SCN Outputs and the Hypothalamic Balance of Life

• Published in: Journal of biological rhythms Vol. 21; no. 6; pp. 458 - 469
• Main Authors: Kalsbeek, A, Palm, I.F, La Fleur, S.E, Scheer, F.A.J.L, Perreau-Lenz, S, Ruiter, M, Kreier, F, Cailotto, C, Buijs, R.M
• Format: Journal Article
• Language: English
• Published: Thousand Oaks, CA SAGE Publications 01-12-2006; Sage Publications; Sage Publications, Inc; SAGE PUBLICATIONS, INC
• Subjects: Animals; Autonomic Nervous System - physiology; Biological Clocks - physiology; Biological control systems; Circadian rhythm; Circadian Rhythm - physiology; Endocrine system; Hormones; Humans; Neurons; Neurons - physiology; Neurotransmitters; Physiological aspects; Suprachiasmatic nucleus; Suprachiasmatic Nucleus - physiology; Suprachiasmatic Nucleus - secretion; Vasopressins - physiology; GABA; glucose; melatonin; corticosterone; glutamate; vasopressin
• ISSN: 0748-7304; 1552-4531
• DOI: 10.1177/0748730406293854

The circadian clock in the suprachiasmatic nucleus (SCN) is composed of thousands of oscillator neurons, each dependent on the cell-autonomous action of a defined set of circadian clock genes. Still, the major question remains how these individual oscillators are organized into a biological clock producing a coherent output able to time all the different daily changes in behavior and physiology. In the present review, the authors discuss the anatomical connections and neurotransmitters used by the SCN to control the daily rhythms in hormone release. The efferent SCN projections mainly target neurons in the medial hypothalamus surrounding the SCN. The activity of these preautonomic and neuroendocrine target neurons is controlled by differentially timed waves of, among others, vasopressin, GABA, and glutamate release from SCN terminals. Together, the data on the SCN control of neuroendocrine rhythms provide clear evidence not only that the SCN consists of phenotypically (i.e., according to neurotransmitter content) different subpopulations of neurons but also that subpopulations should be distinguished (within phenotypically similar groups of neurons) based on the acrophase of their (electrical) activity. Moreover, the specialization of the SCN may go as far as a single body structure, that is, the SCN seems to contain neurons that specifically target the liver, pineal, and adrenal.