Sex differences in androgen responsiveness in the rat brain: Regional differences in the induction of aromatase activity

Charles Roselli, Scott A. Klosterman, Taiwo A. Fasasi

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

The transformation of testosterone (T) to estrogens in brain tissue by cytochrome P-450 aromatase is required for the expression of sexual behaviors in adult male rats. Androgens regulate aromatase activity in the medial preoptic nucleus (MPN), as well as in a reciprocally connected group of forebrain nuclei involved in the regulation of male sexual behaviors. The levels of aromatase in these nuclei are generally greater in males than in females due to sex differences in circulating androgen levels. However, the mechanism of enzyme induction also appears to be sexually dimorphic. The current experiments were undertaken: (1) to characterize and compare the kinetic properties of aromatase in male and female rats and (2) to study sex differences in the dose-response relationship between the administered doses of T and the induction of aromatase in microdissected brain regions. Saturation analysis of aromatase activity in the MPN, bed nucleus of the stria terminalis (BNST), periventricular preoptic area (PVPOA), anterior hypothalamus (AH), and ventromedial hypothalamic nucleus (VMN) indicates that the greater aromatase activity observed in intact males reflects a sex difference in the maximal enzyme velocity, and not a sex difference in the apparent affinity of enzyme for Substrate (Michaelis constant). The dose-response study of aromatase induction in the BNST, PVPOA, and VMN indicated a sex difference in aromatase activity over a range of circulating T levels varying from 0.3 to 35 ng/ml. No sex difference in inducible aromatase activity in AH was observed at any dose of T. The results of this study clearly demonstrate a sexually dimorphic effect of androgen action in the rat brain. Since T both regulates and is the substrate for aromatase in the brain, this sexual dimorphism is potentially an important limitation to the action of T in females and may relate to the enhanced expression of T-stimulated copulatory behavior in males compared to females.

Original languageEnglish (US)
Pages (from-to)139-145
Number of pages7
JournalNeuroendocrinology
Volume64
Issue number2
StatePublished - Aug 1996

Fingerprint

Aromatase
Sex Characteristics
Androgens
Brain
Preoptic Area
Ventromedial Hypothalamic Nucleus
Anterior Hypothalamus
Septal Nuclei
Sexual Behavior
Anterior Hypothalamic Nucleus
Enzyme Induction
Enzymes
Prosencephalon
Cytochrome P-450 Enzyme System
Testosterone
Estrogens

Keywords

  • Aromatase
  • Gonadal steroids
  • Sex dimorphism

ASJC Scopus subject areas

  • Endocrinology
  • Neuroscience(all)

Cite this

Sex differences in androgen responsiveness in the rat brain : Regional differences in the induction of aromatase activity. / Roselli, Charles; Klosterman, Scott A.; Fasasi, Taiwo A.

In: Neuroendocrinology, Vol. 64, No. 2, 08.1996, p. 139-145.

Research output: Contribution to journalArticle

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