Table 1.
Mean number of sessions to criteria in M4+/+ and M4−/− mice. Data are group means ± SEM, with n in parentheses. Mice were trained with either cocaine or liquid food under an FR 1 schedule of reinforcement and subsequently under a PR schedule. M4−/− mice extinguished responding significantly slower than wildtype mice after meeting FR 1 acquisition criteria.
| Criteria | M4+/+ | M4−/− |
|---|---|---|
| Cocaine FR 1 baseline | 2.8 ± 0.5 (13) | 3.2 ± 0.6 (10) |
| Cocaine FR 1 extinction | 2.3 ± 0.3 (13) | 5.1 ± 0.8 (10)** |
| Cocaine PR baseline | 3.3 ± 0.6 (8) | 2.4 ± 0.3 (8) |
| Cocaine PR extinction | 3.9 ± 0.8 (8) | 2.9 ± 0.7 (8) |
| Liquid food FR 1 acquisition | 4.1 ± 0.5 (10) | 3.3 ± 0.4 (13) |
| Liquid food FR 1 extinction | 3.1 ± 0.5 (10) | 2.3 ± 0.3 (13) |
| Liquid food PR baseline | 2.6 ± 0.6 (10) | 2.2 ± 0.3 (9) |
| Liquid food PR extinction | 1.9 ± 0.5 (10) | 3.7 ± 0.8 (9) |
**
p<0.01 versus wildtype, Student’s t test.