Attenuation of social interaction-associated ultrasonic vocalizations and spatial working memory performance in rats exposed to chronic unpredictable stress

Clemastine improves emotional and social deficits in adolescent social isolation mice by reversing demyelination

Adolescence is a critical period for social experience-dependent oligodendrocyte maturation and myelination. Adolescent stress predisposes to cause irreversible changes in brain structure and function with lasting effects on adulthood or beyond. However, the molecular mechanisms linking adolescent social isolation stress with emotional and social competence remain largely unknown. In our study, we found that social isolation during adolescence leads to anxiety-like behaviors, depression-like behaviors, impaired social memory and altered patterns of social ultrasonic vocalizations in mice. In addition, adolescent social isolation stress induces demyelination in the prefrontal cortex and hippocampus of mice, with decreased myelin-related gene expression and disrupted myelin structure. More importantly, clemastine was sufficient to rescue the impairment of emotional and social memory by promoting remyelination. These findings reveal the demyelination mechanism of emotional and social deficits caused by social isolation stress in adolescence, and provides potential therapeutic targets for treating stress-related mental disorders.

The Impact of Chronic Stress on Behavior and Body Mass in New Animal Models

(1) Background: Exposure to different sources of stress can have a significant effect on both psychological and physical processes. (2) Methods: The study took place over a period of 34 days and included a total of 40 animals. Regarding the exposure to chronic stressors, we opted for physiological, non-invasive stressors, e.g., running, swimming, and changes in the intensity of light. An unforeseen stress batch was also created that alternated all these stress factors. The animals were divided into five experimental groups, each consisting of eight individuals. In the context of conducting the open field test for behavioral assessment before and after stress exposure, we aimed to investigate the impact of stress exposure on the affective traits of the animals. We also monitored body mass every two days. (3) Results: The control group exhibited an average increase in weight of approximately 30%. The groups exposed to stress factors showed slower growth rates, the lowest being the running group, recording a rate of 20.55%, and the unpredictable stress group at 24.02%. The anxious behavior intensified in the group with unforeseen stress, in the one with light variations, and in the running group. (4) Conclusions: Our research validates the animal model of intermittent light exposure during the dark phase as a novel method of inducing stress. The modification of some anxiety parameters was observed; they vary according to the type of stress. Body mass was found to increase in all groups, especially in the sedentary groups, likely due to the absence of cognitive, spatial, and social stimuli except for cohabitation.

Reduced length of nodes of Ranvier and altered proteoglycan immunoreactivity in prefrontal white matter in major depressive disorder and chronically stressed rats

Major depressive disorder (MDD) and chronic unpredictable stress (CUS) in animals feature comparable cellular and molecular disturbances that involve neurons and glial cells in gray and white matter (WM) in prefrontal brain areas. These same areas demonstrate disturbed connectivity with other brain regions in MDD and stress-related disorders. Functional connectivity ultimately depends on signal propagation along WM myelinated axons, and thus on the integrity of nodes of Ranvier (NRs) and their environment. Various glia-derived proteoglycans interact with NR axonal proteins to sustain NR function. It is unclear whether NR length and the content of associated proteoglycans is altered in prefrontal cortex (PFC) WM of human subjects with MDD and in experimentally stressed animals. The length of WM NRs in histological sections from the PFC of 10 controls and 10 MDD subjects, and from the PFC of control and CUS rats was measured. In addition, in WM of the same brain region, five proteoglycans, tenascin-R and NR protein neurofascin were immunostained or their levels measured with western blots. Analysis of covariance and t-tests were used for group comparisons. There was dramatic reduction of NR length in PFC WM in both MDD and CUS rats. Proteoglycan BRAL1 immunostaining was reduced at NRs and in overall WM of MDD subjects, as was versican in overall WM. Phosphacan immunostaining and levels were increased in both in MDD and CUS. Neurofascin immunostaining at NRs and in overall WM was significantly increased in MDD. Reduced length of NRs and increased phosphacan and neurocan in MDD and stressed animals suggest that morphological and proteoglycan changes at NRs in depression may be related to stress exposure and contribute to connectivity alterations. However, differences between MDD and CUS for some NR related markers may point to other mechanisms affecting the structure and function of NRs in MDD.

Rodent models for mood disorders - understanding molecular changes by investigating social behavior

Mood disorders, including depressive and bipolar disorders, are the group of psychiatric disorders with the highest prevalence and disease burden. However, their pathophysiology remains poorly understood. Animal models are an extremely useful tool for the investigation of molecular mechanisms underlying these disorders. For psychiatric symptom assessment in animals, a meaningful behavioral phenotype is needed. Social behaviors constitute naturally occurring complex behaviors in rodents and can therefore serve as such a phenotype, contributing to insights into disorder related molecular changes. In this narrative review, we give a fundamental overview of social behaviors in laboratory rodents, as well as their underlying neuronal mechanisms and their assessment. Relevant behavioral and molecular changes in models for mood disorders are presented and an outlook on promising future directions is given.

Activation of the N-methyl-D-aspartate receptor and calcium/calmodulin-dependent protein kinase IIα signal in the rostral anterior cingulate cortex is involved in pain-related aversion in rats with peripheral nerve injury

The rostral anterior cingulate cortex (rACC) of rat brain is associated with pain-related emotions. However, the underlying molecular mechanism remains unclear. Here, we investigated the effects of the N-methyl-D-aspartate (NMDA) receptor and Ca2+/Calmodulin-dependent protein kinase type II (CaMKII)α signal on pain-related aversion in the rACC of a rat model of neuropathic pain (NP). Mechanical and thermal hyperalgesia were examined using von Frey and hot plate tests in a rat model of NP induced by spared nerve injury (SNI) of the unilateral sciatic nerve. Bilateral rACC pretreatment with the CaMKII inhibitor tat-CN21 (derived from the cell-penetrating tat sequence and CaM-KIIN amino acids 43-63) or tat-Ctrl (the tat sequence and the scrambled sequence of CN21) was performed on postoperative days 29-35 in Sham rats or rats with SNI. Spatial memory performance was tested using an eight-arm radial maze on postoperative days 34-35. Pain-related negative emotions (aversions) were evaluated using the place escape/avoidance paradigm on postoperative day 35 following the spatial memory performance test. The percentage of time spent in the light area was used to assess pain-related negative emotions (i.e., aversion). The expression levels of the NMDA receptor GluN2B subunit, CaMKIIα, and CaMKII-Threonine at position 286 (Thr286) phosphorylation in contralateral rACC specimens were detected by Western blot or real time PCR following the aversion test. Our data showed that pretreatment of the rACC with tat-CN21 increased determinate behavior but did not alter hyperalgesia or spatial memory performance in rats with SNI. In addition, tat-CN21 reversed the enhanced CaMKII-Thr286 phosphorylation and had no effect on the upregulated expression of GluN2B, CaMKIIα protein, and mRNA. Our data suggested that activation of the NMDA receptor-CaMKIIα signal in rACC is associated with pain-related aversion in rats with NP. These data may provide a new approach for the development of drugs that modulate cognitive and emotional pain aspects.

Altered GABAergic, glutamatergic and endocannabinoid signaling is accompanied by neuroinflammatory response in a zebrafish model of social withdrawal behavior

Introduction

Deficits in social communication are in the core of clinical symptoms characterizing many neuropsychiatric disorders such as schizophrenia and autism spectrum disorder. The occurrence of anxiety-related behavior, a common co-morbid condition in individuals with impairments in social domain, suggests the presence of overlapping neurobiological mechanisms between these two pathologies. Dysregulated excitation/inhibition balance and excessive neuroinflammation, in specific neural circuits, are proposed as common etiological mechanisms implicated in both pathologies.

Methods and Results

In the present study we evaluated changes in glutamatergic/GABAergic neurotransmission as well as the presence of neuroinflammation within the regions of the Social Decision-Making Network (SDMN) using a zebrafish model of NMDA receptor hypofunction, following sub-chronic MK-801 administration. MK-801-treated zebrafish are characterized by impaired social communication together with increased anxiety levels. At the molecular level, the behavioral phenotype was accompanied by increased mGluR5 and GAD67 but decreased PSD-95 protein expression levels in telencephalon and midbrain. In parallel, MK-801-treated zebrafish exhibited altered endocannabinoid signaling as indicated by the upregulation of cannabinoid receptor 1 (CB1R) in the telencephalon. Interestingly, glutamatergic dysfunction was positively correlated with social withdrawal behavior whereas defective GABAergic and endocannabinoid activity were positively associated with anxiety-like behavior. Moreover, neuronal and astrocytic IL-1β expression was increased in regions of the SDMN, supporting the role of neuroinflammatory responses in the manifestation of MK-801 behavioral phenotype. Colocalization of interleukin-1β (IL-1β) with β₂-adrenergic receptors (β₂-ARs) underlies the possible influence of noradrenergic neurotransmission to increased IL-1β expression in comorbidity between social deficits and elevated anxiety comorbidity.

Discussion

Overall, our results indicate the contribution of altered excitatory and inhibitory synaptic transmission as well as excessive neuroinflammatory responses in the manifestation of social deficits and anxiety-like behavior of MK-801-treated fish, identifying possible novel targets for amelioration of these symptoms.

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Stable long-term individual differences in 50-kHz vocalization rate and call subtype prevalence in adult male rats: Comparisons with sucrose preference

Sucrose preference (SP) is a widely used measure of anhedonia in rat models of depression, yet depressed patients do not reliably show an analogous deficit. As an alternative affect-related measure, adult rat ultrasonic vocalizations (USVs) are attracting interest, but it is unclear whether SP and USVs provide independent measures. Here, we have assessed whether SP and USV emission are correlated in the absence of a depressogenic procedure. To this end, 24 male Long-Evans rats were tested daily for 24 days, with alternating SP tests and USV recordings; after a 3-month hiatus, USV emission was re-evaluated for 6 more days. SP was measured in simultaneous two-bottle choice tests, and USVs were recorded in an open field. The main measures were: SP, 50-kHz call rate, and relative prevalence of trill and flat call subtypes. These measures showed temporally-stable individual differences across the initial 24-day testing period, and at the 3-month USV follow-up tests. Correlational analysis revealed no significant relationships between SP and the three main USV measures. Rats differed consistently, not only in their 50-kHz call rates but also in their 50-kHz call profiles (i.e., the relative prevalence of 14 call subtypes); most rats preferentially emitted either trill or flat calls. Several inter-call subtype associations were detected, including a strong negative relationship between the relative prevalence of flat and trill calls. The 50-kHz call rate was correlated with the relative prevalence of only one call subtype (short calls, negative correlation), but was positively correlated with absolute emission rates for almost all subtypes. In conclusion, adult rats exhibited temporally-stable individual differences over weeks (SP) or months (USVs) of testing. This trait-like stability helped to reveal a lack of relationship between SP and the USV-related variables under study, suggesting that these measures may capture different constructs of possible relevance to animal models of depression.

Sucrose Preference Test as a Measure of Anhedonic Behavior in a Chronic Unpredictable Mild Stress Model of Depression: Outstanding Issues

Despite numerous studies on the neurobiology of depression, the etiological and pathophysiological mechanisms of this disorder remain poorly understood. A large number of animal models and tests to evaluate depressive-like behavior have been developed. Chronic unpredictable mild stress (CUMS) is the most common and frequently used model of depression, and the sucrose preference test (SPT) is one of the most common tests for assessing anhedonia. However, not all laboratories can reproduce the main effects of CUMS, especially when this refers to a decrease in sucrose preference. It is also unknown how the state of anhedonia, assessed by the SPT, relates to the state of anhedonia in patients with depression. We analyzed the literature available in the PubMed database using keywords relevant to the topic of this narrative review. We hypothesize that the poor reproducibility of the CUMS model may be due to differences in sucrose consumption, which may be influenced by such factors as differences in sucrose preference concentration threshold, water and food deprivation, and differences in animals’ susceptibility to stress. We also believe that comparisons between animal and human states of anhedonia should be made with caution because there are many inconsistencies between the two, including in assessment methods. We also tried to offer some recommendations that should improve the reproducibility of the CUMS model and provide a framework for future research.

Intranasal oxytocin reduces pre-courtship aggression and increases paternal response in California mice (Peromyscus californicus)

Oxytocin (OXT) is a neuropeptide that can facilitate prosocial behavior and decrease social stress and anxiety but can also increase aggression in some contexts. We investigated whether acute pulses of intranasal (IN) OXT influenced social behavior during social challenges that are likely to occur throughout the lifespan of a wild mouse. To test this, we examined the acute effects of IN OXT in the male California mouse (Peromyscus californicus), a monogamous, biparental, and territorial rodent, using a within-subjects longitudinal design. Social challenges included a pre-courtship male-female encounter conducted during the (1) initial aggressive and not the following affiliative phase of courtship, (2) same-sex resident intruder test, and (3) parental care test. Consecutive tests and doses were separated by at least two weeks. Males were treated with intranasal infusions of 0.8 IU/kg OXT or saline controls 5-min before each behavioral test, receiving a total of three treatments of either IN OXT or saline control. We predicted that IN OXT would 1) decrease aggression and increase affiliation during the pre-courtship aggression phase, 2) increase aggression during resident intruder paradigms, and 3) increase paternal care and vocalizations during a paternal care test. As predicted, during pre-courtship aggression with a novel female, IN OXT males displayed less contact aggression than control males, although with no change in affiliative behavior. However, post-pairing, during the resident intruder test, IN OXT males did not differ from control males in contact aggression. During the paternal care test, IN OXT males were quicker to approach their pups than control males but did not differ in vocalizations produced, unlike our previous research demonstrating an effect on vocalizations in females. In summary, during pre-courtship aggression and the paternal care test, IN OXT reduced antisocial behavior; however, during the resident intruder test, IN OXT did not alter antisocial behavior. These data suggest that IN OXT promotes prosocial behavior specifically in social contexts that can lead to affiliation.

Regulation of the kynurenine/serotonin pathway by berberine and the underlying effect in the hippocampus of the chronic unpredictable mild stress mice

BACKGROUND

Depression is a common mental disorder and is one of the main causes of disability. Berberine (BBR), the major constituent alkaloid originally from the famous Chinese herb Huanglian (Coptis chinensis), has been shown to exert antidepressant-like effects. This study was to investigate the hypothesis that BBR treats depressive-like behavior by shifting the balance of the kynurenine (KYN)/serotonin (5-HT) pathway toward the 5-HT pathway through downregulated indoleamine 2,3-dioxygenase 1 (IDO1), monoamine oxidase A (MAOA) and upregulated dopamine decarboxylase (DDC) in hippocampus.

METHOD

A chronic unpredictable mild stress (CUMS) mice model of depression was established via 21 days unpredictable stimulation. Then the mice were randomly assigned into six groups, namely control, model, fluoxetine [FLU, (10 mg/kg)], BBRL (25 mg/kg), BBRM (50 mg/kg), and BBRH (100 mg/kg) groups. Behavioral assessments were conducted to evaluate the antidepressant effects of BBR. The levels of 5-HT, KYN, tryptophan (TRP), and 5-hydroxyindoleacetic acid (5-HIAA) in hippocampus were estimated using high performance liquid chromatography (HPLC). The mRNA and protein levels of DDC, MAOA and IDO1 in hippocampus were detected by real-time quantitative polymerase chain reaction (qRT-PCR) and western blot (WB), respectively.

RESULT

The results showed that a successful CUMS mice model was established through 21 days of continuous unpredictable stimulation, as indicated by the significant decrease in locomotor activity and increase in immobility time, reduction in body weight and sucrose preference rate etc. Compared with the normal group, the concentrations of KYN/TRP had significantly increased (p^## <0.01) and 5-HT/5-HIAA had decreased (p^#<0.05) at day 21 in the control group, but then improved after drug treatment with FLU and BBR. Compared with the normal group, the mRNA of IDO1 and MAOA were significantly upregulated (p^#<0.05) in the control group, MAOA and IDO1 gene were downregulated by FLU and BBR treatment. Protein expressions of IDO1 and MAOA was significantly increased (p^#<0.05) and DDC downregulated (p^##<0.01). BBR treatment downregulated IDO1 and MAOA, upregulated DDC.

CONCLUSIONS

BBR reversed the abnormalities of the KYN/5-HT pathway in depressed mice and achieved an excellent antidepressant effect. Its direct impact may be observed as changes in biological indicators in mice hippocampus tissue.

Environmental Contributions to Anhedonia

Anhedonia is a core feature of psychopathological conditions that have recent exposure to stress and trauma as central to their etiology. Indeed, evolutionary accounts of depression suggest that decreased motivation to pursue reward may be an adaptive strategy in the face of social stress, in particular, as it may serve to defuse interpersonal conflict. Through a review of rodent models and research with humans, we show that exposure to stress, particularly when it is chronic, repeated, and/or involves themes of social rejection or defeat, is consistently associated with reduced hedonic capacity ("liking"), motivation to pursue reward ("wanting"), and ability to learn from reward ("reward learning"). Further, across rodent and human research, there is evidence that females show greater stress-induced blunting of reward processing than males. In humans, this sex difference emerges most strongly when examining individual differences in the stress response rather than group differences in stress exposure. We discuss the implications of these findings for understanding the etiology of, and sex differences in, stress-related psychopathology, including depression and addiction.

Swimming exercise reduces the vulnerability to stress and contributes to the AKT/GSK3β/CRMP2 pathway and microtubule dynamics mediated protective effects on neuroplasticity in male C57BL/6 mice

While swimming exercise has been shown to positively affect the development of the nervous system, it still remains unclear whether it reduces the vulnerability to stress. In this study, male C57BL/6 mice were exposed to swimming training for 5 weeks, and then subjected to chronic unpredictable mild stress (CUMS) for 4 weeks. We found that swimming exercise prevented anxiety-like and depressive phenotypes induced by CUMS, including increased anxiety-like behavior in the open field test (OFT) and elevated plus-maze (EPM) test and increased despair behavior in the tail suspension test (TST). Moreover, the control+stress group showed reduced expression of phosphorylated AKT kinase (p-AKT), phosphorylated glycogen synthase kinase-3β (p-GSK3β), and tubulin-tyrosine ligase (Tyr-tubulin) and increased protein expression of phosphorylated collapsin response mediator protein 2 (p-CRMP-2); the control+control, swim+control, and swim+stress groups exhibited higher expression of these proteins than the control+stress group. This study confirmed that swimming exercise could reduce the vulnerability of individuals to stress and that it contributes to the AKT/GSK-3β/CRMP-2 pathway and microtubule dynamics mediated protective effects on neuroplasticity. The AKT/GSK-3β/CRMP-2 pathway and microtubule dynamics may be involved in resilience to stress.

Behavioral and Oxidative Stress Changes in Mice Subjected to Combinations of Multiple Stressors Relevant to Irritable Bowel Syndrome

Background and Objectives: Irritable bowel syndrome (IBS) is a well-known functional gastrointestinal (GI) disorder exhibiting a wide range of symptoms due to individual variability and multifactorial etiology. Stress exposure is a major risk factor for the development of IBS. Here, we investigate the differential effects of psychological stress exposures on behavior and oxidative status in mice by using increasingly complex combinations of etiologic IBS-relevant stressors (maternal separation and chronic unpredictable mild stress combinations). Materials and Methods: Mice were subjected to three different combinations of psychological stress factors and subsequent behavioral cognitive and affective parameters and oxidative status markers (superoxide dismutase and glutathione peroxidase antioxidant activity and malondialdehyde level) in the brain and bowel tissues of the animals were analyzed. Results: GI transit modifications reflected by decreased fecal output, cognitive and affective behavioral deficits were observed in all stress exposed groups, but were more evident for the more complex combinations of stressors. Behavioral deficits were accompanied by mild oxidative stress occurring in the bowel and to a greater extent in brain tissue. Conclusions: The presented data depict the effect of various associations in mimicking IBS symptoms and comorbidities and suggest that an all-inclusive combination of early and adult-life psychological stressors is more effective in IBS symptoms modulation. Oxidative stress in both brain and bowel, suggestive for brain-gut molecular connectivity, may play an important role in IBS mechanistic.

Chronic unpredictable restraint stress increases hippocampal pro-inflammatory cytokines and decreases motivated behavior in rats

Most chronic stress protocols are too laborious or do not abide by the two main characteristics of the stress concept: uncontrollability and unpredictability. The goal of this study was to establish a simple and reliable model of chronic stress, while maintaining the main features of the concept. Animals were exposed to chronic movement restraint with variable duration (2, 4 or 6 h, in an unpredictable schedule) for 3 weeks and assessed in several physiological and behavioral readouts known to reflect chronic stress states. Body weight, levels of plasma corticosterone, hippocampal pro-and anti-inflammatory cytokines, anxiety-like (novelty suppressed feeding and elevated plus maze) and motivated behaviors (sucrose negative contrast test and forced swim test) were evaluated three days after the end of the chronic protocol. Stressed animals had a lower body weight gain, higher levels of cytokines in the hippocampus, reduced suppression of a low concentration sucrose solution and increased immobility in the forced swim test. Based on these data, we suggest that chronic movement restraint with variable duration may be a suitable and simple protocol for the study of changes induced by chronic stress and for the testing of possible treatments relevant to psychiatry.

Ketamine and its metabolite, (2R,6R)-HNK, restore hippocampal LTP and long-term spatial memory in the Wistar-Kyoto rat model of depression

Accumulating evidence implicates dysregulation of hippocampal synaptic plasticity in the pathophysiology of depression. However, the effects of ketamine on synaptic plasticity and their contribution to its mechanism of action as an antidepressant, are still unclear. We investigated ketamine’s effects on in vivo dorsal hippocampal (dHPC) synaptic plasticity and their role in mediating aspects of antidepressant activity in the Wistar-Kyoto (WKY) model of depression. dHPC long-term potentiation (LTP) was significantly impaired in WKY rats compared to Wistar controls. Importantly, a single low dose (5 mg/kg, ip) of ketamine or its metabolite, (2R,6R)-HNK, rescued the LTP deficit in WKY rats at 3.5 h but not 30 min following injection, with residual effects at 24 h, indicating a delayed, sustained facilitatory effect on dHPC synaptic plasticity. Consistent with the observed dHPC LTP deficit, WKY rats exhibited impaired hippocampal-dependent long-term spatial memory as measured by the novel object location recognition test (NOLRT), which was effectively restored by pre-treatment with both ketamine or (2R,6R)-HNK. In contrast, in WKYs, which display abnormal stress coping, ketamine, but not (2R,6R)-HNK, had rapid and sustained effects in the forced swim test (FST), a commonly used preclinical screen for antidepressant-like activity. The differential effects of (2R,6R)-HNK observed here reveal a dissociation between drug effects on FST immobility and dHPC synaptic plasticity. Therefore, in the WKY rat model, restoring dHPC LTP was not correlated with ketamine’s effects in FST, but importantly, may have contributed to the reversal of hippocampal-dependent cognitive deficits, which are critical features of clinical depression. Our findings support the theory that ketamine may reverse the stress-induced loss of connectivity in key neural circuits by engaging synaptic plasticity processes to “reset the system”.

Chronic unpredictable intermittent restraint stress disrupts spatial memory in male, but not female rats

Chronic stress leads to sex-dependent outcomes on spatial memory by producing deficits in males, but not in females. Recently it was reported that compared to daily restraint, intermittent restraint (IR) produced more robust stress and anxiety responses in male rats. Whether IR would be sufficiently robust to impair hippocampal-dependent spatial memory in both male and female rats was investigated. IR involved mixing restraint with non-restraint days over weeks before assessing spatial memory and anxiety profile on the radial arm water maze, object placement, novel object recognition, Y-maze, open field and novelty suppressed feeding. Experiments 1 and 2 used Sprague-Dawley male rats only and determined that IR for 6 h/d (IR6), but not 2 h/d, impaired spatial memory and that task order was important. In experiment 3, IR6 was extended for 6wks before spatial memory testing commenced using both sexes. Unexpectedly, an extended IR6 paradigm failed to impair spatial memory in either sex, suggesting that by 6wks IR6 may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not in females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not in females. We interpret these findings to show that females are more resilient to chronic stress than are males as it pertains to spatial ability.

Risk of Developing Hepatocellular Carcinoma following Depressive Disorder Based on the Expression Level of Oatp2a1 and Oatp2b1

Background

Accumulating evidence from prospective epidemiological studies has showed that depression disorder (DD) is a risk factor for cancer. The aim of this study is to explore the association of DD and the overall occurrence risk of hepatocellular carcinoma (HCC) and the mechanism.

Methods

In this study, 60 mice were randomly divided into four groups: Control group, DD group, HCC group, HCC-DD group. Mice received a chronic dose of reserpine to establish depression model, followed by Diethylnitrosamine and Carbon tetrachloride administration to establish HCC models. Behavioral depression was assessed by sucrose preference test (SPT) and the expression of Serotonin 1A (5-HT1A) receptor in the hippocampal. The expression of Oatp2a1 and Oatp2b1 in the digestive system tissues was detected by PCR and western blotting.

Results

Reserpine-administrated mice had a reducing sucrose preference at Day 14 compared with blank mice (P<0.05). The expression of 5-HT1A receptor in the hippocampal was decreased in DD mice compared with blank mice. The survival analysis indicated that the HCC mice with DD have poorer survival rate compared with the HCC mice. Compared with HCC mice, the expression of Oatp2a1 and Oatp2b1 was lower in liver and stomach tissue and higher in hepatic carcinoma and colon tissue of HCC-DD mice (P<0.05), and the expression of Oatp2a1 was higher in the spleen tissue of HCC-DD mice while the expression of Oatp2b1 was lower (P<0.05). However, no difference was found in the expression of Oatp2a1 and Oatp2b1 in the small intestine tissue between HCC group and HCC-DD group.

Conclusions

DD was the adverse factors for the overall occurrence risk of HCC. Mechanistically, be the downregulation of Oatp2a1 and Oatp2b1 in liver tissue induced by DD might be involved.

The role of prefrontal cortex dopamine D2 and D3 receptors in the mechanism of action of venlafaxine and deep brain stimulation in animal models of treatment-responsive and treatment-resistant depression

AIMS

The Wistar-Kyoto rat has been validated as an animal model of treatment-resistant depression. Here we investigated a role of dopamine D2 and D3 receptors in the ventro-medial prefrontal cortex in the mechanism of action of deep brain stimulation in Wistar-Kyoto rats and venlafaxine in Wistar rats.

METHODS

Wistar or Wistar-Kyoto rats were exposed chronically to chronic mild stress. Wistar rats were treated chronically with venlafaxine (10 mg/kg) beginning after two weeks of chronic mild stress; Wistar-Kyoto rats received two sessions of deep brain stimulation before behavioural tests. L-742,626 (1 µg), a D2 receptor agonist, or 7-OH DPAT (3 µg), a D3 receptor antagonist, were infused into the ventro-medial prefrontal cortex immediately following the exposure trial in the Novel Object Recognition Test, and discrimination between novel and familiar object was tested one hour later.

RESULTS

Chronic mild stress decreased sucrose intake and impaired memory consolidation; these effects were reversed by venlafaxine in Wistar rats and deep brain stimulation in Wistar-Kyoto rats. In control animals, L-742,626 and 7-OH DPAT also impaired memory consolidation. In Wistar rats, venlafaxine reversed the effect of L-742,626 in controls, but not in the chronic mild stress group, and venlafaxine did not reverse the effect of 7-OH DPAT in either group. In Wistar-Kyoto rats, deep brain stimulation reversed the effect of both L-742,626 and 7-OH DPAT in both control and chronic mild stress groups.

CONCLUSIONS

We conclude that the action of venlafaxine to reverse the impairment of memory consolidation caused by chronic mild stress in Wistar rats involves D2 receptors in the ventro-medial prefrontal cortex; but the effect of deep brain stimulation to reverse the same effect in Wistar-Kyoto rats does not.

Spinal cord injury by clip-compression induces anxiety and depression-like behaviours in female rats: The role of the inflammatory response

Traumatic spinal cord injury (SCI) promotes long-term disability that affects mobility and functional independence. The spinal cord inflammatory response after the initial mechanical insult substantially impacts locomotor impairment and development of neuropsychiatric disorders, including anxiety and depression. However, these psychiatric events are scarcely investigated in females. This study investigated the anxiety/depression-like behaviours and inflammatory responses related to the production/release of pro- and anti-inflammatory cytokines in female adult Wistar rats submitted to severe clip-compression SCI. Data showed that SCI impaired the locomotor performance assessment by the BBB scale, but did not alter exploratory activity in open-field test. Animals' locomotor impairment was associated with anxious and depressive-like behaviours characterised by a decreased amount of time in the open arms of the elevated plus-maze test, and the motivational reduction of social interaction and anhedonia assessed by social exploration and sucrose preference tests. By contrast, SCI decreased the immobility time in the forced swimming test. Moreover, SCI caused a significant increase in local and systemic proinflammatory cytokines (TNF-α, INF-γ, IL-1β, and IL-6) and a reduction in the anti-inflammatory cytokine IL-10. Finally, there were significant negative correlations between depression-like behaviour, but not anxiety, and increased plasma concentrations of TNF-α, IL-1β, IL-6, and INF-γ. Additionally, the laminectomy procedure provoked the inflammatory response associated with reduced sucrose intake in Sham animals, although less expressively than in the SCI group. Collectively, these results indicate that SCI by clip-compression in female rats promotes a neuropsychiatric-like profile associated with an imbalance in the production/release of pro- and anti-inflammatory cytokines.

Chronic Unpredictable Stress Reduces Immunostaining for Connexins 43 and 30 and Myelin Basic Protein in the Rat Prelimbic and Orbitofrontal Cortices

Background

Astrocytes and oligodendrocytes are pathologically altered in dorsolateral prefrontal and orbitofrontal cortices in major depressive disorder. In rat models of stress (major depressive disorder risk factor) astrocyte gap junction protein connexin 43 (Cx43) is reduced in the prelimbic cortex. Astrocyte connexins are recognized to strongly influence myelin maintenance in the central nervous system. However, it is unknown whether stress-related changes in Cx43 and the other major astrocyte connexin, Cx30, occur in the orbitofrontal cortex, or whether connexin changes are concurrent with disturbances in myelination.

Methods

Frozen sections containing prelimbic cortex and orbitofrontal cortex of rats subjected to 35 days of chronic unpredictable stress and controls (n = 6/group) were immunolabeled for Cx43, Cx30, and myelin basic protein. Density of Cx43 or Cx30 immunoreactive puncta and area fraction of myelin basic protein immunoreactivity were measured in prelimbic cortex and orbitofrontal cortex and results analyzed with t test or Pearson correlations.

Results

Density of Cx43- and Cx30-positive puncta in both prelimbic cortex and orbitofrontal cortex was lower in chronic unpredictable stress-treated than in control rats. In both regions, the area fraction of myelin basic protein immunoreactivity was also lower in chronic unpredictable stress animals. Myelin basic protein area fraction was positively correlated with the density of Cx43-positive puncta in orbitofrontal cortex, and with Cx30 puncta in prelimbic cortex.

Conclusion

Low Cx43 and Cx30 after chronic unpredictable stress in rat prelimbic cortex and orbitofrontal cortex suggests that reduced astrocytic gap junction density may generalize to the entire prefrontal cortex. Concurrent reduction of Cx43-, Cx30-, and myelin basic protein-immunolabeled structures is consistent with a mechanism linking changes in astrocyte gap junction proteins and disturbed myelin morphology in depression.

Ultrasonic vocalizations as a tool in studying emotional states in rodent models of social behavior and brain disease

Rodents emit ultrasonic vocalizations (USVs) to communicate the presence of positive or negative emotional states and to coordinate social interactions. On this basis, USVs are increasingly being used as a behavioral readout in rodent studies of affect, motivation and social behavior. Notably, several investigations have demonstrated that rodents emit USVs when tested in experimental paradigms that are used in preclinical studies of psychiatric and neurological diseases. Moreover, it has been shown that calling behavior may be influenced by genetic and/or environmental factors (i.e., stress), early rearing conditions that have been implicated in brain disease, as well as psychoactive drugs. Hence, measuring USV emissions has emerged as a useful tool in studying the mechanisms that underlie the emotional disturbances featuring certain brain diseases, as well as in the development of suited pharmacological therapies. This review provides an overview of the behavioral significance of USV emissions and describes the contexts that promote calling behavior in rats and mice. Moreover, the review summarizes the current evidence concerning the use of USVs as a marker of affect in rat and mouse models of sociability, psychiatric diseases and neurological diseases, and discusses the strengths and current limitations of using USVs as a behavioral readout in rodent studies of emotional behavior. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Glucocorticoid receptor activation induces decrease of hippocampal astrocyte number in rats

RATIONALE

The decrease of astrocyte number and hypothalamic-pituitary-adrenal (HPA) axis overactivity are observed in individuals with major depressive disorder. Elevated levels of glucocorticoids induced by hyperactivation of the HPA axis may result in glucocorticoid receptor (GR) activation. However, it is unclear whether there is a direct link between GR activation and the decrease of astrocyte number.

METHODS

Animals were exposed to chronic unpredictable stress (CUS) for 28 days and treated with continuous subcutaneous injections of vehicle or corticosterone (CORT; 40 mg/kg/day) for 21 days. We then administered mifepristone on day 21 after CUS and on day 18 after the CORT treatment. We observed behavioral deficits in the sucrose preference test, open field test, and forced swim test. Protein expression was analyzed using immunofluorescence (IF) and western blot (WB).

RESULTS

Animals exposed to CUS exhibited behavioral deficits in tests measuring anhedonia, anxiety, and despair state. They also had decreases in glial fibrillary acidic protein (GFAP) expression and numbers of GFAP-positive cells in the hippocampus. The behavioral and cellular alterations induced by CUS were reversed by subchronic treatment with the GR antagonist mifepristone. We also found that the subcutaneous injection of glucocorticoids may induce depression-like behavior and reduce GFAP protein expression in rats, which was similarly reversed by mifepristone.

CONCLUSIONS

These findings provide experimental evidence that GR activation due to elevated CORT levels induces the decrease of hippocampal astrocyte number in rats.

Astrocyte pathology in the ventral prefrontal white matter in depression

Astrocyte functions in white matter are less well understood than in gray matter. Our recent study of white matter in ventral prefrontal cortex (vPFC) revealed alterations in expression of myelin-related genes in major depressive disorder (MDD). Since white matter astrocytes maintain myelin, we hypothesized that morphometry of these cells will be altered in MDD in the same prefrontal white matter region in which myelin-related genes are altered. White matter adjacent to vPFC was examined in 25 MDD and 21 control subjects. Density and size of GFAP-immunoreactive (-ir) astrocyte cell bodies was measured. The area fraction of GFAP-ir astrocytes (cell bodies + processes) was also estimated. GFAP mRNA expression was determined using qRT-PCR. The density of GFAP-ir astrocytes was also measured in vPFC white matter of rats subjected to chronic unpredictable stress (CUS) and control animals. Fibrous and smooth GFAP-ir astrocytes were distinguished in human white matter. The density of both types of astrocytes was significantly decreased in MDD. Area fraction of GFAP immunoreactivity was significantly decreased in MDD, but mean soma size remained unchanged. Expression of GFAP mRNA was significantly decreased in MDD. In CUS rats there was a significant decrease in astrocyte density in prefrontal white matter. The decrease in density and area fraction of white matter astrocytes and GFAP mRNA in MDD may be linked to myelin pathology previously noted in these subjects. Astrocyte pathology may contribute to axon disturbances in axon integrity reported by neuroimaging studies in MDD and interfere with signal conduction in the white matter.

Antidepressant-Like Actions of Inhibitors of Poly(ADP-Ribose) Polymerase in Rodent Models

BACKGROUND

Many patients suffering from depressive disorders are refractory to treatment with currently available antidepressant medications, while many more exhibit only a partial response. These factors drive research to discover new pharmacological approaches to treat depression. Numerous studies demonstrate evidence of inflammation and elevated oxidative stress in major depression. Recently, major depression has been shown to be associated with elevated levels of DNA oxidation in brain cells, accompanied by increased gene expression of the nuclear base excision repair enzyme, poly(ADP-ribose) polymerase-1. Given these findings and evidence that drugs that inhibit poly(ADP-ribose) polymerase-1 activity have antiinflammatory and neuroprotective properties, the present study was undertaken to examine the potential antidepressant properties of poly(ADP-ribose) polymerase inhibitors.

METHODS

Two rodent models, the Porsolt swim test and repeated exposure to psychological stressors, were used to test the poly(ADP-ribose) polymerase inhibitor, 3-aminobenzamide, for potential antidepressant activity. Another poly(ADP-ribose) polymerase inhibitor, 5-aminoisoquinolinone, was also tested.

RESULTS

Poly(ADP-ribose) polymerase inhibitors produced antidepressant-like effects in the Porsolt swim test, decreasing immobility time, and increasing latency to immobility, similar to the effects of fluoxetine. In addition, 3-aminobenzamide treatment increased sucrose preference and social interaction times relative to vehicle-treated control rats following repeated exposure to combined social defeat and unpredictable stress, mediating effects similar to fluoxetine treatment.

CONCLUSIONS

The poly(ADP-ribose) polymerase inhibitors 3-aminobenzamide and 5-aminoisoquinolinone exhibit antidepressant-like activity in 2 rodent stress models and uncover poly(ADP-ribose) polymerase as a unique molecular target for the potential development of a novel class of antidepressants.

Dopaminergic mechanisms in memory consolidation and antidepressant reversal of a chronic mild stress-induced cognitive impairment`

Cognitive deficits in depression can be modelled using the novel object recognition (NOR) test, performance in which is impaired by chronic mild stress (CMS). We aimed to examine the involvement of mesocorticolimbic DA terminal regions, and to establish the substrate for CMS-induced impairment of NOR and its reversal by chronic antidepressant treatment. In experiments 1 and 2, we examined the effect of infusions into medial PFC, dorsal hippocampus (HPC), and nucleus accumbens (NAc) shell of D1 and D2 antagonists and D3 agonist, which were predicted to impair NOR with a short (1 h) delay, and of D1 and D2 agonists and D3 antagonist, which were predicted to facilitate NOR with a long (24 h) delay. Using optimal doses identified in experiment 2, in experiments 3 and 4, we examined effects on drug-stimulated NOR of CMS and chronic treatment with venlafaxine (VFX) or risperidone (RSP). We found a wide involvement of DA systems in memory for NOR: D1 receptors in PFC, HPC, and NAc; D3 receptors in PFC and HPC; and D2 receptors in PFC. CMS impaired D2- and D3-mediated effects in PFC and HPC; antidepressants rescued those effects in PFC but not HPC. The involvement of DA in NOR is multifaceted, but the effects of CMS and antidepressants are more discrete, involving D2 and D3 receptors in PFC specifically. While raising many difficult questions, these results suggest that the D2 and D3 receptors in the medial PFC may be an important substrate for cognitive deficits in depression and their remediation.