Evidence that Inhibition of Medial Preoptic Dopaminergic Activity May Be Involved in the Prepubertal Desensitization to the Negative Oestrogen Feedback in Female Rats

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Abstract
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 μg 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 α-methyldopa (α-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 α-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.