The effects of ambient temperature and lighting intensity on wheel-running behavior in a diurnal rodent, the Nile grass rat (Arvicanthis niloticus).

Abstract

Environmental conditions, such as the light-dark cycle and temperature, affect the display of circadian rhythmicity and locomotor activity patterns in mammals. Here, we tested the hypothesis that manipulating these environmental conditions would affect wheel-running activity patterns in a diurnal rodent, the Nile grass rat (Arvicanthis niloticus). Whereas grass rats are diurnal in the field, a subset switch from a day-active to a night-active pattern of activity after the introduction of a running wheel. The mechanism of this chronotype switch remains largely unknown. In the present study, grass rats were presented with running wheels in 12:12 light-dark (LD) conditions. First, subjects were exposed to 25 degrees C during the day and 21 degrees C at night, which resulted in 100% of grass rats expressing diurnal behavior. Subjects were then exposed to manipulations of elevated ambient temperature, which resulted in a significant reduction in wheel-running activity. Reducing ambient temperature below 21 degrees C, however, did not disrupt the expression of diurnality or overall activity. Next, lighting intensity was reduced, which resulted in a switch from a diurnal to a nocturnal chronotype in a subset of animals and reduced overall wheel-running activity. Upon return to baseline lighting intensity, patterns of diurnal activity were restored. Altogether, increases in ambient temperature and decreases in lighting intensity significantly reduced overall wheel-running activity. Importantly, dim light resulted in a temporal niche switch in a subset of grass rats, suggesting a critical role for lighting intensity on the expression of wheel-running activity patterns.

Behavioral and Thermoregulatory Responses to Changes in Ambient Temperature and Wheel Running Availability in Octodon degus

“…Significant relationships identified by linear regression (p < 0.05). (Fogo et al, 2019). Octodon degus is a caviomorph rodent from Central Chile, which has been described as diurnal with major episodes of activity at dawn and dusk (Fulk, 1976).…”

“…Homoeothermic animals, such as the degus, present different coping mechanisms to keep their Tb within the physiological range. One of the most important strategies adopted to maintain thermal homeostasis involves adaptive behavioral responses (Fogo et al, 2019 ). Octodon degus is a caviomorph rodent from Central Chile, which has been described as diurnal with major episodes of activity at dawn and dusk (Fulk, 1976 ).…”

Melanopsin-Containing ipRGCs Are Resistant to Excitotoxic Injury and Maintain Functional Non-Image Forming Behaviors After Insult in a Diurnal Rodent Model

“…Alpha was calculated using the onset of the morning bout to the offset of the evening bout. Onset and offset were identified as described previously (Fogo et al, 2018), by using the Actogram J Program in conjunction with visual inspection of actograms. Masking was assessed by calculating the total activity counts for each subject at ZT14, 18, and 22 during the light pulse and comparing that to the total activity counts the day before in the darkness.…”

“…Additionally, environmental light intensity affects wheel-running patterns in Nile grass rats, suggesting the influence of melanopsin on behavioral outputs in these rodents (Fogo et al, 2018). Therefore, Nile grass rats are an excellent diurnal rodent model for examining the role of ipRGCs.…”

Functional and anatomical variations in retinorecipient brain areas in Arvicanthis niloticus and Rattus norvegicus: implications for the circadian and masking systems

“…Temporal niche refers to the time-of-day during the light-dark cycle in which an organism is active and is defined by the unique levels of ambient light and temperature of the environment present (Kronfeld-Schor & Dayan, 2008). These variations in ambient light and temperature can produce a range of activity patterns, with the two extremes restricting activity primarily to either the day (diurnal; Fogo et al, 2018) or night (nocturnal; Refinetti, 2006). Circadian rhythms and acute responses to light (i.e., masking) have uniquely adapted to regulate activity to these two temporal niches.…”