Female Flinders Sensitive Line rats show estrous cycle-independent depression-like behavior and altered tryptophan metabolism

Metabolomics in Depression: What We Learn from Preclinical and Clinical Evidences

Depression is one of the predominant common mental illnesses that affects millions of people of all ages worldwide. Random mood changes, loss of interest in routine activities, and prevalent unpleasant senses often characterize this common depreciated mental illness. Subjects with depressive disorders have a likelihood of developing cardiovascular complications, diabesity, and stroke. The exact genesis and pathogenesis of this disease are still questionable. A significant proportion of subjects with clinical depression display inadequate response to antidepressant therapies. Hence, clinicians often face challenges in predicting the treatment response. Emerging reports have indicated the association of depression with metabolic alterations. Metabolomics is one of the promising approaches that can offer fresh perspectives into the diagnosis, treatment, and prognosis of depression at the metabolic level. Despite numerous studies exploring metabolite profiles post-pharmacological interventions, a quantitative understanding of consistently altered metabolites is not yet established. The article gives a brief discussion on different biomarkers in depression and the degree to which biomarkers can improve treatment outcomes. In this review article, we have systemically reviewed the role of metabolomics in depression along with current challenges and future perspectives.

Increased depressive-like behaviour of postpartum Flinders sensitive and resistant line rats is reversed by a predictable postpartum stressor

During the peripartum period, women are at an increased risk to develop perinatal distress, presenting as symptoms of depression and/or anxiety. Yet, due to practical and ethical restrictions, our understanding of this condition remains limited. Animal studies that focus on the neuropsychiatric mechanisms associated with the postpartum period, often ignore the genetical predisposition factor. We therefore investigated whether pregnancy could alter the bio-behavioural profile of the Flinders sensitive and resistant line rats, and whether these effects are exacerbated by a postpartum stressor. Postpartum dams were compared to nulliparous controls in behavioural tests, analysing depressive- and anxiety-like behaviours. Next, postpartum dams were subjected to a maternal separation and early weaning (MSEW) regimen, with their behaviour and serotonergic and noradrenergic concentrations compared to rats not separated from their pups. Regardless of strain, pregnancy decreased time spent in the open arms of the elevated plus maze and hippocampal serotonin concentrations. Time spent immobile in the forced swim test was also increased, with a significant effect in the FRL and a strong trend in the FSL rats. MSEW reversed these behaviours in both strains and increased social interaction with a male counterpart in the FSL rats, without influencing hippocampal or cortical serotonin or norepinephrine. Taken together, these results suggest that pregnancy influences postpartum behaviour, in a strain-dependent manner. Contrary to what we expected, MSEW overall decreased depressive- and anxiety-like behaviours, with strain specific differences, indicating that a chronic, predictable stressor may not necessarily adversely affect postpartum behaviour.

Alteration in cerebral blood flow, kynurenines with respect to mood profile in freshly recruited armed forces personnel

The present study is conducted to understand the association of mood profile with the kynurenine pathway (KP) metabolites, and cerebral hemodynamics in freshly recruited central armed forces personnel. Profile of Mood States questionnaire was utilized to assess mood profile, and Total Mood Disturbance (TMD) score was calculated. Transcranial Doppler was used to record blood flow velocity bilaterally of the middle cerebral artery. Chromatographic profile of the kynurenine metabolites was obtained in serum. Further, personnel were stratified according to sociodemographic variables (gender, age and diet) to observe the changes in their KP metabolic status. An activation of the kynurenic acid branch of the KP and the reduction in the mean blood flow velocity, and an increase in Gosling pulsatility index (PI) were observed in females having high TMD score. On gender comparative analysis, kynurenine metabolites of quinolinic acid branch and serotonin were significantly high in males. In males, with increase in age, a significant increase in the quinolinic acid branch of the KP was observed. Furthermore, a significant difference in level metabolites of the KP among the vegetarian and non-vegetarian groups was also observed. In conclusion we observed that increased TMD score was associated with cerebral hypoperfusion and higher vascular resistance along with activation of the KP. Our findings highlighted the importance of multi-facet brain function to showcase the close interaction of various dimensionalities and true picture of the assessee.

Strain-, Sex-, and Time-Dependent Antidepressant-like Effects of Cannabidiol

Cannabidiol (CBD) is a non-intoxicating compound extracted from Cannabis sativa, showing antidepressant-like effects in different rodent models. However, inconsistent results have been described depending on the species and the strain used to assess depressive-like behavior. Moreover, only a few studies investigated the effect of CBD in female rodents. Therefore, we aimed to (i) investigate the effects of CBD in two different strains of mice (Swiss and C57BL/6) and a rat model of depression based on selective breeding (Flinders Sensitive and Resistant Lines, FSL and FRL) subjected to tests predictive of antidepressant-like effects and (ii) investigate the influence of sex in the effects of CBD in both mice and rats. CBD induced an antidepressant-like effect in male Swiss but not in female Swiss or C57BL/6 mice in the tail suspension test (TST). In male FSL rats, CBD produced an antidepressant-like effect 1 h post injection. However, in female FSL, CBD induced a bimodal effect, increasing the immobility time at 1 h and decreasing it at 2 h. In conclusion, strain, sex, and administration time affect CBD's behavioral response to rodents exposed to tests predictive of antidepressant effects.

Ketamine's effect on inflammation and kynurenine pathway in depression: A systematic review

BACKGROUND

Ketamine is a novel rapid-acting antidepressant with high efficacy in treatment-resistant patients. Its exact therapeutic mechanisms of action are unclear; however, in recent years its anti-inflammatory properties and subsequent downstream effects on tryptophan (TRP) metabolism have sparked research interest.

AIM

This systematic review examined the effect of ketamine on inflammatory markers and TRP-kynurenine (KYN) pathway metabolites in patients with unipolar and bipolar depression and in animal models of depression.

METHODS

MEDLINE, Embase, and PsycINFO databases were searched on October 2020 (1806 to 2020).

RESULTS

Out of 807 initial results, nine human studies and 22 animal studies on rodents met the inclusion criteria. Rodent studies provided strong support for ketamine-induced decreases in pro-inflammatory cytokines, namely in interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α and indicated anti-inflammatory effects on TRP metabolism, including decreases in the enzyme indoleamine 2,3-dioxygenase (IDO). Clinical evidence was less robust with high heterogeneity between sample characteristics, but most experiments demonstrated decreases in peripheral inflammation including in IL-1β, IL-6, and TNF-α. Preliminary support was also found for reduced activation of the neurotoxic arm of the KYN pathway.

CONCLUSION

Ketamine appears to induce anti-inflammatory effects in at least a proportion of depressed patients. Suggestions for future research include investigation of markers in the central nervous system and examination of clinical relevance of inflammatory changes.

The rat hippocampal gliovascular system following one week vortioxetine and fluoxetine

We have previously reported that vortioxetine, unlike the selective serotonin reuptake inhibitor fluoxetine, produces a rapid increase of dendritic spine number and Brain Derived Neurotrophic Factor (BDNF)-associated formation of synapses with mitochondrial support in the rat hippocampal CA1 and dentate gyrus. As a continuation of this line of research, and given the putative role of brain glial cells in mediating antidepressant responses the present study investigated early effects of vortioxetine on hippocampal microvasculature and Vascular Endothelial Growth Factor (VEGF) and astrocytes and microglia cells. Rats were treated for 1 week with vortioxetine (1.6 g/kg food chow) or fluoxetine (160 mg/L drinking water) at pharmacologically relevant doses. Stereological principles were used to estimate the number of ALDH1L1 positive astrocytes and Iba1 positive microglia cells, and the length of microvessels in subregions of hippocampus. VEGF protein levels were visualized with immunohistochemistry. Our results showed that vortioxetine significantly increased the number of ramified (resting) microglia and astrocytes accompanied by VEGF level elevation, whereas fluoxetine had no effect after 7 days treatment on these measures. Our findings suggest that astrocytes and microglia may have a role in mediating the pharmacological effects of vortioxetine in rats and that these effects are mediated through mechanisms that go beyond inhibition of the serotonin transporter and may target specific 5-HT receptors. It remains to be investigated whether these findings are relevant for the therapeutic effects of vortioxetine.

Serum Metabolic Profiling Reveals the Antidepressive Effects of the Total Iridoids of Valeriana jatamansi Jones on Chronic Unpredictable Mild Stress Mice

Background

Depression is a long-term complex psychiatric disorder, and its etiology remains largely unknown. Valeriana jatamansi Jones ex Roxb (V. jatamansi) is used in the clinic for the treatment of depression, but there are insufficient reports of its antidepressive mechanisms and a poor understanding of its endogenous substance-related metabolism. The objective of this study was to identify biomarkers related to depression in serum samples and evaluate the antidepressive effects of the iridoid-rich fraction of V. jatamansi (IRFV) in a chronic unpredictable mild stress (CUMS) mouse model.

Methods

Here, CUMS was used to establish a mouse model of depression. Behavioral and biochemical indicators were investigated to evaluate the pharmacodynamic effects. A comprehensive serum metabolomics study by nuclear magnetic resonance (NMR) approach was applied to investigate the pharmacological mechanism of IRFV in CUMS mouse. Subsequently, we used multivariate statistical analysis to identify metabolic markers, such as principal component analysis (PCA) and orthogonal projection to latent structure with discriminant analysis (OPLS-DA), to distinguish between the CUMS mouse and the control group.

Results

After IRFV treatment, the immobility time, sucrose preference, and monoamine neurotransmitter were improved. PCA scores showed clear differences in metabolism between the CUMS group and control group. The PLS-DA or OPLS-DA model exhibited 26 metabolites as biomarkers to distinguish between the CUMS mice and the control mouse. Moreover, IRFV could significantly return 21 metabolites to normal levels.

Conclusion

The results confirmed that IRFV exerted an antidepressive effect by regulating multiple metabolic pathways, including the tricarboxylic acid cycle, the synthesis of neurotransmitters, and amino acid metabolism. These findings provide insights into the antidepressive mechanisms of IRFV.

Rapid effects of S-ketamine on the morphology of hippocampal astrocytes and BDNF serum levels in a sex-dependent manner

The prevalence of major depressive disorder (MDD) is higher in women than men. Importantly, a differential behavioral response by sex to the antidepressant response to ketamine in rodents has been reported. Mechanistically, male depressed-like animals showed an increased spine density after ketamine treatment via restoration of synaptic protein levels while those proteins were not altered in female rats. In addition, preclinical studies indicate that the impairment of astrocytic plasticity is one of the contributing mechanisms in the pathophysiology of MDD. Accordingly, in this study, we determined the effect of sex on the rapid morphological alteration of hippocampal astrocytes and the serum level of BDNF one hour after S-ketamine injection. A single intraperitoneal dose of S-ketamine (15 mg/kg) or saline was injected to the male and female Flinders Sensitive Line (FSL) rats, a genetic animal model of depression and their brains were perfused one hour after treatment. The size of the GFAP positive astrocytes in the hippocampal subregions was measured. The volume of different hippocampal subregions was assessed using the Cavalieri estimator. Moreover, serum levels of BDNF were measured with enzyme-linked immunosorbent assay (ELISA) kits. The volume of hippocampal subregions significantly increased one hour after S-ketamine in both male and female FSL animals. However, a substantial alteration in the morphology of the hippocampal astrocytes was observed only in the female rats. Additionally, significantly increased serum BDNF levels in the female depressed rats were observed one hour after S-ketamine treatment. Our results indicate that the rapid effects of S-ketamine on the morphology of the hippocampal astrocytes and the serum level of BDNF are sex-dependent.

Esketamine and rapastinel, but not imipramine, have antidepressant-like effect in a treatment-resistant animal model of depression

OBJECTIVES

Treatment-resistance to antidepressants is a major problem in the pharmacotherapy of major depressive disorder (MDD). Unfortunately, only a few animal models are suitable for studying treatment-resistant depression, among them repeated treatment with Adrenocorticotropic hormone (ACTH) appears to be useful to mimic treatment-resistance to monoaminergic antidepressants. Therefore, the present work aimed to investigate the effectiveness of s-ketamine and rapastinel (formerly GLYX13), modulators of the glutamatergic N-methyl-D-aspartate receptor in ACTH-treated animals.

METHODS

Naïve male Sprague Dawley rats were subjected to repeated subcutaneous injections with ACTH (100 µg/0.1 ml/rat/day) for 14 days and drug treatment on the test day (open field and forced swim test) with imipramine, s-ketamine or rapastinel. In addition, assessment of plasma levels of corticosterone and ACTH was carried out.

RESULTS

We found that rats repeatedly treated with ACTH for 14 days responded to single injections with s-ketamine (15 mg/kg) and rapastinel (10 mg/kg), but failed to respond to imipramine (15 mg/kg). In the plasma, the levels of corticosterone and ACTH were increased after 14 days of daily treatment with ACTH, independently of the treatment.

CONCLUSION

The present data confirm development of a resistance to treatment following chronic ACTH administration. In addition, the study confirms the possible effectiveness of s-ketamine and rapastinel as treatment options in treatment-resistant depression. Moreover, it highlights the importance of the glutamatergic system in the neurobiology of depression. Further studies are necessary to evaluate how repeated treatment with ACTH leads to a depressed condition resistant to monoaminergic antidepressants.

What do we know about sex differences in depression: A review of animal models and potential mechanisms

Clinical studies have shown that women are more susceptible to depression than men. Sex differences in depression have been associated with social, cultural, as well as biological factors. In spite of extensive preclinical studies in animal models for depression that have been used for understanding the mechanisms of the disease as well as for new drug development, a substantive lack of attention on sex-specific phenotypes in depression might mask the effect of sex on the outcome. In this review article, we summarize findings on the influence of sex on behavior in the most commonly used animal models for depression. We also discuss the potential underlying mechanisms of such sex-dependent variation in the phenotype, particularly in the neuroendocrine system.

Sex-dependent behavior, neuropeptide profile and antidepressant response in rat model of depression

A plethora of animal models of depression is described in the literature, aiming at mimicking different aspects of depression. Understanding the link between depression and stress has been and remains a major focus area for development of animal models, but lines of research with a more mechanistic focus targeting deficiencies in neurotransmitter systems or dysfunctional neuronal circuitries and neuroinflammation are also pursued vigorously. The main objectives of the present study were systematically to evaluate strain and sex characteristics of a genetic animal model, the Flinders Sensitive Line (FSL)/ Flinders Resistant Line (FRL), by applying behavioral, molecular and pharmacological measures relevant to depression, and compare it with the outbred Sprague Dawley rat. In addition, we aimed at comparing across strains and sex the expression of NPY, CRF, CGRP in brain regions critically involved in mood regulation, and investigating the responses to escitalopram. In line with the comparisons of FSL and FRL rats, the FSL rats weighed significantly less than SD rats. Overall, escitalopram treatment for 5-6 weeks did not have a major impact on weight, but displayed a significant antidepressant-like effect, however without any changes in NPY, CRH and CGRP expression. Our comparative study of FSL and SD rat with respect to behavioral characteristic, neuropeptide levels in various brain regions (protein and mRNA levels), and response to long-term antidepressant treatment revealed that female FSL rats showed the most pronounced depressive-like phenotype and response to SSRI treatment. However, these findings were not paralleled by changes in measures of NPY, CRH and CGRP function.

Sex Differences in Hippocampal Memory and Kynurenic Acid Formation Following Acute Sleep Deprivation in Rats

Inadequate sleep is a prevalent problem within our society that can result in cognitive dysfunction. Elevations in kynurenic acid (KYNA), a metabolite of the kynurenine pathway (KP) of tryptophan degradation known to impact cognition, in the brain may constitute a molecular link between sleep loss and cognitive impairment. To test this hypothesis, we investigated the impact of 6 hours of sleep deprivation on memory and KP metabolism (brain and plasma) in male and female rats. Sleep-deprived males were impaired in a contextual memory paradigm, and both sexes were impaired in a recognition memory paradigm. After sleep deprivation, hippocampal KYNA levels increased significantly only in males. The response in hippocampal KYNA levels to sleep loss was suppressed in gonadectomized males, delineating a role of circulating gonadal hormones. Circulating corticosterone, which has previously been linked to KP metabolism, correlated negatively with hippocampal KYNA in sleep-deprived females, however the relationship was not significant in male animals. Taken together, our study introduces striking sex differences in brain KYNA formation and circulating corticosterone in response to sleep deprivation. Relating these findings to sex differences in cognitive outcomes after sleep deprivation may further advance the development of novel therapeutic agents to overcome sleep loss-induced cognitive dysfunction.

Repeated forced-swimming test in intact female rats: behaviour, oestrous cycle and enriched environment

Psychopharmacology used animal models to study the effects of drugs on brain and behaviour. The repeated forced-swimming test (rFST), which is used to assess the gradual effects of antidepressants on rat behaviour, was standardized only in males. Because of the known sex differences in rats, experimental conditions standardized for males may not apply to female rats. Therefore, the present work aimed to standardize experimental and housing conditions for the rFST in female rats. Young or adult Wistar female rats were housed in standard or enriched environments for different experimental periods. As assessed in tested and nontested females, all rats had reached sexual maturity by the time behavioural testing occurred. The rFST consisted of a 15-min session of forced swimming (pretest), followed by 5-min sessions at 1 (test), 7 (retest 1) and 14 days (retest 2) later. The oestrous cycle was registered immediately before every behavioural session. All sessions were videotaped for further analysis. The immobility time of female rats remained similar over the different sessions of rFST independent of the age, the phase of the oestrous cycle or the housing conditions. These data indicate that rFST in female Wistar rats may be reproducible in different experimental conditions.

Effects of vortioxetine on biomarkers associated with glutamatergic activity in an SSRI insensitive model of depression in female rats

The aim of this study was to investigate the antidepressant activity of vortioxetine in a tryptophan (TRP) depletion female rat model of depression and compare it to that of paroxetine using doses that fully occupy the serotonin transporter (SERT). We evaluated the effects of vortioxetine on potential biomarkers associated with TRP depletion including serum aldosterone, corticosterone and IL-6 levels together with indirect indicators of glutamate neurotransmission. Female Sprague-Dawley rats were randomized to control, low TRP, low TRP/paroxetine or low TRP/vortioxetine groups. Vortioxetine and paroxetine were administered via diet (10mg/kg/day) and drinking water (10mg/kg/day) respectively for 14days. Vortioxetine but not paroxetine reversed TRP depletion-induced depressive-like behavior. Vortioxetine reduced TRP depletion-induced increases of serum corticosterone, aldosterone, IL-6 and N-methyl-d-aspartate and α7-nicotinic acetylcholine receptor expression in the amygdala and hippocampus, respectively. Paroxetine demonstrated little effect except a reduction of aldosterone. Vortioxetine but not paroxetine reversed TRP depletion-induced reductions of serum and brain kynurenic acid. In conclusion, vortioxetine, but not paroxetine, enabled reversals of TRP depletion-induced changes of depression-like behavior and markers of glutamatergic activity. These observations support the hypothesis that vortioxetine's antidepressant activity may involve mechanisms beyond SERT inhibition.

Reprint of: Contrasting effects of vortioxetine and paroxetine on pineal gland biochemistry in a tryptophan-depletion model of depression in female rats

We studied the effects of the multi-modal antidepressant, vortioxetine and the SSRI, paroxetine on pineal melatonin and monoamine synthesis in a sub-chronic tryptophan (TRP) depletion model of depression based on a low TRP diet. Female Sprague-Dawley rats were randomised to groups a) control, b) low TRP diet, c) low TRP diet+paroxetine and d) low TRP diet+vortioxetine. Vortioxetine was administered via the diet (0.76mg/kg of food weight) and paroxetine via drinking water (10mg/kg/day) for 14days. Both drugs resulted in SERT occupancies >90%. Vortioxetine significantly reversed TRP depletion-induced reductions of pineal melatonin and serotonin (5-HT) and significantly increased pineal noradrenaline NA. Paroxetine did none of these things. Other studies suggest pineal melatonin synthesis may involve N-methyl-d-aspartate (NMDA) receptors and glutamatergic modulation. Here observed changes may be mediated via vortioxetine's strong 5-HT reuptake blocking action together with possible additional effects on glutamate neurotransmission in the pineal via NMDA receptor-modulation and possibly with added impetus from increased NA output.

OGT-related mitochondrial motility is associated with sex differences and exercise effects in depression induced by prenatal exposure to glucocorticoids

BACKGROUND

Prenatal exposure to glucocorticoids (GCs) has been found to trigger abnormal behaviors and deleterious neurological effects on offspring both in animals and in humans. The sex differences in depression have been replicated in numerous studies across cultures, persisting throughout the reproductive years. As an X-linked gene in rodents and in humans, O-GlcNAc transferase (OGT) may provide a novel perspective for the sex differences in depression.

METHODS

In the last third of pregnancy (gestational day 14-21), rats were subcutaneously administered either 0.13mg/kg dexamethasone-21-phosphate disodium salt (0.1mg/kg DEX) or vehicle (0.9% saline) once a day for 7 days. Adolescent (4 weeks) offspring were then trained in a swimming program or not.

RESULTS

Here we found that adult offspring rats exposed to DEX prenatally exhibited sex-specific depression-like behaviors, males being more vulnerable than females. Swimming exercise ameliorated the above-mentioned depressive syndromes, which may be a compensatory effect for male disadvantage suffering from prenatal stress. Furthermore, the effects of prenatal DEX exposure and swimming exercise on depression were associated with OGT-related mitochondrial motility, including PINK1/Parkin pathway and AKT/GSK3β pathway.

LIMITATIONS

Representative kymographs of mitochondrial motility were not detected and no causal effects were obtained by OGT gene overexpression or gene knockout in this study.

CONCLUSIONS

Our results provide a new perspective for better understanding sex differences and exercise effects in depression and may offer new mechanism-based therapeutic targets for depression.

The α2C-adrenoceptor antagonist, ORM-10921, exerts antidepressant-like effects in the Flinders Sensitive Line rat

Depression involves deficits in monoaminergic neurotransmission. Differential roles for α2A, B and C subtypes of the α2-adrenoceptor (AR) are evident, with selective α2C-AR antagonists purported to have antidepressant and procognitive properties. However, this has not been demonstrated in a genetic animal model of depression. The role of the α2C-AR in modulating two key depression-related behaviours in the Flinders Sensitive Line (FSL) rat was studied using a dose-response analysis following subcutaneous administration with the selective α2C-AR antagonist ORM-10921 (0.03; 0.3 mg/kg), the nonselective α2-AR antagonist idazoxan (3 mg/kg), or vehicle once daily for 14 days. Behaviour in the novel object recognition test, forced swim test (FST) and locomotor activity test was assessed. To ratify the validity of the FSL model, the reference tricyclic antidepressant imipramine (15 mg/kg, intraperitoneally) was used as a comparator drug in the FST. FSL rats demonstrated significantly increased immobility and recognition memory deficits versus Flinders Resistant Line controls, with imipramine significantly reversing said immobility. Similarly, ORM-10921 at both doses but not idazoxan significantly reversed immobility in the FST as well as attenuated cognitive deficits in FSL animals. We conclude that selective α2C-AR antagonism has potential as a novel therapeutic strategy in the treatment of depression and cognitive dysfunction.

Linking the biological underpinnings of depression: Role of mitochondria interactions with melatonin, inflammation, sirtuins, tryptophan catabolites, DNA repair and oxidative and nitrosative stress, with consequences for classification and cognition

The pathophysiological underpinnings of neuroprogressive processes in recurrent major depressive disorder (rMDD) are reviewed. A wide array of biochemical processes underlie MDD presentations and their shift to a recurrent, neuroprogressive course, including: increased immune-inflammation, tryptophan catabolites (TRYCATs), mitochondrial dysfunction, aryl hydrocarbonn receptor activation, and oxidative and nitrosative stress (O&NS), as well as decreased sirtuins and melatonergic pathway activity. These biochemical changes may have their roots in central, systemic and/or peripheral sites, including in the gut, as well as in developmental processes, such as prenatal stressors and breastfeeding consequences. Consequently, conceptualizations of MDD have dramatically moved from simple psychological and central biochemical models, such as lowered brain serotonin, to a conceptualization that incorporates whole body processes over a lifespan developmental timescale. However, important hubs are proposed, including the gut-brain axis, and mitochondrial functioning, which may provide achievable common treatment targets despite considerable inter-individual variability in biochemical changes. This provides a more realistic model of the complexity of MDD and the pathophysiological processes that underpin the shift to rMDD and consequent cognitive deficits. Such accumulating data on the pathophysiological processes underpinning MDD highlights the need in psychiatry to shift to a classification system that is based on biochemical processes, rather than subjective phenomenology.

Contrasting effects of vortioxetine and paroxetine on pineal gland biochemistry in a tryptophan-depletion model of depression in female rats

We studied the effects of the multi-modal antidepressant, vortioxetine and the SSRI, paroxetine on pineal melatonin and monoamine synthesis in a sub-chronic tryptophan (TRP) depletion model of depression based on a low TRP diet. Female Sprague-Dawley rats were randomised to groups a) control, b) low TRP diet, c) low TRP diet+paroxetine and d) low TRP diet+vortioxetine. Vortioxetine was administered via the diet (0.76mg/kg of food weight) and paroxetine via drinking water (10mg/kg/day) for 14days. Both drugs resulted in SERT occupancies >90%. Vortioxetine significantly reversed TRP depletion-induced reductions of pineal melatonin and serotonin (5-HT) and significantly increased pineal noradrenaline NA. Paroxetine did none of these things. Other studies suggest pineal melatonin synthesis may involve N-methyl-d-aspartate (NMDA) receptors and glutamatergic modulation. Here observed changes may be mediated via vortioxetine's strong 5-HT reuptake blocking action together with possible additional effects on glutamate neurotransmission in the pineal via NMDA receptor-modulation and possibly with added impetus from increased NA output.

Anxiolytic effects of muscarinic acetylcholine receptors agonist oxotremorine in chronically stressed rats and related changes in BDNF and FGF2 levels in the hippocampus and prefrontal cortex

RATIONALE

In depressive disorders, one of the mechanisms proposed for antidepressant drugs is the enhancement of synaptic plasticity in the hippocampus and cerebral cortex. Previously, we showed that the muscarinic acetylcholine receptor (mAChR) agonist oxotremorine (Oxo) increases neuronal plasticity in hippocampal neurons via FGFR1 transactivation.

OBJECTIVES

Here, we aimed to explore (a) whether Oxo exerts anxiolytic effect in the rat model of anxiety-depression-like behavior induced by chronic restraint stress (CRS), and (b) if the anxiolytic effect of Oxo is associated with the modulation of neurotrophic factors, brain-derived neurotrophic factor (BDNF) and fibroblast growth factor-2 (FGF2), and phosphorylated Erk1/2 (p-Erk1/2) levels in the dorsal or ventral hippocampus and in the medial prefrontal cortex.

METHODS

The rats were randomly divided into four groups: control unstressed, CRS group, CRS group treated with 0.2 mg/kg Oxo, and unstressed group treated with Oxo. After 21 days of CRS, the groups were treated for 10 days with Oxo or saline. The anxiolytic role of Oxo was tested by using the following: forced swimming test, novelty suppressed feeding test, elevated plus maze test, and light/dark box test. The hippocampi and prefrontal cortex were used to evaluate BDNF and FGF2 protein levels and p-Erk1/2 levels.

RESULTS

Oxo treatment significantly attenuated anxiety induced by CRS. Moreover, Oxo treatment counteracted the CRS-induced reduction of BDNF and FGF2 levels in the ventral hippocampus and medial prefrontal cerebral cortex CONCLUSIONS: The present study showed that Oxo treatment ameliorates the stress-induced anxiety-like behavior and rescues FGF2 and BDNF levels in two brain regions involved in CRS-induced anxiety, ventral hippocampal formation, and medial prefrontal cortex.

Ovariectomy results in inbred strain-specific increases in anxiety-like behavior in mice

Women are at an increased risk for developing affective disorders during times of hormonal flux, including menopause when the ovaries cease production of estrogen. However, while all women undergo menopause, not all develop an affective disorder. Increased vulnerability can result from genetic predisposition, environmental factors and gene by environment interactions. In order to investigate interactions between genetic background and estrogen depletion, we performed bilateral ovariectomy, a surgical procedure that results in estrogen depletion and is thought to model the post-menopausal state, in a genetically defined panel of 37 inbred mouse strains. Seventeen days post-ovariectomy, we assessed behavior in two standard rodent assays of anxiety- and depressive-like behavior, the open field and forced swim tests. We detected a significant interaction between ovariectomy and genetic background on anxiety-like behavior in the open field. No strain specific effects of ovariectomy were observed in the forced swim assay. However, we did observe significant strain effects for all behaviors in both the open field and forced swim tests. This study is the largest to date to look at the effects of ovariectomy on behavior and provides evidence that ovariectomy interacts with genetic background to alter anxiety-like behavior in an animal model of menopause.