Day and Night Comparison to Maximize Learning in Sprague Dawley Rats (Rattus norvegicus)

Abstract

Domesticated mice and laboratory rats have been traditionally viewed as nocturnal creatures, the vast majority of their daily activity occurring during the “dark” phase of their circadian cycle. Behavioral studies of rats have been traditionally performed during their “light” period when rats should be sleeping. The purpose of this study is to examine whether learning using a spatial, novel object recognition paradigm is enhanced if rats are trained and tested during the dark phase of their cycle rather than the light phase. 10 Sprague Dawley rats were placed in an open field apparatus and observed for 6 minutes at a time during their “light” phase. Measurements were made of distance traveled within the open field, speed of travel, time spent within different areas of the field, time spent mobile and immobile, time spent on grooming behavior, and time spent “rearing” (standing upright). Learning was assessed by observing differences in time spent with a novel toy and a familiar toy. All tests were repeated 1 week later during the rats’ “dark” phase, and results for the two phases were compared using a t‐test. Results showed no evidence of learning in either the light or dark phases, indicated by an increased time spent interacting with the non‐novel object compared to the novel object. Locomotor activity, total time spent interacting with both objects, and rearing behavior were significantly increased during the dark phase, while total distance traveled was significantly lower, which is likely related to the increased rearing. Though these results do not indicate enhanced learning in the rats during the dark phase, the observed differences in activity and behaviors compared with the light phase warrant further study as they could have implications for other behavior experiments performed on rats during each phase.Support or Funding InformationResearch reported in this publication was supported by the NIH Common Fund, through the Office of Strategic Coordination, Office of the NIH Director with the linked awards: TL4GM118992, RL5GM118990, UL1GM118991. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. UAF is an affirmative action/equal employment opportunity employer and educational institution: www.alaska.edu/nondiscrimination.