Interaction of Estradiol, Alpha-Melanocyte-Stimulating Hormone, and Dopamine in the Regulation of Sexual Receptivity in the Female Rat

Abstract

Ovariectomized and adrenalectomized rats kept in a reversed lighting system received either 5 µg (once) or 1 µg estradiol benzoate (EB) daily for 2, 3, or 4 days. These treatments induced sexual receptivity in a proportion of the rats, and α-melanocyte-stimulating hormone (α-MSH; 20 µg/rat s.c.) enhanced this proportion. In rats made receptive by 5 µg EB alone, the dopamine (DA) activity in preoptic area and arcuate nucleus was significantly reduced, but the α-MSH concentrations were not affected 54–56 h after EB treatment. Addition of α-MSH significantly increased the DA activity in ventromedial nucleus (VMN) and zona incerta, but this action is unlikely to account for its stimulation of sexual receptivity, since this effect was not blocked by 0.1 mg/kg haloperidol. Treatment with 100 mg/kg Dopa, which induces a presynaptic DA action, stimulated the receptivity in the EB-primed rats and selectively increased the concentration of α-MSH in the VMN, while 50 mg/kg Dopa plus 50 mg/kg benserazide, which induces a postsynaptic DA activity, inhibited the receptivity and reduced the α-MSH levels in the VMN. It is suggested that estradiol stimulates the female sexual receptivity by reducing the activity of a dopaminergic system in arcuate nucleus and preoptic area. α-MSH does not appear to affect this action, although it enhances the effect of steroids on the sexual behaviour, probably at the level of the VMN. The secretion of α-MSH may be under a dopaminergic inhibitory control, and the peptide may autoregulate its own secretion via this dopaminergic system which is sited in zona incerta and VMN.

Interaction of Oestradiol, α-Melanotrophin and Noradrenaline within the Ventromedial Nucleus in the Control of Female Sexual Behaviour

“…Several series of studies have suggested that it is involved in reproductive processes, perhaps acting to enhance the action of gonadal steroids [1][2][3][4]. We have shown that aMSH can stimulate female sex ual behaviour in ovariectomised-adrenalectomised rats primed with low doses of oestradiol [4][5][6][7], The effect is a central one and noted at relatively low concentrations (20-100 ng/rat) after administration into the third ventri cle [4], This may be of physiological importance as aMSH concentrations are raised selectively in the ventromedial nucleus (VMN) in sexually receptive rats [7]. The VMN is an important site in the control of sexual behaviour pos sessing both oestrogen and progesterone receptors and the site at which they are most effective in stimulating recep tivity [8], Others have noted a long-term inhibitory effect when aMSH is injected into the lateral ventricle [9] and so there may be a second and opposing site of aMSH ac tivity.…”

“…Some reports indicate that the behavioural effects of aMSH may be mediated by dopamine, but although aMSH increases hypothalamic dopamine activity [7,10], we have shown that the effect of aMSH on sexual behav iour is not blocked by a dopamine antagonist [7], A few reports have investigated the involvement of 5-hydroxytryptamine (5HT), and shown that aMSH increases corti cal 5HT turnover [11], but has no effect on 5HT in the hypothalamus [12]. Pharmacological evidence, however, indicates it may be involved in the inhibitory effect of aMSH on sexual behaviour [13,14], The evidence is also very sparse for the involvement of noradrenaline (NA) in the action of aMSH.…”

Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist

“…In female rats, ␣-MSH has been shown to facilitate or inhibit the sexually receptive posture lordosis depending on the hormonal status of the animals and whether they are in a low or high state of sexual receptivity, respectively (4-7). Estradiol increases ␣-MSH levels in hypothalamic brain regions associated with female sexual behavior (8,9), suggesting that ␣-MSH release may be one of several intermediaries of estrogen action. Recently, PT-141, a peptide analogue of ␣-MSH, was reported to be erectogenic in men (10,11) by an action believed to occur at central melanocortin type 3 or 4 receptors (12).…”

A Drosophila dopamine 2-like receptor: Molecular characterization and identification of multiple alternatively spliced variants

“…In mammals, dopamine modulates neurologic, cardiovascular, endocrine, and renal functions. In addition, this neurotransmitter regulates motor activity, sexual behavior, and the response to drugs of abuse (1,(3)(4)(5)(6). In Drosophila, known dopamine-mediated functions overlap with those of mammals.…”