Suprachiasmatic hypothalamic nuclei (SCN) in regulation of homeostasis: a role beyond circadian control?

ABSTRACT

The role of suprachiasmatic nuclei (SCN) in the anterior hypothalamus as a master ~24 h oscillator (clock) and synchronizer of the circadian regulatory system is reviewed extensively. In contrast, the ample evidence that SCN also exert a circadian-independent impact on homeostasis and metabolism is underappreciated. Therefore, herein we focus on the evidence for SCN participation in homeostatic (non-circadian) mechanisms in regulation of arterial blood pressure and hydro-mineral balance, plasma glucose level, food intake, renin, ACTH/corticosterone, GH, thyroid hormones and melatonin secretion. We conclude that, in addition to their major role in circadian control, SCN also selectively participate in homeostatic control. The evidence supports a model where the ventrolateral region of SCN and especially its vasointestinal polypeptide (VIP)-containing neurons convey the homeostatic influences of SCN to the metabolic regulatory pathways. The precise mechanisms of the rhythmic wisdom of the body, i.e., how SCN circadian clock and the daily behavioral and endocrine rhythms harmonize with the homeostatic regulatory systems defending the relative constancy of the internal milieu, remain to be elucidated. The non-circadian SCN contributions in responses to homeostatic challenges certainly deserve careful consideration in future studies.

Abbreviations 2-DG: 2-deoxy-D-glucose; AV3V: anteroventral third ventricle region; GRF - growth-hormone-releasing factor; MnPO: median preoptic nucleus; NTS: nucleus of the solitary tract; OVLT: organum vasculosum of the lamina terminalis; PRA: plasma renin activity; SCN: suprachiasmatic nuclei; SD: sleep deprivation; VIP: vasoactive intestinal polypeptide.

KEYWORDS:

• Suprachiasmatic nuclei
• homeostatic control
• water–salt balance
• blood pressure
• glucose
• vip

Acknowledgments

A.G.S. would like to express his gratitude to Prof. Franz Halberg, University of Minnesota, Professors Jacques LeMagnen and Stylianos Nicolaїdis, College de France, and Professors Katsuya Nagai and Hachiro Nakagawa, Osaka University, for their friendliness, encouragement and hospitality.

Disclosure statement

No potential conflict of interest was reported by the author(s).