Antidepressant-like effect of neurotensin administered in the ventral tegmental area in the forced swimming test.

Locomotor activity and behaviour in the forced swimming test were examined in rats which had received neurotensin (0.5-5.0 micrograms) in the ventral tegmental area. Doses of 5 micrograms neurotensin but not lower increased the locomotor activity for at least 2 h. At 0.5 and 1.0 microgram neurotensin significantly increased the time the animals spent in struggling with no changes in general motor activity (swimming). The effect of 1.0 microgram neurotensin on struggling was completely antagonized by 0.5 microgram (-)-sulpiride administered in the posterior nucleus accumbens. The results suggest that activation of the mesolimbic dopamine system through administration of neurotensin in the ventral tegmental area produces antidepressant-like effects. The significance of these findings for a role of endogenous neurotensin in depression remains to be clarified.