Aims: 

The ventral pallidum (VP) and the nucleus accumbens (NAc) are innervated by the mesolimbic dopamine system, and are prominent sites in regulating reinforcement, memory, and learning processes. We investigated the effects of local D2 dopamine agonist quinpirole injections into the VP or the NAc in passive avoidance learning paradigm.

Methods: 

By means of stereotaxic method, cannulae were implanted bilaterally into the VP or NAc of male Wistar rats. The experimental apparatus consisted of a large, well illuminated compartment and a small, dark box. The latency to step in the dark compartment was measured in all sessions. During conditioning the animals received a 0.5 mA electric shock after they had entered the dark box. It was immediately followed by the bilateral injection of D2 dopamine receptor agonist quinpirole in 0.1 mg, 1.0 mg, or 5.0 mg doses (all were dissolved in 0.4 ml physiological saline). Control animals received only vehicle. Tests were executed 24 hours, one week, and two weeks after conditioning (Test1, Test2, Test3 respectively).

Results: 

Injections of 0.1 mg quinpirole into the NAc facilitated learning only during Test1. The 1.0 mg dose increased the step-through latency in all three tests. In the VP none of the injected doses had any effects on the measured parameters.

Conclusion: 

The D2 dopamine receptor agonist quinpirole injections into the NAc effectively improved negative reinforcement and memory formation in the rats, while they had no similar effects in the VP.

Support: 

NKTH-OTKA K 68431 and the HAS