Anxiety- and depressive-like profiles during early- and mid-adolescence in the female Wistar Kyoto rat

Prenatal and postnatal cocaine exposure enhances the anxiety- and depression-like behaviors in rats during cocaine withdrawal

Prenatal drug exposure is a public health problem, which results in profound behavioral problems during childhood and adolescence, mainly represented by an increase in the risk of cocaine abuse at an early age. In rodents, prenatal and postnatal cocaine exposure enhanced locomotor activity and cocaine- or nicotine-induced locomotor sensitization. Various authors consider that the adverse emotional states (anxiety and depression) that occur during cocaine withdrawal are the main factors that precipitate, relapse, and increase chronic cocaine abuse, which could increase the risk of relapse of cocaine abuse. Therefore, the objective of this study was to characterize anxiety- and depression-like behaviors at different times (30, 60, 90, and 120 days) of cocaine withdrawal in rats born to females exposed prenatally and postnatally to cocaine. A group of pregnant female Wistar rats were administered daily from day GD0 to GD21 with cocaine (cocaine preexposure group), and another group of pregnant female rats was administered daily with saline (saline preexposure group). Of the litters resulting from the cocaine-pre-exposed and saline-pre-exposed pregnant female groups, only the male rats were used for the recording of the anxiety- and depression-like behaviors at different times (30, 60, 90, and 120 days) of cocaine withdrawal The study found that prenatal and postnatal cocaine exposure dose-dependent enhanced anxiety- and depression-like behaviors. This suggests that prenatal and postnatal cocaine exposure can result in enhanced vulnerability to cocaine abuse in young and adult humans.

Protective Effects of Resveratrol on Adolescent Social Isolation-Induced Anxiety-Like Behaviors via Modulating Nucleus Accumbens Spine Plasticity and Mitochondrial Function in Female Rats

Social isolation (SI) is a major risk factor for mood disorders in adolescents. The nucleus accumbens (NAc) is an important reward center implicated in psychiatric disorders. Resveratrol (RSV) is one of the most effective natural polyphenols with anti-anxiety and depression effects. However, little is known about the therapeutic effects and mechanisms of RSV on behavioral abnormality of adolescent social stress. Therefore, this study aimed to investigate the underlying mechanism of RSV on the amelioration of SI-induced behavioral abnormality. We found that SI induced anxiety-like behavior and social dysfunction in isolated female rats. Moreover, SI reduced mitochondrial number and ATP levels and increased thin spine density in the NAc. RNA sequencing results showed that SI changed the transcription pattern in the NAc, including 519 upregulated genes and 610 downregulated genes, especially those related to mitochondrial function. Importantly, RSV ameliorated behavioral and spine abnormalities induced by SI and increased NAc ATP levels and mitochondria number. Furthermore, RSV increased the activity of cytochrome C oxidase (COX) and upregulated mRNA levels of Cox5a, Cox6a1 and Cox7c. These results demonstrate that the modulation of spine plasticity and mitochondrial function in the NAc by RSV has a therapeutic effect on mood disorders induced by social isolation.

Improved 3D tracking and automated classification of rodents' behavioral activity using depth-sensing cameras

Analysis of rodents' behavior/activity is of fundamental importance in many research fields. However, many behavioral experiments still rely on manual scoring, with obvious problems in reproducibility. Despite important advances in video-analysis systems and computational ethology, automated behavior quantification is still a challenge. The need for large training datasets, background stability requirements, and reduction to two-dimensional analysis (impairing full posture characterization), limit their use. Here we present a novel integrated solution for behavioral analysis of individual rats, combining video segmentation, tracking of body parts, and automated classification of behaviors, using machine learning and computer vision methods. Low-cost depth cameras (RGB-D) are used to enable three-dimensional tracking and classification in dark conditions and absence of color contrast. Our solution automatically tracks five anatomical landmarks in dynamic environments and recognizes seven distinct behaviors, within the accuracy range of human annotations. The developed free software was validated in experiments where behavioral differences between Wistar Kyoto and Wistar rats were automatically quantified. The results reveal the capability for effective automated phenotyping. An extended annotated RGB-D dataset is also made publicly available. The proposed solution is an easy-to-use tool, with low-cost setup and powerful 3D segmentation methods (in static/dynamic environments). The ability to work in dark conditions means that natural animal behavior is not affected by recording lights. Furthermore, automated classification is possible with only ~30 minutes of annotated videos. By creating conditions for high-throughput analysis and reproducible quantitative measurements of animal behavior experiments, we believe this contribution can greatly improve behavioral analysis research.

The Wistar-Kyoto rat model of endogenous depression: A tool for exploring treatment resistance with an urgent need to focus on sex differences

Major depressive disorder (MDD) is one of the leading causes of years lived with disability and contributor to the burden of disease worldwide. The incidence of MDD has increased by ~20% in the last decade. Currently antidepressant drugs such as the popular selective serotonin reuptake inhibitors (SSRIs) are the leading form of pharmaceutical intervention for the treatment of MDD. SSRIs however, are inefficient in ameliorating depressive symptoms in ~50% of patients and exhibit a prolonged latency of efficacy. Due to the burden of disease, there is an increasing need to understand the neurobiology underpinning MDD and to discover effective treatment strategies. Endogenous models of MDD, such as the Wistar-Kyoto (WKY) rat provide a valuable tool for investigating the pathophysiology of MDD. The WKY rat displays behavioural and neurobiological phenotypes similar to that observed in clinical cases of MDD, as well as resistance to common antidepressants. Specifically, the WKY strain exhibits increased anxiety- and depressive-like behaviours, as well as alterations in Hypothalamic Pituitary Adrenal (HPA) axis, serotonergic, dopaminergic and neurotrophic systems with emerging studies suggesting an involvement of neuroinflammation. More recent investigations have shown evidence for reduced cortical and hippocampal volumes and altered glutamatergic signalling in the WKY strain. Given the growing interest in therapeutics targeting the glutamatergic system, the WKY strain presents itself as a potentially useful tool for screening novel antidepressant drugs and their efficacy against treatment resistant depression. However, despite the sexual dimorphism present in the pathophysiology and aetiology of MDD, sex differences in the WKY model are rarely investigated, with most studies focusing on males. Accordingly, this review highlights what is known regarding sex differences and where further research is needed. Whilst acknowledging that investigation into a range of depression models is required to fully elucidate the underlying mechanisms of MDD, here we review the WKY strain, and its relevance to the clinic.

Wistar Kyoto Rats Display Anhedonia In Consumption but Retain Some Sensitivity to the Anticipation of Palatable Solutions

The Wistar Kyoto (WKY) rat has been proposed as a model of depression-like symptoms. However, anhedonia-a reduction in the response to normatively rewarding events-as a central depression symptom has yet to be fully assessed in this model. We compared WKY rats and Wistar controls, with stress-susceptibility examined by applying mild unpredictable stress to a subset of each group. Anhedonia-like behavior was assessed using microstructural analysis of licking behavior, where mean lick cluster size reflects hedonic responses. This was combined with tests of anticipatory contrast, where the consumption of a moderately palatable solution (4% sucrose) is suppressed in anticipation of a more palatable solution (32% sucrose). WKY rats displayed greatly attenuated hedonic reactions to sucrose overall, although their reactions retained some sensitivity to differences in sucrose concentration. They displayed normal reductions in consumption in anticipatory contrast, although the effect of contrast on hedonic reactions was greatly blunted. Mild stress produced overall reductions in sucrose consumption, but this was not exacerbated in WKY rats. Moreover, mild stress did not affect hedonic reactions or the effects of contrast. These results confirm that the WKY substrain expresses a direct behavioral analog of anhedonia, which may have utility for increasing mechanistic understanding of depression symptoms.

Validation of chronic mild stress in the Wistar-Kyoto rat as an animal model of treatment-resistant depression

A recent review proposed four criteria for an animal model of treatment-resistant depression (TRD): a phenotypic resemblance to a risk factor for depression; enhanced response to stress; nonresponse to antidepressant drugs and response to treatments effective in TRD, such as deep brain stimulation (DBS) of the prefrontal cortex or ketamine. Chronic mild stress (CMS) provides a valid model of depression; the Wistar-Kyoto (WKY) rat is considered to be nonresponsive to antidepressant drugs. Here, we applied CMS to WKY rats. WKY and Wistar rats were exposed to CMS, then treated with saline, imipramine, citalopram or venlafaxine. After 5 weeks of CMS and 3 weeks of drug treatment, all WKY groups were implanted unilaterally with DBS electrodes in the prefrontal cortex, and examined in sucrose intake, elevated plus maze (EPM; decreased entries and time in the open arms) and novel object recognition (decreased exploration) tests, following 2×2 h of DBS. CMS decreased sucrose intake, open arm entries on the EPM, and object recognition. Relative to Wistars, WKY rats showed evidence of increased emotionality in the EPM and novel object recognition tests, and a greater impact of CMS on body weight gain and open arm entries. Wistars responded to drug treatment with an increase in sucrose intake but WKY were nonresponsive to drug treatment on all three behavioural tests. With one exception, DBS reversed the anhedonic, anxiogenic and dyscognitive effects of CMS in all groups of WKY rats. In a further experiment, subacute ketamine (10 mg/kg) also normalized behaviour on all three tests. We conclude that WKY rats subjected to CMS meet all four criteria for a valid model of TRD, and provide a basis for studying the mechanism of action of DBS.

Stressor during Early Adolescence in Hyperreactive Female Wistar Kyoto Rats Induces a 'Double Hit' Manifested by Variation in Neurobehaviors and Brain Monoamines

Stress is an additive factor in the development of depressive-like profiles that mainly onsets during adolescence. However, effects of early post-weaning stress on developing brain neurochemical pathways in inducing anxiety- and depressive-like profiles in vulnerable females have not been extensively studied. The Wistar Kyoto (WKY) rat, a putative model of adolescent depression and stress-sensitivity could elucidate the pathophysiology of stress-related depression in vulnerability. Through such an approach, links between inherent risk for predisposition to depression and homotypic stress, as in a 'double hit' would unravel endocrine regulation, interference in developing neural pathways and neurobehaviors. Here, early adolescent WKY female rats were subjected to 1-h physical restraint over 7 days followed by neurobehavioral testing in the elevated plus maze (EPM) and forced swim test (FST). The stressor's effectiveness was assayed by plasma corticosterone (CORT) and altered functioning in depression-implicated brain areas by assaying monoamines/metabolites. Homotypic stress induced an anxiolytic-like response in the EPM with learned helplessness and reduced struggling behavior in FST. Significant elevation in CORT levels (p < 0.05) indicated an upregulated HPA axis. Medial prefrontal cortex, a still maturing brain area, exhibited increased serotonin (5-HT) metabolite (p < 0.01) and turnover rates (p < 0.01) indicative of altered/maladaptive serotonergic functioning. Nucleus accumbens (p < 0.05) and dorsal striatum (p < 0.01) also depicted increased 5-HT metabolite, with the latter also demonstrating reduced Dopamine turnover (p < 0.01) as a result of homotypic stress. Hence, female WKY rats could constitute a diathesis-stress model to study underlying mechanisms of stress-related depression.

Developmental expression of anxiety and depressive behaviours after prenatal predator exposure and early life homecage enhancement

Stressful events during gestation can have sex-specific effects on brain and behaviour, and may contribute to some of the differences observed in adult stress responding and psychopathology. We investigated the impact of a novel repeated prenatal psychological stress (prenatal predator exposure - PPS) during the last week of gestation in rats on offspring behaviours related to social interaction (play behaviour), open field test (OFT), forced swim test (FST) and sucrose preference test (SP) during the juvenile period and in adulthood. We further examined the role of postnatal environmental, using an enhanced housing condition (EHC), to prevent/rescue any changes. Some effects on anxiety, anhedonia, and stress-related coping behaviours (e.g., OFT, SP and OFT) did not emerge until adulthood. PPS increased OFT anxiety behaviours in adult males, and some OFT and SP behaviours in adult females. Contrary to this, EHC had few independent effects; most were apparent only when combined with PPS. In keeping with age-group differences, juvenile behaviours did not necessarily predict the same adult behaviours although juvenile OFT rearing and freezing, and juvenile FST immobility did predict adult FST immobility and sucrose preference, suggesting that some aspects of depressive behaviours may emerge early and predict adult vulnerability or coping behaviours. Together, these results suggest an important, though complex, role for early life psychological stressors and early life behaviours in creating an adult vulnerability to anxiety or depressive disorders and that environmental factors further modulate the effects of the prenatal stressors.

Heterogeneous stock rats: a model to study the genetics of despair-like behavior in adolescence

Major depressive disorder (MDD) is a complex illness caused by both genetic and environmental factors. Antidepressant resistance also has a genetic component. To date, however, very few genes have been identified for major depression or antidepressant resistance. In this study, we investigated whether outbred heterogeneous stock (HS) rats would be a suitable model to uncover the genetics of depression and its connection to antidepressant resistance. The Wistar Kyoto (WKY) rat, one of the eight founders of the HS, is a recognized animal model of juvenile depression and is resistant to fluoxetine antidepressant treatment. We therefore hypothesized that adolescent HS rats would exhibit variation in both despair-like behavior and response to fluoxetine treatment. We assessed heritability of despair-like behavior and response to sub-acute fluoxetine using a modified forced swim test (FST) in 4-week-old HS rats. We also tested whether blood transcript levels previously identified as depression biomarkers in adolescent human subjects are differentially expressed in HS rats with high vs. low FST immobility. We demonstrate heritability of despair-like behavior in 4-week-old HS rats and show that many HS rats are resistant to fluoxetine treatment. In addition, blood transcript levels of Amfr, Cdr2 and Kiaa1539, genes previously identified in human adolescents with MDD, are differentially expressed between HS rats with high vs. low immobility. These data demonstrate that FST despair-like behavior will be amenable to genetic fine-mapping in adolescent HS rats. The overlap between human and HS blood biomarkers suggest that these studies may translate to depression in humans.

Estrous Cycle Phase-Dependent Changes in Anxiety- and Depression-Like Profiles in the Late Adolescent Wistar-Kyoto Rat

BACKGROUND

Depression often manifests during adolescence when the development and networking of social and emotional brain areas is being influenced by hormones. The Wistar Kyoto (WKY) rat has been proposed as an animal model of adolescent depression with various face, construct, and predictive validities for clinical depression having been established.

PURPOSE

The influence of the estrous cycle on anxiety- and depression-like behaviors in female adolescents may be tested out further using this model.

METHODS

Female adolescent WKY rats were tested for anxiety- and depression-like behaviors in the elevated plus maze and forced swim test (FST) during different phases of the estrous cycle with inbred, age-, and phase-matched Wistar rats as controls.

RESULTS

Wistars in proestrus-estrus demonstrated reduced anxiety levels. WKY also demonstrated increased open arm time and entries and closed arm time, but less than Wistars, and as closed arm entries remained unaffected, it did not translate into a lowering of the anxiety levels. Risk taking and risk assessment behaviors were not affected by estrous phases in WKY, though exploratory behavior was reduced in proestrus-estrus. In Wistars, increased risk taking and decreased risk assessment behaviors were observed during proestrus-estrus. Increased immobility in the FST, indicative of learned helplessness was not influenced by phase in the WKY, which was at variance with Wistars that demonstrated phase-specific differences.

CONCLUSION

Results indicate a masking effect of indicative hormones in this putative model of adolescent depression, with implications for an unravelling of the steroid milieu in predisposed adolescent depression and for taking phase-specific time windows into account for therapeutic interventions.

Brief Social Isolation in the Adolescent Wistar-Kyoto Rat Model of Endogenous Depression Alters Corticosterone and Regional Monoamine Concentrations

The Wistar-Kyoto rat (WKY) model has been suggested as a model of adult and adolescent depression though face, predictive and construct validities of the model to depression remain equivocal. The suitability of the WKY as a diathesis model that tests the double-hit hypothesis, particularly during critical periods of brain and behavioural development remains to be established. Here, effects of post-weaning social isolation were assessed during early adolescence (~30pnd) on behavioural despair and learned helplessness in the forced swim test (FST), plasma corticosterone levels and tissue monoamine concentrations in brain areas critically involved in depression, such as prefrontal cortex, nucleus accumbens, striatum and hippocampus. Significantly increased immobility in the FST was observed in socially-isolated, adolescent WKY with a concomitant increase in corticosterone levels over and above the FST-induced stress. WKY also demonstrated a significantly increased release and utilization of dopamine, as manifested by levels of metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid in nucleus accumbens, indicating that the large dopamine storage pool evident during adolescence induces greater dopamine release when stimulated. The serotonin metabolite 5-hydroxy-indoleacetic acid was also significantly increased in nucleus accumbens, indicating increased utilization of serotonin, along with norepinephrine levels which were also signficantly elevated in socially-isolated adolescent WKY. Differences in neurochemistry suggest that social or environmental stimuli during critical periods of brain and behavioural development can determine the developmental trajectories of implicated pathways.

Immediate and delayed anxiety- and depression-like profiles in the adolescent Wistar-Kyoto rat model of endogenous depression following postweaning social isolation

In order to understand links that exist between inherited risk or predisposition, brain and behavioural development, endocrine regulation and social/environmental stimuli, animal models are crucial. The Wistar-Kyoto (WKY) rat has been shown to have validity as a model of adult and adolescent depression. While sex- and age-specific differences in some of the face, predictive and construct validities of the model such as depression-like behaviours have been established, anhedonia and anxiety using other induced anxiety paradigms such as elevated plus maze remain equivocal. First, post-weaning social isolation effects on inherent and induced anxiety behaviours were tested during two critical time periods, early- and mid-adolescence. Isolation induced immediate effects on novel environment-induced hyperactivity and anxiety-related behaviours. Adolescent WKYs demonstrated reduced 50-kHz ultrasonic vocalizations suggesting agoraphobia-like behaviours. Second, isolated rats, despite being subsequently social-/group-housed demonstrated longer lasting effects on social interaction measures and anhedonia. This establishes that the depression-like profile observed during early- and mid-adolescence persists into late adolescence and early adulthood in WKY. Further, that interventions at a later stage during adolescence may not be able to reverse early adolescent effects in the context of pre-disposition, thus highlighting the irreversibility of being double-hit during critical time periods of brain and behavioural development and maturation.