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The zona incerta (ZI) is a site of dopamine nerve terminals and part of the incertohypothalamic tract (I-H). Previous findings indicate that dopamine in the ZI has a stimulatory control on the release of luteinizing hormone (LH) and occurrence of ovulation. The effect of acute administration into anaesthetised rats of selective D₁ and D₂ dopamine agonists and antagonists injected into the ZI on plasma luteinizing hormone (LH) and on the occurrence of ovulation has now been investigated. It was found that bilateral injections on the day of pro-oestrus of a selective D₁ antagonist, Sch 23390, inhibited ovulation at 10 µg/side/rat. Unilateral injections of a selective D₁ agonist, SKF 38393, at 10 µg/rat stimulated a significant rise in plasma LH concentration in ovariectomised oestrogen-primed rats, and this was partially reversed by systemic pre-treatment with Sch 23390. The selective D₂ agonist, LY 171555, and D₂ antagonists, sulpiride and domperidone, had no effect on plasma LH levels or ovulation. This indicates that D₁ receptors (but not D₂ receptors) in the ZI are involved in the control of gonadotrophin release and may have a physiological function in reproductive processes.