Daily biological timekeeping, best reflected in the perception of lay persons in terms of human "jet-lag" or shift-work maladies, is regulated by a composite interaction of neural pacemaker (SCN) and environmental synchronizing agents. The pacemaker autonomously drives dependent biochemical, physiological and behavioral functions with free-running circadian period under constant environmental conditions close to but not exactly 24-hours, while the environmental entraining or synchronizing agent corrects phase and frequency of the pacemaker to local time. Much mammalian circadian research, particularly the physiological aspect, has been limited to laboratory rats and golden hamsters. In an attempt to distinguish differences between the circadian "wiring" of diurnal mammals and better known nocturnal mammals, the study will examine selected key issues for three diurnal species in successive stages of circadian function including sensory input from the environment for entertainment, physiological properties of the SCN rhythm generator, and behavioral output. Physiological and behavioral circadian output measurements will be employed in these three diurnal rodents to clarify circadian regulation in day-active mammals. The antelope ground squirrel, 13- lined ground squirrel, and eastern chipmunk were chosen as model species to minimize operational problems that have long hindered progress of research on circadian behavioral function in diurnal mammals, and also to assess circadian variation span in ecologically widely divergent desert, prairie, and forest species. Issues will include the light-sampling process for entrainment in lab and field, the role of environmental temperature as well as cyclic body temperature in circadian function, and the delineation of a "light-mimicking" phase response curve system (PRC) by use of intraventricular injection of carbachol; the distribution of key SCN neuropepetides (NP-II, VIP, SS, NPY) will be determined by immunocytochemical methods plus computerized image processing for quantitative determination of co-localized immunoreactivity. Finally, in vitro and in vivo recording of SCN rhythmic output relative to other brain areas will also be investigated. The data may serve as a useful model for better understanding the functioning of diurnal circadian systems of mammals, and more generally for envisioning the means by which the relatively simple neuronal circuitry of the SCN is able to control contrasting nocturnal and diurnal circadian behavior modes.
