Opioid/NMDA receptors blockade reverses the depressant-like behavior of foot shock stress in the mouse forced swimming test

Pharmacological activation of the amygdala, but not single prolonged footshock-induced acute stress, interferes with cue-induced motivation toward food rewards in rats

In the face of threats, animals adapt their behaviors to cope with the situation. Under such circumstances, irrelevant behaviors are usually suppressed. In this study, we examined whether food-seeking motivation would decrease under activation of the amygdala, an important nucleus in the regulation of stress response in the central nervous system, or after a physical acute stress session. In Experiment 1, we pharmacologically activated the basolateral nucleus (BLA) or the central nucleus of the amygdala (CeA) before a cue-induced reinstatement test in rats. Our results showed that activation of the BLA or the CeA abolished cue-induced motivation toward food rewards, while locomotor activity and free food intake were not affected. In Experiments 2 and 3, we further assessed anxiety and despair levels, as well as cue-induced reinstatement, after a single prolonged footshock-induced acute stress in rats. Behaviorally, acute stress did not affect anxiety level, despair level, or cue-induced motivation toward food rewards. Physiologically, there was no difference in cellular activities of the amygdala immediately after acute stress. To conclude, our results suggested that pharmacological activation of the amygdala decreased cue-induced motivation toward food reward. However, physiological acute stress did not immediately interfere with the negative emotions, motivation, or amygdala activities of the animals.

Involvement of kynurenine pathway and N-methyl-d-aspartate receptors in the antidepressant-like effect of vilazodone in the tail suspension test in mice

The present study evaluated the antidepressant-like effects of vilazodone using the tail suspension test in mice. We also investigated the contribution of kynurenine pathway and N-methyl-d-aspartate receptors to this effect. For this purpose, we pretreated animals with sub-effective doses of L-kynurenine, 3-hydroxykynurenine, or quinolinic acid. We then assessed the immobility time, an indicative measure of depressive-like behavior, in the tail suspension test. We also evaluated the possible effects of sub-effective doses of vilazodone combined with sub-effective doses of ketamine (N-methyl-d-aspartate receptor antagonist) in a separate group. Vilazodone (3mg/kg, intraperitoneal) significantly reduced immobility time in the tail suspension test. L-kynurenine (1.7 mg/kg, intraperitoneal), 3-hydroxykynurenine (10 mg/kg, intraperitoneal), and quinolinic acid (3 nmol/site, intracerebroventricular) significantly increased the immobility time in the tail suspension test. The antidepressant-like effects of vilazodone (3mg/kg, intraperitoneal) were inhibited by pre-treatment with non-effective doses of L-kynurenine (0.83 mg/kg, intraperitoneal), 3-hydroxykynurenine (3.33 mg/kg, intraperitoneal), or quinolinic acid (1 nmol/site, intracerebroventricular). Pretreatment of mice with sub-effective doses of ketamine (1 mg/kg, intraperitoneal) optimized the action of a sub-effective dose of vilazodone (0.3mg/kg, intraperitoneal) and reduced the immobility time in the tail suspension test. None of the drugs used in this study induced any changes in locomotor activity in the open field test. The results showed that vilazodone induced an antidepressant-like effect in the tail suspension test, which may be mediated through an interaction with the kynurenine pathway and N-methyl-d-aspartate receptors.

Towards translational modeling of behavioral despair and its treatment in zebrafish

Depression is a widespread and severely debilitating neuropsychiatric disorder whose key clinical symptoms include low mood, anhedonia and despair (the inability or unwillingness to overcome stressors). Experimental animal models are widely used to improve our mechanistic understanding of depression pathogenesis, and to develop novel antidepressant therapies. In rodents, various experimental models of 'behavioral despair' have already been developed and rigorously validated. Complementing rodent studies, the zebrafish (Danio rerio) is emerging as a powerful model organism to assess pathobiological mechanisms of depression and other related affective disorders. Here, we critically discuss the developing potential and important translational implications of zebrafish models for studying despair and its mechanisms, and the utility of such aquatic models for antidepressant drug screening.

Effects of the prenatal exposure to crocin in the expression of withdrawal syndrome on reflexive motor behaviors in mice offspring's

The aim of the current study was to determine effects of the prenatal exposure to crocin in the expression of withdrawal syndrome on reflexive motor behaviors in mice offspring's. Fourteen male mice and 56 adult female mice were randomly divided into seven groups as: control group (morphine-abstinent male and female); group 2, drug-naïve female and morphine-abstinent male; group 3, drug-naïve male and morphine-abstinent females; group 4, drug-naïve male and female. Groups 5-7, were similar to groups 2-4, except crocin (5 mg/kg) were injected to drug-naïve subjects. Following delivery, 20 pups from each litter were selected and behavior and reflexive motor behaviors were determined. Also, blood samples were taken to determine serum antioxidant activity. According to the results, immobility time significantly increased in offspring of the paternal + maternal exposed to morphine swimming test and tail suspension tests (P < 0.05) and significantly decreased in offspring of paternal + maternal exposed to morphine + crocin group (P < 0.05). Ambulation, surface righting, hind-limb suspension, grip strength and front limb suspension significantly decreased in offspring of the mice exposed to morphine (P < 0.05) and significantly improved in offspring of paternal + maternal exposed to morphine + crocin group (P < 0.05). Hind-limb foot angle and negative geotaxis significantly increased in mice with morphine-exposed offspring's (P < 0.05) while improved in offspring of paternal + maternal exposed to morphine + crocin group (P < 0.05). Prenatal exposure to morphine increased Malondialdehyde while decreased Superoxide dismutase, Glutathione peroxidase and total antioxidant status in mice offspring's (P < 0.05) and these results reversed by prenatal exposure to crocin (P < 0.05). In all studied factors, paternal + maternal exposed to morphine + crocin group had better results compared to the other crocin-received drug-naïve groups (P < 0.05). These results suggested prenatal exposure to crocin decreased morphine-induced adverse effect which paternal and maternal exposed to morphine + crocin had the highest prevention against these effects in mice offspring's.

Xanthohumol Attenuates Lipopolysaccharide-Induced Depressive Like Behavior in Mice: Involvement of NF-κB/Nrf2 Signaling Pathways

Depression is the most common psychiatric disorder associated with brain and immune system abnormalities. In recent years, xanthohumol (Xn) a bioactive prenylated flavonoid has received ample attention for its polypharmacological effects, therefore, here we aimed to explore the protective effects of Xn against the LPS-induced depressive-like symptoms mediated by inflammation and oxidative stress. We tested the effect of Xn against LPS-induced behavioural changes in mice by means of forced swimming test (FST), tail suspention test (TST), sucrose preference test (SPT) and open field test (OPT). Examined the neuroinflammation and oxido-nitrosative stress (O&NS) markers and analyze Nrf2 and NF-κB signalling pathways in the hippocampus. Our results indicated that peripheral repeated administration of lipopolysaccharides (LPS) (1 mg/kg, intra peritoneally) induced depressive-like behavior, neuroinflammation and O&NS in mice. Pretreatment with Xn (10 and 20 mg/kg, intra gastrically) reverse the behavioural impairments prophylactically as obvious in the FST and TST without effecting locomotion, however only 20 mg dose improve anhedonic behavior as observed in SPT. Similarly, Xn pretreatment in dose-dependent manner prevented the LPS induced neuro-inflammation and O&NS. Immunofluorescence analysis showed that Xn reduced activated gliosis via attenuation of Iba-1 and GFAP in hippocampus. In addition, Xn considerably reduced the expression of phospho-NF-κB and cleaved caspase-3 while enhanced Nrf2 and HO-1 expression in the hippocampus. To the best of our knowledge, this is the first study to examine the underlying beneficial prophylactic effects of the Xn in neuroinflammation and O&NS mediating depressive-like behaviors.

Combination of MAP6 deficit, maternal separation and MK801 in female mice: A 3-hit animal model of neurodevelopmental disorder with cognitive deficits

Schizophrenia is a major psychiatric disease still lacking efficient treatment, particularly for cognitive deficits. To go further in research of new treatments that would encompass all the symptoms associated with this pathology, preclinical animal models need to be improved. To date, the aetiology of schizophrenia is unknown, but there is increasing evidence to highlight its multifactorial nature. We built a new neurodevelopmental mouse model gathering a triple factor combination (3-M): a genetic factor (partial deletion of MAP6 gene), an early stress (maternal separation) and a late pharmacological factor (MK801 administration, 0.05 mg/kg, i.p., daily for 5 days). The effects of each factor and of their combination were investigated on several behaviours including cognitive functions. While each individual factor induced slight deficits in one or another behavioural test, 3-M conditioning induces a wider phenotype with hyperlocomotion and cognitive deficits (working memory and social recognition). This study confirms the hypothesis that genetic, environmental and pharmacological factors, even if not deleterious by themselves, could act synergistically to induce a deleterious behavioural phenotype. It moreover encourages the use of such combined models to improve translational research on neurodevelopmental disorders.

Molecular Targets of Cannabinoids Associated with Depression

Novel therapeutic strategies are needed to address depression, a major neurological disorder affecting hundreds of millions of people worldwide. Cannabinoids and their synthetic derivatives have demonstrated numerous neurological activities and may potentially be developed into new treatments for depression. This review highlights cannabinoid (CB) receptors, monoamine oxidase (MAO), N-methyl-D-aspartate (NMDA) receptor, gamma-aminobutyric acid (GABA) receptor, and cholecystokinin (CCK) receptor as key molecular targets of cannabinoids that are associated with depression. The anti-depressant activity of cannabinoids and their binding modes with cannabinoid receptors are discussed, providing insights into rational design and discovery of new cannabinoids or cannabimimetic agents with improved druggable properties.

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.

Melatonin attenuated the behavioral despair induced by acute neurogenic stress through blockade of N-methyl D-aspartate receptors in mice

It has been well documented that administration of melatonin could reveal antidepressant-like effect in rodents. However, the protective effect of melatonin on stress-induced depression/anxiety and its underlying mechanism is yet to be understood. In this regard, in the current study, acute foot-shock stress (FSS) was used to evaluate the antidepressant-like effect of melatonin on neurogenic stress-induced depression in mice. Behavioral evaluation was done by using the forced swimming test (FST) and Open-field test (OFT). Melatonin, MK-801, and ketamine (NMDA receptor antagonists), and NMDA (NMDA receptor agonist) were used to elucidate any association between melatonin and NMDA pathway in behavioral despair induced by acute-FSS. Applying acute-FSS to mice significantly induced depressant-like behavior in FST without any significant impact on locomotor activity in the OFT. We observed that melatonin (dose-dependently) significantly improved the depressant-like effect of FSS, but it did not impact the locomotion in animals. Acute injection of MK-801 at sub-effective doses (0.01 mg/kg) or ketamine (0.1 mg/kg) potentiated the antidepressant-like effect of a sub-effective dose of melatonin. However, the sub-effective dose of NMDA (30 mg/kg) abolished the protective effect of melatonin on the behavioral profile of stressed animals. Our results could reflect the antidepressant-like effect of melatonin on neurogenic stress-induced depressive behaviors in mice. Also, our results showed that NMDA receptors could be involved in the antidepressant-like effect of melatonin.

The zebrafish tail immobilization (ZTI) test as a new tool to assess stress-related behavior and a potential screen for drugs affecting despair-like states

BACKGROUND

Affective disorders, especially depression and anxiety, are highly prevalent, debilitating mental illnesses. Animal experimental models are a valuable tool in translational affective neuroscience research. A hallmark phenotype of clinical and experimental depression, the learned helplessness, has become a key target for 'behavioral despair'-based animal models of depression. The zebrafish (Danio rerio) has recently emerged as a promising novel organism for affective disease modeling and CNS drug screening. Despite being widely used to assess stress and anxiety-like behaviors, there are presently no clear-cut despair-like models in zebrafish.

NEW METHOD

Here, we introduce a novel behavioral paradigm, the zebrafish tail immobilization (ZTI) test, as a potential tool to assess zebrafish despair-like behavior. Conceptually similar to rodent 'despair' models, the ZTI protocol involves immobilizing the caudal half of the fish body for 5 min, leaving the cranial part to move freely, suspended vertically in a small beaker with water.

RESULTS

To validate this model, we used exposure to low-voltage electric shock, alarm pheromone, selected antidepressants (sertraline and amitriptyline) and an anxiolytic drug benzodiazepine (phenazepam), assessing the number of mobility episodes, time spent 'moving', total distance moved and other activity measures of the cranial part of the body, using video-tracking. Both electric shock and alarm pheromone decreased zebrafish activity in this test, antidepressants increased it, and phenazepam was inactive. Furthermore, a 5-min ZTI exposure increased serotonin turnover, elevating the 5-hydroxyindoleacetic acid/serotonin ratio in zebrafish brain, while electric shock prior to ZTI elevated both this and the 3,4-dihydroxyphenylacetic acid/dopamine ratios. In contrast, preexposure to antidepressants sertraline and amitriptyline lowered both ratios, compared to the ZTI test-exposed fish.

COMPARISON WITH EXISTINGMETHOD(S)

The ZTI test is the first despair-like experimental model in zebrafish.

CONCLUSIONS

Collectively, this study suggests the ZTI test as a potentially useful protocol to assess stress-/despair-related behaviors, potentially relevant to CNS drug screening and behavioral phenotyping of zebrafish.

NMDA receptors and L-arginine/nitric oxide/cyclic guanosine monophosphate pathway contribute to the antidepressant-like effect of Yueju pill in mice

The present study aims to evaluate the involvement of N-methyl-d-aspartate receptor and nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) system in antidepressant-like effects of Yueju pill (YJ), a Chinese herbal medicine. The immobility time in tail suspension test (TST) and forced swim test (FST) was used to assess the antidepressant effects. Prior administration of L-arginine (750 mg/kg, intraperitoneal [i.p.]), a NO synthase substrate that enhances NO signaling or sildenafil (5 mg/kg, i.p.), a phosphodiesterase 5 inhibitor that enhances cGMP, blunted the antidepressant-like activity of YJ (2.7 g/kg, i.g.). Co-treatment of ineffective dose of YJ (1.35 g/kg, i.g.) with one of the reagents that suppress the NO/cGMP signaling, including methylene blue (10 mg/kg, i.p.), an inhibitor of NO synthase; 7-NI (7-nitroinidazole, 30 mg/kg, i.p.), an nNOS specific inhibitor; L-NAME (10 mg/kg, i.p.), a non-specific inhibitor of NO synthase; and MK-801 (0.05 mg/kg, i.p.), an NMDA receptor antagonist, reduced the immobility time in TST and FST, compared with those in vehicle or single drug treatment groups. Neither above drugs alone or co-administrated with YJ affected locomotor activity or anxiety behavior in open field test. Thus, our results suggest that the antidepressant-like action of YJ may depend on the inhibition of NMDA/NO/cGMP pathway.

Genes involved in stress response influence lithium efficacy in bipolar patients

OBJECTIVES

In mood disorders, chronic stimulation with stress results in aberrant regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Lithium was shown to influence HPA axis function. The underlying genetic background as well as environmental context may influence the stress response, and therefore lithium efficacy. The aim of the present study was to analyze if genetic variants located in genes involved in HPA axis regulation affect the response to long-term lithium treatment in bipolar patients.

METHODS

We included 93 patients with bipolar disorder (32 males and 61 females), aged 31-80 years. The patients had been treated with lithium carbonate for at least 5 years. The magnitude of the lithium response was assessed using the Alda scale. Genotyping was performed for 28 polymorphisms in the genes encoding the following proteins involved in HPA axis regulation: corticotropin-releasing hormone receptor 1 (CRHR1), arginine vasopressin receptor 1B (AVPR1b), FK506 binding protein (FKBP) 5, FKBP4, BCL2-associated athanogene 1 (BAG1), stress induced phosphoprotein 1 (STIP1), glucocorticoid-induced transcript 1 (GLCC1), dual specificity phosphatase 1 (DUSP1) serine and arginine rich splicing factor (SRSF) 3, SRSF9, SRSF5, and acid phosphatase 1 (ACP1). Linkage disequilibrium and haplotype analysis were then performed, followed by statistical analysis (Statistica v.12; Stasoft, Krakow, Poland).

RESULTS

We found a correlation between stressful life events at first episode and worse response to lithium (P=.019). In single marker analysis, we observed a significant association between three FKBP5 polymorphisms (rs1360780, rs7748266 and rs9296158), one ACP1 variant (rs300774) and one glucocorticoid-induced transcript 1 gene (GLCC1) variant (rs37972) and the degree of lithium response. Five out of seven FKBP5 polymorphisms showed strong linkage with one haplotype demonstrating an association with lithium efficacy (P=.008). No relationship was found between the other analyzed polymorphisms and lithium response.

CONCLUSION

The response to lithium may depend on the variants of genes regulating the HPA axis and stressful life events in bipolar patients.

Involvement of opioid system in behavioral despair induced by social isolation stress in mice

Social isolation stress (SIS) as a type of chronic stress could induce depressive- and anxiety-like behaviors. Our study evaluates the role of opioid system on negative behavioral impacts of SIS in male NMRI mice. We investigated effects of morphine, a nonselective opioid receptor (OR) agonist, naltrexone (NLX), an OR antagonist, naltrindole (NLT), a delta opioid receptor (DOR) antagonist, SNC80, a DOR agonist, U-69593, a kappa opioid receptor (KOR) agonist, nor-Binaltorphimine, a selective KOR antagonist and cyprodime hydrochloride a selective mu opioid receptor (MOR) antagonist on depressive- and anxiety-like behaviors. Using RT-PCR we evaluated ORs gene expression in mice brain. Our findings showed that SIS induced anxiety- and depressive-like behavior in the forced swimming test, open field test, splash test and hole-board test. Moreover, administration of SNC-80 significantly mitigated anxiety- and depressive-like behaviors. NLT decreased grooming-activity in the splash test. Excitingly, administration of agents affecting KOR failed to alter the negative effects of SIS. RT-PCR demonstrated that MOR and KOR gene expression decreased in socially isolated mice; however, SIS did not affect DORs expression. Our findings suggest that SIS at least in part, probably via altering endogenous opioids particularly MORs and KORs but not DORs mediated negative impacts on behavior; also, it could be concluded that DORs might be considered as a novel target for studying depression and anxiety.

Acute foot-shock stress decreased seizure susceptibility against pentylenetetrazole-induced seizures in mice: Interaction between endogenous opioids and cannabinoids

BACKGROUND

Stressful conditions affect the brain's neurotransmission and neural pathways that are involved in seizure susceptibility. Stress alters the intensity and/or frequency of seizures. Although evidence indicates that chronic stress exerts proconvulsant effects and acute stress has anticonvulsant properties, the underlying mechanisms which mediate these effects are not well understood. In the present study, we assessed the role of endogenous opioids, endocannabinoids, as well as functional interaction between opioid and cannabinoid systems in the anticonvulsant effects of acute foot-shock stress (FSS) against pentylenetetrazole (PTZ)-induced seizures in mice.

METHODS

Prolonged intermittent FSS was chosen as an acute stress model. Seizure threshold was determined after 30 min of stress induction in male Naval Medical Research Institute (NMRI) mice (20-30 g). Opioid and cannabinoid receptor antagonists were administered before animal placement in the FSS apparatus.

RESULTS

Acute FSS significantly decreased seizure susceptibility in animals. The administration of the cannabinoid receptor 1 (CB₁) antagonist, AM251, completely blocked the anticonvulsant effect of acute FSS at the doses of 1 pg/kg-100 μg/kg but not at 1 fg/kg. Pretreatment with the nonspecific opioid receptor antagonist, naltrexone (NTX), significantly inhibited the anticonvulsant effects of acute FSS at 1 and 2 mg/kg but not at 0.3 mg/kg. However, coadministration of the subeffective doses of AM251 (1 fg/kg) and NTX (0.3 mg/kg) reversed the anticonvulsant effects of acute FSS.

CONCLUSIONS

Opioid and cannabinoid systems are involved in the anticonvulsant effects of acute FSS, and these neurotransmission systems interact functionally in response to acute FSS.

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.

Silica nanoparticle exposure during the neonatal period impairs hippocampal precursor proliferation and social behavior later in life

Introduction

Silica nanoparticles (SiO₂-NPs) are currently among the most widely used nanomaterials, but their potentially adverse effects on brain development remain unknown. The developing brain is extremely sensitive to NP neurotoxicity during the early postnatal period.

Materials and methods

Herein, we investigated the effects of SiO₂-NPs (doses of 10, 20, or 50 mg with a particle size of ~91 nm, equivalent to aerosol mass concentrations 55.56, 111.11, and 277.78 mg/m³, respectively) exposure from postnatal day (P) 1 to P7 on hippocampal precursor proliferation at P8 and long-term neurobehavior in adults.

Results

SiO₂-NP exposure resulted in inflammatory cell infiltration in lung tissue, microglia over-activation in the hippocampal dentate gyrus (DG), and decreased hippocampal precursor proliferation in the DG-subgranular zone at P8. Moreover, after exposure to 20 mg of SiO_2-NPs, mice exhibited social interaction deficits and slight anxiety-like behaviors in adulthood, but this exposure did not induce locomotor activity impairment, depression-like behavior, or short-term memory impairment.

Discussion

These findings suggest that early-age SiO₂-NP exposure induced inflammation and inhibited precursor proliferation in the DG in a dose-dependent manner, which might be related to the social dysfunction observed in adulthood.

The role of nitric oxide-cGMP pathway in selegiline antidepressant-like effect in the mice forced swim test

BACKGROUND

Considering the pivotal role of nitric oxide (NO) pathway in depressive disorders, the aim of the present study was to investigate the antidepressant-like effect of selegiline in mice forced swimming test (FST), and possible involvement of NO-cyclic guanosine monophosphate (cGMP) pathway in this action.

METHODS

After assessment of locomotor activity in open-field test, mice were forced to swim individually and the immobility time of the last 4 min was evaluated. All drugs were given intraperitoneally (ip).

RESULTS

Selegiline (10 mg/kg) decreased the immobility time in the FST similar to fluoxetine (20 mg/kg). Pretreatment with l-arginine (NO precursor, 750 mg/kg) or sildenafil (a phosphodiesterase 5 inhibitor, 5 mg/kg) significantly reversed the selegiline anti-immobility effect. Sub-effective dose of selegiline (1 mg/kg) showed a synergistic antidepressant effect with NG-nitro-l-arginine methyl ester (L-NAME, inhibitor of NO synthase, 10 mg/kg) or 7-nitroindazole (specific neuronal NO synthase inhibitor, 30 mg/kg), but not with aminoguanidine (specific inducible NO synthase inhibitor, 50 mg/kg). Pretreatment of mice with methylene blue (an inhibitor of NO synthase and soluble guanylyl cyclase, 10 mg/kg) significantly produced a synergistic response with the sub-effective dose of selegiline. Neither of the drugs changed the locomotor activity. Also, hippocampal and prefrontal cortex (PFC) nitrite content was significantly lower in selegiline-injected mice compared to saline-administrated mice. Also, co-injection of 7-nitroindazole with selegiline produced a significant reduction in hippocampal or PFC nitrite contents.

CONCLUSIONS

It is concluded that selegiline possesses antidepressant-like effect in mice FST through inhibition of l-arginine-NO-cyclic guanosine monophosphate pathway.

Activation of indoleamine 2, 3- dioxygenase pathway by olanzapine augments antidepressant effects of venlafaxine in mice

Recent clinical studies report antipsychotics as a better option to augment the action of antidepressants in treatment resistant cases. However, the proper mechanisms underlying the antidepressant effect of antipsychotics is still not clear. Indolamine 2, 3 dioxygenase (IDO) pathway is considered to be an important pathway in pro-inflammatory cytokine associated stress-induced depression. The present study investigated the antidepressant effect of venlafaxine, olanzapine and their combinations in chronic forced-swim stress-induced depression in mice. In addition, the role of pro-inflammatory cytokines and IDO-mediated pathway was investigated. Swiss albino mice were subjected to chronic forced-swim stress and evaluation for antidepressant-like activity was performed on 7th, 14th and 21st day following which serum levels of pro-inflammatory cytokines (IL-1β and IL-6 levels) and the levels of hippocampal kynurenine (KYN), tryptophan (TRP) and serotonin (5HT) were estimated. The combination exhibited augmentation of antidepressant-like activity of venlafaxine by olanzapine in chronic forced-swim stress model. Further, it reversed the enhanced serum IL-1β and IL-6 and reverted the increased activity of IDO as measured by ratio of hippocampal KYN/TRP and 5HT/TRP in stressed mice. Augmentation of antidepressant effect of venlafaxine by olanzapine is thus mediated by normalising the shift from KYN to TRP pathway in chronic forced swim induced stressed mice.

Roles of the µ-opioid receptor and its related signaling pathways in the pathogenesis of premenstrual syndrome liver-qi stagnation

The present study aimed to investigate the roles of the µ-opioid receptor (MOR) and its related signaling pathways in the pathogenesis of premenstrual syndrome (PMS) liver-qi stagnation, along with the therapeutic effects of the Shu-Yu capsule in treating the condition. A PMS liver-qi stagnation rat model was established using a chronic restraint stress method. The protein expression level of MOR within rat hippocampal tissue was detected via western blot analysis and cyclic adenosine monophosphate (cAMP) levels within the supernatant of a rat hippocampal cell culture were determined by ELISA. The western blot analysis indicated that the hippocampal expression level of MOR was significantly elevated in the PMS liver-qi stagnation model group. However, subsequent treatment with a Shu-Yu capsule was found to significantly decrease the level of MOR expression. In addition, in vitro experiments were performed, whereby primary hippocampal neurons were treated with model rat serum. It was observed that the level of MOR expression was significantly elevated, while brain-derived neurotrophic factor (BDNF) and cAMP levels in the culture supernatant were significantly decreased. These effects were reversed by treatment with serum from the Shu-Yu capsule-treated rats. Furthermore, when treated with the MOR activator DAMGO, the following were significantly decreased in the primary neurons: Phosphorylation levels of cAMP response element binding protein and extracellular signal-regulated protein kinases (ERK); BDNF expression; and cAMP content in the culture supernatant. These effects were reversed in primary neurons treated with DAMGO and Shu-Yu-containing rat serum. Collectively, the data suggest that increased MOR expression and activation of the cAMP/ERK signaling pathway in the hippocampus may be involved in the pathogenesis of PMS liver-qi stagnation. Furthermore, the efficacy of the Shu-Yu capsule in treating the condition may be via its regulation of MOR receptor signaling.

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.

Lithium attenuates the proconvulsant effect of adolescent social isolation stress via involvement of the nitrergic system

In this study, we tested whether acute administration of lithium mitigates the deleterious effect of adolescent social isolation stress (SIS) on seizure susceptibility. In comparison with socially conditioned (SC) mice, isolated conditioned (IC) mice exhibited an increase in seizure susceptibility to pentylenetetrazole. Acute administration of lithium (10mg/kg) reversed the proconvulsant effect of SIS in IC mice, but this effect was not observed in SC mice. Coadministration of subthreshold doses of lithium (3mg/kg) with nitric oxide synthase (NOS) inhibitors reversed the effect of SIS on seizure susceptibility and decreased hippocampal nitrite levels in IC animals. In addition, a subthreshold dose of a nitric oxide precursor reduced the protective effect of lithium on seizure susceptibility and increased nitrite levels in the hippocampus of IC mice. These results suggest that lithium exerts a protective influence against the proconvulsant effect of adolescent SIS via a nitrergic system that includes activation of neuronal NOS in the hippocampus.

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.

Fluoxetine reverses the behavioral despair induced by neurogenic stress in mice: role of N-methyl-d-aspartate and opioid receptors

Opioid and N-methyl-d-aspartate (NMDA) receptors mediate different effects of fluoxetine. We investigated whether opioid and NMDA receptors are involved in the protective effect of fluoxetine against the behavioral despair induced by acute physical stress in male mice. We used the forced swimming test (FST), tail suspension test (TST), and open-field test (OFT) for behavioral evaluation. We used fluoxetine, naltrexone (opioid receptor antagonist), MK-801 (NMDA receptor antagonist), morphine (opioid receptor agonist), and NMDA (NMDA receptor agonist). Acute foot-shock stress (FSS) significantly induced behavioral despair (depressive-like) and anxiety-like behaviors in tests. Fluoxetine (5 mg/kg) reversed the depressant-like effect of FSS, but it did not alter the locomotion and anxiety-like behavior in animals. Acute administration of subeffective doses of naltrexone (0.3 mg/kg) or MK-801 (0.01 mg/kg) potentiated the antidepressant-like effect of fluoxetine, while subeffective doses of morphine (1 mg/kg) and NMDA (75 mg/kg) abolished this effect of fluoxetine. Also, co-administration of subeffective doses of naltrexone (0.05 mg/kg) and MK-801 (0.003 mg/kg) with fluoxetine (1 mg/kg) induced a significant decrease in the immobility time in FST and TST. Our results showed that opioid and NMDA receptors (alone or in combination) are involved in the antidepressant-like effect of fluoxetine against physical stress.

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

Pramipexole is a dopamine D2 receptor agonist indicated for treating Parkinson disorder. This study was aimed to investigate the effect of pramipexole in forced swimming test (FST) in mice and the possible involvement of activation of D2 receptors and inhibition of N-methyl-d-aspartate (NMDA) receptors and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) on this effect. Intraperitoneal administration of pramipexole (1-3mg/kg) reduced the immobility time in the FST similar to fluoxetine (20mg/kg, i.p.). This effect of pramipexole (1mg/kg, i.p.) was ceased when mice were pretreated with haloperidol (0.15mg/kg, i.p,) and sulpiride (5mg/kg, i.p) as D2 receptor antagonists, NMDA (75mg/kg,i.p.), l-arginine (750mg/kg, i.p., a substrate for nitric oxide synthase) or sildenafil (5mg/kg, i.p., a phosphodiesterase 5 inhibitor). The administration of MK-801 (0.05mg/kg, i.p., a NMDA receptor antagonist) l-NG-Nitro arginine methyl ester (l-NAME, 10mg/kg, i.p., a non-specific nitric oxide synthase (NOS) inhibitor), 7-nitroindazole (30mg/kg, i.p., a neuronal NOS inhibitor) and methylene blue (10mg/kg, i.p.), an inhibitor of both NOS and soluble guanylyl cyclase (sGC) in combination with the sub-effective dose of pramipexole (0.3mg/kg, i.p.) reduced the immobility. Altogether, our data suggest that the antidepressant-like effect of pramipexole is dependent on the activation of D2 receptor and inhibition of either NMDA receptors and/or NO-cGMP synthesis. These results contribute to the understanding of the mechanisms underlying the antidepressant-like effect of pramipexole and reinforce the role of D2 receptors, NMDA receptors and l-arginine-NO-GMP pathway in the antidepressant mechanism of this agent.

Involvement of nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of tropisetron and ondansetron in mice forced swimming test and tail suspension test

Antidepressant-like effects of 5-hydroxytryptamine subtype 3 (5-HT3) antagonists including tropisetron and ondansetron have been previously demonstrated in the literature. It was reported that stimulation of 5-HT3 receptors activate the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway, which is involved in regulation of behavioral and emotional functions. In our study, treating animals with tropisetron (5, 10, and 30mg/kg) and ondansetron (0.01 and 0.1µg/kg) significantly decreased the immobility time in forced swimming test (FST) and tail-suspension test (TST). Co-administration of subeffective doses of tropisetron (1mg/kg) and ondansetron (0.001µg/kg) with subeffective dose of l-NAME (10mg/kg, nonselective NO synthase (NOS) inhibitor) and 7-nitroindazole (25mg/kg, neural NOS inhibitor) exerted antidepressant-like effect in FST and TST, while aminoguanidine (50mg/kg, inducible NOS inhibitor) did not enhance the antidepressant-like effect of 5-HT3 antagonists. Besides, l-arginine (750mg/kg, NO precursor) and sildenafil (5mg/kg, phosphodiesterase inhibitor) suppressed the anti-immobility effect of 5-HT3 antagonists. None of the treatments altered the locomotor behavior of mice in open-field test. Also, hippocampal (but not cortical) nitrite level was significantly lower in tropisetron and ondansetron-treated mice compared with saline-injected mice. Also, co-administration of 7-nitroindazole with tropisetron or ondansetron caused a significant decrease in hippocampal nitrite levels. In conclusion, we suggest that antidepressant-like effect of tropisetron and ondansetron are partially mediated by modulation of NO-cGMP pathway.

Involvement of NMDA receptors and L-arginine/nitric oxide/cyclic guanosine monophosphate pathway in the antidepressant-like effects of topiramate in mice forced swimming test

Topiramate (TPM) is an agent primarily used in the treatment of epilepsy. Using mice model of forced swimming test (FST) the current study was basically aimed to investigate the influence of TPM on depression by inhibiting NMDA receptor and nitric oxide-cGMP production. When TPM was administered in a dose of 20 and 30 mg/kg by i.p. route it reduced the immobility time during FST. However this effect of TPM (30 mg/kg, i.p.) in the FST was abolished when the mice were pretreated either with NMDA (75 mg/kg, i.p.), or l-arginine (750 mg/kg, i.p. NO precursor), or sildenafil (5mg/kg, i.p. Phosphodiesterase 5 inhibitor). The immobility time in the FST was reduced after administration of L-NAME (10mg/kg, i.p, a non-specific NOS inhibitor), 7-nitoinidazol (30 mg/kg, i.p. a nNOS inhibitor) or MK-801 (0.05 mg/kg, i.p, a NMDA receptor antagonist) in combination with a subeffective dose of TPM (10mg/kg, i.p.) as compared with single use of either drug. Co-administrated of lower doses of MK-801 (0.01 mg/kg) or L-NAME (1mg/kg) failed to effect immobility time. However, simultaneous administration of these two agents in the same doses with subeffective dose of TPM (10mg/kg, i.p.), reduced the immobility time during FST. None of these drugs were found to have a profound effect on the locomotor activity per se during the open field test. Taken together, our data demonstrates that TPM exhibit antidepressant-like effect which is accomplished either due to inhibition of NMDA receptors or NO-cGMP production.

NMDA receptor antagonists attenuate the proconvulsant effect of juvenile social isolation in male mice

Experiencing psychosocial stress in early life, such as social isolation stress (SIS), is known to have negative enduring effects on the development of the brain and behavior. In addition to anxiety and depressive-like behaviors, we previously showed that juvenile SIS increases susceptibility to pentylenetetrazole (PTZ)-induced seizures in mice through enhancing the nitrergic system activity in the hippocampus. In this study, we investigated the possible involvement of N-methyl-D-aspartate (NMDA) receptors in proconvulsant effects of juvenile SIS. Applying 4 weeks of SIS to juvenile male mice at postnatal day 21-23, we observed an increased susceptibility to PTZ as well as anxiety and depressive-like behaviors in adult mice. Intraperitoneal (i.p.) administration of NMDA receptor antagonists, MK-801 (0.05 mg/kg) and ketamine (0.5mg/kg), reversed the proconvulsant effects of SIS in Isolated (and not social) housed animals. Co-administration of non-effective doses of nitric oxide synthase (NOS) inhibitors, 7NI (25mg/kg) and L-NAME (10mg/kg), with NMDA receptor antagonists, MK-801 (0.01 mg/kg) and ketamine (0.1mg/kg) attenuated the proconvulsant effects of juvenile SIS only in isolated housed mice. Also, using real time RT-PCR, we showed that hippocampal upregulation of NR2B subunit of NMDA receptor may play a critical role in proconvulsant effects of juvenile SIS by dysregulation of NMDA/NO pathway. In conclusion, results of present study revealed that experiencing SIS during adolescence predisposes the co-occurrence of seizure disorders with psychiatric comorbidities and also, alteration of NMDA receptor structure and function in hippocampus plays a role in proconvulsant effects of juvenile SIS through enhancing the NMDA/NO pathway.

Involvement of NO/cGMP pathway in the antidepressant-like effect of gabapentin in mouse forced swimming test

Based on clinical studies regarding the beneficial effect of gabapentin in depression, we aimed to evaluate the antidepressant-like properties of gabapentin in mice and also the participation of nitric oxide (NO)/cyclic guanosine monophosphate pathway in this effect. The following drugs were used in this study: gabapentin; N(G)-nitro-L-arginine methyl ester (L-NAME), a non-specific NO synthase (NOS) inhibitor; 7-nitroindazole, a specific neuronal NOS inhibitor; aminoguanidine, a specific inducible NOS inhibitor; L-arginine, a NO precursor; and sildenafil, a phosphodiestrase inhibitor. Finally, we studied the behavioral effects through the forced swimming test (FST) and the changes of the hippocampus NO level through nitrite assay. The immobility time was significantly reduced after gabapentin administration. Co-administration of non-effective doses of gabapentin and L-NAME or 7-nitroindazole (7-NI) resulted in antidepressant-like effect in FST, while aminoguanidine did not affect the immobility time of gabapentin-treated mice. Furthermore, the antidepressant-like property of gabapentin was prevented by L-arginine or sildenafil. Also, the hippocampal nitrite level was significantly lower in gabapentin-treated mice relative to saline-injected mice, and co-administration of 7-NI with sub-effective gabapentin caused a significant decrease in hippocampal nitrite levels. Our results indicate that the antidepressant-like effect of gabapentin in the mice FST model is mediated at least in part through nitric oxide/cyclic guanosine monophosphate (cGMP) pathway.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

The involvement of NMDA receptor/NO/cGMP pathway in the antidepressant like effects of baclofen in mouse force swimming test

In the current study, the involvement of N-methyl-d-aspartate receptor (NMDAR) and nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) system in the antidepressant-like effects of baclofen was evaluated by using animal model in forced swimming test. Followed by an open field test for the evaluation of locomotor activity, the immobility time for mice in force swimming test was recorded. Only the last four min was analyzed. Administration of Baclofen (0.5 and 1mg/kg, i.p.) reduced the immobility interval in the FST. Prior administration of l-arginine (750mg/kg, i.p.,) a nitric oxide synthase substrate or sildenafil (5mg/kg, i.p.) a phosphodiesterase 5 into mice suppressed the antidepressant-like activity of baclofen (1mg/kg, i.p.).Co-treatment of 7-nitroindazole (50mg/kg, i.p.,) an inhibitor of neuronal nitric oxide synthase, L-NAME (10mg/kg, i.p.,) a non-specific inhibitor of nitric oxide synthase or MK-801 (0.05mg/kg, i.p.) an NMDA receptor antagonist with subeffective dose of baclofen (0.1mg/kg, i.p.), reduced the immobility time in the FST as compared to the drugs when used alone. Co-administrated of lower doses of MK-801 (0.01mg/kg) or l-NAME (1mg/kg) failed to effect immobility time however, simultaneous administration of these two agents in same dose with subeffective dose of baclofen (0.1mg/kg, i.p.), minimized the immobility time in the FST. Thus, our results support the role of NMDA receptors and l-arginine-NO-GMP pathway in the antidepressant-like action of baclofen.

Evidence for the involvement of NMDA receptors in the antidepressant-like effect of nicotine in mouse forced swimming and tail suspension tests

RATIONALE

The antidepressant action of acute nicotine administration in clinical and animal studies is well recognized. But the underlying mechanism for this effect has not been carefully discovered.

OBJECTIVES

We attempted to evaluate the possible role of N-Methyl-D-aspartate (NMDA) receptors in the antidepressant-like effect of nicotine.

METHODS

After the assessment of locomotor activity in the open-field test, forced swimming test (FST) and tail suspension test (TST) were used to evaluate the antidepressant-like effect of nicotine in mice. We performed intraperitoneal administration of nicotine at different doses and periods before the tests. To assess the possible involvement of NMDA receptors, non-effective doses of NMDA antagonists and an NMDA agonist were obtained and were administered simultaneously with the non-effective and effective doses of nicotine, respectively.

RESULTS

Nicotine (0.2 mg/kg, 30 min before FST/TST) significantly reduced the immobility time of mice similar to fluoxetine (20 mg/kg). Nicotine did not affect the locomotor behavior of mice in open-field test. Co-administration of non-effective doses of NMDA receptor antagonists, ketamine (1 or 0.3 mg/kg), MK-801 (0.05 or 0.005 mg/kg), and magnesium sulfate (10 or 5 mg/kg) with nicotine (0.1 or 0.03 mg/kg) had remarkable synergistic antidepressant effect in both FST and TST. Also, non-effective NMDA (75 or 30 mg/kg) reversed the anti-immobility effect of nicotine (0.2 mg/kg) on mouse FST and TST.

CONCLUSIONS

Our study has for the first time confirmed that the antidepressant-like effect of nicotine on mice is NMDA-mediated, and nicotine presumably exerts this effect by antagonizing the glutamatergic NMDA receptors.

Opioid-dependent regulation of high and low fear responses in two inbred mouse strains

The molecular mechanisms underlying the susceptibility or resilience to trauma-related disorders remain incompletely understood. Opioids modulate emotional learning, but the roles of specific receptors are unclear. Here, we aimed to analyze the contribution of the opioid system to fear responses in two inbred mouse strains exhibiting distinct behavioral phenotypes. SWR/J and C57BL/6J mice were subjected to five consecutive electric footshocks (1mA each), and the contextual freezing time was measured. Stress-induced alterations in gene expression were analyzed in the amygdala and the hippocampus. In both strains, the fear response was modulated using pharmacological tools. SWR/J mice did not develop conditioned fear but exhibited increased transcriptional expression of Pdyn and Penk in the amygdala region. Blocking opioid receptors prior to the footshocks using naltrexone (2 mg/kg) or naltrindole (5 mg/kg) increased the freezing responses in these animals. The C57BL/6J strain displayed high conditioned fear, although no alteration in the mRNA abundance of genes encoding opioid precursors was observed. Double-injection of morphine (20 mg/kg) following stress and upon context re-exposure prevented the enhancement of freezing. Moreover, selective delta and kappa agonists caused a reduction in conditioned fear responses. To summarize, the increased expression of the Pdyn and Penk genes corresponded to reduced intensity of fear responses. Blockade of the endogenous opioid system restored freezing behavior in stress-resistant animals. The pharmacological stimulation of the kappa and delta opioid receptors in stress-susceptible individuals may alleviate fear. Thus, subtype-selective opioid receptor agonists may protect against the development of trauma-related disorders.

In vitro and in vivo efficacy of a potent opioid receptor agonist, biphalin, compared to subtype-selective opioid receptor agonists for stroke treatment

To meet the challenge of identification of new treatments for stroke, this study was designed to evaluate a potent, nonselective opioid receptor (OR) agonist, biphalin, in comparison to subtype selective OR agonists, as a potential neuroprotective drug candidate using in vitro and in vivo models of ischemic stroke. Our in vitro approach included mouse primary neuronal cells that were challenged with glutamate and hypoxic/aglycemic (H/A) conditions. We observed that 10nM biphalin, exerted a statistically significant neuroprotective effect after glutamate challenge, compared to all selective opioid agonists, according to lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Moreover, 10nM biphalin provided superior neuroprotection after H/A-reoxygenation compared to selective opioid agonists in all cases. Our in vitro investigations were supported by in vivo studies which indicate that the nonselective opioid agonist, biphalin, achieves enhanced neuroprotective potency compared to any of the selective opioid agonists, evidenced by reduced edema and infarct ratios. Reduction of edema and infarction was accompanied by neurological improvement of the animals in two independent behavioral tests. Collectively these data strongly suggest that concurrent agonist stimulation of mu, kappa and delta ORs with biphalin is neuroprotective and superior to neuroprotection by activation of any single OR subtype.

Investigating the stress attenuating potential of furosemide in immobilization and electric foot-shock stress models in mice

The present study was designed to investigate the antistress effect of furosemide (sodium potassium chloride co-transporter inhibitor) in immobilization and foot-shock stress-induced behavioral alterations in the mice. Acute stress was induced in Swiss albino mice either by applying electric foot shocks of 0.6-mA intensity of 1-s duration with 30-s inter-shock interval for 1 h or immobilizing for 150 min. The acute stress-induced behavioral changes were assessed by using actophotometer, hole board, open-field, and social interaction tests. Biochemically, the corticosterone levels were estimated in the serum as a biomarker of hypothalamus-pituitary-adrenal (HPA) axis. Acute stress resulted in the development of behavioral alterations and elevation of the corticosterone levels. Intraperitoneal administration of furosemide (25 and 50 mg/kg) significantly attenuated immobilization and foot-shock stress-induced behavioral changes along with normalization of the corticosterone levels. It may be concluded that furosemide produces beneficial effects in reestablishing the behavioral and biochemical alterations in immobilization and foot-shock-induced acute stress in mice.