Figure 5.

HPC-striatum balance is tilted towards facilitated striatal function in mice lacking delta opioid receptors. This imbalance is revealed by impaired performance in HPC-dependent tasks (associative learning), but facilitated acquisition of striatum-dependent tasks (procedural learning) in these animals. Facilitated striatal function in Oprd1^−/− mice is a likely consequence of potentiated striatonigral activity.