Circadian and Interval Timing Mechanisms in the Ovulatory Cycle of the Hen

Abstract

INTRODUCTIONThe object of this paper is to specify the timing processes that regulate the ovulatory cycle of the hen by comparing it with that of the rat. To this end, the temporal events that result in ovulation are characterized as having either circadian (i.e., oscillatory) or interval (i.e., hourglass) properties.When environmental time cues such as light, food, and temperature are eliminated, many circadian rhythms of activity persist, or “free run”, for about 24 hr, suggesting control by an endogenous oscillator. The physiological system that ensures synchronization of an organism’s internal temporal events with the external environment has been called the circadian timing system. In the natural environment, endogenous rhythms are synchronized by physical stimuli called zeitgebers. Such synchronization is possible only over a limited range of periods close to that of the circadian rhythm.Animals also measure and respond to intervals much shorter and longer than 24 hr, .