The dark phase improves genetic discrimination for some high throughput mouse behavioral phenotyping

Dark‐phase testing has previously been shown by others to improve the outcome of some ‘classical’ behavior test situations. However, the importance of such ethological correctness and the effect of the light/dark cycle on high throughput behavioral testing situations such as ‘mutant vs. wild type’ and ‘screening’, are less or unknown, respectively. These testing situations differ from the ‘classical’ in that they are designed primarily to discriminate between genetically different mice rather than provide a detailed assessment of ability or psychosocial state. Here we test the hypotheses that dark‐phase testing affects the outcome of high throughput behavioral tests and that dark‐phase testing improves discrimination between genetically distinct mice (C57BL/6J, 129S1/SvImJ and B6129F1) using high throughput behavioral tests. Our results demonstrate that, although all successful tests showed some effect of phase, only the SHIRPA primary screen, open‐field test and motor learning on the rotarod showed improved strain discrimination in the dark phase. Surprisingly, the social interaction test did not show a clear benefit to either phase, and interestingly, the tail‐flick test discriminated strains better in the light phase. However, since the preponderance of our data shows that dark‐phase testing improves, or does not affect, strain discrimination, we conclude that for these strains and tests, dark‐phase testing provided superior outcomes. If discrimination is not achieved in the dark phase, then light phase‐testing would be undertaken.