A stress steroid triggers anxiety via increased expression of α4βδ GABAA receptors in methamphetamine dependence

Risk of Relapse Assessment Scale for Metamphetamine Abusers: Reliability and Validity Study of the Turkish Version

Background

This study aims to investigate the validity and reliability of the Turkish adaptation of the 16-item Risk of Relapse Assessment Scale (RRAS) for methamphetamine abusers.

Methods

A total of 160 patients diagnosed with methamphetamine use disorder were included in this study to evaluate the validity and reliability of the scale. The comparison of the relationship between the Risk of Relapse Assessment Scale, the Substance Craving Scale, and the Relapse Prediction Scale was also carried out. The validity of the Risk of Relapse Assessment Scale was examined in the first step by exploratory factor analysis. The suitability of the data for exploratory factor analysis was evaluated by Kaiser-Meyer-Olkin test and Barlett's test. Cronbach's α coefficient and corrected item-total correlation value were used to test the reliability of the scale. The validity results of Risk of Relapse Assessment Scale were tested by confirmatory factor analysis. The significance level was set at P < .05 for all analyses.

Results

Considering the examination of the internal consistency values of the Risk of Relapse Assessment Scale, Cronbach's α value was detected to be 0.90, and Cronbach's α value of the subscales ranged from 0.72 to 0.90. The study determined that the goodness of fit values for RRAS were χ 2/df =2.13, P < .001, goodness of fit index = 0.88, comparative fit index = 0.92, normed fit index = 0.86, Trucker-Lewis index = 0.90, root mean square error of approximation = 0.08, and standardized root mean squared residual = 0.06.

Conclusion

Our findings demonstrate that Risk of Relapse Assessment Scale is a valid and reliable measurement tool for assessing the risk of methamphetamine relapse in Turkish.

Oxidative Stress and Inflammatory Biomarkers in People with Methamphetamine Use Disorder

Objective

This study aimed to investigate the blood serum levels of biomarkers specifying oxidative stress status and systemic inflammation between people using methamphetamine (METH) and the control group (CG). Serum thiol/disulfide balance and ischemia-modified albumin levels were studied to determine oxidative stress, and serum interleukin-6 (IL-6) levels and complete blood count (CBC) were to assess inflammation.

Methods

Fifty patients with METH use disorder (MUD) and 36 CG participants were included in the study. Two tubes of venous blood samples were taken to measure oxidative stress, serum thiol/disulfide balance, ischemia-modified albumin, and IL-6 levels between groups. The correlation of parameters measuring oxidative stress and inflammation between groups with sociodemographic data was investigated.

Results

In this study, serum total thiol, free thiol levels, disulfide/native thiol percentage ratios, and serum ischemia- modified albumin levels of the patients were statistically significantly higher than the healthy controls. No difference was observed between the groups in serum disulfide levels and serum IL-6 levels. Considering the regression analysis, only the duration of substance use was a statistically significant factor in explaining serum IL-6 levels. The parameters showing inflammation in the CBC were significantly higher in the patients than in the CG.

Conclusion

CBC can be used to evaluate systemic inflammation in patients with MUD. Parameters measuring thiol/disulfide homeostasis and ischemia-modified albumin can be, also, used to assess oxidative stress.

Long-Term Management of Generalised Anxiety Disorder with Low-Dose Continuous Infusions of Flumazenil: A Case Series

Background: Generalised anxiety disorder (GAD) is a common anxiety disorder associated with social and occupational impairment. Recently, a theory was postulated that dysfunctional gamma aminobutyric acid type A receptors (GABAA) are implicated in anxiety symptomology, which could be corrected by flumazenil, an antagonist at the benzodiazepine binding site on the GABAA receptor. Method: Participants had a primary diagnosis of GAD and were treated initially with an eight-day continuous low-dose flumazenil infusion (total 32 mg at a rate of 4 mg/24 h). Some participants were re-treated with a further four- or eight-day infusion. Treatment response was measured as a 50% reduction in anxiety or stress scores on the Depression Anxiety Stress Scale—21 (DASS-21). Remission was measured as scores ≤3 or ≤7 on the anxiety and stress subscales of the DASS-21, respectively. Results: Eight cases are reported. All cases met the criteria for treatment response on the anxiety and stress subscale of the DASS-21. Remission was achieved in seven participants on the anxiety subscale and in five on the stress subscale. No changes in hepatic, renal, or haematological function were likely attributed to flumazenil. Conclusion: Data suggest that low-dose continuous flumazenil infusion manages GAD symptoms and is safe. Although these results are promising, future randomised control trials are required to confirm these results.

A theory of the anxiolytic action of flumazenil in anxiety disorders

BACKGROUND

Anxiety disorders are highly prevalent affecting up to 33.7% of people over a lifetime. Although many treatment options are available, they are often associated with unacceptable side-effect profiles and approximately one in three patients are treatment resistant. Allopregnanolone, a neuroactive steroid acting as a positive allosteric modulator at the GABA_A receptor, is synthesised in response to stress and acts to negatively modulate the hypothalamic-pituitary-adrenal axis.

FINDINGS

After chronic exposure to and withdrawal from allopregnanolone, an increase in α₄β₂δ GABA_A receptors results in a reduced inhibitory effect of allopregnanolone, resulting in decreased inhibition and, therefore, increased neuronal excitability. The relationship between allopregnanolone and increased α₄β₂δ GABA_A receptors has been demonstrated in animal models during methamphetamine withdrawal and puberty, events both associated with stress. The effect of allopregnanolone during these events is anxiogenic, a paradoxical action to its usual anxiolytic effects. Flumazenil, the GABA_A receptor antagonist, has been shown to cause receptor internalisation of α₄β₂δ GABA_A receptors, which may results in anxiolysis.

CONCLUSION

We propose that chronic stress and chronic exposure to and withdrawal from allopregnanolone in anxiety disorders result in alterations in GABA_A receptor function, which can be corrected by flumazenil. As such, flumazenil may exhibit anxiolytic properties in patients with increased α₄β₂δ GABA_A receptor expression.

Very low dose naltrexone in opioid detoxification: a double-blind, randomized clinical trial of efficacy and safety

Withdrawal syndrome is one of the initial focuses of opioid detoxification. Very low dose naltrexone (VLNTX) has been found to reduce opioid tolerance and dependence in animal and human clinical studies. The aim of this study was to determine the safety and efficacy of VLNTX during early stages of detoxification. In a multi-arm parallel, double-blind, randomized controlled trial, 63 opioid-dependent male participants referring to Imam Reza Rehabilitation Center were allocated to three equal groups using block randomization method. They received 0.125 mg, 0.250 mg of VLNTX or placebo daily for 10 days, together with the routine clonidine-based protocol. Self-reported and observer ratings of withdrawal severity and adverse events were measured on the 1st, 4th and 10th day of treatment. Runny eyes (p = 0.006), anxiety (p = 0.031) and dehydration (p = 0.014) were reduced during the whole 10 days in the 0.125 mg VLNTX-treated group compared to placebo. Only drowsiness (p = 0.043) and dysphoric mood (p < 0.001) were reduced in the 0.250 mg VLNTX-treated group. Results of 1st, 4th, and 10th-day assessment showed that most symptoms reductions were for the 0.125 mg VLNTX and the placebo group in the 1st and 4th days, respectively. On the 10th day, there was not any significant difference between 0.250 mg VLNTX-treated group and placebo group. No adverse effect was observed. In the starting days of detoxification, VLNTX can reduce the withdrawal symptoms, but the efficacy declined by passing time. Further studies are needed to test the utility of this new therapeutic approach.

Pubertal hormones increase hippocampal expression of α4βδ GABAA receptors

CA1 hippocampal expression of α4βδ GABA_A receptors (GABARs) increases at the onset of puberty in female mice, an effect dependent upon the decline in hippocampal levels of the neurosteroid THP (3α-OH-5α-pregnan-20-one) which occurs at this time. The present study further characterized the mechanisms underlying α4βδ expression, assessed in vivo. Blockade of pubertal levels of 17β-estradiol (E₂) (formestane, 0.5 mg/kg, i.p. 3 d) reduced α4 and δ expression by 75-80% (P < 0.05) in CA1 hippocampus of female mice, assessed using Western blot techniques. Conversely, E₂ administration increased α4 and δ expression by 50-100% in adults, an effect enhanced by more than 2-fold by concomitant administration of the 5α-reductase blocker finasteride (50 mg/kg, i.p., 3d, P < 0.05), suggesting that both declining THP levels and increasing E₂ levels before puberty trigger α4βδ expression. This effect was blocked by ICI 182,780 (20 mg/kg, s.c., 3 d), a selective blocker of E₂ receptor-α (ER-α). These results suggest that both the rise in circulating levels of E₂ and the decline in hippocampal THP levels at the onset of puberty trigger maximal levels of α4βδ expression in the CA1 hippocampus.

Effects of GABA active steroids in the female brain with a focus on the premenstrual dysphoric disorder

Premenstrual dysphoric disorder (PMDD) afflicts 3%-5% of women of childbearing age, and is characterised by recurrent negative mood symptoms (eg, irritability, depression, anxiety and emotional lability) during the luteal phase of the menstrual cycle. The aetiology of PMDD is unknown, although a temporal association with circulating ovarian steroids, in particular progesterone and its metabolite allopregnanolone, has been established during the luteal phase. Allopregnanolone is a positive modulator of the GABAA receptor: it is sedative in high concentrations but may precipitate paradoxical adverse effects on mood at levels corresponding to luteal phase concentrations in susceptible women. Saccadic eye velocity (SEV) is a measure of GABAA receptor sensitivity; in experimental studies of healthy women, i.v. allopregnanolone decreases SEV. Women with PMDD display an altered sensitivity to an i.v. injection of allopregnanolone compared to healthy controls in this model. In functional magnetic resonance imaging (fMRI) studies, women with PMDD react differently to emotional stimuli in contrast to controls. A consistent finding in PMDD patients is increased amygdala reactivity during the luteal phase. Post-mortem studies in humans have revealed that allopregnanolone concentrations vary across different brain regions, although mean levels in the brain also reflect variations in peripheral serum concentrations. The amygdala processes emotions such as anxiety and aggression. This is interesting because allopregnanolone is detected at high concentrations within the region into which marked increases in blood flow are measured with fMRI following progesterone/allopregnanolone administration. Allopregnanolone effects are antagonised by its isomer isoallopregnanolone (UC1010), which significantly reduces negative mood symptoms in women with PMDD when administered s.c. in the premenstrual phase. This was shown in a randomised, placebo-controlled clinical trial in which the primary outcome was change in symptom scoring on the Daily Rating of Severity of Problems (DRSP): the treatment reduced negative mood scores (P < .005), as well as total DRSP scores (P < .01), compared to placebo in women with PMDD. In conclusion, the underlying studies of this review provide evidence that allopregnanolone is the provoking factor behind the negative mood symptoms in PMDD and that isoallopregnanolone could ameliorate the symptoms as a result of its ability to antagonise the allopregnanolone effect on the GABAA receptor.

Treatment of premenstrual dysphoric disorder with the GABAA receptor modulating steroid antagonist Sepranolone (UC1010)-A randomized controlled trial

CONTEXT

Allopregnanolone is a metabolite from progesterone and a positive modulator of the GABAA receptor. This endogenous steroid may induce negative mood in sensitive women when present in serum levels comparable to the premenstrual phase. Its endogenous isomer, isoallopregnanolone, has been shown to antagonize allopregnanolone effects in experimental animal and human models.

OBJECTIVE

The objective was to test whether inhibition of allopregnanolone by treatment with the GABAA modulating steroid antagonist (GAMSA) Sepranolone (UC1010) during the premenstrual phase could reduce symptoms of the premenstrual dysphoric disorder (PMDD). The pharmacokinetic parameters of UC1010 when given as a subcutaneous injection were measured in healthy women prior to the study in women with PMDD.

DESIGN

This was an explorative randomized, double-blind, placebo-controlled study.

SETTING

Swedish multicentre study with 10 centers.

PARTICIPANTS

Participants were 26 healthy women in a pharmacokinetic phase I study part, and 126 women with PMDD in a phase II study part. Diagnosis followed the criteria for PMDD in DSM-5 using Daily Record of Severity of Problems (DRSP) and Endicott's algorithm.

INTERVENTION

Subjects were randomized to treatment with UC1010 (10 or 16mg) subcutaneously every second day during the luteal phase or placebo during one menstrual cycle.

OUTCOME MEASURES

The primary outcome measure was the sum of all 21 items in DRSP (Total DRSP score). Secondary outcomes were Negative mood score i.e. the ratings of the 4 key symptoms in PMDD (anger/irritability, depression, anxiety and lability) and impairment (impact on daily life).

RESULTS

26 healthy women completed the pharmacokinetic phase I study and the dosing in the following trial was adjusted according to the results. 106 of the 126 women completed the phase II study. Within this group, a significant treatment effect with UC1010 compared to placebo was obtained for the Total DRSP score (p=0.041) and borderline significance (p=0.051) for the sum of Negative mood score. Nineteen participants however showed symptoms during the follicular phase that might be signs of an underlying other conditions, and 27 participants had not received the medication as intended during the symptomatic phase. Hence, to secure that the significant result described above was not due to chance, a post hoc sub-group analysis was performed, including only women with pure PMDD who completed the trial as intended (n=60). In this group UC1010 reduced Total DRSP scores by 75% compared with 47% following placebo; the effect size 0.7 (p=0.006), and for sum of Negative mood score (p=0.003) and impairment (p=0.010) with the effect size 0.6. No severe adverse events were reported during the treatment and safety parameters (vital signs and blood chemistry) remained normal during the study.

CONCLUSIONS

This explorative study indicates promising results for UC1010 as a potential treatment for PMDD. The effect size was comparable to that of SSRIs and drospirenone containing oral contraceptives. UC1010 was well tolerated and deemed safe.

Anxiety level and correlates in methamphetamine-dependent patients during acute withdrawal

Anxiety is often a core element of withdrawal symptoms; however, risk factors associated with anxiety symptoms during the early stage of withdrawal in methamphetamine (METH) users are not well understood. Two hundred ten METH-dependent subjects who had been abstinent for 1 to 7 days were recruited. We used a set of self-administrative questionnaires eliciting information on sociodemographics, detailed drug use history and anxiety. Beck Anxiety Inventory (BAI) was used to measure anxiety symptoms. METH users had a mean BAI score of 6.9; 72 (34.3%) of the study sample had anxiety symptoms during acute METH withdrawal, including 42 (20.0%) with mild anxiety, 25 (11.9%) with moderate anxiety, and 5 (2.4%) with severe anxiety. In addition, gender (female), higher frequency of drug use, and history of polysubstance use were significantly correlated with anxiety symptoms during acute METH withdrawal. Anxiety symptoms appear to be common during the first week of METH abstinence, and several risk factors are identified.

Role of Prefrontal Serotonergic and Dopaminergic Systems in Encounter-Induced Hyperactivity in Methamphetamine-Sensitized Mice

BACKGROUND

Isolation-reared mice show social encounter-induced hyperactivity with activation of prefrontal serotonergic and dopaminergic systems, but it is not known whether this stress response is observed in other pathological conditions. Here we examined whether the social encounter stimulation induces abnormal behavior during withdrawal in chronic methamphetamine-treated mice.

METHODS

To induce methamphetamine-induced behavioral sensitization, male mice were injected with methamphetamine (1 mg/kg) once daily for 7 days.

RESULTS

The encounter with an intruder elicited hyperactivity 24 h after the last injection of methamphetamine in methamphetamine-sensitized mice. This response was observed even as long as 2 weeks after withdrawal of methamphetamine. The encounter increased c-Fos expression in the prefrontal cortex, dorsal raphe nucleus and ventral tegmental area in methamphetamine-sensitized mice, while it did not in control mice. Furthermore, the encounter increased extracellular serotonin (5-HT) and dopamine, but not noradrenaline, levels in the prefrontal cortex in methamphetamine-sensitized mice. Local injection of 5,7-dihydroxytryptamine and 6-hydroxydopamine into the prefrontal cortex attenuated encounter-induced hyperactivity in methamphetamine-sensitized mice and it markedly decreased prefrontal 5-HT and dopamine levels, respectively. Pharmacological analysis showed that the encounter-induced hyperactivity is mediated by dopamine D1 receptors and 5-HT2A receptors and attenuated by anxiolytics and antidepressants such as diazepam, osemozotan and selective 5-HT reuptake inhibitors. The effect of paroxetine was blocked by the 5-HT3 receptor antagonist azasetron.

CONCLUSIONS

The present study shows that psychological stress elicits hyperactivity with activation of prefrontal 5-HT and dopamine systems in methamphetamine-dependent mice and suggests that the abnormal behavior is associated with anxiety and depression.

Pharmacological treatments for methamphetamine addiction: current status and future directions

INTRODUCTION

Methamphetamine (MA) abuse remains a global health challenge despite intense research interest in the development of pharmacological treatments. This review provides a summary of clinical trials and human studies on the pharmacotherapy of methamphetamine use disorder (MUD). Areas covered: We summarize published clinical trials that tested candidate medications for MUD and also conducted PubMed and Google Scholar searches to identify recently completed clinical trials using the keywords 'methamphetamine' 'addiction' 'pharmacotherapy' and 'clinical trial.' To determine the status of ongoing clinical trials targeting MUD, we also searched the ClinicalTrials.gov online database. We conclude this review with a discussion of current research gaps and future directions. Expert commentary: Clinical trials examining the potential for pharmacotherapies of MUD have largely been negative. Future studies need to address several limitations to reduce the possibility of Type II errors: small sample sizes, high dropout rates or multiple comorbidities. Additionally, new treatment targets, such as MA-induced disruptions in cognition and in the neuroimmune system, merit trials with agents that selectively modulate these processes.

Fragment C Domain of Tetanus Toxin Mitigates Methamphetamine Neurotoxicity and Its Motor Consequences in Mice

BACKGROUND

The C-terminal domain of the heavy chain of tetanus toxin (Hc-TeTx) is a nontoxic peptide with demonstrated in vitro and in vivo neuroprotective effects against striatal dopaminergic damage induced by 1-methyl-4-phenylpyridinium and 6-hydoxydopamine, suggesting its possible therapeutic potential in Parkinson's disease. Methamphetamine, a widely abused psychostimulant, has selective dopaminergic neurotoxicity in rodents, monkeys, and humans. This study was undertaken to determine whether Hc-TeTx might also protect against methamphetamine-induced dopaminergic neurotoxicity and the consequent motor impairment.

METHODS

For this purpose, we treated mice with a toxic regimen of methamphetamine (4mg/kg, 3 consecutive i.p. injections, 3 hours apart) followed by 3 injections of 40 ug/kg of Hc-TeTx into grastrocnemius muscle at 1, 24, and 48 hours post methamphetamine treatment.

RESULTS

We found that Hc-TeTx significantly reduced the loss of dopaminergic markers tyrosine hydroxylase and dopamine transporter and the increases in silver staining (a well stablished degeneration marker) induced by methamphetamine in the striatum. Moreover, Hc-TeTx prevented the increase of neuronal nitric oxide synthase but did not affect microglia activation induced by methamphetamine. Stereological neuronal count in the substantia nigra indicated loss of tyrosine hydroxylase-positive neurons after methamphetamine that was partially prevented by Hc-TeTx. Importantly, impairment in motor behaviors post methamphetamine treatment were significantly reduced by Hc-TeTx.

CONCLUSIONS

Here we demonstrate that Hc-TeTx can provide significant protection against acute methamphetamine-induced neurotoxicity and motor impairment, suggesting its therapeutic potential in methamphetamine abusers.

Flumazenil decreases surface expression of α4β2δ GABAA receptors by increasing the rate of receptor internalization

Increases in expression of α4βδ GABAA receptors (GABARs), triggered by fluctuations in the neurosteroid THP (3α-OH-5α[β]-pregnan-20-one), are associated with changes in mood and cognition. We tested whether α4βδ trafficking and surface expression would be altered by in vitro exposure to flumazenil, a benzodiazepine ligand which reduces α4βδ expression in vivo. We first determined that flumazenil (100 nM-100 μM, IC50=∼1 μM) acted as a negative modulator, reducing GABA (10 μM)-gated current in the presence of 100 nM THP (to increase receptor efficacy), assessed with whole cell patch clamp recordings of recombinant α4β2δ expressed in HEK-293 cells. Surface expression of recombinant α4β2δ receptors was detected using a 3XFLAG reporter at the C-terminus of α4 (α4F) using confocal immunocytochemical techniques following 48 h exposure of cells to GABA (10 μM)+THP (100 nM). Flumazenil (10 μM) decreased surface expression of α4F by ∼60%, while increasing its intracellular accumulation, after 48 h. Reduced surface expression of α4β2δ after flumazenil treatment was confirmed by decreases in the current responses to 100 nM of the GABA agonist gaboxadol. Flumazenil-induced decreases in surface expression of α4β2δ were prevented by the dynamin blocker, dynasore, and by leupeptin, which blocks lysosomal enzymes, suggesting that flumazenil is acting to increase endocytosis and lysosomal degradation of the receptor. Flumazenil increased the rate of receptor removal from the cell surface by 2-fold, assessed using botulinum toxin B to block insertion of new receptors. These findings may suggest new therapeutic strategies for regulation of α4β2δ expression using flumazenil.

GABA withdrawal syndrome: GABAA receptor, synapse, neurobiological implications and analogies with other abstinences

The sudden interruption of the increase of the concentration of the gamma-aminobutyric acid (GABA), determines an increase in neuronal activity. GABA withdrawal (GW) is a heuristic analogy, with withdrawal symptoms developed by other GABA receptor-agonists such as alcohol, benzodiazepines, and neurosteroids. GW comprises a model of neuronal excitability validated by electroencephalogram (EEG) in which high-frequency and high-amplitude spike-wave complexes appear. In brain slices, GW was identified by increased firing synchronization of pyramidal neurons and by changes in the active properties of the neuronal membrane. GW induces pre- and postsynaptic changes: a decrease in GABA synthesis/release, and the decrease in the expression and composition of GABAA receptors associated with increased calcium entry into the cell. GW is an excellent bioassay for studying partial epilepsy, epilepsy refractory to drug treatment, and a model to reverse or prevent the generation of abstinences from different drugs.

Amphetamine-related drugs neurotoxicity in humans and in experimental animals: Main mechanisms

Amphetamine-related drugs, such as 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH), are popular recreational psychostimulants. Several preclinical studies have demonstrated that, besides having the potential for abuse, amphetamine-related drugs may also elicit neurotoxic and neuroinflammatory effects. The neurotoxic potentials of MDMA and METH to dopaminergic and serotonergic neurons have been clearly demonstrated in both rodents and non-human primates. This review summarizes the species-specific cellular and molecular mechanisms involved in MDMA and METH-mediated neurotoxic and neuroinflammatory effects, along with the most important behavioral changes elicited by these substances in experimental animals and humans. Emphasis is placed on the neuropsychological and neurological consequences associated with the neuronal damage. Moreover, we point out the gap in our knowledge and the need for developing appropriate therapeutic strategies to manage the neurological problems associated with amphetamine-related drug abuse.

On Gelsemium and Complementary and Alternative Medicine (CAM) in Anxiety and Experimental Neurology

A recent discussion expanded the debate about the experimental research on Gelsemium in anxiety. Herbal medicine is widely used in anxiety and mood disorders, often with contradictory evidence, although some authors are yet prompted to promote their full introduction in pharmacology as a promising therapy. Complementary and alternative medicine (CAM) in anxiety is particularly appreciated by individual healthcare, but deserves further investigation, as many critical issues have been recently raised. Comments about the ability of negligible doses of Gelsemium hydroalcoholic extracts to affect gene expression were recently reported.

Characterization of neurosteroid effects on hyperpolarizing current at α4β2δ GABAA receptors

RATIONALE

The neurosteroid 3α,5β-THP (3α-OH-5β-pregnan-20-one, pregnanolone) is a modulator of the GABAA receptor (GABAR), with α4β2δ GABARs the most sensitive. However, the effects of 3α,5β-THP at α4β2δ are polarity-dependent: 3α,5β-THP potentiates depolarizing current, as has been widely reported, but decreases hyperpolarizing current by accelerating desensitization.

OBJECTIVES

The present study further characterized 3α,5β-THP inhibition of hyperpolarizing current at this receptor and compared effects of other related steroids at α4β2δ GABARs.

METHODS

α4β2δ GABARs were expressed in HEK-293 cells, and agonist-gated current recorded with whole cell voltage-clamp techniques using a theta tube to rapidly apply agonist before and after application of neurosteroids.

RESULTS

The GABA-modulatory steroids (30 nM) 3α,5α-THP (3α-OH-5α-pregnan-20-one, allopregnanolone) and THDOC (3α,21-dihydroxy-5α-pregnan-20-one) inhibited hyperpolarizing GABA (10 μM)-gated current at α4β2δ GABARs similar to 3α,5β-THP, while the inactive 3β,5β-THP isomer had no effect. Greater inhibition was seen for current gated by the high efficacy agonist gaboxadol (THIP, 100 μM) than for GABA (0.1-1000 μM), consistent with an effect of 3α,5β-THP on desensitization. Inhibitory effects of the steroid were not seen under low [Cl(-)] conditions or in the presence of calphostin C (500 nM), an inhibitor of protein kinase C. Chimeras swapping the IL (intracellular loop) of α4 with α1, when expressed with β2 and δ, produced receptors (α[414]β2δ) which were not inhibited by 3α,5β-THP when GABA-gated current was hyperpolarizing, while α[141]β2δ exhibited steroid-induced polarity-dependent modulation.

CONCLUSIONS

These findings suggest that numerous neurosteroids exhibit polarity-dependent effects at α4β2δ GABARs, which are dependent upon protein kinase C and the IL of α4.

Role of GABA-active neurosteroids in the efficacy of metyrapone against cocaine addiction

Previous research has demonstrated a complicated role for stress and HPA axis activation in potentiating various cocaine-related behaviors in preclinical models of drug dependence. However, the investigation of several antiglucocorticoid therapies has yielded equivocal results in reducing cocaine-related behaviors, possibly because of varying mechanisms of actions. Specifically, research suggests that metyrapone (a corticosterone synthesis inhibitor) may reduce cocaine self-administration in rats via a nongenomic, extra-adrenal mechanism without altering plasma corticosterone. In the current experiments, male rats were trained to self-administer cocaine infusions and food pellets in a multiple, alternating schedule of reinforcement. Metyrapone pretreatment dose-dependently decreased cocaine self-administration as demonstrated previously. Pharmacological inhibition of neurosteroid production by finasteride had significant effects on cocaine self-administration, regardless of metyrapone pretreatment. However, metyrapone's effects on cocaine self-administration were significantly attenuated with bicuculline pretreatment, suggesting a role for GABA-active neurosteroids in cocaine-reinforced behaviors. In vitro binding data also confirmed that metyrapone does not selectively bind to GABA-related proteins. The results of these experiments support the hypothesis that metyrapone may increase neurosteroidogenesis to produce effects on cocaine-related behaviors.