ABSTRACTNeuropeptide Y (NPY) and protein kinase A (PKA) have been implicated in neurobiological responses to ethanol. We have previously reported that mutant mice lacking normal production of the RIIβ subunit of PKA (RIIβ−/− mice) show enhanced sensitivity to the locomotor stimulant effects of ethanol and increased behavioral sensitization relative to littermate wild‐type RIIβ+/+ mice. We now report that RIIβ−/− mice also show increased NPY immunoreactivity in the nucleus accumbens (NAc) core and the ventral striatum relative to RIIβ+/+ mice. These observations suggest that elevated NPY signaling in the NAc and/or striatum may contribute to the increased sensitivity to ethanol‐induced behavioral sensitization that is a characteristic of RIIβ−/− mice. Consistently, NPY−/− mice failed to display ethanol‐induced behavioral sensitization that was evident in littermate NPY+/+ mice. To examine more directly the role of NPY in the locomotor stimulant effects of ethanol, we infused a recombinant adeno‐associated virus (rAAV) into the region of the NAc core of DBA/2J mice. The rAAV‐fibronectin (FIB)‐NPY13–36vector expresses and constitutively secretes the NPY fragment NPY13–36(a selective Y2receptor agonist) from infected cellsin vivo. Mice treated with the rAAV‐FIB‐NPY13–36vector exhibited reduced expression of ethanol‐induced behavioral sensitization compared with mice treated with a control vector. Taken together, the current data provide the first evidence that NPY signaling in the NAc core and the Y2receptor modulate ethanol‐induced behavioral sensitization.