Behavioral and neurochemical effect of daily injection with neurotensin into the ventral tegmental area

Abstract

Many lines of evidence indicate an excitatory role by neurotensin (NT) on mesolimbic dopamine neurons in the ventral tegmental area (VTA). In support of this postulate, NT microinjection into the VTA of rats produces a dopamine-dependent increase in spontaneous motor activity that is associated with an increase in dopamine metabolism in the nucleus accumbens. In this study it was found that after daily intra-VTA injection with NT, both the motor hyperactivity and increase in dopamine metabolism were significantly enhanced. Further, the increased motor response to NT was present after 7 days without daily administration. While the augmented motor response could be produced with the car☐y-terminal fragment NT 8−13, the NH 2-terminal fragment, NT 1−8, was ineffective. The enhancement of motor activity was only produced by NT injection into the A10 dopamine region and not adjacent nuclei. These results suggest that daily administration with NT into the VTA will potentiate the responsiveness of mesolimbic dopamine neurons to subsequent injection with NT.