The loss of VIP impaired recall of contextual fear conditioning. A) Groups of VIP-deficient and WT mice (n = 7–8 per group) were trained on the contextual fear conditioning (2 CS-US pairings) at ZT 3. Mice were then tested for the recall of fear conditions one, two, or three days after training with each animal only being tested once. There was no difference the acquisition of the conditioned fear response during training and all of the groups (24-, 48-, 72-hr time points) exhibited a robust recall of context as measured by freezing behavior. VIP-deficient mice (grey bars) exhibited significant reductions in recall compared to WT mice (black bars) when measured at 48- (P < 0.05) and 72-hrs (P < 0.001) post-training. At one day after training, there was no significant difference in the percent freezing between the genotypes. B) In another experiment, VIP-deficient (grey circles) and WT (black circles) mice were trained and then tested for recall once per day for 7 days (n = 8 per group). Training and testing were conducted at ZT 3. The VIP-deficient mice exhibited significant reductions in recall compared to WT controls (P < 0.01). Post-hoc analysis (t-tests) indicated significant differences between the genotypes when measured at 48- (P = 0.02), 72- (P < 0.001), 96- (P < 0.001) and 120-hrs (P < 0.001) post-training.
Chaudhury et al. BMC Neuroscience 2008 9:63 doi:10.1186/1471-2202-9-63