Changes in dopamine activity in the zona incerta (ZI) over the rat oestrous cycle and the effect of lesions of the ZI on cyclicity: further evidence that the incerto-hypothalamic tract has a stimulatory role in the control of LH release.

Previous results indicate that the dopaminergic system in the anterior medial zona incerta (ZI) exerts a stimulatory effect on LH release. In this report changes in dopamine (DA) turnover in the ZI, preoptic area (POA) and arcuate/median eminence area (ARC/ME) (as assessed by the rate of decline in DA concentration after alpha-methyl-p-tyrosine) have been noted each afternoon (16.00-18.00 h) of the 4 days of the oestrous cycle and also on the morning (9.00-11.00 h) of proestrus (P) and second day of dioestrus (D2). Over the time of the preovulatory LH surge on P, a significant rise in DA turnover was observed in the ZI. As this area contains components of the dopaminergic incerto-hypothalamic (I-H) tract, this study provides evidence to implicate the I-H tract in the physiological stimulation of the preovulatory surge of LH on proestrus. Selective destruction of DA nerve terminals (with 6-hydroxydopamine plus desmethylimipramine) and the various cell bodies (with ibotenic acid) in the ZI both induced a period of dioestrus (9-11 days). The similarity of effect of these two types of lesion indicate that the DA nerve terminals in the ZI stimulate a stimulatory pathway ultimately to induce LH release.