Figure 4

VIP-deficient mice exhibit a daily rhythm in the recall of contextual fear conditioning. Groups of WT (black circles) and VIP-deficient (grey circles) mice were trained at ZT 3 and then tested 24-, 36-, 48- and 60-hrs after training (n = 8 per group). There was no difference in the acquisition between the genotypes (WT: 66 ± 5% freezing; VIP KO: 69 ± 7% freezing). Both genotypes showed evidence for diurnal rhythmicity in recall with significant (P < 0.05) peaks observed at 24- and 48-hrs after training. However, compared to WT mice, the VIP-deficient mice exhibited significantly (P < 0.05) lower recall when measured 36-, 48-, or 60-hrs after training.