Neurosteroids and GABA(A) Receptor Interactions: A Focus on Stress

The role of neurosteroids in posttraumatic stress disorder and alcohol use disorder: A review of 10 years of clinical literature and treatment implications

Rates of alcohol use disorder (AUD) are increasing in men and women and there are high rates of concurrent posttraumatic stress disorder (PTSD) and AUD. AUD and PTSD synergistically increase symptomatology and negatively affect treatment outcomes; however, there are very limited pharmacological treatments for PTSD/AUD. Neurosteroids have been implicated in the underlying neurobiological mechanisms of both PTSD and AUD and may be a target for treatment development. This review details the past ten years of research on pregnenolone, progesterone, allopregnanolone, pregnanolone, estradiol, testosterone and dehydroepiandrosterone/dehydroepiandrosterone-sulfate (DHEA/DHEA-S) in the context of PTSD and AUD, including examination of trauma/alcohol-related variables, such as stress-reactivity. Emerging evidence that exogenous pregnenolone, progesterone, and allopregnanolone may be promising, novel interventions is also discussed. Specific emphasis is placed on examining the application of sex as a biological variable in this body of literature, given that women are more susceptible to both PTSD diagnoses and stress-related alcohol consumption.

Functional role of translocator protein and its ligands in ocular diseases (Review)

The 18 kDa translocator protein (TSPO) is an essential outer mitochondrial membrane protein that is responsible for mitochondrial transport, maintenance of mitochondrial homeostasis and normal physiological cell function. The role of TSPO in the pathogenesis of ocular diseases is a growing area of interest. More notably, TSPO exerts positive effects in regulating various pathophysiological processes, such as the inflammatory response, oxidative stress, steroid synthesis and modulation of microglial function, in combination with a variety of specific ligands such as 1‑(2‑chlorophenyl‑N‑methylpropyl)‑3‑isoquinolinecarboxamide, 4'‑chlorodiazepam and XBD173. In the present review, the expression of TSPO in ocular tissues and the functional role of TSPO and its ligands in diverse ocular diseases was discussed.

Stress and gonadal steroid influences on alcohol drinking and withdrawal, with focus on animal models in females

Sexually dimorphic effects of alcohol, following binge drinking, chronic intoxication, and withdrawal, are documented at the level of the transcriptome and in behavioral and physiological responses. The purpose of the current review is to update and to expand upon contributions of the endocrine system to alcohol drinking and withdrawal in females, with a focus on animal models. Steroids important in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes, the reciprocal interactions between these axes, the effects of chronic alcohol use on steroid levels, and the genomic and rapid membrane-associated effects of steroids and neurosteroids in models of alcohol drinking and withdrawal are described. Importantly, comparison between males and females highlight some divergent effects of sex- and stress-steroids on alcohol drinking- and withdrawal-related behaviors, and the distinct differences in response emphasize the importance of considering sex in the development of novel pharmacotherapies for the treatment of alcohol use disorder.

Corticosteroids as Selective and Effective Modulators of Glycine Receptors

The mechanism of the negative impact of corticosteroids on the induction and progress of mental illness remains unclear. In this work, we studied the effects of corticosteroids on the activity of neuronal glycine receptors (GlyR) and GABA-A receptors (GABAAR) by measuring the chloride current induced by the application of GABA (2 or 5 μM) to isolated cerebellar Purkinje cells (IGABA) and by the application of glycine (100 μM) to pyramidal neurons of the rat hippocampus (IGly). It was found that corticosterone, 5α-dihydrodeoxycorticosterone, allotetrahydrocorticosterone, cortisol, and 17α,21-dihydroxypregnenolone were able to accelerate the desensitization of the IGly at physiological concentrations (IC50 values varying from 0.39 to 0.72 μM). Next, cortisone, 11-deoxycortisol, 11-deoxycorticosterone, 5β-dihydrodeoxycorticosterone, and tetrahydrocorticosterone accelerated the desensitization of IGly with IC50 values varying from 10.3 to 15.2 μM. Allotetrahydrocorticosterone and tetrahydrocorticosterone potentiated the IGABA albeit with high EC50 values (18-23 μM). The rest of the steroids had no effect on IGABA in the range of concentrations of 1-100 μM. Finally, our study has suggested a structural relationship of the 3β-hydroxyl group/3-oxo group with the selective modulatory activity on GlyRs in contrast to the 3α-hydroxyl group that is pivotal for GABAARs. In summary, our results suggest that increased GlyR desensitization by corticosteroids may contribute to brain dysfunction under chronic stress and identify corticosteroids for further development as selective modulators of GlyRs.

Effect of Neurosteroids on Basal and Stress-Induced Oxytocin Secretion in Luteal-Phase and Pregnant Sheep

Oxytocin (OT) is a neuropeptide synthesized in the hypothalamic nuclei that modulates both behavioral and reproductive functions, associated with the increased neurosteroid synthesis in the brain. Therefore, the present study tested the hypothesis that manipulation of central neurosteroid levels could affect oxytocin synthesis and release in non-pregnant and pregnant sheep under both basal and stressful conditions. In Experiment 1, luteal-phase sheep were subjected to a series of intracerebroventricular (icv.) infusions of allopregnanolone (AL, 4 × 15 μg/60 μL/30 min) for 3 days. In Experiment 2, pregnant animals (4th month) received a series of infusions of the neurosteroid synthesis blocker, finasteride (4 × 25 μg/60 μL/30 min), conducted for 3 days. In non-pregnant sheep AL alone was shown to differentially modulate OT synthesis in basal conditions, and strongly inhibit OT response to stress (p < 0.001). In contrast, in pregnant animals, basal and stress-induced OT secretion was significantly (p < 0.001) increased during finasteride infusion compared to controls. In conclusion, we showed that neurosteroids were involved in the control of OT secretion in sheep, particularly under stress and pregnancy conditions and are part of an adaptive mechanism which is responsible for protecting and maintaining pregnancy in harmful situations.

Ablation of Gabra5 Influences Corticosterone Levels and Anxiety-like Behavior in Mice

Stress responses are activated by the hypothalamic-pituitary-adrenal axis (HPA axis), culminating in the release of glucocorticoids. During prolonged periods of secretion of glucocorticoids or inappropriate behavioral responses to a stressor, pathologic conditions may occur. Increased glucocorticoid concentration is linked to generalized anxiety, and there are knowledge gaps regarding its regulation. It is known that the HPA axis is under GABAergic control, but the contribution of the individual subunits of the GABA receptor is largely unknown. In this study, we investigated the relationship between the α5 subunit and corticosterone levels in a new mouse model deficient for Gabra5, which is known to be linked to anxiety disorders in humans and phenologs observed in mice. We observed decreased rearing behavior, suggesting lower anxiety in the Gabra5^-/- animals; however, such a phenotype was absent in the open field and elevated plus maze tests. In addition to decreased rearing behavior, we also found decreased levels of fecal corticosterone metabolites in Gabra5^-/- mice indicating a lowered stress response. Moreover, based on the electrophysiological recordings where we observed a hyperpolarized state of hippocampal neurons, we hypothesize that the constitutive ablation of the Gabra5 gene leads to functional compensation with other channels or GABA receptor subunits in this model.

Effects of acute intravenous lipopolysaccharide administration on the plasma lipidome and metabolome in lactating Holstein cows experiencing hyperlipidemia

INTRODUCTION

The effects of lipopolysaccharides (i.e., endotoxin; LPS) on metabolism are poorly defined in lactating dairy cattle experiencing hyperlipidemia.

OBJECTIVES

Our objective was to explore the effects of acute intravenous LPS administration on metabolism in late-lactation Holstein cows experiencing hyperlipidemia induced by intravenous triglyceride infusion and feed restriction.

METHODS

Ten non-pregnant lactating Holstein cows (273 ± 35 d in milk) were administered a single bolus of saline (3 mL of saline; n [Formula: see text] 5) or LPS (0.375 [Formula: see text]g of LPS/kg of body weight; n [Formula: see text] 5). Simultaneously, cows were intravenously infused a triglyceride emulsion and feed restricted for 16 h to induce hyperlipidemia in an attempt to model the periparturient period. Blood was sampled at routine intervals. Changes in circulating total fatty acid concentrations and inflammatory parameters were measured. Plasma samples were analyzed using untargeted lipidomics and metabolomics.

RESULTS

Endotoxin increased circulating serum amyloid A, LPS-binding protein, and cortisol concentrations. Endotoxin administration decreased plasma lysophosphatidylcholine (LPC) concentrations and increased select plasma ceramide concentrations. These outcomes suggest modulation of the immune response and insulin action. Lipopolysaccharide decreased the ratio of phosphatidylcholine to phosphatidylethanomanine, which potentially indicate a decrease in the hepatic activation of phosphatidylethanolamine N-methyltransferase and triglyceride export. Endotoxin administration also increased plasma concentrations of pyruvic and lactic acids, and decreased plasma citric acid concentrations, which implicate the upregulation of glycolysis and downregulation of the citric acid cycle (i.e., the Warburg effect), potentially in leukocytes.

CONCLUSION

Acute intravenous LPS administration decreased circulating LPC concentrations, modified ceramide and glycerophospholipid concentrations, and influenced intermediary metabolism in dairy cows experiencing hyperlipidemia.

Neurosteroids and early-life programming: An updated perspective

Early-life stress can lead to detrimental offspring outcomes, including an increased risk for mood disorders and hypothalamic-pituitary-adrenal axis dysregulation. Neurosteroids bind to ligand-gated neurotransmitter receptors, rapidly modulating neuronal excitability and promoting termination of stress responses. Reduced neurosteroidogenesis underlies some of the aberrant neuroendocrine and behavioural phenotypes observed in adult prenatally stressed rodents. During development, disruptions in neurosteroid generation and action also lead to long-term programming effects on the off-spring's brain and behaviour. Here, we review recent advances in the field, focusing on the interaction between neurosteroids and early-life stress outcomes in adulthood and in the perinatal period. We also discuss the direction of future research, with emphasis on quantification methods, sex differences, and neurosteroids as targets for therapeutic intervention.

Cortical GABA levels are reduced in young adult binge drinkers: Association with recent alcohol consumption and sex

Binge drinking refers to a pattern of alcohol intake that raises blood alcohol concentration to or above legal intoxication levels. It is common among young adults and is associated with health risks that scale up with alcohol intake. Acute intoxication depresses neural activity via complex signaling mechanisms by enhancing inhibition mediated by gamma-amino butyric acid (GABA), and by decreasing excitatory glutamatergic effects. Evidence primarily rooted in animal research indicates that the brain compensates for the acute depressant effects under the conditions of habitual heavy use. These neuroadaptive changes are reflected in neural hyperexcitability via downregulated inhibitory signaling, which becomes apparent as withdrawal symptoms. However, human evidence on the compensatory reduction in GABA signaling is scant. The neurochemical aspect of this mechanistic model was evaluated in the present study with proton magnetic resonance spectroscopy (¹H-MRS) which is sensitive to GABA plus macromolecule signal (GABA + ). Furthermore, we examined sex differences in GABA + levels as a function of a recent history of binge drinking, given interactions between endogenous neurosteroids, GABA signaling, and alcohol. The study recruited young adult women and men (22.2 ± 2.8 years of age) who were classified as binge drinkers (BDs, N = 52) if they reported ≥ 5 binge episodes in the previous six months. Light drinkers (LDs, N = 49) reported drinking regularly, but not exceeding ≤ 2 binge episodes in the past six months. GABA-edited ¹H-MR spectra were acquired from the occipital cortex at 3 T with the MEGA-PRESS sequence. GABA + signal was analyzed relative to water and total creatine (Cr) levels as a function of binge drinking history and sex. Controlling for within-voxel tissue composition, both GABA + indices showed decreased GABA + levels in BDs relative to LDs. The reduced GABA + concentration was associated with occasional high-intensity drinking in the BD group. This evidence is consistent with compensatory GABA downregulation that accompanies alcohol misuse, tipping the excitation/inhibition balance towards hyperexcitability. Analysis of the time course of GABA + neuroplasticity indicated that GABA + was lowest when measured one day after the last drinking occasion in BDs. While the BD vs LD differences were primarily driven by LD women, there was no interaction between Sex and a history of binge drinking. GABA + was higher in LD women compared to LD men. Aligned with the allostasis model, the mechanistic compensatory GABA downregulation observed in young emerging adults engaging in occasional binge drinking complements direct neural measures of hyperexcitability in BDs. Notably, these results suggest that neuroadaptation to alcohol is detectable at the levels of consumption that are within a normative range, and may contribute to adverse health outcomes.

The impact of different dark chocolate dietary patterns on synaptic potency and plasticity in the hippocampal CA1 area of the rats under chronic isolation stress

INTRODUCTION

Although, stress causes brain dysfunction, consumption of dark chocolate (DC) has positive effects on brain functions. The current study investigated the impact of different DC dietary patterns on synaptic potency and plasticity in the hippocampal CA1 area, as well as food intake and body weight in rats under chronic isolation stress.

METHODS

Thirty-five rats were allocated into five groups of control, stress, and stress accompanied by three DC dietary patterns (stress-compulsory, -optional, and -restricted DC). The stressed rats on a compulsory diet only received DC and the ones on an optional diet received unlimited chow and/or DC. Also, the stressed rats on a restricted diet each received chow freely and only 4 g DC daily. Subsequently, the slope and amplitude of field excitatory postsynaptic potentials (fEPSPs) were assessed based on the Input-Output (I/O) curves and after the longterm potentiation (LTP). Moreover, food intake and body weight were measured for all groups.

RESULTS

The fEPSP slope and amplitude in the I/O curves and after LTP decreased significantly in the stress group compared to the control group. Although the slope and amplitude both enhanced non-significantly in the optional DC diet, these parameters changed significantly in both compulsory and restricted DC dietary patterns compared to the stress group. Also, food intake and body weight decreased significantly in all DC groups.

CONCLUSION

The compulsory and restricted DC dietary patterns reversed the harmful effects of chronic isolation stress on the hippocampal synaptic potency, plasticity, learning, and memory. All DC diets, especially compulsory and restricted ones, reduced food intake and body weight.

GABAA(δ) receptor hypofunction in the amygdala-hippocampal circuit underlies stress-induced anxiety

Dysregulated GABAergic inhibition in the amygdala has long been implicated in stress-related neuropsychiatric disorders. However, the molecular and circuit mechanisms underlying the dysregulation remain elusive. Here, by using a mouse model of chronic social defeat stress (CSDS), we observed that the dysregulation varied drastically across individual projection neurons (PNs) in the basolateral amygdala (BLA), one of the kernel amygdala subregions critical for stress coping. While persistently reducing the extrasynaptic GABA_A receptor (GABA_AR)-mediated tonic current in the BLA PNs projecting to the ventral hippocampus (BLA → vHPC PNs), CSDS increased the current in those projecting to the anterodorsal bed nucleus of stria terminalis (BLA → adBNST PNs), suggesting projection-based dysregulation of tonic inhibition in BLA PNs by CSDS. Transcriptional and electrophysiological analysis revealed that the opposite CSDS influences were mediated by loss- and gain-of-function of δ-containing GABA_ARs (GABA_A(δ)Rs) in BLA → vHPC and BLA → adBNST PNs, respectively. Importantly, it was the lost inhibition in the former population but not the augmentation in the latter population that correlated with the increased anxiety-like behavior in CSDS mice. Virally mediated maintenance of GABA_A(δ)R currents in BLA → vHPC PNs occluded CSDS-induced anxiety-like behavior. These findings clarify the molecular substrate for the dysregulated GABAergic inhibition in amygdala circuits for stress-associated psychopathology.

Comparing the effects of crocin at different doses on excitability and long-term potentiation in the CA1 area, as well as the electroencephalogram responses of rats under chronic stress

Stress adversely affects the cellular and electrophysiological mechanisms of memory; however, crocin has beneficial effects on brain functions. Nonetheless, the electrophysiological effects of using this active saffron component at different doses are not yet studied in rats under chronic restraint stress. Therefore, this study compared the impact of crocin at different doses on the excitability and long-term potentiation (LTP) in the CA1 area of rats, as well as their electroencephalogram (EEG) responses, hippocampal and frontal cortical glucose levels under chronic restraint stress (an emotional stress model). Forty rats were allocated into five groups of control, sham, restraint stress (6 h/day/21 days), and two stress groups receiving intraperitoneal injections of crocin (30, 60 mg/kg/day). Besides measuring the slope and amplitude of field excitatory postsynaptic potentials (fEPSPs) in the input-output and LTP curves, the EEG waves and hippocampal and frontal cortical glucose levels were assessed in all groups. Chronic restraint stress significantly decreased the fEPSP slope and amplitude in the input-output curves and after LTP induction. Both doses of crocin (60 and particularly 30 mg/kg) significantly improved fEPSP slope and amplitude in the stressed groups. Also, stress and crocin only at a dose of 30 mg/kg altered the EEG waves. Hippocampal and frontal cortical glucose levels displayed no significant differences in the experimental groups. Crocin at doses of 60 mg/kg/day and particularly 30 mg/kg/day reversed the harmful effects of chronic restraint stress on LTP as a cellular memory-related mechanism. However, only the lower dose of crocin affected the electrical brain activity in EEG.

Cerebellum-Specific Deletion of the GABAA Receptor δ Subunit Leads to Sex-Specific Disruption of Behavior

Granule cells (GCs) of the cerebellar input layer express high-affinity δ GABA_A subunit-containing GABA_A receptors (δGABA_ARs) that respond to ambient GABA levels and context-dependent neuromodulators like steroids. We find that GC-specific deletion of δGABA_A (cerebellar [cb] δ knockout [KO]) decreases tonic inhibition, makes GCs hyperexcitable, and in turn, leads to differential activation of cb output regions as well as many cortical and subcortical brain areas involved in cognition, anxiety-like behaviors, and the stress response. Cb δ KO mice display deficits in many behaviors, but motor function is normal. Strikingly, δGABA_A deletion alters maternal behavior as well as spontaneous, stress-related, and social behaviors specifically in females. Our findings establish that δGABA_ARs enable the cerebellum to control diverse behaviors not previously associated with the cerebellum in a sex-dependent manner. These insights may contribute to a better understanding of the mechanisms that underlie behavioral abnormalities in psychiatric and neurodevelopmental disorders that display a gender bias.

Rudolph et al. show that deletion of the neuromodulator and hormone-sensitive δGABA_A receptor subunit from cerebellar granule cells results in anxiety-like behaviors and female-specific deficits in social behavior and maternal care. δGABA_A deletion is associated with hyperexcitability of the cerebellar input layer and altered activation of many stress-related brain regions.

Does Stress Trigger Seizures? Evidence from Experimental Models

This chapter describes the experimental evidence of stress modulation of epileptic seizures and the potential role of corticosteroids and neurosteroids in regulating stress-linked seizure vulnerability. Epilepsy is a chronic neurological disorder that is characterized by repeated seizures. There are many potential causes for epilepsy, including genetic predispositions, infections, brain injury, and neurotoxicity. Stress is a known precipitating factor for seizures in individuals suffering from epilepsy. Severe acute stress and persistent exposure to stress may increase susceptibility to seizures, thereby resulting in a higher frequency of seizures. This occurs through the stress-mediated release of cortisol, which has both excitatory and proconvulsant properties. Stress also causes the release of endogenous neurosteroids from central and adrenal sources. Neurosteroids such as allopregnanolone and THDOC, which are allosteric modulators of GABA-A receptors, are powerful anticonvulsants and neuroprotectants. Acute stress increases the release of neurosteroids, while chronic stress is associated with severe neurosteroid depletion and reduced inhibition in the brain. This diminished inhibition occurs largely as a result of neurosteroid deficiencies. Thus, exogenous administration of neurosteroids (neurosteroid replacement therapy) may offer neuroprotection in epilepsy. Synthetic neurosteroid could offer a rational approach to control neurosteroid-sensitive, stress-related epileptic seizures.

Effects of prenatal stress on neuroactive steroid responses to acute stress in adult male and female rats

Acute swim stress results in the robust production of several neuroactive steroids, which act as mediators of the stress response. These steroids include glucocorticoids, and positive GABAA receptor modulatory steroids such as allopregnanolone and tetrahydrocorticosterone (THDOC), which potentiate inhibitory GABA signalling, thereby playing a role in the negative control of the hypothalamic-pituitary-adrenal (HPA) axis. Prenatally stressed (PNS) offspring exhibit increased vulnerability to stress-related disorders and frequently display exaggerated HPA axis responses to stressors during adulthood, which may be a result of reduced neuroactive steroid production and consequently inhibitory signalling. Here, we investigated whether exposure of rats to prenatal social stress from gestational day 16-20 altered neuroactive steroid production under non-stress conditions and in response to an acute stressor (swim stress) in adulthood. Using liquid chromatography-mass spectrometry, nine neuroactive steroids were quantified (corticosterone, deoxycorticosterone [DOC], dihydrodeoxycorticosterone, THDOC, progesterone, dihydroprogesterone, allopregnanolone, pregnenolone, testosterone) in plasma and in five brain regions (frontal cortex, hypothalamus, amygdala, hippocampus, brainstem) of male and female control and PNS rats. There was no difference in the neuroactive steroid profile between control and PNS rats under basal conditions. The increase in circulating corticosterone induced by acute swim stress was similar in control and PNS offspring. However, greater stress-induced corticosterone and DOC concentrations were observed in the brainstem of male PNS offspring, whereas DOC concentrations were lower in the hippocampus of PNS females compared to controls, following acute stress. Although PNS rats did not show deficits in allopregnanolone responses to acute stress, there were modest deficits in the production of THDOC in the brainstem, amygdala, and frontal cortex of PNS males and in the frontal cortex of PNS females. The data suggest that neuroactive steroid modulation of GABAergic signalling following stress exposure may be affected in a sex- and region-specific manner in PNS offspring.

Stress-related memories disrupt sociability and associated patterning of hippocampal activity: a role of hilar oxytocin receptor-positive interneurons

In susceptible individuals, memories of stressful experiences can give rise to debilitating socio-affective symptoms. This occurs even when the ability to retrieve such memories is limited, as seen in patients suffering from traumatic amnesia. We therefore hypothesized that the encoding, rather than retrieval, mechanisms of stress-related memories underlie their impact on social and emotional behavior. To test this hypothesis, we used combinations of stress-enhanced and state-dependent fear conditioning, which engage different encoding mechanisms for the formation of stress-related memories. We found that the encoding of stress-enhanced state-dependent memories robustly and sex specifically impairs sociability in male mice and disrupts the asymmetry of dentate gyrus (DG)/CA3 activity accompanying social interactions. These deficits were restored by chemogenetic inactivation of oxytocin receptor-positive interneurons localized in the hilus (Oxtr-HI), and by inactivation of dorsohippocampal efferents to the caudal lateral septum. Together, our data suggest that disrupted patterning of dorsohippocampal DG/CA3 activity underlies stress-induced sociability deficits, and that Oxtr-HI can be a cellular target for improving these deficits.

Good, better, best: clinical scenarios for the use of L-methylfolate in patients with MDD

Depression is among the most prevalent mental disorders worldwide, and a substantial proportion of patients do not respond adequately to standard antidepressants. Our understanding of the pathophysiology of depression is no longer limited to the chemical imbalance of neurotransmitters, but also involves the interplay of proinflammatory modulators in the central nervous system, as well as folate metabolism. Additional factors such as stress and metabolic disorders also may contribute. Multiple inflammatory, metabolic, and genetic markers have been identified and may provide critical information to help clinicians individualize treatments for patients to achieve optimal outcomes. Recent advancements in research have clarified underlying causes of depression and have led to possible new avenues for adjunctive treatment. Among these is L-methylfolate, a medical food that is thought to enhance synthesis of monoamines (serotonin, norepinephrine, and dopamine), suppress inflammation, and promote neural health. Clinical studies that assessed supplemental use of L-methylfolate in patients with usual care-resistant depression found that it resulted in improved outcomes. Patients with selective serotonin reuptake inhibitor-resistant depression, and particularly subgroups with biomarkers of inflammation or metabolic disorders or folate metabolism-related genetic polymorphisms (or ≥2 of these factors), had the best responses. Considering this, the goals of this review are to 1) highlight recent advances in the pathophysiology of major depressive disorder as it pertains to folate and associated biomarkers and 2) establish the profiles of patients with depression who could benefit most from supplemental use of L-methylfolate.

[Ketamine, psilocybin, and rapid acting antidepressant: new promise for psychiatry?]

The hypothesis of monoaminergic deficiency has long dominated the conceptual framework for the development of new antidepressant strategies, but the limits of conventional antidepressant treatments targeting monoaminergic signaling have motivated the search for new antidepressant pathways. The success of ketamine in the management of depressive disorders has provoked a renewed interest in hallucinogenic substances such as psilocybin targeting the serotonergic signaling 5HT^2A and neurosteroid allosteric modulator of γ-aminobutyric acid (GABAA) receptors such as brexanolone. Unlike conventional treatments, these modulators of glutamatergic, serotonergic and GABAergic systems exert a rapid antidepressant effect ranging from 24hours to a week. Apart from their clinical interest and the fantasized search for a "miracle" molecule that jointly meets the expectations of patients and clinicians, these new targets could lead to the identification of potential new biomarkers for the development of rapid-acting antidepressants and redefine therapeutic strategies in mood disorders.

Effects of allopregnanolone on central reproductive functions in sheep under natural and stressful conditions

Reproductive functions may be affected by internal and external factors that are integrated in the central nervous system (CNS). Stressful stimuli induce the neuroendocrine response of the hypothalamic-pituitary-adrenal axis, as well as the synthesis of the neurosteroid allopregnanolone (AL) in the brain. This study tested the hypothesis that centrally administered AL could affect the expression of certain genes involved in reproductive functions at the hypothalamus and pituitary levels, as well as pulsatile gonadotropin secretion in sheep under both natural and stressful conditions. Luteal-phase sheep (n = 24) were subjected to a three-day (day 12-14 of the estrous cycle) series of control or AL (4 × 15 μg/60 μL/30 min, at 30 min intervals) infusions into the third ventricle. Acute stressful stimuli (isolation from other sheep and partial movement restriction) were used in the third day of infusion. Stressful stimuli reduced kisspeptin-1 mRNA levels in both the mediobasal hypothalamus (MBH) and the preoptic area (POA), while pro-dynorphin (PDYN) mRNA level only in the MBH. AL alone decreased the abundances of these transcripts in both structures. Stress increased the expression of gonadotropin-releasing hormone (GnRH) mRNA in the MBH and POA, luteinizing hormone (LH) β subunit (LHβ) mRNA in the anterior pituitary (AP) and pulsatile LH secretion. In contrast, mRNA level of follicle stimulating hormone (FSH) β subunit (FSHβ) was decreased in the AP, with no effect of stress on pulsatile FSH secretion. In stressed sheep, AL counteracted the increase in GnRH mRNA expression only in the POA, but it decreased the level of this transcript in both hypothalamic tissues when infused alone. AL prevented the stress-induced increase in LHβ mRNA expression in the AP and pulsatile LH secretion, as well as inhibited almost all aspects of FSH secretion when administered alone. The suppressive effect of AL on GnRH receptor mRNA expression was also observed in both MBH and AP. We concluded that acute stress and AL exerted multidirectional effects on hypothalamic centers that regulate reproductive functions and secretory activity of AP gonadotrophs in sheep. However, we indicated the dominant inhibitory effect of AL under natural and stressful conditions.

The Endocrine System and Alcohol Drinking in Females

Sexually dimorphic effects of alcohol exposure throughout life have been documented in clinical and preclinical studies. In the past, rates of alcohol use disorder (AUD) were higher in men than in women, but over the past 10 years, the difference between sexes in prevalence of AUD and binge drinking has narrowed. Recent evidence adds to historical data regarding the influence of sex steroids on alcohol drinking and the interaction with stress-related steroids. This review considers the contribution of the endocrine system to alcohol drinking in females, with a focus on the hypothalamic pituitary gonadal axis and the hypothalamic pituitary adrenal axis and their reciprocal interactions. Emphasis is given to preclinical studies that examined genomic and rapid membrane effects of estrogen, progesterone, glucocorticoids, and GABAergic neurosteroids for their effects on alcohol drinking and models of relapse. Pertinent comparisons to data in males highlight divergent effects of sex and stress steroids on alcohol drinking and emphasize the importance of considering sex in the development of novel pharmacotherapeutic targets for the treatment of AUD. For instance, pharmacological strategies targeting the corticotropin releasing factor and glucocorticoid receptor systems may be differentially effective in males and females, whereas strategies to enhance GABAergic neurosteroids may represent a biomarker of treatment efficacy in both sexes.

Chronic Stress Oppositely Regulates Tonic Inhibition in Thy1-Expressing and Non-expressing Neurons in Amygdala

Chronic or prolonged exposure to stress ranks among the most important socioenvironmental factors contributing to the development of neuropsychiatric diseases, a process generally associated with loss of inhibitory tone in amygdala. Recent studies have identified distinct neuronal circuits within the basolateral amygdala (BLA) engaged in different emotional processes. However, the potential circuit involved in stress-induced dysregulation of inhibitory tones in BLA remains elusive. Here, a transgenic mouse model expressing yellow fluorescent protein under control of the Thy1 promoter was used to differentiate subpopulations of projection neurons (PNs) within the BLA. We observed that the tonic inhibition in amygdala neurons expressing and not expressing Thy1 (Thy1+/-) was oppositely regulated by chronic social defeat stress (CSDS). In unstressed control mice, the tonic inhibitory currents were significantly stronger in Thy1- PNs than their Thy1+ counterparts. CSDS markedly reduced the currents in Thy1- projection neurons (PNs), but increased that in Thy1+ ones. By contrast, CSDS failed to affect both the phasic A-type γ-aminobutyric acid receptor (GABA_AR) currents and GABA_BR currents in these two PN populations. Moreover, chronic corticosterone administration was sufficient to mimic the effect of CSDS on the tonic inhibition of Thy1+ and Thy1- PNs. As a consequence, the suppression of tonic GABA_AR currents on the excitability of Thy1- PNs was weakened by CSDS, but enhanced in Thy1+ PNs. The differential regulation of chronic stress on the tonic inhibition in Thy1+ and Thy1- neurons may orchestrate cell-specific adaptation of amygdala neurons to chronic stress.

Central Actions of 3α,5α-THP Involving NMDA and GABAA Receptors Regulate Affective and Sexual Behavior of Female Rats

The neurosteroid, 5α-pregnan-3α-ol-20-one (known as “allopregnanolone” or 3α,5α-THP), is produced in the midbrain ventral tegmental area (VTA), independent of peripheral sources of progestogens, where it has potential actions at N-methyl-D-aspartate (NMDA) and GABA_A receptors to facilitate rodent sexual behavior. Progestogens can also have anti-anxiety effects, but whether these involve actions of centrally-derived 3α,5α-THP or these receptors to support reproductively-relevant behavior is not well understood. We investigated the extent to which 3α,5α-THP’s actions via NMDA and/or GABA_A receptors in the midbrain VTA influence reproductive behaviors. Estradiol-primed, ovariectomized/adrenalectomized (OVX/ADX) rats received midbrain VTA infusions of vehicle, an NMDA receptor blocker (MK-801; 200 ng), or a GABA_A receptor blocker (bicuculline; 100 ng) followed by a second infusion of vehicle or 3α,5α-THP (100 ng). Reproductively-relevant behaviors were assessed: sexual (paced mating), anxiety-like (elevated plus maze), and social (partner preference, social interaction) behavior. Compared to vehicle, intra-VTA infusions of MK-801 exerted anxiolytic-like effects on elevated plus maze behavior and enhanced lordosis. Unlike prior observations in gonadally-intact rats, intra-VTA bicuculline had no effect on the behavior of OVX/ADX rats (likely due to a floor effect). Subsequent infusions of 3α,5α-THP reversed effects on lordosis and infusions of bicuculline inhibited 3α,5α-THP-facilitated lordosis. Thus, NMDA and GABA_A receptors may act as mediators for reproductive behavioral effects of 3α,5α-THP in the midbrain VTA.

Neurobehavioural complications of sleep deprivation: Shedding light on the emerging role of neuroactive steroids

Sleep deprivation (SD) is associated with a broad spectrum of cognitive and behavioural complications, including emotional lability and enhanced stress reactivity, as well as deficits in executive functions, decision making and impulse control. These impairments, which have profound negative consequences on the health and productivity of many individuals, reflect alterations of the prefrontal cortex (PFC) and its connectivity with subcortical regions. However, the molecular underpinnings of these alterations remain elusive. Our group and others have begun examining how the neurobehavioural outcomes of SD may be influenced by neuroactive steroids, a family of molecules deeply implicated in sleep regulation and the stress response. These studies have revealed that, similar to other stressors, acute SD leads to increased synthesis of the neurosteroid allopregnanolone in the PFC. Whereas this up-regulation is likely aimed at counterbalancing the detrimental impact of oxidative stress induced by SD, the increase in prefrontal allopregnanolone levels contributes to deficits in sensorimotor gating and impulse control, signalling a functional impairment of PFC. This scenario suggests that the synthesis of neuroactive steroids during acute SD may be enacted as a neuroprotective response in the PFC; however, such compensation may in turn set off neurobehavioural complications by interfering with the corticolimbic connections responsible for executive functions and emotional regulation.

Neurosteroids as novel antidepressants and anxiolytics: GABA-A receptors and beyond

The recent FDA approval of the neurosteroid, brexanolone (allopregnanolone), as a treatment for women with postpartum depression, and successful trials of a related neuroactive steroid, SGE-217, for men and women with major depressive disorder offer the hope of a new era in treating mood and anxiety disorders based on the potential of neurosteroids as modulators of brain function. This review considers potential mechanisms contributing to antidepressant and anxiolytic effects of allopregnanolone and other GABAergic neurosteroids focusing on their actions as positive allosteric modulators of GABAA receptors. We also consider their roles as endogenous "stress" modulators and possible additional mechanisms contributing to their therapeutic effects. We argue that further understanding of the molecular, cellular, network and psychiatric effects of neurosteroids offers the hope of further advances in the treatment of mood and anxiety disorders.

Stress and drug abuse-related disorders: The promising therapeutic value of neurosteroids focus on pregnenolone-progesterone-allopregnanolone pathway

The pregnenolone-progesterone-allopregnanolone pathway is receiving increasing attention in research on the role of neurosteroids in pathophysiology, particularly in stress-related and drug use disorders. These disorders involve an allostatic change that may result from deficiencies in allostasis or adaptive responses, and may be downregulated by adjustments in neurotransmission by neurosteroids. The following is an overview of findings that assess how pregnenolone and/or allopregnanolone concentrations are altered in animal models of stress and after consumption of alcohol or cannabis-type drugs, as well as in patients with depression, anxiety, post-traumatic stress disorder or psychosis and/or in those diagnosed with alcohol or cannabis use disorders. Preclinical and clinical evidence shows that pregnenolone and allopregnanolone, operating according to a different or common pharmacological profile involving GABAergic and/or endocannabinoid system, may be relevant biomarkers of psychiatric disorders for therapeutic purposes. Hence, ongoing clinical trials implicate synthetic analogs of pregnenolone or allopregnanolone, and also modulators of neurosteroidogenesis.

microRNA and mRNA profiles in the amygdala are associated with stress-induced depression and resilience in juvenile mice

OBJECTIVES

Major depressive disorder characterized as recurrent negative mood is one of the prevalent psychiatric diseases. Chronic stress plus lack of reward may induce long-term imbalance between reward and penalty circuits in the brain, leading to persistent negative mood. Numerous individuals demonstrate resilience to chronic mild stress. Molecular mechanisms for major depression and resilience in the brain remain unclear.

METHODS

After juvenile mice were treated by the chronic unpredictable mild stress (CUMS) for 4 weeks, they were screened by sucrose preference, Y-maze and forced swimming tests to examine whether their behaviors were depression-like or not. mRNA and miRNA profiles were quantified by high-throughput sequencing in amygdala tissues harvested from control, CUMS-susceptible, and CUMS-resilience mice.

RESULTS

1.5-fold ratio in reads per kilo-base per million reads was set to be the threshold to judge the involvement of mRNAs and miRNAs in the CUMS, major depression, or resilience. In the amygdala from CUMS-susceptible mice, the expression of genes relevant to GABAergic, cholinergic, glutamatergic, dopaminergic, and serotonergic synapses was changed, as well as the expression of genes that encoded signal pathways of PI3K-Akt, calcium, cAMP, MAPK, and drug addiction was imbalanced. The expression of these genes in the amygdala form CUMS-resilience mice was less changed.

CONCLUSIONS

The downregulation of genes relevant to synaptic functions and the imbalance of intra-signaling pathway in the amygdala are associated with major depression. Consistent results through sequencing mRNA and miRNA and using different methods validate our finding and conclusion.

Dynamic Adaptation in Neurosteroid Networks in Response to Alcohol

The term neurosteroid refers to rapid membrane actions of steroid hormones and their derivatives that can modulate physiological functions and behavior via their interactions with ligand-gated ion channels. This chapter will highlight recent advances pertaining to the modulatory effects of a select group of neurosteroids that are primarily potent positive allosteric modulators of γ-aminobutyric acid_A receptors (GABA_ARs). Nanomolar concentrations of neurosteroids, which occur in vivo, potentiate phasic and tonic forms of GABA_AR-mediated inhibition, indicating that both synaptic and extrasynaptic GABA_ARs possess sensitivity to neurosteroids and contribute to the overall ability of neurosteroids to modulate central nervous system excitability. Common effects of alcohol and neurosteroids at GABA_ARs have stimulated research on the ability of neurosteroids to modulate alcohol's acute and chronic effects. Background on neurosteroid pharmacology and biosynthetic enzymes will be provided as it relates to experimental findings. Data will be summarized on alcohol and neurosteroid interactions across neuroanatomical regions and models of intoxication, consumption, dependence, and withdrawal. Evidence supports independent regulation of neurosteroid synthesis between periphery and brain as well as across brain regions following acute alcohol administration and during withdrawal. Local mechanisms for fine-tuning neuronal excitability via manipulation of neurosteroid synthesis exert predicted behavioral and electrophysiological responses on GABA_AR-mediated inhibition. Collectively, targeting neurosteroidogenesis may be a beneficial treatment strategy for alcohol use disorders.

Effects of Different Stressors Are Modulated by Different Neurobiological Systems: The Role of GABA-A Versus CB1 Receptor Gene Variants in Anxiety and Depression

Environmental stress and its interaction with genetic variation are key contributors in the development of depression and anxiety, yet there is a failure to identify replicable genetic variants and gene-interaction effects in the background of these psychiatric symptoms. Recently it has been reported that 5-HTTLPR and NOSI interact with financial but not other types of recent stressors in the development of depression. In the present study we investigated the interaction of GABRA6 rs3219151 and CNR1 rs7766029 in interaction with different types of recent life events on the presence of depression and anxiety in a large general population sample. 2191 participants completed the List of Threatening Experiences questionnaire which covers four categories of stressful life events (financial problems, illness/personal problems, intimate relationships, and social network) experienced over the previous year and the Brief Symptom Inventory for depression and anxiety symptoms. Participants were genotyped for rs3219151 and rs7766029. Data were analyzed with linear regression models with age and gender as covariates. Results indicated that CNR1 rs7766029 interacted significantly with financial but not other types of life events both in case of depression and anxiety symptoms. In contrast, GABRA6 rs3219151 showed a significant interaction with social network related life events in case of anxiety and with illness/personal problem-related life events in case of depression. Our results suggest that the psychological impact of different types of recent stress may be differentially modulated by distinct molecular genetic pathways. Furthermore, in case of certain genetic variants, the occurring psychiatric symptom may depend on the type of stress experienced.

Giving a good start to a new life via maternal brain allostatic adaptations in pregnancy

Successful pregnancy requires adjustments to multiple maternal homeostatic mechanisms, governed by the maternal brain to support and enable survival of the growing fetus and placenta. Such adjustments fit the concept of allostasis (stability through change) and have a cost: allostatic load. Allostasis is driven by ovarian, anterior pituitary, placental and feto-placental hormones acting on the maternal brain to promote adaptations that support the pregnancy and protect the fetus. Many women carry an existing allostatic load into pregnancy, from socio-economic circumstances, poor mental health and in 'developed' countries, also from obesity. These pregnancies have poorer outcomes indicating negative interactions (failing allostasis) between pre-pregnancy and pregnancy allostatic loads. Use of animal models, such as adult prenatally stressed female offspring with abnormal neuroendocrine, metabolic and behavioural phenotypes, to probe gene expression changes, and epigenetic mechanisms in the maternal brain in adverse pregnancies are discussed, with the prospect of ameliorating poor pregnancy outcomes.

Neuroactive Steroids and GABAergic Involvement in the Neuroendocrine Dysfunction Associated With Major Depressive Disorder and Postpartum Depression

Stress and previous adverse life events are well-established risk factors for depression. Further, neuroendocrine disruptions are associated with both major depressive disorder (MDD) and postpartum depression (PPD). However, the mechanisms whereby stress contributes to the underlying neurobiology of depression remains poorly understood. The hypothalamic-pituitary-adrenal (HPA) axis, which mediates the body's neuroendocrine response to stress, is tightly controlled by GABAergic signaling and there is accumulating evidence that GABAergic dysfunction contributes to the impact of stress on depression. GABAergic signaling plays a critical role in the neurobiological effects of stress, not only by tightly controlling the activity of the HPA axis, but also mediating stress effects in stress-related brain regions. Deficits in neuroactive steroids and neurosteroids, some of which are positive allosteric modulators of GABA_A receptors (GABA_ARs), such as allopregnanolone and THDOC, have also been implicated in MDD and PPD, further supporting a role for GABAergic signaling in depression. Alterations in neurosteroid levels and GABAergic signaling are implicated as potential contributing factors to neuroendocrine dysfunction and vulnerability to MDD and PPD. Further, potential novel treatment strategies targeting these proposed underlying neurobiological mechanisms are discussed. The evidence summarized in the current review supports the notion that MDD and PPD are stress-related psychiatric disorders involving neurosteroids and GABAergic dysfunction.

Design, Synthesis, and Pharmacological Evaluation of Novel β2/3 Subunit-Selective γ-Aminobutyric Acid Type A (GABAA) Receptor Modulators

Subunit-selective modulation of γ-aminobutyric acid type A receptors (GABA_AR) is considered to exert fewer side effects compared to unselective clinically used drugs. Here, the β2/3 subunit-selective GABA_AR modulators valerenic acid (VA) and loreclezole (LOR) guided the synthesis of novel subunit-selective ligands with simplified structures. We studied their effects on GABA_ARs expressed in Xenopus laevis oocytes using two-microelectrode voltage clamp technique. Five compounds showed significantly more efficacious modulation of GABA-evoked currents than VA and LOR with retained potency and selectivity. Compound 18 [( E)-2-Cyano-3-(2,4-dichlorophenyl)but-2-enamide] induced the highest maximal modulation of GABA-induced chloride currents ( E_max: 3114 ± 242%), while 12 [( Z)-3-(2,4-dichlorophenyl)but-2-enenitrile] displayed the highest potency (EC₅₀: 13 ± 2 μM). Furthermore, in hippocampal neurons 12 facilitated phasic and tonic GABAergic inhibition, and in vivo studies revealed significantly more potent protection against pentylenetetrazole (PTZ)-induced seizures compared to VA and LOR. Collectively, compound 12 constitutes a novel, simplified, and subunit-selective GABA_AR modulator with low-dose anticonvulsant activity.

Neurosteroid Metabolites of Gonadal Steroid Hormones in Neuroprotection: Implications for Sex Differences in Neurodegenerative Disease

Gonadal steroid hormones are neurotrophic and neuroprotective. These effects are modulated by local metabolism of the hormones within the brain. Such control is necessary to maintain normal function, as several signaling pathways that are activated by gonadal steroid hormones in the brain can also become dysregulated in disease. Metabolites of the gonadal steroid hormones—particularly 3α-hydroxy, 5α-reduced neurosteroids—are synthesized in the brain and can act through different mechanisms from their parent steroids. These metabolites may provide a mechanism for modulating the responses to their precursor hormones, thereby providing a regulatory influence on cellular responses. In addition, there is evidence that the 3α-hydroxy, 5α-reduced neurosteroids are neuroprotective in their own right, and therefore may contribute to the overall protection conferred by their precursors. In this review article, the rapidly growing body of evidence supporting a neuroprotective role for this class of neurosteroids will be considered, including a discussion of potential mechanisms that may be involved. In addition, we explore the hypothesis that differences between males and females in local neurosteroid production may contribute to sex differences in the development of neurodegenerative disease.

FGIN-1-27, an agonist at translocator protein 18 kDa (TSPO), produces anti-anxiety and anti-panic effects in non-mammalian models

FGIN-1-27 is an agonist at the translocator protein 18 kDa (TSPO), a cholesterol transporter that is associated with neurosteroidogenesis. This protein has been identified as a peripheral binding site for benzodiazepines; in anamniotes, however, a second TSPO isoform that is absent in amniotes has been implicated in erythropoiesis. Functional conservation of the central benzodiazepine-binding site located in the GABA_A receptors has been demonstrated in anamniotes and amniotes alike; however, it was not previously demonstrated for TSPO. The present investigation explored the behavioral effects of FGIN-1-27 on an anxiety test in zebrafish (Danio rerio, Family: Cyprinide) and on a mixed anxiety/panic test on wall lizards (Tropidurus oreadicus, Family: Tropiduridae). Results showed that FGIN-1-27 reduced anxiety-like behavior in the zebrafish light/dark preference test similar to diazepam, but with fewer sedative effects. Similarly, FGIN-1-27 also reduced anxiety- and fear-like behaviors in the defense test battery in wall lizards, again producing fewer sedative-like effects than diazepam; the benzodiazepine was also unable to reduce fear-like behaviors in this species. These results A) underline the functional conservation of TSPO in defensive behavior in anamniotes; B) strengthen the proposal of using anamniote behavior as models in behavioral pharmacology; and C) suggest TSPO/neurosteroidogenesis as a target in treating anxiety disorders.

Balancing tonic and phasic inhibition in hypothalamic corticotropin-releasing hormone neurons

KEY POINTS

GABA transporter (GAT) blockade recruits extrasynaptic GABA_A receptors (GABA_A Rs) and amplifies constitutive presynaptic GABA_B R activity. Extrasynaptic GABA_A Rs contribute to a tonic current. Corticosteroids increase the tonic current mediated by extrasynaptic GABA_A Rs.

ABSTRACT

Corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) are integratory hubs that regulate the endocrine response to stress. GABA inputs provide a basal inhibitory tone that constrains this system and circulating glucocorticoids (CORT) are important feedback controllers of CRH output. Surprisingly little is known about the direct effects of CORT on GABA synapses in PVN. Here we used whole-cell patch clamp recordings from CRH neurons in mouse hypothalamic brain slices to examine the effects of CORT on synaptic and extrasynaptic GABA signalling. We show that GABA transporters (GATs) limit constitutive activation of presynaptic GABA_B receptors and ensure high release probability at GABA synapses. GATs in combination with GABA_B receptors also curtail extrasynaptic GABA_A R signalling. CORT has no effect on synaptic GABA signalling, but increases extrasynaptic GABA tone through upregulation of postsynaptic GABA_A receptors. These data show that efficient GABA clearance and autoinhibition control the balance between synaptic (phasic) and extrasynaptic (tonic) inhibition in PVN CRH neurons. This balance is shifted towards increased extrasynaptic inhibition by CORT.

Endogenous neurosteroids influence synaptic GABAA receptors during postnatal development

GABA plays a key role in both embryonic and neonatal brain development. For example, during early neonatal nervous system maturation, synaptic transmission, mediated by GABA_A receptors (GABA_A Rs), undergoes a temporally specific form of synaptic plasticity to accommodate the changing requirements of maturing neural networks. Specifically, the duration of miniature inhibitory postsynaptic currents (mIPSCs), resulting from vesicular GABA activating synaptic GABA_A Rs, is reduced, permitting neurones to appropriately influence the window for postsynaptic excitation. Conventionally, programmed expression changes to the subtype of synaptic GABA_A R are primarily implicated in this plasticity. However, it is now evident that, in developing thalamic and cortical principal- and inter-neurones, an endogenous neurosteroid tone (eg, allopregnanolone) enhances synaptic GABA_A R function. Furthermore, a cessation of steroidogenesis, as a result of a lack of substrate, or a co-factor, appears to be primarily responsible for early neonatal changes to GABAergic synaptic transmission, followed by further refinement, which results from subsequent alterations of the GABA_A R subtype. The timing of this cessation of neurosteroid influence is neurone-specific, occurring by postnatal day (P)10 in the thalamus but approximately 1 week later in the cortex. Neurosteroid levels are not static and change dynamically in a variety of physiological and pathophysiological scenarios. Given that GABA plays an important role in brain development, abnormal perturbations of neonatal GABA_A R-active neurosteroids may have not only a considerable immediate, but also a longer-term impact upon neural network activity. Here, we review recent evidence indicating that changes in neurosteroidogenesis substantially influence neonatal GABAergic synaptic transmission. We discuss the physiological relevance of these findings and how the interference of neurosteroid-GABA_A R interaction early in life may contribute to psychiatric conditions later in life.

Sex-dependent effects of nicotine on the developing brain

The use of tobacco products represents a major public health concern, especially among women. Epidemiological data have consistently demonstrated that women have less success quitting tobacco use and a higher risk for developing tobacco-related diseases. The deleterious effects of nicotine are not restricted to adulthood, as nicotinic acetylcholine receptors regulate critical aspects of neural development. However, the exact mechanisms underlying the particular sensitivity of women to develop tobacco dependence have not been well elucidated. In this mini-review, we show that gonadal hormone-mediated sexual differentiation of the brain may be an important determinant of sex differences in the effects of nicotine. We highlight direct interactions between sex steroid hormones and ligand-gated ion channels critical for brain maturation, and discuss the extended and profound sexual differentiation of the brain. We emphasize that nicotine exposure during the perinatal and adolescent periods interferes with normal sexual differentiation and can induce long-lasting, sex-dependent alterations in neuronal structure, cognitive and executive function, learning and memory, and reward processing. We stress important age and sex differences in nicotine's effects and emphasize the importance of including these factors in preclinical research that models tobacco dependence. © 2016 Wiley Periodicals, Inc.

Structural basis for GABAA receptor potentiation by neurosteroids

Type A γ-aminobutyric acid receptors (GABAARs) are the principal mediators of inhibitory neurotransmission in the human brain. Endogenous neurosteroids interact with GABAARs to regulate acute and chronic anxiety and are potent sedative, analgesic, anticonvulsant and anesthetic agents. Their mode of binding and mechanism of receptor potentiation, however, remain unknown. Here we report crystal structures of a chimeric GABAAR construct in apo and pregnanolone-bound states. The neurosteroid-binding site is mechanically coupled to the helices lining the ion channel pore and modulates the desensitization-gate conformation. We demonstrate that the equivalent site is responsible for physiological, heteromeric GABAAR potentiation and explain the contrasting modulatory properties of 3a versus 3b neurosteroid epimers. These results illustrate how peripheral lipid ligands can regulate the desensitization gate of GABAARs, a process of broad relevance to pentameric ligand-gated ion channels.

A new stress sensor and risk factor for suicide: the T allele of the functional genetic variant in the GABRA6 gene

Low GABA transmission has been reported in suicide, and GABRA6 rs3219151 T allele has been associated with greater physiological and endocrine stress response in previous studies. Although environmental stress also plays a role in suicide, the possible role of this allele has not been investigated in this respect. In our present study effect of rs3219151 of GABRA6 gene in interaction with recent negative life events on lifetime and current depression, current anxiety, as well as lifetime suicide were investigated using regression models in a white European general sample of 2283 subjects. Post hoc measures for phenotypes related to suicide risk were also tested for association with rs3219151 in interaction with environmental stress. No main effect of the GABRA6 rs3219151 was detected, but in those exposed to recent negative life events GABRA6 T allele increased current anxiety and depression as well as specific elements of suicide risk including suicidal and death-related thoughts, hopelessness, restlessness and agitation, insomnia and impulsiveness as measured by the STOP task. Our data indicate that stress-associated suicide risk is elevated in carriers of the GABRA6 rs3219151 T allele with several independent markers and predictors of suicidal behaviours converging to this increased risk.

Stress and Seizures: Space, Time and Hippocampal Circuits

Stress is a major trigger of seizures in people with epilepsy. Exposure to stress results in the release of several stress mediators throughout the brain, including the hippocampus, a region sensitive to stress and prone to seizures. Stress mediators interact with their respective receptors to produce distinct effects on the excitability of hippocampal neurons and networks. Crucially, these stress mediators and their actions exhibit unique spatiotemporal profiles, generating a complex combinatorial output with time- and space-dependent effects on hippocampal network excitability and seizure generation.

What makes you tic? Translational approaches to study the role of stress and contextual triggers in Tourette syndrome

Tourette syndrome (TS) is a neurodevelopmental condition characterized by multiple, recurring motor and phonic tics. Rich empirical evidence shows that the severity of tics and associated manifestations is increased by several stressors and contextual triggers; however, the neurobiological mechanisms responsible for symptom exacerbation in TS remain poorly understood. This conceptual gap partially reflects the high phenotypic variability in tics, as well as the existing difficulties in operationalizing and standardizing stress and its effects in a clinical setting. Animal models of TS may be highly informative tools to overcome some of these limitations; these experimental preparations have already provided critical insights on key aspects of TS pathophysiology, and may prove useful to identify the neurochemical alterations induced by different stressful contingencies. In particular, emerging knowledge on the role of contextual triggers in animal models of TS may inform the development of novel pharmacological interventions to reduce tic fluctuations in this disorder.

Persistent Effects of Developmental Exposure to 17α-Ethinylestradiol on the Zebrafish (Danio rerio) Brain Transcriptome and Behavior

The synthetic estrogen 17α-ethinylestradiol (EE₂) is an endocrine disrupting compound of concern due to its persistence and widespread presence in the aquatic environment. Effects of developmental exposure to low concentrations of EE₂ in fish on reproduction and behavior not only persisted to adulthood, but have also been observed to be transmitted to several generations of unexposed progeny. To investigate the possible biological mechanisms of the persistent anxiogenic phenotype, we exposed zebrafish embryos for 80 days post fertilization to 0, 3, and 10 ng/L EE₂ (measured concentrations 2.14 and 7.34 ng/L). After discontinued exposure, the animals were allowed to recover for 120 days in clean water. Adult males and females were later tested for changes in stress response and shoal cohesion, and whole-brain gene expression was analyzed with RNA sequencing. The results show increased anxiety in the novel tank and scototaxis tests, and increased shoal cohesion in fish exposed during development to EE₂. RNA sequencing revealed 34 coding genes differentially expressed in male brains and 62 in female brains as a result of EE₂ exposure. Several differences were observed between males and females in differential gene expression, with only one gene, sv2b, coding for a synaptic vesicle protein, that was affected by EE₂ in both sexes. Functional analyses showed that in female brains, EE₂ had significant effects on pathways connected to the circadian rhythm, cytoskeleton and motor proteins and synaptic proteins. A large number of non-coding sequences including 19 novel miRNAs were also differentially expressed in the female brain. The largest treatment effect in male brains was observed in pathways related to cholesterol biosynthesis and synaptic proteins. Circadian rhythm and cholesterol biosynthesis, previously implicated in anxiety behavior, might represent possible candidate pathways connecting the transcriptome changes to the alterations to behavior. Further the observed alteration in expression of genes involved in synaptogenesis and synaptic function may be important for the developmental modulations resulting in an anxiety phenotype. This study represents an initial survey of the fish brain transcriptome by RNA sequencing after long-term recovery from developmental exposure to an estrogenic compound.

Acute stress effects on GABA and glutamate levels in the prefrontal cortex: A 7T 1H magnetic resonance spectroscopy study

There is ample evidence that the inhibitory GABA and the excitatory glutamate system are essential for an adequate response to stress. Both GABAergic and glutamatergic brain circuits modulate hypothalamus-pituitary-adrenal (HPA)-axis activity, and stress in turn affects glutamate and GABA levels in the rodent brain. However, studies examining stress-induced GABA and glutamate levels in the human brain are scarce. Therefore, we investigated the influence of acute psychosocial stress (using the Trier Social Stress Test) on glutamate and GABA levels in the medial prefrontal cortex of 29 healthy male individuals using 7 Tesla proton magnetic resonance spectroscopy. In vivo GABA and glutamate levels were measured before and 30 min after exposure to either the stress or the control condition. We found no associations between psychosocial stress or cortisol stress reactivity and changes over time in medial prefrontal glutamate and GABA levels. GABA and glutamate levels over time were significantly correlated in the control condition but not in the stress condition, suggesting that very subtle differential effects of stress on GABA and glutamate across individuals may occur. However, overall, acute psychosocial stress does not appear to affect in vivo medial prefrontal GABA and glutamate levels, at least this is not detectable with current practice ¹H-MRS.

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Psychosocial stress did not alter glutamate and GABA levels in the medial prefrontal cortex in healthy male individuals.

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Moreover, cortisol stress reactivity was not associated with medial prefrontal glutamate and GABA level change over time.

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Together, acute stress does not seem to affect in vivo medial prefrontal 7T MRI GABA and glutamate levels in humans.

Glucocorticoid Induces Incoordination between Glutamatergic and GABAergic Neurons in the Amygdala

BACKGROUND

Stressful life leads to mood disorders. Chronic mild stress is presumably major etiology for depression, and acute severe stress leads to anxiety. These stressful situations may impair hypothalamus-pituitary-adrenal axis and in turn induce synapse dysfunction. However, it remains elusive how the stress hormones mess up subcellular compartments and interactions between excitatory and inhibitory neurons, which we have investigated in mouse amygdala, a structure related to emotional states.

METHODS AND RESULTS

Dexamethasone was chronically given by intraperitoneal injection once a day for one week or was acutely washed into the brain slices. The neuronal spikes and synaptic transmission were recorded by whole-cell patching in amygdala neurons of brain slices. The chronic or acute administration of dexamethasone downregulates glutamate release as well as upregulates GABA release and GABAergic neuron spiking. The chronic administration of dexamethasone also enhances the responsiveness of GABA receptors.

CONCLUSION

The upregulation of GABAergic neurons and the downregulation of glutamatergic neurons by glucocorticoid impair their balance in the amygdala, which leads to emotional disorders during stress.

Impaired GABA synthesis, uptake and release are associated with depression-like behaviors induced by chronic mild stress

Major depression is a prevalent emotion disorder. Chronic stressful life in genetically susceptible individuals is presumably a major etiology that leads to neuron and synapse atrophy in the limbic system. Molecular mechanisms underlying the pathological changes remain elusive. Mice were treated by chronic unpredictable mild stress (CUMS) until they demonstrated depression-like behavior. GABA release in the medial prefrontal cortex was evaluated by cell electrophysiology and imaging. Molecular profiles related to GABA synthesis and uptake were investigated by the high-throughput sequencings of microRNAs and mRNAs as well as western blot analysis in this cortical area. In CUMS-induced depression mice, there appear the decreases in the innervation and function of GABAergic axons and in the levels of mRNAs and proteins of glutamate decarboxylase-67, vesicular GABA transporter and GABA transporter-3. miRNA-15b-5p, miRNA-144-3p, miRNA-582-5p and miRNA-879-5p that directly downregulate such mRNAs increase in this cortex. Our results suggest that chronic mild stress impairs GABA release and uptake by upregulating miRNAs and downregulating mRNAs and proteins, which may constitute the subcellular and molecular mechanisms for the lowered GABA tone in major depression.

TSPO activation modulates the effects of high pressure in a rat ex vivo glaucoma model

We previously reported that elevated pressure induces axonal swelling and facilitates the synthesis of the neurosteroid, allopregnanolone (AlloP), in the ex vivo rat retina. Exogenously applied AlloP attenuates the axonal swelling, suggesting that the neurosteroid plays a neuroprotective role against glaucomatous pressure-induced injuries, although mechanisms underlying neurosteroidogenesis have not been clarified. The aim of this study was to determine whether AlloP synthesis involves activation of translocator protein 18 kD (TSPO) and whether TSPO modulates pressure-induced retinal injury. Ex vivo rat retinas were exposed to various pressures (10, 35, or 75 mmHg) for 24 h. Expression of TSPO, 5α-reductase (5aRD), and AlloP was examined by quantitative real-time RT-PCR, ELISA, immunohistochemistry, and LC-MS/MS. We also examined the effects of TSPO ligands on AlloP synthesis and retinal damage. In this acute model, quantitative real-time RT-PCR and ELISA analyses revealed that elevated pressure facilitated TSPO expression. Similarly, these methods also detected enhanced 5aRD (mostly type II), which was observed in retinal ganglion cells (RGC) and the inner nuclear layer (INL). Atriol, a TSPO antagonist, suppressed pressure mediated AlloP synthesis and induced more severe histological changes in the inner retina when combined with elevated pressure. PK11195, a TSPO ligand that facilitates AlloP synthesis by itself, remarkably diminished pressure-mediated retinal degeneration. These results suggest that AlloP synthesis is induced by sequential activation of TSPO and 5aRD in an ex vivo glaucoma model, and that TSPO agonists may serve as potential therapeutic agents for the prevention of pressure-induced retinal damage.

Incoordination among Subcellular Compartments Is Associated with Depression-Like Behavior Induced by Chronic Mild Stress

BACKGROUND

Major depressive disorder is characterized as persistent low mood. A chronically stressful life in genetically susceptible individuals is presumably the major etiology that leads to dysfunctions of monoamine and hypothalamus-pituitary-adrenal axis. These pathogenic factors cause neuron atrophy in the limbic system for major depressive disorder. Cell-specific pathophysiology is unclear, so we investigated prelimbic cortical GABAergic neurons and their interaction with glutamatergic neurons in depression-like mice.

METHODS

Mice were treated with chronic unpredictable mild stress for 3 weeks until they expressed depression-like behaviors confirmed by sucrose preference, Y-maze, and forced swimming tests. The structures and functions of GABAergic and glutamatergic units in prelimbic cortices were studied by cell imaging and electrophysiology in chronic unpredictable mild stress-induced depression mice vs controls.

RESULTS

In depression-like mice, prelimbic cortical GABAergic neurons show incoordination among the subcellular compartments, such as decreased excitability and synaptic outputs as well as increased reception from excitatory inputs. GABAergic synapses on glutamatergic cells demonstrate decreased presynaptic innervation and increased postsynaptic responsiveness.

CONCLUSIONS

Chronic unpredictable mild stress-induced incoordination in prelimbic cortical GABAergic and glutamatergic neurons dysregulates their target neurons, which may be the pathological basis for depressive mood. The rebalance of compatibility among subcellular compartments would be an ideal strategy to treat neural disorders.

Blood glucose regulation mechanism in depressive disorder animal model during hyperglycemic states

Depression is more common among diabetes people than in the general population. In the present study, blood glucose change in depression animal model was characterized by various types of hyperglycemia models such as d-glucose-fed-, immobilization stress-, and drug-induced hyperglycemia models. First, the ICR mice were enforced into chronic restraint stress for 2h daily for 2 weeks to produce depression animal model. The animals were fed with d-glucose (2g/kg), forced into restraint stress for 30min, or administered with clonidine (5μg/5μl) supraspinally or spinally to produce hyperglycemia. The blood glucose level in depression group was down-regulated compared to that observed in the normal group in d-glucose-fed-, restraint stress-, and clonidine-induced hyperglycemia models. The up-regulated corticosterone level induced by d-glucose feeding or restraint stress was reduced in the depression group while the up-regulation of plasma corticosterone level is further elevated after i.t. or i.c.v. clonidine administration in the depression group. The up-regulated insulin level induced by d-glucose feeding or restraint stress was reduced in the depression group. On the other hand, blood corticosterone level in depression group was up-regulated compared to the normal group after i.t. or i.c.v. clonidine administration. Whereas the insulin level in depression group was not altered when mice were administered clonidine i.t. or i.c.v. Our results suggest that the blood glucose level in depression group is down-regulated compared to the normal group during d-glucose-fed-, immobilization stress-, and clonidine-induced hyperglycemia in mice. The down-regulation of the blood glucose level might be one of the important pathophysiologic changes in depression.