Neurochemical Control of Circadian Rhythms
Final rept. 1 Apr 1986-31 Oct 1991
GEORGIA STATE UNIV ATLANTA
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The central aim of this grant was to identify which of the various neurotransmitters found within the suprachiasmatic nucleus SCN are involved in synchronizing circadian rhythms with the day-night cycle. Our approach was to determine which SCN neurotransmitters are both influenced by light and capable of shifting the phase of circadian rhythms. We have investigated the possible role of a number of neurotransmitters in circadian control e.g. vasopressin, GABA, neuropeptide Y. However, out primary focus has been on the circadian functions of vasoactive intestinal peptide VIP, peptide histidine isoleucine PHI and gastrin releasing peptide GRP. As the result our work on VIP, PHI and GRP we have developed a working hypothesis of the neurochemical mechanisms underlying the synchronization of circadian rhythms with the day-night cycle. The hypothesis, called the ratio hypothesis, states that light communicated to the SCN via afferent pathways sets the ratio of VIPPHI to GRP available for release from SCN neurons by altering the cellular levels of VIPPHI mRNA andor GRP mRNA, and that the ratio of VIPPHI to GRP released from SCN neurons in response to light determines how the circadian clock is reset by light. Peptides, hypothalamus, colocalization, light, gene expression.
- Anatomy and Physiology