Abstract
The domestication process of the laboratory rat has been going on for several hundred generations in stable environmental conditions, which may have affected their physiological and behavioural functions, including their circadian system. Rats tested in our ethological experiments were laboratory-bred wild Norway rats (WWCPS), two strains of pigmented laboratory rats (Brown Norway and Long Evans), and two strains of albino rats (Sprague-Dawley and Wistar). Rats were placed in purpose-built enclosures and their cycle of activity (time spent actively outside the nest) has been studied for one week in standard light conditions and for the next one in round-the-clock darkness. The analysis of circadian pattern of outside-nest activity revealed differences between wild, pigmented laboratory, and albino laboratory strains. During daytime, albino rats showed lower activity than pigmented rats, greater decrease in activity when the light was turned on and greater increase in activity when the light was switched off, than pigmented rats. Moreover albino rats presented higher activity during the night than wild rats. The magnitude of the change in activity between daytime and nighttime was also more pronounced in albino rats. Additionaly, they slept outside the nest more often during the night than during the day. These results can be interpreted in accordance with the proposition that intense light is an aversive stimulus for albino rats, due to lack of pigment in their iris and choroid, which reduces their ability to adapt to light. Pigmented laboratory rats were more active during lights on, not only in comparison to the albino, but also to the wild rats. Since the difference seems to be independent of light intensity, it is likely to be a result of the domestication process. Cosinor analysis revealed a high rhythmicity of circadian cycles in all groups.
Highlights
Brown rats (Rattus norvegicus) are nocturnal mammals and the bulk of their activity takes place at night
As an equivalent of wild Norway rats in this study we used the WWCPS (Warsaw Wild Captive Pisula Stryjek) strain derived in 2006 from breeding pairs obtained from 5 independent colonies of wild rats in Warsaw, Poland [22], [54,55]
Post hoc analysis (Games-Howell method) showed that Brown Norway and Long Evans rats presented lower increase in activity following nightfall than Sprague-Dawley and Wistar rats
Summary
Brown (or Norway) rats (Rattus norvegicus) are nocturnal mammals and the bulk of their activity takes place at night. This ecological adaptation, present in the majority of mammalian species, was probably a result of moving into new ecological niches to avoid predators. 80% of the 12 hours of daylight), while during night they sleep only 30% of time [1]. Analysis of the diurnal activity of rats shows that during the day they mostly sleep Results of learning and memory tests can vary depending on the phase of the diurnal cycle [4]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have