Nocturnal and Diurnal Rhythms in the Unstriped Nile Rat, Arvicanthis niloticus

Abstract

In a laboratory population of unstriped Nile grass rats, Arvicanthis niloticus, individuals with two distinctly different patterns of wheel-running exist. One is diurnal and the other is relatively nocturnal. In the first experiment, the authors found that these patterns are strongly influenced by parentage and by sex. Specifically, offspring of two nocturnal parents were significantly more likely to express a nocturnal pattern of wheel-running than were offspring of diurnal parents, and more females than males were nocturnal. In the second experiment, the authors found that diurnal and nocturnal wheel-runners were indistinguishable with respect to the timing of postpartum mating, which always occurred in the hours before lights-on. Here they also found that both juvenile and adult A. niloticus exhibited diurnal patterns of general activity when housed without a wheel, even if they exhibited nocturnal activity when housed with a wheel. In the third experiment, the authors discovered that adult female A. niloticus with nocturnal patterns of wheel-running were also nocturnal with respect to general activity and core body temperature when a running wheel was available, but they were diurnal when the running wheel was removed. Finally, a field study revealed that all A. niloticus were almost exclusively diurnal in their natural habitat. Together these results suggest that individuals of this species are fundamentally diurnal but that access to a running wheel shifts some individuals to a nocturnal pattern.

Stimulation of sexual behavior in the male rat by galanin-like peptide

“…Since rats are nocturnal, this time frame may have resulted in a blunted magnitude in the measured behaviors. However, mating behavior in rats has been shown to occur both nocturnally and diurnally, and the levels of sexual behaviors in this experiment are similar to that reported previously (Blanchong et al, 1999;Logan and Leavitt, 1992). Similarly, Stefanick (1983) reported no significant time-of-day effects on reflexive erections.…”

Functional Analysis of Circadian Pacemaker Neurons inDrosophila melanogaster

“…Furthermore, different rat strains that displayed unimodal or multimodal activity patterns, respectively, all exhibited the same unimodal rhythm in melatonin synthesis (Klante et al, 1999). Individual Nile grass rats changed their activity patterns from unimodal-diurnal to bimodal-nocturnal after introducing a running wheel (Blanchong et al, 1999). Despite this dramatic effect on the activity patterns, the wheel had little effect on the circadian pacemaker, and the spatial and temporal patterns of c-Fos expression in the SCN remained similar (Smale et al, 2003).…”

Sensitivity of the hypothalamic paraventricular nucleus to the locomotor-activating effects of neuromedin U in obesity

“…Although activity in a running wheel may be modulated by similar brain circuits as spontaneous activity, the presence of running wheels results in several aberrant effects on the amount and pattern of activity as well as on other aspects of energy balance in several rodent species including rats [4,5,13,38,80,83] and thus has independent, confounding influences on energy expenditure. All measurements took place during the light phase of the activity cycle.…”