Figure 2.

Opioid effects on social play are mediated through μ-opioid receptors in the NAc. Intra-NAc infusion of the selective μ-opioid receptor agonist DAMGO (0.1–10 ng/0.3 μl) increased pinning (a) and pouncing (b); the δ-opioid receptor agonist DPDPE (0.3–3 μg/0.3 μl) had no effect (c, d), whereas the κ-opioid receptor agonist U69593 (0.01–1 μg/0.3 μl) decreased pinning (e) and pouncing (f). Intra-NAc infusion of the selective μ-opioid receptor antagonist CTAP (0.3–3 μg/0.3 μl) reduced both pinning (g) and pouncing (h). Data represent mean ± SEM frequency of pinning and pouncing. *p < 0.05, **p < 0.01 versus vehicle (Tukey's post hoc test; n = 7–8 per treatment group).