Is there a right or better time to test your animals in nociceptive behavioral assays?
Some people say morning, some say afternoon. What do you think?
From my experience, the mice seem to be the most subdued (chill, quiet, not fidgety) in the afternoon. But that may just be because they have had more time to acclimate to the testing environment. For example, for von Frey, I put the mice in their containers around 9 am, and then by 12 pm they seem to get quiet. But it takes a few hours.
A recent paper by Minett et al. actually looked at this, von Frey thresholds at different times of the day, and found significant diurnal variation. In the early afternoon (1-3 PM), the mice have the highest mechanical thresholds.
(From Minett et al. 2014)
If this is true, it would have implications for all of our behavior experiments and in particular, time course experiments.
Perhaps the best we can achieve is consistency. Test the same time every day. But when you do a battery of assays, or if assays stretch across the whole day (a time course of von Frey), then there is no avoiding the potential drift in behavioral responses due to circadian rhythm or whatever.
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