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

L-arginine metabolism ameliorates age-related cognitive impairment by Amuc_1100-mediated gut homeostasis maintaining

Aging-induced cognitive impairment is associated with a loss of metabolic homeostasis and plasticity. An emerging idea is that targeting key metabolites is sufficient to impact the function of other organisms. Therefore, more metabolism-targeted therapeutic intervention is needed to improve cognitive impairment. We first conducted untargeted metabolomic analyses and 16S rRNA to identify the aging-associated metabolic adaption and intestinal microbiome change. Untargeted metabolomic analyses of plasma revealed L-arginine metabolic homeostasis was altered during the aging process. Impaired L-arginine metabolic homeostasis was associated with low abundance of intestinal Akkermansia muciniphila (AKK) colonization in mice. Long-term supplementation of AKK outer membranes protein-Amuc_1100, rescued the L-arginine level and restored cognitive impairment in aging mice. Mechanically, Amuc_1100 acted directly as a source of L-arginine and enriched the L-arginine-producing bacteria. In aged brain, Amuc_1100 promoted the superoxide dismutase to alleviated oxidation stress, and increased nitric oxide, derivatives of L-arginine, to improve synaptic plasticity. Meanwhile, L-arginine repaired lipopolysaccharide-induced intestinal barrier damage and promoted growth of colon organoid. Our findings indicated that aging-related cognitive impairment was closely associated with the disorders of L-arginine metabolism. AKK-derived Amuc_1100, as a potential postbiotic, targeting the L-arginine metabolism, might provide a promising therapeutic strategy to maintain the intestinal homeostasis and cognitive function in aging.

The antidepressant-like effect of doxycycline is associated with decreased nitric oxide metabolite levels in the prefrontal cortex

Doxycycline is an antibiotic that has shown neuroprotective, anti-inflammatory, and antidepressant-like effects. Low doses of doxycycline revert the behavioral and neuroinflammatory responses induced by lipopolysaccharide treatment in a mice model of depression. However, the molecular mechanisms involved in the antidepressant action of doxycycline are not yet understood. Doxycycline inhibits the synthesis of nitric oxide (NO), which increases after stress exposure. Inducible NO synthase (iNOS) inhibition also causes antidepressant-like effects in animal models sensitive to antidepressant-like effects such as the forced swimming test (FST). However, no direct study has yet investigated if the antidepressant-like effects of doxycycline could involve changes in NO-mediated neurotransmission. Therefore, this study aimed at investigating: i) the behavioral effects induced by doxycycline alone or in association with ineffective doses of a NO donor (sodium nitroprusside, SNP) or an iNOS inhibitor (1400 W) in mice subjected to the FST; and ii) doxycycline effects in NO metabolite levels in the prefrontal cortex and hippocampus these animals. Male mice (8 weeks) received i.p. injection of saline or doxycycline (10, 30, and 50 mg/kg), alone or combined with SNP (0.1, 0.5, and 1 mg/kg) or 1400 W (1, 3, and 10 µg/kg), and 30 min later were submitted to the FST. Animals were sacrificed immediately after, and NO metabolites nitrate/nitrite (NOx) were measured in the prefrontal cortex and hippocampus. Doxycycline (50 mg/kg) reduced both the immobility time in the FST and NOx levels in the prefrontal cortex of mice compared to the saline group. The antidepressant-like effect of doxycycline in the FST was prevented by SNP (1 mg/kg) pretreatment. Additionally, sub-effective doses of doxycycline (30 mg/kg) associated with 1400 W (1 µg/kg) induced an antidepressant-like effect in the FST. Altogether, our data suggest that the reducing NO levels in the prefrontal cortex through inhibition of iNOS could be related to acute doxycycline treatment resulting in rapid antidepressant-like effects in mice.

Ketamine alleviating depressive-like behaviors is associated with regulation of nNOS–CAPON–Dexras1 complex in chronic unpredictable mild stress rats

Background

A growing number of studies have demonstrated that ketamine induces rapid and sustained antidepressant action. Neuronal nitric oxide synthase (nNOS) signaling has been explored for the treatment of neuropsychiatric disorders for decades. But the effect of ketamine on nNOS signaling is poorly understood. The aim of the present study was to investigate the effect of ketamine on nNOS signaling in a chronic unpredictable mild stress (CUMS) model of depression.

Methods

Forty-eight rats were randomly divided into four groups: the control group of healthy rats (group C), the healthy rats treated with ketamine 10 mg/kg for 3 days (group CK), the rats model of stress-induced depression group (group D), and the depressed group treated with ketamine 10 mg/kg for 3 days (group DK). The sucrose preference test and open field test were used to assess behavioral changes. Immunohistochemistry, immunofluorescence, and real-time PCR analysis were carried out to measure the expression of nNOS, CAPON, and Dexras1 in the prefrontal cortex (PFC) of the CUMS rats.

Results

Compared with healthy rats, the total distance traveled, the rearing counts, the sucrose preference percentage (SPP), and CAPON and Dexras1 expression in the PFC significantly decreased, while nNOS expression increased in CUMS rats. After treating with ketamine, the total distance traveled, the rearing counts, the SPP, and CAPON and Dexras1 expression significantly increased, while nNOS expression significantly decreased.

Conclusion

The results indicated that ketamine improved the depressive behavior of rats, which may be related to the reduced nNOS expression and enhanced CAPON and Dexras1 expression.

The role of the excitation:inhibition functional balance in the mPFC in the onset of antidepressants

Currently available antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs), generally require weeks to months to produce a therapeutic response, but the mechanism of action underlying the delayed onset of antidepressant-like action remains to be elucidated. The balance between excitatory glutamatergic pyramidal neurons and inhibitory γ-aminobutyric acid (GABA) interneurons, i.e., the excitation:inhibition functional (E:I) balance, in the medial prefrontal cortex (mPFC) is critical in regulating several behaviors and might play an important mediating role in the mechanism of rapid antidepressant-like action reported by several studies. In the present study, the multichannel electrophysiological technique was used to record the firing activities of pyramidal neurons and interneurons and investigate the effects of a single dose of fluoxetine and ketamine (both 10 mg/kg, i.p.) on the E:I functional balance in the rat mPFC after 90 min or 24 h, and the forced swimming test (FST) was used to evaluate the antidepressant-like effects of fluoxetine and ketamine. The present study also explored the effects of chronic treatment with fluoxetine (10 mg/kg, i.g.) for 7 d or 21 d on the E:I functional balance in the mPFC. The present results suggested that a single dose of ketamine could both significantly increase the firing activities of pyramidal neurons and significantly decrease the firing activities of interneurons in the mPFC and exerted significant antidepressant-like action on the FST after 90 min and 24 h, but fluoxetine had no such effects under the same conditions. However, chronic treatment with fluoxetine for 21 d (but not 7 d) could significantly affect the firing activities of pyramidal neurons and interneurons in the mPFC. Taken together, the present results indicated that rapid regulation of the E:I functional balance in the mPFC might be an important common mechanism of rapid-acting antidepressants and the delayed onset of SSRIs might be partly attributed to their inability to rapidly regulate the E:I functional balance in the mPFC. The present study provided a new entry point to the development of rapid-acting antidepressants.

Protection by ginseng saponins against cyclophosphamide-induced liver injuries in rats by induction of cytochrome P450 expression and mediation of the l-arginine/nitric oxide pathway based on metabolomics

Ginseng saponins (GS) are the main active compounds in Panax ginseng and have been proven to be highly effective in attenuating the side effects of chemotherapy. However, there have been no reports on the mechanism of action of GS. Treatment with GS has certain benefits, including decreasing the toxicity levels in the liver [alanine aminotransferase (ALT), albumin (ALB), alkaline phosphatase (ALP), aspartate transaminase (AST)], reducing oxidative stress [malondialdehyde (MDA), nitric oxide (NO)], diminishing inflammatory factors [interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) levels], and augmenting the levels of glutathione (GSH) and superoxide dismutase (SOD). The pharmacokinetics study showed that the area under the curve from 0 to 24 hr (AUC 0-24 hr) of 4-ketocyclophosphamide (4-KetoCTX) and carboxyphosphamide (CPM) was significantly increased after GS treatment. This study found that GS treatment can reduce chloroacetaldehyde (CAA) production by affecting CYP3A4, CYP2B6, and CYP2C9 protein expression in the liver. For the metabolomics study, GS attenuated the abnormalities of amino acid metabolic pathways in CP-induced liver injuries of rats and significantly enhanced the l-arginine level while reducing the serum nitric oxide (NO) level. This outcome was confirmed by the inhibition of the activities of NO synthase in the liver of rats.

Serum Metabonomic Study on the Antidepressant-like Effects of Ellagic Acid in a Chronic Unpredictable Mild Stress-Induced Mouse Model

As a polyphenol, ellagic acid (EA) has shown potential antidepressant activity. In this study, the effects and serum metabolomic analysis of EA against depression were investigated using a chronic unpredictable mild stress-induced (CUMS) model. EA (20 or 100 mg/kg body weight) significantly ameliorated the CUMS-induced depression-like behaviors, including reduced body weight, decreased sucrose preference, and increased immobility time in both the tail suspension test and the forced swimming test. Furthermore, EA attenuated the CUMS-induced hippocampal damage and significantly increased the brain-derived neurotrophic factor (BDNF) and the serotonin (5-HT) levels as well as suppressed the inflammatory response. The metabolomics analysis showed that the disturbance of glycerophospholipid (phosphatidylethanolamine and phosphatidylinositol), amino acid (l-arginine and N-stearoyl serine), and purine (uric acid) metabolism induced by CUMS was attenuated by the EA treatment. Furthermore, the correlation analysis indicated that the metabolite changes were strongly correlated with behavioral disorders, BDNF, 5-HT, and inflammatory cytokines levels. This study provided new insights for the antidepressant effects of EA and suggests that EA may be a potential nutraceutical for improving the management of depression.

Repeated ketamine administration redeems the time lag for citalopram's antidepressant-like effects

Current available antidepressants exhibit low remission rate with a long response lag time. Growing evidence has demonstrated acute sub-anesthetic dose of ketamine exerts rapid, robust, and lasting antidepressant effects. However, a long term use of ketamine tends to elicit its adverse reactions. The present study aimed to investigate the antidepressant-like effects of intermittent and consecutive administrations of ketamine on chronic unpredictable mild stress (CUMS) rats, and to determine whether ketamine can redeem the time lag for treatment response of classic antidepressants. The behavioral responses were assessed by the sucrose preference test, forced swimming test, and open field test. In the first stage of experiments, all the four treatment regimens of ketamine (10 mg/kg ip, once daily for 3 or 7 consecutive days, or once every 7 or 3 days, in a total 21 days) showed robust antidepressant-like effects, with no significant influence on locomotor activity and stereotype behavior in the CUMS rats. The intermittent administration regimens produced longer antidepressant-like effects than the consecutive administration regimens and the administration every 7 days presented similar antidepressant-like effects with less administration times compared with the administration every 3 days. In the second stage of experiments, the combination of ketamine (10 mg/kg ip, once every 7 days) and citalopram (20 mg/kg po, once daily) for 21 days caused more rapid and sustained antidepressant-like effects than citalopram administered alone. In summary, repeated sub-anesthestic doses of ketamine can redeem the time lag for the antidepressant-like effects of citalopram, suggesting the combination of ketamine and classic antidepressants is a promising regimen for depression with quick onset time and stable and lasting effects.

Maternal deprivation increases microglial activation and neuroinflammatory markers in the prefrontal cortex and hippocampus of infant rats

A relationship between neuroinflammation and the development of psychiatric disorder have been revealed by many studies in the past decade. Although studies have shown that stressors can induce long-term changes that may be related to behavioral responses, these alterations have been poorly studied soon after a stressor, such as maternal deprivation (MD). Thus, this study was designed to investigate the acute effect of experimental induction of MD on inflammatory and microglial activation markers in the brain of infant rats. Early MD was induced from postnatal day (PND) 1-10. On PND 10 the prefrontal cortex (PFC) and hippocampus from MD and control groups were removed to investigate microglial activation and neuroinflammatory markers. In the PFC the expressions of cluster of differentiation molecule 11B (CD11B), toll-like receptor (TLR)-2, and TLR-4 were increased in rats subjected to MD. The arginase expression was elevated in the PFC and hippocampus of maternally deprived rats. The cytokines interleukin-5 (IL-5), -6, -7, -10, tumor necrosis factor (TNF-α), and interferon gamma (INF-γ) were increased in the PFC of MD rats group. In the PFC the macrophage inflammatory proteins (MIP)-1α levels were reduced in MD rats group. In the hippocampus only the levels of TNF-α and INF-γ were elevated in infant rats subjected to MD. In conclusion, our results support the hypothesis that neuroinflammation and microglial activation, mainly in the PFC, could be involved with changes in the brain resident cells following MD, and these alterations could be associated to the development of psychiatric conditions late in life.

Nitric oxide signalling and antidepressant action revisited

Studies about the pathogenesis of mood disorders have consistently shown that multiple factors, including genetic and environmental, play a crucial role on their development and neurobiology. Multiple pathological theories have been proposed, of which several ultimately affects or is a consequence of dysfunction in brain neuroplasticity and homeostatic mechanisms. However, current clinical available pharmacological intervention, which is predominantly monoamine-based, suffers from a partial and lacking response even after weeks of continuous treatment. These issues raise the need for better understanding of aetiologies and brain abnormalities in depression, as well as developing novel treatment strategies. Nitric oxide (NO) is a gaseous unconventional neurotransmitter, which regulates and governs several important physiological functions in the central nervous system, including processes, which can be associated with the development of mood disorders. This review will present general aspects of the NO system in depression, highlighting potential targets that may be utilized and further explored as novel therapeutic targets in the future pharmacotherapy of depression. In particular, the review will link the importance of neuroplasticity mechanisms governed by NO to a possible molecular basis for the antidepressant effects.

A brief history of antidepressant drug development: from tricyclics to beyond ketamine

OBJECTIVE

Although monoaminergic-targeted drugs have prompted great advances in the development of treatments for depression, the need for new options persists, since these drugs still have a delayed clinical effect and most patients do not respond properly to them. Recently, the observation of the antidepressant effects of ketamine brought on a new wave of studies regarding the comprehension of the neurobiology of depression and the development of new and more effective antidepressant drugs.

METHODS

Thus, in this paper, we present a historical review of the development of monoaminergic antidepressant drugs and the role of ketamine as the introductory agent of a new era in the research of the neurobiology of depression.

RESULTS

Firstly, we review how the pharmacological treatment for major depression started, and we point out the main drugs discovered, the researchers involved, and how the studies developed have contributed to the understanding of the neurobiology of depression. Secondly, the major problems regarding the clinical efficacy and acceptance of these drugs are discussed, and the introduction of the glutamatergic system as a target for antidepressant drugs is presented. Finally, we review how ketamine revealed itself as an exciting option towards obtaining pharmacological agents to treat depression, through the understanding of biological markers.DiscussionKetamine contributed to confirm that different targets of the glutamatergic system and neurotrophic pathways are strictly related to the neurobiology of depression. There are several antidepressant drugs based on ketamine's mechanism of action already in the pipeline, and glutamatergic-targeted antidepressants may be on the market in the near future.

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.

Antidepressant drugs for beta amyloid-induced depression: A new standpoint?

Mounting evidence suggests that depression represents a risk factor and an early manifestation of Alzheimer's disease (AD). Neuropsychiatric symptoms may derive from neurobiological changes in specific brain areas and may be considered prodromal of dementia. We have previously reported the depressive-like profile in rats receiving a single intracerebroventricular injection of soluble amyloid beta protein (ßA). Here, we verified the effect of different classes of antidepressants on the ßA-induced depressive behavior and on cortical monoamine levels. To these purposes, the forced swimming test was performed and cortical levels of serotonin (5-HT) and noradrenaline (NA) were quantified by high performance liquid chromatography (HPLC). We found that acute fluoxetine (20mg/kg, s.c.), reboxetine (10mg/kg, s.c.), and ketamine (15mg/kg, i.p.) significantly reduced the immobility in ßA-treated rats compared to controls. Fluoxetine and reboxetine reversed 5-HT reduction, while βA-induced NA increase was further enhanced by all treatments. Treatments with fluoxetine, reboxetine and ketamine were able to revert soluble ßA-induced decrease of cortical BDNF levels, while only fluoxetine and ketamine, but not reboxetine, had the same effects on cortical NGF expression. Moreover, plasma soluble ßA-levels were lowered by fluoxetine, but not reboxetine and ketamine, treatments. Our data suggest that different classes of antidepressants yield a short-acting effect on rat soluble ßA-induced depressive profile. Thus, we hypothesize a novel common mechanism of action of these drugs also based upon a "ßA lowering" effect. Although further investigations are still needed, our study might open a new scenario for unravelling the molecular antidepressant mechanisms of these drugs.

Acute and chronic treatment with quetiapine induces antidepressant-like behavior and exerts antioxidant effects in the rat brain

Many studies note that changes in oxidative balance are involved in the pathogenesis of major depressive disorder (MDD) and in the success of some antidepressants. Quetiapine exerts a therapeutic response and induces changes in physiological mechanisms that appear to underlie MDD. The objective of this study was to evaluate the antidepressant and antioxidant effects of quetiapine (20 mg /kg) in adult animals. Sixty minutes after an acute treatment or the last administration of chronic treatment (14 days) with quetiapine, animals were subjected to the forced swimming test (FST) to evaluate mobility parameters. Then, the hippocampus, prefrontal cortex (CPF), amygdala and nucleus accumbens (NAc) were removed for the assessment of oxidative stress parameters. Both acute and chronic treatments exerted antidepressant-like effects. Myeloperoxidase (MPO) activity was reduced in the amygdala after acute treatment and in the hippocampus, PFC and amygdala after chronic treatment. In addition, after chronic treatment, the levels of thiobarbituric reactive species (TBARS) were reduced in the amygdala and NAc, and the protein carbonyl content was reduced in the CPF. Superoxide dismutase (SOD) activity increased in the NAc after acute and chronic treatments. Catalase (CAT) activity increased in the PFC after acute treatment and in the NAc after acute and chronic treatments. The concentration of nitrite/nitrate was lower in the CPF after chronic treatment. These results corroborate the antidepressant effect of quetiapine and indicate that quetiapine exhibits an antioxidant profile, a physiological mechanism that appears be involved in the therapeutic function of quetiapine in individuals resistant to classical antidepressant treatments.

Ketamine upregulates eNOS expression in human astroglial A172 cells: Possible role in its antidepressive properties

Ketamine is a potent anti-depressive agent. Nitric oxide plays an essential role in neuronal transmission and cerebral blood flow and has been implicated in the pathophysiology of major depressive disorder as well as cardiovascular functioning. We investigated the effect of ketamine on eNOS expression in human A172 astroglial cells. Ketamine (50-500μM) increased eNOS expression at 4-24h in a concentration-dependent manner. This effect was mediated by NMDA receptor, Akt inhibition and ERK1/2 activation and was synergistically augmented by rapamycin. The combined effect on the vascular, immune and neuronal systems may be relevant to the rapid antidepressive effect of ketamine.

Antinociceptive and Anti-Inflammatory Effects of Ketamine and the Relationship to Its Antidepressant Action and GSK3 Inhibition

Ketamine (KET), a NMDA antagonist, exerts an antidepressant effect at subanaesthetic doses and possesses analgesic and anti-inflammatory activities. We evaluated the involvement of KET antinociceptive and anti-inflammatory effects with its antidepressant action. Male Swiss mice were subjected to formalin, carrageenan-induced paw oedema and forced swimming tests, for assessing antinociceptive, anti-inflammatory and antidepressant effects. The treatment groups were as follows: control, KET (2, 5 and 10 mg/kg), lithium (LI: 5 mg/kg) and KET2 + LI5 combination. Immunohistochemistry analyses (TNF-α, iNOS, COX-2 and GSK3) in oedematous paws were performed. KET5 and KET10 reduced licking times in neurogenic (22 and 38%) and inflammatory (67 and 78%) phases of the formalin test, respectively, as related to controls. While LI5 inhibited the second phase by 24%, the licking time was inhibited by 26 and 59% in the KET2 + LI5 group (first and second phases). Furthermore, oedema volumes were reduced by 37 and 45% in the KET5 and KET10 groups, respectively. Oedema reductions were 29% in the LI5 group and 48% in the KET2 + LI5 group. In the forced swimming test, there were 23, 38 and 53% decreases in the immobility time in KET2, KET5 and KET10 groups, respectively. While LI5 caused no significant effect, decreases of 52% were observed with KET2 + LI5. KET also decreased TNF-α, iNOS, COX-2 and GSK3 immunostainings in oedematous paws, effects intensified with KET2 + LI5. We showed that KET presents antinociceptive and anti-inflammatory effects associated with its antidepressant response. Furthermore, our results indicate the close involvement of GSK3 inhibition and blockade of inflammatory responses, in the antidepressant drug effect.

Enriched Flavonoid Fraction from Cecropia pachystachya Trécul Leaves Exerts Antidepressant-like Behavior and Protects Brain Against Oxidative Stress in Rats Subjected to Chronic Mild Stress

The purpose of this study was to assess the effect of an enriched C-glycosyl flavonoids fraction (EFF-Cp) from Cecropia Pachystachya leaves on behavior, mitochondrial chain function, and oxidative balance in the brain of rats subjected to chronic mild stress. Male Wistar rats were divided into experimental groups (saline/no stress, saline/stress, EFF-Cp/no stress, and EFF-Cp/stress). ECM groups were submitted to stress for 40 days. On the 35th ECM day, EFF-Cp (50 mg/kg) or saline was administrated and the treatments lasted until the 42nd day. On the 41st and 42nd days, the animals were submitted to the splash test and the forced swim test. After these behavioral tests, the enzymatic activity of mitochondrial chain complexes and oxidative stress were analyzed. EFF-Cp reversed the depressive-like behavior induced by ECM. It also reversed the increase in thiobarbituric acid reactive species, myeloperoxidase activity, and nitrite/nitrate concentrations in some brain regions. The reduced activities of the antioxidants superoxide dismutase and catalase in some brain regions were also reversed by EFF-Cp. The most pronounced effect of EFF-Cp on mitochondrial complexes was an increase in complex IV activity in all studied regions. Thus, it is can be concluded that EFF-Cp exerts an antidepressant-like effect and that oxidative balance may be an important physiological process underlying these effects.

Ketamine-an update on its clinical uses and abuses

This review highlights the recent clinical research that supports the therapeutic utility of ketamine as a multifaceted drug. After long-term use as a dissociative anesthetic, it has re-emerged as a useful agent for ameliorating pain, asthmaticus, and depression. In addition, it is also a substance of abuse. Chronic ketamine abuse over prolonged periods (weeks, months, and years) can produce toxicity to the gastrointestinal and urinary tract. In this review, we described the recent progress on its clinical uses and abuses.

Antidepressant-like effects induced by NMDA receptor blockade and NO synthesis inhibition in the ventral medial prefrontal cortex of rats exposed to the forced swim test

RATIONALE

Systemic treatment with NMDA receptor (NMDAR) antagonists, inhibitors of neuronal nitric oxide synthase (nNOS) or of soluble guanylyl cyclase (sGC), induce antidepressant-like effects in rats. Increased levels of glutamate and nitric oxide (NO) in the medial prefrontal cortex (MPFC) of stressed animals have been described in the literature. However, the role of the NMDAR-nNOS-sGC pathway of the MPFC in the mediation of forced swim-induced behaviors remains unclear.

OBJECTIVE

The aim of this work was to test the hypothesis that the inhibition of the NMDAR-nNOS-sGC pathway in the ventral MPFC (infralimbic (IL) or prelimbic (PL)) would elicit antidepressant-like effects in the forced swim test (FST).

METHODS

Rats implanted with cannulae aimed at the PL or the IL were exposed to the FST and injected with LY235959 (NMDAR antagonist), NPA (nNOS inhibitor), ODQ (sGC inhibitor), or carboxy-PTIO (NO scavenger). Additional groups received the AMPA antagonist, NBQX, before the effective doses of LY235959 or NPA.

RESULTS

LY235959 administration into PL or IL before the FS pretest produced no effects. Administration of LY235959 (3 and 10 nmol/0.2 μL) after pretest was effective only when administered into the PL. However, the administration of NPA (0.01 nmol/0.2 μL), c-PTIO (1.0 nmol/0.2 μL), and ODQ (1.0 nmol/0.2 μL) into the PL or IL before the FST produced antidepressant-like effects. NBQX blocked the antidepressant-like effect of LY235959 but not of NPA.

CONCLUSION

Blocking NMDAR or NO signaling in the vMPFC, either in the IL or the PL, induces antidepressant-like effects in the rat FST. These effects seemingly occur through independent mechanisms, since NBQX blocked the former effect but not the latter.

Nitric oxide involvement in the antidepressant-like effect of ketamine in the Flinders sensitive line rat model of depression

OBJECTIVE

We investigated whether the nitric oxide (NO) precursor, L-arginine, can prevent the antidepressant-like action of the fast-acting antidepressant, ketamine, in a genetic rat model of depression, and/or induce changes in the glutamate (Glu)/N-methyl-D-aspartate receptor (NMDAR)/NO/cyclic guanosine monophosphate (cGMP) signalling pathway. Hereby it was evaluated whether the NO signalling system is involved in the antidepressant mechanism of ketamine.

METHODS

Flinders sensitive line (FSL) rats received single i.p. injections of ketamine (15 mg/kg) with/without pre-treatment (30 min prior) with L-arginine (500 mg/kg). Depression-like behaviour was assessed in the forced swim test (FST) in terms of immobility, and the activation state of the Glu/NMDAR/NO/cGMP pathway was evaluated ex vivo in the frontal cortex and hippocampus regions in terms of total constitutive NOS (cNOS) activity and cGMP concentration.

RESULTS

L-Arginine pre-treatment prevented the antidepressant-like effect of ketamine in the FST, as well as a ketamine-induced increase in cGMP levels in the frontal cortex and hippocampus of FSL rats. Ketamine reduced cNOS activity only in the hippocampus, and this effect was not reversed by L-arginine.

CONCLUSION

Both the behavioural and molecular results from this study indicate an involvement for the NO signalling pathway in the antidepressant action of ketamine. Although not easily interpretable, these findings broaden our knowledge of effects of ketamine on the NO system.

Antidepressant-like effect of nitric oxide synthase inhibitors and sildenafil against lipopolysaccharide-induced depressive-like behavior in mice

Inflammation, oxidative and nitrosative stress underlie depression being assessed in rodents by the systemic administration of lipopolysacharide (LPS). There is an increasing body of evidence of an involvement of nitric oxide (NO) pathway in depression, but this issue was not investigated in LPS-induced model. Thus, herein we evaluated the effects of NO-pathway-modulating drugs, named aminoguanidine, l-NAME, sildenafil and l-arginine, on the behavioral (forced swimming test [FST], sucrose preference [SPT] and prepulse inhibition [PPI] of the startle) and neurochemical (glutathione [GSH], lipid peroxidation, IL-1β) alterations in the prefrontal cortex, hippocampus and striatum as well as in BDNF levels in the hippocampus 24h after LPS (0.5mg/kg, i.p.) administration, a time-point related to depressive-like behavior. Twenty-four hours post LPS there was an increase in immobility time in the FST, decrease in sucrose preference and PPI levels accompanied by a decrease in GSH levels and an increase in lipid peroxidation, IL-1β and hippocampal BDNF levels suggestive of a depressive-like state. The pretreatment with the NOS inhibitors, l-NAME and aminoguanidine as well as sildenafil prevented the behavioral and neurochemical alterations induced by LPS, although sildenafil and l-NAME were not able to prevent the increase in hippocampal BDNF levels induced by LPS. The iNOS inhibitor, aminoguanidine, and imipramine prevented all behavioral and neurochemical alterations induced by LPS. l-arginine did not prevent the alterations in immobility time, sucrose preference and GSH induced by LPS. Taken together our results show that the NO-cGMP pathway is important in the modulation of the depressive-like alterations induced by LPS.

The activation of adenosine monophosphate-activated protein kinase in rat hippocampus contributes to the rapid antidepressant effect of ketamine

Recent studies have shown a rapid, robust, and lasting antidepressant effect of ketamine that makes ketamine a promising antidepressant drug. However, the mechanisms underlying this rapid antidepressant effect remain incompletely understood. The goal of the present study was to determine whether adenosine monophosphate-activated protein kinase (AMPK) was involved in ketamine's rapid antidepressant effect during the forced swimming test (FST). In the first stage of experiment, a lower level of phosphorylated form of AMPK (p-AMPK) in the hippocampus and a longer immobility time were observed in the depressed rats during FST; whereas ketamine reversed these changes at 30min after the administration. In the second stage of experiment, we observed that, ketamine up-regulated the levels of p-AMPK and brain-derived neurotrophic factor (BDNF) in the hippocampus of the depressed rats. Moreover, AMPK agonist strengthened the antidepressant effect of ketamine with an up-regulation of BDNF, while AMPK antagonist attenuated the antidepressant effect of ketamine with a down-regulation of BDNF. In conclusion, our results suggest that the activation of AMPK in rat hippocampus is involved in the procedure of ketamine exerting rapid antidepressant effect through the up-regulation of BDNF.