Positive reinforcing effect of neurotensin microinjection into the ventral pallidum in conditioned place preference test.

The ventral pallidum (VP) is innervated by the mesolimbic dopaminergic system and it has a key role in motivation, reward, and memory processes. Neurotensin (NT) is an important neuromodulator which has been shown to modulate reinforcement in the ventral tegmental area, in the ventral mesencephalic region and in the central nucleus of amygdala. Neurotensin receptor 1 (NTR1) has already been detected in the VP in abundance, but its role in rewarding and reinforcing processes is not fully understood yet. In our present experiments, the effects of NT on positive reinforcement were investigated in the VP. In conditioned place preference (CPP) test, male Wistar rats were microinjected bilaterally with 100 ng or 250 ng NT in the volume of 0.4 μl. In other groups of animals, 35 ng NTR1 antagonist SR 48692 was applied by itself, or microinjected 15 min before 100 ng NT treatment. One hundred ng dose of NT induced CPP, whereas animals injected with 250 ng NT did not exhibit significant differences from the vehicle group. Antagonist pretreatment inhibited the effect of NT, while the antagonist applied by itself had no effect. Our results show that NT injected into the VP is involved in positive reinforcement. This effect is specific to NTR1 receptors because the development of CPP can be prevented by specific antagonist.