Evidence that inhibition of medial preoptic dopaminergic activity may be involved in the prepubertal desensitization to the negative oestrogen feedback in female rats.

Immature female rats were bilaterally lesioned in the medial preoptic area (MPOA) or hypothalamic ventromedial-arcuate region (VMAR) at 21 days of age and daily injected with the dopamine (DA) agonist bromocriptine (CB-154) through day 26. Estimation of the serum LH and FSH concentrations following ovariectomy and two injections of 0.05 micrograms oestradiol benzoate (OB)/100 g b.w. revealed that the desensitization to the negative feedback effect of OB induced by lesioning of the MPOA was almost completely prevented by CB-154. A similar effect of the drug was not found in rats lesioned in the VMAR. The DA antagonist alpha-methyldopa (alpha-MD) was then bilaterally implanted in the MPOA or VMAR of 28-day-old females. Evaluation of the gonadotrophin-inhibiting effect of OB on days 30-31 showed that medial preoptic, but not hypothalamic implants of alpha-MD reduced the sensitivity to the inhibitory action of OB. It is proposed that diminution of the dopaminergic activity in the MPOA may play a role in the prepubertal desensitization to the negative oestrogen feedback in female rats.