Aftereffects of microinjections of neurotensin into the substantia nigra of the brain on conditioned motor responses in rats with lesions to serotoninergic neurons.

The effects of neurotensin microinjections into the substantia nigra of the brain on the performance of motor reactions in response to positive (food reinforcement) and negative (unreinforced) conditioned signals were studied, along with the characteristic aftereffects of these microinjections in rats with lesions to serotoninergic neurons in the dorsal cervical nucleus. Lesions were produced by local administration of the selective neurotoxin 5,7-dihydroxytryptamine. Microinjections of neurotensin were found to weaken the disinhibitory effects of neurotoxin on extinction of intersignal responses and extinction of conditioned motor reactions in response to presentation of negative stimuli, but to have no marked effect on the performance of reactions evoked by positive conditioned signals.