Potentiation of the antidepressant-like effect of desipramine or reboxetine by metyrapone in the forced swimming test in rats

Influence of the selective antagonist of the NR2B subunit of the NMDA receptor, traxoprodil, on the antidepressant-like activity of desipramine, paroxetine, milnacipran, and bupropion in mice

Pre-clinical and clinical studies indicated that a blockade of the NMDA receptor complex creates new opportunities for the treatment of affective disorders, including depression. The aim of the present study was to assess the influence of traxoprodil (10 mg/kg) on the activity of desipramine (10 mg/kg), paroxetine (0.5 mg/kg), milnacipran (1.25 mg/kg), and bupropion (10 mg/kg), each at sub-therapeutic doses. Moreover, brain levels of traxoprodil and tested agents were determined using HPLC. The obtained results were used to ascertain the nature of occurring interaction between traxoprodil and studied antidepressants. The experiment was carried out on naïve adult male Albino Swiss mice. Traxoprodil and other tested drugs were administered intraperitoneally. The influence of traxoprodil on the activity of selected antidepressants was evaluated in forced swim test (FST). Locomotor activity was estimated to exclude false positive/negative data. To assess the influence of traxoprodil on the concentration of used antidepressants, their levels were determined in murine brains using HPLC. Results indicated that traxoprodil potentiated activity of all antidepressants examined in FST and the observed effects were not due to the increase in locomotor activity. Only in the case of co-administration of traxoprodil and bupropion, increased bupropion concentrations in brain tissue were observed. All tested agents increased the traxoprodil levels in the brain. Administration of a sub-active dose of traxoprodil with antidepressants from different chemical groups, which act via enhancing monoaminergic transduction, caused the antidepressant-like effect in FST in mice. The interactions of traxoprodil with desipramine, paroxetine, milnacipran, and bupropion occur, at least partially, in the pharmacokinetic phase.

Chronic stress and antidepressant induced changes in Hdac5 and Sirt2 affect synaptic plasticity

Changes in histone acetylation could contribute to the pathogenesis of depression and antidepressant therapy. Using the chronic social defeat stress (CSDS) model of depression and different antidepressant treatments we studied the regulation of histone deacetylases (Hdac׳s) and synaptic plasticity markers in the prefrontal cortex (PFC). Further, functional implication of identified Hdac׳s in brain plasticity was explored. Mice were exposed to CSDS (10 days) followed by saline or imipramine (4 weeks). PFC Hdac׳s mRNA abundance was studied and compared to human׳s. Further, protein expression of acetylated histones (AcH3 and AcH4), neuroplasticity markers (CREB and pro-BDNF) and selected Hdac׳s were analyzed. Moreover, other antidepressants (fluoxetine and reboxetine) and selective HDAC inhibitors were studied. CSDS increased Hdac5 and Sirt2 mRNA whereas repeated imipramine did the opposite. Accordingly, stress and imipramine induced opposite changes on AcH3, AcH4 and CREB expression. At protein level, CSDS upregulated nuclear fraction of Hdac5 and repeated imipramine and reboxetine increased its phosphorylated form (p-Hdac5), mainly located in the cytoplasm. Moreover, Sirt2 was downregulated by all monoaminergic antidepressants. Further, repeated treatment with the class IIa Hdac inhibitor MC1568 and the Sirt2 inhibitor 33i for three weeks increased synaptic plasticity in the prefrontal cortex. Our results suggest that Hdac5 and Sirt2 upregulation could constitute stable stress-induced neuronal adaptations. Noteworthy, the SIRT2 upregulation in depressed patients supports the interest of this target for therapeutic intervention. On the other hand, cytoplasmic Hdac5 export and Sirt2 downregulation induced by monoaminergic antidepressants could contribute to the well-known beneficial effects of antidepressants on brain plasticity.

A potential association between Toxoplasma gondii infection and schizophrenia in mouse models

Schizophrenia is a serious neuropsychiatric disease of uncertain etiology, which causes human mental disorder and affects about 1% of the population. In recently years, some studies showed that some cases of schizophrenia may be associated with Toxoplasma gondii infection. In order to investigate a potential association between Toxoplasma infection and schizophrenia, we investigated the relative clinical symptom of schizophrenia such as learning and memory capability, depression and stereotypy to find some useful information by behavioral test in mouse models. Our results demonstrated that mice from Toxoplasma infection and MK-801 administration (as the model of schizophrenia) were impaired in learning and memory capability, and they had more serious depression and stereotypy compared with the control mice, especially the mice from congenital Toxoplasma infection. In addition, our results clearly showed that the number of cysts in brain tissue of congenital Toxoplasma infection mice was significantly low than in acquired Toxoplasma infected mice. Collectively, these results suggested a potential association between Toxoplasma infection and schizophrenia.

The activation of α1-adrenoceptors is implicated in the antidepressant-like effect of creatine in the tail suspension test

The antidepressant-like activity of creatine in the tail suspension test (TST) was demonstrated previously by our group. In this study we investigated the involvement of the noradrenergic system in the antidepressant-like effect of creatine in the mouse TST. In the first set of experiments, creatine administered by i.c.v. route (1 μg/site) decreased the immobility time in the TST, suggesting the central effect of this compound. The anti-immobility effect of peripheral administration of creatine (1 mg/kg, p.o.) was prevented by the pretreatment of mice with α-methyl-p-tyrosine (100 mg/kg, i.p., inhibitor of tyrosine hydroxylase), prazosin (1 mg/kg, i.p., α1-adrenoceptor antagonist), but not by yohimbine (1 mg/kg, i.p., α2-adrenoceptor antagonist). Creatine (0.01 mg/kg, subeffective dose) in combination with subeffective doses of amitriptyline (1 mg/kg, p.o., tricyclic antidepressant), imipramine (0.1 mg/kg, p.o., tricyclic antidepressant), reboxetine (2 mg/kg, p.o., selective noradrenaline reuptake inhibitor) or phenylephrine (0.4 μg/site, i.c.v., α1-adrenoceptor agonist) reduced the immobility time in the TST as compared with either drug alone. These results indicate that the antidepressant-like effect of creatine is likely mediated by an activation of α1-adrenoceptor and that creatine produces synergistic effects in the TST with antidepressants that modulate noradrenaline transporter, suggesting that an improvement in the response to the antidepressant therapy may occur when creatine is combined with these antidepressants. Furthermore, the synergistic effect of creatine (0.01 mg/kg, p.o.) and reboxetine (2 mg/kg, p.o.) combination was abolished by the α1-adrenoceptor antagonist prazosin, indicating that the antidepressant-like effect of combined therapy is likely mediated by an activation of α1-adrenoceptor.

Increased antidepressant-like effect of desipramine combined with central stimulants (caffeine and amphetamine) in mice

Desipramine is a widely used antidepressive agent that inhibits the reuptake of noradrenaline and serotonin, and central stimulants such as caffeine and amphetamine help to release noradrenaline and serotonin. This work aimed to evaluate whether the combination of these agents could produce a stronger antidepressant-like effect than either of the drugs alone. To this end, male mice were treated with different doses of desipramine, caffeine, amphetamine, desipramine-caffeine and desipramine-amphetamine. The results showed that all drugs produced decreased immobility time in the forced swimming model. The combined treatment of desipramine (0.31, 1.0 or 3.1 mg/kg i.p.) with caffeine or amphetamine (0.31 or 1 mg/kg i.p.) reduced immobility time greater than either of those drugs alone. The combined treatment of desipramine (0.31, 1 and 3.1 mg/kg i.p.) with amphetamine or caffeine (0.1 and 1 mg/kg i.p.) did not increase the motor activity significantly compared to the control. These results also suggested that drugs which promote the release of noradrenaline and serotonin could increase antidepressant-like effect of desipramine.

N-palmitoylethanolamide, an endocannabinoid, exhibits antidepressant effects in the forced swim test and the tail suspension test in mice

The antidepressant-like effects of N-palmitoylethanolamide (PEA), a putative endocannabinoid, was investigated in mice using the tail suspension test (TST) and the forced swimming test (FST). In TST, PEA (10, 20, and 40 mg/kg) produced a statistically significant reduction in immobility (50, 32, and 34%, respectively, vs. the control group), whereas fluoxetine (20 mg/kg) reduced immobility by 38%. In FST, PEA (5, 10, and 20 mg/kg) produced a statistically significant reduction in immobility (15, 21, and 36%, respectively), whereas fluoxetine (20 mg/kg) reduced immobility by 18%. Moreover, PEA (20 mg/kg) did not significantly change motor activity in a spontaneous behavioral test. In conclusion, PEA (dose range of 5-40 mg/kg) administered orally reduced immobility in TST and FST, comparable to the antidepressant effect of fluoxetine, and had no effect on spontaneous activity in mice.

Neuroactive steroids in affective disorders: target for novel antidepressant or anxiolytic drugs?

In the past decades considerable evidence has emerged that so-called neuroactive steroids do not only act as transcriptional factors in the regulation of gene expression but may also alter neuronal excitability through interactions with specific neurotransmitter receptors such as the GABA(A) receptor. In particular, 3α-reduced neuroactive steroids such as allopregnanolone or allotetrahydrodeoxycorticosterone have been shown to act as positive allosteric modulators of the GABA(A) receptor and to play an important role in the pathophysiology of depression and anxiety. During depression, the concentrations of 3α,5α-tetrahydroprogesterone and 3α,5β-tetrahydroprogesterone are decreased, while the levels of 3β,5α-tetrahydroprogesterone, a stereoisomer of 3α,5α-tetrahydroprogesterone, which may act as an antagonist for GABAergic steroids, are increased. Antidepressant drugs such as selective serotonin reuptake inhibitors (SSRIs) or mirtazapine apparently have an impact on key enzymes of neurosteroidogenesis and have been shown to normalize the disequilibrium of neuroactive steroids in depression by increasing 3α-reduced pregnane steroids and decreasing 3β,5α-tetrahydroprogesterone. Moreover, 3α-reduced neuroactive steroids have been demonstrated to possess antidepressant- and anxiolytic-like effects both in animal and human studies for themselves. In addition, the translacator protein (18 kDa) (TSPO), previously called peripheral benzodiazepine receptor, is the key element of the mitochondrial import machinery supplying the substrate cholesterol to the first steroidogenic enzyme (P450scc), which transforms cholesterol into pregnenolone, the precursor of all neurosteroids. TSPO ligands increase neurosteroidogenesis and are a target of novel anxiolytic drugs producing anxiolytic effects without causing the side effects normally associated with conventional benzodiazepines such as sedation or tolerance. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.