GABA Regulates the Rat Hypothalamic-Pituitary-Adrenocortical Axis via Different GABA-A Receptor ��-Subtypes

Anxiety-like behavior and GABAergic system in ovariectomized rats exposed to chronic mild stress

Stress or low level of estrogen could promote anxiety and depression; thus, it is of interest to investigate the combined effect of mild stress and the lack of estrogen on mental disorders by utilizing an animal model. This study was conducted to assess anxiety- and depressive- like behaviors in ovariectomized (Ovx) rats exposed to chronic mild stress (CMS) and determine the alteration in gamma-aminobutyric acid (GABA)-related transmission. Ovx rats were randomly assigned into four groups: (1) estrogen replacement (E2-NoCMS), (2) estrogen replacement and exposure to CMS (E2-CMS), (3) vehicle (VEH-NoCMS), and (4) vehicle and exposure to CMS (VEH-CMS). Following 4-week CMS, VEH groups (VEH-NoCMS and VEH-CMS) showed a similar level of anxiety-like behavior in elevated T-maze, whereas E2-CMS, VEH-NoCMS and VEH-CMS showed anxiety-like behavior in open field. The depressive-like behavior in the force swimming test tended to be affected by estrogen deprivation than CMS. The alteration of the GABAergic system as determined from the GABA level and mRNA expression of GABA-related transmission (i.e., glutamic acid decarboxylase, GABA transporter and GABA_A subunits) showed that the GABA level in the amygdala and frontal cortex was affected by CMS. For mRNA expression, the mRNA profile in the amygdala and hippocampus of VEH-NoCMS and E2-CMS was the same but different from those of VEH-NoCMS and E2-CMS. In addition, compared with E2-NoCMS, the mRNA profile in the frontal cortex was similar in VEH-NoCMS, E2-CMS, and VEH-CMS. These findings indicated that the underlying mechanism of the GABAergic system was differently modified, although VEH-NoCMS and VEH-CMS showed anxiety-like behavior. The findings of this study may provide a comprehensive understanding of the modulation of the GABAergic system during estrogen deprivation under CMS, as observed in menopausal women who were daily exposed to stress.

Involvement of the GABAergic system in PTSD and its therapeutic significance

The neurobiological mechanism of post-traumatic stress disorder (PTSD) is poorly understood. The inhibition of GABA neurons, especially in the amygdala, is crucial for the precise regulation of the consolidation, expression, and extinction of fear conditioning. The GABAergic system is involved in the pathophysiological process of PTSD, with several studies demonstrating that the function of the GABAergic system decreases in PTSD patients. This paper reviews the preclinical and clinical studies, neuroimaging techniques, and pharmacological studies of the GABAergic system in PTSD and summarizes the role of the GABAergic system in PTSD. Understanding the role of the GABAergic system in PTSD and searching for new drug targets will be helpful in the treatment of PTSD.

Basal Cortisol Levels Are Increased in Patients with Mild Cognitive Impairment: Role of Insomnia and Short Sleep Duration

BACKGROUND

Mild cognitive impairment (MCI) is frequent in elderly and a risk factor for dementia. Both insomnia and increased cortisol levels are risk factors for MCI.

OBJECTIVE

We examined cross-sectionally whether increased cortisol levels are associated with short sleep duration (SSD) and/or the insomnia short sleep duration (ISS) phenotype, in elderly with MCI.

METHODS

One hundred twenty-four participants with MCI and 84 cognitively non-impaired controls (CNI)≥60 years underwent medical history, physical examination, neuropsychiatric evaluation, neuropsychological testing, 3-day actigraphy, assessment of subjective insomnia symptoms, and a single morning plasma cortisol level. The short sleep phenotypes were defined by sleep efficiency below the median of the entire sample (i.e.,≤81%) with at least one insomnia symptom (ISS) or without (SSD). ANOVA models were used to compare the various sleep phenotypes to those who did not present either short sleep or insomnia symptoms [non-insomnia (NI)].

RESULTS

MCI participants had higher cortisol levels compared to the CNI group (p = 0.009). MCI participants with insomnia (n = 44) or SSD (n = 38) had higher cortisol levels compared to the NI group (n = 42; p = 0.014 and p = 0.045, respectively). Furthermore, MCI participants with ISS phenotype but not those with insomnia with normal sleep duration had higher cortisol levels compared to NI (p = 0.011 and p = 0.4, respectively). Both linear trend analyses showed that cortisol reached the highest levels in the ISS phenotype.

CONCLUSION

The ISS and SSD phenotypes are associated with increased cortisol levels in elderly with MCI. Improving sleep quality and duration and decreasing cortisol levels may delay further cognitive decline.

Drugs and bugs: Negative affect, psychostimulant use and withdrawal, and the microbiome

BACKGROUND AND OBJECTIVES

A growing body of literature demonstrates that the human microbiota plays a crucial role in health and disease states, as well as in the body's response to stress. In addition, the microbiome plays a role in psychological well-being and regulating negative affect. Regulation of negative affect is a factor in psychostimulant abuse disorders. We propose a risk chain in which stress leads to negative affect that places an individual at risk to develop or relapse to psychostimulant abuse disorder. Stress, negative affect, and psychostimulant use all alter the gut microbiome.

METHODS

This review brings together the literature on affective disorders, stress, and psychostimulant abuse disorders to assess possible modulatory actions of the gut-brain axis to regulate these conditions.

RESULTS

Studies reviewed across the various disciplines suggest that the dysbiosis resulting from drug use, drug withdrawal, or stress may cause an individual to be more susceptible to addiction and relapse. Probiotics and prebiotics reduce stress and negative affect.

SCIENTIFIC SIGNIFICANCE

Treatment during the withdrawal phase of psychostimulant abuse disorder, when the microbiome is altered, may ameliorate the symptoms of stress and negative affect leading to a reduced risk of relapse to psychostimulant use.

Effects of trazodone versus cognitive behavioral therapy in the insomnia with short sleep duration phenotype: a preliminary study

STUDY OBJECTIVES

The insomnia with objective short sleep duration phenotype is associated with increased risk for adverse health outcomes, physiological hyperarousal, and a blunted response to cognitive behavioral therapy for insomnia (CBT-I). Whether insomnia with objective short sleep duration responds better to pharmacological treatment compared to CBT-I has not been examined.

METHODS

Participants included 15 patients with chronic insomnia (86.7% female), aged 45.3 ± 8.1 years. Eight patients were randomized to CBT-I and 7 to trazodone. Patients were examined with 2 weeks of actigraphy, salivary cortisol, and the insomnia severity index at 3 time points (pretreatment, 3-month posttreatment, and 6-month follow-up). Mixed between-within-subjects analysis of variance and univariate analysis of covariance were conducted to assess the impact of trazodone and CBT-I on patients' total sleep time, salivary cortisol, and insomnia severity index scores across the 3 time points.

RESULTS

Trazodone, but not CBT-I, significantly lengthened total sleep time (when measured with actigraphy) both at posttreatment (51.01 minutes vs -11.73 minutes; P = .051; Cohen's d = 1.383) and at follow-up (50.35 minutes vs -7.56 minutes; P = .012; Cohen's d = 1.725), respectively. In addition, trazodone, but not CBT-I, showed a clinically meaningful decrease in salivary cortisol from pretreatment to posttreatment (-36.07% vs -11.70%; Cohen's d = 0.793) and from pretreatment to follow-up (-21.37% vs -5.79%; Cohen's d = 0.284), respectively. Finally, there were no differences on insomnia severity index scores between the trazodone and the CBT-I groups.

CONCLUSIONS

The current preliminary, open-label, randomized trial suggests that trazodone, but not CBT-I, significantly improves objective sleep duration and reduces hypothalamic-pituitary-adrenal axis activation, suggesting a differential treatment response in the insomnia with objective short sleep duration phenotype.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: Study of Trazodone & Cognitive Behavioral Therapy to Treat Insomnia; URL: https://clinicaltrials.gov/ct2/show/NCT01348542; Identifier: NCT01348542.

Modeling psychiatric comorbid symptoms of epileptic seizures in zebrafish

Epilepsy is a debilitating neurological disorder characterized by recurrent unprovoked seizures. Anxiety, cognitive deficits, depressive-like symptoms, and social dysfunction are psychiatric comorbidities with high prevalence in epileptic patients. Due to the genetic and behavioral tractability, the zebrafish is a promising model organism to understand the neural bases involved in epilepsy-related comorbidities. Here, we aimed to characterize some behavioral phenotypes paralleling those observed in epilepsy-related comorbidities after a single pentylenetetrazole (PTZ) exposure in zebrafish. We also analyzed the influence of whole-body cortisol levels in the behavioral responses measured. Fish were exposed to 10 mM PTZ for 20 min to induce epileptic seizures. After 24 h recovery period, locomotion and anxiety-like responses (novel tank and light-dark tests), social interaction (shoaling behavior task), and memory retention (inhibitory avoidance protocol) were assessed. Basically, PTZ impaired habituation to novelty stress, evoked anxiogenic-like behaviors, disrupted shoaling, and caused memory consolidation deficits in zebrafish without changing whole-body cortisol levels. In conclusion, our novel findings further validate the use of zebrafish as a suitable tool for modeling epilepsy-related comorbidities in translational neuropsychiatric research.

Suramin is a novel competitive antagonist selective to α1β2γ2 GABAA over ρ1 GABAC receptors

GABA_A and GABA_C receptors are both GABA-gated chloride channels with distinct pharmacological properties, mainly in their sensitivity to bicuculline and gabazine. In this study, we found that suramin, a purinergic receptor antagonist, is a novel competitive antagonist selective to GABA_A over GABA_C receptors. Specifically, suramin antagonized the GABA-induced current and the spontaneous opening current of the wild type α1β2γ2 GABA_A receptor with high-level expression in Xenopus oocytes. The antagonism was concentration dependent with an IC₅₀ that varied depending on the concentration of GABA, and with the lowest IC₅₀ of 0.43 μM when antagonizing the spontaneous current. Thus, its potency is slightly higher than bicuculline on the same GABA_A receptor. Suramin also antagonized the mouse native brain GABA receptors micro-transplanted into the Xenopus oocytes with its potency depending on the GABA concentration. In addition, in the presence of two fixed concentrations of suramin, the GABA concentration response of the receptor was shifted to the right without reduction of the maximum current. Thus, our results are consistent with that suramin is a competitive antagonist for the α1β2γ2 GABA_A receptor. Interestingly, the rank order of maximum allosteric inhibition (efficacy) of spontaneous current of the GABA_A receptor by three competitive antagonists was suramin > bicuculline > gabazine, similar to the rank order of their molecular weight. In contrast, similar to bicuculline, suramin has much lower potency in antagonizing the GABA-induced current of the ρ1 GABA_C receptor. In conclusion, we have identified a novel GABA_A receptor competitive antagonist, which is selective to the α1β2γ2 over ρ1 GABA receptors.

Risk of Type 2 Diabetes in Patients With Nonapnea Sleep Disorders in Using Different Types of Hypnotics: A Population-Based Retrospective Cohort Study

There has been insufficient evidence on whether exposure to hypnotics affects the risk of type 2 diabetes (T2DM). The aim of this study was to examine patients with nonapnea sleep disorders using zolpidem, benzodiazepines (BZDs), or a combination of both, and their risk of T2DM. This was a population-based retrospective cohort study using data from 1997 to 2011. Data from the Taiwan National Health Insurance Research Database were employed for this study. A total of 45,602 patients with nonapnea sleep disorders and use of hypnotics were identified as the study cohort. The control cohort comprised 40,799 age- and sex-matched patients. We conducted a Cox proportional hazard regression analysis to estimate the effects of hypnotics on risk of T2DM. The overall incidence of T2DM was 20.1 per 1000 person-years for patients using zolpidem, which was significantly higher than that of the control group (11.9 per 1000 person-years). Overall, patients with nonapnea sleep disorders using zolpidem had a higher risk of T2DM compared with patients not using zolpidem and the control cohort (adjusted hazard ratio [HR] = 1.41, 95% confidence interval [CI] = 1.35-1.48). We also observed a significantly higher risk of T2DM in patients with both zolpidem and BZD use (adjusted HR = 1.77, 95% CI = 1.64-1.91) than that of those without zolpidem use and BZD use. Compared with patients not using hypnotics, patients using zolpidem had a higher risk of developing T2DM; the risk was particularly pronounced in those using both zolpidem and BZDs.

Activation of GABA-A receptors during postnatal brain development increases anxiety- and depression-related behaviors in a time- and dose-dependent manner in adult mice

Disturbances of the gamma-amino butyric acid-ergic (GABAergic) system during postnatal development can have long-lasting consequences for later life behavior, like the individual's response to stress. However, it is unclear which postnatal windows of sensitivity to GABA-ergic modulations are associated with what later-life behavioral outcomes. Therefore, we sought to determine whether neonatal activation of the GABA-A receptor during two postnatal periods, an early window (postnatal day 3-5) and a late window (postnatal day 14-16), can affect anxiety- and depression-related behaviors in male mice in later life. To this end, mice were treated with either saline or muscimol (50, 100, 200, 300 and 500μg/kg) during the early and late postnatal periods. An additional group of mice was treated with the GABA-A receptor antagonist bicuculline+muscimol. When grown to adulthood male mice were exposed to behavioral tests to measure anxiety- and depression-related behaviors. Baseline and stress-induced corticosterone (CORT) levels were also measured. The results indicate that early postnatal and to a lesser extent later postnatal exposure to the GABA-A receptor agonist muscimol increased anxiety-like behavior and stress-induced CORT levels in adults. Moreover, the early postnatal treatment with muscimol increased depression-like behavior with increasing baseline CORT levels. The anxiogenic and depression-like later-life consequences could be antagonized by bicuculline. Our findings suggest that GABA-A receptor signaling during early-life can influence anxiety- and depression-related behaviors in a time- and dose-dependent manner in later life. Our findings help to increase insight in the developmental mechanisms contributing to stress-related disorders.

[Interaction between hypnotic agents and the hypothalamic-pituitary-adrenocorticotropic axis during surgery]

During stress, the relationship between the central nervous system and the immune system is essential to maintain homeostasis. The main neuroendocrine system involved in this interaction is the hypothalamic-pituitary-adrenal axis (HPA), which via the synthesis of glucocorticoids will modulate the intensity of the inflammatory response. Anaesthetic agents could be interacting with the HPA axis during surgery. Although etomidate currently remains in the center of the discussions, it seems, at least experimentally, that most hypnotics have the capacity to modulate the synthesis of adrenal steroids. Nevertheless, with the large literature on this subject, etomidate seems to be the most deleterious hypnotic agent on the HPA axis function. Its use should be limited when HPA axis is already altered.

Alterations in brain-derived neurotrophic factor in the mouse hippocampus following acute but not repeated benzodiazepine treatment

Benzodiazepines (BZs) are safe drugs for treating anxiety, sleep, and seizure disorders, but their use also results in unwanted effects including memory impairment, abuse, and dependence. The present study aimed to reveal the molecular mechanisms that may contribute to the effects of BZs in the hippocampus (HIP), an area involved in drug-related plasticity, by investigating the regulation of immediate early genes following BZ administration. Previous studies have demonstrated that both brain derived neurotrophic factor (BDNF) and c-Fos contribute to memory- and abuse-related processes that occur within the HIP, and their expression is altered in response to BZ exposure. In the current study, mice received acute or repeated administration of BZs and HIP tissue was analyzed for alterations in BDNF and c-Fos expression. Although no significant changes in BDNF or c-Fos were observed in response to twice-daily intraperitoneal (i.p.) injections of diazepam (10 mg/kg + 5 mg/kg) or zolpidem (ZP; 2.5 mg/kg + 2.5 mg/kg), acute i.p. administration of both triazolam (0.03 mg/kg) and ZP (1.0 mg/kg) decreased BDNF protein levels within the HIP relative to vehicle, without any effect on c-Fos. ZP specifically reduced exon IV-containing BDNF transcripts with a concomitant increase in the association of methyl-CpG binding protein 2 (MeCP2) with BDNF promoter IV, suggesting that MeCP2 activity at this promoter may represent a ZP-specific mechanism for reducing BDNF expression. ZP also increased the association of phosphorylated cAMP response element binding protein (pCREB) with BDNF promoter I. Future work should examine the interaction between ZP and DNA as the cause for altered gene expression in the HIP, given that BZs can enter the nucleus and intercalate into DNA directly.

Changes in the brain expression of alpha-2 subunits of the GABA-A receptor after chronic restraint stress in low- and high-anxiety rats

This study assessed the mechanisms underlying the behavioral differences between high- (HR) and low-anxiety (LR) rats selected for their behavior in the contextual fear test (i.e., the duration of the freezing response was used as a discriminating variable). Rats were subjected to chronic restraint stress (21 days, 3h daily). We found that in the HR group, chronic restraint stress decreased rat activity in the Porsolt test and reduced the concentration of corticosterone in the prefrontal cortex. The behavioral changes were accompanied by a lower expression of alpha-2 GABA-A receptor subunits in the secondary motor cortex (M2 area) and in the dentate gyrus of the hippocampus (DG) compared to LR restraint animals. Moreover, restraint stress increased the density of alpha-2 GABA-A subunits in the basolateral amygdala (BLA) in HR rats and decreased the expression of these subunits in the DG and M2 areas compared to the HR control group. The present results suggest that, in HR rats exposed to chronic restraint stress, the function of hippocampal and cortical GABAergic neurotransmission is attenuated and that this effect could have important influences on the functioning of the hypothalamic-pituitary-adrenal axis and on depressive symptoms.

Detection of neuronal activity and metabolism in a model of dehydration-induced anorexia in rats at 14.1 T using manganese-enhanced MRI and 1H MRS

In this study, hypothalamic activation was performed by dehydration-induced anorexia (DIA) and overnight food suppression (OFS) in female rats. The assessment of the hypothalamic response to these challenges by manganese-enhanced MRI showed increased neuronal activity in the paraventricular nuclei (PVN) and lateral hypothalamus (LH), both known to be areas involved in the regulation of food intake. The effects of DIA and OFS were compared by generating T-score maps. Increased neuronal activation was detected in the PVN and LH of DIA rats relative to OFS rats. In addition, the neurochemical profile of the PVN and LH were measured by (1) H MRS at 14.1T. Significant increases in metabolite levels were measured in DIA and OFS relative to control rats. Statistically significant increases in γ-aminobutyric acid were found in DIA (p=0.0007) and OFS (p<0.001) relative to control rats. Lactate increased significantly in DIA (p=0.03), but not in OFS, rats. This work shows that manganese-enhanced MRI coupled to (1) H MRS at high field is a promising noninvasive method for the investigation of the neural pathways and mechanisms involved in the control of food intake, in the autonomic and endocrine control of energy metabolism and in the regulation of body weight.

Dysfunctional neurotransmitter systems in fibromyalgia, their role in central stress circuitry and pharmacological actions on these systems

Fibromyalgia is considered a stress-related disorder, and hypo- as well as hyperactive stress systems (sympathetic nervous system and hypothalamic-pituitary-adrenal axis) have been found. Some observations raise doubts on the view that alterations in these stress systems are solely responsible for fibromyalgia symptoms. Cumulative evidence points at dysfunctional transmitter systems that may underlie the major symptoms of the condition. In addition, all transmitter systems found to be altered in fibromyalgia influence the body's stress systems. Since both transmitter and stress systems change during chronic stress, it is conceivable that both systems change in parallel, interact, and contribute to the phenotype of fibromyalgia. As we outline in this paper, subgroups of patients might exhibit varying degrees and types of transmitter dysfunction, explaining differences in symptomatoloy and contributing to the heterogeneity of fibromyalgia. The finding that not all fibromyalgia patients respond to the same medications, targeting dysfunctional transmitter systems, further supports this hypothesis.

Blockade of GABA(A) receptors in the paraventricular nucleus of the hypothalamus attenuates voluntary ethanol intake and activates the hypothalamic-pituitary-adrenocortical axis

The paraventricular nucleus (PVN) in the hypothalamus is the main integration site that controls the hypothalamic-pituitary-adrenal (HPA) neuroendocrine stress system. Disruption of this system has been linked with alcoholism, but the specific role of the PVN has not been fully explored. Of particular interest is the ability of γ-aminobutyric acid type A receptors (GABA(A)Rs) in the PVN, to regulate ethanol self-administration behavior, as these receptors appear to play an essential role in mediating the effects of ethanol in the central nervous system and in the regulation of PVN activity. We observed that Long-Evans rats, in the intermittent access to 20% ethanol paradigm, consumed high amounts of ethanol and subsequently developed ethanol dependence. Microinjection of the GABA(A)R antagonist picrotoxin into the PVN, but not to the lateral ventricle of the brain, significantly reduced the intake of ethanol, but not the intake of sucrose. Picrotoxin-induced reduction was mimicked by another GABA(A)R antagonist bicuculline but was attenuated by the GABA(A)R agonist muscimol. Moreover, increased ethanol consumption was associated with lowered blood corticosterone levels, indicating a blunted HPA signaling, which was reversed by intra-PVN injection of picrotoxin, as indicated by the increased Fos immunostaining-positive cells in the PVN and the increased blood corticosterone levels. Taken together, our data provide evidence that in ethanol-dependent rats, the function of GABA(A)Rs in the PVN is upregulated, leading to a dampened HPA system. Moreover, it demonstrates that the GABA(A)R antagonists normalize HPA axis signaling and reduce excessive ethanol drinking. Therefore, drugs targeting GABA(A)Rs may be beneficial for alcoholics.

Modeling seizure-related behavioral and endocrine phenotypes in adult zebrafish

Larval zebrafish (Danio rerio) have recently been suggested as a high-throughput experimental model of epilepsy-related pathogenetic states. Here we use adult zebrafish to study behavioral symptoms associated with drug-evoked seizures. Experimental epilepsy-like states were evoked in zebrafish by exposure for 20min to three chemoconvulsant drugs: caffeine (250mg/L; 1.3mM), pentylenetetrazole (1.5g/L; 11.0mM) and picrotoxin (100mg/L; 0.17mM). Fish behavior was analyzed using manual and video-tracking methods (Noldus Ethovision XT7). Compared to their respective controls, all three drug-treated groups showed robust seizure-like responses (hyperactivity bouts, spasms, circular and corkscrew swimming) accompanied by elevated whole-body cortisol levels (assessed by ELISA). In contrast, control fish did not display seizure-like behaviors and had significantly lower cortisol levels. Paralleling behavioral and endocrine phenotypes observed in clinical and rodent studies, our data implicates adult zebrafish as an emerging experimental model for epilepsy research.

Long-term benzodiazepine use and salivary cortisol: the Netherlands Study of Depression and Anxiety (NESDA)

BACKGROUND

As benzodiazepines (BZDs) have anxiolytic effects, it is expected that they influence the stress system. During short-term treatment, BZD use was found to suppress cortisol levels. However, little research has been done on the effects of long-term BZD administration on the hypothalamic-pituitary-adrenal (HPA) axis.

METHODS

The association between long-term BZD use and cortisol levels was investigated in subjects of the Netherlands Study of Depression and Anxiety with a lifetime diagnosis of anxiety or depression (n = 1531). The subjects were categorized as "daily BZD users" (n = 96), "infrequent BZD users" (n = 172), and "nonusers" (n = 1263). Possible associations between characteristics of BZD use (dose, duration, and dependence) and salivary cortisol levels were analyzed.

MAIN OUTCOME MEASURE

Subjects provided 7 saliva samples, from which 4 cortisol indicators were calculated: the cortisol awakening response, diurnal slope, evening cortisol, and cortisol suppression after ingestion of 0.5 mg of dexamethasone.

RESULTS

Daily users used BZDs for a median duration of 26.5 months and had a median daily dosage of 6.0 mg as measured in diazepam equivalents. Evening cortisol levels were significantly lower in daily users (P = 0.004; effect size: d = 0.24) and infrequent users (P = 0.04; effect size: d = 0.12) compared to nonusers. We did not find significant differences in the cortisol awakening response, diurnal slope, or in the dexamethasone suppression test.

CONCLUSIONS

Despite the finding of slightly lower evening cortisol levels in daily and infrequent BZD users compared to nonusers, results indicate that long-term BZD use is not convincingly associated with HPA axis alterations.