, n=3). The early peak may represent sympathetic vasomotor activity in both the adrenal and lumbar sympathetic nerves. However, the late sympathetic response noted in the adrenal nerve is mediated by a glutamatergic input and may be involved in the control of catecholamine secretion from adrenal chromaffin cells.Grant Funding Source: National Health and Medical Research Council of Australia