Evidence that the dopaminergic incerto-hypothalamic tract has a stimulatory effect on ovulation and gonadotrophin release.

2 micrograms dopamine (DA) were injected into particular hypothalamic sites containing dopaminergic nerve terminals, on the morning of pro-oestrus in cyclic rats, in which ovulation was blocked by administration of 35 mg/kg pento-barbitone Na, in the afternoon of pro-oestrus. DA in a specific area of the zona incerta (ZI) (medial area at A 5.4 mm; de Groot atlas), and medial anterior hypothalamus (AH) overcame the pentobarbitone block and induced ovulation. Injections into the median eminence and preoptic area were ineffective, as were injections of 5-hydroxytryptamine and nor-adrenaline into the ZI. Injection of 2 micrograms haloperidol and lesions in the ZI inhibited ovulation in otherwise untreated cyclic rats. Lesions induced constant dioestrus for 14 +/- 0.7 days, but the animals were not pseudopregnant. 2 micrograms DA were also injected into the ZI of ovariectomised rats primed with 2 micrograms oestradiol benzoate 48 h before; this treatment stimulated a rise in plasma LH approximately 40 min later. These findings indicate that the dopaminergic incerto-hypothalamic tract which has nerve terminals in the ZI and AH has a stimulatory role in the control of gonadotrophin release.