Neonatal exposure to estradiol decreases hypothalamic allopregnanolone concentrations and alters agonistic and sexual but not affective behavior in adult female rats.

Exposure of developing female rats to estradiol during the perinatal period induced long-lasting dysregulation of gonadal axis and decreased cerebrocortical and plasma concentrations of allopregnanolone. We have now examined the effects of neonatal estradiol administration in female rats on hypothalamic allopregnanolone concentrations and on exploratory, affective, agonistic and sexual behaviors as well as social learning. A single administration of ß-estradiol 3-benzoate (EB, 10µg) on the day of birth resulted in a delay of vaginal opening, acyclicity and ovarian failure. These alterations were associated with a significant decrease in the concentrations of allopregnanolone in the hypothalamus at 21 and 60days, but not at 7days, after birth. Neonatal administration of EB also increased agonistic behaviors in adult rats, such as dominant behaviors and following of an ovariectomized intruder, while living attacks unaffected. EB-treated rats showed also an increase in anogenital investigation, associated with a drastic reduction in spontaneous and induced female sexual behaviors (receptivity and proceptivity). In contrast, neonatal administration of EB did not affect locomotor activity, anxiety- and mood-related behaviors, the social transmission of flavor preferences, and seizures sensitivity. These effects of estradiol suggest that it plays a major role in regulation of both the abundance of allopregnanolone and the expression of agonistic and sexual behaviors, while failing to influence affective behaviors and social learning. Thus, the pronounced and persistent decrease in hypothalamic allopregnanolone concentration may be related to the manifestation of agonistic and sexual behaviors.

Changes in GABAA receptor gamma 2 subunit gene expression induced by long-term administration of oral contraceptives in rats.

The effects of oral contraceptives (OCs) on neurosteroid concentrations were evaluated in female rats and women. In rats, ethynylestradiol and levonorgestrel (0.030 and 0.125 mg, respectively, subcutaneously) administered daily for 6 weeks reduced the concentrations of pregnenolone (-41%) progesterone (-74%) and allopregnanolone (-79%) in the cerebral cortex; the plasma concentrations of these steroids were also reduced but by smaller extents. OC administration for 3 months also reduced the serum concentrations of pregnenolone, progesterone and allopregnanolone in women. Chronic administration of OCs in rats increased the abundance of gamma-aminobutyric acid type A (GABA(A)) receptor gamma 2L and gamma 2S subunit mRNAs and the relative protein in the cerebral cortex, while the amounts of various alpha and beta subunit mRNAs were unaffected. Ovariectomy did not modify the effect of OCs administration on the concentrations of neurosteroids in the rat cerebral cortex (but not in the plasma) as well as on the GABA(A) receptor gene expression, suggesting a direct effect of OCs in brain. Finally, rats treated with OCs exhibited an anxiety-like behavior in the elevated plus-maze test. These results indicate that long-term treatment with OCs induced a persistent reduction in the concentrations of pregnenolone, progesterone and its GABA(A) receptor-active metabolite, allopregnanolone, both in rats and women. In rats this effect was associated with a plastic adaptation of GABA(A) receptor gene expression in the rat cerebral cortex.

Putative glycine receptors in Hydra: a biochemical and behavioural study.

Glycine acts as an inhibitory transmitter in the lower brain stem and spinal cord of vertebrate species, while very few data are yet available to support a similar role in invertebrate nervous systems. Here we report the identification and characterization of glycine receptors in the freshwater polyp Hydra vulgaris (Cnidaria, Hydrozoa) by biochemical and behavioural studies. Saturation experiments revealed the occurrence of one population of binding sites of nanomolar affinity (KD = 33 nm) and low capacity (Bmax = 79 fmol/mg protein) for [(3)H]strychnine. The addition of glycine or taurine (0.1 microm-1 mm) produced a dose-dependent inhibition of [(3)H]strychnine binding. Beta-alanine (0.1-1 mm) did not significantly affect [(3)H]strychnine binding. The pharmacological properties of these receptors compare with those of vertebrate glycine receptors. Stimulation of Hydra polyps by reduced glutathione resulted in a significant increase in the duration of mouth opening in the presence of glycine, taurine or beta-alanine. The enhancement of the response was related both to amino acid (10-100 microm) and to glutathione concentration (1-10 microm). The effects of glycine or its agonists were suppressed by strychnine (1-10 microm). D-serine, a glycine agonist at the vertebrate NMDA receptor, produced opposite effects to those of glycine. The effects of d-serine were suppressed by 5,7-dichlorokynurenic acid but not by strychnine. In vitro, [(3)H]strychnine binding was not displaced by d-serine. These results indicate a dual action of glycine in Hydra tissues. The hypothesis that NMDA receptors may also be present in this elementary nervous system is proposed.

Caffeine-induced increases in the brain and plasma concentrations of neuroactive steroids in the rat.

The effects of caffeine, a naturally occurring stimulant, on the brain and plasma concentrations of neuroactive steroids were examined in the rat. A single intraperitoneal injection of caffeine induced dose- and time-dependent increases in the concentrations of pregnenolone, progesterone, and 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in the cerebral cortex. The increases were significant at a caffeine dose of 25 mg/kg and greatest (+188, +388, and +71%, respectively) at a dose of 100 mg/kg in rats killed 30 min after caffeine administration. Caffeine also increased the plasma concentrations of pregnenolone and progesterone with a dose-response relation similar to that observed in the brain, whereas the caffeine-induced increase in the plasma concentration of allopregnanolone was maximal at a dose of 50 mg/kg. Caffeine increased the plasma concentration of corticosterone, but it had no effect on the brain or plasma concentrations of 3alpha, 21-dihydroxy-5alpha-pregnan-20-one and dehydroepiandrosterone. Moreover, the brain and plasma concentrations of pregnenolone, progesterone, and allopregnanolone were not affected by caffeine in adrenalectomized-orchiectomized rats. These results suggest that neuroactive steroids may modulate the stimulant and anxiogenic effects of caffeine.