Spatial and activity-dependent catecholamine release in rat adrenal medulla under native neuronal stimulation

Abstract

Neuroendocrine chromaffin cells of the adrenal medulla in rat receive excitatory synaptic input through anterior and posterior divisions of the sympathetic splanchnic nerve. Upon synaptic stimulation, the adrenal medulla releases the catecholamines, epinephrine, and norepinephrine into the suprarenal vein for circulation throughout the body. Under sympathetic tone, catecholamine release is modest. However, upon activation of the sympathoadrenal stress reflex, and increased splanchnic firing, adrenal catecholamine output increases dramatically. Moreover, specific stressors can preferentially increase release of either epinephrine (i.e., hypoglycemia) or norepinephrine (i.e., cold stress). The mechanism for this stressor‐dependent segregated release of catecholamine species is not yet fully understood. We tested the hypothesis that stimulation of either division of the splanchnic selects for epinephrine over norepinephrine release. We introduce an ex vivo rat preparation that maintains native splanchnic innervation of the adrenal gland and we document experimental advantages and limitations of this preparation. We utilize fast scanning cyclic voltammetry to detect release of both epinephrine and norepinephrine from the adrenal medulla, and report that epinephrine and norepinephrine release are regulated spatially and in a frequency‐dependent manner. We provide data to show that epinephrine is secreted preferentially from the periphery of the medulla and exhibits a higher threshold and steeper stimulus‐secretion function than norepinephrine. Elevated stimulation of the whole nerve specifically enhances epinephrine release from the peripheral medulla. Our data further show that elimination of either division from stimulation greatly attenuated epinephrine release under elevated stimulation, while either division alone can largely support norepinephrine release.

Monitoring the Secretory Behavior of the Rat Adrenal Medulla by High-Performance Liquid Chromatography-Based Catecholamine Assay from Slice Supernatants

“…Regarding E and NE secretion, we observed a bias toward a shift from central to peripheral E and NE release upon ACh challenges, suggesting that peripheral and central CA secretion might be differentially regulated. Along the same line, an attempt to answer this thorny issue has been recently reported using an elegant ex vivo spinal–splanchnic nerve–adrenal preparation ( 85 ). The authors showed that upon robust splanchnic nerve stimulation, E seems to be preferentially released from the periphery and NE secreted from the center of the medulla.…”

Synaptotagmin-7 participates in the regulation of acetylcholine release and short-term presynaptic facilitation in splanchnic nerve terminals

“…The variation in firing rate, in turn, may reflect the changing demands placed on them as effectors of the sympathetic stress response (39). In experimental paradigms mimicking strong sympathetic activation of chromaffin cell secretion, splanchnic input has been stimulated at rates that ranged from 10 -20 Hz (30,38,40). We sought to determine whether the splanchnic synapse fa- cilitates even at these high firing rates, or whether it might undergo depression.…”

Innervated adrenomedullary microphysiological system to model prenatal nicotine and opioid exposure

“…Once isolated from animals or differentiated from stem cells, both AMCCs and cultured adrenal slices lack neural regulation. Both in vivo and ex vivo models have been used to investigate the SAM axis, and together have helped establish our current understanding of neurogenic control of CAT release (26). Due to the confounding impact of autonomic regulation and other feedback mechanisms, however, in vivo approaches are ill-suited for developing a comprehensive understanding of the cellular mechanisms regulating CAT release.…”