Environmental enrichment reduces adolescent anxiety- and depression-like behaviors of rats subjected to infant nerve injury

An investigation on the role of oxytocin in chronic neuropathic pain in a Wistar rat model

Introduction Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect with ineffective preventative and curative treatment. Currently, only Duloxetine has been recommended as effective treatment for CIPN, which has shown individual-dependent, short-term analgesic effects, with limiting adverse effects and poor bioavailability. The neuropeptide, oxytocin, may offer significant analgesic and anxiolytic potential, as it exerts central and peripheral attenuating effects on nociception. However, it is unknown whether the intervention administered in a model of CIPN is an effective therapeutic alternative or adjuvant. Materials and Methods The intervention was divided into two phases. Phase 1 aimed to induce CIPN in adult Wistar rats using the chemotherapeutic agent Paclitaxel. Mechanical (electronic von Frey filament) and thermal (acetone evaporation test and Hargreaves test) hypersensitivity testing were used to evaluate changes due to the neuropathic induction. Phase 2 consisted of a 14-day intervention period with saline (o.g.), duloextine (o.g.), or oxytocin (i.n.) administered as treatment. Following the intervention, anxiety-like behaviour was assessed using the elevated plus maze (EPM) and light-dark box protocols. Analysis of peripheral plasma corticosterone, peripheral plasma oxytocin, and hypothalamic oxytocin concentrations were assessed using ELISA assays. Results The findings showed that we were able to successfully establish a model of chemotherapy-induced peripheral neuropathy during Phase 1, determined by the increase in mechanical and thermal nociceptive responses following Paclitaxel administration. Furthermore, the animals treated with oxytocin displayed a significant improvement in mechanical sensitivity over the intervention phase, indicative of an improvement in nociceptive sensitivity in the presence of neuropathic pain. Animals that received Paclitaxel and treated with oxytocin also displayed significantly greater explorative behaviour during the EPM, indicative of a reduced presence of anxiety-like behaviour. Conclusion Our results support the hypothesis that intranasally administered oxytocin may augment the analgesic and anxiolytic effects of duloxetine in a chemotherapy induced peripheral neuropathy model in a Wistar rat. Future studies should consider administering the treatments in combination to observe the potential synergistic effects.

Effects of Exercise Training and L-Arginine Loaded Chitosan Nanoparticles on Hippocampus Histopathology, β-Secretase Enzyme Function, APP, Tau, Iba1and APOE-4 mRNA in Aging Rats

The objective of this study was to evaluate the combined and independent effects of exercise training and L-Arginine loaded chitosan nanoparticles (LA CNPs) supplementation on hippocampal Tau, App, Iba1, and ApoE gene expression, oxidative stress, β-secretase enzyme activity, and hippocampus histopathology in aging rats. Thirty-five male Wistar rats were randomly assigned to five groups (n = 7 in each): Young (8 weeks old), Old (20 months old), old + L-arginine supplementation (Old Sup), old + exercise (Old Exe) and old + L-arginine supplementation + exercise (Old Sup + Exe). LA CNPs were administered to the supplement groups through gavage at a dosage of 500 mg/kg/day for 6-weeks. Exercise groups were subjected to a swimming exercise program five days/week for the same duration. Upon the completion of their interventions, the animals underwent behavioral and open-field task tests and were subsequently sacrificed for hippocampus genetic and histopathological evaluation. For histopathological analysis of brain, Cresyl violet staining was used. Congo Red staining was employed to confirm amyloid plaques in the hippocampus. Expressions of Tau, App, Iba1, and ApoE genes were determined by real-time PCR. In contrast to the Old group, Old Exe and Old Sup + Exe groups spent more time in the central space in the open field task (p < 0.05) and have more live cells in the hippocampus. Old rats (Old, Old Sup and Old Exe groups) exhibited a significant Aβ peptide accumulation and increases in APP, Tau, Iba1, APOE-4 mRNA and MDA, along with decreases in SOD compared to the young group (p < 0.05). However, LA CNPs supplementation, exercise, and their combination (Old Sup, Old Exe and Old Sup + Exe) significantly reduced MDA, Aβ plaque as well as APP, Tau, Iba1, and APOE-4 mRNA compared to the Old group (p < 0.05). Consequently, the administration of LA CNPs supplements and exercise might regulate the risk factors of hippocampus cell and tissue.

Environmental factors and their impact on chronic pain development and maintenance

It is more than recognized and accepted that the environment affects the physiological responses of all living things, from bacteria to superior vertebrates, constituting an important factor in the evolution of all species. Environmental influences range from natural processes such as sunlight, seasons of the year, and rest to complex processes like stress and other mood disorders, infections, and air pollution, being all of them influenced by how each creature deals with them. In this chapter, it will be discussed how some of the environmental elements affect directly or indirectly neuropathic pain, a type of chronic pain caused by a lesion or disease of the somatosensory nervous system. For that, it was considered the edge of knowledge in translational research, thus including data from human and experimental animals as well as the applicability of such findings.

Digital Therapeutics for Improving Effectiveness of Pharmaceutical Drugs and Biological Products: Preclinical and Clinical Studies Supporting Development of Drug + Digital Combination Therapies for Chronic Diseases

Limitations of pharmaceutical drugs and biologics for chronic diseases (e.g., medication non-adherence, adverse effects, toxicity, or inadequate efficacy) can be mitigated by mobile medical apps, known as digital therapeutics (DTx). Authorization of adjunct DTx by the US Food and Drug Administration and draft guidelines on "prescription drug use-related software" illustrate opportunities to create drug + digital combination therapies, ultimately leading towards drug-device combination products (DTx has a status of medical devices). Digital interventions (mobile, web-based, virtual reality, and video game applications) demonstrate clinically meaningful benefits for people living with Alzheimer's disease, dementia, rheumatoid arthritis, cancer, chronic pain, epilepsy, depression, and anxiety. In the respective animal disease models, preclinical studies on environmental enrichment and other non-pharmacological modalities (physical activity, social interactions, learning, and music) as surrogates for DTx "active ingredients" also show improved outcomes. In this narrative review, we discuss how drug + digital combination therapies can impact translational research, drug discovery and development, generic drug repurposing, and gene therapies. Market-driven incentives to create drug-device combination products are illustrated by Humira® (adalimumab) facing a "patent-cliff" competition with cheaper and more effective biosimilars seamlessly integrated with DTx. In conclusion, pharma and biotech companies, patients, and healthcare professionals will benefit from accelerating integration of digital interventions with pharmacotherapies.

Toll-like Receptor 2-Melatonin Feedback Loop Regulates the Activation of Spinal NLRP3 Inflammasome in Morphine-Tolerant Rats

BACKGROUND AND PURPOSE

Morphine is amongst the most effective analgesics available for the management of severe pain. However, prolonged morphine treatment leads to analgesic tolerance which limits its clinical usage. Previous studies have demonstrated that melatonin ameliorates morphine tolerance by reducing neuroinflammation. However, little is known about the relationship between Toll like receptor 2 (TLR2) and neuroinflammation in morphine tolerance. The aim of this study was to explore the role of TLR2 in morphine tolerance and its connections with melatonin and Nod-like receptor protein 3 (NLRP3) inflammasome.

METHODS

Sprague-Dawley rats were treated with morphine for 7 days and tail-flick latency test was performed to identify the induction of analgesic tolerance. The roles of TLR2 in microglia activation and morphine tolerance were assessed pharmacologically, and the possible interactions between melatonin, TLR2 and NLRP3 inflammasome were investigated.

KEY RESULTS

Morphine tolerance was accompanied by increased TLR2 expression and NLRP3 inflammasome activation in spinal cord. whereas melatonin level was down-regulated. Chronic melatonin administration resulted in a reduced TLR2 expression and NLRP3 inflammasome activation. Moreover, the analgesic effect of morphine was partially restored. Inhibition of TLR2 suppressed the microglia and NLRP3 inflammasome activation, as well as restored the spinal melatonin level while attenuated the development of morphine tolerance. Furthermore, the inhibition of microglia activation ameliorated morphine tolerance via inhibiting TLR2-NLRP3 inflammasome signaling in spinal cord.

CONCLUSION

In this study, we directly demonstrate a TLR2-melatonin negative feedback loop regulating microglia and NLRP3 inflammasome activation during the development of morphine tolerance.

Diazepam and exercise training combination synergistically reduces lipopolysaccharide-induced anxiety-like behavior and oxidative stress in the prefrontal cortex of mice

Anxiety-related disorders are among the most important risks for global health, especially in recent years due to the COVID-19 pandemic. Benzodiazepines like diazepam are generally used to treat anxiety disorders, but the overall outcome is not always satisfactory. This is why psychiatrists encourage patients with anxiety to change their lifestyle habits to decrease the risk of anxiety recurrence. However, the effect of diazepam and exercise in combination is unknown. This study aimed to investigate the effect of diazepam alone or in combination with swimming exercise on lipopolysaccharide (LPS)-induced anxiety-like behavior and oxidative stress in the hippocampus and prefrontal cortex of mice. Mice were exposed to diazepam and swimming exercise alone or in combination with each other and then received LPS. We assessed anxiety-like behavior using open field and light-dark box and measured oxidative markers including glutathione (GSH), malondialdehyde (MDA), and glutathione disulfide (GSSG) in the hippocampus and prefrontal cortex. The findings showed that LPS increased anxiety-related symptoms and oxidative stress by decreasing GSH and increasing MDA and GSSG levels in the prefrontal cortex but not in the hippocampus. Although diazepam alone did not reduce anxiety-like behavior and oxidative stress, it in combination with exercise significantly decreased anxiety-like behavior and oxidative stress in the prefrontal cortex of LPS-treated mice. This drug and exercise combination also displayed a more effective effect in comparison with exercise alone. Overall, this study suggests that diazepam in combination with swimming exercise has higher efficacy on anxiety-like behavior and oxidative stress than when they are used alone.

Preterm rat survival is enhanced by gestational environmental enrichment

Throughout the last decade, the estimated global human preterm birth rate was 10.6 %, with higher rates in Asia, South America, and Africa. Preterm individuals, even in adulthood, are more likely to develop cardiorespiratory, renal, and metabolic disorders. On the other hand, when experimental animals are housed in an enriched environment during gestation, the development of the progeny in utero is accelerated, compared to standard housing conditions. By terminating gestation one and a half days before parturition, we investigated whether environmental enrichment restricted to gestation may have an impact on progeny survival. Our results demonstrate that the gestational enriched environment tripled the rat´s offspring survival, which was associated with decreased expression of anxiety-like behaviors in the pregnant mother. Sex of the offspring was not a factor in determining survival. We discuss the effect of increased secretion of various trophic factors and hormones induced by the enriched environment on progeny survival.

Long-term environmental enrichment overcomes depression, learning, and memory impairment in elderly CD-1 mice with maternal sleep deprivation exposure

Early-life stress disrupts central nervous system development and increases the risk of neuropsychiatric disorder in offspring based on rodent studies. Maternal sleep deprivation (MSD) in rodents has also been associated with depression and cognitive decline in adult offspring. However, it is not known whether these issues persist into old age. Environmental enrichment is a non-pharmacological intervention with proven benefits in improving depression and cognitive impairment; however, it is unclear whether these benefits hold for aging mice following MSD exposure. The aim of this study was to explore the effects of MSD on depression and cognition in elderly offspring CD-1 mice and to determine whether long-term environmental enrichment could alleviate these effects by improving neuroinflammation and synaptic plasticity. The offspring mice subjected to MSD were randomly assigned to either a standard environment or an enriched environment. At 18 months of age, the forced swimming and tail suspension tests were used to evaluated depression-like behaviors, and the Morris water maze test was used to evaluate cognitive function. The expression levels of hippocampal proinflammatory cytokines and synaptic plasticity-associated proteins were also measured. MSD increased depression-like behaviors and impaired cognition function in aging CD-1 offspring mice. These effects were accompanied by upregulated interleukin (IL)-1β, IL-6, and tumor necrosis factor-α expression, and downregulated brain-derived neurotrophic factor, tyrosine kinase receptor B, postsynaptic density-95, and synaptophysin expression in the hippocampus. All of these changes were reversed by long-term exposure to an enriched environment. These findings suggest that MSD exerts long-term effects on the behaviors of offspring in mice, leading to depression and cognitive impairment in older age. Importantly, long-term environmental enrichment could counteract the behavior difficulties induced by MSD through improving hippocampal proinflammatory cytokines and synaptic plasticity-associated proteins.

The Molecular Effects of Environmental Enrichment on Alzheimer's Disease

Environmental enrichment (EE) is an environmental paradigm encompassing sensory, cognitive, and physical stimulation at a heightened level. Previous studies have reported the beneficial effects of EE in the brain, particularly in the hippocampus. EE improves cognitive function as well as ameliorates depressive and anxiety-like behaviors, making it a potentially effective neuroprotective strategy against neurodegenerative diseases such as Alzheimer's disease (AD). Here, we summarize the current evidence for EE as a neuroprotective strategy as well as the potential molecular pathways that can explain the effects of EE from a biochemical perspective using animal models. The effectiveness of EE in enhancing brain activity against neurodegeneration is explored with a view to differences present in early and late life EE exposure, with its potential application in human being discussed. We discuss EE as one of the non pharmacological approaches in preventing or delaying the onset of AD for future research.

Beneficial effects and neurobiological aspects of environmental enrichment associated to major depressive disorder and autism spectrum disorder

A suitable enriched environment favors development but can also influence behavior and neuronal circuits throughout development. Studies have shown that environmental enrichment (EE) can be used as an essential tool or combined with conventional treatments to improve psychiatric and neurological symptoms, including major depressive disorder (MDD) and autism spectrum disorder (ASD). Both disorders affect a significant percentage of the world's population and have complex pathophysiology. Moreover, the available treatments for MDD and ASD are still inadequate for many affected individuals. Experimental models demonstrate that EE has significant positive effects on behavioral modulation. In addition, EE has effects on neurobiology, including improvement in synaptic connections and neuroplasticity, modulation of neurotransmissions, a decrease in inflammation and oxidative stress, and other neurobiology effects that can be involved in the pathophysiology of MDD and ASD. Thus, this review aims to describe the leading behavioral and neurobiological effects associated with EE in MDD and ASD.

Monoamine Neurotransmitters Control Basic Emotions and Affect Major Depressive Disorders

Major depressive disorder (MDD) is a common and complex mental disorder, that adversely impacts an individual’s quality of life, but its diagnosis and treatment are not accurately executed and a symptom-based approach is utilized in most cases, due to the lack of precise knowledge regarding the pathophysiology. So far, the first-line treatments are still based on monoamine neurotransmitters. Even though there is a lot of progress in this field, the mechanisms seem to get more and more confusing, and the treatment is also getting more and more controversial. In this study, we try to review the broad advances of monoamine neurotransmitters in the field of MDD, and update its effects in many advanced neuroscience studies. We still propose the monoamine hypothesis but paid special attention to their effects on the new pathways for MDD, such as inflammation, oxidative stress, neurotrophins, and neurogenesis, especially in the glial cells, which have recently been found to play an important role in many neurodegenerative disorders, including MDD. In addition, we will extend the monoamine hypothesis to basic emotions; as suggested in our previous reports, the three monoamine neurotransmitters play different roles in emotions: dopamine—joy, norepinephrine—fear (anger), serotonins—disgust (sadness). Above all, this paper tries to give a full picture of the relationship between the MDD and the monoamine neurotransmitters such as DA, NE, and 5-HT, as well as their contributions to the Three Primary Color Model of Basic Emotions (joy, fear, and disgust). This is done by explaining the contribution of the monoamine from many sides for MDD, such the digestive tract, astrocytes, microglial, and others, and very briefly addressing the potential of monoamine neurotransmitters as a therapeutic approach for MDD patients and also the reasons for its limited clinical efficacy, side effects, and delayed onset of action. We hope this review might offer new pharmacological management of MDD.

Olfactory loss is a predisposing factor for depression, while olfactory enrichment is an effective treatment for depression

The loss of olfactory stimulation correlates well with at least 68 widely differing neurological disorders, including depression, and we raise the possibility that this relationship may be causal. That is, it seems possible that olfactory loss makes the brain vulnerable to expressing the symptoms of these neurological disorders, while daily olfactory enrichment may decrease the risk of expressing these symptoms. This situation resembles the cognitive reserve that is thought to protect people with Alzheimer’s neuropathology from expressing the functional deficit in memory through the cumulative effect of intellectual stimulation. These relationships also resemble the functional response of animal models of human neurological disorders to environmental enrichment, wherein the animals continue to have the induced neuropathology, but do not express the symptoms as they do in a standard environment with restricted sensorimotor stimulation.

Behavioral effects of environmental enrichment on male and female wistar rats with early life stress experiences

Exposure to adverse childhood experiences or early life stress experiences (ELSs) increase the risk of non-adaptive behaviors and psychopathology in adulthood. Environmental enrichment (EE) has been proposed to minimize these effects. The vast number of methodological variations in animal studies underscores the lack of systematicity in the studies and the need for a detailed understanding of how enrichment interacts with other variables. Here we evaluate the effects of environmental enrichment in male and female Wistar rats exposed to adverse early life experiences (prenatal, postnatal, and combined) on emotional (elevated plus maze), social (social interaction chamber), memory (Morris water maze) and flexibility tasks. Our results—collected from PND 51 to 64—confirmed: 1) the positive effect of environmental enrichment (PND 28–49) on anxiety-like behaviors in animals submitted to ELSs. These effects depended on type of experience and type of enrichment: foraging enrichment reduced anxiety-like behaviors in animals with prenatal and postnatal stress but increased them in animals without ELSs. This effect was sex-dependent: females showed lower anxiety compared to males. Our data also indicated that females exposed to prenatal and postnatal stress had lower anxious responses than males in the same conditions; 2) no differences were found for social interactions; 3) concerning memory, there was a significant interaction between the three factors: A significant interaction for males with prenatal stress was observed for foraging enrichment, while physical enrichment was positive for males with postnatal stress; d) regarding cognitive flexibility, a positive effect of EE was found in animals exposed to adverse ELSs: animals with combined stress and exposed to physical enrichment showed a higher index of cognitive flexibility than those not exposed to enrichment. Yet, within animals with no EE, those exposed to combined stress showed lower flexibility than those exposed to both prenatal stress and no stress. On the other hand, animals with prenatal stress and exposed to foraging-type enrichment showed lower cognitive flexibility than those with no EE. The prenatal stress-inducing conditions used here 5) did not induced fetal or maternal problems and 6) did not induced changes in the volume of the dentate gyrus of the hippocampus.

Sex-dependent effects of postweaning exposure to an enriched environment on visceral pain and anxiety- and depression-like behaviors induced by neonatal maternal separation

BACKGROUND

Neonatal maternal separation (NMS) can lead to visceral pain and anxiety- and depression-like behaviors. An enriched environment (EE) can alleviate NMS-induced pain and mental disorders, but previous studies have mostly been performed in male animals. Therefore, the aim of this study was to investigate whether the effects of EE were sex dependent at different stages of development.

METHODS

Female and Male C57BL/6 J mice that had been subjected to NMS alone and those subjected to both NMS and exposed to EE were used in this study. The visceral pain threshold test (PTT), open field test (OFT), sucrose preference test (SPT), and forced swimming test (FST) were conducted to evaluate visceral pain, anxiety-like behavior, and depression-like behavior in mice, respectively.

RESULTS

Compared with the male mice in the NMS group without EE exposure, those exposed to EE from postnatal day (P)21 to 41 showed an increase of the visceral pain threshold in the PTT, an increase of the central time and central distance in the OFT, an increase of the sucrose preference rate in the SPT, and a decrease of the time of immobility in the FST. Compared with both female and male mice in the NMS group without EE exposure, those exposed to EE from P21 to P61 had an increase of the visceral pain threshold in the PTT, an increase of the central time and central distance in the OFT, an increase in the sucrose preference rate in the SPT, and a decrease of the time of immobility in the FST.

CONCLUSIONS

EE is more effective in male NMS mice, while longer EE is required in female NMS mice for positive effects.

The influence of the enriched environment in different periods on neonatal maternal separation-induced visceral pain, anxiousness, and depressive behaviors

BACKGROUND

Neonatal maternal separation (NMS) is a major early life stress that can induce visceral pain and mental disorders. We have shown that an enriched environment (EE) can alleviate NMS-induced negative effects, but the time window over which EE works is unclear. Therefore, this study aimed to investigate the time window through which EE alleviates NMS-induced visceral pain, anxiousness, and depressive behaviors.

METHODS

In this study, we used male C57BL/6J mice. The mice were randomly divided into five groups: control group, NMS group, prepubertal EE group (EE1 group), pubertal EE group (EE2 group), and adult EE group (EE3 group). The visceral pain threshold test (PTT), open field test (OFT), elevated plus maze (EPM), forced swimming test (FST), and sucrose preference test (SPT) were performed in all five groups to assay visceral pain, anxiety-, and depression-like behaviors in mice, respectively. Enzyme-linked immunosorbent assay (ELISA) for corticosterone was performed in all five groups to assess the function of the hypothalamic-pituitary-adrenal (HPA) axis.

RESULTS

There was no significant change in weight between groups. It was shown that NMS induced visceral pain, anxiety, and depression, and EE1 and EE2 reversed these negative effects, but EE3 had no significant effect. Likewise, EE1 and EE2 reversed the NMS-induced increase of corticosterone, but EE3 did not.

CONCLUSIONS

Adverse life experiences in early life can lead to visceral pain, anxiety, and depression in adulthood, which can be effectively prevented by EE interventions in prepuberty and puberty.

Providing Environmental Enrichment without Altering Behavior in Male and Female Wistar Rats (Rattus norvegicus)

In research using animal models, subjects are commonly maintained under standard housing conditions, mainly because of the idea that enhancing welfare conditions could alter experimental data. Another common practice in many laboratories relates to the preponderant use of males. Several reasons justifying this practice include the rapid hormonal and endocrine change in females, which may require a higher number of female animals to achieve more homogenous groups, thereby creating a dilemma with the reduction principle in animal research. In past decades, a relationship between enriched environments and enhanced cognitive functions has been reported in rats, but many of those enriched environmental protocols were not systematically or rigorously studied, leading to unexpected effects on behavior. Here we report the effects of 4 types of housing conditions (standard, structural changes, exercise, and foraging) in Wistar rats on anxiety (elevated plus maze), exploratory (open field), and stress vulnerability (forced swim test) responses. Sex was used as a blocking factor. Data show no effect of housing conditions on anxiety and exploratory behaviors, but do show an effect on stress responses. These results suggest the possibility of using a protocol for environmental enrichment without concern about altering experimental data. From this stand, new ways to enhance animal welfare in research laboratories could be designed and implemented.

The Relative Benefits of Environmental Enrichment on Learning and Memory are Greater When Stressed: A Meta-analysis of Interactions in Rodents

Environmental enrichment ("EE") is expected to alleviate the negative effects of stress on cognitive performance. However, there are complexities associated with interpreting interactions that obscure determining the benefit EE may play in mitigating the negative effects of stress. To clarify these complexities, we conducted a systematic review with meta-analysis on the main and interactive effects of EE and stress on learning and memory in rodents. We show that EE and stress interact 'synergistically' where EE provides a greater relative benefit to stressed individuals compared to those reared in conventional housing. Importantly, EE can fully-compensate for the negative effects of stress where stressed individuals with EE performed equally to enriched individuals without a stress manipulation. Additionally, we show the importance of other mediating factors, including the order of treatment exposure, duration and type of stress, type of EE, and type of cognitive assays used. This study not only quantifies the interactions between EE and stress, but also provides a clear example for how to conduct and interpret meta-analysis of interactions.

An enriched environment reduces chronic stress-induced visceral pain through modulating microglial activity in the central nucleus of the amygdala

Cognitive behavioral therapy (CBT) improves the quality of life for patients with brain-gut disorders; however, the underlying mechanisms of CBT remain to be explored. Previously, we showed that environmental enrichment (EE), an experimental paradigm that mirrors positive behavioral intervention, ameliorates chronic stress-induced visceral hypersensitivity in a rodent model via mechanisms involving altered activity in the central nucleus of amygdala (CeA). In the present study, we investigated whether microglia-mediated synaptic plasticity in the CeA is a potential mechanism underlying the protective effects of EE against stress-induced visceral hypersensitivity. We stereotaxically implanted corticosterone (CORT) micropellets onto the dorsal margin of the CeA shown previously to induce colonic hypersensitivity. Animals were housed in EE cages or standard cages for 14 days after CORT implantation. Visceral sensitivity was assessed via visceromotor behavioral response to colorectal distension. Microglial morphology, microglia-mediated synaptic engulfment, and the expression of synaptic pruning-related signals complement component 1q (C1q), complement component 3 (C3), and C3 receptor (C3R) were measured using immunofluorescence and RNAscope assay. We found that housing CORT implanted rats in EE cages for 14 days attenuated visceral hypersensitivity in both male and female rats as compared with control rats maintained in standard housing. EE reduced CORT-induced microglial remodeling and microglia-mediated synaptic pruning with reduced C1q and CR3, but not C3, expression. Our data suggest that exposure to EE is sufficient to ameliorate stress-induced visceral pain via reducing amygdala microglia-modulated neuronal plasticity.NEW & NOTEWORTHY Clinical studies show that cognitive behavioral therapy (CBT) is effective in ameliorating visceral pain in patient with irritable bowel syndrome (IBS), yet the underlying mechanisms remain unexplored. By using environmental enrichment (EE), an experimental paradigm that mirrors positive behavioral intervention, we demonstrated that microglia-mediated synaptic plasticity in the CeA explains, plays a role, at least in part, in the positive effects of EE to reduce visceral hypersensitivity.

Environmental Enrichment Protects Against Sepsis-Associated Encephalopathy-Induced Learning and Memory Deficits by Enhancing the Synthesis and Release of Vasopressin in the Supraoptic Nucleus

Background

As a severe complication of sepsis, sepsis-associated encephalopathy (SAE) usually manifests as impaired learning and memory ability in survivors. Previous studies have reported that environmental enrichment (EE) can increase the learning and memory ability in different brain injury models. However, there has been no research on the possible positive effect of EE on SAE.

Aim

The present study aimed to test the effect of EE on SAE-induced impairment of learning and memory and its related mechanisms.

Methods

A Morris water maze test (MWM) was used to evaluate the learning and memory ability of SAE rats that received EE housing or not. The expression of vasopressin (VP) was assessed using immunofluorescence microscopy and enzyme-linked immunosorbent assays (ELISAs). The synthesis of VP in the supraoptic nucleus (SON) was determined using quantitative real-time reverse transcription-PCR analysis. Moreover, inflammatory markers and brain-derived neurotrophic factor (BDNF) were detected using ELISA.

Results

The results showed that SAE induced a decreased learning and memory ability, while EE reversed this impairment. EE also enhanced the synthesis and secretion of VP in the SON. Blocking the action of VP in the hippocampus interrupted the EE-induced amelioration of learning and memory impairment. Moreover, EE induced changes to the levels of BDNF and cytokines in the hippocampus and these effects were mediated by VP binding to the VP receptor 1a.

Conclusion

Our findings demonstrated that the enhanced synthesis and secretion of VP in the SON are a key determinant responsible for EE-induced alleviation of learning and memory deficits caused by SAE.

Astaxanthin alleviates neuropathic pain by inhibiting the MAPKs and NF-κB pathways

Neuropathic pain is a complex condition that usually lasts a lifetime and has a major negative impact on life after injury. Improving pain management is an important and unmet need. Astaxanthin (AST) is a natural marine medicine with effective antioxidant and anti-inflammatory properties and neuroprotective effects. However, few mechanisms can explain the role of AST in the treatment of neuropathic pain. In the present study, we examined its potential to eliminate spinal nerve ligation (SNL) damage by inhibiting the phosphorylation of extracellular signal-regulated kinase (ERK)1/2, phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), nuclear factor-κB (NF-κB) p65 and the inflammatory response. The results of behavior tests indicated the promising role of AST in analgesic effect in SNL mice. AST decreased the neuronal and non-neuronal activation, the levels of the inflammatory signaling mediators (p-ERK1/2 p-p38 MAPK and NF-κB p65) and inflammatory cytokine expression (interleukin [IL]-1, IL-17, IL-6, and tumor necrosis factor-α [TNF-α]. These results suggest that AST is a promising candidate to reduce nociceptive hypersensitization after SNL.

Effects of low-dose alcohol exposure in adolescence on subsequent alcohol drinking in adulthood in a rat model of depression

OBJECTIVE

Adolescence drinking and subsequent development of alcohol use disorder (AUD) is a worldwide health concern. In particular, mood dysregulation or early alcohol exposure can be the cause of heavy drinking in some individuals or a consequence of heavy drinking in others.

METHODS

This study investigated the effects of voluntary alcohol intake during adolescence, i.e. continuous 10% alcohol access between postnatal days (PND) 29 to 43 and olfactory bulbectomy (OBX) model of depression (performed on PND 59) on alcohol drinking in Wistar rats during adulthood (PND 80-120, intermittent 20% alcohol access). In addition, the effect of NBQX, an AMPA/kainate receptor antagonist (5 mg/kg, IP) on spontaneous alcohol consumption was examined.

RESULTS

Rats exposed to 10% alcohol during adolescence exhibited a lower 20% alcohol intake in the intermittent paradigm during adulthood, while the OBX-induced phenotype did not exert a significant effect on the drinking behaviour. NBQX exerted a transient reduction on alcohol intake in the OBX rats.

CONCLUSIONS

Our results indicate that exposure to alcohol during adolescence can affect alcohol drinking in adulthood and that further exploration of AMPA and/or kainate receptor antagonists in co-morbid alcoholism-depression is warranted.

Environmental enrichment ameliorates high-fat diet induced olfactory deficit and decrease of parvalbumin neurons in the olfactory bulb in mice

Overweight induced by high-fat diet (HFD) represents one of the major health concerns in modern societies, which can cause lasting peripheral and central metabolic disorders in all age groups. Specifically, childhood obesity could lead to life-long impact on brain development and functioning. On the other hand, environmental enrichment (EE) has been demonstrated to be beneficial for learning and memory. Here, we explored the impact of high-fat diet on olfaction and organization of olfactory bulb cells in adolescent mice, and the effect of EE intervention thereon. Puberty mice (3-week-old) fed with HFD for 10 weeks exhibited poorer odor sensitivity and olfactory memory relative to controls consuming standard chows. The behavioral deficits were rescued in the HFD group with EE intervention. Neuroanatomically, parvalbumin (PV) interneurons in the olfactory bulb (OB) were reduced in the HFD-fed animals relative to control, while EE intervention also normalized this alteration. In contrast, cells expressing calbindin (CB), doublecortin (DCX) in the OB were not altered. Our findings suggest that PV interneurons may play a crucial role in mediating the HFD-induced olfactory deficit in adolescent mice, and can also serve a protective effect of EE against the functional deficit.

Depression-like behavior associated with E/I imbalance of mPFC and amygdala without TRPC channels in mice of knockout IL-10 from microglia

Depression has a growing impact on public health. Accumulating evidence supports an association between depression and increased immune system activity. IL-10 is a key cytokine that inhibits excessive inflammatory responses and is related to the anti-inflammatory and protective functions of the central nervous system (CNS). Cx3cr1^CreERIL-10^-/- mice were used in our study. We aimed to identify the role of IL-10 in microglia in depression and anxiety-like behavior. We performed a series of behavioral tests on the mice; the Cx3cr1^CreERIL-10^-/- male mice showed depression- and anxiety-like behavior compared with the littermates. The expression of transient receptor potential canonical 5 (TRPC5) decreased in both the medial prefrontal cortex (mPFC) and amygdala regions. The cytokines IL-1β and IL-6 increased, and IL-10 was decreased by western blotting. The knockout mice showed different trends in the effects of synaptic proteins. In the mPFC, IL-10 knockout induced a decrease in NR2B and synaptophysin; in the amygdala region, there was a significant increase in NR2B and PSD95. IL-10 knockout from microglia induced a decrease in GAD67 and parvalbumin (Pv) in the mPFC, but not in the amygdala. Our results showed enhanced depression and anxiety-like behavior in the Cx3cr1^CreER IL-10^-/- mice, which could be related to an imbalance in local excitatory and inhibitory transmission, as well as neuroinflammation in the mPFC and amygdala. This imbalance was associated with increased local inflammation. Although many studies have demonstrated the role of TRPC channels in emotional responses, our study showed that TRPC was not involved in this process in Cx3cr1^CreERIL-10^-/- mice.

Effect of Environmental Complexity and Stocking Density on Fear and Anxiety in Broiler Chickens

Barren housing and high stocking densities may contribute to negative affective states in broiler chickens, reducing their welfare. We investigated the effects of environmental complexity and stocking density on broilers' attention bias (measure of anxiety) and tonic immobility (measure of fear). In Experiment 1, individual birds were tested for attention bias (n = 60) and in Experiment 2, groups of three birds were tested (n = 144). Tonic immobility testing was performed on days 12 and 26 (n = 36) in Experiment 1, and on day 19 (n = 72) in Experiment 2. In Experiment 1, no differences were observed in the attention bias test. In Experiment 2, birds from high-complexity pens began feeding faster and more birds resumed feeding than from low-complexity pens following playback of an alarm call, suggesting that birds housed in the complex environment were less anxious. Furthermore, birds housed in high-density or high-complexity pens had shorter tonic immobility durations on day 12 compared to day 26 in Experiment 1. In Experiment 2, birds from high-density pens had shorter tonic immobility durations than birds housed in low-density pens, which is contrary to expectations. Our results suggest that birds at 3 weeks of age were less fearful under high stocking density conditions than low density conditions. In addition, results indicated that the complex environment improved welfare of broilers through reduced anxiety.

Decreased kynurenine pathway potentiate resilience to social defeat effect on cocaine reward

The kynurenine (KYN) pathway of tryptophan (TRP) degradation is activated by stress and inflammatory factors. It is now well established that social stress induces the activation of the immune system, with central inflammation and KYN metabolism being two of the main factors linking stress with depression. The aim of the present study was to evaluate the long-lasting changes in the KYN pathway induced by social defeat (SD) associated with the resilience or susceptibility to an increase in the conditioned rewarding effects of cocaine. Mice were exposed to repeated SD and 3 weeks later, a conditioned place preference (CPP) induced by a subthreshold dose of cocaine (1.5 mg/kg) was developed. KYN levels in plasma, cerebellum, hippocampus, striatum and limbic forebrain were studied at the end of the CPP procedure. Changes in the KYN pathway after exposure to pharmacological (oxytocin and indomethacin) and environmental interventions (environmental enrichment) were also evaluated. Our results showed that defeated susceptible (SD-S) mice had higher conditioning scores than resilient mice (SD-R). In addition, although KYN concentration was elevated in all defeated mice, SD-R mice showed smaller increases in KYN concentration in the cerebellum than SD-S mice. Oxytocin or Indomethacin treatment before SD normalized cocaine-induced CPP, although the increase in the KYN pathway was maintained. However, environmental enrichment before SD normalized cocaine-induced CPP and prevented the increase in the KYN pathway. The present study highlights the role of the KYN pathway and anti-inflammatory drugs acting on TRP metabolism as pharmacological targets to potentiate resilience to social stress effects.

Enrichment Protocol for Rat Models

An environmental enrichment (EE) cage consisting of a broad living area and various stimulators triggers social, cognitive, and physical activities. EE has been utilized in a wide range of neurological and non-neurological studies. However, the details of the environmental enrichment protocol were not well described in these studies. This has resulted in uncertainty and inconsistency in methodology, which may thus fail to replicate environmental enrichment effects, influencing the study outcome. Here we describe the basic guidelines and present an easy-to-follow protocol for environmental enrichment in rat models. © 2021 Wiley Periodicals LLC. Basic Protocol: Environmental enrichment housing.

Housing quality and behavior affect brain health and anxiety in healthy Japanese adults

Countless studies in animals have shown how housing environments and behaviors can significantly affect anxiety and brain health, giving valuable insight as to whether this is applicable in the human context. The relationship between housing, behavior, brain health, and mental wellbeing in humans remains poorly understood. We therefore explored the interaction of housing quality, weekend/holiday sedentary behavior, brain structure, and anxiety in healthy Japanese adults. Whole-brain structural magnetic resonance imaging (MRI) methods based on gray matter volume and fractional anisotropy were used as markers for brain health. Correlation tests were conducted, and then adjusted for multiple comparisons using the False Discovery Rate method. Housing quality and weekend/holiday sedentary behavior were associated with fractional anisotropy, but not with gray matter volume. Fractional anisotropy showed significant associations with anxiety. Lastly, both weekend/holiday sedentary behavior and housing quality were indirectly associated with anxiety through fractional anisotropy. These results add to the limited evidence surrounding the relationship among housing, behavior, and the brain. Furthermore, these results show that behavior and housing qualities can have an indirect impact on anxiety through neurobiological markers such as fractional anisotropy.

How environmental enrichment balances out neuroinflammation in chronic pain and comorbid depression and anxiety disorders

Depression and anxiety commonly occur in chronic pain states and the coexistence of these diseases worsens outcomes for both disorders and may reduce treatment adherence and response. Despite the advances in the knowledge of chronic pain mechanisms, pharmacological treatment is still unsatisfactory. Research based on exposure to environmental enrichment is currently under investigation and seems to offer a promising low-cost strategy with no side effects. In this review, we discuss the role of inflammation as a major biological substrate and aetiological factor of chronic pain and depression/anxiety and report a collection of preclinical evidence of the effects and mechanisms of environmental enrichment. As microglia participates in the development of both conditions, we also discuss microglia as a potential target underlying the beneficial actions of environmental enrichment in chronic pain and comorbid depression/anxiety. We also discuss how alternative interventions under clinical guidelines, such as environmental enrichment, may improve treatment compliance and patient outcomes.

Effects of enriched environment on depression and anxiety-like behavior induced by early life stress: A comparison between different periods

BACKGROUND

Brain development is a prolonged process and it is sensitive to the environment during critical periods. Stress in early life is believed to increase vulnerability to depression, while enriched environment (EE) has beneficial effects on neural plasticity and depression. In this study, we compared the therapeutic effect of EE during different periods on early life stress-induced depression, and investigated the role of brain-derived neurotrophic factor (BDNF) and protein kinase B (AKT) on the effect of EE. Plasma corticosterone level was also detected to evaluate the reactivity of hypothalamic-pituitary-adrenal axis.

METHODS

C57BL/6 mice were subjected to a 4-h maternal separation (MS) procedure during postnatal days 2-21. After this separation, the mice were assigned to standard environment groups (SE), EE in the early period groups (3-8 weeks, EEE) and EE in the adult groups (8-13 weeks, EEA). Depression and anxiety behavior were evaluated at 14-weeks of age. The plasma corticosterone was quantified utilizing enzyme-linked immunosorbent assay. Hippocampus BDNF and AKT/p-AKT were detected using Western blotting.

RESULTS

The results showed that MS increased depression and anxiety level, while EE in both intervention periods alleviated the symptoms of depression and anxiety. The EEE group showed better effects in terms of anhedonia and anxiety than the EEA group. The difference in despair behavior between the EEE and EEA groups was not significant. MS increased plasma corticosterone level, while EE decreased corticosterone level in both intervention periods. EE increased BDNF and p-AKT expression in the hippocampus, with stronger effects in the EEE group.

CONCLUSION

EE during the early development period was more effective in alleviating depression and anxiety induced by early life stress. BDNF and AKT may play a significant role in the effect of EE, and further research is needed to explore the detailed neurobiological mechanisms.

The Contribution of Microglia to the Development and Maturation of the Visual System

Microglia, the resident immune cells of the central nervous system (CNS), were once considered quiescent cells that sat in readiness for reacting to disease and injury. Over the last decade, however, it has become clear that microglia play essential roles in maintaining the normal nervous system. The retina is an easily accessible part of the central nervous system and therefore much has been learned about the function of microglia from studies in the retina and visual system. Anatomically, microglia have processes that contact all synapses within the retina, as well as blood vessels in the major vascular plexuses. Microglia contribute to development of the visual system by contributing to neurogenesis, maturation of cone photoreceptors, as well as refining synaptic contacts. They can respond to neural signals and in turn release a range of cytokines and neurotrophic factors that have downstream consequences on neural function. Moreover, in light of their extensive contact with blood vessels, they are also essential for regulation of vascular development and integrity. This review article summarizes what we have learned about the role of microglia in maintaining the normal visual system and how this has helped in understanding their role in the central nervous system more broadly.

The Melatonin and Enriched Environment Ameliorated Low Protein-Induced Intrauterine Growth Retardation by IGF-1 And mtor Signaling Pathway and Autophagy Inhibition in Rats

CDATA[Aim: The present study investigated whether melatonin (MEL) and enriched environment (EE) might protect against intrauterine growth retardation (IUGR) in rats.

METHODS

Sprague-Dawley rats were randomly allocated to 3 groups: control (C), model (M) and EE+MEL group. Animals were housed in an enriched environment (EE+MEL group) or remained in a standard environment (C group, M group). IUGR rat model was built by feeding a low protein diet during pregnancy. MEL was administered by gavaging. At day 1 post-birth, the baseline characteristics and serum biochemical parameters, morphology of liver and small intestine, enzyme activities, and mRNA expression levels of fetal rats were determined. The autophagy marker LC3 and Beclin1 were determined by western blot analysis.

RESULTS

EE+MEL markedly improved the baseline characteristics, hepatic and intestinal morphology of IUGR fetuses. In addition, the lactase activities in the fetal intestine were markedly increased by the EE+MEL. The levels of serum somatostatin (SST), Growth hormone (GH), GH releasing hormone (GHRH), Insulin-like Growth Factor 1 (IGF-1), triiodothyronine (T3), and tetraiodothyronine (T4) were found to be recovered by EE+MEL. In addition, the EE+MEL significantly ameliorated the mRNA expression of SST, GHRH, and GHRH receptor (GHRHR), GH, GHR, IGF-1, and IGF-1 receptor (IGF1R), IGF binding protein-1 (IGFBP1), mammalian target of rapamycin (mTOR), S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4EBP1) in fetuses. In IUGR fetal livers, LC3 and Beclin1 were found to be increased at birth, while LC3 and Beclin1 were observed to be significantly decreased in the EE+MEL group.

CONCLUSION

EE+MEL could improve fetal rats' baseline characteristics, serum biochemical parameters, birth weight, intestinal and hepatic morphology and enzyme activities. These effects could be explained by the activation of the IGF-1/IGFBP1 and IGF-1/mTOR/S6K1/4EBP1 signaling pathway and autophagy inhibition.

Importance of Non-pharmacological Approaches for Treating Irritable Bowel Syndrome: Mechanisms and Clinical Relevance

Chronic visceral pain represents a major unmet clinical need with the severity of pain ranging from mild to so severe as to prevent individuals from participating in day-to-day activities and detrimentally affecting their quality of life. Although chronic visceral pain can be multifactorial with many different biological and psychological systems contributing to the onset and severity of symptoms, one of the major triggers for visceral pain is the exposure to emotional and physical stress. Chronic visceral pain that is worsened by stress is a hallmark feature of functional gastrointestinal disorders such as irritable bowel syndrome (IBS). Current pharmacological interventions for patients with chronic visceral pain generally lack efficacy and many are fraught with unwanted side effects. Cognitive behavioral therapy (CBT) has emerged as a psychotherapy that shows efficacy at ameliorating stress-induced chronic visceral pain; however, the molecular mechanisms underlying CBT remain incompletely understood. Preclinical studies in experimental models of stress-induced visceral pain employing environmental enrichment (EE) as an animal model surrogate for CBT are unraveling the mechanism by which environmental signals can lead to long-lasting changes in gene expression and behavior. Evidence suggests that EE signaling interacts with stress and nociceptive signaling. This review will (1) critically evaluate the behavioral and molecular changes that lead to chronic pain in IBS, (2) summarize the pharmacological and non-pharmacological approaches used to treat IBS patients, and (3) provide experimental evidence supporting the potential mechanisms by which CBT ameliorates stress-induced visceral pain.

Electroacupuncture Alleviates Chronic Pain-Induced Anxiety Disorders by Regulating the rACC-Thalamus Circuitry

Anxiety is a common comorbidity associated with chronic pain, which results in chronic pain complexification and difficulty in treatment. Electroacupuncture (EA) is commonly used to treat chronic pain and anxiety. However, the underlying mechanisms of the EA effect are largely unknown. Here, we showed that a circuitry underlying chronic pain induces anxiety disorders, and EA can treat them by regulating such circuitry. Using chemogenetic methods, we found that chemogenetic activation of the rostral anterior cingulate cortex (rACC) glutamatergic output to the thalamus induced anxiety disorders in control rats. Then, chemogenetic inhibition of the rACC-thalamus circuitry reduced anxiety-like behavior produced by intraplantar injection of the complete Freund's adjuvant (CFA). In this study, we examined the effects of EA on a rat model of CFA-mediated anxiety-like behaviors and the related mechanisms. We found that chemogenetic activation of the rACC-thalamus circuitry effectively blocked the effects of EA on chronic pain-induced anxiety-like behaviors in CFA rats. These results demonstrate an underlying rACC-thalamus glutamatergic circuitry that regulates CFA-mediated anxiety-like behaviors. This study also provides a potential mechanistic explanation for EA treatment of anxiety caused by chronic pain.

Minocycline in neurodegenerative and psychiatric diseases: An update

BACKGROUND AND PURPOSE

Minocycline is a broad-spectrum antibiotic, effective as a chronic treatment for recurrent bacterial infections. Beyond its antibiotic action, minocycline also has important anti-inflammatory, antioxidant and antiapoptotic properties. Its efficacy has therefore been evaluated in many neurodegenerative and psychiatric diseases that have an inflammatory basis. Our aim was to review preclinical and clinical studies performed in neurological and psychiatric diseases whose treatment involved the use of minocycline and thereby to discern the possible beneficial effect of minocycline in these disorders.

METHODS

Completed and ongoing preclinical studies and clinical trials of minocycline for both neurodegenerative diseases and psychiatric disorders, published from January 1995 to January 2020, were identified through searching relevant databases (https://www.ncbi.nlm.nih.gov/pubmed/, https://clinicaltrials.gov/). A total of 74 preclinical studies and 44 clinical trials and open-label studies were selected.

RESULTS

The results of the nearly 20 years of research identified are diverse. While minocycline mostly proved to be effective in animal models, clinical results showed divergent outcomes, with positive results in some studies counterbalanced by a number of cases with no significant improvements. Specific data for each disease are further individually described in this review.

CONCLUSIONS

Despite minocycline demonstrating antioxidant and anti-inflammatory effects, discrepancies between preclinical and clinical data indicate that we should be cautious in analyzing the outcomes. Improving and standardizing protocols and refining animal models could help us to determine if minocycline really is a useful drug in the treatment of these pathologies.

Environmental enrichment alters neurobehavioral development following maternal immune activation in mice offspring with epilepsy

Epilepsy is a chronic brain disease affecting millions of people worldwide. Anxiety-related disorders and cognitive deficits are common in patients with epilepsy. Previous studies have shown that maternal infection/immune activation renders children more vulnerable to neurological disorders later in life. Environmental enrichment has been suggested to improve seizures, anxiety, and cognitive impairment in animal models. The present study aimed to explore the effects of environmental enrichment on seizure scores, anxiety-like behavior, and cognitive deficits following maternal immune activation in offspring with epilepsy. Pregnant mice were treated with lipopolysaccharides-(LPS) or vehicle, and offspring were housed in normal or enriched environments during early adolescence to adulthood. To induce epilepsy, adult male and female offspring were treated with Pentylenetetrazol-(PTZ), and then anxiety-like behavior and cognitive functions were assessed. Tumor-necrosis-factor (TNF)-α and interleukin (IL) 10 were measured in the hippocampus of offspring. Maternal immune activation sex-dependently increased seizure scores in PTZ-treated offspring. Significant increases in anxiety-like behavior, cognitive impairment, and hippocampal TNF-α and IL-10 were also found following maternal immune activation in PTZ-treated offspring. However, there was no sex difference in these behavioral abnormalities in offspring. Environmental enrichment reversed the effects of maternal immune activation on behavioral and inflammatory parameters in PTZ-treated offspring. Overall, the present findings highlight the adverse effects of prenatal maternal immune activation on seizure susceptibility and psychiatric comorbidities in offspring. This study suggests that environmental enrichment may be used as a potential treatment approach for behavioral abnormalities following maternal immune activation in PTZ-treated offspring.

Enrichment Environment Positively Influences Depression- and Anxiety-Like Behavior in Serotonin Transporter Knockout Rats through the Modulation of Neuroplasticity, Spine, and GABAergic Markers

The serotonin transporter (5-HTT in humans, SERT in rodents) is the main regulator of serotonergic transmission in the brain. The short allelic variant of the 5-HTT gene is in humans associated with psychopathologies and may enhance the vulnerability to develop depression after exposure to stressful events. Interestingly, the short allele also increases the sensitivity to a positive environment, which may buffer the vulnerability to depression. Since this polymorphism does not exist in rodents, male SERT knockout (SERT^−/−) rats were tested to explore the molecular mechanisms based on this increased predisposition. This article investigates the influences of a positive manipulation, namely, enriched environment (EE), on the depressive-like behavior observed in SERT^−/− rats. We found that one month of EE exposure normalized the anhedonic and anxious-like phenotype characteristics of this animal model. Moreover, we observed that EE exposure also restored the molecular alterations in the prefrontal cortex by positively modulating the expression of the neurotrophin Bdnf, and of spines and gamma-aminobutyric acid (GABA)ergic markers. Overall, our data confirm the depression-like phenotype of SERT^−/− rats and highlight the ability of EE to restore behavioral and molecular alterations, thus promoting the opportunity to use EE as a supporting non-pharmacological approach to treat mood disorders.

Comparative study of oral and intranasal puerarin for prevention of brain injury induced by acute high-altitude hypoxia

Human activities in the areas of high altitude have increased significantly recently. Brain is highly sensitive to changing of oxygen pressure due to high altitude, and this physiological response may lead to serious brain injury, such as learning and memory disabilities. Puerarin is a phytoestrogen with many pharmacological activities, such as treatment of neurological disorders. However, most of current drugs can not easily enter brain through the blood-brain barrier (BBB). The nose-to-brain route can bypass BBB for brain-targeting. Here, thermosensitive in situ hydrogels (TISGs) of puerarin were prepared with poloxamers 407, poloxamers 188 and propylene glycol to improve bioavailability and brain targeting. In vitro drug release in simulated nasal fluids, rheological properties and cilia toxicity of puerarin TISGs were explored. The pharmacodynamics and pharmacokinetics of puerarin by intranasal (i.n.) and oral (p.o.) administrations were also evaluated. The viscosity of puerarin TISGs tended to increase obviously with increased temperature. The puerarin release profile and transmucosal process of puerarin TISGs could be described with the first-order kinetics equation, depending on drug diffusion. The cilia toxicity of puerarin TISGs was not obvious. Rat models of hypobarism/hypoxia-induced brain injury were established with a hypobaric simulation chamber. Morris water maze and open filed tests indicated that puerarin TISGs improved the spatial memory and spontaneous exploratory behavior of the rats suffering from hypoxia-induced brain injury. Furthermore, puerarin TISGs decreased the level of oxidative stress cytokines (malondialdehyde (MDA) and glutathione (GSH)) in the peripheral circulation, alleviated the cerebral histological lesions, and relieved the expression of hypoxia-inducible factor-1α (HIF-1α). Intranasal puerarin TISGs were absorbed quickly with a shorter T_max (10.0 ± 5.7 min) compared to that of oral puerarin (36 ± 13.4 min). In addition, the relative bioavailability of i.n. puerarin TISGs was high to 300% compared to oral administration of puerarin. The area under the curve (AUC) of brain after i.n. administration of puerarin TISGs was 954.5 ± 335.1 h.ng/mL, while no puerarin was detected in the brain after oral administration. Therefore, i.n. puerarin TISGs led to excellent brain targeting effect. Puerarin TISGs are an effective neuroprotector formulation for prevention of brain injury induced by acute high-altitude hypoxia.

Improvement of autophagy dysfunction as a potential mechanism for environmental enrichment to protect blood-brain barrier in rats with vascular cognitive impairment

Vascular cognitive impairment (VCI) is the second most common cause of dementia after Alzheimer's disease, and the cognitive impairment is one of the common effects of VCI. Unfortunately, it lacks effective therapeutic treatments at present. In our previous study, environmental enrichment (EE), as an early intervention for lifestyle modification, can ameliorate cognitive impairment by attenuating hippocampal blood-brain barrier (BBB) injury in chronic cerebral hypoperfusion (CCH) rats. However, the underlying mechanism remains unclear. Here, we found CCH rats in the standard environment (SE) developed cognitive impairment and BBB damage, which were significantly alleviated with the EE intervention. Meantime, EE improved the autophagy dysfunction caused by CCH in the hippocampus of rats, suggesting that the effect of EE on cognitive function and BBB may be related to the improvement of autophagy pathway.

Environmental Complexity and Research Outcomes

Environmental complexity is an experimental paradigm as well as a potential part of animals' everyday housing experiences. In experimental uses, researchers add complexity to stimulate brain development, delay degenerative brain changes, elicit more naturalistic behaviors, and test learning and memory. Complexity can exacerbate or mitigate behavioral problems, give animals a sense of control, and allow for expression of highly driven, species-typical behaviors that can improve animal welfare. Complex environments should be designed thoughtfully with the animal's natural behaviors in mind, reported faithfully in the literature, and evaluated carefully for unexpected effects.

Transient receptor potential V1 (TRPV1) modulates the therapeutic effects for comorbidity of pain and depression: The common molecular implication for electroacupuncture and omega-3 polyunsaturated fatty acids

Chronic pain and depression are conditions that are highly comorbid and present with overlapping clinical presentations and common pathological biological pathways in neuroinflammation, both of which can be reversed by the use of electroacupuncture (EA) and omega-3 polyunsaturated fatty acids (PUFAs). Transient receptor potential V1 (TRPV1), a Ca²⁺ permeable ion channel that can be activated by inflammation, is reported to be involved in the development of chronic pain and depression. Here, we investigated the role of TRPV1 and its related pathways in the murine models of cold stress-induced nociception and depression. Female C57BL/6 wild type and TRPV1 knockout mice were subjected to intermittent cold-stress (ICS) to initiate depressive-like and chronic pain behaviors, respectively. The Bio-Plex ELISA technique was utilized to analyze inflammatory mediators in mice plasma. The western blot and immunostaining techniques were used to analyze the presence of TRPV1 and related molecules in the medial prefrontal cortex (mPFC), hippocampus, periaqueductal gray (PAG), and amygdala. The ICS model significantly induced chronic pain (mechanical: 2.55 ± 0.31 g; thermal: 8.12 ± 0.87 s) and depressive-like behaviors (10.95 ± 0.95% in the center zone; 53.14 ± 4.01% in immobility). The treatment efficacy of EA, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) were observed in both nociceptive and depression test results. Inflammatory mediators were increased after ICS induction and further reversed by the use of EA, EPA and DHA. A majority of TRPV1 proteins and related molecules were significantly decreased in the mPFC, hippocampus and PAG of mice. This decrease can be reversed by the use of EA, EPA and DHA. In contrast, these molecules were increased in the mice's amygdala, and were attenuated by the use of EA, EPA and DHA. Our findings indicate that these inflammatory mediators can regulate the TRPV1 signaling pathway and initiate new potential therapeutic targets for chronic pain and depression treatment.

Enriched environment effect on lipopolysaccharide-induced spatial learning, memory impairment and hippocampal inflammatory cytokine levels in male rats

Neuro-inflammation is responsible for cognitive impairments and neurodegenerative diseases such as Alzheimer's disease. In this study, we aimed to investigate the enriched environment (EE) effect on learning and memory impairment as well as on pro-inflammatory cytokines changes induced by lipopolysaccharide (LPS). LPS injection (1 mg/kg/i.p, days 1, 3, 5, and 7) was used to develop the animal model of neuro-inflammation. Twenty-eight male Wistar rats were used in the experiment and randomly divided into 4 groups: 1) sham (S), 2) sham + enriched environment (SE), 3) LPS (L), and 4) LPS + EE (LE). Two different housing conditions, including standard environment (SE) and enriched environment, were used. The Morris Water Maze (MWM) test was used to examine animals learning and memory. IL-1β, IL-10, and TNF-α levels were measured in the brain using ELISA. We found that LPS significantly impaired learning and memory (p < 0.05) in the MWM task, but EE could significantly improve learning and memory impairment (p < 0.05). IL-1 and IL-10 levels dramatically increased in the LPS group (P < 0.05), whereas EE could decrease and increase IL-1β and IL-10 values in the LPS + EE group (P < 0.05), respectively. TNF-α levels were traced but had not detectable values in the hippocampus. Thus, we can conclude that EE has healing effects on LPS induced neuro-inflammation and can improve learning and memory deficit; however, further studies are needed to support the findings of our study.

Experimentally Induced Sepsis Causes Extensive Hypomyelination in the Prefrontal Cortex and Hippocampus in Neonatal Rats

Neonatal sepsis is associated with cognitive deficit in the later life. Axonal myelination plays a pivotal role in neurotransmission and formation of learning and memory. This study aimed to explore if systemic lipopolysaccharide (LPS) injection would induce hypomyelination in the prefrontal cortex and hippocampus in developing septic neonatal rats. Sprague-Dawley rats (1-day old) were injected with LPS (1 mg/kg) intraperitoneally. By electron microscopy, axonal hypomyelination was evident in the subcortical white matter and hippocampus. The expression of myelin proteins including CNPase, MBP, PLP and MAG was downregulated in both areas of the brain at 7, 14 and 28 days after LPS injection. The frequency of MBP and PLP-positive oligodendrocyte was significantly reduced using in situ hybridization in the cerebral cortex and hippocampus at the corresponding time points after LPS injection, whereas the expression of NG2 and PDGFRα was noticeably increased. In tandem with this was reduction of Olig1 and Olig2 expressions which are involved in differentiation/maturation of OPCs. Expression of NFL, NFM, and NFH was significantly downregulated, indicating that axon development was disrupted after LPS injection. Morris Water Maze behavioral test, Open field test, Rotarod test, and Pole test were used to evaluate neurological behaviors of 28 days rats. The rats in the LPS group showed the impairment of motor coordination, balance, memory, and learning ability and represented bradykinesia and anxiety-like behavior. The present results suggest that following systemic LPS injection, differentiation/maturation of OPCs was affected which may be attributed to the inhibition of transcription factors Olig1 and Olig2 expression resulting in impairment to axonal development. It is suggested that this would ultimately lead to axonal hypomyelination in the prefrontal cortex and hippocampus, which may be associated with neurological deficits in later life.

Minocycline prevents the depressive-like behavior through inhibiting the release of HMGB1 from microglia and neurons

BACKGROUND

Our previous study reports the causal role of high mobility group box 1 (HMGB1) in the development of depression; and we find glycyrrhizic acid (GZA) can be a potential treatment for major depressive disorder (MDD) considering its inhibition of HMGB1 activity. This study aims to further explore the exact cell types that release HMGB1 in the hippocampus.

METHODS

We detected the effects of microglia conditioned medium on primary astrocytes and neurons. The effects of minocycline on depressive-like behaviors were tested in BABLB/c mice after four weeks of chronic unpredictable mild stress (CUMS) exposure. Furthermore, the immunofluorescence (IF) assays, hematoxylin-eosin (HE) and TUNEL staining were used to observe hippocampal slices to evaluate the release of HMGB1. The cytoplasmic translocations of HMGB1 protein were assayed by western-blot.

RESULTS

Exposure to CUMS caused an active release of HMGB1 from microglia and neurons in the hippocampus. After minocycline administration for inhibiting the activation of microglia, both microglia and neurons reduced the release of HMGB1 and the protein level of central and peripheral HMGB1 recovered accordingly. Along with blocking the release of HMGB1, behavioral and cognitive deficits induced by CUMS were improved significantly by minocycline. In addition, the supernatant of primary microglia stimulated the secretion of HMGB1 in primary neurons, not in astrocytes, at 24 h after 4 h-LPS treatment.

CONCLUSION

All the evidence supported our hypotheses that microglia and neurons are the main cell sources of HMGB1 release under CUMS condition, and that the release of HMGB1 by microglia may play an important role in the development of depressive-like behavior.

Behavioral, Biochemical and Electrophysiological Changes in Spared Nerve Injury Model of Neuropathic Pain

Neuropathic pain is a pathological condition induced by a lesion or disease affecting the somatosensory system, with symptoms like allodynia and hyperalgesia. It has a multifaceted pathogenesis as it implicates several molecular signaling pathways involving peripheral and central nervous systems. Affective and cognitive dysfunctions have been reported as comorbidities of neuropathic pain states, supporting the notion that pain and mood disorders share some common pathogenetic mechanisms. The understanding of these pathophysiological mechanisms requires the development of animal models mimicking, as far as possible, clinical neuropathic pain symptoms. Among them, the Spared Nerve Injury (SNI) model has been largely characterized in terms of behavioral and functional alterations. This model is associated with changes in neuronal firing activity at spinal and supraspinal levels, and induces late neuropsychiatric disorders (such as anxious-like and depressive-like behaviors, and cognitive impairments) comparable to an advanced phase of neuropathy. The goal of this review is to summarize current findings in preclinical research, employing the SNI model as a tool for identifying pathophysiological mechanisms of neuropathic pain and testing pharmacological agent.

Increased EZH2 Levels in Anterior Cingulate Cortex Microglia Aggravate Neuropathic Pain by Inhibiting Autophagy Following Brachial Plexus Avulsion in Rats

After brachial plexus avulsion (BPA), microglia induce inflammation, initiating and maintaining neuropathic pain. EZH2 (enhancer of zeste homolog 2) has been implicated in inflammation and neuropathic pain, but the mechanisms by which it regulates neuropathic pain remain unclear. Here, we found that EZH2 levels were markedly upregulated during BPA-induced neuropathic pain in vivo and in vitro, stimulating pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6) secretion in vivo. In rats with BPA-induced neuropathic pain, mechanical and cold hypersensitivities were induced by EZH2 upregulation and inhibited by EZH2 downregulation in the anterior cingulate cortex. Microglial autophagy was also significantly inhibited, with EZH2 inhibition activating autophagy and reducing neuroinflammation in vivo. However, this effect was impaired by inhibiting autophagy with 3-methyladenine, suggesting that the MTOR signaling pathway is a functional target of EZH2. These data suggest that EZH2 regulates neuroinflammation and neuropathic pain via a novel MTOR-mediated autophagy signaling pathway, providing a promising approach for managing neuropathic pain.