Figure 4.

Contextual fear conditioning, contextual discrimination, and emergence neophobia in 5-HT_2C receptor mutant and wild-type mice. (A) After preexposure and two pairings of the tone and footshock in the conditioning chamber, reexposure to this chamber produced freezing responses that appeared to be moderately diminished in mutants; however, this effect was not statistically significant (P = 0.11). On subsequent placement in the altered chamber, freezing rates were significantly decreased in wild-type mice relative to rates in the shock context (∗ paired t test, P < 0.001). In contrast, mutants exhibited equivalent rates of freezing in both enclosures (paired t test, P > 0.05). During subsequent exposure to the tone, freezing rates increased to a similar extent in both groups (n = 13 mutant, n = 11 wild-type mice). Error bars represent the SEM. (B) After three days of discrimination training, mutant and wild-type animals did not differ in freezing rates in the shock context or the nonshock context (n = 12 mutant, n = 12 wild-type mice). (C) Reduced emergence latencies (latency for all four paws to emerge) in mutant mice (P < 0.05), indicative of diminished emergence neophobia (n = 12 mutant, n = 12 wild-type mice). Error bars represent the SEM.