Maternal treatment with a selective delta-opioid receptor agonist during gestation has a sex-specific pro-cognitive action in offspring: mechanisms involved.

Background: There is growing evidence that the treatment of several mental disorders can potentially benefit from activation of delta-opioid receptors. In the future, delta-agonists with a safe pharmacological profile can be used for the treatment of mood disorders in pregnant women. However, the data on prenatal exposure to delta-opioid agonists are missing. The present study is aimed to test the hypothesis that the activation of delta-opioid receptors during gravidity has positive effects on the behaviour accompanied by changes in glutamate and monoamine neurotransmission. Methods: Gestating Wistar rats were chronically treated with a selective delta-agonist SNC80 or vehicle. Adult male and female offspring underwent novel object recognition (for the assessment of cognition) and open field (for the assessment of anxiety and habituation) tests, followed by in vivo electrophysiological examination of the activity of hippocampal glutamate and midbrain serotonin (5-HT) and dopamine neurons. Results: We found that the maternal treatment with SNC80 did not affect the offspring's anxiety, habituation, and 5-HT neuronal firing activity. Female offspring of SNC80-treated dams exhibited improved novelty recognition associated with decreased firing rate and burst activity of glutamate and dopamine neurons. Conclusion: Maternal treatment with delta-opioid agonists during gestation may have a pro-cognitive effect on offspring without any negative effects on anxiety and habituation. The putative pro-cognitive effect might be mediated via mechanism(s) involving the firing activity of hippocampal glutamate and mesolimbic dopamine neurons.

Treatment with Glycyrrhiza glabra Extract Induces Anxiolytic Effects Associated with Reduced Salt Preference and Changes in Barrier Protein Gene Expression.

We have previously identified that low responsiveness to antidepressive therapy is associated with higher aldosterone/cortisol ratio, lower systolic blood pressure, and higher salt preference. Glycyrrhiza glabra (GG) contains glycyrrhizin, an inhibitor of 11ß-hydroxysteroid-dehydrogenase type-2 and antagonist of toll-like receptor 4. The primary hypothesis of this study is that food enrichment with GG extract results in decreased anxiety behavior and reduced salt preference under stress and non-stress conditions. The secondary hypothesis is that the mentioned changes are associated with altered gene expression of barrier proteins in the prefrontal cortex. Male Sprague-Dawley rats were exposed to chronic mild stress for five weeks. Both stressed and unstressed rats were fed a diet with or without an extract of GG roots for the last two weeks. GG induced anxiolytic effects in animals independent of stress exposure, as measured in elevated plus maze test. Salt preference and intake were significantly reduced by GG under control, but not stress conditions. The gene expression of the barrier protein claudin-11 in the prefrontal cortex was increased in control rats exposed to GG, whereas stress-induced rise was prevented. Exposure to GG-enriched diet resulted in reduced ZO-1 expression irrespective of stress conditions. In conclusion, the observed effects of GG are in line with a reduction in the activity of central mineralocorticoid receptors. The treatment with GG extract or its active components may, therefore, be a useful adjunct therapy for patients with subtypes of depression and anxiety disorders with heightened renin-angiotensin-aldosterone system and/or inflammatory activity.

The role of the GABAergic cells of the median raphe region in reinforcement-based learning.

Learning and memory are important in everyday life as well as in pathological conditions. The median raphe region (MRR) contributes to memory formation; however, its precise role and the neurotransmitters involved have yet to be elucidated. To address this issue, we stimulated the MRR neurons of mice by chemogenetic technique and studied them in the operant conditioning and active avoidance tests. The virus carrier infected a variety of neuron types including both GABAergic and glutamatergic ones. Behavior was not influenced by stimulation. We hypothesize that the lack of effect was due to opposing effects exerted via GABAergic and glutamatergic neurons. Therefore, next we used VGAT-Cre mice that allowed the specific manipulation of MRR-GABAergic neurons. The stimulation did not affect behavior in the learning phase of the operant conditioning task, but increased reward preference and total responses when operant contingencies were reversed. The enhanced responsiveness might be a proclivity to impulsive behavior. Stimulation facilitated learning in the active avoidance test but did not affect reversal learning in this paradigm. Our findings suggest that MRR-GABAergic neurons are involved in both learning and reversal learning, but the type of learning that is affected depends on the task.

Selected neuroendocrine factors as potential molecular biomarkers of early non-affective psychosis course in relation to treatment outcome: A pilot study.

The aim of this pilot study was to find whether the dysregulation of neuroendocrine biomarker signaling pathways in the first episode of non-affective psychosis is a predictive factor of treatment outcome. Patients with the first episode of non-affective psychosis (N = 29) were examined at admission, at discharge, and at follow-up (N = 23). The biomarkers included serum aldosterone, cortisol, free thyroxine, thyroid stimulating hormone, and prolactin. We revealed lower baseline aldosterone and higher baseline cortisol concentrations in patients with very good outcome compared to those with good outcome after one year. We failed to reveal any significant association between treatment outcome and neurohumoral biomarkers in the whole sample at 1-year follow-up. However, baseline aldosterone concentrations negatively correlated with total PANSS scores at the discharge. Lower baseline aldosterone and higher baseline cortisol concentrations have the potential to predict a more favorable outcome for patients with the first episode of psychosis.

Bridging the mood and stress hormone levels between mothers and their babies: The study design and first preliminary results.

The neurobiological mechanisms involved in the influence of post-partum maternal mood fluctuations on child development are far from being understood. Here we present the design of an ongoing study aimed to test the hypothesis that the mental state of the mother has an impact on her neonate which is manifested by similarities in the neuroendocrine function of the mother and the child. The hypothesis is being tested under both stress and non-stress conditions in mothers and babies aged 3-4 days and 7-9 months. The focus will be given to correlations with maternal postpartum mood. To confirm the correctness of methodological approaches and the feasibility of the study several preliminary analyses were performed. Salivary alpha-amylase activity as a marker of sympathetic activation and cortisol as the effective hormone of the hypothalamic-pituitary-adrenocortical axis were measured. The obtained results showed the feasibility of saliva sampling in neonates using a sampling time of 120 s. The analysis of cortisol in hair revealed increased concentrations during the third trimester of pregnancy, which is consistent with the knowledge of high cortisol concentrations during pregnancy. A positive correlation was observed between salivary cortisol values before and after the stress test in mother-infant dyads at both the post-partum period and 7-9 months thereafter. Understanding the mechanisms involved in "the bridge" between the mother and her baby will help to develop necessary interventions directed to help mothers in the early postpartum period.

Altered responsiveness to glutamatergic modulation by MK-801 and to repeated stress of immune challenge in female dopamine transporter knockout rats.

Chronic stress is a key factor in psychiatric and neurological disorders often worsening disease symptoms. In this study, a unique animal model, the dopamine transporter knockout (DAT-KO) rat exhibiting behavioral signs resembling those occurring in mania, schizophrenia, attention deficit hyperactivity disorder, and obsessive-compulsive disorder was used. We have tested the hypothesis that the hyperdopaminergic state in DAT-KO rats (i) modulates behavioral response to the NMDA antagonist MK-801 (dizocilpine) and (ii) leads to abnormal endocrine and immune activation under subchronic stress induced by an immune challenge. Glutamatergic modulation with MK-801 induced a different behavioral pattern. While the WT rats responded to MK-801 injection with a robust rise in their locomotor activity, the hyperactive DAT-KO rats exhibited reduced locomotion. Signs of chronic stress including increased basal corticosterone and aldosterone but blunted anxiety were demonstrated in rats lacking the DAT. Repeated injections of increasing doses of lipopolysaccharide (LPS, 5 days) did not modify plasma prolactin concentrations which were however significantly lower in DAT-KO than in WT rats. Concentrations of plasma high mobility group box 1 (HMGB1) protein were significantly higher in LPS-treated DAT-KO than in WT rats. The gene expression of interleukin-6 in the anterior pituitary increased under the stress induced by the immune challenge in the WT but not the DAT-KO rats. The most evident differences between the genotypes were revealed in the spleen. The splenic gene expression of interleukin-1ß, interleukin-6, and HMGB1 was lower and that of ferritin was higher in DAT-KO compared to WT rats. Obtained results emphasize the functional interaction of the endocrine and immune systems with monoamine and glutamatergic neurotransmission in the mechanisms leading to behavioral alterations and psychiatric disorders associated with dopamine dysfunction.

Effects of chronic delta-opioid receptor agonist on the excitability of hippocampal glutamate and brainstem monoamine neurons, anxiety, locomotion, and habituation in rats.

BACKGROUND: Short-term treatment with non-peptide agonists of delta-opioid receptors, such as agonist SNC80, induced behavioral effects in rodents, which could be modulated via changes in central neurotransmission. The present experiments aimed at testing the hypothesis that chronic treatment with SNC80 induces anxiolytic effects associated with changes in hippocampal glutamate and brainstem monoamine pathways. METHODS: Adult male Wistar rats were used in experiments. Rats were treated with SNC80 (3 mg/kg/day) for fourteen days. Neuronal excitability was assessed using extracellular in vivo single-unit electrophysiology. The behavioral parameters were examined using the elevated plus maze and open field tests. RESULTS: Chronic SNC80 treatment increased the excitability of hippocampal glutamate and ventral tegmental area dopamine neurons and had no effect on the firing activity of dorsal raphe nucleus serotonin cells. Chronic SNC80 treatment induced anxiolytic effects, which were, however, confounded by increased locomotor activity clearly confirmed in an open field test. The ability to cope with stressful situations and habituation processes in a novel environment was not influenced by chronic treatment with SNC80. CONCLUSION: Our study suggests that the psychoactive effects of SNC80 might be explained by its ability to stimulate hippocampal glutamate and mesolimbic dopamine transmission.

Role of miR-124-3p in regulatory mechanisms of Gpm6a expression in the hippocampus of chronically stressed rats.

The neuronal membrane glycoprotein M6a (GPM6A) belongs to the family of myelin proteolipid protein and plays a role in neuronal remodeling and plasticity. Decreased expression of GPM6A mRNA is observed in the hippocampal tissue of suicide victims who suffered from depression and after chronic stress exposure in animals. The regulatory mechanisms that impact expression of GPM6A under chronic stress or in pathological conditions are not well understood. Previously, miRNAs miR-133b, miR-124-3p, and miR-9-5p have been shown to regulate the expression of Gpm6a mRNA under normal conditions. Here, we employed the paradigm of chronic-restraint stress in rats and using quantitative polymerase chain reaction (qPCR) showed down-regulation of expression of Gpm6a and the brain-derived neurotrophic factor (Bdnf) genes at mRNA level as well as miR-133b, and miR-124-3p, but not miR-9-5p in the hippocampus of chronically stressed rats. Furthermore, we observed alterations in the expression of histone deacetylase (Hdac5) and myocyte enhancer factor 2C (Mef2c) mRNAs. Our data suggest that chronic stress influences Gpm6a expression by miR-124-mediated impact on the expression of Hdac5 and Mef2c. Upon miR-124 over-expression in hippocampal neurons cultured in vitro, we observed enhanced neuronal arborization as evaluated by Sholl analysis, increased Gpm6a and Mef2c expression, and decreased Hdac5 expression. Moreover, treatment of hippocampal neurons cultured in vitro with BDNF resulted in an elevation in the miR-124-3p expression, a decrease in the miR-9-5p expression but did not affect miR-133b. This was accompanied by augmented expression of Gpm6a and Mef2c mRNAs and significantly lower levels of Hdac5 mRNA. Altogether, these results indicate that the regulatory mechanism that influence expression of Gpm6a under chronic stress involves miR-124-mediated impact on the expression of Hdac5 and Mef2c and a role of BDNF in the activation of Gpm6a expression.

A viewpoint on aldosterone and BMI related brain morphology in relation to treatment outcome in patients with major depression.

An abundance of knowledge has been collected describing the involvement of neuroendocrine parameters in major depression. The hypothalamic-pituitary-adrenocortical (HPA) axis regulating cortisol release has been extensively studied; however, attempts to target the HPA axis pharmacologically to treat major depression have failed. This review focuses on the importance of the adrenocortical stress hormone aldosterone, which is released by adrenocorticotropic hormone and angiotensin, and the mineralocorticoid receptor (MR) in depression. Depressed patients, in particular those with atypical depression, have signs of central hyperactivation of the aldosterone sensitive MR, potentially as a consequence of a reactive aldosterone release induced by low blood pressure and as a result of low sensitivity of peripheral MR. This is reflected in reduced heart rate variability, increased salt appetite and sleep changes in this group of patients. In addition, enlarged brain ventricles, compressed corpus callosum and changes of the choroid plexus are associated with increased aldosterone (in relation to cortisol). Furthermore, subjects with these features often show obesity. These characteristics are related to a worse antidepressant treatment outcome. Alterations in choroid plexus function as a consequence of increased aldosterone levels, autonomic dysregulation, metabolic changes and/or inflammation may be involved. The characterization of this regulatory system is in its early days but may identify new targets for therapeutic interventions.

Stress Hormones Cortisol and Aldosterone, and Selected Markers of Oxidative Stress in Response to Long-Term Supplementation with Omega-3 Fatty Acids in Adolescent Children with Depression.

Late childhood and adolescence are crucial periods of brain development with high vulnerability to environmental insults. The aim of this study was to test the hypotheses that in adolescents with depression (a) 12 weeks-supplementation with omega-3 fatty acids results in the attenuation of salivary stress hormone concentrations; (b) the mentioned supplementation improves potentially disrupted daily rhythm of stress hormones; (c) stress hormone concentrations correlate with values of selected markers of oxidative stress. The sample consisted of 60 patients suffering from depression aged 11-18 years. Hormone concentrations in saliva were measured in the morning and midday before (baseline) and after (6, 12 weeks) food supplementation with omega-3 or omega-6 (as comparator) fatty acids. Morning cortisol decreased in response to omega-3 but not omega-6 fatty acids at 12 weeks compared to baseline. No changes were observed in aldosterone concentrations. The obtained results show that adolescent children with depression preserved the daily rhythm of both stress hormones. Baseline morning cortisol concentrations correlated positively with depression severity and lipoperoxides, and negatively with docosahexaenoic acid. Aldosterone concentrations correlated positively with 8-isoprostane. Thus, both hormones showed positive correlation with the selected markers of oxidative stress suggesting that enhanced stress hormone secretion may be associated with increased oxidative tissue damage in adolescent children with depression. This study was registered with the ISRCTN registry (DEPOXIN study, ISRCTN81655012).

Effects of acute and chronic administration of trace amine-associated receptor 1 (TAAR1) ligands on in vivo excitability of central monoamine-secreting neurons in rats.

Trace amine-associated receptor 1 (TAAR1) has been recently identified as a target for the future antidepressant, antipsychotic, and anti-addiction drugs. Full (e.g. RO5256390) and partial (e.g. RO5263397) TAAR1 agonists showed antidepressant-, antipsychotic- and anti-addiction-like behavioral effects in rodents and primates. Acute RO5256390 suppressed, and RO5263397 stimulated serotonin (5-HT) neurons of the dorsal raphe nucleus (DRN) and dopamine neurons of the ventral tegmental area (VTA) in brain slices, suggesting that the behavioral effects of TAAR1 ligands involve 5-HT and dopamine. For more comprehensive testing of this hypothesis, we examined acute and chronic effects of RO5256390 and RO5263397 on monoamine neurons in in vivo conditions. Excitability of 5-HT neurons of the DRN, noradrenaline neurons of the locus coeruleus (LC), and dopamine neurons of the VTA was assessed using single-unit electrophysiology in anesthetized rats. For acute experiments, RO5256390 and RO5263397 were administered intravenously; neuronal excitability after RO5256390 and RO5263397 administration was compared to the basal activity of the same neuron. For chronic experiments, RO5256390 was administered orally for fourteen days prior to electrophysiological assessments. The neuronal excitability in RO5256390-treated rats was compared to vehicle-treated controls. We found that acute RO5256390 inhibited 5-HT and dopamine neurons. This effect of RO5256390 was reversed by the subsequent and prevented by the earlier administration of RO5263397. Acute RO5256390 and RO5263397 did not alter the excitability of LC noradrenaline neurons in a statistically significant way. Chronic RO5256390 increased excitability of 5-HT neurons of the DRN and dopamine neurons of the VTA. In conclusion, the putative antidepressant and antipsychotic effects of TAAR1 ligands might be mediated, at least in part, via the modulation of excitability of central 5-HT and dopamine neurons.

Exposure to chronic stressor upsurges the excitability of serotoninergic neurons and diminishes concentrations of circulating corticosteroids in rats two weeks thereafter.

BACKGROUND: Exposure to predator scent (PS) has been used as a model of stress associated with danger to life and body integrity. Under stress conditions, the brain serotoninergic (5-HT) system plays an important role. METHODS: We tested the hypothesis that repeated PS exposure alters the excitability of 5-HT neurons of the dorsal raphe nucleus. To study the mechanisms involved, we approached serum and adrenal corticosterone and aldosterone concentrations, as well as brain-derived neurotrophic factor (BDNF) expression. Adult male Sprague-Dawley rats were exposed to PS for 10 min daily for 10 consecutive days. Two weeks after the last exposure, electrophysiological and biochemical assessments were performed. RESULTS: Measurements by in vivo electrophysiology showed increased firing activity of 5-HT neurons in rats exposed to PS. Exposure to PS resulted in reduced serum corticosterone and aldosterone concentrations. Concentrations of both corticosteroids in the adrenal glands and the relative weight of the adrenals were unaffected. The gene expression of hippocampal BDNF of rats exposed to PS remained unaltered. PS exposure failed to induce changes in the gene expression of selected adrenal steroidogenic factors. CONCLUSION: Reduced corticosteroid concentrations in the blood appear to be the result of increased metabolism and/or tissue uptake rather than altered steroidogenesis. The decrease in circulating corticosterone in rats who experienced repeated PS may represent part of the mechanisms leading to increased excitability of 5-HT neurons. The increase in 5-HT neuronal activity might be an important compensatory mechanism designated to diminish the harmful effects of the repeated PS exposure on the brain.

Psychotropic Drug Effects on Steroid Stress Hormone Release and Possible Mechanisms Involved.

There is no doubt that chronic stress accompanied by adrenocortical stress hormone release affects the development and treatment outcome of several mental disorders. Less attention has been paid to the effects of psychotropic drugs on adrenocortical steroids, particularly in clinical studies. This review focuses on the knowledge related to the possible modulation of cortisol and aldosterone secretion under non-stress and stress conditions by antipsychotic drugs, which are being used in the treatment of several psychotic and affective disorders. The molecular mechanisms by which antipsychotic drugs may influence steroid stress hormones include the modulation of central and/or adrenocortical dopamine and serotonin receptors, modulation of inflammatory cytokines, influence on regulatory mechanisms in the central part of the hypothalamic-pituitary axis, inhibition of corticotropin-releasing hormone gene promoters, influencing glucocorticoid receptor-mediated gene transcription, indirect effects via prolactin release, alteration of signaling pathways of glucocorticoid and mineralocorticoid actions. Clinical studies performed in healthy subjects, patients with psychosis, and patients with bipolar disorder suggest that single and repeated antipsychotic treatments either reduce cortisol concentrations or do not affect its secretion. A single and potentially long-term treatment with dopamine receptor antagonists, including antipsychotics, has a stimulatory action on aldosterone release.

Steroid stress hormone changes throughout the menstrual cycle: A rise in evening aldosterone concentration in early luteal phase precedes the symptoms of premenstrual syndrome.

There is still a lack of consistent evidence on dysregulation of steroid stress hormones cortisol and aldosterone in premenstrual syndrome (PMS). We aimed to test the hypothesis that, in healthy women, salivary aldosterone concentrations are higher in those with PMS compared to controls, particularly during the luteal phase of the menstrual cycle. In total, 99 female subjects (49 women with and 50 women without PMS) participated in a prospective non-interventional case-control study. Saliva sampling was performed in the follicular (day 8), early luteal (day 20) and late luteal phase (2 days before expected onset of bleeding) of the menstrual cycle in the morning and the evening. The results confirmed the hypothesis that salivary aldosterone concentrations are higher in women with PMS during the early luteal phase compared to controls (p < .01) in the evening. Early luteal phase aldosterone concentrations positively correlated with the frequency of premenstrual symptoms. Women with PMS exhibited a flatter morning to evening aldosterone slope compared to controls (p < .05). Morning and evening salivary cortisol concentrations were unchanged throughout the menstrual cycle in both groups of women. In conclusion, evening salivary aldosterone, but not cortisol concentrations, are increased in women with PMS during the early luteal phase compared to controls. Cortisol does not appear to be involved in the mechanisms contributing to the course of PMS. High evening salivary aldosterone in the early luteal phase may represent an important risk factor and could be of predictive value for the occurrence of premenstrual symptoms.

Trophic factors as potential therapies for treatment of major mental disorders.

Notwithstanding major advances in psychotherapeutics, their efficacy and specificity remain limited. The slow onset of beneficial outcomes and numerous adverse effects of widely used medications remain of chief concern, warranting in-depth studies. The majority of frontline therapies are thought to enhance the endogenous monoaminergic drive, to initiate a cascade of molecular events leading to lasting functional and structural plasticity. They also involve alterations in trophic factor signalling, including brain-derived neurotrophic factor (BDNF), VGF (non-acronymic), vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), glial cell-derived neurotrophic factor (GDNF), and others. In several major mental disorders, emerging data suggest protective and restorative effects of trophic factors in preclinical models, when applied on their own. Antidepressant outcomes of VGF and FGF2, for instance, were shown in experimental animals, while BDNF and GDNF prove useful in the treatment of addiction, schizophrenia, and autism spectrum disorders. The main challenge with the effective translation of these and other findings in the clinic is the knowledge gap in action mechanisms with potential risks, as well as the lack of effective platforms for validation under clinical settings. Herein, we review the state-of-the-art and advances in the therapeutic use of trophic factors in several major neuropsychiatric disorders.

Food Enrichment with Glycyrrhiza glabra Extract Suppresses ACE2 mRNA and Protein Expression in Rats-Possible Implications for COVID-19.

Angiotensin converting enzyme 2 (ACE2) is a key entry point of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus known to induce Coronavirus disease 2019 (COVID-19). We have recently outlined a concept to reduce ACE2 expression by the administration of glycyrrhizin, a component of Glycyrrhiza glabra extract, via its inhibitory activity on 11beta hydroxysteroid dehydrogenase type 2 (11betaHSD2) and resulting activation of mineralocorticoid receptor (MR). We hypothesized that in organs such as the ileum, which co-express 11betaHSD2, MR and ACE2, the expression of ACE2 would be suppressed. We studied organ tissues from an experiment originally designed to address the effects of Glycyrrhiza glabra extract on stress response. Male Sprague Dawley rats were left undisturbed or exposed to chronic mild stress for five weeks. For the last two weeks, animals continued with a placebo diet or received a diet containing extract of Glycyrrhiza glabra root at a dose of 150 mg/kg of body weight/day. Quantitative PCR measurements showed a significant decrease in gene expression of ACE2 in the small intestine of rats fed with diet containing Glycyrrhiza glabra extract. This effect was independent of the stress condition and failed to be observed in non-target tissues, namely the heart and the brain cortex. In the small intestine we also confirmed the reduction of ACE2 at the protein level. Present findings provide evidence to support the hypothesis that Glycyrrhiza glabra extract may reduce an entry point of SARS-CoV-2. Whether this phenomenon, when confirmed in additional studies, is linked to the susceptibility of cells to the virus requires further studies.

The continued need for animals to advance brain research.

Policymakers aim to move toward animal-free alternatives for scientific research and have introduced very strict regulations for animal research. We argue that, for neuroscience research, until viable and translational alternatives become available and the value of these alternatives has been proven, the use of animals should not be compromised.

Tight junction proteins in the small intestine and prefrontal cortex of female rats exposed to stress of chronic isolation starting early in life.

BACKGROUND: Simultaneous evaluation of barrier protein expression in the gut and the brain and their modulation under stress conditions have not been studied before now. As the permeability and function of the gut and blood-brain barrier are different and both express the MRs, we hypothesized that stress of post-weaning social isolation induces changes in tight junction protein expression in the gut which are (1) independent of changes in the brain and (2) are mediated via the mineralocorticoid receptor (MR). METHODS: First, using UPLC-MS/MS we have successfully validated and selected a dose (1.2 mg/rat/day) of the MR antagonist spironolactone to treat female rats exposed to stress of chronic isolation or control conditions from postnatal day 21 for 9 weeks. KEY RESULTS: Isolation stress caused an enhancement of gene expression of occludin and ZO-1 and a decrease in claudin-5 and MR expression in both the small intestine and prefrontal cortex. Isolation stress failed to decrease claudin-5 (small intestine) and MR (prefrontal cortex) gene expression in spironolactone-treated rats. MR blockade resulted in a decrease in claudin-15 expression in the small intestine. Anxiogenic effect of chronic stress, measured in elevated plus-maze test, was partly prevented by spironolactone treatment. CONCLUSIONS & INFERENCES: Claudins, the main regulators of intestinal barrier permeability responded to chronic stress of social isolation and/or simultaneous blockade of MR in female rats by alterations independent of changes in the brain cortex. The results suggest a physiological role of MR in the control of claudin expression in the small intestine, but not in the brain cortex.