Research Opportunities in Autonomic Neural Mechanisms of Cardiopulmonary Regulation: A Report From the National Heart, Lung, and Blood Institute and the National Institutes of Health Office of the Director Workshop.

This virtual workshop was convened by the National Heart, Lung, and Blood Institute, in partnership with the Office of Strategic Coordination of the Office of the National Institutes of Health Director, and held September 2 to 3, 2020. The intent was to assemble a multidisciplinary group of experts in basic, translational, and clinical research in neuroscience and cardiopulmonary disorders to identify knowledge gaps, guide future research efforts, and foster multidisciplinary collaborations pertaining to autonomic neural mechanisms of cardiopulmonary regulation. The group critically evaluated the current state of knowledge of the roles that the autonomic nervous system plays in regulation of cardiopulmonary function in health and in pathophysiology of arrhythmias, heart failure, sleep and circadian dysfunction, and breathing disorders. Opportunities to leverage the Common Fund's SPARC (Stimulating Peripheral Activity to Relieve Conditions) program were characterized as related to nonpharmacologic neuromodulation and device-based therapies. Common themes discussed include knowledge gaps, research priorities, and approaches to develop novel predictive markers of autonomic dysfunction. Approaches to precisely target neural pathophysiological mechanisms to herald new therapies for arrhythmias, heart failure, sleep and circadian rhythm physiology, and breathing disorders were also detailed.

Life-long serotonin reuptake deficiency results in complex alterations in adrenomedullary responses to stress.

This study examined whether serotonin transporter (SERT) deficiency influences adrenal serotonin (5-HT), catecholamine and Angiotensin II (Ang II) systems, and the hormonal response to acute restraint stress. Control SERT mice (+/+) expressed high numbers of SERT binding sites in adrenal medulla. Fifteen minutes of restraint stress increased adrenal 5-HT, adrenomedullary tyrosine hydroxylase (TH) mRNA expression and plasma epinephrine (EPI), and norepinephrine levels without alterations in adrenal catecholamine content. In SERT+/+, these responses coincided with a significant increase in adrenomedullary Ang II AT(2) receptor expression. SERT-deficient mice did not express SERT binding sites; their adrenal 5-HT was significantly depleted and further reduced after stress. They had exaggerated stress-induced EPI release into plasma, the increase in TH transcription did not occur, adrenal catecholamine content was decreased compared with SERT+/+, and stress induced a reduction rather than increase in the number of adrenomedullary AT(2) receptors. SERT-/- mice also possessed decreased pituitary 5-HT. Their pituitary ACTH was reduced after stress, but stress-induced increases in plasma ACTH and corticosterone were not different from those of SERT+/+ mice. Our results indicate that SERT function not only restrains stress-induced EPI release but also is required for the increase in adrenal catecholamine synthesis and AT(2) receptor expression.

Exaggerated adrenomedullary response to immobilization in mice with targeted disruption of the serotonin transporter gene.

This study examined whether serotonin transporter (5-HTT) gene knockout influences adrenomedullary, sympathoneural, or hypothalamo-pituitary-adrenal responses to acute immobilization. In conscious, cannulated mice, arterial plasma concentrations of catecholamines, ACTH, and corticosterone were measured at baseline and after 15 min of immobilization. Tissue levels of serotonin (5-HT), catecholamines, and hormones were also measured in pituitary and adrenal glands. At baseline, adrenal and pituitary 5-HT concentrations in knockout (5-HTT(-/-)) mice were markedly lower than those in littermate control (5-HTT(+/+)) mice, whereas the groups did not differ in levels of catecholamines or hormones in plasma or tissue. Immobilization increased plasma levels of catecholamines, ACTH, and corticosterone in all genotypes. 5-HTT(-/-) mice had exaggerated responses of plasma epinephrine to immobilization and significant reductions in adrenal epinephrine, norepinephrine, and 5-HT contents compared with values in littermate controls. Pituitary ACTH was significantly reduced after immobilization in 5-HTT(-/-) mice only, but increases in plasma ACTH and corticosterone levels did not differ between genotypes. The results suggest that one 5-HTT function is to restrain adrenomedullary activation in response to immobilization. Exaggerated adrenomedullary responses seem to be an autonomic correlate of the anxiety-like behaviors in 5-HTT knockout mice.