Modulatory role for prolactin in the elevation of striatal dopamine receptor density induced by chronic treatment with dopamine receptor antagonists

The chronic administration of haloperidol (HAL), domperidone (DOM), or sulpiride (SUL) increased the density of striatal dopamine (DA) receptors in intact but not in hypophysectomized (Hypox) male rats. This effect was independent of changes in body weight of the rats and of the drugs' abilities to produce cataleptic behavior. All treatments of intact rats increased serum rat prolactin (rPRL) concentrations, while Hypox rats had rPRL levels equivalent to zero. At the doses used in these studies, the striatal DA receptor densities were increased only if the rPRL levels were also increased. Chronic cysteamine (CYS) treatment decreased body weight gain, acutely decreased cataleptic behavior to HAL, decreased serum rPRL levels, and prevented the increase in serum rPRL levels due to HAL administration. While CYS itself did not alter striatal DA receptor density, it prevented the increase in density associated with the chronic administration of HAL (1 mg/kg). Since CYS decreased rPRL levels, these results lend further support to the hypothesis that rPRL (and prolactin in general) is a pituitary hormone with modulatory action on the increase in striatal DA receptor density.