Nitric oxide and major depression

Oxidative stress and psychological disorders

Oxidative stress is an imbalance between cellular production of reactive oxygen species and the counteracting antioxidant mechanisms. The brain with its high oxygen consumption and a lipid-rich environment is considered highly susceptible to oxidative stress or redox imbalances. Therefore, the fact that oxidative stress is implicated in several mental disorders including depression, anxiety disorders, schizophrenia and bipolar disorder, is not surprising. Although several elegant studies have established a link between oxidative stress and psychiatric disorders, the causal relationship between oxidative stress and psychiatric diseases is not fully determined. Another critical aspect that needs much attention and effort is our understanding of the association between cellular oxidative stress and emotional stress. This review examines some of the recent discoveries that link oxidative status with anxiety, depression, schizophrenia and bipolar disorder. A discussion of published results and questions that currently exist in the field regarding a causal relationship between oxidative and emotional stress is also provided.

Serum methylarginines and incident depression in a cohort of older adults

BACKGROUND

Methylarginines are endogenous nitric oxide synthase inhibitors that have been implicated in depression. This study measured serum concentrations of l-arginine, asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in a representative sample of older community-dwelling adults and determined their association with incident depression over 6-years of follow-up.

METHODS

Data on clinical, lifestyle, and demographic characteristics, methylated arginines, and l-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults (Median age=64 years; IQR=60-70) from the Hunter Community Study. Clinical depression was defined as a Centre for Epidemiological Studies Depression Scale (CES-D) score ≥16 or use of antidepressant medications.

RESULTS

In adjusted analyses ADMA (Q3), SDMA (Q2), l-arginine (Q2), gender, and asthma remained statistically significant predictors of incident depression at follow-up. Quartile 3 of ADMA concentration was associated with 3.5 times the odds of developing depression compared with Q1 (OR=3.54; 95% CI: 1.25-9.99).

LIMITATIONS

Limitations of our study include the use of a subjective self-reported questionnaire tool using a dichotomous cut-off, together with use of antidepressant medications, as proxies for clinical depression. Moreover, similarly to most population studies on methylated arginines, the measurement of ADMA and SDMA from blood does not necessarily reflect intracellular concentrations of these compounds. Finally, there were no measures of nitric oxide metabolites to determine if these levels were altered in the presence of elevated methylarginines and depression.

CONCLUSIONS

After adjusting for clinical, demographic, biochemical, and pharmacological confounders, higher serum ADMA was independently associated with incident depression at 6-years follow-up.

Increase in nitric oxide levels and mitochondrial membrane potential in platelets of untreated patients with major depression

Alterations in platelet activity have been associated with the onset of major depressive disorder (MDD) and with ischemic cardiovascular events through mechanisms that remain unknown. The present study evaluated nitric oxide (NO) levels, mitochondrial membrane potential (PMMP), and P-selectin expression in platelets from 30 untreated MDD patients and 30 matched controls by flow cytometry. In addition, tryptophan and serotonin concentrations were measured in the whole blood by high performance liquid chromatography. Patients were assessed with the Mini International Neuropsychiatric Interview and the Hamilton Depression Rating Scale. The patients had not had antidepressant treatment or any other pharmacological interventions for at least 1 year. MDD patients significantly differed from controls in levels of major fluorescent platelets for NO, PMMP, and P-selectin compared with those observed in control subjects. Serotonin concentrations in MDD patients did not differ from those in controls These results demonstrate that untreated MDD patients show increased platelet activation, suggesting an alteration in the platelet function.

Effects of doxycycline on depressive-like behavior in mice after lipopolysaccharide (LPS) administration

Current evidences support inflammation, oxidative and nitrogen stress, as well as brain-derived neurotrophic factor (BDNF) signaling mechanisms as important in depression pathophysiology. Tetracycline antibiotics have anti-inflammatory and antioxidant properties. Preliminary evidence indicates that minocycline has antidepressant properties. Doxycycline (DOXY) has favorable pharmacokinetic and safety profiles when compared to other tetracycline congeners. The antidepressant activity of DOXY has not been adequately investigated. This study evaluated the effects of DOXY (25 and 50 mg/kg, i.p.) on LPS-induced (0.5 mg/kg, i.p.) depressive-like behavior. Doxycycline was administered 30 min before LPS (pre-LPS) or 1.5 and 23.5 h following LPS (post-LPS) administration in mice. LPS-treated animals presented an increase in immobility time in the forced swimming test (FST) when compared to controls 24 h after endotoxin administration. Similarly to imipramine (IMI-10 mg/kg, i.p.), DOXY at both doses prevented and reversed LPS-induced alterations in the FST. IL-1β content was increased 24 h after LPS administration in striatum, hippocampus and prefrontal cortex. IMI and DOXY prevented and reversed LPS-induced increase in IL-1β. IMI and DOXY also prevented and reversed LPS-induced alterations in nitrite content and oxidative stress parameters (lipid peroxidation and reduced glutathione levels). Both DOXY and IMI prevented LPS-induced decrease in hippocampal BDNF levels. Taken together, our results demonstrate that DOXY is comparable to IMI in effectively ameliorate LPS-induced depressive-like behavior, providing a rationale for testing DOXY's antidepressant efficacy in humans.

Antidepressant-like effect of α-tocopherol in a mouse model of depressive-like behavior induced by TNF-α

Taking into account that pro-inflammatory cytokines and oxidative and nitrosative stress are implicated in the pathogenesis of depression and that α-tocopherol has antidepressant, anti-inflammatory and antioxidant properties, this study investigated the ability of α-tocopherol to abolish the depressive-like behavior induced by i.c.v. administration of TNF-α in the mouse TST. Additionally, we investigated the occurrence of changes in the levels of Bcl2 and Bax and phosphorylation of GSK-3β (Ser9) in the hippocampus of mice. The administration of TNF-α (0.001fg/site, i.c.v.) increased the immobility time in the TST, which was prevented by the administration of α-tocopherol at the doses of 10, 30 and 100mg/kg (p.o.). Subeffective doses of α-tocopherol (10mg/kg, p.o.) and/or the antidepressants fluoxetine (5mg/kg, p.o.), imipramine (0.1mg/kg, p.o.) and bupropion (1mg/kg, p.o.), the NMDA receptor antagonist MK-801 (0.001mg/kg, p.o.) or the neuronal nitric oxide synthase inhibitor 7-nitroindazole (25mg/kg, i.p.) prevented the depressive-like effect induced by TNF-α. None of the treatments altered the locomotor activity of mice. Treatment with TNF-α and/or α-tocopherol did not alter the levels of Bax and Bcl2 or the phosphorylation of GSK-3β in the hippocampus of mice. Together, our results show a synergistic antidepressant-like effect of α-tocopherol with antidepressants against the depressive-like behavior induced by an inflammatory insult, suggesting that this vitamin may be useful to optimize conventional pharmacotherapy of depression, including depressive states associated with inflammatory conditions.

Possible role of adrenomedullin and nitric oxide in major depression

Adrenomedullin (ADM) and nitric oxide (NO) have been implicated in the pathogenesis of certain psychiatric disorders such as schizophrenia and bipolar disorder. ADM induces vasorelaxation by activating adenylate cyclase and stimulating the release of NO. These two molecules are known to influence cerebral activity. In this study, we aimed to examine the serum levels of ADM and NO in patients with major depression (MD). We enrolled 50 patients with MD and 50 healthy control subjects. The diagnosis of MD was established on the basis of a structured clinical interview using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). The severity of depressive symptoms was evaluated using Hamilton's 17-item Depression Rating Scale. The mean serum levels of ADM and NO in patients with MD were significantly higher than those in healthy subjects (p=0.001, for both). The severity of psychomotor retardation in patients with MD was significantly correlated with the ADM (r=0.37, p=0.007) and NO levels (r=0.29, p=0.038). The patients with obvious psychomotor retardation had significantly higher levels of ADM and NO than did the patients with no psychomotor retardation (p=0.025, p=0.030). A significantly positive correlation was found between ADM and NO levels in patients with MD (r=0.79, p=0.001). Serum levels of ADM and NO levels were not correlated with the severity or duration of depression or depressive symptoms (except psychomotor retardation). In conclusion, our study indicates that serum levels of ADM and NO are elevated in patients with MD and that increased serum levels of ADM and NO may be associated with psychomotor retardation. The ADM-NO system may serve as a new target in the treatment of patients with MD and psychomotor retardation.

Protective effect of Hsp70i against chronic social isolation stress in the rat hippocampus

Stress-related glucocorticoids and glutamate release has been implicated in depression. Glutamate neurotoxicity is mediated, in part, by the production of nitric oxide via nitric oxide synthase (NOS) isoforms and mitochondrial damage. We previously reported that chronic social isolation stress triggers proapoptotic signaling in the rat prefrontal cortex, but not in the hippocampus. Given that the hippocampus is highly sensitive to stress, we examined signaling cascades underlying the hippocampal cellular protection through the NOS pathway, antioxidant capacity and heat shock protein (Hsp) expression. We investigated neuronal (nNOS) and inducible (iNOS) protein levels, subcellular protein distributions of nuclear factor-κB (NF-κB), CuZnSOD and MnSOD activity, reduced glutathione (GSH), stress-inducible Hsp70 (Hsp70i) protein expression and serum corticosterone (CORT) levels of rats exposed to 21 days of chronic social isolation, an animal model of depression, alone or in combination with 2 h of acute immobilization or cold stress (combined stress). Both acute stressors elevated CORT, with lesser magnitude increase in chronically isolated rats exposed to novel acute stress as compared to acute stressors alone, indicating compromised HPA axis activity. Acute cold decreased nuclear CuZnSOD activity and stimulated NF-κB nuclear translocation. Chronic social isolation resulted in no activation of NF-κB, but led to decreased GSH, iNOS and increased nNOS and Hsp70i levels, alterations that remained following combined stressors. Decreased mitochondrial MnSOD activity after combined stressors suggests compromised detoxifying capacity. These data indicate that Hsp70i upregulation may provide hippocampal cellular protection against chronic social isolation stress mediated by downregulation of iNOS protein expression through suppression of NF-κB activation.

Small-molecule inhibitors at the PSD-95/nNOS interface have antidepressant-like properties in mice

Previous studies have demonstrated that nitric oxide (NO) synthase inhibitors are as efficacious as tricyclic antidepressants in preclinical antidepressant screening procedures and in attenuating behavioural deficits associated with animal models of depression. The N-methyl-D-aspartate receptor (NMDA-R) complex gates Ca(2+), which interacts with calmodulin to subsequently activate NO synthase. We hypothesised that uncoupling neuronal nitric oxide synthase (nNOS) from the NMDA-R through the scaffolding protein postsynaptic density protein 95 (PSD-95) would produce behavioural antidepressant effects similar to NO synthase inhibitors. Small-molecule inhibitors of the PSD-95/nNOS interaction, IC87201 (0.01-2 mg/kg) and ZL006 (10 mg/kg) were tested for antidepressant properties in tests of antidepressant activity namely the tail suspension and forced swim tests in mice. We now report that IC87201 and ZL006 produce antidepressant-like responses in the forced swimming test (FST) and tail suspension test (TST) following a single administration in mice. By contrast to the tricyclic antidepressant imipramine (25 mg/kg), the effects are not observed 1 h following drug administration but are apparent 24 and 72 h later. Furthermore prior exposure to the TST or FST is required in order to observe the antidepressant-related activity. Similar delayed and sustained antidepressant-like effects were observed following TRIM (50 mg/kg) and ketamine (30 mg/kg) in the TST. The antidepressant-like effects of ZL006 also generalise to IC87201 in the TST. IC87201 was devoid of effects on locomotor activity and step-through latency in the passive avoidance cognition test. These data support the hypothesis that targeting the PSD-95/nNOS interaction downstream of NMDA-R produces antidepressant effects and may represent a novel class of therapeutics for major depressive disorders.

Chronic social isolation induces NF-κB activation and upregulation of iNOS protein expression in rat prefrontal cortex

Exposure of an organism to stress, results in oxidative stress and increased nitric oxide (NO) production in the brain. The role of the processes caused by chronic stress in the prefrontal cortex has not been fully investigated. Considering that chronic stress increases NO production by the enzyme nitric oxide synthase (NOS), we examined the cytosolic neuronal (nNOS) or inducible (iNOS) protein levels in the prefrontal cortex of rats exposed to 21d of chronic social isolation stress, an animal model of depression, alone or in combination with 2h of acute immobilization or cold (4°C) stress (combined stress). Antioxidative status via cytosolic CuZnSOD and mitochondrial MnSOD activity, cytosolic redox status via reduced glutathione (GSH) concentration were determined. Furthermore, cytosolic inducible heat shock protein 70 (Hsp70i), cytosolic/nuclear distributions of NF-κB and serum corticosterone (CORT) were also investigated to elucidate the possible mechanism involved in the cellular NOS pathway. Our results showed that both acute stressors led to increases of CORT and nNOS protein while iNOS protein expression was unaffected. In contrast to the acute stress, chronic social isolation compromised hypothalamic-pituitary-adrenal axis functioning such that the normal stress response was impaired following subsequent acute stressors. Downregulated redox GSH status as well as decreased activity of CuZnSOD and MnSOD suggests the existence of oxidative stress which remained as such following combined stressors. Changes in redox-status associated with decreased Hsp70i protein expression enabled NF-κB translocation into the nucleus, causing increased cytosolic nNOS and iNOS protein expression. Results suggest that NOS signaling pathway plays a differential role between acute and chronic stress whereby state of oxidative/nitrosative stress after chronic social isolation is caused, at least in part, by NF-κB activation and increased iNOS protein expression.

Synaptic plasticity in depression: molecular, cellular and functional correlates

Synaptic plasticity confers environmental adaptability through modification of the connectivity between neurons and neuronal circuits. This is achieved through changes to synapse-associated signaling systems and supported by complementary changes to cellular morphology and metabolism within the tripartite synapse. Mounting evidence suggests region-specific changes to synaptic form and function occur as a result of chronic stress and in depression. Within subregions of the prefrontal cortex (PFC) and hippocampus structural and synapse-related findings seem consistent with a deficit in long-term potentiation (LTP) and facilitation of long-term depression (LTD), particularly at excitatory pyramidal synapses. Other brain regions are less well-studied; however the amygdala may feature a somewhat opposite synaptic pathology including reduced inhibitory tone. Changes to synaptic plasticity in stress and depression may correlate those to several signal transduction pathways (e.g. NOS-NO, cAMP-PKA, Ras-ERK, PI3K-Akt, GSK-3, mTOR and CREB) and upstream receptors (e.g. NMDAR, TrkB and p75NTR). Deficits in synaptic plasticity may further correlate disrupted brain redox and bioenergetics. Finally, at a functional level region-specific changes to synaptic plasticity in depression may relate to maladapted neurocircuitry and parallel reduced cognitive control over negative emotion.

Inhibition of the L-arginine-nitric oxide pathway mediates the antidepressant effects of ketamine in rats in the forced swimming test

Converging evidence shows that the acute administration of a sub-anaesthetic dose ketamine produces fast-acting and robust antidepressant properties in patients suffering from major depressive disorder. However, the underlying mechanisms have not been fully elucidated. The present study aimed to investigate the role of the L-arginine-nitric oxide pathway in the antidepressant effects of ketamine in rats performing the forced swimming test (FST). Ketamine (10 mg/kg) significantly decreased immobility times in the FST and the activities of total nitric oxide synthases (T-NOS), inducible NOS (iNOS), and endothelial NOS (eNOS) in the rat hippocampus. Interestingly, the plasma activities of T-NOS, iNOS, and eNOS increased after administration of ketamine. Furthermore, the activities of neuronal NOS (nNOS) did not change significantly in either the hippocampus or plasma after ketamine administration. The antidepressant effects of ketamine were prevented by pre-treatment with l-arginine (750 mg/kg). Pre-treatment with the NOS inhibitor L-NG-nitroarginine methyl ester at a sub-antidepressant dose of 50 mg/kg and ketamine at a sub-antidepressant dose of 3 mg/kg reduced immobility time in the FST compared to treatment with either drug alone. None of the drugs affected crossing and rearing scores in the open field test. These results suggest that the L-arginine-nitric oxide pathway is involved in the antidepressant effects of ketamine observed in rats in the FST and this involvement is characterised by the inhibition of brain T-NOS, iNOS, and eNOS activities.

The neuroprogressive nature of major depressive disorder: pathways to disease evolution and resistance, and therapeutic implications

In some patients with major depressive disorder (MDD), individual illness characteristics appear consistent with those of a neuroprogressive illness. Features of neuroprogression include poorer symptomatic, treatment and functional outcomes in patients with earlier disease onset and increased number and length of depressive episodes. In such patients, longer and more frequent depressive episodes appear to increase vulnerability for further episodes, precipitating an accelerating and progressive illness course leading to functional decline. Evidence from clinical, biochemical and neuroimaging studies appear to support this model and are informing novel therapeutic approaches. This paper reviews current knowledge of the neuroprogressive processes that may occur in MDD, including structural brain consequences and potential molecular mechanisms including the role of neurotransmitter systems, inflammatory, oxidative and nitrosative stress pathways, neurotrophins and regulation of neurogenesis, cortisol and the hypothalamic-pituitary-adrenal axis modulation, mitochondrial dysfunction and epigenetic and dietary influences. Evidence-based novel treatments informed by this knowledge are discussed.

Ameliorative effect of Curcumin on seizure severity, depression like behavior, learning and memory deficit in post-pentylenetetrazole-kindled mice

Epilepsy is a chronic neurological disorder and generally associated with certain psychiatric comorbidities. Among several comorbidities depressive behavior and cognitive impairment has been reported to be most debilitating comorbidity associated with epilepsy. This study was envisaged to evaluate the ameliorative effect of Curcumin on depression like behavior and cognitive impairment observed in pentylenetetrazole kindled animals. Male Swiss Albino mice were kindled with subconvulsive dose of pentylenetetrazole (35 mg/kg, i.p.). Successfully kindled animals were used in the study to observe the effect of different treatments. Treatment groups received phenytoin (30 mg/kg) and Curcumin (50, 100 and 200mg/kg) for 15 days. The animals were challenged with pentylenetetrazole (35 mg/kg, i.p.) on day 5, 10 and 15 and seizure severity score, immobility period, number of mistakes and step down latency were recorded. On 15th day, all the animals were sacrificed after behavioral evaluations and their brain was isolated and homogenized to estimate brain norepinephrine, serotonin, total nitrite level and acetylcholinesterase activity. Phenytoin treatment significantly improved the depressive like behavior along with its anticonvulsant effect, however was unable to improve memory impairment. Curcumin significantly attenuated seizure severity, depression like behavior and memory impairment in kindled animals, in dose dependent manner. These results were supported by the biochemical modulation of brain monoamine, nitrosative stress level and acetylcholinesterase activity. Thus present study concluded that Curcumin has the ameliorative effect on seizure severity, depression like behavior and memory impairment in pentylenetetrazole kindled mice, possibly via central monoaminergic modulation and inhibitory effect on nitrosative stress and acetylcholinesterase activity.

Estradiol reduces depressive-like behavior through inhibiting nitric oxide/cyclic GMP pathway in ovariectomized mice

Estradiol decline has been associated with depressive-like behavior in female mice and NO has been suggested to play a major role in the pathogenesis of major depression. This study was conducted to investigate the antidepressant-like effects of acute estradiol administration in female ovariectomized (OVX) mice and the possible role of nitric oxide (NO)/cyclic GMP (cGMP) pathway. To this end, bilateral ovariectomy was performed in female mice and different doses of estradiol were injected alone or in combination with non-specific NO synthase (NOS) inhibitor (L-NAME), selective neural NOS (nNOS) inhibitor (7-NI), an NO precursor (L-arginine) or selective phosphodiesterase type 5 inhibitor (sildenafil). The duration of immobility was recorded in the forced swimming test (FST) to assess the depressive behavior. Moreover, hippocampal levels of NO were determined in select groups. 10 days following the procedure, OVX mice showed significantly prolonged immobility time in comparison with the sham group. Estradiol (3, 10, and 30 μg/kg, s.c.), when injected 1 h prior to FST, exerted antidepressant-like effects in OVX mice. Both L-NAME (30 mg/kg, i.p.), and 7-NI (50 mg/kg, i.p.) significantly reduced the immobility times of OVX mice. Administration of a sub-effective dose of L-NAME (10mg/kg), 15 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) had a robust antidepressant-like effect in OVX mice. Also a sub-effective dose of 7-NI (25 mg/kg), 30 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) showed antidepressant-like effect in OVX mice. Both the NO precursor L-arginine (750 mg/kg, i.p.) and the cGMP-specific phosphodiesterase type 5 inhibitor sildenafil (5 mg/kg, i.p.), 30 min before estradiol treatment, prevented the antidepressant-like effect of a potent dose of estradiol (10 μg/kg, s.c.) in OVX mice. The present findings suggest that suppression of the NO synthase/NO/cGMP pathway may be involved in the antidepressant-like effects of estradiol in OVX mice.

GTP cyclohydrolase 1 gene haplotypes as predictors of SSRI response in Japanese patients with major depressive disorder

BACKGROUND

Tetrahydrobiopterin (BH4) plays an important role in the biosynthesis of serotonin, melatonin and catecholamines, all of which are implicated in the pathophysiology of mood disorders (MDs), including major depressive disorder (MDD) and bipolar disorder (BP). Production of BH4 is regulated by GTP cyclohydrolase transcription and activity. Thus, we considered the GTP cyclohydrolase gene (GCH1) to be a good candidate gene in the pathophysiology of MDs and of the serotonin selective reuptake inhibitors (SSRIs) response in MDD, and conducted a case-control study utilizing three SNPs (rs8007267, rs3783641 and rs841) and moderate sample sizes (405 MDD patients, including 262 patients treated by SSRIs, 1022 BP patients and 1805 controls).

METHOD

A multiple logistic regression analysis was carried out to compare the frequencies of each SNP genotype for the target phenotype across patients and controls in several genetic models, while adjusting for possible confounding factors. A clinical response was defined as a decrease of more than 50% from the baseline score on the Structured Interview Guide for Hamilton Rating Scale for Depression (SIGH-D) within 8 weeks, and clinical remission as a SIGH-D score of less than 7 at 8 weeks.

RESULT

No associations between three SNPs in GCH1 and MDD or BP were observed; however, GCH1 was associated with SSRI therapeutic response in MDD in all the marker's haplotype analysis (Global P value=0.0379).

CONCLUSIONS

Results suggest that GCH1 may predict response to SSRI in MDD in the Japanese population. Nevertheless, a replication study using larger samples may be required for conclusive results, since our sample size was small.

Multiple antidepressant potential modes of action of curcumin: a review of its anti-inflammatory, monoaminergic, antioxidant, immune-modulating and neuroprotective effects

Curcumin is the principal curcuminoid of the popular Indian spice turmeric and has attracted increasing attention for the treatment of a range of conditions. Research into its potential as a treatment for depression is still in its infancy, although several potential antidepressant mechanisms of action have been identified. Research completed to date on the multiple effects of curcumin is reviewed in this paper, with a specific emphasis on the biological systems that are compromised in depression. The antidepressant effects of curcumin in animal models of depression are summarised, and its influence on neurotransmitters such as serotonin and dopamine is detailed. The effects of curcumin in moderating hypothalamus-pituitary-adrenal disturbances, lowering inflammation and protecting against oxidative stress, mitochondrial damage, neuroprogression and intestinal hyperpermeability, all of which are compromised in major depressive disorder, are also summarised. With increasing interest in natural treatments for depression, and efforts to enhance current treatment outcomes, curcumin is presented as a promising novel, adjunctive or stand-alone natural antidepressant.

Novel therapeutic targets in depression: minocycline as a candidate treatment

Mood disorders are marked by high rates of non-recovery, recurrence, and chronicity, which are insufficiently addressed by current therapies. Several patho-etiological models have been proposed that are not mutually exclusive and include but are not limited to the monoamine, inflammatory, neurotrophic, gliotrophic, excitatory, and oxidative stress systems. A derivative of these observations is that treatment(s) which target one or more of these mechanistic steps may be capable of mitigating, or preventing, disparate psychopathological features. Minocycline is an agent with pleiotropic properties that targets multiple proteins and cellular processes implicated in the patho-etiology of mood disorders. Moreover, preclinical and preliminary clinical evidence suggests that minocycline possesses antidepressant properties. Herein, we provide the rationale for conducting a randomized, controlled trial to test the antidepressant properties of minocycline.

Plasma amino acid levels discriminate between control subjects and mildly depressed elderly women

BACKGROUND AND AIMS

Depression is the most common of all psychiatric disorders and the role of amino acid transmitters in this pathology has been recently studied. We undertook this study to investigate if the plasma levels of L-arginine, L-citrulline, L-glutamic acid, L-glutamine, L-asparagine and other amino acids, the L-citrulline/L-arginine and the L-tyrosine/L-phenylalanine ratios, and the nitrite levels are modified in mildly depressed women and if such changes are related to olfactory dysfunction.

METHODS

Plasma samples were obtained from elderly female subjects (n = 21) with mild depression and (n = 48) controls. Amino acids were analyzed with high-performance liquid chromatography, plasma nitrite levels were measured using the Griess method, and olfactory performance was assessed by the combined testing of odor identification, odor discrimination, odor recognition, and the olfactory threshold.

RESULTS

Compared to controls, depressed patients had a significantly higher concentration of L-arginine and a significantly lower L-citrulline/L-arginine ratio when the effect of other variables is not taken into account. A logistic regression model allowed us to identify two risk factors for mild depression, L-arginine and L-glutamic acid, and two protective factors, L-asparagine and the L-tyrosine/L-phenylalanine ratio. Additionally, a significant increase in nitrite levels in depressed women was found. No significant differences were found between the percentage of depressed and control women that identified the odors.

CONCLUSIONS

We identified that the amino acids L-arginine and L-glutamic acid are risk factors for mild depression, whereas L-asparagine and the L-tyrosine/L-phenylalanine ratio are protective factors.

Guanosine produces an antidepressant-like effect through the modulation of NMDA receptors, nitric oxide-cGMP and PI3K/mTOR pathways

Guanosine is an extracellular signaling molecule implicated in the modulation of glutamatergic transmission and neuroprotection. The present study evaluated the antidepressant-like effect of guanosine in the forced swimming test (FST) and in the tail suspension test (TST) in mice. The contribution of NMDA receptors as well as l-arginine-NO-cGMP and PI3K-mTOR pathways to this effect was also investigated. Guanosine administered orally produced an antidepressant-like effect in the FST (0.5-5 mg/kg) and TST (0.05-0.5 mg/kg). The anti-immobility effect of guanosine in the TST was prevented by the treatment of mice with NMDA (0.1 pmol/site, i.c.v.), d-serine (30 μg/site, i.c.v., a co-agonist of NMDA receptors), l-arginine (750 mg/kg, i.p., a substrate for nitric oxide synthase), sildenafil (5 mg/kg, i.p., a phosphodiesterase 5 inhibitor), LY294002 (10 μg/site, i.c.v., a reversible PI3K inhibitor), wortmannin (0.1 μg/site, i.c.v., an irreversible PI3K inhibitor) or rapamycin (0.2 nmol/site, i.c.v., a selective mTOR inhibitor). In addition, the administration of ketamine (0.1 mg/kg, i.p., a NMDA receptor antagonist), MK-801 (0.001 mg/kg, i.p., another NMDA receptor antagonist), 7-nitroindazole (50 mg/kg, i.p., a neuronal nitric oxide synthase inhibitor) or ODQ (30 pmol/site i.c.v., a soluble guanylate cyclase inhibitor) in combination with a sub-effective dose of guanosine (0.01 mg/kg, p.o.) reduced the immobility time in the TST when compared with either drug alone. None of the treatments affected locomotor activity. Altogether, results firstly indicate that guanosine exerts an antidepressant-like effect that seems to be mediated through an interaction with NMDA receptors, l-arginine-NO-cGMP and PI3K-mTOR pathways.

Involvement of different types of potassium channels in the antidepressant-like effect of ascorbic acid in the mouse tail suspension test

Considering that the administration of ascorbic acid elicits an antidepressant-effect in mice by a mechanism which involves an interaction with N-methyl-D-aspartate receptors and the l-arginine-nitric oxide-cGMP pathway and taking into account that the stimulation of this pathway is associated with the activation of potassium (K⁺) channels, this study investigated the involvement of different types of K⁺ channels on the effect of ascorbic acid in the mouse tail suspension test (TST). Intracerebroventricular administration of tetraethylammonium (TEA, a non-specific blocker of K⁺ channels, 25 pg/site), glibenclamide (an ATP-sensitive K⁺ channel blocker, 0.5 pg/site), charybdotoxin (a large- and intermediate conductance calcium-activated K⁺ channel blocker, 25 pg/site) or apamin (a small-conductance calcium-activated K⁺ channel blocker, 10 pg/site) was able to produce a synergistic effect with a sub-effective dose of ascorbic acid (0.1 mg/kg) given orally (p.o.). The antidepressant-like effect of ascorbic acid (1 mg/kg, p.o.) in the TST was prevented by the pre-treatment of mice with cromakalim (a K⁺ channel opener, 10 μg/site, i.c.v.) and minoxidil (10 μg/site, i.c.v.). Moreover, cromakalim abolished the synergistic effect elicited by the combined treatment with sub-effective doses of ascorbic acid and 7-nitroindazole. The administration of the K⁺ channel modulators alone or in combination with ascorbic acid did not affect the locomotion of mice. Together, our results show that the antidepressant-like effect of ascorbic acid in the TST may involve, at least in part, the modulation of neuronal excitability, via inhibition of K⁺ channels.

Immunohistochemical evidence for impaired nitric oxide signaling of the locus coeruleus in bipolar disorder

Nitric oxide (NO) is an important messenger in brain signaling and influences the balance of monoaminergic and glutamatergic neurotransmission. Alterations of NO signaling are thought to play a crucial role in the pathophysiology of mood disorders. The locus coeruleus (LC) comprises the largest group of norepinephrine containing neurons in the mammalian brain. These norepinephrinergic LC neurons are able to generate NO. Immunohistochemical staining of neuronal nitric oxide synthase (nNOS)-immunoreactive (ir) neurons was performed in the LC of the brains of 10 patients with bipolar I disorder (BD), 8 patients with major depressive disorder (MDD) and 16 control cases (C). Analysis of variance (ANOVA) revealed significant differences between the groups, and post hoc tests indicated a lower nNOS-ir neuron number in bipolar patients than in controls (left -34%, right -17%). The total number of Nissl-stained LC neurons showed no changes between major depressive disorder patients, bipolar patients and controls. In the mood disorder patients, illness duration correlated negatively with nNOS-ir neuronal number (r=-0.74, p=0.002). A reduced relative amount of NO in the LC of bipolar patients is likely a result of a compensation for increased glutamatergic activity. The current data on nNOS suggest a dysregulation of the nitrergic system in bipolar disorder. Future studies may clarify the potential role of glial cells in the context of the described nNOS deficit.

Neuronal NOS inhibitor and conventional antidepressant drugs attenuate stress-induced fos expression in overlapping brain regions

Recent evidence indicates that the administration of inhibitors of neuronal nitric oxide synthase (nNOS) induces antidepressant-like effects in animal models such as the forced swimming test (FST). However, the neural circuits involved in these effects are not yet known. Therefore, this study investigated the expression of Fos protein, a marker of neuronal activity, in the brain of rats submitted to FST and treated with the preferential nNOS inhibitor, 7-nitroindazole (7-NI), or with classical antidepressant drugs (Venlafaxine and Fluoxetine). Male Wistar rats were submitted to a forced swimming pretest (PT) and, immediately after, started receiving a sequence of three ip injections (0, 5, and 23 h after PT) of Fluoxetine (10 mg/kg), Venlafaxine (10 mg/kg), 7-NI (30 mg/kg) or respective vehicles. One hour after the last drug injection the animals were submitted to the test session, when immobility time was recorded. After the FST they were sacrificed and had their brains removed and processed for Fos immunohistochemistry. Independent group of non-stressed animals received the same drug treatments, or no treatment (naïve). 7-NI, Venlafaxine or Fluoxetine reduced immobility time in the FST, an antidepressant-like effect. None of the treatments induce significant changes in Fos expression per se. However, swimming stress induced significant increases in Fos expression in the following brain regions: medial prefrontal cortex, nucleus accumbens, locus coeruleus, raphe nuclei, striatum, hypothalamic nucleus, periaqueductal grey, amygdala, habenula, paraventricular nucleus of hypothalamus, and bed nucleus of stria terminalis. This effect was attenuated by 7-NI, Venlafaxine or Fluoxetine. These results show that 7-NI produces similar behavioral and neuronal activation effects to those of typical antidepressants, suggesting that these drugs share common neurobiological substrates.

The role of nitric oxide in orofacial pain

Nitric oxide (NO) is a free radical gas that has been shown to be produced by nitric oxide synthase (NOS) in different cell types and recognized to act as a neurotransmitter or neuromodulator in the nervous system. NOS isoforms are expressed and/or can be induced in the related structures of trigeminal nerve system, in which the regulation of NOS biosynthesis at different levels of gene expression may allow for a fine control of NO production. Several lines of evidence suggest that NO may play a role through multiple mechanisms in orofacial pain processing. This report will review the latest evidence for the role of NO involved in orofacial pain and the potential cellular mechanisms are also discussed.

Antidepressant-like effect of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol, a putative trace amine receptor ligand involves l-arginine-nitric oxide-cyclic guanosine monophosphate pathway

1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol is a novel putative trace amine receptor modulator hypothesized to be useful for treatment-resistant depression. In our previous study, we have demonstrated the antidepressant-like effect of this molecule in mouse forced swim and tail suspension tests and shown to act via modulating the levels of norepinephrine, serotonin and dopamine. The present study attempts to explore the involvement of l-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol in the mouse forced swim test. The antidepressant-like action of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol (8 mg/kg, i.p) was reversed by pretreatment with L-arginine (750 mg/kg, i.p.), a nitric oxide precursor. In contrast, pretreatment with methylene blue (a soluble guanlyate cyclase inhibitor and nitric oxide synthase (NOS) inhibitor) or 7-nitroindazole (a specific neuronal NOS inhibitor) potentiated the antidepressant-like effect of sub-effective dose of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol (2mg/kg, i.p.) in this test model. Furthermore, the antidepressant-like effect of this molecule (8 mg/kg, i.p.) was reversed by sildenafil (5mg/kg, i.p.), a phosphodiesterase inhibitor. In conclusion, the antidepressant-like action of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol involved L-arginine-nitric oxide-cyclic guanosine monophospate signaling pathway.

Rhinacanthus nasutus protects cultured neuronal cells against hypoxia induced cell death

Rhinacanthus nasutus (L.) Kurz (Acanthaceae) is an herb native to Thailand and Southeast Asia, known for its antioxidant properties. Hypoxia leads to an increase in reactive oxygen species in cells and is a leading cause of neuronal damage. Cell death caused by hypoxia has been linked with a number of neurodegenerative diseases including some forms of dementia and stroke, as well as the build up of reactive oxygen species which can lead to diseases such as Huntington's disease, Parkinson's disease and Alzeheimer's disease. In this study we used an airtight culture container and the Mitsubishi Gas Company anaeropack along with the MTT assay, LDH assay and the trypan blue exlusion assay to show that 1 and 10 µg mL⁻¹ root extract of R. nasutus is able to significantly prevent the death of HT-22 cells subjected to hypoxic conditions, and 0.1 to 10 µg mL⁻¹ had no toxic effect on HT-22 under normal conditions, whereas 100 µg mL⁻¹ reduced HT-22 cell proliferation. We also used H₂DCFDA staining to show R. nasutus can reduce reactive oxygen species production in HT-22 cells.

Electroconvulsive therapy: a novel hypothesis for the involvement of purinergic signalling

It is proposed that ATP is released from both neurons and glia during electroconvulsive therapy (ECT) and that this leads to reduction of depressive behaviour via complex stimulation of neurons and glia directly via P2X and P2Y receptors and also via P1 receptors after extracellular breakdown of ATP to adenosine. In particular, A(1) adenosine receptors inhibit release of excitatory transmitters, and A(2A) and P2Y receptors may modulate the release of dopamine. Sequential ECT may lead to changes in purinoceptor expression in mesolimbic and mesocortical regions of the brain implicated in depression and other mood disorders. In particular, increased expression of P2X7 receptors on glial cells would lead to increased release of cytokines, chemokines and neurotrophins. In summary, we suggest that ATP release following ECT involves neurons, glial cells and neuron-glial interactions acting via both P2 and after breakdown to adenosine via P1 receptors. We suggest that ecto-nucleotidase inhibitors (increasing available amounts of ATP) and purinoceptor agonists may enhance the anti-depressive effect of ECT.