Influence of neurotransmitters on sexual differentiation of brain structure and function

Newborn rats received daily subcutaneous treatment with compounds which influence serotoninergic, cholinergic, alpha-adrenergic and beta-adrenergic activity. In adulthood luteinizing hormone (LH) secretion pattern, female sexual behavior, and the volume of the sexually dimorphic nucleus of the preoptic are (SDN-POA) were determined. Postnatal administration of l-tryptophan increased the volume of the SDN-POA significantly when given alone or when given simultaneously with testosterone propionate (TP). Para-chlorophenyl-alanine (pCPA) also increased SDN-POA volume, but did not potentiate the stimulating influence of TP. Clonidine had no effect per se on SDN-POA development, but it significantly potentiated the effect of TP in females. Salbutamol increased SDN-POA volume in females and in males. Postnatal treatment of female rats with the alpha-adrenergic receptor antagonists prazosine and yohimbine or with the nicotin receptor antagonist mecamylamine had permanent potentiating effects on the pattern of LH secretion, whereas postnatal treatment with beta-adrenergic compounds reduced the LH-release response to gonadal steroids in adulthood. Postnatal treatment with clonidin or l-tryptophane inhibited differentiation of the capacity for lordosis behavior. Beta-receptor agonists postnatally had a potentiating effect on the capacity for lordosis behavior in female and male rats. Cholinergic stimulation postnatally inhibited differentiation of the capacity for lordosis behavior in female rats, but prevented the inhibitory effect of postnatal androgenization. There was no correlation between SDN-POA volume and any of the two functional parameters.

Postnatal treatment of rats with adrenergic receptor agonists or antagonists influences differentiation of sexual behavior

The aim of the study was to investigate the possible role of the adrenergic system in development and differentiation of neural centers controlling sexual behavior in adulthood. For this purpose normal and androgenized female rats were treated with the alpha 1-receptor antagonist prazosin, the alpha 2-receptor agonist clonidine, or the alpha 2-receptor antagonist yohimbine-HCl throughout the first week of life. In adulthood all animals were ovariectomized and, after appropriate hormone-priming, they were tested for the capacity to display female and male sexual behavior patterns. Alteration of adrenergic transmission during the critical postnatal period for sexual differentiation of neural centers resulted in significant changes in the capacity to express female lordosis behavior in adulthood. In nonandrogenized animals clonidine significantly reduced the capacity for lordosis behavior. In androgenized animals clonidine had the opposite effect; it attenuated the inhibitory effect of testosterone propionate (TP) on differentiation of lordosis behavior. Prazosin, which was without effect in nonandrogenized animals, also attenuated the inhibitory effect of TP on differentiation of lordosis behavior. Yohimbine was without effect in androgenized and nonandrogenized animals. There was no influence of any of the adrenergic drugs on differentiation of male sexual behavior. In conclusion, differentiation of lordosis behavior seems to be mediated or modulated via adrenergic transmission. The defeminizing effect of testosterone postnatally on the differentiation of lordosis behavior seems to be expressed via alpha 1-adrenergic transmission, and diminished adrenergic activity during the postnatal period seems to protect the developing brain against this effect of testosterone.

Pre- and postnatal influence of an estrogen antagonist and an androgen antagonist on differentiation of the sexually dimorphic nucleus of the preoptic area in male and female rats

The volume of the sexually dimorphic nucleus in the preoptic area (SDN-POA) of the rat brain is severalfold larger in adult male rats than in adult females. This sex difference in brain structure was previously shown to develop under the influence of androgenic and estrogenic hormones during the perinatal period. We tried to clarify the differential role played by androgens and estrogens during development and differentiation of the SDN-POA by treating male and female rats during an extended pre- and postnatal period either with the estrogen antagonist tamoxifen or with the androgen antagonist cyproterone acetate. Treatment with tamoxifen did not alter serum levels of testosterone in male rats during the perinatal period, but it inhibited development and differentiation of the SDN-POA. Pre- and postnatal treatment of male rats with cyproterone acetate resulted in female phenotypic appearance, but it had no influence on differentiation of the SDN-POA. Perinatal treatment of female rats with tamoxifen resulted in permanent anovulatory sterility, but did not influence SDN-POA differentiation. Treatment of female rats with cyproterone acetate had no influence on SDN-POA differentiation or on the capacity to ovulate. Since pre- and postnatal treatment of male rats with cyproterone acetate is known from previous studies to femenize sexual behavior patterns and to retain the mode for cyclic gonadotropin release, and since the same treatment did not influence differentiation of the SDN-POA in the present study, it may be concluded that the SDN-POA is not directly involved in the control of female sexual behavior and in the control of the gonadotropic hormone release pattern.(ABSTRACT TRUNCATED AT 250 WORDS)