Antidepressant effect of pramipexole in mice forced swimming test: A cross talk between dopamine receptor and NMDA/nitric oxide/cGMP pathway

Pramipexole improves depression-like behavior in diabetes mellitus with depression rats by inhibiting NLRP3 inflammasome-mediated neuroinflammation and preventing impaired neuroplasticity

BACKGROUND

Diabetes mellitus (DM) is frequently associated with the occurrence and development of depression, and the co-occurrence of diabetes mellitus with depression (DD) may further reduce patients' quality of life. Recent research indicates that dopamine receptors (DRs) play a crucial role in immune and metabolic regulation. Pramipexole (PPX), a D2/3R agonist, has demonstrated promising neuroprotective and immunomodulatory effects. Nevertheless, the therapeutic effects and mechanisms of action of PPX on DM-induced depression are not clear at present.

METHODS

Depression, DM, and DD were induced in a rat model through a combination of a high-fat diet (HFD) supplemented with streptozotocin (STZ) and chronic unpredictable mild stress (CUMS) combined with solitary cage rearing. The pathogenesis of DD and the neuroprotective effects of DRs agonists were investigated using behavioral assays, enzyme-linked immunosorbent assay (ELISA), hematoxylin-eosin (HE) staining, Nissl staining, Western blotting (WB) and immunofluorescence (IF).

RESULTS

DD rats exhibited more severe dopaminergic, neuroinflammatory, and neuroplastic impairments and more pronounced depressive behaviors than rats with depression alone or DM. Our findings suggest that DRs agonists have significant therapeutic effects on DD rats and that PPX improved neuroplasticity and decreased neuroinflammation in the hippocampus of DD rats while also promoting DG cell growth and differentiation, ultimately mitigating depression-like behaviors.

LIMITATION

Our study is based on a rat model. Further evidence is needed to determine whether the therapeutic effects of PPX apply to patients suffering from DD.

CONCLUSIONS

Neuroinflammation mediated by damage to the dopaminergic system is one of the key pathogenic mechanisms of DD. We provide evidence that PPX has a neuroprotective effect on the hippocampus in DD rats and the mechanism may involve the inhibition of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation by DRs to attenuate the neuroinflammatory response and neuroplasticity damage.

Fatty acid-binding protein 5 differentially impacts dopamine signaling independent of sex and environment

Epidermal/brain fatty acid-binding protein 5 (FABP5) plays an integral role in the intracellular trafficking of bioactive lipids/endocannabinoids and the subsequent initiation of cellular cascades affecting cannabinoid and dopamine (DA) systems. Social isolation (SI) and environmental enrichment (EE) during adolescence have been shown to impact DA signaling, and, specifically, DA transporter (DAT) and receptor levels of DA type 1 (D1) and 2 (D2); however, the relationship between FABP5, environment and DA signaling remains unclear. The present study quantified DAT and DA receptor levels in male/female FABP5-/- and FABP5+/+ mice raised in either SI or EE. Results showed that FABP5-/- mice had 6.09-8.81% greater D1 levels in striatal sub-regions of the caudal brain, independent of sex or environment. D1 levels were 8.03% greater only in the olfactory tubercle of enrichment-reared animals. In summary, these results supported that FABP5 plays an important function in regulating striatal DA signaling, and this may have important implications as a target with therapeutic potential for various psychiatric disorders.

Designing lisuride intranasal nanocarrier system for reduction of oxidative damage with enhanced dopamine level in brain for Parkinsonism

In the present study, nanoemulsion (NE) loaded with lisuride were formulated for delivering drug to brain via intranasal route. Dopamine levels, pharmacokinetic, and antioxidant activity were estimated. Antioxidant effect of lisuride NE was assessed in-vivo using oxidative stress models revealing symptoms like those of Parkinson's disease. Intranasally administered lisuride NE-treated group revealed a greater number of antioxidant enzymes, such as superoxide dismutase (SOD) and glutathione (GSH) as compared to the intravenously administered lisuride suspension in haloperidol rat model. Additionally, it was observed that lisuride NE can decrease dopamine loss. When lisuride NE was administered intranasally resulted in considerably higher dopamine concentrations (17.48 ± 0.05 ng/mL) in comparison to rats receiving haloperidol (7.28 ± 0.02 ng/mL). From study, it is suggested that NE is a possible strategy to deliver lisuride intranasally to lower free radical damage and prevent the biochemical alterations associated with Parkinson's disease.

A systematic review of studies investigating the acute effects of N-methyl-D-aspartate receptor antagonists on behavioural despair in normal animals suggests poor predictive validity

The ability of the N-methyl-D-aspartate receptor antagonist ketamine to induce a rapid and sustained antidepressant effect has led to a surge in pre-clinical studies investigating underlying mechanisms and seeking novel treatments. Animal models are key to this research as they can provide a behavioural readout linking underlying mechanisms to clinical benefits. However, quantifying depression-related behaviours in rodents represents a major challenge with the validity of traditional methods such as models of behavioural despair (forced swim test and tail suspension test) a topic of debate. While there is good evidence to support the value of using these behavioural readouts to study the effects of stress, these approaches have largely failed to detect reliable phenotypic effects in other disease models. In this systematic review, we identified publications which had tested N-methyl-D-aspartate receptor antagonists in normal animals using either the forced swim test or tail suspension test. We compared findings for different doses and time points and also drugs with different clinical profiles to investigate how well the outcomes in the rodent model predicted their effects in the clinic. Despite clear evidence that N-methyl-D-aspartate receptor antagonists reduce immobility time and hence exhibit an antidepressant profile in these tasks, we found similar effects with both clinically effective drugs as well as those which have failed to show efficacy in clinical trials. These findings suggest that behavioural despair tests in normal animals do not provide a good method to predict clinical efficacy of N-methyl-D-aspartate receptor antagonists.

A natural carotenoid crocin exerts antidepressant action by promoting adult hippocampal neurogenesis through Wnt/β-catenin signaling

INTRODUCTION

Adult hippocampal neurogenesis (AHN) is acknowledged to play a critical role in depression. Emerging evidence suggests that the Wnt/β-catenin pathway can modulate hippocampal neurogenesis. Crocin, a natural carotenoid, possesses antidepressant property. Yet, how it affects neurogenesis and exerts antidepressant response remains unknown.

OBJECTIVE

To explore the role of AHN and Wnt/β-catenin in the antidepressant action of crocin.

METHODS

Depressive-related behaviors, including sucrose preference test (SPT), tail suspension test (TST), forced swimming test (FST), and sexual behaviors were performed following crocin treatment. Neurogenesis was characterized via immunohistochemistry, immunofluorescence, Golgi staining and electrophysiology approach. Wnt/β-catenin signaling was examined with western blot analysis. The role of AHN Wnt/β-catenin cascade in crocin's antidepressant response was assessed by conditional removal of glial fibrillary acidic protein (GFAP)-expressing newborn neural cells, temozolomide administration, microinfusion of Dkk1 or viral-mediated shRNA of Wnt3a.

RESULTS

Crocin decreased the immobility duration in TST and FST without impairing the performance in sexual behaviors. Crocin boosted the proliferation and differentiation of progenitors, and promoted dendritic maturation and functional integration of hippocampal newborn neurons. Conditional removal of GFAP-expressing neural cells or temozolomide administration impaired the antidepressant response of crocin. Additionally, Wnt/β-catenin signaling was promoted following crocin treatment. In chronic unpredictable mild stress (CUMS) murine model, crocin treatment displayed antidepressant response in SPT, FST and TST, and restored the neurogenesis levels and Wnt/β-catenin signaling impaired by CUMS. Infusion of Dickkopf-1 (DKK1) or knockdown of Wnt3a in the hippocampus impaired the antidepressant response of crocin.

CONCLUSION

Crocin exerted antidepressant response, which was dependent on enhancement of AHN and activation of the Wnt/β-catenin pathway.

Neuroprotective effect of sumatriptan in pentylenetetrazole-induced seizure is mediated through N-methyl-D-aspartate/nitric oxide and cAMP response element-binding protein signaling pathway

Seizure occurs as a result of uncontrolled electrical disturbances within the brain. Various biomolecules such as N-methyl-D-aspartate (NMDA), nitric oxide (NO), and cAMP response element-binding protein (CREB) have been implicated in the pathophysiology of seizure. Sumatriptan is a specific 5-Hydroxytryptamine 1B/1D receptor agonist and has neuroprotective effects in various neuropsychiatric disorders. In the current study, we tried to investigate the possible interaction of sumatriptan with NMDA/NO and CREB signaling pathway in PTZ induced seizure. For this purpose, various agonist and antagonist of NMDA such as MK-801 and Ketamine, NO precursor L-ARG, and NOS inhibitors L-NAME and 7-NI were co-administered with sumatriptan in PTZ induced seizure model. The level of nitrite in mice hippocampus was determined by Griess reaction. The gene expression of NR1, NR2A, NR2B, and CREB were quantified by quantitative real time-polymerase chain reaction (qRT-PCR). Furthermore, the involved neuronal nitric oxide synthase (nNOS) protein expression was examined via western blot analysis. Effective dose of sumatriptan (1.2 mg/kg) alone and subeffective dose of sumatriptan (0.3 mg/kg) in combination with NMDA and/or NO antagonist showed significant (P < 0.001) anticonvulsant activity in mice. Furthermore, sumatriptan significantly inhibited the PTZ-induced mRNA expression of NR2A (P < 0.0001), NR2B (P < 0.05), and CREB (P < 0.01). Also, the expression of nNOS protein in PTZ treated group was reversed by sumatriptan (P < 0.01). Hence, current findings suggest that the anticonvulsant effect of sumatriptan was due to down regulation of NMDA/NO and CREB signaling pathway.

An Experimental Medicine Investigation of the Effects of Subacute Pramipexole Treatment on Emotional Information Processing in Healthy Volunteers

Treatment with the dopamine D2/D3 receptor agonist pramipexole has demonstrated promising clinical effects in patients with depression. However, the mechanisms through which pramipexole might alleviate depressive symptoms are currently not well understood. Conventional antidepressant drugs are thought to work by biasing the processing of emotional information in favour of positive relative to negative appraisal. In this study, we used an established experimental medicine assay to explore whether pramipexole treatment might have a similar effect. Employing a double-blind, parallel-group design, 40 healthy volunteers (aged 18 to 43 years, 50% female) were randomly allocated to 12 to 15 days of treatment with either pramipexole (at a peak daily dose of 1.0 mg pramipexole salt) or placebo. After treatment was established, emotional information processing was assessed on the neural level by measuring amygdala activity in response to positive and negative facial emotional expressions, using functional magnetic resonance imaging (MRI). In addition, behavioural measures of emotional information processing were collected at baseline and on drug, using an established computerized task battery, tapping into different cognitive domains. As predicted, pramipexole-treated participants, compared to those receiving placebo, showed decreased neural activity in response to negative (fearful) vs. positive (happy) facial expressions in bilateral amygdala. Contrary to our predictions, however, pramipexole treatment had no significant antidepressant-like effect on behavioural measures of emotional processing. This study provides the first experimental evidence that subacute pramipexole treatment in healthy volunteers modifies neural responses to emotional information in a manner that resembles the effects of conventional antidepressant drugs.

Antidepressant-like effect of ethanol in mice forced swimming test is mediated via inhibition of NMDA/nitric oxide/cGMP signaling pathway

There is evidence for a dramatic relationship between depression and alcohol consumption. Depressed patients may abuse ethanol because this agent reduces the symptoms of depression. In the current study, we aimed to investigate the NMDA/nitric oxide/cGMP pathway in the antidepressant-like effect of ethanol in an animal model of behavioral despair. Animals were subjected to locomotor activity in an open-field test separately, followed by a forced swimming test. During the forced swimming test (FST), ethanol (2 and 2.5 g/kg) significantly decreased the immobility time without altering the locomotor activity of animals. The antidepressant-like effect of ethanol (2.5 g/kg) was reversed by co-administration of N-methyl-D-aspartate (NMDA, 75 mg/kg), L-arginine (750 mg/kg), or sildenafil (5 mg/kg). In contrast, co-administration of MK-801 (0.05 mg/kg), ketamine (1 mg/kg), and ifenprodil (0.5 mg/kg) as antagonists of NMDAR, and NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), 7-nitroindazole (7-NI, 30 mg/kg), and methylene blue (10 mg/kg) as inhibitors of nitric oxide synthase (NOS), or 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) (20 mg/kg), a nitric oxide/cyclic-guanosine monophosphate (NO-cGMP) inhibitor, with a subeffective dose of ethanol (1.5 g/kg), significantly decreased the immobility time in the FST. Furthermore, injection of ethanol 2.5 g/kg alone or 1.5 g/kg with a 7-NI subeffective dose, significantly decreased the nitrite levels in the hippocampus and prefrontal cortex. Hence, it is concluded that blockade of NMDA receptors and the nitric oxide/cyclic-guanosine monophosphate (NO-cGMP) pathway might be involved in the antidepressant-like effect of ethanol in mice.

Effect of 5-HT6 Receptor Ligands Combined with Haloperidol or Risperidone on Antidepressant-/Anxiolytic-Like Behavior and BDNF Regulation in Hippocampus and Prefrontal Cortex of Rats

BACKGROUND

The presence of depressive and anxiety symptoms in patients with schizophrenia may have an important impact on treatment and compliance. Hence, interventions addressing such comorbidity in schizophrenia should be explored. One target may be a serotonergic 5-HT₆ receptor (5-HT₆R) since its ligands displayed antidepressant- and anxiolytic-like activities in preclinical experiments.

METHODS

Acute and chronic (21 days) administration of haloperidol or risperidone in combination with a selective 5-HT₆R agonist (WAY-181187) or antagonist (SB-742457) to rats was performed for detecting antidepressant- and anxiolytic-like behaviors. In addition, the level of brain-derived neurotrophic factor (BDNF) protein and its gene expression in hippocampus and prefrontal cortex were determined.

RESULTS

Both single and chronic administration of WAY-181187 with haloperidol produced antidepressant- and anxiolytic-like activities. SB-742457 did not provide full benefits in terms of improvement of haloperidol-induced adverse mood effects. However, the administration of SB-742457 with risperidone triggered its anxiolytic-like activity. Both 5-HT₆R ligands evoked no changes in haloperidol-induced effects on BDNF level. WAY-181187 induced repression of the BDNF gene while SB-742457 increased its expression in both structures. 5-HT₆R ligands, when combined with risperidone, did not change BDNF protein level and increased gene expression in the hippocampus, while they elevated BDNF level and potentiated gene expression in the prefrontal cortex.

CONCLUSION

The combined administration of WAY-181187 and haloperidol provided the greatest benefits, which were manifested by antidepressant-like effects and suppression of the anxiogenic-like properties. The combined administration of risperidone with both agonist and antagonist resulted only in an anxiolytic-like effect. It seems that the anxiolytic-like effects induced by haloperidol or risperidone with the addition of 5-HT₆R ligands are task-specific. The data on BDNF protein and gene expression did not fully correspond with the behavioral outcomes, and thus it appears that other factors/mechanisms are involved in the observed antidepressant- and/or anxiolytic-like effects.

Antidepressant-like Effect of Merazin Hydrate Depends on NO/ERK by Suppressing Its Downstream NF-κB or Nonactivating CREB/BDNF in Mouse Hippocampus

Merazin hydrate (MH), an essential ingredient of Fructus aurantii, has been identified to have an antidepressant-like effect. However, the molecular mechanisms of MH modulate depressive behavior are largely uncharacterized. Here, in lipopolysaccharide-induced mice, we identified that a single administration of MH recovered depressive behaviors and down-regulated the expressions of neuronal nitric oxide synthase (nNOS) in the hippocampus after 1 day. Activation of nNOS by l-arginine led to depressive behaviors, and inhibition of nNOS contributed to antidepressive behaviors. Notably, MH only reversed the expression of nNOS's downstream NF-κB and not the CREB/BDNF pathway in the hippocampus, and MH's antidepressant-like effects were prevented by Asatone (an agonist of NF-κB) and not H89 (an antagonist of CREB). MH also normalized the expressions of GFAP and IB-1 in dentate gyrus in the hippocampus and inflammatory factors such as IL-1β, IL-10, and TNF-α in serum. Overall, our studies reveal the molecular mechanisms of MH's antidepressant-like effect.

CTRP3 acts as a novel regulator in depressive-like behavior associated inflammation and apoptosis by meditating p38 and JNK MAPK signaling

Depression is a complicated etiological pattern, and its pathology and effective treatments are highly limited.C1q-tumor necrosis factor-related protein-3 (CTRP3) is an adipokine, playing crucial roles in metabolic regulatory properties. However, the effects of CTRP3 on depression are largely unknown. In the present study, we found that CTRP3 expression levels were markedly reduced in hippocampus of mice with depression induced by chronic unpredictable mild stress (CUMS). In mouse model with depression, CTRP3-deficient mice aggravated depression-associated behaviors, as evidenced by the reduced locomotor activity and sucrose consumption, while the elevated immobility time in the tail suspension test (TST) and forced swimming test (FST). Moreover, CUMS-induced neuron death and increased expression of cleaved Caspase-3 were significantly accelerated by CTRP3 knockout. Furthermore, CTRP3 deletion intensified pro-inflammatory response in CUMS-exposed mice, which was associated with the activation of nuclear factor-κB(NF-κB) signaling. The activity of mitogen-activated protein kinases (MAPKs), including p38 and JNK, was further promoted in hippocampus of CTRP3-knockout mice with CUMS exposure. In contrast,CTRP3 over-expression showed anti-apoptotic and anti-inflammatory effects in lipopolysaccharide (LPS)-treated microglial cells. Importantly, the in vitro experiments demonstrated that CTRP3 knockdown-exacerbated apoptosis and inflammatory responsewere remarkably abrogated by the blockage of p38 and JNK signaling pathways in microglia stimulated by LPS. Next, in CUMS-exposed mice with CTRP3 deficiency, suppressing p38 and JNK markedly alleviated depressive-like behavior,hippocampal neuron death, apoptosis and inflammation. Therefore, CTRP3 may be an innovative therapeutic target for treating patients with depression through regulating p38 and JNK signaling.

Selegiline Recovers Synaptic Plasticity in the Medial Prefrontal Cortex and Improves Corresponding Depression-Like Behavior in a Mouse Model of Parkinson's Disease

In patients with Parkinson’s disease (PD), non-motor symptoms (NMS) including depression and anxiety are often recognized before motor symptoms develop. Monoamine oxidase (MAO)-B inhibitors are therapeutically effective for motor symptoms; however, their effects on NMS in PD are yet to be fully assessed. Here, we aimed to explore the antidepressant-like effects of propargyl MAO-B inhibitors, selegiline and rasagiline, in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a PD model, and to elucidate the mechanisms underlying these effects. Four repeated intraperitoneal injections of MPTP at 17.5 mg/kg to C57BL/6 mice led to a partial reduction in the number of nigrostriatal tyrosine hydroxylase-positive neurons and to the extension of immobility time during the tail suspension test (TST), without any obvious induction of motor deficits. A single subcutaneous administration of selegiline at 10 mg/kg shortened the extended immobility time of MPTP mice in the TST, without any increase in motor activities, suggesting that selegiline exerts antidepressant-like effects. In this test, rasagiline did not produce antidepressant-like effects, although the inhibitory effect of 3 mg/kg rasagiline on brain MAO activity was comparable to that of 10 mg/kg selegiline. The shortened immobility time in the TST correlated with reduced cortical dopamine (DA) turnover rates in MPTP mice treated with selegiline, but not in MPTP mice treated with rasagiline. These results suggest that MAO inhibition does not entirely account for the antidepressant-like effects of selegiline. Administration of selegiline (10 mg/kg), but not rasagiline (1 mg/kg), to MPTP mice restored the impaired long-term potentiation induced by high-frequency stimulation in the medial prefrontal cortex (mPFC), and normalized the reduced phosphorylation of Ca²⁺/calmodulin-dependent protein kinase IIα, which is known to be involved in neuroplasticity, in the frontal cortex. In MPTP mice, the antiparkinsonian drug pramipexole (0.3 mg/kg), a DA D₂ and D₃ receptor agonist, that has been shown to be effective in treating depression in PD, ameliorated depression-like behavior and synaptic dysfunction in the mPFC. Taken together, the antidepressant-like effects of selegiline in MPTP mice are attributable to the restoration of impaired synaptic plasticity in the mPFC, suggesting its potential for treating depression in early PD.

Implication of NMDA-NO pathway in the antidepressant-like effect of ellagic acid in male mice

Depression is one the common psychiatric disorders through the world. Nitric oxide (NO) and N-methyl-d-aspartate receptor (NMDA-R) are involved in the pathophysiology of depression. Previous studies have been reported various pharmacological properties for ellagic acid (EA). We aimed to evaluate possible involvement of NMDA-NO pathway in the antidepressant-like effect of EA. To do this, we used relevant behavioral tests to evaluate depressive-like behavior. In order to find effective and sub-effective doses of agents, mice treated with EA (6.25, 12.5, 25, 50 and 100 mg/kg), L-NAME (5 and 10 mg/kg), L-arg (25 and 50 mg/kg), NMDA (75 and 150 mg/kg) and ketamine (0.25 and 0.5 mg/kg). Furthermore, mice were treated with combination of sub-effective dose of EA plus sub-effective doses of L-NAME and/or ketamine as well as treated with effective dose of EA in combination of effective doses of L-arg and/or NMDA. Level of NO and gene expression of NR2A and NR2B subunits of NMDA-R were assessed in the hippocampus. Results showed that EA dose dependently provoked antidepressant-like effects and also decreased the hippocampal NO level as well as expression of NMDA-Rs. Co-administration of sub-effective doses of L-NAME or ketamine with sub-effective dose of EA potentiated the effect of EA on behaviors, NO level as well as NMDA-Rs gene expression in the hippocampus. However, co-treatment of effective dose of EA with effective doses of L-arg or NMDA mitigated effects of EA. In conclusion, our data suggested that NMDA-NO, partially at least, are involved in the antidepressant-like effect of EA.

Chronic stress impairs the aquaporin-4-mediated glymphatic transport through glucocorticoid signaling

BACKGROUND

The glymphatic system has recently been proposed to function as a brain-wide macroscopic system for the clearance of potentially harmful molecules, such as amyloid beta (e.g., Aβ), from the brain parenchyma. Previous literatures have established that the glymphatic function is dramatically suppressed by aging, traumatic brain injury, and some diseases. However, the effect of chronic stress on the glymphatic function and its underlying mechanism remains largely unknown.

METHODS

Adult mice were randomly divided into four groups: chronic unpredictable mild stress (CUMS)-treated group, CUMS simultaneously treated with mifepristone (MFP) group, dexamethasone (DEX)-treated group, and control group. Stress response was observed by assessing the change of body weight, plasma corticosterone level, and behavior tests. The level of Aβ42 in cerebral tissue was assessed by ELISA. The glymphatic function was determined by using fluorescence tracer injection. The expression and localization of aquaporin-4 (AQP4) were evaluated by immunohistochemistry and western blot. The transcription level of AQP4 and anchoring molecules was evaluated by real-time PCR.

FINDINGS

Compared with control group, CUMS-treated mice exhibited the impairment of global glymphatic function especially in the anterior brain. This change was accompanied by the decreased expression and polarization of AQP4, reduced transcription of AQP4, agrin, laminin, and dystroglycan in the anterior cortex. Similarly, the glucocorticoid receptor (GR) agonist DEX exposure could reduce the glymphatic function and AQP4 expression. Moreover, the GR antagonist MFP treatment could significantly rescue the glymphatic function and reverse the expression and polarization of AQP4 impaired by CUMS.

CONCLUSION

Chronic stress could impair the AQP4-mediated glymphatic transport in the brain through glucocorticoid signaling. Our results also suggest that GR antagonist could be beneficial to rescue the glymphatic function suppressed by chronic stress.

Ropinirole Augmentation for Depression: A Randomized Controlled Trial Pilot Study

OBJECTIVE

Evidence both from animal and human studies suggests a role for dopaminergic pathways in the treatment of depression. Ropinirole, a selective agonist of dopamine D2/D3, is in use for the treatment of parkinsonism. Preliminary evidence suggests that such agonists might be useful as antidepressants. We tested whether an add-on ropinirole is an effective in depressed patients.

METHODS

We conducted a double-blind, randomized, placebo-controlled trial of add-on ropinirole in depressed patients unresponsive to at least one antidepressant. We recruited 32 unipolar and bipolar patients who remained depressed (modified 21-item Hamilton Depression Rating Scale) despite at least 4 weeks of treatment with an adequate dose of antidepressant medication. Patients received either 2 mg of oral ropinirole or placebo twice daily added on to their current medication and were evaluated weekly for 7 weeks using the Hamilton Depression Rating Scale and Montgomery-Asberg Depression Rating Scale.

RESULTS

No difference in primary or secondary outcome measures was detected between the treatment and control groups.

DISCUSSION

These results differ from previous studies and are unexpected in light of theoretical considerations. This may indicate that there are differences in pharmacological activity between ropinirole and other dopaminergic agents such as pramipexole.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Nitric oxide involvement in additive antidepressant-like effect of agmatine and lithium in mice forced swim test

Lithium is still the main agent in the management of mood disorders such as depression. Likewise, agmatine protects the central nervous system (CNS) against depression. The aim of the present study was to examine the possible additive antidepressant-like effect of agmatine and lithium in mice forced swim test (FST) as well as exploration of the probable involvement of nitric oxide (NO) pathway in this response. Results showed that pretreatment with a subeffective dose of agmatine (0.01 mg/kg) augmented the antidepressant-like effect of lithium subeffective dose (3 mg/kg) (P < 0.001). L-NG-nitroarginine methyl ester (L-NAME, nonspecific nitric oxide synthase [NOS] inhibitor) at doses of 10 and 30 mg/kg, and 7-nitroindazole (7-NI, neuronal NOS inhibitor) at doses of 15 and 30 mg/kg potentiated the antidepressant-like effect of the subeffective combination of lithium (3 mg/kg) and agmatine (0.001 mg/kg) (P < 0.001, P < 0.01, respectively). However, various doses of aminoguanidine (25 and 50 mg/kg, inducible NOS inhibitor) failed to alter the immobility time of the same combination (P > 0.05). Moreover, pretreatment with subeffective doses of L-arginine (substrate for NOS, 300 and 750 mg/kg) reversed the augmenting antidepressant-like effect of agmatine (0.01 mg/kg) on lithium (3 mg/kg) (P < 0.001). Our results revealed that agmatine enhances the antidepressant-like effects of lithium and the NO pathway might mediate this phenomenon. In addition, constitutive NOS plays a dramatic role in this response.

Pathologic role of nitrergic neurotransmission in mood disorders

Mood disorders are chronic, recurrent mental diseases that affect millions of individuals worldwide. Although over the past 40 years the biogenic amine models have provided meaningful links with the clinical phenomena of, and the pharmacological treatments currently employed in, mood disorders, there is still a need to examine the contribution of other systems to the neurobiology and treatment of mood disorders. This article reviews the current literature describing the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby the treatment of mood disorders. The hypothesis has arisen from several observations including (i) altered NO levels in patients with mood disorders; (ii) antidepressant effects of NO signaling blockers in both clinical and pre-clinical studies; (iii) interaction between conventional antidepressants/mood stabilizers and NO signaling modulators in several biochemical and behavioral studies; (iv) biochemical and physiological evidence of interaction between monoaminergic (serotonin, noradrenaline, and dopamine) system and NO signaling; (v) interaction between neurotrophic factors and NO signaling in mood regulation and neuroprotection; and finally (vi) a crucial role for NO signaling in the inflammatory processes involved in pathophysiology of mood disorders. These accumulating lines of evidence have provided a new insight into novel approaches for the treatment of mood disorders.

Monoaminergic and aminoacidergic receptors are involved in the antidepressant-like effect of ginsenoside Rb1 in mouse hippocampus (CA3) and prefrontal cortex

Ginsenoside Rb1 (Rb1), as the major bioactive ingredient of Panax ginseng C.A. Meyer, elicited a novel antidepressant-like effect in the forced swim test (FST) in chronic unpredictable mild stress (CUMS) rats in our previous study. To further explore the molecular mechanism of Rb1 on the neurotransmitters such as 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), norepinephrine (NE), dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), glutamate (Glu) and gamma-aminobutyric acid (GABA) in this antidepressant-like effect, the neurochemical changes in the monoaminergic and aminoacidergic receptors were investigated in the present pharmacological study by using reuptake inhibitors, receptors agonists and antagonists. The results showed that a sub-effective dose of Rb1 (5 mg/kg, p.o.) co-administered with fluoxetine (1 mg/kg, i.p., a selective serotonin reuptake inhibitor), reboxetine (2.5 mg/kg, i.p., a noradrenalin reuptake inhibitor), bupropion (10 mg/kg, i.p., a dopaminergic reuptake inhibitor), Mk-801 (0.05 mg/kg, i.p., an N-methyl-d-aspartic acid (NMDA) receptor antagonist) or baclofen (0.1 mg/kg, i.p., a selective GABA agonist) significantly decreased the immobility time in the FST. In addition, pretreating mice with NAN190 (0.5 mg/kg, i.p., a 5-HT_1A receptor antagonist), ketanserin (5 mg/kg, i.p., a 5-HT_2A/2C receptor antagonist), ondansetron (1 mg/kg, i.p., a 5-HT_3A receptor antagonist), prazosin (1 mg/kg, i.p., an α₁-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α₂-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, i.p., a selective D₁ receptor antagonist), haloperidol (0.2 mg/kg, i.p., a non-selective D₂ receptor antagonist), NMDA (75 mg/kg, i.p., an agonist at the glutamate site) or bicuculline (4 mg/kg, i.p., a competitive GABA antagonist) reversed the antidepressant-like effect of Rb1 (10 mg/kg, p.o.) in the FST. The results obtained for the neurotransmitters in the mouse hippocampus (CA3) and prefrontal cortex showed that Rb1 up-regulated the levels of 5-HT, 5-HIAA, NE, DA, and GABA and decreased the level of Glu. However, there were no significant differences in HVA or DOPAC. Furthermore, there were no significant alterations in the total path of spontaneous locomotor activity in all treatments. These results suggest that both monoaminergic (serotonergic, noradrenergic and dopaminergic) and aminoacidergic (glutamatergic and GABAergic) receptors may be involved in the antidepressant-like effect of Rb1.

Revisiting the validity of the mouse forced swim test: Systematic review and meta-analysis of the effects of prototypic antidepressants

One problem area regarding animal models for affective disorders is unclear reproducibility, including external validity or generalizability. One way to evaluate external validity is with systematic reviews and meta-analyses. The current study presents a meta-analysis of the effects of prototypic antidepressants in the mouse forced swim test (FST). We identified studies that examined effects of antidepressants in the FST in mice and used standard protocol, male mice and acute drug administration. We calculated Effect sizes using Cohen's d, homogeneity using Q statistic and correlations using Pearson's correlation. Results indicate that all drugs reduce immobility in the FST. However, effect sizes for most drugs are heterogeneous and do not show a consistent dose/response relationship across variability factors. Reducing variability by examining only one strain or data from individual laboratories partially increases dose response relationship. These findings suggest that whereas the FST is a valid tool to qualitatively screen antidepressant effects its validity in the context of hierarchical comparison between doses or compounds might be relevant only to single experiments.

Schisandrin rescues depressive-like behaviors induced by chronic unpredictable mild stress via GDNF/ERK1/2/ROS and PI3K/AKT/NOX signaling pathways in mice

The current study aimed to prove the antidepressant-like effects and the probable mechanisms of Schisandrin on depression, which induced by chronic unpredictable mild stress (CUMS) in mice. Four weeks of CUMS exposure resulted in depressive-like behavior, as indicated by the significant decrease in sucrose consumption and increase the immobility time in the forced swim test, but without any influence on the locomotor activity. Further, there were significant downregulations of GDNF/ERK1/2/ROS and PI3K/AKT/NOX signaling pathways in the hippocampus and prefrontal cortex in depressed mice. Treatment of mice with Schisandrin (30mg/kg) and Fluoxetine (10mg/kg) significantly ameliorated all the behavioral and biochemical changes induced by CUMS. These results suggest that Schisandrin produces an antidepressant-like effect in CUMS-induced mice, which possibly mediated, at least in part, by rectifying the signaling pathways of GDNF/ERK1/2/ROS and PI3K/AKT/NOX.

Possible involvement of ATP-sensitive potassium channels in the antidepressant-like effects of gabapentin in mouse forced swimming test

Gabapentin as an anticonvulsant drug also has beneficial effects in treatment of depression. Previously, we showed that acute administration of gabapentin produced an antidepressant-like effect in the mouse forced swimming test (FST) by a mechanism that involves the inhibition of nitric oxide (NO). Considering the involvement of NO in adenosine triphosphate (ATP)-sensitive potassium channels (KATP), in the present study we investigated the involvement of KATP channels in antidepressant-like effect of gabapentin. Gabapentin at different doses (5–10 mg/kg) and fluoxetine (20 mg/kg) were administrated by intraperitoneal route, 60 and 30 min, respectively, before the test. To clarify the probable involvement of KATP channels, mice were pretreated with KATP channel inhibitor or opener. Gabapentin at dose 10 mg/kg significantly decreased the immobility behavior of mice similar to fluoxetine (20 mg/kg). Co-administration of subeffective dose (1 mg/kg) of glibenclamide (inhibitor of KATP channels) with gabapentin (3 mg/kg) showed a synergistic antidepressant-like effect. Also, subeffective dose of cromakalim (opener of KATP channels, 0.1 mg/kg) inhibited the antidepressant-like effect of gabapentin (10 mg/kg). None of the treatments had any impact on the locomotor movement. Our study, for the first time, revealed that antidepressant-like effect of gabapentin in mice is mediated by blocking the KATP channels.

Attenuation of acute restraint stress-induced depressive like behavior and hippocampal alterations with protocatechuic acid treatment in mice

Protocatechuic acid ethyl ester (PCA), a phenolic compound, exhibits neuroprotective effects through improving endogenous antioxidant enzymatic and nonezymatic system. Based on the role of oxidative stress in modulating depressive disorders and the relationship between neuroprotective and antioxidant potential of PCA, we studied if its antidepressant like effect is associated by modulation of cerebral cortex and hippocampal antioxidant alterations. Acute restraint stress (ARS) is known to induce depressive like behavior by neuronal oxidative damage in mice. Swiss albino mice subjected to ARS exhibited an increased immobility time in forced swim test, elevated serum corticosterone and produced oxidative stress dependent alterations in cerebral cortex and hippocampus mainly increased thiobarbituric acid reactive substances and reduced catalase (CAT), superoxide dismutase (SOD) activity. Treatment with PCA was able to prevent stress induced immobility time in forced swim test without altering locomotor activity in mice. Further, PCA treatment attenuated the elevation of serum corticosterone, lipid peroxidation and restored enzymatic antioxidants in cerebral cortex and hippocampus in ARS mice. Altogether, the experimental findings demonstrate the notion that PCA exhibit antidepressant like activity might be related, at least in part, to its capability of modulating antioxidant defense system and oxidative damage induced by ARS in cerebral cortex and hippocampus in mice and thus maintain the pro-/anti-oxidative homeostasis.

Mechanism of depression as a risk factor in the development of Alzheimer's disease: the function of AQP4 and the glymphatic system

BACKGROUND

Many studies have indicated that a history of depression increases the risk of developing Alzheimer's disease (AD); however, the potential pathogenestic mechanism by which depression functions as a high risk factor for AD remains unknown. Recently, a "cerebral lymphatic system" referred to as "glymphatic system" has been demonstrated to be responsible for neuronal extracellular waste protein clearance via a paravascular pathway. However, the function of glymphatic pathway has not been determined in depressive disorders.

METHODS

The present study used an animal model of chronic unpredictable mild stress (CUMS) to determine the function of glymphatic pathway by using fluorescence tracers. Immunohistochemistry was used to assess the accumulation of endogenous mouse and exogenous human amyloid beta 42 (Aβ42) in CUMS-treated mice with or without treatment with antidepressant fluoxetine.

FINDINGS

Glymphatic pathway circulation was impaired in mice treated with CUMS; moreover, glymphatic pathway dysfunction suppressed Aβ42 metabolism, because the accumulation of endogenous and exogenous Aβ42 was increased in the brains of the CUMS-treated mice. However, treatment with fluoxetine reversed these destructive effects of CUMS on glymphatic system. In anhedonic mice, the expression of the water channel aquaporin 4 (AQP4), a factor in glymphatic pathway dysfunction, was down-regulated in cortex and hippocampus.

CONCLUSION

The dysfunction of glymphatic system suggested why a history of depression may be a strong risk factor for AD in anhedonic mice. We hope our study will contribute to an understanding of the risk mechanism of depressive disorder in the development of AD and the mechanisms of antidepressant therapies in AD.

Anticonvulsant effect of dextrometrophan on pentylenetetrazole-induced seizures in mice: Involvement of nitric oxide and N-methyl-d-aspartate receptors

Dextrometrophan (DM), widely used as an antitussive, has recently generated interest as an anticonvulsant drug. Some effects of dextrometrophan are associated with alterations in several pathways, such as inhibition of nitric oxide synthase (NOS) enzyme and N-methyl d-aspartate (NMDA) receptors. In this study, we aimed to investigate the anticonvulsant effect of acute administration of dextrometrophan on pentylenetetrazole (PTZ)-induced seizures and the probable involvement of the nitric oxide (NO) pathway and NMDA receptors in this effect. For this purpose, seizures were induced by intravenous PTZ infusion. All drugs were administrated by intraperitoneal (i.p.) route before PTZ injection. Our results demonstrate that acute DM treatment (10-100mg/kg) increased the seizure threshold. In addition, the nonselective NOS inhibitor L-NAME (10mg/kg) and the neural NOS inhibitor, 7-nitroindazole (40mg/kg), at doses that had no effect on seizure threshold, augmented the anticonvulsant effect of DM (3mg/kg), while the inducible NOS inhibitor, aminoguanidine (100mg/kg), did not affect the anticonvulsant effect of DM. Moreover, the NOS substrate l-arginine (60mg/kg) blunted the anticonvulsant effect of DM (100mg/kg). Also, NMDA antagonists, ketamine (0.5mg/kg) and MK-801 (0.05mg/kg), augmented the anticonvulsant effect of DM (3mg/kg). In conclusion, we demonstrated that the anticonvulsant effect of DM is mediated by a decline in neural nitric oxide activity and inhibition of NMDA receptors.

The role of NMDA receptor and nitric oxide/cyclic guanosine monophosphate pathway in the antidepressant-like effect of dextromethorphan in mice forced swimming test and tail suspension test

Depression is a devastating disorder which has a high impact on the wellbeing of overall society. As such, need for innovative therapeutic agents are always there. Most of the researchers focused on N-methyl-d-aspartate receptor to explore the antidepressant like activity of new therapeutic agents. Dextromethorphan is a cough suppressant agent with potential antidepressant activity reported in mouse force swimming test. Considering N-methyl-d-aspartate as a forefront in exploring antidepressant agents, here we focused to unpin the antidepressant mechanism of dextromethorphan targeting N-methyl-d-aspartate receptor induced nitric oxide-cyclic guanosine monophosphate signaling. Dextromethorphan administered at a dose of 10 and 30mg/kg i.p significantly reduced the immobility time. Interestingly, this effect of drug (30mg/kg) was inhibited when the animals were pretreated either with N-methyl-d-aspartate (75mg/kg), or l-arginine (750mg/kg) as a nitric oxide precursor and/or sildenafil (5mg/kg) as a phosphodiesterase 5 inhibitor. However, the antidepressant effect of Dextromethorphan subeffective dose (3mg/kg) was augmented when the animals were administered with either L-NG-Nitroarginine methyl ester (10mg/kg) non-specific nitric oxide synthase inhibitor, 7-Nitroindazole (30mg/kg) specific neural nitric oxide synthase inhibitor, MK-801 (0.05mg/kg) an N-methyl-d-aspartate receptor antagonist but not aminoguanidine (50mg/kg) which is specific inducible nitric oxide synthase inhibitor as compared to the drugs when administered alone. No remarkable effect on locomotor activity was observed during open field test when the drugs were administered at the above mentioned doses. Therefore, it is evident that the antidepressant like effect of Dextromethorphan is owed due to its inhibitory effect on N-methyl-d-aspartate receptor and NO- Cyclic guanosine monophosphate pathway.

Antidepressant-like effect of pramipexole in an inflammatory model of depression

Pramipexole (PPX), a dopamine D2/3 receptor preferring agonist, is currently in use for the treatment of Parkinson's disease symptoms and restless legs syndrome. Recently, anti-inflammatory properties of PPX have been shown in an autoimmune model of multiple sclerosis, and case reports indicate PPX ameliorates depressive symptoms. Since peripheral inflammation is known to induce depression-like behavior in rodents, we assessed the potential antidepressant effect of PPX in an inflammatory model of depression induced by LPS. Repeated (daily for 7days, 1mg/kg, i.p.), but not acute (1h before LPS) treatment with PPX abolished the depression-like behavior induced by LPS (0.1mg/kg, i.p.) in the forced swim test, and the anhedonic behavior in the splash test. Interestingly, PPX per se decreased interleukin 1β levels and reversed LPS-induced increase in its content in mice hippocampus⋅ Repeated PPX treatment also prevented the increase in hippocampal levels of the 3-nitrotyrosine protein adducts induced by LPS. Haloperidol (0.2mg/kg, i.p.) and sulpiride (50mg/kg, i.p.) were unable to prevent the antidepressant-like effect of PPX in LPS-treated mice. Altogether, these results suggest that the observed antidepressant-like effect of PPX in LPS-treated mice may be dependent on its anti-inflammatory properties and may not be related to dopamine D2 receptor activation.

Pharmacological evidence for the involvement of the NMDA receptor and nitric oxide pathway in the antidepressant-like effect of lamotrigine in the mouse forced swimming test

Lamotrigine is an anticonvulsant agent that shows clinical antidepressant properties. The aim of the present study was to investigate the involvement of N-methyl-d-aspartate (NMDA) receptors and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) synthesis in possible antidepressant-like effect of lamotrigine in forced swimming test (FST) in mice. Intraperitoneal administration of lamotrigine (10mg/kg) decreased the immobility time in the FST (P<0.01) without any effect on locomotor activity in the open-field test (OFT), while higher dose of lamotrigine (30mg/kg) reduced the immobility time in the FST (P<0.001) as well as the number of crossings in the OFT. Pretreatment of animals with NMDA (75mg/kg), l-arginine (750mg/kg, a substrate for nitric oxide synthase [NOS]) or sildenafil (5mg/kg, a phosphodiesterase [PDE] 5 inhibitor) reversed the antidepressant-like effect of lamotrigine (10mg/kg) in the FST. Injection of l-nitroarginine methyl ester (l-NAME, 10mg/kg, a non-specific NOS inhibitor), 7-nitroindazole (30mg/kg, a neuronal NOS inhibitor), methylene blue (20mg/kg, an inhibitor of both NOS and soluble guanylate cyclase [sGC]), or MK-801 (0.05mg/kg), ketamine (1mg/kg), and magnesium sulfate (10mg/kg) as NMDA receptor antagonists in combination with a sub-effective dose of lamotrigine (5mg/kg) diminished the immobility time of animals in the FST compared with either drug alone. None of the drugs produced significant effects on the locomotor activity in the OFT. Based on our findings, it is suggested that the antidepressant-like effect of lamotrigine might mediated through inhibition of either NMDA receptors or NO-cGMP synthesis.