Strain-dependent modification of behavior following antidepressant treatment

Supplementation with Lactobacillus helveticus NS8 alleviated behavioral, neural, endocrine, and microbiota abnormalities in an endogenous rat model of depression

Introduction

Major depressive disorder is a condition involving microbiota-gut-brain axis dysfunction. Increasing research aims to improve depression through gut microbiota regulation, including interventions such as probiotics, prebiotics, and fecal microbiota transplants. However, most research focuses on exogenous depression induced by chronic stress or drugs, with less attention given to endogenous depression. Additionally, research on gut mycobiota in depression is significantly less than that on gut bacteria.

Methods

In the present study, Wistar-Kyoto rats were used as an endogenous depression and treatment-resistant depression model, while Wistar rats served as controls. Differences between the two rat strains in behavior, gut bacteria, gut mycobiota, nervous system, endocrine system, immune system, and gut barrier were evaluated. Additionally, the effects of Lactobacillus helveticus NS8 supplementation were investigated.

Results

Wistar-Kyoto rats demonstrated increased depressive-like behaviors in the forced swimming test, reduced sucrose preference in the sucrose preference test, and decreased locomotor activity in the open field test. They also exhibited abnormal gut bacteria and mycobiota, characterized by higher bacterial α-diversity but lower fungal α-diversity, along with increased butyrate, L-tyrosine, and L-phenylalanine biosynthesis from bacteria. Furthermore, these rats showed dysfunction in the microbiota-gut-brain axis, evidenced by a hypo-serotonergic system, hyper-noradrenergic system, defective hypothalamic-pituitary-adrenal axis, compromised gut barrier integrity, heightened serum inflammation, and diminished gut immunity. A 1-month L. helveticus NS8 intervention increased the fecal abundance of L. helveticus; reduced the abundance of Bilophila and Debaryomycetaceae; decreased immobility time but increased climbing time in the forced swimming test; reduced hippocampal corticotropin-releasing hormone levels; decreased hypothalamic norepinephrine levels; increased hippocampal glucocorticoid receptor, brain-derived neurotrophic factor dopamine, and 5-hydroxyindoleacetic acid content; and improved the gut microbiota, serotonergic, and noradrenergic system.

Conclusion

The depressive phenotype of Wistar-Kyoto rats is not only attributed to their genetic context but also closely related to their gut microbiota. Abnormal gut microbiota and a dysfunctional microbiota-gut-brain axis play important roles in endogenous depression, just as they do in exogenous depression. Supplementing with probiotics such as L. helveticus NS8 is likely a promising approach to improve endogenous depression and treatment-resistant depression.

The need for guidance in antidepressant drug development: Revisiting the role of the forced swim test and tail suspension test

Depressive disorders are one of the most common mental disorders globally and progress in treating these disorders has been hampered, in part, by a lack of suitable nonclinical efficacy tests. Two common tests used in nonclinical efficacy studies of antidepressants-the forced swim test (FST) and tail suspension test (TST)-have come under criticism in recent years for their inconsistency and lack of validity, yet they continue to be used in the pharmaceutical industry. In this review, we provide a rationale for why international pharmaceutical regulatory and guidance agencies should begin issuing direction on methods for non-clinical efficacy testing that traditionally use the FST and TST, particularly considering that some regulators, such as those in the U.S. and E.U., allow the authorization of clinical trials to proceed without requiring tests in animals. The area of antidepressant drug discovery represents an important opportunity for reducing the attrition of psychiatric drugs, harmonizing regulatory requirements, and reducing animal use. Specific recommendations for the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) have been provided.

Preclinical models of treatment-resistant depression: challenges and perspectives

Treatment-resistant depression (TRD) is a subgroup of major depressive disorder in which the use of classical antidepressant treatments fails to achieve satisfactory treatment results. Although there are various definitions and grading models for TRD, common criteria for assessing TRD have still not been established. However, a common feature of any TRD model is the lack of response to at least two attempts at antidepressant pharmacotherapy. The causes of TRD are not known; nevertheless, it is estimated that even 60% of TRD patients are so-called pseudo-TRD patients, in which multiple biological factors, e.g., gender, age, and hormonal disturbances are concomitant with depression and involved in antidepressant drug resistance. Whereas the phenomenon of TRD is a complex disorder difficult to diagnose and successfully treat, the search for new treatment strategies is a significant challenge of modern pharmacology. It seems that despite the complexity of the TRD phenomenon, some useful animal models of TRD meet the construct, the face, and the predictive validity criteria. Based on the literature and our own experiences, we will discuss the utility of animals exposed to the stress paradigm (chronic mild stress, CMS), and the Wistar Kyoto rat strain representing an endogenous model of TRD. In this review, we will focus on reviewing research on existing and novel therapies for TRD, including ketamine, deep brain stimulation (DBS), and psychedelic drugs in the context of preclinical studies in representative animal models of TRD.

Positive maternal affect during mother-litter interaction is reduced in new mother rats exhibiting a depression-like phenotype

The experience of positive affect during new motherhood is considered essential for a healthy mother-infant relationship, with life-long consequences for both mother and child. Affective availability and contingent responsiveness are often compromised in mothers experiencing postpartum depression, yet how maternal affect impacts parenting is not fully understood. In this study, we used the Wistar-Kyoto (WKY) rat model of depression and ultrasonic vocalizations to examine the relationship between maternal affect and parenting. We examined the affective and behavioral response of WKY and control new mother rats during social interactions with their offspring. Our results show that WKY mothers displayed altered USV signaling accompanying substantial disturbances in their maternal caregiving. In addition, WKY mothers failed to adjust vocal frequency in coordination with offspring proximity and interaction compared to control mothers. A follow up experiment demonstrated that the administration of the adenosine A2A receptor antagonist MSX-3 ameliorated both maternal behavioral deficits and low positive affect in WKY mothers. Together, our results highlight the importance of maternal positive affect in the dyad relationship and suggest a role for the striatopallidal pathway in the affective processing of parenting.

The Greater Impact of Paternal, Compared to Maternal, Hereditary Background on Depressive-Like Behavior in Wistar Kyoto Rats with Different Amino Acid Metabolism in the Pup Brain

In the pathogenesis of depression, heredity is believed to be a major factor. However, the mechanism by which heredity contributes to the onset of depression is not fully understood. Wistar Kyoto (WKY) rats have been used as an animal model for depression because of their increased depression-like behavior compared to Wistar (WIS) rats. In the present study, pups crossbred from WKY × WIS rats were used to evaluate locomotor activity in an open field test (OFT) and depression-like behavior in a forced swimming test (FST), with a focus on amino acid metabolism. Pups in the WKY♂ × WKY♀ group showed lower locomotor activity in the OFT and higher depression-like behavior in the FST than those in the WIS♂ × WIS♀ group. In addition, multiple regression analysis showed that the paternal strain had a greater effect than the maternal strain on locomotor activity and depression-like behavior in OFT and FST, respectively. Several amino acids in the brainstem, hippocampus, and striatum were significantly decreased through the influence of the WKY paternal strain, but not the WKY maternal strain. Based on these data from comparing WKY and WIS rats, we hypothesize that the hereditary effects of the WKY paternal strain on behavioral tests are partially caused by dysregulation of the amino acid metabolism in the brain.

Habenula as a Possible Target for Treatment-Resistant Depression Phenotype in Wistar Kyoto Rats

The mechanisms of treatment-resistant depression (TRD) are not clear and are difficult to study. An animal model resembling human TRD is the Wistar Kyoto rat strain. In the present study, we focused on selecting miRNAs that differentiate rats of the WKY strain from Wistar Han (WIS) rats in two divisions of the habenula, the lateral and medial (LHb and MHb, respectively). Based on our preliminary study and literature survey, we identified 32 miRNAs that could be potentially regulated in the habenula. Six miRNAs significantly differentiated WKY rats from WIS rats within the MHb, and three significantly differentiated WKY from WIS rats within the LHb. Then, we selected relevant transcripts regulated by those miRNAs, and their expression in the habenular nuclei was investigated. For mRNAs that differentiated WKY rats from WIS rats in the MHb (Cdkn1c, Htr7, Kcnj9, and Slc12a5), their lower expression correlated with a higher level of relevant miRNAs. In the LHb, eight mRNAs significantly differentiated WKY from WIS rats (upregulated Htr4, Drd2, Kcnj5, and Sstr4 and downregulated Htr2a, Htr7, Elk4, and Slc12a5). These data indicate that several important miRNAs are expressed in the habenula, which differentiates WKY rats from WIS rats and in turn correlates with alterations in the expression of target transcripts. Of particular note are two genes whose expression is altered in WKY rats in both LHb and MHb: Slc12a5 and Htr7. Regulation of KCC2 via the 5-HT7 receptor may be a potential target for the treatment of TRD.

Insufficiency of ventral hippocampus to medial prefrontal cortex transmission explains antidepressant non-response

BACKGROUND

There is extensive evidence that antidepressant drugs restore normal brain function by repairing damage to ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC). While the damage is more extensive in hippocampus, the evidence of treatments, such as deep brain stimulation, suggests that functional changes in prefrontal cortex may be more critical. We hypothesized that antidepressant non-response may result from an insufficiency of transmission from vHPC to mPFC.

METHOD

Antidepressant non-responsive Wistar Kyoto (WKY) rats were subjected to chronic mild stress (CMS), then treated with chronic daily administration of the antidepressant drug venlafaxine (VEN) and/or repeated weekly optogenetic stimulation (OGS) of afferents to mPFC originating from vHPC or dorsal HPC (dHPC).

RESULTS

As in many previous studies, CMS decreased sucrose intake, open-arm entries on the elevated plus maze (EPM), and novel object recognition (NOR). Neither VEN nor vHPC-mPFC OGS alone was effective in reversing the effects of CMS, but the combination of chronic VEN and repeated OGS restored normal behaviour on all three measures. dHPC-mPFC OGS restored normal behaviour in the EPM and NOR test irrespective of concomitant VEN treatment, and had no effect on sucrose intake.

CONCLUSIONS

The synergism between VEN and vHPC-mPFC OGS supports the hypothesis that the antidepressant non-responsiveness of WKY rats results from a failure of antidepressant treatment fully to restore transmission in the vHPC-mPFC pathway.

Perspectives for therapy of treatment-resistant depression

A high proportion of depressed patients fail to respond to antidepressant drug treatment. Treatment-resistant depression (TRD) is a major challenge for the psychopharmacology of mood disorders. Only in the past decade have novel treatments, including deep brain stimulation (DBS) and ketamine, been discovered that provide rapid and sometimes prolonged relief to a high proportion of TRD sufferers. In this review, we consider the current status of TRD from four perspectives: the challenge of developing an appropriate regulatory framework for novel rapidly acting antidepressants; the efficacy of non-pharmacological somatic therapies; the development of an animal model of TRD and its use to understand the neural basis of antidepressant non-response; and the potential for rapid antidepressant action from targets (such as 5-HT_1A receptors) beyond the glutamate receptor.

AMPA receptors mediate the pro-cognitive effects of electrical and optogenetic stimulation of the medial prefrontal cortex in antidepressant non-responsive Wistar-Kyoto rats

BACKGROUND

The chronic mild stress (CMS) procedure is a widely used animal model of depression, and its application in Wistar-Kyoto (WKY) rats has been validated as a model of antidepressant-refractory depression. While not responding to chronic treatment with antidepressant drugs, WKY rats do respond to acute deep brain stimulation (DBS) of the medial prefrontal cortex (mPFC). In antidepressant-responsive strains there is evidence suggesting a role for AMPA subtype of glutamate receptor in the action mechanism of both antidepressants and DBS.

METHODS

Animals were subjected to CMS for 6 to 8 weeks; sucrose intake was monitored weekly and novel object recognition (NOR) test was conducted following recovery from CMS. Wistars were treated chronically with venlafaxine (VEN), while WKY were treated acutely with either DBS, optogenetic stimulation (OGS) of virally-transduced (AAV5-hSyn-ChR2-EYFP) mPFC or ventral hippocampus, or acute intra-mPFC injection of the AMPA receptor positive allosteric modulator CX-516. The AMPA receptor antagonist NBQX was administered, at identical sites in mPFC, immediately following the exposure trial in the NOR.

RESULTS

Sucrose intake and NOR were suppressed by CMS, and restored by VEN in Wistars and by DBS, OGS, or CX-516 in WKY. However, OGS of the ventral hippocampal afferents to mPFC was ineffective. A low dose of NBQX selectively blocked the procognitive effect of VEN, DBS and OGS.

CONCLUSIONS

These results suggest that activation of AMPA receptors in the mPFC represents a common pathway for the antidepressant effects of both conventional (VEN) and novel (DBS, OGS) antidepressant modalities, in both antidepressant responsive (Wistar) and antidepressant-resistant (WKY) rats.

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.

Cell encapsulation enhances antidepressant effect of the mesenchymal stem cells and counteracts depressive-like behavior of treatment-resistant depressed rats

Despite the advances in pharmacological therapies, only the half of depressed patients respond to currently available treatment. Thus, the need for further investigation and development of effective therapies, especially those designed for treatment-resistant depression, has been sorely needed. Although antidepressant effects of mesenchymal stem cells (MSCs) have been reported, the potential benefit of this cell therapy on treatment-resistant depression is unknown. Cell encapsulation may enhance the survival rate of grafted cells, but the therapeutic effects and mechanisms mediating encapsulation of MSCs remain unexplored. Here, we showed that encapsulation enhanced the antidepressant effects of MSCs by attenuating depressive-like behavior of Wistar Kyoto (WKY) rats, which are considered as a promising animal model of treatment-resistant depression. The implantation of encapsulated MSCs (eMSCs) into the lateral ventricle counteracted depressive-like behavior and enhanced the endogenous neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus, whereas the implantation of MSCs without encapsulation or the implantation of eMSCs into the striatum did not show such ameliorative effects. eMSCs displayed robust and stable secretion of vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor, fibroblast growth factor-2, and ciliary neurotrophic factor (CNTF), and the implantation of eMSCs into the lateral ventricle activated relevant pathways associated with these growth factors. Additionally, eMSCs upregulated intrinsic expression of VEGF and CNTF and their receptors. This study suggests that the implantation of eMSCs into the lateral ventricle exerted antidepressant effects likely acting via neurogenic pathways, supporting their utility for depression treatment.

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.

The Antidepressant-Like Effects of a Clinically Relevant Dose of Ketamine Are Accompanied by Biphasic Alterations in Working Memory in the Wistar Kyoto Rat Model of Depression

Major depressive disorder (MDD) is the leading cause of disability worldwide. The majority of antidepressant drugs require several weeks or months of treatment to demonstrate efficacy and a subset of patients are resistant to such interventions. Ketamine demonstrates rapid and long-lasting antidepressant effects in treatment resistant patients; however, side effects may limit its widespread clinical utility. The pharmaceutical industry is engaged in developing novel rapid-acting antidepressant drugs and the establishment of clinically relevant assays are needed to advance this process. Wistar Kyoto (WKY) rats are a valuable model of many of the characteristics of MDD and their resistance to selective serotonin reuptake inhibitors (SSRIs) in several behavioral paradigms emulates treatment resistance in clinical populations. Here, we confirmed the depressive-like phenotype of WKY rats in comparison to Sprague Dawley rats, characterized by increased immobility in the forced swim test, decreased locomotor activity and entries to the centre in the open field test, anhedonia in the female urine sniffing test and working memory deficits in the delayed non-match to position task. Single subcutaneous administration of 5 mg/kg ketamine in WKY rats mirrored the plasma exposure produced by the antidepressant dose in the clinic and rescued depressive-like behaviors. The same dose induced transient side effects, including decreased locomotor activity and reduced positive affect-associated vocalizations. Furthermore, ketamine acutely impaired working memory but induced pro-cognitive effects at a later time point. These data confirm the WKY rat as a preclinical model of depression. Ketamine's efficacy in recovering this depressive-like phenotype while inducing transient dissociative-like effects supports this as a translational model suitable for investigating novel antidepressant drugs.

Antidepressant effects of moxidectin, an antiparasitic drug, in a rat model of depression

Substantial data indicate that an imbalance in gut microbiome (GM), also referred to as dysbiosis, may play an important role in depression. Moreover, drugs that normalize GM can result in an antidepressant-like effect. It was reported recently that moxidectin (MOX), an antiparasitic drug commonly used in veterinary medicine, has a positive influence on microbiota implicated in mood regulation. We undertook this study to determine whether MOX would actually show antidepressant-like properties in an animal model of depression and whether it would affect the hippocampal and frontal cortex levels of brain-derived neurotrophic factor (BDNF) or tumor necrosis factor (TNF)-alpha, peptides that have been implicated in pathogenesis of depression and effectiveness of various antidepressants. Adult male Wistar-Kyoto rats, a putative animal model of depression, were treated with a single dose of MOX (2.5 mg/kg, i.p.) and their performance in the open field locomotor activity (OFLA) as well as in the forced swim test (FST) was evaluated at 24 h, one week and two weeks after the single injection. A separate group of rats were injected with 2.5 mg/kg MOX and sacrificed 24 h later for neurochemical evaluations. MOX resulted in a decrease in immobility score after 24 h, whereas OFLA was not affected. Concomitant with the 24 h behavioral effects, the levels of hippocampal and frontal cortical BDNF were significantly increased, whereas the levels of TNF-alpha in both these areas were significantly decreased. The decrease in immobility scores was still evident after one week, but not 2 weeks of rest. These results indicate long lasting antidepressant effects of a single MOX dose and suggest potential utility of this drug in treatment-resistant depression.

Chronic administration of buprenorphine in combination with samidorphan produces sustained effects in olfactory bulbectomised rats and Wistar-Kyoto rats

BACKGROUND

The combination of buprenorphine, a partial mu-opioid receptor agonist and a functional kappa-opioid receptor antagonist, with samidorphan, a functional mu-opioid receptor antagonist, is being developed as an adjunct therapy for major depressive disorder, in order to harness the mood-enhancing effects of opioids without unwanted side-effects such as a risk of addiction. Acute and subacute administration of the combination of buprenorphine and samidorphan is effective in reducing forced swim immobility in the Wistar-Kyoto rat, but the chronic effects have not been examined.

AIMS AND METHODS

The purpose of this study was to assess if chronic (14-day) administration of buprenorphine (0.1 mg/kg, subcutaneous) alone or in combination with samidorphan (0.3 mg/kg, subcutaneous) maintains antidepressant-like activity in the olfactory bulbectomised rat model and the Wistar-Kyoto rat, two models that exhibit ongoing behavioural deficits in tests commonly used to study effects of antidepressants.

RESULTS

Olfactory bulbectomised-induced hyperactivity was attenuated by chronic administration of buprenorphine alone and in combination with samidorphan, to that of sham control activity levels. Neither buprenorphine nor samidorphan altered stress-associated defecation in sham or olfactory bulbectomised rats in the open field. In Wistar-Kyoto rats, buprenorphine alone significantly reduced forced swim immobility and increased locomotor activity three hours post-final dosing. Buprenorphine plus samidorphan significantly reduced forced swim immobility without changing locomotor activity at this time point. Buprenorphine alone also significantly reduced forced swim immobility 24 h post-final dosing.

CONCLUSION

Chronic treatment of buprenorphine alone or buprenorphine plus samidorphan is effective in reversing behavioural deficits in distinct non-clinical paradigms. These non-clinical results complement the antidepressant effect of this combination observed in clinical studies.

Individual differences in inflammatory and oxidative mechanisms of stress-related mood disorders

Emotional stress leads to the development of peripheral disorders and is recognized as a modifiable risk factor for psychiatric disorders, particularly depression and anxiety. However, not all individuals develop the negative consequences of emotional stress due to different stress coping strategies and resilience to stressful stimuli. In this review, we discuss individual differences in coping styles and the potential mechanisms that contribute to individual vulnerability to stress, such as parameters of the immune system and oxidative state. Initial differences in inflammatory and oxidative processes determine resistance to stress and stress-related disorders via the alteration of neurotransmitter content in the brain and biological fluids. Differences in coping styles may serve as possible predictors of resistance to stress and stress-related disorders, even before stressful conditions. The investigation of natural variabilities in stress resilience may allow the development of new methods for preventive medicine and the personalized treatment of stress-related conditions.

Effects of vitamin D and paricalcitol on epileptogenesis and behavioral properties of WAG/Rij rats with absence epilepsy

AIM

Vitamin D (Vit D) has been considered as a neurosteroid and has a pivotal role in neuroprotection including epilepsy. Vit D regulator acts via a Vit D receptor (VDR). WAG/Rij rats have a genetically epileptic model of absence epilepsy with comorbidity of depression. The aim of the present study was to investigate the effect of Vit D and paricalcitol (PRC) on WAG/Rij rats.

MATERIAL AND METHODS

Sixty-three male WAG/Rij rats and seven male Wistar rats were used. The effects of acute and chronic treatment with Vit D (5.000 and 60.000 IU/kg, i.p) and PRC (0.5, 5 and 10 μg/kg, i.p) on absence seizures, and related psychiatric comorbidity were investigated in WAG/Rij rats. Depression-like behavior was assayed by using the forced swimming test (FST) and; anxiety-like behavior by using the open field test (OFT).

RESULTS

Acute Vit D treatments (5.000 and 60.000 IU/kg) similarly reduced the number and duration of spike-wave discharges (SWDs) and showed anxiolytic-antidepressive effect whereas there were no significant changes in other measured parameters between the daily and the bolus dose of Vit D. Acute administration of PRC (0.5, 5 and 10 μg/kg) showed anti-convulsive and anxiolytic-antidepressive effect. The dose (0.5 μg/kg) of PRC was the most effective dose. Chronic treatment was more effective than acute therapy in all parameters.

CONCLUSION

The results of the present study demonstrate that Vit D and PRC have antiepileptic and anxiolytic-antidepressive effects on the absence epilepsy in WAG/Rij rats.

Antidepressant effects of C-Terminal domain of the heavy chain of tetanus toxin in a rat model of depression

The C-terminal domain of the heavy chain of tetanus toxin (Hc-TeTx) may be of therapeutic potential in motor impairments associated with Parkinson disease (PD). Since depression is a common co-morbid condition with PD, we undertook this study to determine whether Hc-TeTx might also show antidepressant-like properties and whether central brain-derived neurotrophic factor (BDNF) and/or tumor necrosis factor (TNF)-alpha are also affected by it. Adult male Wistar-Kyoto rats, a putative animal model of depression, were treated with various doses of Hc-TeTx (0, 20, 40 and 60 μg/kg, IM) and their performance in the open field locomotor activity (OFLA) as well as in the forced swim test (FST) was evaluated at 24 h, one week and two weeks after the single injection. A separate group of rats were injected with 60 μg/kg Hc-TeTx and sacrificed 24 h later for neurochemical evaluations. Hc-TeTx resulted in a dose-dependent decrease in immobility score after 24 h, whereas OFLA was not affected. Concomitant with the 24 h behavioral effects, the levels of hippocampal and frontal cortical BDNF were significantly increased, whereas the levels of TNF-alpha in both these areas were significantly decreased. The decrease in immobility scores following higher doses of Hc-TeTx were still evident after one week, but not 2 weeks of rest. These results indicate long lasting antidepressant effects of a single Hc-TeTx dose and suggest potential utility of Hc-TeTx in PD-depression co-morbidity.

Depression-related disturbances in rat maternal behaviour are associated with altered monoamine levels within mesocorticolimbic structures

The ability of mothers to sensitively attune their maternal responses to the needs of their developing young is fundamental to a healthy mother-young relationship. The biological mechanisms that govern how mothers adjust caregiving to the dynamic changes in the demands of the young remain an open question. In the present study, we examined whether changes in monoamine levels, within discrete mesocorticolimbic structures involved in cognitive and motivational processes key to parenting, modulate this flexibility in caregiving across the postpartum period. The present study used a Wistar-Kyoto (WKY) animal model of depression and control Sprague-Dawley (SD) rats, which differ dramatically in their cognitive, motivational, and parenting performance. Levels of the monoamine neurotransmitters, dopamine, noradrenaline and serotonin, as well as their major metabolites, were measured within the medial prefrontal cortex, striatum, nucleus accumbens and medial preoptic area of SD and WKY mothers at early (postpartum day [PPD]7-8), late (PPD15-16) and weaning (PPD25) postpartum stages using high-performance liquid chromatography with electrochemical detection. Consistent with our prior work, we find that caregiving of SD mothers declined as the postpartum period progressed. Relative to nulliparous females, early postpartum mothers had lower intracellular concentrations of monoamines, as well as lower noradrenaline turnover, and an elevated serotonin turnover within most structures. Postpartum behavioural trajectories subsequently corresponded to a progressive increase in all three monoamine levels within multiple structures. Compared to SD mothers, WKY mothers were inconsistent and disorganised in caring for their offspring and exhibit profound deficits in maternal behaviour. Additionally, WKY mothers had generally lower levels of all three monoamines, as well as different patterns of change across the postpartum period, compared to SD mothers, suggesting dysfunctional central monoamine pathways in WKY mothers as they transition and experience motherhood. Taken together, the results of the present study suggest a role for monoamines at multiple mesocorticolimbic structures with repect to modulating caregiving behaviours attuned to the changing needs of the young.

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.

Locomotor and anti-immobility effects of buprenorphine in combination with the opioid receptor modulator samidorphan in rats

Modulation of the opioid system has re-emerged as a potential therapeutic avenue for treating depression, with efficacy of a fixed-dose combination of buprenorphine (BUP), a partial μ-opioid receptor (MOR) agonist and κ-opioid receptor (KOR) antagonist, and samidorphan (SAM), a potent MOR antagonist, as an adjuvant treatment in patients with major depressive disorder (MDD). To advance understanding of the mechanism of action underlying this combination, we examined BUP, SAM and their combination in a series of rat behavioural assays. We examined effects on locomotor activity in Sprague Dawley (SD) rats over an extended period of time in a home-cage tracking system, and behavioural despair (immobility) in the forced swim test (FST), a commonly-used test to study antidepressants, in SD and Wistar-Kyoto (WKY) rats. Strain differences in opioid receptor and prepropeptide mRNA expression in the brain (prefrontal cortex, amygdala, hippocampus and striatum) were examined using qRT-PCR. BUP produced locomotor hyperactivity in SD rats from 2 to 6 h following administration, which was attenuated by SAM. In SD rats, a low, but not a high, dose of SAM in combination with BUP counteracted swim-stress induced immobility. This effect was not seen with BUP alone. In contrast, BUP alone reduced immobility in WKY rats, and this effect was enhanced by a low, but not high, dose of SAM. In WKY rats, MOR mRNA expression was higher in the hippocampus and lower in the striatum vs. SD rats. KOR mRNA expression was higher in the amygdala and nociceptin receptor (NOP) mRNA expression was lower in the hippocampus vs. SD rats. Differences in opioid receptor expression may account for the differential behavioural profile of WKY and SD rats. In summary, administration of BUP, a MOR receptor agonist together with a MOR opioid-receptor antagonist, SAM, reduces behavioural despair in animal models traditionally used to study effects of antidepressants.

Distinct effects of early-life experience and trait aggression on cardiovascular reactivity and recovery

We previously demonstrated independent effects of early-life experience (ELE) and trait aggression (TA) on resting heart rate (HR) and mean arterial pressure (MAP) in rats. The present study examined the effects of TA and ELE on stress-evoked cardiovascular reactivity and recovery. Pups born to Wistar-Kyoto dams were exposed to daily 180-min periods of maternal separation (MS) during the first two weeks of life, and aggression was assessed in adult offspring using the resident-intruder test. Radiotelemetry was then used to record stress-evoked HR and MAP responses in response to: strobe light, novel environment, intruder rat, or restraint. Maximal HR and MAP responses were quantified as indices of reactivity, and exponential decay curves were fitted to determine decay constants as a measure of recovery. Strobe light was the weakest stressor, evoking the lowest increases in MAP and HR, which were significantly greater in MS-exposed rats irrespective of TA. In contrast, reactivity to and recovery from exposure to a novel environment or an intruder were significantly influenced by TA, but not ELE. TA animals exhibited greater reactivity in both of these paradigms, with either decreased (novel environment) or increased (intruder) recovery. Restraint stress induced the largest changes in HR and MAP with the slowest recovery, and these responses were shaped by a significant ELE x TA interaction. These data indicate that cardiovascular reactivity and recovery are influenced by ELE, TA, or ELE x TA interaction depending on stressor aversiveness as well as its physical and psychological dimensions.

Encapsulated stem cells ameliorate depressive-like behavior via growth factor secretion

As prevalence of depression continues to rise around the world, there remains a stagnation of available treatments as the affected population grows. The subset of treatment-resistant depression also is on the rise highlighting the need for innovative treatments to address this issue. Mesenchymal stem cells (MSCs) have been reported to attenuate depression-like behaviors, however, the effects of encapsulation of MSCs have yet to be investigated. Encapsulation of MSCs exhibited prolonged survival of exogenous cell injection accompanied with increased secretion of neurotrophic factors including vascular endothelial growth factor, ciliary neurotrophic factor, and others. The enhanced expression of these factors highlights the ability of encapsulated MSCs to upregulate the respective signaling pathways, which are associated with depression pathology and activation of neurogenesis. This treatment identifies a promising therapeutic option for depression, specifically treatment-resistant depression. Further, evaluation of long-term effects of the treatment is warranted. This paper is a review article. Referred literature in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching various databases including PubMed. Some original themes in this article come from the laboratory practice in our research center and the authors' experiences.

Inducing a long-term potentiation in the dentate gyrus is sufficient to produce rapid antidepressant-like effects

Recent hypotheses propose that one prerequisite to obtain a rapid antidepressant (AD) effect would reside in processes of synaptic reinforcement occurring within the dentate gyrus (DG) of the hippocampus independently from neurogenesis. However, to date no relationship has been established between an increased DG synaptic plasticity, and rapid AD-like action. To the best of our knowledge, this study shows for the first time that inducing a long-term potentiation (LTP) within the DG by stimulating the perforant pathway (PP) is sufficient to induce such effects. Thus, Sprague-Dawley rats having undergone a successful LTP displayed a significant reduction of immobility when passed acutely 3 days thereafter in the forced swimming test (FST). Further, in a longitudinal paradigm using the pseudo-depressed Wistar-Kyoto rat strain, LTP elicited a decrease of FST immobility after only 2 days, whereas the AD desipramine was not effective before 16 days. In both models, the influence of LTP was transient, as it was no more observed after 8-9 days. No effects were observed on the locomotor activity or on anxiety-related behavior. Theta-burst stimulation of a brain region anatomically adjacent to the PP remained ineffective in the FST. Immunoreactivity of DG cells for phosphorylated histone H3 and doublecortin were not modified three days after LTP, indicating a lack of effect on both cell proliferation and neurogenesis. Finally, depleting brain serotonin contents reduced the success rate of LTP but did not affect its subsequent AD-like effects. These results confirm the 'plastic DG' theory of rapid AD efficacy. Beyond, they point out stimulations of the entorhinal cortex, from which the PP originates, as putative new approaches in AD research.

Regional Specific Modulation of Stress-Induced Neuronal Activation Associated with the PSD95/NOS Interaction Inhibitor ZL006 in the Wistar Kyoto Rat

BACKGROUND

To determine brain areas involved in the antidepressant-related behavioral effects of the selective neuronal nitric oxide synthase inhibitor 1-(2-Trifluoro-methyl-phenyl) imidazole (TRIM) and experimental test compound 4-((3,5-dichloro-2-hydroxybenzyl)amino)-2-hydroxybenzoic acid (ZL006), an inhibitor of the PSD of 95 kDa/neuronal nitric oxide synthase interaction in the N-methyl-D-aspartic acid receptor signalling pathway, regional specific expression of the neuronal activation marker c-FOS was assessed following exposure to the forced swimming test in the Wistar Kyoto rat.

METHODS

Wistar Kyoto rats were subjected to a 15-minute swim pretest (pre-forced swimming test) period on day 1. At 24, 5, and 1 hour prior to the 5-minute test, which took place 24 hours following the pre-forced swimming test, animals were treated with TRIM (50 mg/kg; i.p.), ZL006 (10 mg/kg; i.p.), or saline vehicle (1 mL/kg i.p). Behavior was recorded during both pretest and test periods.

RESULTS

Both TRIM and ZL006 decreased immobility time in Wistar Kyoto rats in the forced swimming test. Exposure to the forced swimming test increased c-FOS immunoreactivity in the lateral septum, paraventricular nucleus of the hypothalamus, periaqueductal grey, dentate gyrus, and ventral CA1 of the hippocampus compared with non-forced swimming test-exposed controls. Forced swimming test-induced c-FOS immunoreactivity was further increased in the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus following treatment with TRIM or ZL006. By contrast, forced swimming test-induced c-FOS immunoreactivity was reduced in dorsal dentate gyrus and ventral CA1 following treatment with TRIM or ZL006. Exposure to the forced swimming test resulted in an increase in NADPH diaphorase staining in the paraventricular nucleus of the hypothalamus. This forced swimming test-induced increase was attenuated following treatment with ZL006 and points to the paraventricular nucleus as a brain region where ZL006 acts to attenuate forced swimming test-induced neuronal nitric oxide synthase activity while concomitantly regulating region specific neuronal activation associated with an antidepressant-related response.

CONCLUSIONS

This study identified a pattern of enhanced and reduced forced swimming test-related c-FOS immunoreactivity indicative of a regulated network where inhibition of nitric oxide coupled to the N-methyl-D-aspartic acid receptor leads to activation of the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus with concomitant inhibition of the hippocampus.

Role of cortical alpha-2 adrenoceptors in alcohol withdrawal-induced depression and tricyclic antidepressants

INTRODUCTION

Although a role for alpha-2 adrenoceptors (alpha-2 ARs) in alcohol use disorder (AUD) and depression is suggested, very little information on a direct interaction between alcohol and these receptors is available.

METHODS

In this study adult female Wistar and Wistar-Kyoto (WKY) rats, a putative animal model of depression, were exposed to alcohol vapor 3h daily for 10days (blood alcohol concentration ∼150mg%) followed by daily injection of 10mg/kg of imipramine (IMP, a selective norepinephrine NE/serotonin reuptake inhibitor) or nomifensine (NOMI, a selective NE/dopamine reuptake inhibitor). On day 11 animals were tested for open field locomotor activity (OFLA) and forced swim test (FST) and were sacrificed 2h later for measurement of alpha-2 ARs densities in the frontal cortex and hippocampus using [3H]RX 821002 as the specific ligand.

RESULTS

Chronic alcohol treatment increased the immobility in the FST, without affecting OFLA in both Wistar and WKY rats, suggesting induction of depressive-like behavior in Wistar rats and an exacerbation of this behavior in WKY rats. Alcohol treatment also resulted in an increase in cortical but not hippocampal alpha-2 ARs densities in both Wistar and WKY rats. The behavioral effects of alcohol were completely blocked by IMP and NOMI and the neurochemical effects (increases in alpha-2 ARs) were significantly attenuated by both drugs in both strains.

CONCLUSIONS

The results suggest a role for cortical alpha-2 ARs in alcohol withdrawal-induced depression and that selective subtype antagonists of these receptors may be of adjunct therapeutic potential in AUD-depression co-morbidity.

Hippocampal neurogenesis of Wistar Kyoto rats is congenitally impaired and correlated with stress resistance

The hippocampus is thought to be an important region for depression. However, the relationship between hippocampal neurogenesis and depression is still controversial. Wistar Kyoto (WKY) rats are frequently used as a depression model. WKY rats are known to show physiologically abnormal features, and these features resemble abnormalities seen in depressed patients. However, the neurogenesis of WKY rats is still unknown. In this study, we first evaluated the neurogenesis of WKY rats and compared it to that of Wistar (WIS) rats. No strain effect was observed in the number of cells positive for 5-bromo-2'-deoxyuridine (BrdU) and BrdU/Doublecortin (Dcx) in the subventricular zone (SVZ). However, the number of BrdU- and BrdU/Dcx-positive cells in the dentate gyrus (DG) of the hippocampus was significantly lower in WKY rats than in WIS rats. Next, we evaluated the correlation between neurogenesis and behavior tests. Behavior tests did not affect neurogenesis in either strain. Hippocampal neurogenesis correlated negatively with the results of a forced swim test (FST) on day 2 in each strain. That is, rats with a lower level of native neurogenesis in the DG showed a higher level of learned helplessness induced by the inescapable stress of the FST on day 1. Our findings indicate that hippocampal neurogenesis in WKY rats is congenitally impaired in contrast to that in WIS rats. Native cell proliferation and neurogenesis in the DG are correlated with stress resistance. These findings may be useful for developing new targets for depression treatment.

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.

A2 noradrenergic neurons regulate forced swim test immobility

The Wistar-Kyoto (WKY) rat is a widely used animal model of depression, which is characterized by dysregulation of noradrenergic signaling. We previously demonstrated that WKY rats show a unique behavioral profile on the forced swim test (FST), characterized by high levels of immobility upon initial exposure and a greater learning-like response by further increasing immobility upon re-exposure than the genetically related Wistar rats. In the current study we aimed to determine whether altered activation of brainstem noradrenergic cell groups contributes to this behavioral profile. We exposed WKY and Wistar rats, to either 5min of forced swim or to the standard two-day FST (i.e. 15min forced swim on Day 1, followed by 5min on Day 2). We then stained their brains for FOS/tyrosine hydroxylase double-immunocytochemistry to determine potential differences in the activation of the brainstem noradrenergic cell groups. We detected a relative hyperactivation in the locus coeruleus of WKY rats when compared to Wistars in response to both one- and two-day forced swim. In contrast, within the A2 noradrenergic cell group, WKY rats exhibited diminished levels of FOS across both days of the FST, suggesting their lesser activation. We followed up these observations by selectively lesioning the A2 neurons, using anti-dopamine-β-hydroxylase-conjugated saporin, in Wistar rats, which resulted in increased FST immobility on both days of the test. Together these data indicate that the A2 noradrenergic cell group regulates FST behavior, and that its hypoactivation may contribute to the unique behavioral phenotype of WKY rats.

Glial fibrillary acidic protein (GFAP) immunoreactivity correlates with cortical perfusion parameters determined by bolus tracking arterial spin labelling (bt-ASL) magnetic resonance (MR) imaging in the Wistar Kyoto rat

Alterations in astrocyte number and function have been implicated in the pathophysiology of a number of psychiatric disorders. The development of magnetic resonance imaging (MRI) as a tool in the animal laboratory has enabled an investigation of the relationship between pathological and neuroimaging markers in animal models. However the physiological processes which underlie these markers and their role in mediating behavioural deficits is still poorly understood. Rodent models have provided us with important insights into physiological and cellular mechanisms which may mediate anxiety and depression-related behaviours. The Wistar-Kyoto (WKY) rat is a strain which endogenously expresses highly anxious and depressive-like behaviours and has previously been reported to exhibit alterations in immunoreactivity for the astrocytic marker glial fibrillary acidic protein (GFAP) in brain sub-regions relative to more stress resilient out-bred strains. Here we report that the depressive and anxiety-like behaviours exhibited by the WKY rat strain are associated with alterations in brain morphology including a decrease in hippocampal volume, coupled with reduced resting state frontal cortical perfusion as assessed by MR bolus tracking arterial spin labelling (bt-ASL) relative to the out-bred Wistar strain. Pre-limbic cortical GFAP immunoreactivity and astrocyte cell number were positively correlated with cortical blood perfusion in the WKY strain. These experiments provide a link between pathological and neuroimaging markers of aberrant astrocytic function and add validity to the WKY rat as a model for co-morbid anxiety and depression.

Cocaine self-administration in Wistar-Kyoto rats: a behavioral and biochemical analysis

Depression and cocaine abuse disorders are common concurrent diagnoses. In the present study, we employed Wistar-Kyoto (WKY) rats that showed a depressive-like phenotype to study intravenous cocaine self-administration and extinction/reinstatement procedures. We also investigated the basal tissue level of neurotransmitters, their metabolites and plasma corticosterone (CORT) concentrations in WKY rats, bulbectomized (OBX) rats, and control rats. The WKY rats exhibited an attenuation of the cocaine-associated lever presses and cocaine intake during the acquisition/maintenance of cocaine self-administration only under specific conditions. Active lever presses exhibited by the WKY rats and control animals did not differ during the extinction training and cocaine-seeking behaviors. The WKY rats demonstrated alterations in the basal levels of dopamine, norepinephrine, and serotonin in selected brain structures involved in depression and drug addiction. The changes in the level of neurotransmitters in these animals refer not only to the control (Wistar) rats but also to bulbectomized animals, which represent another depression model. Furthermore, we identified unchanged levels of CORT in the WKY and OBX rats during the light phase and free-stress conditions. This finding suggests that WKY rats should not be used to investigate the co-occurrence of depression and cocaine addiction, as this rat strain does not show an enhanced risk of relapse.

Role of adrenomedullin in the cerebrospinal fluid-contacting nucleus in the modulation of immobilization stress

The contribution of the cerebrospinal fluid-contacting nucleus (CSF-contacting nucleus) and adrenomedullin (ADM) to the developmental modulation of stressful events remains controversial. This study explored the effects of endogenous ADM in the CSF-contacting nucleus on immobilization of stress-induced physiological parameter disorders and glucocorticoid hormone releasing hormone (CRH), rat plasma corticosterone expression, and verification of such effects by artificially lowering ADM expression in the CSF-contacting nucleus by targeted ablation of the nucleus. Immunohistochemical experiments showed that ADM-like immunoreactivity and the calcitonin receptor-like receptor (CRLR) marker were localized in the CSF-contacting nucleus. After 7 continuous days of chronic immobilization stress (CIS), animals exhibited anxiety-like behavior. Also, an increase in serum corticosterone, and enhanced expression of ADM in the CSF-contacting nucleus were observed, following activation by CIS. The intracerebroventricular (i.c.v.) administration of the ADM receptor antagonist AM22-52 significantly reduced ADM in the CSF-contacting nucleus, additionally, blocked the effects of ADM, meaning the expression of CRH in the hypothalamic paraventricular nucleus (Pa) and serum corticosterone level were increased, and the physiological parameters of the rats became correspondingly deteriorated. Additionally, the i.c.v. administration of cholera toxin subunit B-saporin (CB-SAP), a cytotoxin coupled to a cholera toxin subunit, completely eliminated the CSF-contacting nucleus, worsening the reaction of the body to CIS. The collective results demonstrated that ADM acted as a stress-related peptide in the CSF-contacting nucleus, and its lower expression and blocked effects in the nucleus contributed to the deterioration of stress-induced physiologic parameter disorders as well as the excessive expressions of stress-related hormones which were part of the hypothalamic-pituitary-adrenal (HPA) axis.

Behavioral and molecular responses to electroconvulsive shock differ between genetic and environmental rat models of depression

Depression׳s causes play a role in individuals׳ different responses to antidepressant treatments, which require advancements. We investigated the mechanisms behind and responses to a highly effective antidepressant treatment, electroconvulsive therapy (ECT), in rat models with different (genetic or environmental) depression causes. Wistar Kyoto (WKY) rats and Wistar rats treated with chronic unpredictable mild stresses (CUMS) were used as genetic and environmental rat models of depression, respectively. The rats underwent electroconvulsive shock (ECS, the animal analog of ECT) or sham ECS. We performed a sucrose preference test, open field test, and Morris water maze to assess behavior. Hippocampal neuron numbers were measured with Nissl stain. Hippocampal BDNF, CREB, and p-CREB proteins were assayed with ELISA or western blotting. The main results showed that ECS impaired WKY rats׳ memories but improved CUMS rats׳ memories. It elevated hippocampal BDNF and CREB proteins only in CUMS rats, while it improved depressive behavior and hippocampal p-CREB protein levels in both rats, with more effective regulations in the CUMS rats. ECS did not change the hippocampal neuron number in both rats. These findings suggest that ECS exerted up-regulating effects on hippocampal BDNF and CREB (and its phosphorylation) in depressed rats, and the environmental model responded better.

Dysfunctional inhibitory mechanisms in locus coeruleus neurons of the wistar kyoto rat

BACKGROUND

The noradrenergic nucleus locus coeruleus (LC) has functional relevance in several psychopathologies such as stress, anxiety, and depression. In addition to glutamatergic and GABAergic synaptic inputs, the activation of somatodendritic α2-adrenoceptors is the main responsible for LC activity regulation. The Wistar Kyoto (WKY) rat exhibits depressive- and anxiety-like behaviors and hyperresponse to stressors. Thus, the goal of the present study was to investigate in vitro the sensitivity of α2-adrenoceptors, as well as the glutamatergic and GABAergic synaptic activity on LC neurons of the WKY strain.

METHODS

For that purpose patch-clamp whole-cell recordings were done in LC slices.

RESULTS

The α2-adrenoceptors of LC neurons from WKY rats were less sensitive to the effect induced by the agonist UK 14 304 as compared to that recorded in the Wistar (Wis) control strain. In addition, the GABAergic input to LC neurons of WKY rats was significantly modified compared to that in Wis rats, since the amplitude of spontaneous GABAergic postsynaptic currents was reduced and the half-width increased. On the contrary, no significant alterations were detected regarding glutamatergic input to LC neurons between rat strains.

CONCLUSIONS

These results point out that in WKY rats the inhibitory control exerted by α2-adrenoceptors and GABAergic input onto LC neurons is dysregulated. Overall, this study supports in this animal model the hypothesis that claims an imbalance between the glutamatergic-GABAergic systems as a key factor in the pathophysiology of depression.

Modulation of OCT3 expression by stress, and antidepressant-like activity of decynium-22 in an animal model of depression

The organic cation transporter-3 (OCT3) is a glucocorticoid-sensitive uptake mechanism that has been shown to regulate the bioavailability of monoamines in brain regions that are implicated in the pathophysiology of depression. In the present study, the relative impacts of acute stress alone and acute stress with a history of repeated stress (chronic+acute) were evaluated in two strains of rats: the stress-vulnerable Wistar-Kyoto (WKY) strain and the somewhat more stress-resilient Long-Evans (LE) strain. OCT3 mRNA was significantly upregulated in the hippocampus of LE rats 2h after exposure to acute restraint stress, but not in acutely-restrained rats with a history of repeated social defeat stress. WKY rats exhibited a very different pattern. OCT3 mRNA was unaffected by acute restraint stress alone but was robustly upregulated after repeated+acute stress. There was also a corresponding increase in cytosolic OCT3 protein following repeated+acute stress in WKY rats 3h after presentation of the acute stressor. These results are consistent with the hypothesis that altered expression of the OCT3 may play a role in stress coping, and strain differences in regulation of this expression may contribute to differences in physiological and behavioral responses to stress. Furthermore, the OCT3 inhibitor, decynium 22 (1 and 10μg/kg, i.p.) reduced immobility of WKY rats, but not that of LE rats, in the forced swim test, suggesting that blockade of the OCT3 has antidepressant-like effects. Since WKY rats also appear to be resistant to the behavioral effects of traditional antidepressants, this also suggests that OCT3 antagonism may be an alternative therapeutic strategy for the treatment of depression in individuals who do not respond to conventional antidepressants.

Effects of desipramine treatment on stress-induced up-regulation of norepinephrine transporter expression in rat brains

RATIONALE

Many studies demonstrate down-regulation of the norepinephrine transporter (NET) by desipramine (DMI) in vitro and in stress-naive rats. Little is known regarding regulation of the NET in stressed animals.

OBJECTIVE

The present study was designed to investigate effects of DMI on the expression of NET and protein kinases in the stress rat.

METHODS

Adult Fischer 344 rats were subjected to chronic social defeat (CSD) for 4 weeks. DMI (10 mg/kg, intraperitoneal (i.p.)) was administered concurrently with CSD or 1 or 2 weeks after cessation of CSD. Sucrose consumption, NET expression, and protein kinases were measured.

RESULTS

CSD significantly increased messenger RNA (mRNA) and protein levels of NET in the locus coeruleus, as well as NET protein levels in the hippocampus, frontal cortex, and amygdala. These effects were nearly abolished when DMI was administered concurrently with CSD. CSD-induced up-regulation of NET expression in the locus coeruleus, hippocampus, and amygdala lasted at least 2 weeks after cessation of CSD, an effect that was significantly attenuated by 1 or 2 weeks of DMI treatment starting from cessation of the CSD. Concurrent administration of DMI with CSD did not markedly interfere with CSD-induced decreases in protein levels of protein kinases A and C in these brain regions, but it did reverse the CSD-induced reduction in phosphorylated cAMP response element-binding (pCREB) protein levels in most brain regions.

CONCLUSION

These findings suggest that NET regulation by DMI occurs in both stressed and behaviorally naive rats, and DMI-induced changes in pCREB may be involved.

Antidepressant-like effects of buprenorphine in rats are strain dependent

The prevalence of major depressive disorder and the limited efficacy of conventional drug treatments provide significant impetus to develop novel and more rapidly acting antidepressants for individuals with treatment resistant forms of depression. The primary goal of these studies was to ascertain whether buprenorphine (BPN), a medically available drug with mixed effects at opioid receptors, was effective in behavioral tests using the Wistar Kyoto (WKY) rat strain, a rodent model of exaggerated depressive and anxiety behaviors that demonstrates resistance to certain antidepressants. As WKY rats are maintained by different sources, we assessed the behavioral effects of BPN using the modified rat forced swim test (FST) and the emergence test in WKY rat colonies obtained from different vendors. BPN dose-dependently reduced immobility and increased swimming behavior in the FST and reduced emergence latencies in two WKY lines (Charles River (WKY/NCrl) and Harlan laboratories (WKY/NHsd)) that also showed high baseline immobility in the FST. WKY rats from Taconic (WKY/NTac) did not show high baseline immobility in the FST or anxiety as had been previously reported, suggesting a drift in the phenotype of rats from this supplier. Furthermore, BPN did not reduce immobility in the FST or reduce latencies in the emergence test in WKY rats from Taconic. BPN also failed to produce antidepressant-like effects in Wistar and Sprague-Dawley rats. These results indicate a striking strain-selectivity for the effects of BPN, producing antidepressant and anxiolytic-like responses in WKY/NCrl and WKY/NHsd lines but not in the normosensitive control Wistar and Sprague-Dawley strains.