DHEA and estradiol levels in brain, gonads, adrenal glands, and plasma of developing male and female European starlings.

Traditionally, sexual differentiation of the brain was thought to be driven by gonadal hormones, particularly testosterone (T). However, recent studies in songbirds suggest that other steroids may also be important. For example, dehydroepiandrosterone (DHEA) can be synthesized by the gonads, adrenal glands, and/or brain and locally metabolized into T and 17β-estradiol (E(2)).

17beta-Estradiol levels in male zebra finch brain: combining Palkovits punch and an ultrasensitive radioimmunoassay.

Local aromatization of testosterone into 17beta-estradiol (E(2)) is often required for the physiological and behavioral actions of testosterone. In most vertebrates, aromatase is expressed in a few discrete brain regions. While many studies have measured brain aromatase mRNA or activity, very few studies have measured brain E(2) levels, particularly in discrete brain regions, because of technical challenges.

Cortisol and corticosterone in immune organs and brain of European starlings: developmental changes, effects of restraint stress, comparison with zebra finches.

Glucocorticoids (GCs) are produced in the adrenal glands and also in extra-adrenal sites, including immune organs and brain. Here, we examined regulation of systemic GC levels in plasma and local GC levels in immune organs and brain during development. We conducted two studies and examined a total of 462 samples from 70 subjects.

Sexual differentiation of the spinal nucleus of the bulbocavernosus is not mediated solely by androgen receptors in muscle fibers.

The spinal nucleus of the bulbocavernosus (SNB) neuromuscular system is a highly conserved and well-studied model of sexual differentiation of the vertebrate nervous system. Sexual differentiation of the SNB is currently thought to be mediated by the direct action of perinatal testosterone on androgen receptors (ARs) in the bulbocavernosus/levator ani muscles, with concomitant motoneuron rescue. This model has been proposed based on surgical and pharmacological manipulations of developing rats as well as from evidence that male rats with the testicular feminization mutation (Tfm), which is a loss of function AR mutation, have a feminine SNB phenotype.

Neurosteroids, immunosteroids, and the Balkanization of endocrinology.

Traditionally, the production and regulation of steroid hormones has been viewed as a multi-organ process involving the hypothalamic-pituitary-gonadal (HPG) axis for sex steroids and the hypothalamic-pituitary-adrenal (HPA) axis for glucocorticoids. However, active steroids can also be synthesized locally in target tissues, either from circulating inactive precursors or de novo from cholesterol. Here, we review recent work demonstrating local steroid synthesis, with an emphasis on steroids synthesized in the brain (neurosteroids) and steroids synthesized in the immune system (immunosteroids).

Sex differences in DHEA and estradiol during development in a wild songbird: Jugular versus brachial plasma.

Sexual differentiation of the brain has traditionally been thought to be driven by gonadal hormones, particularly testosterone (T). Recent studies in songbirds and other species have indicated that non-gonadal sex steroids may also be important. For example, dehydroepiandrosterone (DHEA)--a sex steroid precursor that can be synthesized in the adrenal glands and/or brain--can be converted into active sex steroids, such as 17beta-estradiol (E(2)), within the brain.