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Sexual behaviour of neonatally castrated rats injected during infancy with oestrogen and dihydrotestosterone
Insights
Neonatal exposure to testosterone or estrogenic compounds is crucial for organizing male sexual behaviors and suppressing female patterns in rats. Dihydrotestosterone alone did not influence these outcomes, highlighting the importance of androgen aromatization.
Area of Science:
- Neuroendocrinology
- Developmental Biology
- Reproductive Science
Background:
- Neonatal androgen exposure is critical for sexual differentiation of the brain and reproductive tract in mammals.
- The roles of specific androgens and their metabolites, like estrogens derived from androgens, in organizing male sexual behaviors are not fully elucidated.
- Understanding these processes is key to comprehending reproductive development and potential disruptions.
Purpose of the Study:
- To investigate the effects of neonatal administration of testosterone, dihydrotestosterone, or an estrogenic compound on reproductive development and behavior in male rats.
- To determine the necessity of androgen aromatization versus 5alpha-reduction for the organization of male sexual behaviors and gonadotropin secretion.
- To assess the role of these steroids in penis development and copulatory efficiency.
Main Methods:
- Male rats were castrated on postnatal day 1 and injected with testosterone, dihydrotestosterone, RU 2858 + dihydrotestosterone, or oil from days 1 to 5.
- Gonadotropin secretion was assessed by examining corpora lutea in ovarian grafts in adulthood.
- Sexual behavior was evaluated following injections of estradiol benzoate and progesterone.
- Penis development and copulatory efficiency (intromission/mount ratio) were measured.
Main Results:
- Testosterone and the estrogenic compound (RU 2858 + dihydrotestosterone) suppressed cyclic gonadotropin secretion and adult female sexual behavior.
- Dihydrotestosterone alone did not affect gonadotropin secretion or female behavior.
- Both testosterone and dihydrotestosterone enhanced penis development, which correlated with copulatory efficiency.
- Ejaculation was observed only in rats treated with testosterone or the estrogenic compound.
Conclusions:
- Neonatal androgen action via neural aromatization to estrogens is essential for suppressing female reproductive neuroendocrine and behavioral patterns.
- Estrogenic metabolites of androgens are critical for organizing male sexual behaviors, including ejaculation.
- Peripheral 5alpha-reduction to dihydrotestosterone is necessary for the complete development of the male genital tract but not sufficient for organizing male sexual behaviors on its own.
Abstract:
Male rats were castrated on the day of birth (day 1) and injected with either testosterone, dihydrotestosterone, a synthetic oestrogen (RU 2858 + dihydrotestosterone, or oil from days 1 to 5. The aromatizable androgen, testosterone, and RU 2858 suppressed both cyclic gonadotrophin secretion, indicated by the absence of corpora lutea from implanted ovarian grafts, and the behavioural response to oestradiol benzoate + progesterone injections in adulthood. The 5alpha-reduced androgen, dihydrotestosterone alone did not affect gonadotrophin secretion or female receptive behaviour, but like testosterone, it increased penis development in response to testosterone propionate, and this was positively correlated with copulatory efficiency, i.e. the ratio of intromission to mount frequencies. Nevertheless, ejaculation only occurred among animals that had received testosterone or RU 2858 + dihydrotestosterone. The results support the concept that during the preinatal period, neural conversion of androgens to oestrogens is important both for the suppression of female gonadotrophin secretion and behaviour patterns as well as for the organization of male behaviour patterns. The 5alpha-reduction of unsaturated C19-steriods to dihydrotestosterone in peripheral tissues is also required to complete the development of the male genital tract.