The effects of feedback lighting on the circadian rhythm of locomotor activity and the reproductive maturation of the male Djungarian Hamster(Phodopus sungorus)†

Abstract

The non-parametric model of entrainment suggests that brief pulses of light, delivered between dusk and dawn can simulate the phasing effects of full photoperiods or even constant light (LL). Feedback lighting (LDFB) is a lighting condition where individual animals, otherwise in constant darkness (DD), are exposed to light in response to a monitored behavior. The specific purpose of this type of illumination is to expose the circadian cycle to light only during the subjective night. LDFB has been used to support this hypothesis in several species of nocturnal rodents and one species of diurnal primate by producing similar free-running periods in LDFB as in LL. This lighting condition has also been used to test the hypothesis that exposing the subjective night to even short duration light pulses will maintain reproductive function in long day breeders. In the Syrian hamster (Mesocricetus auratus), however, LDFB is not as photostimulatory as LL despite extensive light exposure during the subjective night. In the experiments presented here, a group of immature male Djungarian hamsters (Phodopus sungorus) were placed in individual light-tight sound attenuated chambers where they had free access to food, water and an activity wheel. The animals were exposed to one of four lighting conditions [DD, LL, LDFB or a neighbor control of feedback lighting (LDFB NC)] for approximately 30 days shortly after weaning. LDFB NC is a lighting condition where a neighbor control hamster receives the identical lighting regime as a paired animal exposing itself to LDFB, yet the neighbor has no control over it. A fifth group was exposed to a light-dark cycle of 16 hours of light and 8 hours of dark (LD16:8). This group was housed in cages in a colony room and did not have access to a running wheel. The free-running periods of the locomotor activity rhythms for hamsters exposed to LDFB and LL were not similar, unlike the results for rats, Syrian hamsters, mice, monkeys and even mature Djungarian hamsters. Immature hamsters exposed to DD and LDFB NC developed more slowly than animals exposed to LL or LD16:8, while hamsters in LDFB developed at an intermediate rate. Thus, it appears that LDFB, although capable of inducing reproductive function in immature Djungarian hamsters, is not as photostimulatory as may have been expected from current photoperiodic models, despite substantial light exposure during the subjective night. Furthermore, this data may suggest that the circadian system of 18-48 day old Djungarian hamsters are still undergoing organizational maturation.

Phenotypic Differences in Reentrainment Behavior and Sensitivity to Nighttime Light Pulses in Siberian Hamsters

“…The circadian system of Siberian hamsters (Phodopus sungorus sungorus) has been characterized in detail by several laboratories. Circadian organization in this species is consistent with that of other nocturnal rodents with respect to parameters such as their photic PRC (Milette and Turek, 1986;Puchalski and Lynch, 1991a), conformity to Aschoff's rule (Ferraro, 1988;Puchalski and Lynch, 1991b), and behavior under various T-cycles (i.e., LD cycles different from 24 h) (Darrow and Goldman, 1985;Puchalski and Lynch, 1994). Recent studies have, however, revealed that unlike other nocturnal rodents, hamster circadian rhythms are prone to disruption by various light treatments.…”

Light induces c-fos and per1 expression in the suprachiasmatic nucleus of arrhythmic hamsters

“…This also appears to be the case for Siberian hamsters that free-run, rather than become arrhythmic, after a 5-h phase delay of the LD cycle (25). These animals tend to free-run with a mean rhythm period that is no different from hamsters housed in LL (7,8,19). Although these phenomena suggest that the behavior of unentrained free-running or arrhythmic hamsters bears some similarity to animals held in LL, their failure to regain rhythms in DD does not.…”