Time Course of Behavioral Alteration and mRNA Levels of Neurotrophic Factor Following Stress Exposure in Mouse

Chronic infection by atypical Toxoplasma gondii strain induces disturbance in microglia population and altered behaviour in mice

Toxoplasma gondii chronic infection is characterized by the establishment of tissue cysts in the brain and increased levels of IFN-γ, which can lead to brain circuitry interference and consequently abnormal behaviour in mice. In this sense, the study presented here sought to investigate the impact of chronic infection by two T. gondii strains in the brain of infection-resistant mice, as a model for studying the involvement of chronic neuroinflammation with the development of behavioural alterations. For that, male BALB/c mice were divided into three groups: non-infected (Ni), infected with T. gondii ME49 clonal strain (ME49), and infected with TgCkBrRN2 atypical strain (CK2). Mice were monitored for 60 days to establish the chronic infection and then submitted to behavioural assessment. The enzyme-linked immunosorbent assay was used for measurement of specific IgG in the blood and levels of inflammatory cytokines and neurotrophic factors in the brain, and the cell's immunophenotype was determined by multiparametric flow cytometry. Mice infected with ME49 clonal strain displayed hyperlocomotor activity and memory deficit, although no signs of depressive- and/or anxiety-like behaviour were detected; on the other hand, chronic infection with CK2 atypical strain induced anxiety- and depressive-like behaviour. During chronic infection by CK2 atypical strain, mice displayed a higher number of T. gondii brain tissue cysts and inflammatory infiltrate, composed mainly of CD3⁺ T lymphocytes and Ly6C^hi inflammatory monocytes, compared to mice infected with the ME49 clonal strain. Infected mice presented a marked decrease of microglia population compared to non-infected group. Chronic infection with CK2 strain produced elevated levels of IFN-γ and TNF-ɑ in the brain, decreased NGF levels in the prefrontal cortex and striatum, and altered levels of fractalkine (CX3CL1) in the prefrontal cortex and hippocampus. The persistent inflammation and the disturbance in the cerebral homeostasis may contribute to altered behaviour in mice, as the levels of IFN-γ were shown to be correlated with the behavioural parameters assessed here. Considering the high incidence and life-long persistence of T. gondii infection, this approach can be considered a suitable model for studying the impact of chronic infections in the brain and how it impacts in behavioural responses.

Direct evidence for the involvement of intestinal reactive oxygen species in the progress of depression via the gut-brain axis

Depression is a serious global social problem. Various therapeutic drugs have been developed based on the monoamine hypothesis; however, treatment-resistant depression is a common clinical issue. Recently, the gut-brain axis, which is associated with the hypothesis that the intestinal environment affects the brain, has garnered significant interest, and several studies have attempted to treat brain disorders based on this axis. These attempts include fecal transplantation, probiotics and prebiotics. In this study, we focused on intestinal reactive oxygen species (ROS) because excessive ROS levels disturb the intestinal environment. To elucidate the impact of scavenging intestinal ROS on depression treatment via the gut-brain axis, a novel polymer-based antioxidant (siSMAPo^TN), which was distributed only in the intestine and did not diffuse into the whole body after oral administration, was used. siSMAPo^TN selectively scavenged intestinal ROS and protected the intestinal environment from damage caused by chronic restraint stress (CRS). In addition, siSMAPo^TN suppressed physiological and behavioral depression-related symptoms in the CRS mouse model.

Ryanodine receptors are involved in the improvement of depression-like behaviors through electroconvulsive shock in stressed mice

BACKGROUND

Electroconvulsive therapy (ECT) is effective for treating depression. However, the mechanisms underlying the antidepressant effects of ECT remain unknown. Depressed patients exhibit abnormal Ca²⁺ kinetics. Early stages of the intracellular Ca²⁺ signaling pathway involve the release of Ca²⁺ from the endoplasmic reticulum (ER) via Ca²⁺ release channels.

OBJECTIVE

We considered that depression may be improved via ECT-induced normalization of intracellular Ca²⁺ regulation through the Ca²⁺ release channels. The current study aimed to investigate the effects of ECT on two Ca²⁺ release channels, ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP₃Rs).

METHODS

A mouse depression-like model subjected to water immersion with restraint stress was administered electroconvulsive shock (ECS) therapy. Their depression-like status was behaviorally and histologically assessed using forced swimming tests, novelty-suppressed feeding tests, and by evaluating neurogenesis in the hippocampal dentate gyrus, respectively. A RyRs blocker, dantrolene, was administered prior to ECS, and the changes in depression-like conditions were examined.

RESULTS

The protein expressions of RyR1 and RyR3 significantly increased in the hippocampus of the mouse model with depression-like symptoms. This increase was attenuated as depression-like symptoms were reduced due to ECS application. However, pre-injection with dantrolene reduced the antidepressant effects of ECS.

CONCLUSIONS

A significant increase in RyRs expression in a depression-like state and exacerbation of depression-like symptoms by RyRs inhibitors may be caused by RyRs dysfunction, suggesting overexpression of RyRs is a compensatory effect. Normalization of RyRs expression levels by ECS suggests that ECT normalizes the Ca²⁺ release via RyRs. Thus, normalizing the function of RyRs may play an important role in the therapeutic effect of ECT.

Long-term stability and characteristics of behavioral, biochemical, and molecular markers of three different rodent models for depression

OBJECTIVE

The present study was designed to explore the long-term differences between three mouse models for depression.

METHOD

In the present study, the unpredictable chronic mild stress (UCMS) model, the glucocorticoid/corticosterone model, and the olfactory bulbectomy model were compared at two, three, and five weeks after model induction. Behavioral testing performed included forced-swimming, tail suspension, open-field and elevated plus-maze tests. In addition, 5-hydroxytryptamine (5-HT) and dopamine levels, and mRNA and protein expressions related to 5-HT synthesis, transport, and signaling were analyzed in the hippocampus of tested animals.

RESULTS

Our results revealed that each model demonstrated a specific profile of markers, whereas the stability of them differed over testing time.

CONCLUSIONS

Each model provided a unique set of advantages that can be considered depending on the context and aims of each study. Among the three models, the UCMS model was mostly stable and appeared to the best model for testing long-term depression-like state.

Preliminary investigation of the effect of oral supplementation of Lactobacillus plantarum strain SNK12 on mRNA levels of neurotrophic factors and GABA receptors in the hippocampus of mice under stress-free and sub-chronic mild social defeat-stressing conditions

The effect of Lactobacillus plantarum SNK12 (CPLP) supplementation on mRNA levels of hippocampal neurotrophic factors and gamma aminobutyric acid receptors (GABA_R) was tested. In Experiment 1, stress-free, unsupplemented and CPLP (4 × 10⁸ cells/head)-supplemented male C57BL/6J (B6) mice were the experimental animals. In Experiment 2, intruder (male, B6) mice [negative control; unsupplemented, sub-chronic mild social defeat stress (sCSDS)-induced; and CPLP-supplemented, sCSDS-induced] were exposed to aggressor mice (adult male Slc:ICR). mRNA levels of neurotrophic factors and GABA_R in hippocampal samples of these mice were analyzed. In CPLP-supplemented mice of both experiments, mRNA levels of bdnf, nt-3, and GABA_R were upregulated. Moreover, a tendency toward the improvement of habituation ability (Experiment 1) and behavior (Experiment 2) was observed in mice, which may be associated with upregulated neurotrophic factors and GABA_R. We demonstrated that oral supplementation of CPLP to stress-free and stress-induced mice upregulated mRNA levels of hippocampal neurotrophic factors and GABA_R.

Roman chamomile inhalation combined with clomipramine treatment improves treatment-resistant depression-like behavior in mice

It is well known that chamomile is one of the oldest known medicinal herbs and has been used to treat various disorders, but it is mainly German chamomile. The effects of Roman chamomile on depression still unclear. In this study, we used chronically stressed mice to investigate whether inhalation of Roman chamomile essential oil affects depression-like behavior. We previously reported that restraint and water immersion stress produce depression-like behavior and a blunted response to the tricyclic antidepressant clomipramine. Each mouse was exposed to restraint and water immersion stress for 15 days, and resistance to the effect of clomipramine was induced in a behavioral despair paradigm. In the present study, we found that cotreatment with clomipramine and inhalation of Roman chamomile attenuated depression-like behavior in a forced swim test. Next, we examined the hippocampal mRNA levels of two cytokines, tumor necrosis factor (TNF) alpha and interleukin-6 (IL-6); a neurotrophic factor, brain derived-neurotrophic factor (BDNF); and nerve growth factor (NGF). TNF alpha, IL-6 and BDNF mRNA levels did not change in the hippocampus of stressed mice. However, the NGF mRNA level was significantly decreased, and this decrease was not attenuated by treatment with clomipramine or inhalation of Roman chamomile alone. We also examined whether Roman chamomile combined with clomipramine treatment affects hippocampal neurogenesis and serum corticosterone levels. Stressed mice had fewer doublecortin (DCX)-positive cells in the subgranular zone of the dentate gyrus, but this was significantly attenuated by Roman chamomile and clomipramine treatment. In addition, the serum corticosterone level was also significantly decreased by treatment with Roman chamomile and clomipramine. These results suggest that Roman chamomile inhalation may enhance the antidepressant effect of clomipramine by increasing hippocampal neurogenesis and modulating corticosterone levels in patients with treatment-resistant depression.

Enduring Effects of Paternal Deprivation in California Mice (Peromyscus californicus): Behavioral Dysfunction and Sex-Dependent Alterations in Hippocampal New Cell Survival

Early-life experiences with caregivers can significantly affect offspring development in human and non-human animals. While much of our knowledge of parent-offspring relationships stem from mother-offspring interactions, increasing evidence suggests interactions with the father are equally as important and can prevent social, behavioral, and neurological impairments that may appear early in life and have enduring consequences in adulthood. In the present study, we utilized the monogamous and biparental California mouse (Peromyscus californicus). California mouse fathers provide extensive offspring care and are essential for offspring survival. Non-sibling virgin male and female mice were randomly assigned to one of two experimental groups following the birth of their first litter: (1) biparental care: mate pairs remained with their offspring until weaning; or (2) paternal deprivation (PD): paternal males were permanently removed from their home cage on postnatal day (PND) 1. We assessed neonatal mortality rates, body weight, survival of adult born cells in the dentate gyrus of the hippocampus, and anxiety-like and passive stress-coping behaviors in male and female young adult offspring. While all biparentally-reared mice survived to weaning, PD resulted in a ~35% reduction in survival of offspring. Despite this reduction in survival to weaning, biparentally-reared and PD mice did not differ in body weight at weaning or into young adulthood. A sex-dependent effect of PD was observed on new cell survival in the dentate gyrus of the hippocampus, such that PD reduced cell survival in female, but not male, mice. While PD did not alter classic measures of anxiety-like behavior during the elevated plus maze task, exploratory behavior was reduced in PD mice. This observation was irrespective of sex. Additionally, PD increased some passive stress-coping behaviors (i.e., percent time spent immobile) during the forced swim task—an effect that was also not sex-dependent. Together, these findings demonstrate that, in a species where paternal care is not only important for offspring survival, PD can also contribute to altered structural and functional neuroplasticity of the hippocampus. The mechanisms contributing to the observed sex-dependent alterations in new cell survival in the dentate gyrus should be further investigated.

Role of Glia in Stress-Induced Enhancement and Impairment of Memory

Both acute and chronic stress profoundly affect hippocampally-dependent learning and memory: moderate stress generally enhances, while chronic or extreme stress can impair, neural and cognitive processes. Within the brain, stress elevates both norepinephrine and glucocorticoids, and both affect several genomic and signaling cascades responsible for modulating memory strength. Memories formed at times of stress can be extremely strong, yet stress can also impair memory to the point of amnesia. Often overlooked in consideration of the impact of stress on cognitive processes, and specifically memory, is the important contribution of glia as a target for stress-induced changes. Astrocytes, microglia, and oligodendrocytes all have unique contributions to learning and memory. Furthermore, these three types of glia express receptors for both norepinephrine and glucocorticoids and are hence immediate targets of stress hormone actions. It is becoming increasingly clear that inflammatory cytokines and immunomodulatory molecules released by glia during stress may promote many of the behavioral effects of acute and chronic stress. In this review, the role of traditional genomic and rapid hormonal mechanisms working in concert with glia to affect stress-induced learning and memory will be emphasized.