Modulation of behavioral and hippocampal transcriptomic responses in rat prolonged chronic unpredictable stress model by fluoxetine, eicosapentaenoic acid and lipopolysaccharide

Animal models are widely used to study common stress-induced affective disorders, such as anxiety and depression. Here, we examine behavioral and brain transcriptomic (RNA-seq) responses in rat prolonged chronic unpredictable stress (PCUS) model, and their modulation by 4-week treatment with fluoxetine, eicosapentaenoic acid (EPA), lipopolysaccharide (LPS) and their combinations. Overall, chronic stress produced anxiety-like phenotype, corrected by fluoxetine alone or in combination with EPA or LPS. EPA was anxiolytic in several tests, whereas LPS alone increased anxiety. PCUS evoked pronounced transcriptomic changes in rat hippocampi, differentially expressing >200 genes, while all pharmacological manipulations (except fluoxetine+EPA) affected only few genes. Gpr6, Drd2 and Adora2a were downregulated by chronic stress in a treatment-resistant manner, suggesting highly conserved nature of these pathogenetic genomic responses to chronic stress. Overall, these findings support the validity of rat PCUS paradigm as an effective tool to study stress-related pathologies, and calls for further research to probe how various conventional and novel drugs modulate behavioral and brain transcriptomic biomarkers of chronic stress in rodent models.

The biochemical estimation of the nitric oxide system in prenatally stressed rats

Introduction. Pregnancy development following unfavorable conditions could facilitate disorders of nitric oxide (NO) production during offspring’s postnatal life and «program» offspring’s cardiovascular diseases. Investigation of particular features and mechanisms of nitric oxide synthesis and action disorders following prenatal stress will promote expansion of considerations about pathogenesis of different cardiovascular diseases and propose new approaches to their prevention and management.The aim of the investigation is to assess the nature of nitric oxide synthesis and action in mature rats whose mothers were exposed to chronic «unpredictable» stress during pregnancy. Materials and methods. Pregnant rats were subdivided into the «control» and «stress» groups (in 20 animals). The rats from the «stress» group were exposed to multiple different stressors at various intervals, such as 1-day famine; 20-min. immobilization in the water at room temperature; 1-day contact with cats’ excrements. In the blood serum of 3-mo offspring (n=96, including «control» males – 24, «control» females – 26, «stress» males – 22, «stress» females – 24) concentration of the stable products of NO degradation – nitrates/nitrites (NO3–/NO2–), endothelial (eNOS) and inducible (iNOS) isoforms of the NO-synthase, inhibitor of NO-synthase asymmetric dimethylargininne (ADMA), cyclic guanosine monophosphate (cGMP), lipid peroxidation products – diene conjugates (DC) and malonic dialdehyde (MDA) and C-reactive protein (hsCRP) was detected. Results. The decrease of eNOS and cGMP concentration (by 12.9 and 31.9 %, respectively), increase of iNOS, hsCRP and ADMA concentration (by 49.9, 20.3 и 63.1 %, respectively) without statistically significant fluctuation in the NO3–/NO2– level and accumulation of DC and MDA by 21.1 % and 1.5 times in a prenatally stressed male rats’ blood serum were found (as compared with «control» male rats). In a blood serum of female rats, whose mothers were exposed to chronic «unpredictable» stress during pregnancy, a tendency to eNOS concentration decreasing, and increase of iNOS by 30.6 %, hsCRP by 23.9 % and MDA by 2.3 times without statistically significant changes in cGMP, ADMA, NO3–/NO2–, and DC concentration were detected (as compared with «control» female rats). Conclusion. Identified changes of the nitric oxide system synthesis and action in the prenatally stressed male rats could argue the high risk of their cardiovascular system lesion.

Chronic Unpredictable Stress Alters Brain Tryptophan Metabolism and Impairs Working Memory in Mice without Causing Depression-Like Behaviour

Chronic stress is a well-known risk factor in major depressive disorder and disrupts the kynurenine and serotonin pathways of tryptophan metabolism. Here, we characterize the temporal central and peripheral changes in tryptophan metabolism and concomitant depressive-like behavioural phenotype induced during the progression of chronic unpredictable stress (CUS). Mice were exposed to 0, 10, 20, or 30 days of CUS followed by a panel of behavioural assays to determine depressive-like phenotypes. Immediately after behavioural testing, plasma and brain tissue were collected for metabolic analysis. While anhedonia-like and anxiety-like behaviours were unaffected by stress, nesting behaviour and cognitive deficits became apparent in response to CUS exposure. While CUS caused a transient reduction in circulating quinolinic acid, no other tryptophan metabolites significantly changed in response to CUS. In the brain, tryptophan, kynurenine, picolinic acid, and 5-hydroxyindoleacetic acid concentrations were significantly elevated in CUS-exposed mice compared with non-stress control animals, while kynurenic acid, xanthurenic acid, and serotonin decreased in CUS-exposed mice. Metabolic turnover of serotonin to the major metabolite 5-hydroxyindoleacetic acid was markedly increased in response to CUS. These results suggest that CUS impairs hippocampal-dependent working memory and enhances nascent nesting behaviour in C57BL/6J male mice, and these behaviours are associated with increased brain kynurenine pathway metabolism leading to accumulation of picolinic acid and a significant reduction in serotonin levels.

Beneficial effects of running exercise on hippocampal microglia and neuroinflammation in chronic unpredictable stress-induced depression model rats

Running exercise has been shown to relieve symptoms of depression, but the mechanisms underlying the antidepressant effects are unclear. Microglia and concomitant dysregulated neuroinflammation play a pivotal role in the pathogenesis of depression. However, the effects of running exercise on hippocampal neuroinflammation and the number and activation of microglia in depression have not been studied. In this study, rats were subjected to chronic unpredictable stress (CUS) for 5 weeks followed by treadmill running for 6 weeks. The depressive-like symptoms of the rats were assessed with a sucrose preference test (SPT). Immunohistochemistry and stereology were performed to quantify the total number of ionized calcium-binding adapter molecule 1 (Iba1)+ microglia, and immunofluorescence was used to quantify the density of Iba1+/cluster of differentiation 68 (CD68)+ in subregions of the hippocampus. The levels of proinflammatory cytokines in the hippocampus were measured by qRT-PCR and ELISA. The results showed that running exercise reversed the decreased sucrose preference of rats with CUS-induced depression. In addition, CUS increased the number of hippocampal microglia and microglial activation in rats, but running exercise attenuated the CUS-induced increases in the number of microglia in the hippocampus and microglial activation in the dentate gyrus (DG) of the hippocampus. Furthermore, CUS significantly increased the hippocampal levels of inflammatory factors, and the increases in inflammatory factors in the hippocampus were suppressed by running exercise. These results suggest that the antidepressant effects of exercise may be mediated by reducing the number of microglia and inhibiting microglial activation and neuroinflammation in the hippocampus.

Ginsenoside Rg1 Ameliorates Neuroinflammation via Suppression of Connexin43 Ubiquitination to Attenuate Depression

Depression is an inflammation-associated disease that results in major depression as inflammation increases and progresses. Ginsenoside Rg1 (Rg1), the major bioactive ingredient derived from ginseng, possesses remarkable anti-depressant and anti-inflammatory effects. Our previous studies showed that the pathogenesis of depression was concomitant with the acceleration of connexin43 (Cx43) ubiquitin degradation, while Rg1 could upregulate Cx43 expression to attenuate depression. However, whether the ubiquitination of Cx43 is the specific correlation between depression and inflammation, and how Rg1 ameliorates neuroinflammation to attenuate depression, are still under investigation. In in vivo experiments, Rg1 treatment significantly ameliorated depression-like behaviors in rats subjected to chronic unpredictable stress (CUS). Moreover, these CUS rats treated with Rg1 exhibited attenuated neuroinflammation, together with the suppression of Cx43 ubiquitination. In in vitro experiments, Rg1 reduced the secretion of inflammatory cytokines and the ubiquitination of Cx43 in lipopolysaccharide-induced glial cells. Furthermore, treatment with ubiquitin-proteasome inhibitor MG132 suppressing the ubiquitination of Cx43 ameliorated lipopolysaccharide-induced neuroinflammation. The results suggest that Rg1 attenuates depression-like behavioral performances in CUS-exposed rats; and the main mechanism of the antidepressant-like effects of Rg1 appears to involve protection against neuroinflammation via suppression of Cx43 ubiquitination. In conclusion, Rg1 could ameliorate neuroinflammation via suppression of Cx43 ubiquitination to attenuate depression, which represents the perspective of an innovative therapy of Rg1 in the treatment of inflammation-associated depression.

Modulation of behavioral and neurochemical responses of adult zebrafish by fluoxetine, eicosapentaenoic acid and lipopolysaccharide in the prolonged chronic unpredictable stress model

Long-term recurrent stress is a common cause of neuropsychiatric disorders. Animal models are widely used to study the pathogenesis of stress-related psychiatric disorders. The zebrafish (Danio rerio) is emerging as a powerful tool to study chronic stress and its mechanisms. Here, we developed a prolonged 11-week chronic unpredictable stress (PCUS) model in zebrafish to more fully mimic chronic stress in human populations. We also examined behavioral and neurochemical alterations in zebrafish, and attempted to modulate these states by 3-week treatment with an antidepressant fluoxetine, a neuroprotective omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA), a pro-inflammatory endotoxin lipopolysaccharide (LPS), and their combinations. Overall, PCUS induced severe anxiety and elevated norepinephrine levels, whereas fluoxetine (alone or combined with other agents) corrected most of these behavioral deficits. While EPA and LPS alone had little effects on the zebrafish PCUS-induced anxiety behavior, both fluoxetine (alone or in combination) and EPA restored norepinephrine levels, whereas LPS + EPA increased dopamine levels. As these data support the validity of PCUS as an effective tool to study stress-related pathologies in zebrafish, further research is needed into the ability of various conventional and novel treatments to modulate behavioral and neurochemical biomarkers of chronic stress in this model organism.