Sensitivity of dopamine receptors in the lateral hypothalamus is altered in 6-hydroxydopamine treated rats.

Amine accumulation is observed in the lateral hypothalamus (LH) after nigrostriatal neurons degenerate. It has been proposed that this accumulation is a source of amines which are released into the hypothalamus thereby affecting the function of adjacent aminergic receptors. To approximate this condition of continuous exposure of LH receptors to endogenous amines, dopamine (DA) was injected into the LH of rats once daily for 5 consecutive days. A control group received 4 daily injections of tartaric acid vehicle and then DA on day 5. Rats pretreated with DA showed severe impairment of open field performance and motor reflex control on day 5 when they were compared to control animals which received vehicle pretreatment. In a second study, the DA receptor antagonist haloperidol was injected into the area of amine accumulation in the LH to determine whether this might block amine release from areas of accumulation thereby to attenuate lesion-induced rotation. Haloperidol administered once daily for 4 out of 7 days, once daily for 7 days or via a continuous infusion for 7 days, all reduced d,l-amphetamine-induced turning to control levels. These results suggest that prolonged exposure of hypothalamic DA receptors alters their sensitivity to subsequent doses of DA and that amine released from areas of accumulation may be blocked by haloperidol to enhance behavioral recovery from DA depleting lesions. Moreover, these findings indicate that the hypothalamus participates in the behavioral effects induced by DA depleting lesions and highlight the importance of hypothalamic pathology in Parkinson's disease.