New findings regarding light intensity and its effects as a zeitgeber in the Sprague-Dawley rat

Circadian rhythmicities are oscillations of physiological cycles designed to create temporal organization. Circadian rhythms ensure that physiological mechanisms are expressed in proper relationship to each other and the 24 hour day. Light is the main zeitgeber ("time giver") for biological clocks. The daily variations in light intensity from dawn to dusk, and seasonally due to the rotation of the earth, act upon organisms to give them photoperiodic information. This entrainment allows them to vary biologically to prepare for reproduction, hibernation, migration and the daily adaptations necessary for survival. In most mammals, the suprachiasmatic nucleus of the anterior hypothalamus has been implicated as the central diving mechanism of circadian rhythmicity. The photic input from the retina, via the retino-hypothalamic tract, and modulation from the pineal gland help regulate the clock. In this study we investigated the effects of low light intensity on the circadian system of the Sprague-Dawley rat. A series of light intensity experiments were conducted to determine if a light level of 0.1 Lux will maintain entrained circadian rhythms of feeding, drinking, and locomotor activity.