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 11β-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.

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-1β, 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.

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.

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.

Relationships between antenatal corticosteroids and catecholamine blood pressure support in neonates: considering of maternal stress-related diseases

Healthy child development is under the influence of prenatal and perinatal exposure to stress stimuli. The aim of this study is to test the hypotheses that (1) neonates requiring catecholamine blood pressure support are more often born to mothers with stress-related cardiometabolic diseases, (2) maternal stress-related diseases are associated with more frequent requirement of maternal corticosteroid treatment and (3) antenatal steroid exposure of neonates reduces the need of postnatal catecholamine support. A retrospective cohort study was performed on a sample of 427 mature (13%), preterm (64%) and extremely preterm (23%) neonates of both sexes. Mothers at risk of preterm delivery were treated with dexamethasone. The blood pressure support in neonates was performed by intravenous treatment via umbilical or epicutaneous venous catheter with dopamine (5 ug/kg/min) or dobutamine (5 ug/kg/min) or a combination of both. The results showed a lack of association between maternal stress-related diseases and the complicated outcome of their neonates. Maternal treatment with corticosteroid dexamethasone was associated with lower frequency of catecholamine blood pressure support requirement. Catecholamine support was more needed in male infants. Thus, the occurrence of maternal cardiometabolic stress-related diseases does not appear to be related to the need of catecholamine support in the neonate. In agreement with the second hypothesis, a more frequent maternal corticosteroid treatment was associated with the presence of maternal stress-related diseases. Most importantly, the obtained results support the hypothesis on positive influence of maternal glucocorticoid administration on cardiovascular outcome of the neonate, representing an additional beneficial effect of antenatal corticosteroids. LAY SUMMARY Maternal hypertension, diabetes and obesity, which belong to cardiometabolic stress-related diseases, failed to show a negative influence on neonatal health as was determined by the need of catecholamine blood pressure support in a large sample of 427 immature and mature newborns. Since glucocorticoids are often viewed as negative agents that should be avoided, the important finding of the present study is the beneficial effect of maternal corticosteroid treatment on blood pressure stability of the neonate.

Dopamine concentrations and dopamine receptor gene expression in emotion-related brain structures of female adult rats exposed to stress of chronic isolation from weaning

It is known that early-life stress events induce profound consequences on emotional brain regions including amygdala, involved in emotional processing and the ventral tegmental area (VTA), which contains neuron cell bodies of the mesolimbic dopaminergic system. The aim of this study is to test the hypothesis that stress induced by long-term social isolation from weaning in female rats is associated with alterations in amygdalar dopamine receptor gene expression and VTA dopamine concentrations. Rats were weaned on postnatal day 21 and then exposed to stress of chronic isolation for 9 weeks. Control animals were housed socially. Amygdalar dopamine D1 but not D2 receptor gene expression was decreased in isolated rats compared to controls. Dopamine concentrations in the VTA were enhanced following chronic isolation. A negative correlation was observed between amygdalar D1 gene expression and dopamine concentrations in the VTA. In conclusion, a reduction of dopamine D1 receptor gene expression in the amygdala in response to stress induced by chronic isolation in female rats was accompanied by an increase in dopamine concentration in the VTA. Further studies are needed to understand the physiological significance, if any, of negative association of amygdalar dopamine receptor D1 gene expression and dopamine concentrations in the VTA.