The effects of microinjection of neurotensin into the caudate nucleus of the rat brain on the performance and extinction of a conditioned motor reflex.

The studies reported here demonstrate that microinjection of neurotensin into the caudate nucleus of the rat brain facilitated extinction of a conditioned motor reflex with reinforcement provided by drinking. Neurotensin had positive effects on the process of post-extinction inhibition in subsequent experiments. Neurotensin microinjections had no marked effect on the performance of the conditioned reflex, though it weakened the emotional tension of the animals in an "open field" test. It is concluded that the functional importance of neurotensin at the level of the caudate nucleus is associated less with the regulation of motor function than with optimizing the motivational-emotional state of the animal.