Mu and Delta Opioid Receptors Oppositely Regulate Motor Impulsivity in the Signaled Nose Poke Task
Figure 2
Oprm1−/− mice perform better in the signaled nose poke task.
Performance on Phase 4 of the signaled nose poke task for mu-opioid receptor knockout mice and their wild-type controls on a HYB (A–D) and BL6 (E–H) backgrounds. A and E: Efficiency ratios (rewards/nose pokes) increased across sessions with Oprm1 −/− mice on both genetic backgrounds performing significantly better than wild-type controls. Mice lacking the Oprm1 gene exhibited lower levels of responding throughout Phase 4 testing; this phenotypic difference was most apparent during the pre-CS period (Fig. 2B and 2F), when animals must learn to inhibit responding in order to maximize the number of rewards earned. C and G: Responses on the rewarded side during the 20-s inter-trial interval (ITI) decreased across sessions with lower overall responses in the Oprm1−/− groups and in the HYB strain. D and H: Conditioned responding (rewards/signals) increased across sessions with no genotype or background differences. Oprm1 +/+ HYB, n = 11; Oprm1 +/+ BL6, n = 12; Oprm1 −/− HYB, n = 10; Oprm1 −/− BL6, n = 11.