VIP-deficient mice that have arrhythmic patterns of wheel-running activity exhibit a circadian rhythm in the recall of contextual fear conditioning. A) Example of wheel-running activity from a VIP-deficient mouse that maintained a circadian rhythm in wheel-running activity. Bars at top of panel indicate the LD cycle. The locomotor activity is double-plotted as an aid to visual analysis. The mouse was placed into DD on the day indicted by the arrow on the right. B) Example of wheel-running activity from a VIP-deficient mouse that was judged to by arrhythmic on a circadian time-scale by visual analysis and periodogram. C) Both rhythmic and arrhythmic VIP-deficient mice were trained at CT 3 and then tested every 6-hrs between 24- and 72-hrs after training. These experiments were conducted in constant darkness to measure the endogenous rhythmicity. For the rhythmic mice (dark grey circles), the onset of locomotor activity was used to estimate phase while, for the arrhythmic mice (grey diamonds), the time of the prior LD cycle was used. Both groups of VIP-deficient mice exhibited circadian rhythms in the recall of fear conditioning with significant (P < 0.05) peaks 24-, 48-, and 72-hrs post training.
Chaudhury et al. BMC Neuroscience 2008 9:63 doi:10.1186/1471-2202-9-63