CIRCADIAN TIMEKEEPING IN HYPERACTIVE AND HYPERTENSIVE INBRED RAT STRAINS

Inbred strains have been used to study genetic and physiological relat ionships among different aspects of circadian timekeeping, as well as relationships between circadian rhythmicity and other strain-specific traits. The present study characterized several features of circadian timekeeping in genetically hyperactive (WKHA) and genetically hyperten sive (WKHT) inbred strains, derived from spontaneously hypertensive (S HR) and Wistar-Kyoto (WKY) rats. WKHAs and WKHTs differed in free-runn ing period, steady-state entrainment to light-dark cycles, and photic phase shifting, and relationships among these measures were consistent with previous studies of species, strain, and individual differences. Because both WKHTs and SHRs show short circadian periods relative to their respective comparison strains, this trait may cosegregate geneti cally with hypertension. In contrast, because WKHAs and SHRs show simi lar photic entrainment and phase shifting, these circadian functions m ay cosegregate with open-field hyperactivity. Finally, because neither WKHAs nor WKHTs show the SHR's excessive levels of home-cage running wheel activity, this trait is not related to either hypertension or op en-field activity. Further work would be required to elucidate specifi c genetic and/or physiological linkages among these variables.