DESCRIPTION: (Applicant's abstract) Many physiological processes and behaviors in virtually all eukaryotes exhibit endogenous circadian rhythmicity. In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus drives these rhythms and serves as the critical neural pacemaker. During aging, many rhythms exhibit shorter periods, phase advances, attenuated amplitudes and temporal desynchronization and fragmentation. In elderly humans, this results in fragmentation of sleep-activity rhythms and desynchronization of endocrine rhythms which may lead to poor health. The long-term objectives of this proposal are to understand (1) the critical cellular and molecular mechanisms that translate the oscillations of individual neurochemicals and cells into the coordinated, synchronized and precise rhythms characteristic of the SCN and (2) how changes in these mechanisms influence declining pacemaker function during aging. Vasoactive intestinal peptide (VIP) and somatostatin (SRIF) may play key roles as communicators of differential afferent input, broadcasters of efferent messages of circadian time or modulators of entrainment. Therefore, the applicant will use cellular and molecular methods to address the following specific aims: (1) characterize the temporal pattern of VIP and SRIF (a) secretion and cellular peptide expression, and (b) levels of mRNA and primary transcript in organotypic cultures containing the SCN. (2) assess the ability of 5HT to phase shift the rhythms of VIP and SRIF secretion in organotypic slices and compare this to its ability to phase shift in dispersed cell cultures. (3) mimic the effects of age on VIP and SRIF by targeted suppression of VIP and/or SRIF via antisense oligonucleotides administered to organotypic slices or dispersed cell cultures and determine the effect on the pattern of expression of the other peptide. The applicant will assess whether 5HT can still phase shift the rhythms of these peptides when VIP or SRIF is suppressed. The applicant states that forthcoming information will deepen our understanding of the cellular and molecular mechanisms that underlie rhythmic activity of the SCN and how changes in these mechanisms may lead to aging-like desynchronization of circadian function. Together with the IRPGs submitted by Drs. Duncan and McMahon, they will focus on this area using a broad array of methods and approaches that is not possible with any single investigator.