Helena M. Abelaira

Animal models as tools to study the pathophysiology of depression

The incidence of depressive illness is high worldwide, and the inadequacy of currently available drug treatments contributes to the significant health burden associated with depression. A basic understanding of the underlying disease processes in depression is lacking; therefore, recreating the disease in animal models is not possible. Popular current models of depression creatively merge ethologically valid behavioral assays with the latest technological advances in molecular biology. Within this context, this study aims to evaluate animal models of depression and determine which has the best face, construct, and predictive validity. These models differ in the degree to which they produce features that resemble a depressive-like state, and models that include stress exposure are widely used. Paradigms that employ acute or sub-chronic stress exposure include learned helplessness, the forced swimming test, the tail suspension test, maternal deprivation, chronic mild stress, and sleep deprivation, to name but a few, all of which employ relatively short-term exposure to inescapable or uncontrollable stress and can reliably detect antidepressant drug response.

The role of mTOR in depression and antidepressant responses

The aim of this study was to characterize the mTOR signaling cascade in depression and the actions that antidepressant drugs have on this pathway. Herein, a literature review was performed by verification and comparison of textbooks and journal articles that describe the characterization of the mTOR signaling cascade and its relationship to depression and antidepressant drugs, especially ketamine. Postmortem studies have shown robust deficits in the mammalian target of rapamycin (mTOR) signaling in the prefrontal cortex of subjects diagnosed with major depressive disorder. However, besides the mTOR signaling pathway having an antidepressant response to various drugs, this seems to be more associated with antidepressant N-methyl-d-aspartate (NMDA) receptor antagonists, such as ketamine. The characterization of the mTOR signaling pathway in depression and its action in response to antidepressants show great potential for the identification of new therapeutic targets for the development of antidepressant drugs.

Ketamine and imipramine in the nucleus accumbens regulate histone deacetylation induced by maternal deprivation and are critical for associated behaviors.

Studies indicate that histone deacetylation is important for long term changes related to stress and antidepressant treatment. The present study aimed to evaluate the effects of the classic antidepressant imipramine, and of an antagonist of the N-methyl-d-asparte (NMDA) receptor, ketamine, on behavior and histone deacetylase (HDAC) activity in the brains of maternally deprived adult rats. To this aim, deprived and non-deprived (control) male Wistar rats were divided into the following groups: non-deprived+saline; non-deprived+imipramine (30 mg/kg); non-deprived+ketamine (15 mg/kg); deprived+saline; deprived+imipramine (30 mg/kg); and deprived+ketamine (15 mg/kg). The drugs were administrated once a day for 14 days during their adult phase. Their behavior were then assessed using the forced swimming and open field tests. In addition, the HDAC activity was evaluated in the prefrontal cortex, hippocampus, amygdala and nucleus accumbens using the kit ELISA-sandwich test. In deprived rats treated with saline, we observed an increase in the immobility time, but treatments with imipramine and ketamine were able to reverse this alteration, decreasing the immobility time. Also, there was a decrease on number of crossings with imipramine treatment in non-deprived rats, and an increase on number of crossings with ketamine treatment in deprived rats. The HDAC activity did not alter in the prefrontal cortex, hippocampus and amygdala by deprivation or via treatment with imipramine or ketamine. However, in the nucleus accumbens we observed an increase of HDAC activity in the deprived rats, and interestingly, imipramine and ketamine treatments were able to decrease HDAC activity in this brain area. These findings provide a novel insight into the epigenetic regulation of histone deacetylase in the nucleus accumbens caused by imipramine and ketamine, and indicate that molecular events are necessary to reverse specific stress-induced behavior.

MAPK signaling correlates with the antidepressant effects of ketamine

Studies have pointed to a relationship between MAPK kinase (MEK) signaling and the behavioral effects of antidepressant drugs. So, in the present study we examined the behavioral and molecular effects of ketamine, an antagonist of the N-methyl-d-aspartate receptor (NMDA), which has been shown to have an antidepressant effect after the inhibition of MEK signaling in Wistar rats. Our results showed that acute administration of the MEK inhibitor PD184161, produced depressive-like behavior and stopped antidepressant-like effects of ketamine in the forced swimming test. The phosphorylation of extracellular signal-regulated kinase 1/2 (pERK 1/2) was decreased by PD184161 in the amygdala and nucleus accumbens, and the effects of ketamine on pERK 1/2 in the prefrontal cortex and hippocampus were inhibited by PD184161. The ERK 2 levels were decreased by PD184161 in the nucleus accumbens; and the effects of ketamine were blocked in this brain area. The p38 protein kinase (p38MAPK) and proBDNF were inhibited by PD184161, and the MEK inhibitor prevented the effects of ketamine in the nucleus accumbens. In addition, ketamine increased pro-BDNF levels in the hippocampus. In conclusion, our findings demonstrated that an acute blockade of MAPK signaling lead to depressive-like behavior and stopped the antidepressant response of ketamine, suggesting that the effects of ketamine could be mediated, at least in part, by the regulation of MAPK signaling in these specific brain areas.

Epigenetic and epistatic interactions between serotonin transporter and brain-derived neurotrophic factor genetic polymorphism: Insights in depression

Epidemiological studies have shown significant results in the interaction between the functions of brain-derived neurotrophic factor (BDNF) and 5-HT in mood disorders, such as major depressive disorder (MDD). The latest research has provided convincing evidence that gene transcription of these molecules is a target for epigenetic changes, triggered by stressful stimuli that starts in early childhood and continues throughout life, which are subsequently translated into structural and functional phenotypes culminating in depressive disorders. The short variants of 5-HTTLPR and BDNF-Met are seen as forms which are predisposed to epigenetic aberrations, which leads individuals to a susceptibility to environmental adversities, especially when subjected to stress in early life. Moreover, the polymorphic variants also feature epistatic interactions in directing the functional mechanisms elicited by stress and underlying the onset of depressive disorders. Also emphasized are works which show some mediators between stress and epigenetic changes of the 5-HTT and BDNF genes, such as the hypothalamic-pituitary-adrenal (HPA) axis and the cAMP response element-binding protein (CREB), which is a cellular transcription factor. Both the HPA axis and CREB are also involved in epistatic interactions between polymorphic variants of 5-HTTLPR and Val66Met. This review highlights some research studying changes in the epigenetic patterns intrinsic to genes of 5-HTT and BDNF, which are related to lifelong environmental adversities, which in turn increases the risks of developing MDD.

Imipramine reverses alterations in cytokines and BDNF levels induced by maternal deprivation in adult rats.

A growing body of evidence is pointing toward an association between immune molecules, as well brain-derived neurotrophic factor (BDNF) and the depression. The present study was aimed to evaluate the behavioral and molecular effects of the antidepressant imipramine in maternally deprived adult rats. To this aim, maternally deprived and non-deprived (control group) male rats were treated with imipramine (30mg/kg) once a day for 14 days during their adult phase. Their behavior was then assessed using the forced swimming test. In addition to this, IL-10, TNF-α and IL-1β cytokines were assessed in the serum and cerebrospinal fluid (CSF). In addition, BDNF protein levels were assessed in the prefrontal cortex, hippocampus and amygdala. In deprived rats treated with saline was observed an increase on immobility time, compared with non-deprived rats treated with imipramine (p<0.05). Deprived rats treated with saline presented a decrease on BDNF levels in the amygdala (p<0.05), compared with all other groups. The IL-10 levels were decreased in the serum (p<0.05). TNF-α and IL-1β levels were increased in the serum and CSF of deprived rats treated with saline (p<0.05). Interestingly, imipramine treatment reversed the effects of maternal deprivation on BDNF and cytokines levels (p<0.05). Finally, these findings further support a relationship between immune activation, neurotrophins and the depression, and considering the action of imipramine, it is suggested that classic antidepressants could exert their effects by modulating the immune system.

A single dose of S-ketamine induces long-term antidepressant effects and decreases oxidative stress in adulthood rats following maternal deprivation

Ketamine, an antagonist of N‐methyl‐d‐aspartate receptors, has produced rapid antidepressant effects in patients with depression, as well as in animal models. However, the extent and duration of the antidepressant effect over longer periods of time has not been considered. This study evaluated the effects of single dose of ketamine on behavior and oxidative stress, which is related to depression, in the brains of adult rats subjected to maternal deprivation. Deprived and nondeprived Wistar rats were divided into four groups nondeprived + saline; nondeprived + S‐ketamine (15 mg/kg); deprived + saline; deprived + S‐ketamine (15 mg/kg). A single dose of ketamine or saline was administrated during the adult phase, and 14 days later depressive‐like behavior was assessed. In addition, lipid damage, protein damage, and antioxidant enzyme activities were evaluated in the rat brain. Maternal deprivation induces a depressive‐like behavior, as verified by an increase in immobility and anhedonic behavior. However, a single dose of ketamine was able to reverse these alterations, showing long‐term antidepressant effects. The brains of maternally deprived rats had an increase in protein oxidative damage and lipid peroxidation, but administration of a single dose of ketamine reversed this damage. The activities of antioxidant enzymes superoxide dismutase and catalase were reduced in the deprived rat brains. However, ketamine was also able to reverse these changes. In conclusion, these findings indicate that a single dose of ketamine is able to induce long‐term antidepressant effects and protect against neural damage caused by oxidative stress in adulthood rats following maternal deprivation.

Synergist effects of n-acetylcysteine and deferoxamine treatment on behavioral and oxidative parameters induced by chronic mild stress in rats

A growing body of evidence has pointed to a relationship between oxidative stress and depression. Thus, the present study was aimed at evaluating the effects of the antioxidants n-acetylcysteine (NAC), deferoxamine (DFX) or their combination on sweet food consumption and oxidative stress parameters in rats submitted to 40days of exposure to chronic mild stress (CMS). Our results showed that in stressed rats treated with saline, there was a decrease in sweet food intake and treatment with NAC or NAC in combination with DFX reversed this effect. Treatment with NAC and DFX decreased the oxidative damage, which include superoxide and TBARS production in submitochondrial particles, and also thiobarbituric acid reactive substances (TBARS) levels and carbonyl proteins in the prefrontal cortex, amygdala and hippocampus. Treatment with NAC and DFX also increased the activity of the antioxidant enzymes, superoxide dismutase and catalase in the same brain areas. Even so, a combined treatment with NAC and DFX produced a stronger increase of antioxidant activities in the prefrontal cortex, amygdala and hippocampus. The results described here indicate that co-administration may induce a more pronounced antidepressant activity than each treatment alone. In conclusion, these results suggests that treatment with NAC or DFX alone or in combination on oxidative stress parameters could have positive effects against neuronal damage caused by oxidative stress in major depressive disorders.

Effects of acute and chronic treatment elicited by lamotrigine on behavior, energy metabolism, neurotrophins and signaling cascades in rats.

The present study was aimed to investigate the behavioral and molecular effects of lamotrigine. To this aim, Wistar rats were treated with lamotrigine (10 and 20 mg/kg) or imipramine (30 mg/kg) acutely and chronically. The behavior was assessed using forced swimming test. Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), Proteina Kinase B (PKB, AKT), glycogen synthase kinase 3 (GSK-3) and B-cell lymphoma 2 (Bcl-2) levels, citrate synthase, creatine kinase and mitochondrial chain (I, II, II-III and IV) activities were assessed in the brain. The results showed that both treatments reduced the immobility time. The BDNF were increased in the prefrontal after acute treatment with lamotrigine (20 mg/kg), and the BDNF and NGF were increased in the prefrontal after chronic treatment with lamotrigine in all doses. The AKT increased and Bcl-2 and GSK-3 decreased after both treatments in all brain areas. The citrate synthase and creatine kinase increased in the amygdala after acute treatment with imipramine. Chronic treatment with imipramine and lamotrigine (10 mg/kg) increased the creatine kinase in the hippocampus. The complex I was reduced and the complex II, II-III and IV were increased, but related with treatment and brain area. In conclusion, lamotrigine exerted antidepressant-like, which can be attributed to its effects on pathways related to depression, such as neurotrophins, metabolism energy and signaling cascade.

Tianeptine exerts neuroprotective effects in the brain tissue of rats exposed to the chronic stress model

Animal models of chronic stress represent valuable tools by which to investigate the behavioral, endocrine and neurobiological changes underlying stress-related psychopathologies, such as major depression, and the efficacy of antidepressant therapies. The present study was aimed at investigating the neurochemical effects of the antidepressant tianeptine in rats exposed to the chronic stress model. To this aim, rats were subjected to 40days of chronic unpredictable stressful stimuli, after which the animals received saline or tianeptine (15mg/kg) once a day for 7days. Additionally, IL-6, IL-1, TNF-α levels and oxidative stress parameters were assessed in the prefrontal cortex (PFC), hippocampus (HPC), amygdala (AMY) and nucleus accumbens (NAc) in all of the experimental groups studied. The results indicated that chronic mild stress and tianeptine did not exercise any effects on cytokines in all of the structures studied; in the PFC and AMY thiobarbituric acid reactive substances (TBARS) levels were decreased in control rats treated with tianeptine in the HPC; superoxide dismutase (SOD) activity was found to have decreased in stressed rats treated with saline in the PFC, HPC, AMY and NAc, and tianeptine reversed this effect; catalase (CAT) activity was found to have decreased in the PFC, HPC and NAc of stressed rats treated with saline, but was shown to have increased in stressed rats treated with tianeptine, and tianeptine also reversed the decreases in CAT activity in stressed rats treated with saline, suggesting that tianeptine exerted antioxidant activity. In conclusion, the present findings open new vistas on the pharmacological activity of tianeptine, in particular, concerning its ability to attenuate oxidative stress.