Steroid profiles in quail brain and serum: Sex and regional differences and effects of castration with steroid replacement

Abstract

Both systemic and local production contribute to the concentration of steroids measured in the brain. This idea was originally based on rodent studies and was later extended to other species, including humans and birds. In quail, a widely used model in behavioural neuroendocrinology, it was demonstrated that all enzymes needed to produce sex steroids from cholesterol are expressed and active in the brain, although the actual concentrations of steroids produced were never investigated. We carried out a steroid profiling in multiple brain regions and serum of sexually mature male and female quail by gas chromatography coupled with mass spectrometry. The concentrations of some steroids (eg, corticosterone, progesterone and testosterone) were in equilibrium between the brain and periphery, whereas other steroids (eg, pregnenolone (PREG), 5α/β-dihydroprogesterone and oestrogens) were more concentrated in the brain. In the brain regions investigated, PREG sulphate, progesterone and oestrogen concentrations were higher in the hypothalamus-preoptic area.Progesterone and its metabolites were more concentrated in the female than the male brain, whereas testosterone, its metabolites and dehydroepiandrosterone were more concentrated in males, suggesting that sex steroids present in quail brain mainly depend on their specific steroidogenic pathways in the ovaries and testes. However, the results of castration experiments suggested that sex steroids could also be produced in the brain independently of the peripheral source. Treatment with testosterone or oestradiol restored the concentrations of most androgens or oestrogens, respectively, although penetration of oestradiol in the brain appeared to be more limited. These studies illustrate the complex interaction between local brain synthesis and the supply from the periphery for the steroids present in the brain that are either directly active or represent the substrate of centrally located enzymes. K E Y W O R D Sbrain aromatisation, brain steroid concentrations, gas chromatography, mass spectrometry, preoptic area (16:8 hour light/dark photocycle). We first describe the methods that are common to all experiments and, in a second step, we describe the specific protocols of each experiment.All experimental procedures were conducted in agreement with the Belgian and French laws on the "Protection and Welfare of Animals" and on the "Protection of experimental animals" and were approved by the Ethics Committee for the Use of Animals at the University of Liège. | Brain collection and dissectionBirds were rapidly killed by decapitation without anaesthesia to avoid potential changes in steroid concentrations. Trunk blood was collected and, after centrifugation, serum was stored at −80°C until assayed for steroid content (0.5-1.0 mL used in the assays). Brains were immediately extracted from the skull and dissected into four great subdivisions: the hypothalamus-POA (30-60 mg), the telencephalon (TEL) (300-450 mg), the optic lobes (OL) (120-180 mg) and the cerebellum (CB) (90-110 mg)....

Profiling of systemic and brain steroids in male songbirds: Seasonal changes in neurosteroids

“…Because the BnST expresses many androgen receptors, 18,61 it is surprising that T and 5α‐DHT levels are low in this region. It is also noteworthy that androstenedione and 5α‐DHT levels are much higher in some regions than in the blood (up to 20‐fold higher), similar to a recent study in quail using gas chromatography‐mass spectrometry 62 . Cyp17a1 (an enzyme that synthesises androstenedione) is expressed in the songbird brain, 63 with high levels in the VMH and low levels in the LS (similar to androstenedione levels observed here).…”

“…It is also noteworthy that androstenedione and 5α-DHT levels are much higher in some regions than in the blood (up to 20-fold higher), similar to a recent study in quail using gas chromatography-mass spectrometry. 62 Cyp17a1 (an enzyme that synthesises androstenedione) is expressed in the songbird brain, 63 with high levels in the VMH and low levels in the LS (similar to androstenedione levels observed here). Thus, we speculate that androstenedione is synthesised locally in the brain.…”

How technical progress reshaped behavioral neuroendocrinology during the last 50 years… and some methodological remarks

“…A testosterone assay without previous separation from 5α-DHT presumably provides reasonably accurate values because 5α-DHT is present in low concentrations in most mammals but in birds another closely related metabolite, 5β-DHT is present in very large concentrations and if an antibody against testosterone cross-reacts just by a few percent, this might provide a completely false evaluation of its concentration. We recently showed that 5β-DHT is approximately 10 times more concentrated than testosterone in the brain of male Japanese quail (Liere et al, 2019). If there is just a small cross reactivity with 5β-DHT of an antibody against testosterone, this might significantly distort the results but suppliers never report cross-reactivity with this steroid.…”

Rapid changes in brain estrogen concentration during male sexual behavior are site and stimulus specific

“…The resulting changes in local E 2 concentrations are less clear. A host of studies indicate that brain steroid concentrations are not a direct reflection of concentrations circulating in the blood (In rodents 10 – 12 ; in quail 13 ) which led to the discovery that the brain itself can synthesize steroids from cholesterol, independent from the supply of systemic precursors, these are the so-called neurosteroids 14 , 15 .…”