Sexually dimorphic effects of testosterone administration on brain allopregnanolone in gonadectomized rats

Effect of estetrol administration on brain and serum allopregnanolone in intact and ovariectomized rats

INTRODUCTION

Estetrol (E4), a naturally occurring estrogen only produced by the human fetal liver, is being evaluated in human studies for potential use in contraception and menopausal care. The present study was designed to profile E4 in the central nervous system, to assess the in vivo effects of E4 administration on allopregnanolone (AP) synthesis in specific brain structures and to evaluate whether E4 has synergic or antagonistic effects on estradiol-mediated AP synthesis.

MATERIAL AND METHODS

Intact female adult rats received different doses of E4, and ovariectomized OVX rats received different doses of E4 or E2V or combinations of both drugs. The concentrations of AP were assessed in the frontal and parietal cortex, hippocampus, hypothalamus, anterior pituitary, and serum.

RESULTS

E4 did not alter AP in intact animals in any region. E4 at a dosage of 5mg/kg/day increased AP levels in different brain areas and in the serum of OVX animals. However, in the presence of estradiol, E4 showed an estrogen-antagonistic effect on the brain and serum levels of AP.

CONCLUSION

E4 increases the CNS and peripheral levels of AP, behaving as a weak estrogen-agonist in OVX rats. The antagonistic effect observed with E2V co-administration further profile E4 as a natural SERM.

Age-related Purkinje cell death is steroid dependent: RORα haplo-insufficiency impairs plasma and cerebellar steroids and Purkinje cell survival

A major problem of ageing is progressive impairment of neuronal function and ultimately cell death. Since sex steroids are neuroprotective, their decrease with age may underlie age-related neuronal degeneration. To test this, we examined Purkinje cell numbers, plasma sex steroids and cerebellar neurosteroid concentrations during normal ageing (wild-type mice, WT), in our model of precocious ageing (Rora(+/sg), heterozygous staggerer mice in which expression of the neuroprotective factor RORα is disrupted) and after long-term hormone insufficiency (WT post-gonadectomy). During normal ageing (WT), circulating sex steroids declined prior to or in parallel with Purkinje cell loss, which began at 18 months of age. Although Purkinje cell death was advanced in WT long-term steroid deficiency, this premature neuronal loss did not begin until 9 months, indicating that vulnerability to sex steroid deficiency is a phenomenon of ageing Purkinje neurons. In precocious ageing (Rora(+/sg)), circulating sex steroids decreased prematurely, in conjunction with marked Purkinje cell death from 9 months. Although Rora(+/sg) Purkinje cells are vulnerable through their RORα haplo-insufficiency, it is only as they age (after 9 months) that sex steroid failure becomes critical. Finally, cerebellar neurosteroids did not decrease with age in either genotype or gender; but were profoundly reduced by 3 months in male Rora(+/sg) cerebella, which may contribute to the fragility of their Purkinje neurons. These data suggest that ageing Purkinje cells are maintained by circulating sex steroids, rather than local neurosteroids, and that in Rora(+/sg) their age-related death is advanced by premature sex steroid loss induced by RORα haplo-insufficiency.

Evidence for suppressant effects of testosterone on sex-typical ethanol intake in male Sprague-Dawley rats

Previous studies have shown that adult female rats consume more ethanol than adult males. Castration of male rats has been found to increase their ethanol intake and preference to levels significantly elevated above their sham-gonadectomized counterparts and similar to levels observed in females. The purpose of the present experiment was to examine whether testosterone replacement in castrated adult male rats would be sufficient to restore the relatively low levels of ethanol drinking characteristic of intact adult male rats. Males were either gonadectomized and implanted with a testosterone propionate pellet (RPL), gonadectomized and implanted with a placebo pellet (GX), sham-gonadectomized and implanted with a placebo pellet (SH), or were left non-manipulated (NM). Voluntary ethanol intake was measured using a 2h limited-access drinking paradigm, with access to two bottles: one containing water, and the other a sweetened ethanol solution. Hormone replacement was sufficient to return ethanol intake and preference of castrates to levels comparable to both SH and NM control males. Ethanol preference of RPL males was also significantly suppressed compared to GX males by the end of the measurement period, whereas these group comparisons did not reach statistical significance for g/kg ethanol intake. These data suggest that testosterone serves to suppress ethanol preference in male rats, and may contribute to the sex differences in ethanol preference and consumption commonly reported in adult rats.

An ex vivo multi-electrode approach to evaluate endogenous hormones and receptor subtype pharmacology on evoked and spontaneous neuronal activity within the ventromedial hypothalamus; translation from female receptivity

INTRODUCTION

The ventromedial hypothalamus (VMH) controls female rodent copulatory behavior, which can be modulated by injection of various compounds into the VMH. Aim. The aim was to determine whether evoked excitatory postsynaptic potentials (EPSPs) or single-unit activity within the VMH ex vivo is a better parameter to predict lordosis.

METHODS

VMH slices were placed onto a 64 microelectrode chip and spontaneous single-unit activity was recorded or slices stimulated to evoke EPSPs.

MAIN OUTCOME MEASURES

The sodium channel blocker, tetrodotoxin and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX) inhibited EPSPs, confirming EPSPs were glutamatergic in origin. The GABA(A) antagonist bicuculline potentiated EPSPs implying endogenous GABA tone. Single-unit activity was abolished by tetrodotoxin but unaffected by DNQX or bicuculline.

RESULTS

Glutamatergic neurotransmission was greatest during metestrous and following ovariectomization. The number of regions within the VMH eliciting single-unit activity was reduced following ovariectomy without changing spike frequency. Adrenergic agents increasing lordosis via the VMH in vivo, decreased glutamate neurotransmission but increased single-unit activity. Conversely, agents decreasing lordosis via the VMH increased glutamatergic neurotransmission and inhibited single-unit activity (8-OH-DPAT, [D-Ala(2), N-Me-Phe(4), Gly-ol(5)]-enkephalin, corticotropin releasing factor, bicuculline). Melanocortin and pituitary adenylate cyclase-activating polypeptide agonists had no effect.

CONCLUSIONS

Here we present a novel, robust VMH in vitro technique that (i) is consistent with the hypothesis that glutamate via non-NMDA receptors inhibits lordosis; (ii) glutamate is under the endogenous tone of GABA and steroid hormones; (iii) inhibition of lordosis during metestrous and following ovariectomy potentiates glutamatergic neurotransmission; (iv) activation of G(q)- and G(i)-coupled receptors decreases and increases glutamate neurotransmission, respectively, with an inverse correlation on single-unit activity; (v) activation of G(s)-coupled receptors has no direct effect on glutamate or single-unit activity; and (vi) potency, receptor subtypes and localization can be determined prior to in vivo studies.