Behavioral analysis of the effect of neurotensin injected into the ventral mesencephalon on investigatory and spontaneous motor behavior in the rat.

The present experiments examined in detail the behavioral response to microinfusions of neurotensin (NT) into the ventral tegmental area (VTA), substantia nigra (SN) and hippocampus (HPC). The behavioral apparatus consisted of an eight-hole box in which investigatory and spontaneous motor behavior were recorded. Three doses (0.175, 0.5, 4.0 micrograms) of NT were injected into the VTA. The main effect of NT was a strong augmentation of rearing (frequency and duration) both in the periphery and center of the arena, accompanied by a small increase in locomotion and decreased grooming. NT had no effect on the strategy, organization, or duration of exploration but did augment frequency of hole visits towards the end of the session. NT injected into the SN and HPC had no effect on investigatory and spontaneous behavior with the exception of an increase in peripheral locomotion after HPC-NT injections. The results are discussed in terms of a modulatory role of endogenous NT on mesolimbic dopamine neurons.