Chronic imipramine treatment differentially alters the brain and plasma amino acid metabolism in Wistar and Wistar Kyoto rats

The anti-depression effect and potential mechanism of the petroleum ether fraction of CDB: Integrated network pharmacology and metabolomics

The combination of Chaidangbo (CDB) is an antidepressant traditional Chinese medicine (TCM) prescription simplified by Xiaoyaosan (a classic antidepressant TCM prescription) through dismantling research, which has the effect of dispersing stagnated liver qi and nourishing blood in TCM theory. Although the antidepressant effect of CBD has been confirmed in animal studies, the material basis and possible molecular mechanism for antidepressant activity in CBD have not been clearly elucidated. Herein, we investigated the effects and potential mechanisms of CDB antidepressant fraction (petroleum ether fraction of CDB, PEFC) on chronic unpredictable mild stress (CUMS)-induced depression-like behavior in mice using network pharmacology and metabolomics. First, a UPLC-QE/MS was employed to identify the components of PEFC. To extract active ingredients, SwissADME screening was used to the real PEFC components that were found. Potential PEFC antidepressant targets were predicted based on a network pharmacology approach, and a pathway enrichment analysis was performed for the predicted targets. Afterward, a CUMS mouse depression model was established and LC-MS-based untargeted hippocampal metabolomics was performed to identify differential metabolites, and related metabolic pathways. Finally, the protein expressions in mouse hippocampi were determined by Western blot to validate the network pharmacology and metabolomics deduction. A total of 16 active compounds were screened in SwissADME that acted on 73 core targets of depression, including STAT3, MAPKs, and NR3C1; KEGG enrichment analysis showed that PEFC modulated signaling pathways such as PI3K-Akt signaling pathway, endocrine resistance, and MAPK to exert antidepressant effects. PEFC significantly reversed abnormalities of hippocampus metabolites in CUMS mice, mainly affecting the synthesis and metabolism of glycine, serine, and threonine, impacting catecholamine transfer and cholinergic synapses and regulating the activity of the mTOR signaling pathway. Furthermore, Western blot analysis confirmed that PEFC significantly influenced the main protein levels of the PI3K/Akt/mTOR signaling pathways in the hippocampus of mice subjected to CUMS. This study integrated metabolomics, network pharmacology and biological verification to explore the potential mechanism of PEFC in treating depression, which is related to the regulation of amino acid metabolism dysfunction and the activation of PI3K/Akt/mTOR signaling pathways in the hippocampus. The comprehensive strategy also provided a reasonable way for unveiling the pharmacodynamic mechanisms of multi-components, multi-targets, and multi-pathways in TCM with antidepressant effect.

Effect of chronic unpredictable stress in female Wistar-Kyoto rats subjected to progesterone withdrawal: Relevance for Premenstrual Dysphoric Disorder neurobiology

Premenstrual Dysphoric Disorder (PMDD) is related to an abrupt drop in progesterone and impairments in the HPA axis that cause anxiety. Suffering persons report higher daily-life stress and anxiety proneness that may contribute to developing PMDD, considered a chronic stress-related disorder. Here, we explored the effect of chronic unpredictable stress (CUS) in rats subjected to progesterone withdrawal (PW) and evaluated gene expression of HPA axis activation in the stress-vulnerable Wistar-Kyoto (WKY) rat strain that is prone to anxiety. Ovariectomized WKY rats were randomly assigned to CUS or Standard-housed conditions (SHC) for 30 days. To induce PW, animals received 2 mg/kg of progesterone on day 25th for 5 days; 24 h later, they were tested using the anxiety-like burying behavior test (BBT). After behavioral completion, rats were euthanized, and brains were extracted to measure Crh (PVN) and Nr3c1 (hippocampus) mRNA. Blood corticosterone and vasopressin levels were determined. Results showed that PW exacerbated anxiety-like behaviors through passive coping in CUS-WKY. PW decreased Crh-PVN mRNA and the Nr3c1-hippocampal mRNA expression in SHC. CUS decreased Crh-PVN mRNA compared to SHC, and no further changes were observed by PW or BBT exposure. CUS reduced Nr3c1-hippocampal gene expression compared to SHC animals, and lower Nr3c1 mRNA was detected due to BBT. The PW increased corticosterone in SHC and CUS rats; however, CUS blunted corticosterone when combined with PW+BBT and similarly occurred in vasopressin concentrations. Chronic stress blunts the response of components of the HPA axis regulation when PW and BBT (systemic and psychogenic stressors, respectively) are presented. This response may facilitate less adaptive behaviors through passive coping in stress-vulnerable subjects in a preclinical model of premenstrual anxiety.

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.

Cannabinoid Receptor 2 Blockade Prevents Anti-Depressive-like Effect of Cannabidiol Acid Methyl Ester in Female WKY Rats

The pathophysiology of major depressive disorder (MDD) is diverse and multi-factorial, yet treatment strategies remain limited. While women are twice as likely to develop the disorder as men, many animal model studies of antidepressant response rely solely on male subjects. The endocannabinoid system has been linked to depression in clinical and pre-clinical studies. Cannabidiolic Acid-Methyl Ester (CBDA-ME, EPM-301) demonstrated anti-depressive-like effects in male rats. Here, we explored acute effects of CBDA-ME and some possible mediating mechanisms, using a depressive-like genetic animal model, the Wistar-Kyoto (WKY) rat. In Experiment 1, Female WKY rats underwent the Forced swim test (FST) following acute CBDA-ME oral ingestion (1/5/10 mg/kg). In Experiment 2, Male and female WKY rats underwent the FST after injection of CB1 (AM-251) and CB2 (AM-630) receptor antagonists 30 min before acute CBDA-ME ingestion (1 mg/kg, males; 5 mg/kg, females). Serum levels of Brain-Derived Neurotrophic Factor (BDNF), numerous endocannabinoids and hippocampal Fatty Acid Amide Hydrolase (FAAH) levels were assessed. Results indicate that females required higher doses of CBDA-ME (5 and 10 mg/kg) to induce an anti-depressive-like effect in the FST. AM-630 blocked the antidepressant-like effect in females, but not in males. The effect of CBDA-ME in females was accompanied by elevated serum BDNF and some endocannabinoids and low hippocampal expression of FAAH. This study shows a sexually diverse behavioral anti-depressive response to CBDA-ME and possible underlying mechanisms in females, supporting its potential use for treating MDD and related disorders.

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

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

Decreased stress-induced depression-like behavior in lactating rats is associated with changes in the hypothalamic-pituitary-adrenal axis, brain monoamines, and brain amino acid metabolism

Depression-like behavior during lactation may relate to changes in the hypothalamic-pituitary-adrenal (HPA) axis, brain monoamines, and brain amino acid metabolism. This study investigated how the behavior, HPA axis activity, brain monoamines, and brain free amino acid metabolism of rats were changed by stress or lactation period. Rats were separated into four groups: (1) control lactating (n = 6), (2) stress lactating (n = 6), (3) control virgin (n = 7), and (4) stress virgin (n = 7) and restrained for 30 min a total of ten times (once every other day) from postnatal day (PND) 1. Depression-like behavior in the forced swimming test (FST) on PND 10 and concentration of corticosterone in plasma, as well as monoamines and L-amino acids including β-alanine, γ-aminobutyric acid, cystathionine, 3-methyl-histidine and taurine in the prefrontal cortex and hypothalamus on PND 19 were measured. The plasma corticosterone concentration, measured just after restraint stress, was significantly higher in the stress groups, versus the control groups, but there were no significant differences between control and stress lactating groups. Depression-like behavior (immobility) in the FST was significantly lower in the lactating groups, versus the virgin groups. Stress enhanced dopamine and glutamate, and decreased threonine and glycine concentrations in the hypothalamus. In addition, 3-methoxy-4-hydroxyphenylglycol (MHPG), threonine and ornithine concentrations in the prefrontal cortex were significantly higher in the lactating groups compared with the virgin groups. Changes in plasma corticosterone concentration, monoamine, and amino acid metabolism may relate to stress-induced depression-like behavior in lactating rats. Lay summary This study revealed that reduced depression-like behavior in lactating, relative to virgin rats, was associated with changes in monoamine and amino acid metabolism in the prefrontal cortex of the brain. In addition, the effect of stress on monoamine and amino acid metabolism is prominently observed in the hypothalamus and may be related to neuroendocrine stress axis activity and secretion of corticosterone. This study suggested that stress-induced depression-like behavior may be associated with several changes in the stress axis, brain monoamines, and brain amino acid metabolism. These parameters were associated with attenuated depression-like behavior in lactating rats.

Differences in free amino acid concentrations in milk between Wistar and Wistar Kyoto rats

Wistar Kyoto (WKY) rats, an animal depression model, display abnormal behaviors such as hypoactivity and depression-like behavior compared with Wistar (WIS) rats as a control. A previous study confirmed a dysfunction of amino acid metabolism in the brain of WKY rats compared with that of WIS rats. At the neonatal stage, free amino acids in milk are important nutrients because they act as immediate nutrients for offspring and may affect later health and behavior of the offspring. Therefore, the present study aimed to investigate free amino acid concentrations in milk and the relationships between free amino acid concentrations in milk and plasma in WIS and WKY rats. The concentrations of ten of the determined free amino acids in milk were significantly higher, but only L-methionine was significantly lower, in WKY rats. Six free amino acids had significantly higher concentrations in colostrum and two free amino acids had higher concentrations in matured milk. Free amino acid concentrations in plasma changed by both genetic background and lactation stage; however, the patterns of change in most free amino acid concentrations except for taurine in plasma were similar between WIS and WKY rats. The transport ratio of free amino acids from plasma to milk was not similar among the free amino acids tested, and each free amino acid was influenced by the genetic background and/or the type of milk.

Amitriptyline at an Environmentally Relevant Concentration Alters the Profile of Metabolites Beyond Monoamines in Gilt-Head Bream

The antidepressant amitriptyline is a widely used selective serotonin reuptake inhibitor that is found in the aquatic environment. The present study investigates alterations in the brain and the liver metabolome of gilt-head bream (Sparus aurata) after exposure at an environmentally relevant concentration (0.2 µg/L) of amitriptyline for 7 d. Analysis of variance-simultaneous component analysis is used to identify metabolites that distinguish exposed from control animals. Overall, alterations in lipid metabolism suggest the occurrence of oxidative stress in both the brain and the liver-a common adverse effect of xenobiotics. However, alterations in the amino acid arginine are also observed. These are likely related to the nitric oxide system that is known to be associated with the mechanism of action of antidepressants. In addition, changes in asparagine and methionine levels in the brain and pantothenate, uric acid, and formylisoglutamine/N-formimino-L-glutamate levels in the liver could indicate variation of amino acid metabolism in both tissues; and the perturbation of glutamate in the liver implies that the energy metabolism is also affected. These results reveal that environmentally relevant concentrations of amitriptyline perturb a fraction of the metabolome that is not typically associated with antidepressant exposure in fish. Environ Toxicol Chem 2019;00:1-13. © 2019 SETAC.

Elevated CYP2C19 expression is associated with depressive symptoms and hippocampal homeostasis impairment

The polymorphic CYP2C19 enzyme metabolizes psychoactive compounds and is expressed in the adult liver and fetal brain. Previously, we demonstrated that the absence of CYP2C19 is associated with lower levels of depressive symptoms in 1472 Swedes. Conversely, transgenic mice carrying the human CYP2C19 gene (2C19TG) have shown an anxious phenotype and decrease in hippocampal volume and adult neurogenesis. The aims of this study were to: (1) examine whether the 2C19TG findings could be translated to humans, (2) evaluate the usefulness of the 2C19TG strain as a tool for preclinical screening of new antidepressants and (3) provide an insight into the molecular underpinnings of the 2C19TG phenotype. In humans, we found that the absence of CYP2C19 was associated with a bilateral hippocampal volume increase in two independent healthy cohorts (N=386 and 1032) and a lower prevalence of major depressive disorder and depression severity in African-Americans (N=3848). Moreover, genetically determined high CYP2C19 enzymatic capacity was associated with higher suicidality in depressed suicide attempters (N=209). 2C19TG mice showed high stress sensitivity, impaired hippocampal Bdnf homeostasis in stress, and more despair-like behavior in the forced swim test (FST). After the treatment with citalopram and 5-HT_1A receptor agonist 8OH-DPAT, the reduction in immobility time in the FST was more pronounced in 2C19TG mice compared with WTs. Conversely, in the 2C19TG hippocampus, metabolic turnover of serotonin was reduced, whereas ERK1/2 and GSK3β phosphorylation was increased. Altogether, this study indicates that elevated CYP2C19 expression is associated with depressive symptoms, reduced hippocampal volume and impairment of hippocampal serotonin and BDNF homeostasis.

Single and chronic L-serine treatments exert antidepressant-like effects in rats possibly by different means

In the present study, the effects of both single (6 mmol L-serine/10 ml/kg orally administrated) and chronic (2% L-serine solution freely given for 28 days) treatments on depression-like behavior were evaluated in Wistar rats, representing the control, and Wistar Kyoto rats, representing an animal model of depression. Both single and chronic L-serine treatments decreased the duration of immobility, which is an index of a depressive-like state, in the forced swimming test in both strains. However, the decreases in the duration of immobility appear to be regulated differently by the different mechanisms involved in single and chronic L-serine treatments. In the prefrontal cortex and hippocampus, single L-serine treatment increased the concentrations of L-serine, but not D-serine, while chronic L-serine treatment increased those of D-serine, but not L-serine. These data suggest that the antidepressant-like effects of single and chronic L-serine treatments may have been induced by the increased L-serine and D-serine concentrations, respectively, in the brain. In addition, chronic L-serine treatment increased cystathionine concentrations in the hippocampus and prefrontal cortex in Wistar rats, but not in Wistar Kyoto rats, suggesting that Wistar Kyoto rats have an abnormality in the serine-cystathionine metabolic pathway. In conclusion, single and chronic L-serine treatments may induce antidepressant-like effects via the different mechanisms related to serine metabolism in the brain.

Hippocampal and motor fronto-cortical neuroligin1 is increased in an animal model of depression

Neuroligins (NLGNs) regulate synaptic excitability, neuronal signaling and sleep. We hypothesize that alteration of NLGNs is involved in the pathology of depression and tested the hypothesis in a model of depression using Wistar Kyoto (WKy) rat and its control, the Wistar (Wis) rat. We first evaluated behavioral deficits using the forced swim test and then characterized alterations of NLGN1 and NLGN2 with RT-PCR and Western Blotting in the prefrontal cortex, motor frontal cortex and hippocampus. Compared with controls of Wis rats, (1) the WKy rats had significantly shorter swim time and longer immobile time; (2) NLGN1 mRNA levels was higher in the motor frontal cortex and hippocampus in the WKy model; (3) NLGN1 protein was significantly higher in the motor frontal cortex, the prefrontal cortex and the hippocampus in the WKy model; (4) NLGN2 mRNA was significantly higher in the motor frontal cortex but significantly lower in the hippocampus in the WKy model. We concluded that NLGN1 gene and protein expression is higher in the motor frontal cortex, hippocampus and in the prefrontal cortex in the WKy rats suggesting that alterations of NLGN1 is involved in the pathology of depression but need to be further evaluated in human.