Antidepressant-like effects of mineralocorticoid but not glucocorticoid antagonists in the lateral septum: interactions with the serotonergic system

Differential Alterations of Expression of the Serotoninergic System Genes and Mood-Related Behavior by Consumption of Aspartame or Potassium Acesulfame in Rats

The use of aspartame (ASP) and potassium acesulfame (ACK) to reduce weight gain is growing; however, contradictory effects in body mass index control and neurobiological alterations resulting from artificial sweeteners consumption have been reported. This study aimed to evaluate the impact of the chronic consumption of ASP and ACK on mood-related behavior and the brain expression of serotonin genes in male Wistar rats. Mood-related behaviors were evaluated using the swim-forced test and defensive burying at two time points: 45 days (juvenile) and 95 days (adult) postweaning. Additionally, the mRNA expression of three serotoninergic genes (Slc6a4, Htr1a, and Htr2c) was measured in the brain areas (prefrontal cortex, hippocampus, and hypothalamus) involved in controlling mood-related behaviors. In terms of mood-related behaviors, rats consuming ACK exhibited anxiety-like behavior only during the juvenile stage. In contrast, rats consuming ASP showed a reduction in depressive-like behavior during the juvenile stage but an increase in the adult stage. The expression of Slc6a4 mRNA increased in the hippocampus of rats consuming artificial sweeteners during the juvenile stage. In the adult stage, there was an upregulation in the relative expression of Slc6a4 and Htr1a in the hypothalamus, while Htr2c expression decreased in the hippocampus of rats consuming ASP. Chronic consumption of ASP and ACK appears to have differential effects during neurodevelopmental stages in mood-related behavior, potentially mediated by alterations in serotoninergic gene expression.

Imbalanced glucocorticoid and mineralocorticoid stress hormone receptor function has sex-dependent and independent regulatory effects in the mouse hippocampus

Many stress-related neuropsychiatric disorders display pronounced sex differences in their frequency and clinical symptoms. Glucocorticoids are primary stress hormones that have been implicated in the development of these disorders but whether they contribute to the observed sex bias is poorly understood. Glucocorticoids signal through two closely related nuclear receptors, the glucocorticoid (GR) and mineralocorticoid receptor (MR). To elucidate the sex-specific and independent actions of glucocorticoids in the hippocampus, we developed knockout mice lacking hippocampal GR, MR, or both GR and MR. Mice deficient in hippocampal MR or both GR and MR showed an altered molecular phenotype of CA2 neurons and reduced anxiety-like behavior in both sexes, but altered stress adaptation behavior only in females and enhanced fear-motivated cue learning only in males. All three knockout mouse models displayed reduced sociability but only in male mice. Male and female mice deficient in both hippocampal GR and MR exhibited extensive neurodegeneration in the dentate gyrus. Global transcriptomic analysis revealed a marked expansion in the number of dysregulated genes in the hippocampus of female knockout mice compared to their male counterparts; however, the overall patterns of gene dysregulation were remarkably similar in both sexes. Within and across sex comparisons identified key GR and MR target genes and associated signaling pathways underlying the knockout phenotypes. These findings define major sex-dependent and independent effects of GR/MR imbalances on gene expression and functional profiles in the hippocampus and inform new strategies for treating men and women with stress-related neuropsychiatric disorders.

The Engagement of Cytochrome P450 Enzymes in Tryptophan Metabolism

Tryptophan is metabolized along three main metabolic pathways, namely the kynurenine, serotonin and indole pathways. The majority of tryptophan is transformed via the kynurenine pathway, catalyzed by tryptophan-2,3-dioxygenase or indoleamine-2,3-dioxygenase, leading to neuroprotective kynurenic acid or neurotoxic quinolinic acid. Serotonin synthesized by tryptophan hydroxylase, and aromatic L-amino acid decarboxylase enters the metabolic cycle: serotonin → N-acetylserotonin → melatonin → 5-methoxytryptamine→serotonin. Recent studies indicate that serotonin can also be synthesized by cytochrome P450 (CYP), via the CYP2D6-mediated 5-methoxytryptamine O-demethylation, while melatonin is catabolized by CYP1A2, CYP1A1 and CYP1B1 via aromatic 6-hydroxylation and by CYP2C19 and CYP1A2 via O-demethylation. In gut microbes, tryptophan is metabolized to indole and indole derivatives. Some of those metabolites act as activators or inhibitors of the aryl hydrocarbon receptor, thus regulating the expression of CYP1 family enzymes, xenobiotic metabolism and tumorigenesis. The indole formed in this way is further oxidized to indoxyl and indigoid pigments by CYP2A6, CYP2C19 and CYP2E1. The products of gut-microbial tryptophan metabolism can also inhibit the steroid-hormone-synthesizing CYP11A1. In plants, CYP79B2 and CYP79B3 were found to catalyze N-hydroxylation of tryptophan to form indole-3-acetaldoxime while CYP83B1 was reported to form indole-3-acetaldoxime N-oxide in the biosynthetic pathway of indole glucosinolates, considered to be defense compounds and intermediates in the biosynthesis of phytohormones. Thus, cytochrome P450 is engaged in the metabolism of tryptophan and its indole derivatives in humans, animals, plants and microbes, producing biologically active metabolites which exert positive or negative actions on living organisms. Some tryptophan-derived metabolites may influence cytochrome P450 expression, affecting cellular homeostasis and xenobiotic metabolism.

Forced swim stressor: Trends in usage and mechanistic consideration

The acquired immobility response during the “forced swim test (FST)” is not a rodent model of depression, but the test has some validity in predicting a compound's antidepressant potential. Nevertheless, 60% of the about 600 papers that were published annually the past 2 years label the rodent's immobility response as depression‐like behaviour, but the relative contribution per country is changing. When the Editors‐in‐Chief of 5 journals publishing most FST papers were asked for their point of view on labelling immobility as depression‐like behaviour and despair, they responded that they primarily rely on the reviewers regarding scientific merit of the submission. One Editor informs authors of the recent NIMH notice (https://grants.nih.gov/grants/guide/notice‐files/NOT‐MH‐19‐053.html) which encourages investigators to use animal models “for” addressing neurobiological questions rather than as model “of” specific mental disorders. The neurobiological questions raised by use of the FST fall in two categories. First, research on the role of endocrine and metabolic factors, with roots in the 1980s, and with focus on the bottom‐up action of glucocorticoids on circuits processing salient information, executive control and memory consolidation. Second, recent findings using novel technological and computational advances that have allowed great progress in charting top‐down control in the switch from active to passive coping with the inescapable stressor executed by neuronal ensembles of the medial prefrontal cortex via the peri‐aquaductal grey. It is expected that combining neural top‐down and endocrine bottom‐up approaches will provide new insights in the role of stress‐coping and adaptation in pathogenesis of mental disorders.

Hypertension Drug Therapy

Hypertension is still the number one global killer. No matter what causes are, lowering blood pressure can significantly reduce cardiovascular complications, cardiovascular death, and total death. Unfortunately, some hypertensive individuals simply do not know having hypertension. Some knew it but either not being treated or treated but blood pressure does not achieve goal. The reasons for inadequate control of blood pressure are many. One important reason is that we are not very familiar with antihypertensive agents and less attention has been paid to comorbidities, complications as well as the hypertension-modified target organ damage in patients with hypertension. The right antihypertensive drug was not given to the right hypertensive patients at right time. This reviewer studied comprehensively the literature, hopefully that the review will help improve antihypertensive drug selection and antihypertensive therapy.

Impact of adolescent stress on the expression of stress-related receptors in the hippocampus of animals exposed to alcohol prenatally

Many functions of the hippocampus are affected by prenatal alcohol exposure (PAE). In particular, dysregulation of the stress response is especially important because individuals with PAE carry increased risks for exposure to stressful environments throughout life. Little is known, though, about how adolescent stress in the context of PAE-related stress system dysregulation may further alter hippocampal development. Here, we investigate the short- and long-term effects of adolescent chronic mild stress (CMS) on mRNA expression of stress-related mineralocorticoid (MR), glucocorticoid (GR), and type 1 CRH (CRHR1) receptors in the dorsal and ventral hippocampal formation of PAE and control rats. Our results indicate that PAE affects the expression of stress-related receptors in the hippocampus; however, PAE effects were more prominent during adolescence, as MR and CRHR1 mRNA expression were altered in both male and female PAE animals, with GR mRNA expression alterations observed only in PAE female. In adulthood, the effects of PAE were restricted to alterations in CRHR1 mRNA expression in females, while there were no effects in males. In contrast, the effects of adolescent CMS were more pronounced in adulthood, long after stress exposure termination. Importantly, PAE animals were less responsive to adolescent CMS, with effects only on CRHR1 in PAE animals compared to the altered MR, GR, and CRHR1 mRNA expression observed in controls. Together, our results show that PAE and adolescent CMS induce dynamic alterations in the expression of stress-related receptors in the hippocampal formation that manifest differently depending on the age and sex of the animal.

Aqueous Extract of Pomegranate Alone or in Combination with Citalopram Produces Antidepressant-Like Effects in an Animal Model of Menopause: Participation of Estrogen Receptors

It has been reported that the aqueous extract of pomegranate (AE-PG) has polyphenols with estrogenic-like activities. The present work determines if AE-PG alone or in combination with the selective serotonin reuptake inhibitor, citalopram, has antidepressant-like effects. It was also analyzed the participation of estrogen receptors (ER). AE-PG (0.1, 1.0, 10, or 100 mg/kg) was evaluated in ovariectomized female Wistar rats subjected to the forced swimming test. The effects induced by AE-PG were compared with those of citalopram (2.5, 5.0, 10, and 20.0 mg/kg) and 17β-estradiol (E2; 2.5 5.0, and 10 μg/rat). Likewise, the combination of suboptimal doses of AE-PG (0.1 mg/kg) plus citalopram (2.5 mg/kg) was evaluated. To determine if ER participates in the antidepressant-like action of pomegranate, the estrogen antagonist tamoxifen (15 mg/kg) was administered with AE-PG (1 mg/kg). AE-PG produced antidepressant-like actions with a similar behavioral profile induced by citalopram and E2. Suboptimal doses of citalopram plus AE-PG produced antidepressant-like effects. Tamoxifen was able to block AE-PG's antidepressant-like actions. These results confirm the participation of ER in AE-PG's antidepressant-like effects. Furthermore, the additive effects observed with the combined treatment of AE-PG plus citalopram could be advantageous in the treatment of depressive disorders, such as menopause.

Differential effects of imipramine and CORT118335 (Glucocorticoid receptor modulator/mineralocorticoid receptor antagonist) on brain-endocrine stress responses and depression-like behavior in female rats

Depression is commonly associated with hypothalamic-pituitary adrenal (HPA) axis dysfunction that primarily manifests as aberrant glucocorticoid secretion. Glucocorticoids act on Type I mineralocorticoid (MR) and Type II glucocorticoid receptors (GR) to modulate mood and endocrine responses. Successful antidepressant treatment normalizes HPA axis function, in part due to modulatory effects on MR and GR in cortico-limbic structures. Although women are twice as likely to suffer from depression, little is known about how antidepressants modulate brain, endocrine, and behavioral stress responses in females. Here, we assessed the impact of CORT118335 (GR modulator/MR antagonist) and imipramine (tricyclic antidepressant) on neuroendocrine and behavioral responses to restraint or forced swim stress (FST) in female rats (n=10-12/group). Increased immobility CORT118335 in the FST is purported to reflect passive coping or depression-like behavior. CORT118335 dampened adrenocorticotropic hormone (ACTH) and corticosterone responses to the FST, but did not affect immobility. Imipramine suppressed ACTH, but had minimal effects on corticosterone responses to FST. Despite these marginal effects, imipramine decreased immobility, suggesting antidepressant efficacy. In an effort to link brain-endocrine responses with behavior, c-Fos was assessed in HPA axis and mood modulatory regions in response to the FST. CORT118335 upregulated c-Fos expression in the paraventricular nucleus of the hypothalamus. Imipramine decreased c-Fos in the basolateral amygdala and hippocampus (CA1 and CA3), but increased c-Fos in the central amygdala. These data suggest the antidepressant-like (e.g., active coping) properties of imipramine may be due to widespread effects on cortico-limbic circuits that regulate emotional and cognitive processes.

Coping with the Forced Swim Stressor: Towards Understanding an Adaptive Mechanism

In the forced swim test (FST) rodents progressively show increased episodes of immobility if immersed in a beaker with water from where escape is not possible. In this test, a compound qualifies as a potential antidepressant if it prevents or delays the transition to this passive (energy conserving) behavioural style. In the past decade however the switch from active to passive "coping" was used increasingly to describe the phenotype of an animal that has been exposed to a stressful history and/or genetic modification. A PubMed analysis revealed that in a rapidly increasing number of papers (currently more than 2,000) stress-related immobility in the FST is labeled as a depression-like phenotype. In this contribution we will examine the different phases of information processing during coping with the forced swim stressor. For this purpose we focus on the action of corticosterone that is mediated by the closely related mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) in the limbic brain. The evidence available suggests a model in which we propose that the limbic MR-mediated response selection operates in complementary fashion with dopaminergic accumbens/prefrontal executive functions to regulate the transition between active and passive coping styles. Upon rescue from the beaker the preferred, mostly passive, coping style is stored in the memory via a GR-dependent action in the hippocampal dentate gyrus. It is concluded that the rodent's behavioural response to a forced swim stressor does not reflect depression. Rather the forced swim experience provides a unique paradigm to investigate the mechanistic underpinning of stress coping and adaptation.

GABAA/benzodiazepine receptor complex mediates the anxiolytic-like effect of Montanoa tomentosa

ETHNOPHARMACOLOGICAL RELEVANCE

Montanoa tomentosa also named Cihuapatli is a native plant of Mexico that has been used in traditional medicine for the last five centuries mainly as a remedy for reproductive impairments. However, there are reports indicating that this plant was also consumed by Mexican ancient people for its relaxing properties. In order to corroborate this information, the present study was conducted to evaluate the effect of Montanoa tomentosa lyophilisate (MT) on rat׳s anxiety-like behavior and to analyze its mechanism of action.

MATERIALS AND METHODS

The anxiolytic-like action of MT (1.5, 3.0, 6.0 and 12.0 mg/kg) was investigated in male Wistar rats tested in three animal models of anxiety: the burying behavior, the elevated plus maze and the hole-board tests. As a positive control, the anti-anxiety effects of different doses of the selective GABAA receptor agonist muscimol were also analyzed. In order to evaluate the participation of the GABAA and oxytocin receptors in the anxiolytic-like actions of MT, the GABAA receptors blockers picrotoxin (0.25 and 0.50 mg/kg), bicuculline (2.0 mg/kg) and flumazenil (5.00 and 10.0 mg/kg), the neurosteroid inhibitor finasteride (50.0 and 100 mg/kg) and the oxytocin receptor antagonist atosiban (0.25 µg) were used. Finally, to evaluate general activity, and motor coordination, the open field and rota-rod tests were used.

RESULTS

MT at 3.0 mg/kg showed anxiolytic-like effects in the three anxiety paradigms without affecting reactivity, general motor activity or motor coordination; however, at higher doses sedative effects were observed. Picrotoxin (0.25 and 0.50 mg/kg), flumazenil (10.0 mg/kg) and finasteride (100 mg/kg) antagonized the anxiolytic-like actions of MT in the burying behavior test. In the plus maze and hole-board tests bicuculline (2.0 mg/kg) blocked the effects of the plant as well. Atosiban (0.25 µg) did not antagonize the anxiolytic-like actions of MT.

CONCLUSIONS

The results corroborate the anxiolytic-like actions of Montanoa tomentosa and suggest that this effect is mediated through GABAA receptors but not oxytocin receptors.

Forebrain glucocorticoid receptor gene deletion attenuates behavioral changes and antidepressant responsiveness during chronic stress

Stress is an important risk factor for mood disorders. Stress also stimulates the secretion of glucocorticoids, which have been found to influence mood. To determine the role of forebrain glucocorticoid receptors (GR) in behavioral responses to chronic stress, the present experiments compared behavioral effects of repeated social defeat in mice with forebrain GR deletion and in floxed GR littermate controls. Repeated defeat produced alterations in forced swim and tail suspension immobility in floxed GR mice that did not occur in mice with forebrain GR deletion. Defeat-induced changes in immobility in floxed GR mice were prevented by chronic antidepressant treatment, indicating that these behaviors were dysphoria-related. In contrast, although mice with forebrain GR deletion exhibited antidepressant-induced decreases in tail suspension immobility in the absence of stress, this response did not occur in mice with forebrain GR deletion after defeat. There were no marked differences in plasma corticosterone between genotypes, suggesting that behavioral differences depended on forebrain GR rather than on abnormal glucocorticoid secretion. Defeat-induced gene expression of the neuronal activity marker c-fos in the ventral hippocampus, paraventricular thalamus and lateral septum correlated with genotype-related differences in behavioral effects of defeat, whereas c-fos induction in the nucleus accumbens and central and basolateral amygdala correlated with genotype-related differences in behavioral responses to antidepressant treatment. The dependence of both negative (dysphoria-related) and positive (antidepressant-induced) behaviors on forebrain GR is consistent with the contradictory effects of glucocorticoids on mood, and implicates these or other forebrain regions in these effects.

A double-hit model of stress dysregulation in rats: implications for limbic corticosteroid receptors and anxious behavior under amitriptyline treatment

Adversity during early life can lead to diverging endocrine and behavioral responses to stress in adulthood. In our laboratory, we evaluated the long-term effects of early life adversity and its interaction with chronic stress during adulthood. We propose this as a model of vulnerability to dysregulation of the stress response. We hypothesized that rats subjected to both protocols would show differential expression of corticosteroid receptors measured as number of neurons immunoreactive for glucocorticoid receptors (GR) or mineralocorticoid receptors (MR), in limbic areas related to the control of anxiety-like behavior. We also evaluated the effect of amitriptyline expecting to prevent the outcomes of the model. Male Wistar rats were separated from the mother (MS) for 4.5 h every day for the first 3 weeks of life. From postnatal day 50, rats were subjected to chronic variable stress (CVS) during 24 d (five types of stressor at different times of day). During the stress protocol, the rats were administered amitriptyline (10 mg/kg i.p.) daily. MS evoked lower MR expression in the central amygdaloid nucleus and this was reversed by amitriptyline. Furthermore, CVS increased MR immunoreactivity in the hippocampal area CA2 and increased anxious behavior; both effects were prevented by the antidepressant. When MS was combined with CVS during adulthood, there was a reduction of locomotor activity, with no corrective effect of amitriptyline. The differential effects among groups could mean that MS would promote an alternative phenotype that is expressed when facing CVS (a double hit) later in life.