Core temperature in the female rat: effect of pinealectomy or altered lighting

Abstract

Radiotelemetry of core temperature in unrestrained, mature female rats revealed the existence of a 24-h rhythm that was bimodal. The principal peak occurred during the night under control conditions of 14 h light and 10 h darkness, and a less pronounced, secondary peak occurred 3-4 h after the onset of the light phase. Shifts in the phase of the photoperiod or alteration of the proportion of light per day revealed that the temperature rhythm was entrained by light, but that the two component peaks were governed by different aspects of the lighting regimen. Exposure of rats to continuous darkness, continuous light, or to a 20-h photoperiod revealed that the primary rhythm was endogenous, entrained by circadian photoperiods only, whereas the secondary rhythm was exogenous, requiring a circadian light/dark rhythm. A relationship between mean core temperature and ttion pressure, end-systolic L was constant, despite variations in filling and therefore independent of initial L and delta L; moreover, the L to which the ventricle shortened was determined by the course of the systolic force L-relation. Thus, irrespective of loading, delta L occurs within the confines of the contractile state-depdendent isovolumic force-L relation and where the latter is equivalent to the end-systolic force-length relation.

Ingestive behavior and body temperature during the ovarian cycle in normotensive and hypertensive rats

“…Such methods have been used to obtain data on abdominal T b in two rat strains. In one case, Holtzman rats housed in standard laboratory cages showed higher T b in the dark phase of E when T b was recorded six to nine times per day (28,34). More detail of the daily T b rhythm during the ovarian cycle was provided in a study with female Sprague-Dawley (SD) rats of the Charles River strain CD, whose T b was recorded every 10 min (18).…”

Prehatch entrainment of circadian rhythms in the domestic chick using different light regimes

“…We therefore sought a different measure to evaluate the presence of circadian rhythms. Many animals show circadian variation in body temperature (e.g., Aschoff, 1970;Fuller & Sulzman, 1982;Spencer, Shirer, & Yochim, 1976). In particular, domestic chicks exhibit significantly higher body temperatures in the day as compared to the night (Hayne, Rovee-Collier, & Gargano, 1986), so we employed this dependent measure in this experiment.…”

Mathematical Models of the Circadian Sleep-Wake Cycle.

“…This subject, who is a "night owl" in the 24-hr day, waking up around "noon," becomes an "early bird" in the 26W-hr day, waking at the crack of "dawn." These advances are predicted by oscillator theory, which states that as the period of the Zeitgeber increases, the phase of circadian rhythms advances (3,46). Notice, however, that the temperature rhythm advances more than the activity rhythm.…”

“…This effect is well documented in numerous plant circadian rhythms (14), and it also seems widespread in rhythms of animal behavior and physiology, e.g., in chicken brain temperatures (5), chaffinch oxygen consumption (43), and body temperatures in rats (21,46) and squirrel monkeys (24). In humans, also, there is evidence that the amplitudes of various physiological oscillations decrease in association with the change from entrained to free-running conditions, e.g., in body temperature and plasma cortisol (49,53).…”

“…However, it has been shown that synchronization of a rhythm by environmental stimuli, including "subtle stimuli" (49), is effective because of phase control, not frequency control. Because phase control is not compatible with frequency transformation (46), this sole alternative to the concept of self-sustainment has been ruled out.…”