Figure 3.

In the NAc, β-endorphin but not enkephalins positively modulates social play behavior. Intra-NAc infusion of the endogenous opioid peptide β-endorphin (0.01–1 μg/0.3 μl) increased pinning (a) and pouncing (b), whereas both met-enkephalin (met-enk) (0.1–5 μg/0.3 μl) (c, d) and the enkephalinase inhibitor thiorphan (0.1–1 μg/0.3 μl) (e, f) had no effect. Data represent mean ± SEM frequency of pinning and pouncing. *p < 0.05, **p < 0.01 versus vehicle (Tukey's post hoc test; n = 6–8 per treatment group).