Tolerance to allopregnanolone with focus on the GABA-A receptor.

Many studies have suggested a relationship between stress, sex steroids, and negative mental and mood changes in humans. The progesterone metabolite allopregnanolone is a potent endogenous ligand of the γ-amino butyric acid -A (GABA-A) receptor, and the most discussed neuroactive steroid. Variations in the levels of neuroactive steroids that influence the activity of the GABA-A receptor cause a vulnerability to mental and emotional pathology. There are physiological conditions in which allopregnanolone production increases acutely (e.g. stress) or chronically (e.g. menstrual cycle, pregnancy), thus exposing the GABA-A receptor to high and continuous allopregnanolone concentrations. In such conditions, tolerance to allopregnanolone may develop. We have shown that both acute and chronic tolerances can develop to the effects of allopregnanolone. Following the development of acute allopregnanolone tolerance, there is a decrease in the abundance of the GABA-A receptor α4 subunit and the expression of the α4 subunit mRNA in the ventral-posteriomedial nucleus of the thalamus. Little is known about the mechanism behind allopregnanolone tolerance and its effects on assembly of the GABA-A receptor composition. The exact mechanism of the allopregnanolone tolerance phenomena remains unclear. The purpose of this review is to summarize certain aspects of current knowledge concerning allopregnanolone tolerance and changes in the GABA-A receptors.

Persistence of tolerance to the anaesthetic effect of allopregnanolone in male rats.

Both acute and chronic tolerance can develop to allopregnanolone-a gamma-aminobutyric acid (GABA)-modulatory progesterone metabolite. Here we investigated if acute tolerance to allopregnanolone persisted for 1 or 2 days after the induction and thus could be the initial part of chronic tolerance. Male rats were anaesthetised with allopregnanolone (i.v) to the deep anaesthesia level of the silent second (SS), which is an EEG burst suppression of 1 s or more. They were divided into four groups: SS1-anaesthesia to the first silent second; LAn (long anaesthesia)-90 min anaesthesia at the SS level; SS2;D1-90 min anaesthesia and SS induction 1 day later; SS2;D2-90 min anaesthesia and SS induction 2 days later. Allopregnanolone concentrations in tissue and serum were analysed. Levels of the GABAA receptor alpha2, alpha4, gamma2(S+L) and delta subunits mRNAs were analysed by in situ hybridisation. Acute tolerance was induced during the 90 min anaesthesia. Tolerance persisted for 1 day, since the dose of allopregnanolone needed to induce a new SS anaesthesia was increased after 1 day. The level of alpha4 subunit mRNA expression in the ventral posteriomedial nucleus of thalamus was negatively related to the tolerance parameters, the SS dose of allopregnanolone and DeltaSS (SS dose difference between days). Allopregnanolone threshold anaesthesia lasting 90 min induces acute tolerance that persisted for at least 1 day, which could be used as the start of a chronic tolerance. The alpha4 subunit may be involved in allopregnanolone caused effects in the brain.

GABA(A) receptor changes in acute allopregnanolone tolerance.

To study acute tolerance, rats were anesthetized with interrupted i.v. allopregnanolone infusions where the "silent second" in the electroencephalogram (EEG) was the target. Animals were killed either directly at the first silent second or at the silent second level after 30 or 90 min of anaesthesia. Acute tolerance was demonstrated at 90 min of anaesthesia as earlier shown. In situ hybridization showed a decreased expression of the gamma-aminobutyric acid(A) (GABA(A)) receptor subunit alpha4mRNA amount in the thalamus ventral-posteriomedial nucleus of the tolerant rats. A parallel change in the abundance of the alpha4 subunit was detected with immunohistochemistry. The increase in maintenance dose rate (MDR) was significantly negatively correlated with the alpha4mRNA in the thalamus ventral-posteriomedial nucleus, and positively correlated with alpha2mRNA in different hippocampal subregions. There was also a positive relationship between the alpha1mRNA amounts in the different hippocampal subregions, with significant differences between groups. These changes in GABA(A) receptor subunits mRNA expression and protein (alpha4) might be of importance for the development of acute tolerance to allopregnanolone.

Neuroactive steroid effects on cognitive functions with a focus on the serotonin and GABA systems.

This article will review neuroactive steroid effects on serotonin and GABA systems, along with the subsequent effects on cognitive functions. Neurosteroids (such as estrogen, progesterone, and allopregnanolone) are synthesized in the central and peripheral nervous system, in addition to other tissues. They are involved in the regulation of mood and memory, in premenstrual syndrome, and mood changes related to hormone replacement therapy, as well as postnatal and major depression, anxiety disorders, and Alzheimer's disease. Estrogen and progesterone have their respective hormone receptors, whereas allopregnanolone acts via the GABA(A) receptor. The action of estrogen and progesterone can be direct genomic, indirect genomic, or non-genomic, also influencing several neurotransmitter systems, such as the serotonin and GABA systems. Estrogen alone, or in combination with antidepressant drugs affecting the serotonin system, has been related to improved mood and well being. In contrast, progesterone can have negative effects on mood and memory. Estrogen alone, or in combination with progesterone, affects the brain serotonin system differently in different parts of the brain, which can at least partly explain the opposite effects on mood of those hormones. Many of the progesterone effects in the brain are mediated by its metabolite allopregnanolone. Allopregnanolone, by changing GABA(A) receptor expression or sensitivity, is involved in premenstrual mood changes; and it also induces cognitive deficits, such as spatial-learning impairment. We have shown that the 3beta-hydroxypregnane steroid UC1011 can inhibit allopregnanolone-induced learning impairment and chloride uptake potentiation in vitro and in vivo. It would be important to find a substance that antagonizes allopregnanolone-induced adverse effects.

The effect of a low dose of alcohol on allopregnanolone serum concentrations across the menstrual cycle in women with severe premenstrual syndrome and controls.

BACKGROUND: Neurosteroids have been proposed to play an important role in the interaction between alcohol and GABA(A) receptors and for the symptomatology of premenstrual dysphoric disorder (PMDD). The primary aim of this study was to investigate possible alcohol-induced changes in allopregnanolone serum concentrations across different menstrual cycle phases in women with severe premenstrual syndrome (PMS) and controls. METHODS: The allopregnanolone and cortisol responses to a low-dose of alcohol were evaluated in 14 women with and 12 women without severe premenstrual syndrome in the follicular and late luteal phases. The effect of a 30-min intravenous alcohol infusion (0.2 g/kg) on allopregnanolone and cortisol serum concentrations was compared to placebo, and compared between cycle phases and groups. Blood samples for measuring allopregnanolone were taken at baseline 25, 55, and 75 min after the start of the alcohol infusion. RESULTS: In the late luteal phase, the alcohol infusion decreased allopregnanolone levels, compared to baseline levels as well as to placebo. The difference in allopregnanolone levels between alcohol and placebo was evident 25 min (P < 0.01), 55 min (P < 0.01), and 75 min (P < 0.05) after start of the infusion. There was no change in allopregnanolone levels during the alcohol infusion in the follicular phase. Also, no difference in alcohol-induced allopregnanolone response between PMS patients and control subjects was detected. Cortisol levels declined during both the placebo and alcohol infusion, but did not differ with respect to which infusion had been given. CONCLUSION: During the late luteal phase, independent of PMS diagnosis, the low-dose alcohol infusion resulted in decreasing peripheral allopregnanolone levels.

Isoallopregnanolone; an antagonist to the anaesthetic effect of allopregnanolone in male rats.

The interaction of isoallopregnanolone (3 beta-OH-5 alpha-pregnan-20-one) on allopregnanolone (3 alpha-OH-5 alpha-pregnan-20-one) induced anaesthesia was studied in male rats using burst suppression of 1 s ("silent second") with an electroencephalographic-threshold method. The i.v. administration of isoallopregnanolone was varied in relation to induction of "silent second". Pre-treatment with isoallopregnanolone (12.5-50 mg/kg iv) 2 min prior to the threshold test gave an increase in the threshold dose of allopregnanolone (ANOVA df(3;36), F=13.61, P<0.001), which was dose dependent (r=0.73, b [slope]=0.08, df=38, P<0.001). After isoallopregnanolone pre-treatment, but not in the controls, anaesthesia time was positively related to the dose of allopregnanolone (r=0.52, b=1.72, df=28, P<0.01). Anaesthesia times were not influenced by a corresponding administration of isoallopregnanolone immediately after induction of "silent second". When allopregnanolone and isoallopregnanolone were infused together at molar ratios of 1:1, 1:1.23, 1:1.43, a linear increase of the threshold doses of allopregnanolone was seen in relation to the dose of isoallopregnanolone (r=0.86, b=0.40, df=8, P<0.01). Thus isoallopregnanolone can antagonise the anaesthetic action of allopregnanolone.

No difference in responsiveness to a low dose of alcohol between healthy women and men.

The purpose of the current study was to examine gender-related differences in alcohol responsiveness by comparing the effect of a low-dose intravenous alcohol infusion upon saccadic eye movements, self-rated sedation and intoxication scores. The functional sensitivity to a low dose of alcohol in 12 healthy women and 12 healthy men was evaluated by comparing the effects of an intravenous alcohol infusion on a number of saccadic eye movement measures, including saccadic eye velocity (SEV), saccade latency, saccade accuracy, saccade deceleration and self-rated levels of intoxication and sedation. The infusion of a low dose of alcohol induced a decrease in SEV and increased saccade deceleration and self-rated scores of intoxication in both males and females. Saccade accuracy was also significantly deteriorated by alcohol in both groups. The alcohol infusion did not induce any main gender-related differences in the saccade or visual analogue scale measurements. According to the findings of the present study, no gender differences in the responsiveness to a low-dose alcohol infusion were found.

Altered sensitivity to alcohol in the late luteal phase among patients with premenstrual dysphoric disorder.

BACKGROUND: Affective disorders, and possibly also premenstrual dysphoric disorder (PMDD) are risk factors for alcohol abuse in women. Although the majority of prior studies have indicated that alcohol sensitivity does not differ between menstrual cycle phases, patients with PMDD have thus far not been studied. METHODS: We have evaluated the functional sensitivity to a low dose of alcohol in 12 women with and 12 women without PMDD in the mid-follicular and late luteal phases of the menstrual cycle, by comparing the effects of an intravenous alcohol infusion on a number of saccadic eye movement measures, including saccadic eye velocity (SEV), saccade deceleration, and self-rated levels of intoxication. RESULTS: PMDD patients displayed blunted SEV (p<0.01) and saccade deceleration responses (p<0.01) to alcohol infusion in the late luteal phase compared to the mid-follicular phase. Control subjects, on the other hand, did not change their SEV or saccade deceleration responses to alcohol between cycle phases. CONCLUSION: These findings are compatible with altered saccadic eye movement sensitivity in response to alcohol among PMDD patients, particularly in the late luteal phase of the menstrual cycle.

The role of hormones and hormonal treatments in premenstrual syndrome.

Premenstrual syndrome (PMS) is a menstrual cycle-linked condition with both mental and physical symptoms. Most women of fertile age experience cyclical changes but consider them normal and not requiring treatment. Up to 30% of women feel a need for treatment. The aetiology is still unclear, but sex steroids produced by the corpus luteum of the ovary are thought to be symptom provoking, as the cyclicity disappears in anovulatory cycles when a corpus luteum is not formed. Progestogens and progesterone together with estrogen are able to induce similar symptoms as seen in PMS. Symptom severity is sensitive to the dosage of estrogen. The response systems within the brain known to be involved in PMS symptoms are the serotonin and GABA systems. Progesterone metabolites, especially allopregnanolone, are neuroactive, acting via the GABA system in the brain. Allopregnanolone has similar effects as benzodiazepines, barbiturates and alcohol; all these substances are known to induce adverse mood effects at low dosages in humans and animals. SSRIs and substances inhibiting ovulation, such as gonadotrophin-releasing hormone (GnRH) agonists, have proven to be effective treatments. To avoid adverse effects when high dosages of GnRH agonists are used, add-back hormone replacement therapy is recommended. Spironolactone also has a beneficial effect, although not as much as SSRIs and GnRH agonists.

Pathogenesis in menstrual cycle-linked CNS disorders.

That 3alpha-hydroxy-5alpha/beta-pregnane steroids (GABA steroids) have modulatory effects on the GABA-A receptor is well known. In behavioral studies in animals high exogenous dosages give concentrations not usually reached in the brain under physiological conditions. Animal and human studies show that GABA-A receptor-positive modulators like barbiturates, benzodiazepines, alcohol, and allopregnanolone have a bimodal effect. In pharmacological concentrations they are CNS depressants, anesthetic, antiepileptic, and anxiolytic. In low dosages and concentrations, reached endogenously, they can induce adverse emotional reactions in up to 20% of individuals. GABA steroids can also induce tolerance to themselves and similar substances, and rebound occurs at withdrawal. Menstrual cycle-linked disorders can be understood by the concept that they are caused by the action of endogenously produced GABA-steroids through three mechanisms: (a) direct action, (b) tolerance induction, and (c) withdrawal effect. Examples of symptoms and disorders caused by the direct action of GABA steroids are sedation, memory and learning disturbance, clumsiness, increased appetite, worsening of petit mal epilepsy, negative mood as tension, irritability and depression during hormone treatments, and the premenstrual dysphoric disorder (PMDD). A continuous exposure to GABA steroids causes tolerance, and women with PMDD are less sensitive to GABA-A modulators. A malfunctioning GABA-A receptor system is related to stress sensitivity, concentration difficulties, loss of impulse control, irritability, anxiety, and depression. An example of withdrawal effect is "catamenial epilepsy," when seizures increase during menstruation after the withdrawal of GABA steroids. Similar phenomena occur at stress since the adrenals produce GABA steroids during stress.