Modulation of dopamine D1 receptor binding by neurotensin in the rat striatum

The effect of neurotensin on binding characteristics of dopamine D1 receptors was examined in the rat striatal membranes through radioreceptor assay. Neurotensin or its analogs were added to incubation medium of[(3)H]SCH 23390 saturation or dopamine/[(3)H]SCH 23390 inhibition experimental systems. Neurotensin did not modulate D1 antagonist binding but converted a part of D1 agonist high affinity binding sites to a low affinity state. Neurotensin(8-13) had the same potency as neurotensin itself, whereas neurotensin(1-8) had only weak activity in modulating D1 agonist binding. GTP and neurotensin had the same effect on D1 agonist binding. However, when both neurotensin and GTP were added, the result was the same as with either alone. These data suggest that neurotensin modulates the functional state of D1 receptors probably via a GTP binding protein in the rat striatum.