Effect of neurotensin and its fragments neurotensin-(1-6) and neurotensin-(8-13) on dopamine release from cat striatum.

At low concentrations, neurotensin (10(-9) M) enhanced electrically evoked release of dopamine. At higher concentrations, neurotensin (10(-7) M) also enhanced basal release of dopamine. The carboxy-terminal sequence of neurotensin-(8-13) was fully active and enhanced both electrically evoked and basal release. In contrast, the amino-terminal fragment neurotensin-(1-6) did not enhance electrically evoked release of dopamine even at high concentrations (10(-6) M). However, it retained the ability to enhance basal dopamine release. Combination of different doses of apomorphine with a subthreshold (10(-10) M) and submaximal concentrations (10(-9) M) of neurotensin gave clear additive effects. It is concluded that in the cat striatum neurotensin stimulates dopamine release by a direct effect on its own neurotensin receptor, and does not modulate the sensitivity of presynaptic dopamine autoreceptors. Furthermore, it is suggested that there exist at least two types of neurotensin receptors in the cat striatum. One type stimulates evoked dopamine release and another influences basal release of dopamine.