Mechanisms of action of antidepressants: from neurotransmitter systems to signaling pathways

Protective effects of antidepressant citalopram against abnormal APP processing and amyloid beta-induced mitochondrial dynamics, biogenesis, mitophagy and synaptic toxicities in Alzheimer's disease

The purpose of this study is to study the neuroprotective role of selective serotonin reuptake inhibitor (SSRI), citalopram, against Alzheimer's disease (AD). Multiple SSRIs, including citalopram, are reported to treat patients with depression, anxiety and AD. However, their protective cellular mechanisms have not been studied completely. In the current study, we investigated the protective role of citalopram against impaired mitochondrial dynamics, defective mitochondrial biogenesis, defective mitophagy and synaptic dysfunction in immortalized mouse primary hippocampal cells (HT22) expressing mutant APP (SWI/IND) mutations. Using quantitative RT-PCR, immunoblotting, biochemical methods and transmission electron microscopy methods, we assessed mutant full-length APP/C-terminal fragments and Aβ levels and mRNA and protein levels of mitochondrial dynamics, biogenesis, mitophagy and synaptic genes in mAPP-HT22 cells and mAPP-HT22 cells treated with citalopram. Increased levels of mRNA levels of mitochondrial fission genes, decreased levels of fusion biogenesis, autophagy, mitophagy and synaptic genes were found in mAPP-HT22 cells relative to WT-HT22 cells. However, mAPP-HT22 cells treated with citalopram compared to mAPP-HT22 cells revealed reduced levels of the mitochondrial fission genes, increased fusion, biogenesis, autophagy, mitophagy and synaptic genes. Our protein data agree with mRNA levels. Transmission electron microscopy revealed significantly increased mitochondrial numbers and reduced mitochondrial length in mAPP-HT22 cells; these were reversed in citalopram-treated mAPP-HT22 cells. Cell survival rates were increased in citalopram-treated mAPP-HT22 relative to citalopram-untreated mAPP-HT22. Further, mAPP and C-terminal fragments werealso reduced in citalopram-treated cells. These findings suggest that citalopram reduces mutant APP and Aβ and mitochondrial toxicities and may have a protective role of mutant APP and Aβ-induced injuries in patients with depression, anxiety and AD.

Opioid and/or Psychotropic Use Increases Intraprocedural Sedation Drug Requirements

Objectives Acute pain management in opioid users can be challenging in the perioperative period. This study focuses on whether use of opioids increases sedation medication requirements in patients undergoing port placement under moderate sedation.

Materials and Methods A retrospective review was performed on all patients undergoing port placement between June 1, 2017, and June 30, 2019. Exclusion criteria included receiving general anesthesia, no sedation, and errors in data entry. Data collection included demographics, use of opioids, benzodiazepines, antidepressants, tobacco, alcohol, and sedation data.

Results Opioid, benzodiazepine, and selective serotonin reuptake inhibitors (SSRIs)/serotonin-norepinephrine reuptake inhibitors (SNRIs) use was significantly associated with higher sedation drug dose requirements. Patients using opioids required 10.5% higher doses of midazolam compared with nonusers. Benzodiazepine users required 16.3% additional dosage of midazolam than nonusers. Finally, patients on SSRIs/SNRIs medications required 11.8% higher midazolam dosing when compared with nonusers.

Conclusion Anticipating higher needs of sedation medications during procedures in patients with history of psychotropic agents use can allow for more effective sedation and patient satisfaction. More patient and provider awareness is needed on this topic, as health care policy is moving toward value-based healthcare, with patient satisfaction surveys being one of its indicators.

Evaluation of neurobehavioral activities of ethanolic extract of Psidium guajava Linn leaves in mice model

Background

The complementary and alternative medicines have particular importance in treating various comorbid conditions including anxiety and depression which prevalence will be raised to the second highest risk of morbidity, triggering a noteworthy socioeconomic burden. Ethanolic extract of leaves of Psidium guajava Linn (EEPG) was investigated to evaluate the anxiolytic and anti-depressant activity into two different doses (200 mg/kg and 400 mg/kg of body weight) on Swiss Albino male mice utilizing experimental paradigms of anxiety and depression. The extract was also subjected to phytochemical screening.

Results

Phytochemicals screening showed the presence of numerous types of active constituents in extract, for example, flavonoids, alkaloids, terpenoids, and steroids. The experimental results revealed that in case of anxiolytic activity tests, a statistical significant (p < 0.05 vs group I) effect is observed in EPMT model, hole cross model, light and dark model in both doses, whereas in hole-board model, marble burying model tests, a statistical considerable effect is observed only at the dose of 400 mg/kg although at the dose of 200 mg/kg, anxiolytic effect is also expressed and in case of anti-depressant activity test, the statistical significant effect is observed only at the dose of 400 mg/kg. All the results are comparable with the effect of standard drugs used.

Conclusions

Taken together, the present research work evidences the anxiolytic and anti-depressant effects of EEPG, but further investigation needed to find out the underlying mechanism of action and to isolate and purify the specific components that are responsible for aforementioned activities.

Limonene through Attenuation of Neuroinflammation and Nitrite Level Exerts Antidepressant-Like Effect on Mouse Model of Maternal Separation Stress

METHODS

Mice were randomly divided into experimental groups as follows: the control group received normal saline and MS groups received normal saline, limonene (10 and 20 mg/kg), L-NAME (10 mg/kg), L-arginine (L-arg) (75 mg/kg), limonene (10 mg/kg) plus L-NAME, and limonene (20 mg/kg) plus L-arg. Behavioral tests including the forced swimming test (FST), open field test (OFT), and splash test were performed. Finally, serum and hippocampal nitrite levels as well as the expression of inflammatory genes (IL-1β and TNF-α) in the hippocampus were measured.

RESULTS

We showed that MS caused depressive-like behavior. Treatment of MS mice with limonene reduced the duration of immobility time in FST and increases the grooming activity time in the splash test. Limonene also reduces serum and brain nitrite levels and reduces the expression of IL-1β and TNF-α in the hippocampus. We found that L-NAME potentiated the effects of a subeffective dose of limonene.

CONCLUSION

We concluded that the antidepressant-like effects of limonene are probably mediated through inhibition of neuroinflammation and attenuation of nitrite levels in the hippocampus.

Curcumin Attenuates Chronic Unpredictable Mild Stress-Induced Depressive-Like Behaviors via Restoring Changes in Oxidative Stress and the Activation of Nrf2 Signaling Pathway in Rats

Accumulating evidence has demonstrated that oxidative stress is associated with depression. Our present study aimed at investigating the antidepressant effect and the possible mechanisms of curcumin (CUR) in chronic unpredictable mild stress- (CUMS-) induced depression model in rats. After exposure to CUMS for four weeks, the rats showed depressive-like behavior, and the depressive-like behaviors in CUMS-treated rats were successfully corrected after administration of CUR. In addition, CUR could effectively decrease protein expression of oxidative stress markers (Nox2, 4-HNE, and MDA) and increase the activity of CAT. CUR treatment also reversed CUMS-induced inhibition of Nrf2-ARE signaling pathway, along with increasing the mRNA expression of NQO-1 and HO-1. Furthermore, the supplementation of CUR also increased the ratio of pCREB/CREB and synaptic-related protein (BDNF, PSD-95, and synaptophysin). In addition, CUR could effectively reverse CUMS-induced reduction of spine density and total dendritic length. In conclusion, the study revealed that CUR relieves depressive-like state through the mitigation of oxidative stress and the activation of Nrf2-ARE signaling pathway.

Evaluation of the neuropharmacological effects of Gardenin A in mice

This work describes the neuropharmacological (sedative, anxiolytic, antidepressant, and anticonvulsant) actions of Gardenin A (GA) (0.1-25 mg/kg p.o.), a flavonoid found in medicinal plants. The sedative effects of GA were assessed with the pentobarbital-induced sleep test. The anxiolytic actions of GA were evaluated with the elevated plus-maze, the light-dark box test, the exploratory cylinder assay, and the open field test. Motor coordination was evaluated with the rotarod test and the open field test. The antidepressant-like actions of GA were evaluated with the tail suspension test and forced swimming test. The mechanisms of the anxiolytic-like and antidepressant-like effects of GA were assessed using inhibitors of neurotransmission pathways. The anticonvulsant activity of GA was evaluated with the strychnine-induced seizure test. The sedative effects of GA were evident only at a dose of 25 mg/kg, which increased the duration of sleep but did not alter sleep onset. GA showed anxiolytic-like actions with activity comparable to that of clonazepam in all experimental tests. The GABA_A receptor antagonist bicuculline reversed the anxiolytic-like effects of GA. Furthermore, GA showed significant antidepressant-like actions in both models with activity comparable to that of fluoxetine. Yohimbine, an α2-adrenoceptor blocker, inhibited the antidepressant-like actions of GA. In addition, GA (1-10 mg/kg) did not affect locomotor coordination in mice and delayed the onset of convulsions. These findings suggest that GA induces anxiolytic-like effects and has anticonvulsant actions by the possible involvement of the GABAergic system. The antidepressant-like actions of GA may be mediated by noradrenergic neurotransmission.

New drugs are not enough‑drug repositioning in oncology: An update

Drug repositioning refers to the concept of discovering novel clinical benefits of drugs that are already known for use treating other diseases. The advantages of this are that several important drug characteristics are already established (including efficacy, pharmacokinetics, pharmacodynamics and toxicity), making the process of research for a putative drug quicker and less costly. Drug repositioning in oncology has received extensive focus. The present review summarizes the most prominent examples of drug repositioning for the treatment of cancer, taking into consideration their primary use, proposed anticancer mechanisms and current development status.

Calotropis procera attenuates chronic unpredictable mild stress-induced depression in experimental animals

Calotropis procera (CP; Apocynaceae) is reported to have several neuroprotective activities however it's anti-depressant activity yet to be established. Therefore, the present study was proposed to evaluate the anti-depressant activity of the standardized ethanolic extract of CP (ECP) in chronic unpredictable mild stress (CUMS) paradigm exposed male rats. Animals were exposed to CUMS from day-1 (D-1) to D-28 except control group animals of the experimental schedule. ECP (50, 100 and 200 mg/kg, p.o.) and Imipramin (15.0 mg/kg, p.o.) were administered for seven consecutive days after CUMS paradigm. On D-35, ECP (200 mg/kg) significantly attenuated immobility period of the animals in both forced-swim and tail suspension and improved behavioural parameters in open-field and anhedonia in sucrose feeding tests. ECP (200 mg/kg) attenuated CUMS-induced hyperactivity of HPA-axis function. Further, ECP (200 mg/kg) mitigated CUMS-induced decrease in serotonin (5-HT), increase in 5-hydroxy indole acetic acid (5-HIAA) and increase in the ratio of 5-HIAA/5-HT in hippocampus and pre-frontal cortex. The CUMS-induced decrease in the level of expression of BDNF was significantly reversed with ECP (200 mg/kg) treatment. Moreover, ECP (200 mg/kg) significantly reduced the CUMS-induced decrease in the mitochondrial function and integrity in terms of level of formazan formed and intensity of tetramethyl rhodamine methylester dye in both the brain regions respectively. Therefore, ECP (200 mg/kg) mitigates CUMS-induced alterations in the behaviours, HPA-axis function, serotonergic activity, neurogenesis and mitochondrial function in the rodents. Thus, it can be assumed that ECP could be a potential alternative candidate in the management of depression.

Nod-like receptors are critical for gut-brain axis signalling in mice

KEY POINTS

•Nucleotide binding oligomerization domain (Nod)-like receptors regulate cognition, anxiety and hypothalamic-pituitary-adrenal axis activation. •Nod-like receptors regulate central and peripheral serotonergic biology. •Nod-like receptors are important for maintenance of gastrointestinal physiology. •Intestinal epithelial cell expression of Nod1 receptors regulate behaviour.

ABSTRACT

Gut-brain axis signalling is critical for maintaining health and homeostasis. Stressful life events can impact gut-brain signalling, leading to altered mood, cognition and intestinal dysfunction. In the present study, we identified nucleotide binding oligomerization domain (Nod)-like receptors (NLR), Nod1 and Nod2, as novel regulators for gut-brain signalling. NLR are innate immune pattern recognition receptors expressed in the gut and brain, and are important in the regulation of gastrointestinal physiology. We found that mice deficient in both Nod1 and Nod2 (NodDKO) demonstrate signs of stress-induced anxiety, cognitive impairment and depression in the context of a hyperactive hypothalamic-pituitary-adrenal axis. These deficits were coupled with impairments in the serotonergic pathway in the brain, decreased hippocampal cell proliferation and immature neurons, as well as reduced neural activation. In addition, NodDKO mice had increased gastrointestinal permeability and altered serotonin signalling in the gut following exposure to acute stress. Administration of the selective serotonin reuptake inhibitor, fluoxetine, abrogated behavioural impairments and restored serotonin signalling. We also identified that intestinal epithelial cell-specific deletion of Nod1 (VilCre⁺ Nod1^f/f ), but not Nod2, increased susceptibility to stress-induced anxiety-like behaviour and cognitive impairment following exposure to stress. Together, these data suggest that intestinal epithelial NLR are novel modulators of gut-brain communication and may serve as potential novel therapeutic targets for the treatment of gut-brain disorders.

The Gut Microbiota Links Dietary Polyphenols With Management of Psychiatric Mood Disorders

The pathophysiology of depression is multifactorial yet generally aggravated by stress and its associated physiological consequences. To effectively treat these diverse risk factors, a broad acting strategy is required and is has been suggested that gut-brain-axis signaling may play a pinnacle role in promoting resilience to several of these stress-induced changes including pathogenic load, inflammation, HPA-axis activation, oxidative stress and neurotransmitter imbalances. The gut microbiota also manages the bioaccessibility of phenolic metabolites from dietary polyphenols whose multiple beneficial properties have known therapeutic efficacy against depression. Although several potential therapeutic mechanisms of dietary polyphenols toward establishing cognitive resilience to neuropsychiatric disorders have been established, only a handful of studies have systematically identified how the interaction of the gut microbiota with dietary polyphenols can synergistically alleviate the biological signatures of depression. The current review investigates several of these potential mechanisms and how synbiotics, that combine probiotics with dietary polyphenols, may provide a novel therapeutic strategy for depression. In particular, synbiotics have the potential to alleviate neuroinflammation by modulating microglial and inflammasome activation, reduce oxidative stress and balance serotonin metabolism therefore simultaneously targeting several of the major pathological risk factors of depression. Overall, synbiotics may act as a novel therapeutic paradigm for neuropsychiatric disorders and further understanding the fundamental mechanisms of gut-brain-axis signaling will allow full utilization of the gut microbiota's as a therapeutic tool.

The cellular and molecular basis of major depressive disorder: towards a unified model for understanding clinical depression

Major depressive disorder (MDD) is considered a serious public health issue that adversely impacts an individual's quality of life and contributes significantly to the global burden of disease. The clinical heterogeneity that exists among patients limits the ability of MDD to be accurately diagnosed and currently, a symptom-based approach is utilized in many cases. Due to the complex nature of this disorder, and lack of precise knowledge regarding the pathophysiology, effective management is challenging. The aetiology and pathophysiology of MDD remain largely unknown given the complex genetic and environmental interactions that are involved. Nonetheless, the aetiology and pathophysiology of MDD have been the subject of extensive research, and there is a vast body of literature that exists. Here we overview the key hypotheses that have been proposed for the neurobiology of MDD and highlight the need for a unified model, as many of these pathways are integrated. Key pathways discussed include neurotransmission, neuroinflammation, clock gene machinery pathways, oxidative stress, role of neurotrophins, stress response pathways, the endocannabinoid and endovanilloid systems, and the endogenous opioid system. We also describe the current management of MDD, and emerging novel therapies, with particular focus on patients with treatment-resistant depression (TRD).

MicroRNAs expressed in depression and their associated pathways: A systematic review and a bioinformatics analysis

Depression is a debilitating mental illness, one of the most prevalent worldwide. MicroRNAs have been studied to better understand the biological mechanisms that regulate this disease. This study review systematically the literature to identify which microRNAs are currently being associated with depression and their related pathways. The electronic search was conducted in PubMed, Scopus, Scielo, ISI Web of Knowledge, and PsycINFO databases, using the search terms "Depressive Disorder" or "Depression" and "MicroRNAs". After, microRNAs that were up and down-regulated in depression were analyzed by bioinformatics. We observed that among the 77 microRNAs cited by included studies, 54 had their levels altered in depressed individuals compared to controls, 30 being up-regulated and 24 down-regulated. The bioinformatics analysis revealed that among the up-regulated microRNAs there were 81 total and 43 union pathways, with 15 presenting a significant difference. Among the down-regulated microRNAs, 67 total and 45 union pathways were found, with 14 presenting a significant difference. The miR-17-5p and let-7a-5p were the most frequently found microRNAs in the statistically significant pathways. In this study a panel of altered microRNAs in depression was created with their related pathways, which is a step towards understanding the complex network of microRNAs in depression.

The potential effects of Ocimum basilicum on health: a review of pharmacological and toxicological studies

INTRODUCTION

Basil (Ocimum basilicum L., OB) is a plant world widely used as a spice and a typical ingredient of the healthy Mediterranean diet. In traditional medicine, OB is indicated for many maladies and conditions; OB-containing nutritional supplements are increasingly sold. Conversely, safety concerns have been raised about the promutagens and procarcinogens alkenylbenzenes contained in OB. Areas covered: A critical review of the current status of OB as a nutraceutical, the pharmacology of its bioactive components, the rationale for its indications, and its safety. Expert opinion: Due to the polyphenolic and flavonoidic content, OB can be considered as an important ingredient in healthy diets; OB preparations may be effective as chemopreventive agents or adjunctive therapy in the treatment of different clinical conditions. From a toxicological perspective, since the tumorigenic potential of alkenylbenzenes is counteracted by other OB constituents such as nevadensin, it can be concluded that OB consumption in food and preparations is safe. The only concern relates to OB essential oils: in this case, a concentration limit for alkenylbenzenes should be precautionary defined, and the use of plant chemotypes with no or low levels of these alkylbenzenes for the preparation of essential oils should be made compulsory.

Phytochemistry and pharmacology of anti-depressant medicinal plants: A review

Stress renders an individual to experience mental pressure and exhaustion which brings about feelings of anxiety, depression, anger and/or other negative emotions. Depression affects a person's state of mind, behaviour, health and is often associated with suicide. The use of anti-depressant drugs as therapeutic agents is associated with symptoms such as, delayed onset of action, side-effects, drug-drug and dietary interactions, sexual dysfunction, cardiac toxicity, etc. Thus, there is need to target these issues and improve current treatment options. Medicinal plants have long been used in discovering novel treatment strategies and compounds with promising roles in treating various disease conditions. There has been an increase, worldwide, in the use of medicinal plants and herbs for developing nutraceuticals for treatment of depression and other psychiatric disorders. Medicinal plants in their natural forms are valuable as they are rich in various phytochemical compounds. These phytochemical compounds have pharmacological roles in treating various diseases conditions; apart from being widely available in nature and commercially beneficial. The phytochemical compounds in plants are constantly being explored through various experimental studies to determine the molecular basis of how medicinal plants work in relation to drugs and diseases and to develop neutraceuticals for improving conditions. This review summarizes 110 medicinal plants and their phytochemical constituents that have been shown to possess anti-depressant activity. This review also highlights the various mechanisms of anti-depressant action of some of these plants and their plant parts like roots, stem, leaves, flowers, fruit or whole plant; phytochemical compounds showing anti-depressant activity such flavanoids, steroids, saponins, sugars, lectins, alkaloids, etc.; and various anti-depressant screening models used such as tail suspension test, forced swim test, chronic unpredictable stress test, sucrose preference test, monoamine oxidase inhibition assay, learned helplessness test, open field test, hole board test, etc. However, mechanistic evaluation of many of these plants still needs to be investigated and explored.

Drug repurposing may generate novel approaches to treating depression

Objectives

The breakthrough advancements in scientific medical research have greatly improved our understanding of the pathogenesis of depression, encouraging drug discoverers to take a shorter path than ever through drug repurposing to generate new antidepressant medications. In addition to reduced noradrenergic and serotonergic neurotransmission in the brain, other coincidence features such as glutamate neurotoxicity, inflammation and/or cerebrovascular insufficiency are implicated in the pathogenesis of major depressive disorder and late-life depression. This short review discusses the progress made in repurposing drugs for antidepressant actions.

Key findings

Drugs being repurposed as antidepressants act on novel drug targets, thereby treating resistant depression and improving remission rate. Drugs such as ketamine, dextromethorphan/quinidine and scopolamine are rapidly acting antidepressants targeting glutamate receptors. Nimodipine and quetiapine are efficient add-on therapy for late-life depression. Anti-inflammatory drugs, statins, insulin sensitizers, minocycline could remarkably contribute to treating refractory depression.

Summary

Drug repurposing represents an alternative approach to cope with major obstacles, including financial insufficiency and unavoidable long lag evaluation time, undermining the classical pathway of developing new hit compounds into clinically approved antidepressants.

Ascorbic Acid to Manage Psychiatric Disorders

Ascorbate has critical roles in the central nervous system (CNS); it is a neuromodulator of glutamatergic, cholinergic, dopaminergic, and γ-aminobutyric acid (GABA)-ergic neurotransmission, provides support and structure to neurons, and participates in processes such as differentiation, maturation, and survival of neurons. Over the past decade, antioxidant properties of ascorbate have been extensively characterized and now it is known that this compound is highly concentrated in the brain and neuroendocrine tissues. All this information raised the hypothesis that ascorbate may be involved in neurological disorders. Indeed, the biological mechanisms of ascorbate in health and disease and its involvement in homeostasis of the CNS have been the subject of extensive research. In particular, evidence for an association of this vitamin with schizophrenia, major depressive disorder, and bipolar disorder has been provided. Considering that conventional pharmacotherapy for the treatment of these neuropathologies has important limitations, this review aims to explore basic and human studies that implicate ascorbic acid as a potential therapeutic strategy. Possible mechanisms involved in the beneficial effects of ascorbic acid for the management of psychiatric disorders are also discussed.

Antidepressant-Like Effect of Lipid Extract of Channa striatus in Chronic Unpredictable Mild Stress Model of Depression in Rats

This study evaluated the antidepressant-like effect of lipid extract of C. striatus in chronic unpredictable mild stress (CUMS) model of depression in male rats and its mechanism of action. The animals were subjected to CUMS for six weeks by using variety of stressors. At the end of CUMS protocol, animals were subjected to forced swimming test (FST) and open field test followed by biochemical assay. The CUMS protocol produced depressive-like behavior in rats by decreasing the body weight, decreasing the sucrose preference, and increasing the duration of immobility in FST. The CUMS protocol increased plasma corticosterone and decreased hippocampal and prefrontal cortex levels of monoamines (serotonin, noradrenaline, and dopamine) and brain-derived neurotrophic factor. Further, the CUMS protocol increased interleukin-6 (in hippocampus and prefrontal cortex) and nuclear factor-kappa B (in prefrontal cortex but not in hippocampus). The lipid extract of C. striatus (125, 250, and 500 mg/kg) significantly (p < 0.05) reversed all the above parameters in rats subjected to CUMS, thus exhibiting antidepressant-like effect. The mechanism was found to be mediated through decrease in plasma corticosterone, increase in serotonin levels in prefrontal cortex, increase in dopamine and noradrenaline levels in hippocampus and prefrontal cortex, increase in BDNF in hippocampus and prefrontal cortex, and decrease in IL-6 and NF-κB in prefrontal cortex.

Maternal separation in early life modifies anxious behavior and Fos and glucocorticoid receptor expression in limbic neurons after chronic stress in rats: effects of tianeptine

Early-life adversity can lead to long-term consequence persisting into adulthood. Here, we assess the implications of an adverse early environment on vulnerability to stress during adulthood. We hypothesized that the interplay between early and late stress would result in a differential phenotype regarding the number of neurons immunoreactive for glucocorticoid receptor (GR-ir) and neuronal activity as assessed by Fos immunoreactivity (Fos-ir) in brain areas related to stress responses and anxiety-like behavior. We also expected that the antidepressant tianeptine could correct some of the alterations induced in our model. Male Wistar rats were subjected to daily maternal separation (MS) for 4.5 h during the first 3 weeks of life. As adults, the rats were exposed to chronic stress for 24 d and they were treated daily with tianeptine (10 mg/kg intraperitoneal) or vehicle (isotonic saline). Fos-ir was increased by MS in all structures analyzed. Chronic stress reduced Fos-ir in the hippocampus, but increased it in the paraventricular nucleus. Furthermore, chronic stress increased GR-ir in hippocampus (CA1) and amygdala in control non-MS rats. By contrast, when MS and chronic stress were combined, GR-ir was decreased in these structures. Additionally, whereas tianeptine did not affect Fos-ir, it regulated GR-ir in a region-dependent manner, in hippocampus and amygdala opposing in some cases the stress or MS effects. Furthermore, tianeptine reversed the MS- or stress-induced anxious behavior. The interplay between MS and chronic stress observed indicates that MS rats have a modified phenotype, which is expressed when they are challenged by stress in later life.

Effects of Electroacupuncture on Chronic Unpredictable Mild Stress Rats Depression-Like Behavior and Expression of p-ERK/ERK and p-P38/P38

We investigate the antidepressant-like effect and mechanism of electroacupuncture (EA) on a chronic unpredictable mild stress rats depression-like behavior. In our study, depression in rats was induced by unpredictable chronic mild stress (UCMS) and isolation for four weeks. Male Sprague-Dawley rats were randomly divided into four groups: Normal, Model, EA, and Sham EA. EA treatment was administered for two weeks, once a day for five days a week. Two acupoints, Yintang (EX-HN3) and Baihui (GV20), were selected. For sham EA, acupuncture needles were inserted shallowly into the acupoints: EX-HN3 and GV20. No electrostimulator was connected. The antidepressant-like effect of the electroacupuncture treatment was measured by sucrose intake test, open field test, and forced swimming test in rats. The protein levels of phosphorylated extracellular regulated protein kinases (p-ERK1/2)/ERK1/2 and p-P38/P38 in the hippocampus (HP) were examined by Western blot analysis. Our data demonstrate that EA treatment decreased the immobility time of forced swimming test and improved the sucrose solution intake in comparison to unpredictable chronic mild stress and placebo sham control. Electroacupuncture may act on depression by enhancing p-ERK1/2 and p-p38 in the hippocampus.

Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands

Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies.

Downregulation of β1 -adrenergic receptors in rat C6 glioblastoma cells by hyperforin and hyperoside from St John's wort

OBJECTIVES

While the use of St John's wort extracts as treatment for mild to moderate depression is well established the mode of action is still under investigation. Individual constituents of St John's wort extract were tested for possible effects on the β1 AR density and a subsequent change in downstream signalling in rat C6 glioblastoma cells.

METHODS

The effect of compounds from St John's wort extract on the downregulation of β1 -adrenergic receptor-GFP fusion proteins (β1 AR-green fluorescent protein (GFP)) of transfected rat C6 gliobastoma cells (C6-β1 AR-GFP) was investigated by means of confocal laser scanning microscopy (LSM). The influence on the lateral mobility of β1 AR-GFP in C6-β1 AR-GFP was investigated by fluorescence correlation spectroscopy. The formation of second messenger was determined by c-AMP-assay.

KEY FINDINGS

Confocal LSM revealed that pretreatment of cells with 1 μm of hyperforin and hyperoside for 6 days, respectively, led to an internalization of β1 AR-GFP under non-stimulating conditions. Observation by fluorescence correlation spectroscopy showed two diffusion time constants for control cells, with τdiff1  = 0.78 ± 0.18 ms and τdiff2  = 122.53 ± 69.41 ms, similarly distributed. Pretreatment with 1 μm hyperforin or 1 μm hyperoside for 3 days did not alter the τdiff values but decreased the fraction of τdiff1 whereas the fraction of τdiff2 increased significantly. An elevated level of β1 AR-GFP with hindered lateral mobility was in line with β1 AR-GFP internalization induced by hyperforin and hyperoside, respectively. A reduced β1 -adrenergic responsiveness was assumed for C6 gliobastoma cells after pretreatment for 6 days with 1 μm of both hyperforin and hyperoside, which was confirmed by decreased cAMP formation of about 10% and 5% under non-stimulating conditions. Decrease in cAMP formation by 23% for hyperforin and 15% for hyperoside was more pronounced after stimulation with 10 μm dobutamine for 30 min.

CONCLUSIONS

The treatment of C6 gliobastoma cells with hyperforin and hyperoside results in a reduced β1 AR density in the plasma membrane and a subsequent reduced downstream signalling.

Influence of genetic polymorphisms in the glutamatergic and GABAergic systems and their interactions with environmental stressors on antidepressant response

Aim: To investigate the role of genetic polymorphisms in glutamatergic and GABAergic genes and their interactions with environmental stressors in antidepressant response. Methods: A set of 114 SNPs of 34 glutamatergic and GABAergic genes, mainly in promoter and coding regions, were genotyped in 281 Chinese Han major depressive disorder patients. The 17-item Hamilton Depression Rating Scale was used to evaluate the symptom severity and therapeutic efficacy. Childhood Trauma Questionnaire and Life Events Scale were used for assessing early-onset and recent stressful life events, respectively. Results: The single SNPs rs1954787 (GRIK4), rs1992647 (GABRA6), rs10036156 (GABRP) and rs3810651 (GABRQ) were significantly associated with antidepressant response, as were haplotypes in GRIK4 and GABRP genes. A genetic interaction between rs11542313 (GAD1), rs13303344 (GABRD) and rs2256882 (GABRE) was identified as impacting therapeutic response. SNPs in GRIA3 demonstrated interactions with early-onset adverse events and recent negative life stress that influence treatment outcome. Conclusion: Genetic polymorphisms in the glutamatergic and GABAergic systems and certain genetic interactions, as well as gene–environment interactions, are associated with antidepressant response.

Original submitted 9 July 2012; Revision submitted 1 January 2013

Homocysteine alters cerebral microvascular integrity and causes remodeling by antagonizing GABA-A receptor

High levels of homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), are associated with cerebrovascular diseases, such as vascular dementia, stroke, and Alzheimer's disease. The γ-amino butyric acid (GABA) is an inhibitory neurotransmitter and a ligand of GABA-A receptor. By inhibiting excitatory response, it may decrease complications associated with vascular dementia and stroke. Hcy specifically competes with the GABA-A receptors and acts as an excitotoxic neurotransmitter. Previously, we have shown that Hcy increases levels of NADPH oxidase and reactive oxygen species (ROS), and decreases levels of thioredoxin and peroxiredoxin by antagonizing the GABA-A receptor. Hcy treatment leads to activation of matrix metalloproteinases (MMPs) in cerebral circulation by inducing redox stress and ROS. The hypothesis is that Hcy induces MMPs and suppresses tissue inhibitors of metalloproteinase (TIMPs), in part, by inhibiting the GABA-A receptor. This leads to degradation of the matrix and disruption of the blood brain barrier. The brain cortex of transgenic mouse model of HHcy (cystathionine β-synthase, CBS-/+) and GABA-A receptor null mice treated with and without muscimol (GABA-A receptor agonist) was analysed. The mRNA levels were measured by Q-RT-PCR. Levels of MMP-2, -9, -13, and TIMP-1, -2, -3, and -4 were evaluated by in situ labeling and PCR-gene arrays. Pial venular permeability to fluorescence-labeled albumin was assessed with intravital fluorescence microscopy. We found that Hcy increases metalloproteinase activity and decreases TIMP-4 by antagonizing the GABA-A receptor. The results demonstrate a novel mechanism in which brain microvascular permeability changes during HHcy and vascular dementias, and have therapeutic ramifications for microvascular disease in Alzheimer's patients.

Antidepressant-like effect of extract from Polygala paniculata: involvement of the monoaminergic systems

CONTEXT

Polygala paniculata Linnaeus (Polygalaceae) has shown neuroprotective effects, but there is no report about its antidepressant potential.

OBJECTIVE

The antidepressant-like effect of the hydroalcoholic extract from P. paniculata and some of the possible mechanisms involved in this effect were investigated in forced swimming test (FST).

MATERIALS AND METHODS

Mice received extract by oral route and were submitted to FST and open-field test. Animals were forced to swim and the total immobility time was registered (6-min period). A reduction in the immobility time is considered an antidepressant-like effect. In order to investigate the involvement of the monoaminergic systems, mice were treated with pharmacological antagonists before administration of the extract.

RESULTS

The acute administration of the hydroalcoholic extract from P. paniculata produced an antidepressant-like effect, since it significantly reduced the immobility time in FST (0.01-30 mg/kg) as compared to control group, without changing locomotor activity. Pretreatment of mice with yohimbine (1 mg/kg, i.p., α₂-adrenoceptor antagonist), propranolol (1 mg/kg, i.p., β-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., dopamine D₁ receptor antagonist) or sulpiride (50 mg/kg, i.p., dopamine D₂ receptor antagonist) prevented the antidepressant-like effect of the extract in FST (30 mg/kg). Moreover, ketanserin (5 mg/kg, i.p., preferential 5-HT(2A) receptor antagonist) enhanced the effect of the extract in FST.

DISCUSSION AND CONCLUSION

The results of the present study indicate that the extract from P. paniculata has an antidepressant-like action that is likely mediated by an interaction with the serotonergic (5-HT2A receptors), noradrenergic (α₂ and β-receptor) and dopaminergic (D₁ and D₂ receptors) systems.

Heterotrimeric g proteins: insights into the neurobiology of mood disorders

Mood disorders such as major depression and bipolar disorder are common, severe, chronic and often life-threatening illnesses. Suicide is estimated to be the cause of death in up to approximately 10-15% of individuals with mood disorders. Alterations in the signal transduction through G protein-coupled receptor (GPCR) pathways have been reported in the etiopathology of mood disorders and the suicidal behavior. In this regard, the implication of certain GPCR subtypes such as alpha(2A)-adrenoceptor has been repeatedly described using different approaches. However, several discrepancies have been recently reported in density and functional status of the heterotrimeric G proteins both in major depression and bipolar disorder. A compilation of the most relevant research topics about the implication of heterotrimeric G proteins in the etiology of mood disorders (i.e., animal models of mood disorders, studies in peripheral tissue of depressive patients, and studies in postmortem human brain of suicide victims with mood disorders) will provide a broad perspective of this potential therapeutic target field. Proposed causes of the discrepancies reported at the level of G proteins in postmortem human brain of suicide victims will be discussed.

Antidepressant-like action of the ethanolic extract from Tabebuia avellanedae in mice: evidence for the involvement of the monoaminergic system

The antidepressant-like effect of the ethanolic extract obtained from barks of Tabebuia avellanedae, a plant widely employed in folk medicine, was investigated in two predictive models of depression: forced swimming test (FST) and tail suspension test (TST) in mice. Additionally, the mechanisms involved in this antidepressant-like action and the effects of the association of the extract with the antidepressants fluoxetine, desipramine and bupropion in the TST were investigated. The extract from T. avellanedae produced an antidepressant-like effect, in the FST (100 mg/kg, p.o.) and in the TST (10-300 mg/kg, p.o.), without accompanying changes in ambulation when assessed in the open-field test. The anti-immobility effect of the extract (30 mg/kg, p.o.) in the TST was prevented by pre-treatment of mice with ketanserin (5 mg/kg, i.p., a preferential 5-HT(2A) receptor antagonist), prazosin (1 mg/kg, i.p., an alpha(1)-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an alpha(2)-adrenoceptor antagonist), propranolol (2 mg/kg, i.p., a beta-adrenoceptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D(2) receptor antagonist) and SCH23390 (0.05 mg/kg, s.c., a dopamine D(1) receptor antagonist). The combined administration of a subeffective dose of WAY100635 (0.1 mg/kg, s.c., a selective 5-HT(1A) receptor antagonist) and a subeffective dose of the extract (1 mg/kg, p.o.) produced a significant reduction in the immobility time in the TST. In addition, the combination of fluoxetine (1 mg/kg, p.o.), desipramine (0.1 mg/kg, p.o.), or bupropion (1 mg/kg, p.o.) with a subeffective dose of the extract (1 mg/kg, p.o.) produced a synergistic antidepressant-like effect in the TST, without causing hyperlocomotion in the open-field test. It may be concluded that the extract from T. avellanedae produces an antidepressant-like effect in the FST and in the TST that is dependent on the monoaminergic system. Taken together, our results suggest that T. avellanedae deserves further investigation as a putative alternative therapeutic tool that could help the conventional pharmacotherapy of depression.

Antidepressant-like effect of the extract of Rosmarinus officinalis in mice: involvement of the monoaminergic system

Rosemary, Rosmarinus officinalis L. (Labiatae) has several therapeutic applications in folk medicine in curing or managing a wide range of diseases, including depression. In this study, the effect of the hydroalcoholic extract of the stems and leaves of this plant was investigated in two behavioral models, the forced swimming test (FST) and tail suspension test (TST) in mice. The extract of R. officinalis produced an antidepressant-like effect, since the acute treatment of mice with the extract by p.o. route significantly reduced the immobility time in the FST (100 mg/kg) and TST (10-100 mg/kg), as compared to a control group, without accompanying changes in ambulation in the open-field test. Moreover, the repeated administration (14 days) of the hydroalcoholic extract of R. officinalis by p.o. route also produced an antidepressant-like effect in the TST (100-300 mg/kg). The pretreatment of mice with p-chlorophenylalanine (PCPA, 100 mg/kg, i.p., an inhibitor of serotonin synthesis, for 4 consecutive days), NAN-190 (0.5 mg/kg, i.p., a 5-HT(1A) receptor antagonist), ketanserin (5 mg/kg, i.p., a 5-HT(2A) receptor antagonist), 1-(m-chlorophenyl) biguanide (mCPBG, 10 mg/kg, i.p., a 5-HT(3) receptor agonist), prazosin (1 mg/kg, i.p., an alpha(1-)adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., a dopamine D(1) receptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D(2) receptor antagonist), but not yohimbine (1 mg/kg, i.p., an alpha(2-)adrenoceptor antagonist) was able to reverse the anti-immobility effect of the extract (10 mg/kg, p.o.) in the TST. The combination of MDL72222, (0.1 mg/kg, i.p., a 5-HT(3) receptor antagonist) with a sub-effective dose of the extract of R. officinalis (1 mg/kg, p.o.) produced an anti-immobility effect in the TST. The results suggest that the antidepressant action of the extract of R. officinalis is mediated by an interaction with the monoaminergic system and that this plant should be further investigated as an alternative therapeutic approach for the treatment of depression.

Differential effects of octopamine and tyramine on the central pattern generator for Manduca flight

The biogenic amine, octopamine, modulates a variety of aspects of insect motor behavior, including direct action on the flight central pattern generator. A number of recent studies demonstrate that tyramine, the biological precursor of octopamine, also affects invertebrate locomotor behaviors, including insect flight. However, it is not clear whether the central pattern generating networks are directly affected by both amines, octopamine and tyramine. In this study, we tested whether tyramine affected the central pattern generator for flight in the moth, Manduca sexta. Fictive flight was induced in an isolated ventral nerve cord preparation by bath application of the octopamine agonist, chlordimeform, to test potential effects of tyramine on the flight central pattern generator by pharmacological manipulations. The results demonstrate that octopamine but not tyramine is sufficient to induce fictive flight in the isolated ventral nerve cord. During chlordimeform induced fictive flight, bath application of tyramine selectively increases synaptic drive to depressor motoneurons, increases the number of depressor spikes during each cycle and decreases the depressor phase. Conversely, blocking tyramine receptors selectively reduces depressor motoneuron activity, but does not affect cycle by cycle elevator motoneuron spiking. Therefore, octopamine and tyramine exert distinct effects on the flight central pattern generating network.

Chronic fluoxetine bidirectionally modulates potentiating effects of serotonin on the hippocampal mossy fiber synaptic transmission

Selective serotonin reuptake inhibitors (SSRIs) have been used to treat various psychiatric disorders. Although the cellular mechanisms underlying amelioration of particular symptoms are mostly unknown, recent studies have shown critical importance of the dentate gyrus of the hippocampus in behavioral effects of SSRIs in rodents. Here, we show that serotonin potentiates synaptic transmission between mossy fibers, the sole output of the dentate granule cells, and CA3 pyramidal cells in mouse hippocampal slices. This potentiation is mediated by activation of 5-HT(4) receptors and intracellular cAMP elevation. A chronic treatment of mice with fluoxetine, a widely used SSRI, bidirectionally modulates the 5-HT-induced potentiation: Fluoxetine enhances the potentiation induced by lower concentrations of serotonin, while attenuates that by the higher concentration, which represents stabilization of synaptic 5-HT action. In contrast to the chronic treatment, an acute application of fluoxetine in slices induces a leftward shift in the dose-response curve of the 5-HT-induced potentiation. Thus, acute and chronic fluoxetine treatments have distinct effects on the serotonergic modulation of the mossy fiber synaptic transmission. Exposure of mice to novel environments induces increases in locomotor activity and hippocampal extracellular 5-HT levels. In mice chronically treated with fluoxetine, the novelty-induced hyperactivity is reduced without significant alterations in home cage activity and motor skills. Our results suggest that the chronic fluoxetine treatment can stabilize the serotonergic modulation of the central synaptic transmission, which may contribute to attenuation of hyperactive behaviors.

Diverse antidepressants increase CDP-diacylglycerol production and phosphatidylinositide resynthesis in depression-relevant regions of the rat brain

Background

Major depression is a serious mood disorder affecting millions of adults and children worldwide. While the etiopathology of depression remains obscure, antidepressant medications increase synaptic levels of monoamine neurotransmitters in brain regions associated with the disease. Monoamine transmitters activate multiple signaling cascades some of which have been investigated as potential mediators of depression or antidepressant drug action. However, the diacylglycerol arm of phosphoinositide signaling cascades has not been systematically investigated, even though downstream targets of this cascade have been implicated in depression. With the ultimate goal of uncovering the primary postsynaptic actions that may initiate cellular antidepressive signaling, we have examined the antidepressant-induced production of CDP-diacylglycerol which is both a product of diacylglycerol phosphorylation and a precursor for the synthesis of physiologically critical glycerophospholipids such as the phosphatidylinositides. For this, drug effects on [³H]cytidine-labeled CDP-diacylglycerol and [³H]inositol-labeled phosphatidylinositides were measured in response to the tricyclics desipramine and imipramine, the selective serotonin reuptake inhibitors fluoxetine and paroxetine, the atypical antidepressants maprotiline and nomifensine, and several monoamine oxidase inhibitors.

Results

Multiple compounds from each antidepressant category significantly stimulated [³H]CDP-diacylglycerol accumulation in cerebrocortical, hippocampal, and striatal tissues, and also enhanced the resynthesis of inositol phospholipids. Conversely, various antipsychotics, anxiolytics, and non-antidepressant psychotropic agents failed to significantly induce CDP-diacylglycerol or phosphoinositide synthesis. Drug-induced CDP-diacylglycerol accumulation was independent of lithium and only partially dependent on phosphoinositide hydrolysis, thus indicating that antidepressants can mobilize CDP-diacylglycerol from additional pools lying outside of the inositol cycle. Further, unlike direct serotonergic, muscarinic, or α-adrenergic agonists that elicited comparable or lower effects on CDP-diacylglycerol versus inositol phosphates, the antidepressants dose-dependently induced significantly greater accumulations of CDP-diacylglycerol.

Conclusion

Chemically divergent antidepressant agents commonly and significantly enhanced the accumulation of CDP-diacylglycerol. The latter is not only a derived product of phosphoinositide hydrolysis but is also a crucial intermediate in the biosynthesis of several signaling substrates. Hence, altered CDP-diacylglycerol signaling might be implicated in the pathophysiology of depression or the mechanism of action of diverse antidepressant medications.

Flight initiation and maintenance deficits in flies with genetically altered biogenic amine levels

Insect flight is one of the fastest, most intense and most energy-demanding motor behaviors. It is modulated on multiple levels by the biogenic amine octopamine. Within the CNS, octopamine acts directly on the flight central pattern generator, and it affects motivational states. In the periphery, octopamine sensitizes sensory receptors, alters muscle contraction kinetics, and enhances flight muscle glycolysis. This study addresses the roles for octopamine and its precursor tyramine in flight behavior by genetic and pharmacological manipulation in Drosophila. Octopamine is not the natural signal for flight initiation because flies lacking octopamine [tyramine-beta-hydroxylase (TbetaH) null mutants] can fly. However, they show profound differences with respect to flight initiation and flight maintenance compared with wild-type controls. The morphology, kinematics, and development of the flight machinery are not impaired in TbetaH mutants because wing-beat frequencies and amplitudes, flight muscle structure, and overall dendritic structure of flight motoneurons are unaffected in TbetaH mutants. Accordingly, the flight behavior phenotypes can be rescued acutely in adult flies. Flight deficits are rescued by substituting octopamine but also by blocking the receptors for tyramine, which is enriched in TbetaH mutants. Conversely, ablating all neurons containing octopamine or tyramine phenocopies TbetaH mutants. Therefore, both octopamine and tyramine systems are simultaneously involved in regulating flight initiation and maintenance. Different sets of rescue experiments indicate different sites of action for both amines. These findings are consistent with a complex system of multiple amines orchestrating the control of motor behaviors on multiple levels rather than single amines eliciting single behaviors.

Antidepressive-like effects of electroacupuncture in rats

Here, we investigate the effects of electroacupunture on the depressive-like symptoms in learned helplessness and forced swim tests in rats. Electroacupuncture stimulation (EA) was provided at ST-36 (Zusanli) and SP-6 (Sanyinjiao) acupoints. A positive control group was treated with imipramine. To verify the effects of EA over serotonergic system, other additional groups received daily, for three days, p-chlorophenylalanine and after two days, were submitted to behavioral tests. EA, like imipramine, enhanced the successful active avoidance in the learned helplessness and diminished the time spent in immobility position in the forced swim test, without affecting the number of squares crossed in the open field test. The administration of p-chlorophenylalanine abolished the antidepressive-like effect of EA. EA generates a clear antidepressant effect in two different animal models of depression, and this effect is related, at least in part, to the serotonergic system.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrain with few synapses, and where deficits in serotonergic function appeared to play a major role in depression. We propose that serotonin reuptake inhibitors may produce antidepressant effects through increasing serotonergic neurotrophism in serotonin nerve cells and their targets by transactivation of receptor tyrosine kinases (RTK), involving direct or indirect receptor/RTK interactions. Early chemical neuroanatomical work on the monoamine neurons, involving primitive nervous systems and analysis of peptide neurons, indicated the existence of alternative modes of communication apart from synaptic transmission. In 1986, Agnati and Fuxe introduced the theory of two main types of intercellular communication in the brain: wiring and volume transmission (WT and VT). Synchronization of phasic activity in the monoamine cell clusters through electrotonic coupling and synaptic transmission (WT) enables optimal VT of monoamines in the target regions. Experimental work suggests an integration of WT and VT signals via receptor-receptor interactions, and a new theory of receptor-connexin interactions in electrical and mixed synapses is introduced. Consequently, a new model of brain function must be built, in which communication includes both WT and VT and receptor-receptor interactions in the integration of signals. This will lead to the unified execution of information handling and trophism for optimal brain function and survival.

Tandem regulation of phosphoinositide signaling and acute behavioral effects induced by antidepressant agents in rats

RATIONALE

Antidepressants increase synaptic monoamine concentrations, but the subsequent signaling events that produce the beneficial clinical effects remain unclear. Diverse antidepressants increase CDP-diacylglycerol, a crucial step in phosphoinositide signaling. Serotonin 5HT(2) receptors, implicated in depression or the actions of some antidepressants, signal through phosphoinositide hydrolysis. Thus, cross talk between antidepressant-induced CDP-diacylglycerol and 5HT(2) signaling could contribute to the antidepressant mechanism.

OBJECTIVE

The objective of the study was to test the hypotheses that antidepressants enhance net signaling via 5HT(2) receptors by augmenting the supply of phosphoinositide substrates and that this action contributes to the behavioral effects of the drugs.

MATERIALS AND METHODS

Brain slices pre-labeled with [(3)H]inositol in the presence of various antidepressant concentrations were washed and incubated with the 5HT(2) agonist, alpha-methylserotonin, followed by measuring phosphoinositide synthesis and inositol phosphate accumulation. Further, rats administered antidepressants after pretreatment with neomycin to inhibit metabolic utilization of phosphoinositides were behaviorally evaluated in the forced swim test.

RESULTS

Diverse antidepressants significantly enhanced phosphoinositide synthesis. While alpha-methylserotonin increased inositol phosphate accumulation, this effect was significantly accentuated in hippocampal or cortical tissues pre-incubated in the presence of imipramine, desipramine, fluoxetine, paroxetine, or maprotiline. Drug-induced behavioral antidepressant effects were reversed by neomycin pretreatment, whereas neomycin alone did not alter basal immobility times.

CONCLUSIONS

Antidepressants probably exert tandem neurochemical effects by increasing synaptic monoamine concentrations and by producing phosphoinositides used in 5HT(2) receptor signaling. This combination of actions may constitute the mechanism of at least the acute behavioral effects of the drugs and could implicate aberrant neurolipid signaling in the pathophysiology of depression.

A preclinical and clinical rationale for quetiapine in mood syndromes

The main objective of this review is to discuss results from preclinical studies that aim to elucidate the putative mechanistic basis of the antidepressant action of quetiapine. Results from pivotal, randomized clinical trials in bipolar depression are also briefly reviewed. The authors conducted a PubMed search of all English-language articles published between January 1990 and December 2006. The key search term was quetiapine paired with: serotonin, dopamine, noradrenaline, glutamate, gamma-aminobutyric acid, signal transduction, neurogenesis, oxidative stress, glucocorticoid, antidepressant, major depressive disorder, bipolar disorder and randomized controlled trial. The search was augmented with a manual review of relevant article reference lists. Articles selected for review were based on author consensus, adequacy of sample size, the use of standardized experimental procedures, validated assessment measures and overall manuscript quality. Quetiapine enhances central serotonergic neurotransmission via its high affinity for serotonergic receptors (e.g., 5-HT2A receptor antagonism and partial agonistic activity at the 5-HT1A receptor). Activation of the 5HT1A receptor results in an increase in prefrontal cortex dopaminergic neurotransmission. Affinity for the alpha2-adrenoceptor mediates a relative increase in extracellular noradrenergic release in the prefrontal cortex. Emerging evidence indicates that quetiapine's principal, active, human plasma metabolite, N-desalkyl quetiapine, has high affinity for, and is a potent inhibitor of, the noradrenergic transporter. This latter finding is a point of commonality with other conventional antidepressant agents and may differentiate quetiapine from other atypical antipsychotics. Activity at other intracellular targets (e.g., signal transduction pathways and nerve growth transcription factors), neurotransmitters, inflammatory and oxidative stress networks, and endocrine systems may also mediate the antidepressant effects of quetiapine. The in vitro pharmacodynamic profile of quetiapine is predictive of antidepressant activity in mood syndromes. Available clinical evidence has established quetiapine as an effective monotherapy in bipolar depression.

Proteomic analysis of rat cortical neurons after fluoxetine treatment

The known neurochemical effect of most currently available antidepressants is the enhancement of the synaptic levels of monoamine neurotransmitters. However, the existence of other mechanisms has been suggested to justify the significant delay between the modulation of the monoaminergic system and the clinical effects. In order to investigate the effects of the antidepressant fluoxetine (a prototypical serotonin selective re-uptake inhibitor) and to improve the understanding of its mechanism of action, we performed a proteomic investigation in rat primary cortical neurons exposed sub-chronically to this antidepressant. Cortical neurons were treated for 3 days with 1 microM fluoxetine or vehicle. Protein extracts were processed for 2D gel characterization. Image analysis allowed the identification of six proteins differently expressed by more than 100% and seven proteins differently expressed by more than 50% (P<0.05). Nine proteins were identified by mass spectrometry. Among them, cyclophilin A, 14-3-3 protein z/delta and GRP78 are involved in neuroprotection, in serotonin biosynthesis and in axonal transport, respectively. This study showed that the primary culture of cortical neurons is a suitable system for studying the effects of fluoxetine action and may contribute to improve the understanding of fluoxetine psychotherapeutic action and the mechanisms mediating the long-term effects of this antidepressant treatment.

Antidepressant-mediated reversal of abnormal behavior and neurodegeneration in mice following olfactory bulbectomy

Olfactory bulbectomy is an established animal model of depression that has been mostly investigated in rats. As in human major depression, bulbectomy induces behavioral alterations that can be ameliorated by chronic antidepressant treatment. Furthermore, bulbectomy in rats is known to induce neurodegeneration in some brain areas. The aim of the present study was to evaluate patterns of behavioral alterations and neurodegeneration, and their drug-induced reversibility, in bulbectomized mice. Our results reveal that in mice bulbectomy increases locomotor activity and induces deficits in the passive avoidance test, comparable to the effects seen in rats. Bulbectomy also induced neuronal degeneration, visualized by incorporation of Fluoro-Jade B, in the piriform cortex and the posterolateral cortical amygdaloid nucleus (PLCo). Chronic treatment with the antidepressant amitriptyline protected neurons in both areas and efficiently reversed abnormal locomotor activity induced by bulbectomy. Treatment with citalopram was effective in reversing the behavioral deficits induced by bulbectomy, but did not protect against neurodegeneration. Our data indicate significant overlap between mice and rats in terms of behavioral alterations and neurodegeneration following olfactory bulbectomy. However, there are differences in drug-mediated reversibility of neurodegeneration suggesting that neurodegeneration and protection may be "second-order" features in this animal model of depression. This may also be relevant in the context of studies using genetically altered mice.