BDNF-TrkB signaling in the nucleus accumbens shell of mice has key role in methamphetamine withdrawal symptoms

The Effectiveness of Mindfulness in the Treatment of Methamphetamine Addiction Symptoms: Does Neuroplasticity Play a Role?

INTRODUCTION

Methamphetamine is a highly stimulating psychoactive drug that causes life-threatening addictions and affects millions of people around the world. Its effects on the brain are complex and include disturbances in the neurotransmitter systems and neurotoxicity. There are several known treatment methods, but their effectiveness is moderate. It must be emphasised that no drugs have been approved for treatment. For this reason, there is an urgent need to develop new, effective, and safe treatments for methamphetamine. One of the potential treatments is mindfulness meditation. In recent years, this technique has been researched extensively in the context of many neurological and psychiatric disorders.

METHODS

This review explores the use of mindfulness in the treatment of methamphetamine addiction. Searches were conducted in the PubMed/Medline, Research Gate, and Cochrane databases.

RESULTS

Ten studies were identified that used mindfulness-based interventions in the treatment of methamphetamine addiction. The results show that mindfulness is an effective form of reducing hunger, risk of relapses, stress indicators, depression, and aggression, alone or in combination with transcranial direct current stimulation (tDCS). Mindfulness also improved the cognitive function in addicts. The included studies used only behavioural measures. The potential mechanisms of mindfulness in addiction were explained, and it was proposed that it can induce neuroplasticity, alleviating the symptoms of addiction.

CONCLUSIONS

Evidence from the studies suggest that mindfulness may be an effective treatment option for methamphetamine addiction, used alone or in combination with tDCS. However, further high-quality research is required to establish the role of this treatment option in this field. The use of neuroimaging and neurophysiological measures is fundamental to understand the mechanisms of mindfulness.

Esketamine mitigates cognitive impairment following exposure to LPS by modulating the intestinal flora/subdiaphragmatic vagus nerve/spleen axis

INTRODUCTION

Susceptibility to secondary infection often increases after primary infection. Secondary infections can lead to more severe inflammatory injuries; however, the underlying mechanisms are not yet fully elucidated.

OBJECTIVE

To investigate whether esketamine treatment immediately after primary lipopolysaccharide (LPS) exposure could alleviate cognitive impairment caused by secondary infection.

METHODS

Mice were injected intraperitoneally (IP) with LPS (5 mg/kg) 10 days apart. Esketamine (10, 15, or 30 mg/kg) was administered IP immediately after the primary LPS injection. Splenectomy or subdiaphragmatic vagotomy (SDV) was performed 7 days before secondary LPS exposure or broad-spectrum antibiotic administration.

RESULTS

Splenomegaly was observed after the primary LPS injection on Days 3 and 10. Splenomegaly was attenuated by treatment with 30 mg/kg esketamine. Esketamine treatment prevented increased plasma proinflammatory cytokines levels and cognitive dysfunction induced by secondary LPS exposure. Mice that underwent splenectomy or SDV had lower proinflammatory cytokines levels, higher hippocampal brain-derived neurotrophic factor (BDNF) levels, and improved cognitive function 1 day after secondary infection, which was not further improved by esketamine. Fecal microbiota transplantation (FMT) from endotoxic mice treated with esketamine attenuated hippocampal BDNF downregulation and cognitive dysfunction only in pseudo germ-free (PGF) mice without splenectomy. FMT with fecal suspensions from esketamine-treated endotoxic mice abrogated splenomegaly only in PGF mice without SDV. Blocking BDNF signaling blocked esketamine's ameliorating effects on secondary LPS exposure-induced cognitive dysfunction.

CONCLUSION

The intestinal flora/subdiaphragmatic vagus nerve/spleen axis-mediated hippocampal BDNF downregulation significantly affected secondary LPS-induced systemic inflammation and cognitive dysfunction. Esketamine preserves cognitive function via this mechanism.

7,8-Dihydroxyflavone and Neuropsychiatric Disorders: A Translational Perspective from the Mechanism to Drug Development

7,8-Dihydroxyflavone (7,8-DHF) is a kind of natural flavonoid with the potential to cross the blood-brain barrier. 7,8-DHF effectively mimics the effect of brain-derived neurotrophic factor (BDNF) in the brain to selectively activate tyrosine kinase receptor B (TrkB) and downstream signaling pathways, thus playing a neuroprotective role. The preclinical effects of 7,8-DHF have been widely investigated in neuropsychiatric disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), depression, and memory impairment. Besides the effect on TrkB, 7,8-DHF could also function through fighting against oxidative stress, cooperating with estrogen receptors, or regulating intestinal flora. This review focuses on the recent experimental studies on depression, neurodegenerative diseases, and learning and memory functions. Additionally, the structural modification and preparation of 7,8-DHF were also concluded and proposed, hoping to provide a reference for the follow-up research and clinical drug development of 7,8-DHF in the field of neuropsychiatric disorders.

Cannabidiol inhibits methamphetamine-induced dopamine release via modulation of the DRD1-MeCP2-BDNF-TrkB signaling pathway

RATIONALE

Adaptive alteration of dopamine (DA) system in mesocorticolimbic circuits is an extremely intricate and dynamic process, which contributes to maintaining methamphetamine (METH)-related disorders. There are no approved pharmacotherapies for METH-related disorders. Cannabidiol (CBD), a major non-psychoactive constituent of cannabis, has received attention for its therapeutic potential in treating METH-related disorders. However, the major research obstacles of CBD are the yet to be clarified mechanisms behind its therapeutic potential. Recent evidence showed that DA system may be active target of CBD. CBD could be a promising dopaminergic medication for METH-related disorders.

OBJECTIVES

We investigated the role of the DA receptor D1 (DRD1)-methyl-CpG-binding protein 2 (MeCP2)-brain-derived neurotrophic factor (BDNF)-tyrosine receptor kinase B (TrkB) signaling pathway in DA release induced by METH. Investigating the intervention effects of CBD on the DRD1-MeCP2-BDNF-TrkB signaling pathway could help clarify the underlying mechanisms and therapeutic potential of CBD in METH-related disorders.

RESULTS

METH (400 μM) significantly increased DA release from primary neurons in vitro, which was blocked by CBD (1 μM) pretreatment. METH (400 μM) significantly increased the expression levels of DRD1, BDNF, and TrkB, but decreased the expression of MeCP2 in the neurons, whereas CBD (1 μM) pretreatment notably inhibited the protein changes induced by METH. In addition, DRD1 antagonist SCH23390 (10 μM) inhibited the DA release and protein change induced by METH in vitro. However, DRD1 agonist SKF81297 (10 μM) induced DA release and protein change in vitro, which was also blocked by CBD (1 μM) pretreatment. METH (2 mg/kg) significantly increased the DA level in the nucleus accumbens (NAc) of rats with activation of the DRD1-MeCP2-BDNF-TrkB signaling pathway, but these changes were blocked by CBD (40 or 80 mg/kg) pretreatment.

CONCLUSIONS

This study indicates that METH induces DA release via the DRD1-MeCP2-BDNF-TrkB signaling pathway. Furthermore, CBD significantly inhibits DA release induced by METH through modulation of this pathway.

Microglial ERK-NRBP1-CREB-BDNF signaling in sustained antidepressant actions of (R)-ketamine

(R,S)-ketamine elicits rapid-acting and sustained antidepressant actions in treatment-resistant patients with depression. (R)-ketamine produces longer-lasting antidepressant effects than (S)-ketamine in rodents; however, the precise molecular mechanisms underlying antidepressant actions of (R)-ketamine remain unknown. Using isobaric Tag for Relative and Absolute Quantification, we identified nuclear receptor-binding protein 1 (NRBP1) that could contribute to different antidepressant-like effects of the two enantiomers in chronic social defeat stress (CSDS) model. NRBP1 was localized in the microglia and neuron, not astrocyte, of mouse medial prefrontal cortex (mPFC). (R)-ketamine increased the expression of NRBP1, brain-derived neurotrophic factor (BDNF), and phosphorylated cAMP response element binding protein (p-CREB)/CREB ratio in primary microglia cultures thorough the extracellular signal-regulated kinase (ERK) activation. Furthermore, (R)-ketamine could activate BDNF transcription through activation of CREB as well as MeCP2 (methyl-CpG binding protein 2) suppression in microglia. Single intracerebroventricular (i.c.v.) injection of CREB-DNA/RNA heteroduplex oligonucleotides (CREB-HDO) or BDNF exon IV-HDO blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. Moreover, microglial depletion by colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX3397 blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. In addition, inhibition of microglia by single i.c.v. injection of mannosylated clodronate liposomes (MCLs) significantly blocked the antidepressant-like effects of (R)-ketamine in CSDS susceptible mice. Finally, single i.c.v. injection of CREB-HDO, BDNF exon IV-HDO or MCLs blocked the beneficial effects of (R)-ketamine on the reduced dendritic spine density in the mPFC of CSDS susceptible mice. These data suggest a novel ERK-NRBP1-CREB-BDNF pathways in microglia underlying antidepressant-like effects of (R)-ketamine.

Repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages prevents schizophrenia-relevant phenotypes in adult offspring after maternal immune activation: a role of TrkB signaling

Maternal immune activation (MIA) plays a role in the etiology of schizophrenia. MIA by prenatal exposure of polyinosinic:polycytidylic acid [poly(I:C)] in rodents caused behavioral and neurobiological changes relevant to schizophrenia in adult offspring. We investigated whether the novel antidepressant (R)-ketamine could prevent the development of psychosis-like phenotypes in adult offspring after MIA. We examined the effects of (R)-ketamine (10 mg/kg/day, twice weekly for 4 weeks) during juvenile and adolescent stages (P28-P56) on the development of cognitive deficits, loss of parvalbumin (PV)-immunoreactivity in the medial prefrontal cortex (mPFC), and decreased dendritic spine density in the mPFC and hippocampus from adult offspring after prenatal poly(I:C) exposure. Furthermore, we examined the role of TrkB in the prophylactic effects of (R)-ketamine. Repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages significantly blocked the development of cognitive deficits, reduced PV-immunoreactivity in the prelimbic (PrL) of mPFC, and decreased dendritic spine density in the PrL of mPFC, CA3 and dentate gyrus of the hippocampus from adult offspring after prenatal poly(I:C) exposure. Furthermore, pretreatment with ANA-12 (TrkB antagonist: twice weekly for 4 weeks) significantly blocked the beneficial effects of (R)-ketamine on cognitive deficits of adult offspring after prenatal poly(I:C) exposure. These data suggest that repeated intermittent administration of (R)-ketamine during juvenile and adolescent stages could prevent the development of psychosis in adult offspring after MIA. Therefore, (R)-ketamine would be a potential prophylactic drug for young subjects with high-risk for psychosis.

Administration of brain-derived neurotrophic factor in the ventral tegmental area produces a switch from a nicotine nondependent D1R-mediated motivational state to a nicotine dependent-like D2R-mediated motivational state

Brain-derived neurotrophic factor (BDNF) has been implicated in the transition from a nondependent motivational state to a drug-dependent and -withdrawn motivational state. Chronic nicotine can increase BDNF in the rodent brain and is associated with smoking severity in humans; however, it is unknown whether this increased BDNF is linked functionally to the switch from a nicotine-nondependent to a nicotine-dependent state. We used a place conditioning paradigm to measure the conditioned responses to nicotine, showing that a dose of acute nicotine that nondependent male mice find aversive is found rewarding in chronic nicotine-treated mice experiencing withdrawal. A single BDNF injection in the ventral tegmental area (in the absence of chronic nicotine treatment) caused mice to behave as if they were nicotine-dependent and in withdrawal, switching the neurobiological substrate mediating the conditioned motivational effects from dopamine D1 receptors to D2 receptors. Quantification of gene expression of BDNF and its receptor, tropomyosin-receptor-kinase B (TrkB), revealed an increase in TrkB mRNA but not BDNF mRNA in the VTA in nicotine-dependent and -withdrawn mice. These results suggest that BDNF signaling in the VTA is a critical neurobiological substrate for the transition to nicotine dependence. The modulation of BDNF signaling may be a promising new pharmacological avenue for the treatment of addictive behavior.

RhANP attenuates endotoxin-derived cognitive dysfunction through subdiaphragmatic vagus nerve-mediated gut microbiota-brain axis

BACKGROUND

Atrial natriuretic peptide (ANP) secreted from atrial myocytes is shown to possess anti-inflammatory, anti-oxidant and immunomodulatory effects. The aim of this study is to assess the effect of ANP on bacterial lipopolysaccharide (LPS)-induced endotoxemia-derived neuroinflammation and cognitive impairment.

METHODS

LPS (5 mg/kg) was given intraperitoneally to mice. Recombinant human ANP (rhANP) (1.0 mg/kg) was injected intravenously 24 h before and/or 10 min after LPS injection. Subdiaphragmatic vagotomy (SDV) was performed 14 days before LPS injection or 28 days before fecal microbiota transplantation (FMT). ANA-12 (0.5 mg/kg) was administrated intraperitoneally 30 min prior to rhANP treatment.

RESULTS

LPS (5.0 mg/kg) induced remarkable splenomegaly and an increase in the plasma cytokines at 24 h after LPS injection. There were positive correlations between spleen weight and plasma cytokines levels. LPS also led to increased protein levels of ionized calcium-binding adaptor molecule (iba)-1, cytokines and inducible nitric oxide synthase (iNOS) in the hippocampus. LPS impaired the natural and learned behavior, as demonstrated by an increase in the latency to eat the food in the buried food test and a decrease in the number of entries and duration in the novel arm in the Y maze test. Combined prophylactic and therapeutic treatment with rhANP reversed LPS-induced splenomegaly, hippocampal and peripheral inflammation as well as cognitive impairment. However, rhANP could not further enhance the protective effects of SDV on hippocampal and peripheral inflammation. We further found that PGF mice transplanted with fecal bacteria from rhANP-treated endotoxemia mice alleviated the decreased protein levels of hippocampal polyclonal phosphorylated tyrosine kinase receptor B (p-TrkB), brain-derived neurotrophic factor (BDNF) and cognitive impairment, which was abolished by SDV. Moreover, TrkB/BDNF signaling inhibitor ANA-12 abolished the improving effects of rhANP on LPS-induced cognitive impairment.

CONCLUSIONS

Our results suggest that rhANP could mitigate LPS-induced hippocampal inflammation and cognitive dysfunction through subdiaphragmatic vagus nerve-mediated gut microbiota-brain axis.

Alleviation of Methamphetamine Sensitization by Partially Lesioning Dopaminergic Terminals with 6-Hydroxydopamine in Nucleus Accumbens

Amphetamine-type stimulants have become important and popular abused drugs worldwide. Methamphetamine (Meth) sensitization, characterized by a progressive increase in behavioral responses after repeated administration, has been reported in rodents and patients. This behavioral effect has been used as a laboratory model to study drug addiction and schizophrenia. The mesolimbic dopaminergic pathway plays a significant role in the development of Meth behavioral sensitization. Previous studies have reported that the ablation of nucleus accumbens (NAc) by electrolytic or thermal lesioning attenuates addictive behavior to opioids in animals. However, these studies were only conducted in opioid addictive rodents. Furthermore, these ablation procedures also damaged the non-dopaminergic neurons and fibers passing through the NAc. The purpose of this study was to examine the therapeutic effect of NAc lesioning by a selective dopaminergic toxin in Meth-sensitized animals. Adult mice received repeated administration of Meth for 7 days. Open-field locomotor activity and stereotype behavior were significantly increased after Meth treatment, suggesting behavior sensitization. A partial lesion of dopaminergic terminals was made through stereotaxic administration of dopaminergic toxin 6-hydroxydopamine (6-OHDA) to the NAc in the Meth -sensitized mice. Meth behavioral sensitization was significantly antagonized after the lesioning. Brain tissue was collected for qRT-PCR analysis. Repeated administration of Meth increased the expression of tyrosine hydroxylase (TH), BDNF, and Shati, a marker for Meth sensitization, in the NAc. Treatment with 6-OHDA significantly antagonized the upregulation of TH and Shati. Taken together, these data suggest that local administration of 6-OHDA mitigated Meth sensitization in chronic Meth-treated animals. Our data support a new surgical treatment strategy for Meth abuse.

Tetrahydropalmatine Regulates BDNF through TrkB/CAM Interaction to Alleviate the Neurotoxicity Induced by Methamphetamine

Tetrahydropalmatine (THP) has analgesic, hypnotic, sedative, and other pharmacological effects. Brain-derived neurotrophic factor (BDNF) plays an important role in neuronal plasticity, growth, and development. However, their mechanism of action in methamphetamine (MA)-induced neurotoxicity remains unclear. This study aims to explore the important role of BDNF in MA neurotoxicity and whether THP can regulate BDNF through the interaction between tyrosine kinase receptor B (TrkB)/calmodulin (CAM) to alleviate the neurotoxicity induced by MA. SD rats were randomly divided into control, MA, and MA + THP groups. Stereotyped behavior test, captive rejection test, open field test (OFT), and Morris water maze (MWM) were used to evaluate the anxiety, aggression, cognition, learning, and memory. Extracted hippocampus and mesencephalon tissue were detected by Western blot, HE staining, and immunohistochemistry. TUNEL staining was used to detect apoptosis. MOE was used for bioinformatics prediction, and coimmunoprecipitation was used to confirm protein interactions. Long-term abuse of MA resulted in lower weight gain ratio and nerve cell damage and caused various neurotoxicity-related behavioral abnormalities: anxiety, aggression, cognitive motor disorders, and learning and memory disorders. MA-induced neurotoxicity is related to the down-regulation of BDNF and apoptosis. THP attenuated the MA-induced neurotoxicity by decreasing CAM, increasing TrkB, phosphorylating Akt, up-regulating NF-κB and BDNF, and inhibiting cell apoptosis. MA can induce neurotoxicity in rats. BDNF may play a vital role in MA-induced neurotoxicity. THP regulates BDNF through TrkB/CAM interaction to alleviate the neurotoxicity induced by MA. THP may be a potential therapeutic drug for the neurotoxic and neurodegenerative diseases related to MA.

Intranasal administration of transforming growth factor-β1 elicits rapid-acting antidepressant-like effects in a chronic social defeat stress model: A role of TrkB signaling

(R,S)-ketamine causes rapid-acting and sustained antidepressant effects in treatment-resistant patients with depression although the precise molecular mechanisms underlying its antidepressant action remain unclear. We recently reported that transforming growth factor (TGF)-β1 might contribute to the antidepressant-like effects of (R)-ketamine that is a more potent enantiomer in rodents. Although TrkB signaling plays a role in the antidepressant-like actions of (R,S)-ketamine and its enantiomers, the role of TrkB signaling in the antidepressant effects of TGF-β1 remains unclear. Using behavioral tests such as tail-suspension test (TST), forced swimming test (FST), and 1% sucrose preference test (SPT), we investigated whether a single intranasal administration of the recombinant TGF-β1 (1.5 and 3.0 μg/kg) causes rapid and sustained antidepressant-like effects in a chronic social defeat stress (CSDS) model. Both doses of TGF-β1 significantly attenuated the increased immobility time of TST and FST in the CSDS susceptible mice. High dose of TGF-β1, but not low dose, significantly ameliorated the decreased sucrose preference of SPT in the CSDS susceptible mice. Pretreatment with a TrkB antagonist ANA-12 (0.5 mg/kg) blocked the antidepressant-like effects of TGF-β1 in CSDS susceptible mice. The data suggest that intranasal administration of TGF-β1 could elicit rapid-acting antidepressant-like effects via TrkB stimulation in a CSDS model. Therefore, it is likely that intranasal administration of TGF-β1 would be a novel therapeutic approach for depression.

Olfactory learning and memory in the greater short-nosed fruit bat Cynopterus sphinx: the influence of conspecifics distress calls

This study was designed to test whether Cynopterus sphinx distress calls influence olfactory learning and memory in conspecifics. Bats were exposed to distress calls/playbacks (PBs) of distress calls/modified calls and were then trained to novel odors. Bats exposed to distress calls/PBs made significantly fewer feeding attempts and bouts of PBs exposed to modified calls, which significantly induced the expression of c-Fos in the caudomedial neostriatum (NCM) and the amygdala compared to bats exposed to modified calls and trained controls. However, the expression of c-Fos in the hippocampus was not significantly different between the experimental groups. Further, protein phosphatase-1 (PP-1) expression was significantly lower, and the expression levels of E1A homologue of CREB-binding protein (CBP) (P300), brain-derived neurotrophic factor (BDNF) and its tyrosine kinase B1 (TrkB1) receptor were significantly higher in the hippocampus of control/bats exposed to modified calls compared to distress calls/PBs of distress call-exposed bats. Exposure to the call possibly alters the reciprocal interaction between the amygdala and the hippocampus, accordingly regulating the expression levels of PP1, P300 and BDNF and its receptor TrkB1 following training to the novel odor. Thus, the learning and memory consolidation processes were disrupted and showed fewer feeding attempts and bouts. This model may be helpful for understanding the contributions of stressful social communications to human disorders.

Levo-tetrahydropalmatine: A new potential medication for methamphetamine addiction and neurotoxicity

Levo-tetrahydropalmatine (l-THP) is mainly derived from the dried tuber of the Papaveraceae plant Corydalis, also called Corydalis B, which is a drug with analgesic, hypnotic, sedative and other effects. Methamphetamine (METH) belongs to the central nervous stimulant and is a highly addictive drug. It is an urgent problem to study the mechanism of methamphetamine neurotoxicity and to search for the therapeutic targets of the METH addiction. This review is aimed to discuss the pharmacological mechanism and the protective effects of l-THP on METH-induced neurotoxicity, and to explore the therapeutic prospects of l-THP for METH addiction to provide an innovative application of l-THP in clinic. It was found that exposure to METH leads to the compulsive drug-seeking and drug-taking behavior, which is ultimately resulted in METH addiction and neurotoxicity. L-THP has the inhibitory effects on the incidence, maintenance and relapse of METH addiction. L-THP can effectively enhance the plasticity of nerve cells and improve the function of nerve cells where brain-derived neurotrophic factor (BDNF) and its pathways play a protective role. Therefore, l-THP has the potential to become an important therapeutic drug for METH addiction and neurotoxicity.

Suggesting 7,8-dihydroxyflavone as a promising nutraceutical against CNS disorders

7,8-dihydroxyflavone (DHF), a naturally-occurring plant-based flavone, is a high-affinity tyrosine kinase receptor B (TrkB) agonist and a bioactive molecule of therapeutic interest for neuronal survival, differentiation, synaptic plasticity and neurogenesis. In the family of neurotrophic factors, this small BDNF-mimetic molecule has attracted considerable attention due to its oral bioavailability and ability to cross the blood-brain barrier. Recent evidences have shed light on the neuroprotective role of this pleiotropic flavone against several neurological disorders, including Alzheimer's disease, Parkinson's disease, cerebral ischemia, Huntington's disease, and other CNS disorders. DHF also elicits potent protective actions against toxins-induced insults to brain and neuronal cells. DHF shows promising anti-oxidant and anti-inflammatory properties in ameliorating the neurodegenerative processes affecting the CNS. This review provides an overview of the significant neuroprotective potentials of DHF and discusses how it exerts its multitudinous beneficial effects by modulating different pathways linked with the pathophysiology of CNS disorders, and thus proposes it to be a nutraceutical against a broad spectrum of neurological disorders.

Dextran sulfate sodium-induced inflammation and colitis in mice are ameliorated by (R)-ketamine, but not (S)-ketamine: A role of TrkB signaling

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that causes long-lasting inflammation and colitis in the gastrointestinal tract. Depression is a common symptom in patients with UC. (R)-ketamine is a new safer antidepressant than (R,S)-ketamine and (S)-ketamine. Here, we examined the effects of two ketamine enantiomers on the dextran sulfate sodium (DSS)-induced colitis model of UC. Ingestion of 3% DSS in drinking water for 14 days increased the scores of Disease Activity Index (DAI) in mice. Repeated administration of (R)-ketamine (10 mg/kg/day, 14 days or last 7 days), but not (S)-ketamine (10 mg/kg/day, 14 days or last 7 days), significantly ameliorated the increased DAI score and increased blood levels of interleukin-6 (IL-6) in DSS-treated mice. In addition, (R)-ketamine, but not (S)-ketamine, attenuated the reduced colonic length in DSS-treated mice. Furthermore, DSS-induced increased DAI score and blood IL-6 levels were significantly ameliorated after subsequent repeated administration of (R)-ketamine (10 mg/kg/day for last 7 days), but not 5-aminosalicyclic acid (50 mg/kg/day for last 7 days). Moreover, the pretreatment with a tropomyosin-receptor-kinase B (TrkB) antagonist ANA-12 (0.5 mg/kg) significantly blocked the beneficial effects of (R)-ketamine in DSS-induced UC model. The study shows that (R)-ketamine can produce beneficial effects in DSS-induced colitis model through TrkB stimulation. Therefore, (R)-ketamine may be a novel therapeutic drug for inflammatory bowel diseases such as UC.

Rapid-acting and long-lasting antidepressant-like action of (R)-ketamine in Nrf2 knock-out mice: a role of TrkB signaling

The transcription nuclear factor-erythroid factor 2-related factor 2 (Nrf2) plays a key role in inflammation that is involved in depression. We previously reported that Nrf2 knock-out (KO) mice exhibit depression-like phenotypes through systemic inflammation. (R)-ketamine, an enantiomer of ketamine, has rapid-acting and long-lasting antidepressant-like effects in rodents. We investigated whether (R)-ketamine can produce antidepressant-like effects in Nrf2 KO mice. Effects of (R)-ketamine on the depression-like phenotypes in Nrf2 KO mice were examined. Furthermore, the role of TrkB in the antidepressant-like actions of (R)-ketamine was also examined. In the tail-suspension test (TST) and forced swimming test (FST), (R)-ketamine (10 mg/kg) significantly attenuated the increased immobility times of TST and FST in the Nrf2 KO mice. In the sucrose preference test (SPT), (R)-ketamine significantly ameliorated the reduced preference of SPT in Nrf2 KO mice. Decreased expression of synaptic proteins (i.e., GluA1 and PSD-95) in the medial prefrontal cortex (mPFC) of Nrf2 KO mice was significantly ameliorated after a single injection of (R)-ketamine. Furthermore, the pre-treatment with the TrkB antagonist ANA-12 (0.5 mg/kg) significantly blocked the rapid and long-lasting antidepressant-like effects of (R)-ketamine in Nrf2 KO mice. Furthermore, ANA-12 significantly antagonized the beneficial effects of (R)-ketamine on decreased expression of synaptic proteins in the mPFC of Nrf2 KO mice. These findings suggest that (R)-ketamine can produce rapid and long-lasting antidepressant-like actions in Nrf2 KO mice via TrkB signaling.

Nutritional Ketosis as a Potential Treatment for Alcohol Use Disorder

Alcohol use disorder (AUD) is a chronic, relapsing brain disorder, characterized by compulsive alcohol seeking and disrupted brain function. In individuals with AUD, abstinence from alcohol often precipitates withdrawal symptoms than can be life threatening. Here, we review evidence for nutritional ketosis as a potential means to reduce withdrawal and alcohol craving. We also review the underlying mechanisms of action of ketosis. Several findings suggest that during alcohol intoxication there is a shift from glucose to acetate metabolism that is enhanced in individuals with AUD. During withdrawal, there is a decline in acetate levels that can result in an energy deficit and could contribute to neurotoxicity. A ketogenic diet or ingestion of a ketone ester elevates ketone bodies (acetoacetate, β-hydroxybutyrate and acetone) in plasma and brain, resulting in nutritional ketosis. These effects have been shown to reduce alcohol withdrawal symptoms, alcohol craving, and alcohol consumption in both preclinical and clinical studies. Thus, nutritional ketosis may represent a unique treatment option for AUD: namely, a nutritional intervention that could be used alone or to augment the effects of medications.

BDNF receptor antagonism during the induction of morphine dependence exacerbates the severity of physical dependence and ameliorates psychological dependence in rats

This study examined the effects of systemic administration of the TrkB receptor antagonist (ANA-12) during induction of morphine dependence on the severity of physical and psychological dependence and the cerebrospinal fluid (CSF) BDNF levels in morphine-dependent and withdrawn rats. Rats became morphine-dependent by increasing daily doses of morphine for 7 days, along with ANA-12 injection. Then, rats were tested for the severity of physical dependence on morphine (spontaneous withdrawal signs), anxiety-like (the elevated plus maze), depressive-like (sucrose preference test) behaviors after spontaneous morphine withdrawal. Also, the CSF BDNF levels were assessed 2 h after the last dose of morphine and day 13 after morphine withdrawal in morphine-dependent and withdrawn rats. We found that the morphine withdrawal signs were significantly higher in morphine dependent rats receiving ANA-12 on days of 5-7 after morphine withdrawal, also ANA-12 exacerbated overall dependence severity. While, the percentage of time spent in the open arms and sucrose preference were higher in morphine-dependent rats receiving ANA-12 than morphine-dependent rats receiving saline. Also, the ANA-12 injection decreased the CSF BDNF levels following morphine dependence, while increased it after morphine withdrawal. We conclude that the ANA-12 exacerbated the severity of physical morphine dependence but attenuated the anxiety/depressive-like behaviors in morphine-dependent and withdrawn rats. Also, ANA-12 injection was able to reverse the changes in the CSF BDNF levels. Therefore, ANA-12 is not more likely to complete treatment for opiate addiction.

Astragaloside IV improves neurobehavior and promotes hippocampal neurogenesis in MCAO rats though BDNF-TrkB signaling pathway

Astragaloside IV (AST) as the main active ingredient of Astragalus membranaceus. Clinical and laboratory-based studies have demonstrated the effects of AST on cerebral protection and angiogenesis after ischemia stroke. In addition, several reports investigated the effect of AST on proliferation of neural stem cells. The current study was aimed to evaluate the influence of AST on neurogenesis in hippocampal dentate gyrus (DG) of MCAO rats and to explore the possible mechanisms. In this study, the neurobehavioral tests (Ludmila Belayev 12-point scoring, Screen test, fore limb placing test) had been employed to investigate the effect of AST treatment against functional deficit of MCAO rats. The immunofluorescence staining, western-blot and qRT-PCR was performed to evaluate the effects of AST on proliferation, differentiation and maturity of neural stemr cells in hippocampus. Moreover, we investigated the possible mechanism of the AST treatment in promoting neurogenesis after ischemic stroke. The findings indicated that AST treatment ameliorated the neurobehavior of MCAO rats. The results indicated that AST treatment possessed the potential to improve proprioceptive sense and motor function of MCAO rats. AST treatment sustained neuronal viability and stimulates sensorimotor integration functional recovery in MCAO rats. The results suggested that AST improved neurobehavior deficit after ischemic stroke. Furthermore, AST promoted neurogenesis through upregulating the expressing of BNDF/TrkB signaling pathway. Therefore AST might be a promising therapeutic agent for ischemic stroke.

Neuroprotective and neuro-survival properties of safinamide against methamphetamine-induced neurodegeneration: Hypothetic possible role of BDNF/TrkB/PGC-1α signaling pathway and mitochondrial uncoupling protein -2(UCP-2)

Methamphetamine is a behavioral psychostimulant that has a high potential for misuse and induction of neurotoxicity. Safinamide is a novel inhibitor of monoamine oxidase B (MAOB) with neuroprotective properties. Methamphetamine abuse causes dysfunction in the respiratory chain of the mitochondria, but the specific signaling mechanism and role of the uncoupling protein-2(UCP-2) remain unclear. As we know, some indirect evidence indicates that neurodegeneration can be caused by inhibition of the brain-derived neurotrophic factor (BDNF) receptor, TrkB and its downstream signaling pathway, such as the PGC-1α protein. Neuroprotective strategies and approaches to the management, treatment or prevention of methamphetamine-induced neurodegeneration by modulating BDNF / TrkB / PGC-1α-UCP-2 can be considered as novel therapeutic approaches to these psychostimulant neurochemical and neurobehavioral approaches. Previous studies have shown that safinamide, a monoamine oxidase-B (MAOB) inhibitor, can function as a neuroprotective agent and inhibit the neurodegenerative process especially in Parkinson's disease but its impact on other neurodegenerative processes and drug-induced neurotoxicity remain unclear. Although there is some evidence that BDNF / TrkB / PGC-1α-UCP-2 signaling pathway and mitochondrial UCP-2 mediated safinamide induced neuroprotection but it's exact and precise mechanism of action and neuroprotective effects in neurodegenerative disorder and the protective properties against methamphetamine induced neurodegeneration and the role of BDNF / TrkB / PGC-1α signaling pathway and role of mitochondrial UCP-2 in this process have not yet been clarified. Therefore, in subjects addicted to methamphetamine, we hypothesized that safinamide will provide neuroprotection against methamphetamine-prompted neurodegeneration, and it appears that BDNF / TrkB / PGC-1α signaling pathway and mitochondrial UCP-2 are likely to play a critical role.

Neurochemical and behavioral comparisons of contingent and non-contingent methamphetamine exposure following binge or yoked long-access self-administration paradigms

RATIONALE

Abuse of the psychostimulant methamphetamine (METH) can cause long-lasting damage to brain monoaminergic systems and is associated with profound mental health problems for users, including lasting cognitive impairments. Animal models of METH exposure have been useful in dissecting the molecular effects of the drug on cognition, but many studies use acute, non-contingent "binge" administrations of METH which do not adequately approximate human METH use. Long-term METH exposure via long-access (LgA) self-administration paradigms has been proposed to more closely reflect human use and induce cognitive impairments.

OBJECTIVE

To better understand the role of contingency and patterns of exposure in METH-induced cognitive impairments, we analyzed behavioral and neurochemical outcomes in adult male rats, comparing non-contingent "binge" METH administration with contingent (LgA) METH self-administration and non-contingent yoked partners.

RESULTS

Binge METH (40 mg/kg, i.p., over 1 day) dramatically altered striatal and hippocampal dopamine, DOPAC, 5-HT, 5-HIAA, BDNF, and TrkB 75 days after drug exposure. In contrast, 6-h LgA METH self-administration (cumulative 24.8-48.9 mg METH, i.v., over 16 days) altered hippocampal BDNF in both contingent and yoked animals but reduced striatal 5-HIAA in only contingent animals. Neurochemical alterations following binge METH administration were not accompanied by cognitive deficits in Morris water maze, novel object recognition, or Y-maze tests. However, contingent LgA METH self-administration resulted in impaired spatial memory in the water maze.

CONCLUSIONS

Overall, substantial differences in neurochemical markers between METH exposure and self-administration paradigms did not consistently translate to deficits in cognitive tasks, highlighting the complexity of correlating METH-induced neurochemical changes with cognitive outcomes.

Isoliquiritigenin Attenuates Anxiety-Like Behavior and Locomotor Sensitization in Rats after Repeated Exposure to Nicotine

As important components of positive and negative reinforcement, locomotor sensitization and withdrawal anxiety following repeated exposure to nicotine (NIC) constitute crucial risk factors for relapse to NIC use after abstinence. Glycyrrhiza radix (G. radix), an important tonic used in traditional Oriental medicine, has not only anxiolytic effects but also reduces NIC-induced locomotor sensitization. Isoliquiritigenin (ISL), a bioactive ingredient of G. radix, also exhibits neuropharmacological effects, including anxiolytic action. Previously, we reported that ISL suppressed cocaine-induced extracellular dopamine release in the nucleus accumbens shell (NaccSh) and attenuated methamphetamine-induced neurotoxicity. The present study was performed to evaluate the effects of ISL on both NIC withdrawal anxiety and locomotor sensitization. Adult male rats received subcutaneous administration of NIC hydrogen tartrate (0.4 mg/kg, twice a day) for 7 days followed by 4 days of withdrawal. During the period of NIC withdrawal, the rats received four intragastric treatments with ISL (3, 10, or 30 mg/kg/day). All three doses of ISL significantly inhibited NIC withdrawal-induced anxiety-like behaviors in the elevated plus maze (EPM) test, but only the 10 mg/kg/day and 30 mg/kg/day ISL doses attenuated locomotor sensitization induced by a challenge dose of NIC. Intracerebroventricular ISL also inhibited both NIC-induced withdrawal anxiety and locomotor sensitization, but intra-NaccSh injection of ISL blocked only NIC locomotor sensitization, which was abolished by post-ISL infusion of tert-butyl hydroperoxide (an oxidant) or N-methyl-d-aspartate (NMDA) into the NaccSh. Moreover, there was increased protein expression of phosphorylated Erk1/2 in the NIC-sensitized NaccSh, which was suppressed by ISL. Taken together, these results suggest that ISL can inhibit repeated NIC-induced withdrawal anxiety and locomotor sensitization, and the latter is mediated by antagonizing accumbal reactive oxygen species and NMDA receptor signaling.

Dynamic Fas signaling network regulates neural stem cell proliferation and memory enhancement

Activation of Fas (CD95) is observed in various neurological disorders and can lead to both apoptosis and prosurvival outputs, yet how Fas signaling operates dynamically in the hippocampus is poorly understood. The optogenetic dissection of a signaling network can yield molecular-level explanations for cellular responses or fates, including the signaling dysfunctions seen in numerous diseases. Here, we developed an optogenetically activatable Fas that works in a physiologically plausible manner. Fas activation in immature neurons of the dentate gyrus triggered mammalian target of rapamycin (mTOR) activation and subsequent brain-derived neurotrophic factor secretion. Phosphorylation of extracellular signal-regulated kinase (Erk) in neural stem cells was induced under prolonged Fas activation. Repetitive activation of this signaling network yielded proliferation of neural stem cells and a transient increase in spatial working memory in mice. Our results demonstrate a novel Fas signaling network in the dentate gyrus and illuminate its consequences for adult neurogenesis and memory enhancement.

Plasma BDNF and TrkB mRNA in PBMCs Are Correlated With Anti-depressive Effects of 12-Weeks Supervised Exercise During Protracted Methamphetamine Abstinence

Purpose: The aim of this study was to evaluate the potential neurotrophic factors and expression of neurotrophin receptors in peripheral blood mononuclear cells linked with the antidepressant action of exercise intervention during protracted methamphetamine (METH) abstinence.

Materials and Methods: A total of 72 male METH addicts, including 47 individuals with depression and 25 individuals without depression, were recruited in this study. Individuals with depression were divided into the depression control group and the depression exercised group. Consequently, 12 weeks of supervised exercise intervention was applied. Depression and anxiety were analyzed; plasma brain-derived neurotrophic factor (BDNF), neuronal growth factor (NGF), neurotrophin-3 (NT-3), NT-4, and proBDNF levels were tested using enzyme-linked immunosorbent assay; the mRNA expressions of TrkA, TrkB-FL, TrkB-T1, TrkCB, and P75NTR in peripheral blood mononuclear cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR).

Results: NT-4 plasma levels were correlated with depression (r = −0.330, p = 0.005), which remained significant after Bonferroni correction. In addition, the BDNF and NT-3 levels in the plasma were significantly correlated with depression (r = −0.268, p = 0.023; r = −0.259, p = 0.028), but did not reach significance after Bonferroni correction. The BDNF, NT-3, and NT-4 plasma levels were significantly different between the depressive control group and the depressive exercise group using pre-exercise values as the covariate. The fold changes in TrkB-FL and TrkB-T1 mRNA in peripheral blood mononuclear cells between the post-exercise and pre-exercise demonstrated a remarkable decrease (fold change = −11.056 and −39.055).

Conclusions: Exercise intervention can alleviate depression and anxiety during protracted METH abstinence. Decrease in BDNF and the expression of TrkB in peripheral blood mononuclear cells occur following the exercise intervention.

Effect of chronic methamphetamine injection on levels of BDNF mRNA and its CpG island methylation in prefrontal cortex of rats

Methamphetamine (METH) is a highly addictive psychostimulant. Its abuse causes problems in cognition, attention, or psychiatric conditions such as psychosis. Prefrontal cortex is involved in many aspects of drug addiction and in mental disorders similar to those triggered by METH. Brain-derived neurotrophic factor (BDNF), plays important roles in modulating different aspects of addiction, and is implicated in psychiatric conditions reminiscent of those suffered by METH-abusers. Male Wistar rats were intra-peritoneally injected with METH (8 mg/kg/day) for 14 days while control group received normal saline. After extraction of prefrontal cortices, expression of BDNF IV splice variant and methylation level of its CpG island were evaluated. The relative expression of BDNF IV in METH-treated group was 2.15 fold higher than the control group. Seven out of 29 CpG sites were significantly hypomethylated in the METH group, although none survived Bonferroni adjustment. However, the overall methylation level of the 29 CpGs was significantly lower in METH cases than in controls. We discuss the importance of our results and its implications in detail.

Optogenetic Modulation of TrkB Signaling in the Mouse Brain

Optogenetic activation of receptors has advantages compared with chemical or ligand treatment because of its high spatial and temporal precision. Especially in the brain, the use of a genetically encoded light-tunable receptor is superior to direct infusion or systemic drug treatment. We applied light-activatable TrkB receptors in the mouse brain with reduced basal activity by incorporating Cry2PHR mutant, Opto-cytTrkB(E281A). Upon AAV mediated gene delivery, this form was expressed at sufficient levels in the mouse hippocampus (HPC) and medial entorhinal cortex (MEC) retaining normal canonical signal transduction by the blue light stimulus, even by delivery of noninvasive LED light on the mouse head. Within target cells, where its expression was driven by a cell type-specific promoter, Opto-cytTrkB(E281A)-mediated TrkB signaling could be controlled by adjusting light-stimulating conditions. We further demonstrated that Opto-cytTrkB(E281A) could locally induce TrkB signaling in axon terminals in the MEC-HPC. In summary, Opto-cytTrkB(E281A) will be useful for elucidating time- and region-specific roles of TrkB signaling ranging from cellular function to neural circuit mechanisms.

Time and region-dependent manner of increased brain derived neurotrophic factor and TrkB in rat brain after binge-like methamphetamine exposure

Methamphetamine (MA), a synthetic derivate of amphetamine, has become a major drug of abuse worldwide. This study investigated the effect of binge-like MA dosing (4 x 4 mg/kg, s.c., 2 h (h) apart) at a range of different time points (from 2 h to 7 days after treatment) on brain-derived neurotrophic factor (BDNF) levels and its receptors, TrkB and p75^NTR. BDNF levels were significantly increased in the frontal cortex from 2 to 36 h after treatment, returning to normal within 48 h after treatment. In the striatum, BDNF expression was increased at 12 and 24 h after binge-like MA treatment and had returned to normal at 36 h. Increased expression of the TrkB receptor was observed in the frontal cortex at 2, 24 and 48 h after MA treatment and in the striatum at 24 and 48 h after the MA regimen. A significant increase in the p75^NTR receptor was also noted in the striatum but not the frontal cortex, and it was less pronounced than the effect on TrkB receptor expression. These findings show that the binge-like regimen of MA affects expression of BDNF and its receptors, particularly the TrkB receptor, in a time and region dependent manner, and highlights the importance of the frontal cortex and the striatum in the response following MA binge-like dosing.

Brain-derived neurotrophic factor-TrkB signaling in the medial prefrontal cortex plays a role in the anhedonia-like phenotype after spared nerve injury

Although depressive symptoms including anhedonia (i.e., loss of pleasure) frequently accompany pain, little is known about the risk factors contributing to individual differences in pain-induced anhedonia. In this study, we examined if signaling of brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-receptor-kinase B (TrkB) contribute to individual differences in the development of neuropathic pain-induced anhedonia. Rats were randomly subjected to spared nerved ligation (SNI) or sham surgery. The SNI rats were divided into two groups based on the results of a sucrose preference test. Rats with anhedonia-like phenotype displayed lower tissue levels of BDNF in the medial prefrontal cortex (mPFC) compared with rats without anhedonia-like phenotype and sham-operated rats. In contrast, tissue levels of BDNF in the nucleus accumbens (NAc) of rats with an anhedonia-like phenotype were higher compared with those of rats without anhedonia-like phenotype and sham-operated rats. Furthermore, tissue levels of BDNF in the hippocampus, L2-5 spinal cord, muscle, and liver from both rats with or without anhedonia-like phenotype were lower compared with those of sham-operated rats. A single injection of 7,8-dihydroxyflavone (10 mg/kg; TrkB agonist), but not ANA-12 (0.5 mg/kg; TrkB antagonist), ameliorated reduced sucrose preference and reduced BDNF-TrkB signaling in the mPFC in the rats with anhedonia-like phenotype. These findings suggest that reduced BDNF-TrkB signaling in the mPFC might contribute to neuropathic pain-induced anhedonia, and that TrkB agonists could be potential therapeutic drugs for pain-induced anhedonia.

MPTP-induced dopaminergic neurotoxicity in mouse brain is attenuated after subsequent intranasal administration of (R)-ketamine: a role of TrkB signaling

RATIONALE

Parkinson's disease (PD) is characterized as a chronic and progressive neurodegenerative disorder, and PD patients have non-motor features such as depressive symptoms. Although there are several available medications to treat PD symptoms, these medications do not prevent the progression of the disease.

OBJECTIVE

(R)-ketamine has greater and longer-lasting antidepressant effects than (S)-ketamine in animal models of depression. This study was undertaken to investigate whether two enantiomers of ketamine and its metabolite norketamine shows neuroprotective effects in an animal model of PD.

METHODS

Effects of (R)-ketamine, (S)-ketamine, and their metabolites on MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced reduction of dopamine transporter (DAT) and tyrosine hydroxylase (TH) in the mouse striatum and substantia nigra (SNr) were examined.

RESULTS

MPTP-induced reduction of DAT in the striatum was attenuated by subsequent repeated intranasal administration of both enantiomers of ketamine although (R)-ketamine was more potent than (S)-ketamine. MPTP-induced reduction of TH in the striatum and SNr was attenuated by administration of (R)-ketamine, but not (S)-ketamine. Interestingly, MPTP-induced reduction of DAT in the striatum was also attenuated by a single intranasal administration of (R)-ketamine. In contrast, MPTP-induced reduction of DAT in the striatum was not attenuated by repeated intranasal administration of two enantiomers of norketamine. Furthermore, the pretreatment with TrkB antagonist ANA-12 significantly blocked the neuroprotective effects of (R)-ketamine in the MPTP-induced reduction of DAT in the striatum.

CONCLUSIONS

These findings suggest that (R)-ketamine can protect against MPTP-induced neurotoxicity in the mouse brain via TrkB activation. Therefore, (R)-ketamine could represent a therapeutic drug for neurodegenerative disorders such as PD.

Association Between Brain-Derived Neurotrophic Factor Val66Met Polymorphism and Methamphetamine Use Disorder: A Meta-Analysis

Background: Several studies had examined the association between brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and methamphetamine (METH) use disorder, whereas the results were conflicting. The aim of this study was to conduct a meta-analysis to achieve a pooled effect size of the association between BDNF Val66Met polymorphism and METH use disorder. Methods: Literature searches were conducted in PubMed, EMBASE, and Cochrane Library up to July, 2020. All relevant studies on the relationship of BDNF Val66Met polymorphism and METH addiction were retrieved. Pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated in the dominant, recessive, co-dominant, and allele model to appraise the association. Results: Seven case-control studies with a total of 2,204 subjects (956 METH-dependent cases and 1,248 healthy controls) were included in this meta-analysis. The results showed a significant correlation between BDNF Val66Met polymorphism and METH dependence in overall population under different genetic models. However, subgroup analysis indicated that the association only existed in Han Chinese but not in other Asian populations. Conclusion: Although the current data indicate that BDNF Val66Met polymorphism might be a potential genetic factor for METH use disorder, more researches are needed to prove its role in different populations.

Phencyclidine-induced cognitive deficits in mice are ameliorated by subsequent repeated intermittent administration of (R)-ketamine, but not (S)-ketamine: Role of BDNF-TrkB signaling

The N-methyl-d-aspartate receptor (NMDAR) antagonists including phencyclidine (PCP) and ketamine produce cognitive deficits in rodents and humans. We previously reported that (R)-ketamine produced the beneficial effects compared to (S)-ketamine in several animal models including depression. Here we compared the effects of two enantiomers of ketamine on cognitive deficits in mice after repeated administration of PCP. PCP (10 mg/kg/day for 10 days)-induced cognitive deficits were ameliorated by subsequent repeated intermittent administration of (R)-ketamine (10 mg/kg/day, twice weekly for 2-weeks), but not (S)-ketamine. Western blot analysis showed decreased levels of brain-derived neurotrophic factor (BDNF) and decreased ratio of phosphorylated-TrkB (p-TrkB) to TrkB in the prefrontal cortex (PFC) and hippocampus of PCP-treated mice. Furthermore, PCP-induced reduction of BDNF and p-TrkB/TrkB ratio in the PFC and hippocampus of PCP-treated mice was ameliorated by subsequent intermittent administration of (R)-ketamine. Interestingly, the beneficial effects of (R)-ketamine were blocked by pretreatment with TrkB inhibitor ANA-12. These findings suggest that (R)-ketamine could ameliorate PCP-induced cognitive deficits via activation of BDNF-TrkB signaling in the brain. Therefore, (R)-ketamine could be a potential therapeutic drug for cognitive impairment in patients with schizophrenia.

Rapid-acting antidepressant ketamine, its metabolites and other candidates: A historical overview and future perspective

Major depressive disorder (MDD) is one of the most disabling psychiatric disorders. Approximately one-third of the patients with MDD are treatment resistant to the current antidepressants. There is also a significant therapeutic time lag of weeks to months. Furthermore, depression in patients with bipolar disorder (BD) is typically poorly responsive to antidepressants. Therefore, there exists an unmet medical need for rapidly acting antidepressants with beneficial effects in treatment-resistant patients with MDD or BD. Accumulating evidence suggests that the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine produces rapid and sustained antidepressant effects in treatment-resistant patients with MDD or BD. Ketamine is a racemic mixture comprising equal parts of (R)-ketamine (or arketamine) and (S)-ketamine (or esketamine). Because (S)-ketamine has higher affinity for NMDAR than (R)-ketamine, esketamine was developed as an antidepressant. On 5 March 2019, esketamine nasal spray was approved by the US Food and Drug Administration. However, preclinical data suggest that (R)-ketamine exerts greater potency and longer-lasting antidepressant effects than (S)-ketamine in animal models of depression and that (R)-ketamine has less detrimental side-effects than (R,S)-ketamine or (S)-ketamine. In this article, the author reviews the historical overview of the antidepressant actions of enantiomers of ketamine and its major metabolites norketamine and hydroxynorketamine. Furthermore, the author discusses the other potential rapid-acting antidepressant candidates (i.e., NMDAR antagonists and modulators, low-voltage-sensitive T-type calcium channel inhibitor, potassium channel Kir4.1 inhibitor, negative modulators of γ-aminobutyric acid, and type A [GABA_A ] receptors) to compare them with ketamine. Moreover, the molecular and cellular mechanisms of ketamine's antidepressant effects are discussed.

Protein arginine methyltransferase-1 deficiency restrains depression-like behavior of mice by inhibiting inflammation and oxidative stress via Nrf-2

Current evidence indicates that depression is accompanied by the activation of inflammatory response and oxidative stress. Protein arginine methyltransferase 1 (PRMT1) is a histone methyltransferase that methylates Arg3 on histone H4, playing crucial role in regulating various pathological processes. In the study, we attempted to explore the effects of PRMT1 on animal model with depression through a single administration of lipopolysaccharide (LPS). Our results indicated that PRMT1 knockout (PRMT1^-/-) improved LPS-induced anxiety- and depressive-like behavior, along with up-regulated expression levels of brain-derived neurotrophic factor (BDNF) and PSD-95. Furthermore, PRMT1 deficiency significantly improved LPS-induced changes in dendritic spine density in the areas of prefrontal cortex (PFC), CA3 and dentate gyrus (DG), and nucleus accumbens (NAc). In addition, PRMT1 deletion ameliorated the neuroinflammatory responses, as evidenced by the reduced expression of interleukin 1β (IL-1β) and tumor necrosis factor (TNF)-α, which might be through repressing nuclear factor-κB (NF-κB) signaling. Moreover, oxidative stress induced by LPS was alleviated by PRMT1 knockout in hippocampus of mice at least partly via promoting Nrf-2 expressions. The anti-depressant effects of PRMT1 inhibition were verified in LPS-incubated astrocytes. Importantly, we found that PRMT1 knockout-alleviated inflammation and oxidative stress triggered by LPS were significantly recovered by the suppression of Nrf-2. Therefore, Nrf-2 was markedly involved in PRMT1-regulated depression-like behavior. Taken together, the results indicated that PRMT1 might be an important therapeutic target for developing effective treatment to prevent depressive-like behavior.

Repeated cocaine exposure dysregulates BDNF expression and signaling in the mesocorticolimbic pathway of the adolescent rat

Objectives: Long-term abstinence following cocaine exposure up-regulates brain-derived neurotrophic factor (BDNF) expression in the mesocorticolimbic pathway. Given the increased vulnerability to drug abuse typical of adolescence, we hypothesized that changes in BDNF expression may become manifest early after the end of cocaine treatment in the adolescent brain.Methods: Rats received cocaine injections from postnatal day 28 (PND28) to PND42 and the mesocorticolimbic expression of BDNF was measured by real-time PCR and Western blotting at PND43.Results: In the ventral tegmental area, BDNF-tropomyosin receptor kinase B (TrΚB) expression and phosphorylation are enhanced while the intracellular signaling is unaltered. In the nucleus accumbens (NAc) shell and core, BDNF and its signaling were down-regulated. In the prelimbic (PL) cortex, we found reduced BDNF expression and increased phosphoprylation of TrΚB, ERK and AKT. In the infralimbic (IL) cortex, increased BDNF expression was coupled with reduced activity and expression of its downstream targets. To evaluate the role of glutamate on BDNF-independent changes, we investigated the expression of the transporter GLT-1 and the activation of the NMDA receptor subunit GluN2B, which were both increased in the PL cortex while reduced in the IL cortex.Conclusions: Our results show that adolescent cocaine exposure modulates BDNF system early after treatment in the mesocorticolimbic pathway, identifying a complex but specific set of changes that could provide clues for treatment.

Sex-specific differences in adult cognition and neuroplasticity following repeated combinatory stress and TrkB receptor antagonism in adolescence

Evidence supports brain-derived neurotrophic factor (BDNF) and its primary receptor tyrosine-related kinase B (TrkB) as targets in the treatment of mood disorders. This study characterized the impact of a 10-day combinatory stress paradigm (alternating days of restraint stress and forced swim) and administration of the selective TrkB antagonist ANA-12 (0.5 mg/kg, i.p.) during adolescence in male and female Wistar rats on adulthood behavioral and neurochemical responses. The social interaction/preference (SIT/SP), and Y maze conditioned place preference (YMCPP) and passive avoidance tests (YMPAT), initiated on PND 62, served to determine sex-related behavioral responses. Results support reduced sociability in females in the SIT/SP, but no impact of ANA-12 to regulate sociability or social memory. Blockade of TrkB during adolescence facilitated YMCPP-related reward behavior in both sexes, and reduced YMPAT fear conditioning in females. Following behavioral testing, rats were exposed to 5-min acute forced swim and brains collected 2 h post swim to determine effects of adolescent TrkB blockade and stress exposure on neurochemical regulators of stress and plasticity. Findings show elevated glucocorticoid receptor (GR-) and TrkB-immunoreactivity (ir) in the amygdalar central nucleus, and GR-ir in the hypothalamic paraventricular nucleus of females compared to males. In the hippocampal CA1, BDNF-ir was lower in females versus males, and GR-ir was elevated in stress versus non-stress males. Together, we demonstrate that inherent sex-specific differences, which may modulate impact of adolescence stress exposure and TrkB inhibition, differentially affect male and female adulthood behavior and biochemical response profiles, suggesting that these responses are in part conditioned by prior experience.

TrkB Activation during a Critical Period Mimics the Protective Effects of Early Visual Experience on Perception and the Stability of Receptive Fields in Adult Superior Colliculus

During a critical period in development, spontaneous and evoked retinal activity shape visual pathways in an adaptive fashion. Interestingly, spontaneous activity is sufficient for spatial refinement of visual receptive fields (RFs) in superior colliculus (SC) and visual cortex (V1), but early visual experience is necessary to maintain inhibitory synapses and stabilize RFs in adulthood (Carrasco et al., 2005, 2011; Carrasco and Pallas, 2006; Balmer and Pallas, 2015a). In V1, BDNF and its high-affinity receptor TrkB are important for development of visual acuity, inhibition, and regulation of the critical period for ocular dominance plasticity (Hanover et al., 1999; Huang et al., 1999; Gianfranceschi et al., 2003). To examine the generality of this signaling pathway for visual system plasticity, the present study examined the role of TrkB signaling during the critical period for RF refinement in SC. Activating TrkB receptors during the critical period (P33-P40) in dark reared subjects produced normally refined RFs, and blocking TrkB receptors in light-exposed animals resulted in enlarged adult RFs like those in dark reared animals. We also report here that deprivation- or TrkB blockade-induced RF enlargement in adulthood impaired fear responses to looming overhead stimuli and negatively impacted visual acuity. Thus, early TrkB activation is both necessary and sufficient to maintain visual RF refinement, robust looming responses, and visual acuity in adulthood. These findings suggest a common signaling pathway exists for the maturation of inhibition between V1 and SC.SIGNIFICANCE STATEMENT Receptive field refinement in superior colliculus differs from more commonly studied examples of critical period plasticity in visual pathways in that it does not require visual experience to occur; rather, spontaneous activity is sufficient. Maintenance of refinement beyond puberty requires a brief, early exposure to light to stabilize the lateral inhibition that shapes receptive fields. We find that TrkB activation during a critical period can substitute for visual experience in maintaining receptive field refinement into adulthood, and that this maintenance is beneficial to visual survival behaviors. Thus, as in some other types of plasticity, TrkB signaling plays a crucial role in receptive field refinement.

Methamphetamine binge administration dose-dependently enhanced negative affect and voluntary drug consumption in rats following prolonged withdrawal: role of hippocampal FADD

While prior studies have established various interacting mechanisms and neural consequences (i.e. monoaminergic nerve terminal damage) that might contribute to the adverse effects caused by methamphetamine administration, the precise mechanisms that mediate relapse during withdrawal remain unknown. This study evaluated the long-term consequences of binge methamphetamine administration (three pulses/day, every 3 hours, 4 days, i.p.; dose-response: 2.5, 5 and 7.5 mg/kg) in adult Sprague-Dawley rats at two behavioral levels following 25 days of withdrawal: (1) negative affect (behavioral despair-forced-swim test, and anhedonia-1% sucrose consumption, two-bottle choice test) and (2) voluntary methamphetamine consumption (20 mg/l, two-bottle choice test). Striatal and hippocampal brain samples were dissected to quantify monoamines content by high-performance liquid chromatography and to evaluate neurotoxicity (dopaminergic and serotonergic markers) and neuroplasticity markers [i.e. cell fate regulator (Fas-associated protein with death domain) FADD] by Western blot. The results showed that methamphetamine administration induced dose-dependent negative effects during prolonged withdrawal in adult rats. In particular, rats treated repeatedly with methamphetamine (7.5 mg/kg) showed (1) enhanced negative affect-increased anhedonia associated with behavioral despair, (2) increased voluntary methamphetamine consumption, (3) enhanced neurotoxicity-decreased dopamine and metabolites in striatum and decreased serotonin in hippocampus, (4) altered neuroplasticity markers-decreased FADD protein and increased p-FADD/FADD balance selectively in hippocampus and (5) higher consumption rates of methamphetamine that were associated with lower FADD content in hippocampus. These results confirm that methamphetamine withdrawal dose-dependently induced negative affect and decreased monoamines content, while also increased voluntary methamphetamine consumption and suggested a role for hippocampal FADD neuroplasticity in these drug-withdrawal adaptations.

The role of neurotrophic factors in manic-, anxious- and depressive-like behaviors induced by amphetamine sensitization: Implications to the animal model of bipolar disorder

BACKGROUND

Bipolar disorder (BD) and substance use disorders share common symptoms, such as behavioral sensitization. Amphetamine-induced behavioral sensitization can serve as an animal model of BD. Neurotrophic factors have an important role in BD pathophysiology. This study evaluated the effects of amphetamine sensitization on behavior and neurotrophic factor levels in the brains of rats.

METHODS

Wistar rats received daily intraperitoneal (i.p) injections of dextroamphetamine (d-AMPH) 2 mg/kg or saline for 14 days. After seven days of withdrawal, the animals were challenged with d-AMPH (0.5 mg/kg, i.p) and locomotor behavior was assessed. In a second protocol, rats were similarly treated with d-AMPH (2 mg/kg, i.p) for 14 days. After withdrawal, without d-AMPH challenge, depressive- and anxiety-like behaviors were evaluated through forced swimming test and elevated plus maze. Levels of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin 3 (NT-3), neurotrophin 4/5 (NT-4/5) and glial-derived neurotrophic factor (GDNF) were evaluated in the frontal cortex, hippocampus, and striatum.

RESULTS

D-AMPH for 14 days augmented locomotor sensitization to a lower dose of d-AMPH (0.5 mg/kg) after the withdrawal. d-AMPH withdrawal induced depressive- and anxious-like behaviors. BDNF, NGF, and GDNF levels were decreased, while NT-3 and NT-4 levels were increased in brains after d-AMPH sensitization.

LIMITATIONS

Although d-AMPH induces manic-like behavior, the mechanisms underlying these effects can also be related to phenotypes of drug abuse.

CONCLUSIONS

Together, vulnerability to mania-like behavior following d-AMPH challenge and extensive neurotrophic alterations, suggest amphetamine-induced behavioral sensitization is a good model of BD pathophysiology.

Acupuncture on the Stress-Related Drug Relapse to Seeking

Drug addiction is a chronic relapsing disease, which causes serious social and economic problems. The most important trial for the successful treatment of drug addiction is to prevent the high rate of relapse to drug-seeking behaviors. Opponent process as a motivational theory with excessive drug seeking in the negative reinforcement of drug dependence reflects both loss of brain reward system and recruitment of brain stress system. The negative emotional state produced by brain stress system during drug withdrawal might contribute to the intense drug craving and drive drug-seeking behaviors via negative reinforcement mechanisms. Decrease in dopamine neurotransmission in the nucleus accumbens and recruitment of corticotropin-releasing factor in the extended amygdala are hypothesized to be implicated in mediating this motivated behavior. Also, a brain stress response system is hypothesized to increase drug craving and contribute to relapse to drug-seeking behavior during the preoccupation and anticipation stage of dependence caused by the exposure to stress characterized as the nonspecific responses to any demands on the body. Acupuncture has proven to be effective for reducing drug addiction and stress-related psychiatric disorders, such as anxiety and depression. Furthermore, acupuncture has been shown to correct reversible brain malfunctions by regulating drug addiction and stress-related neurotransmitters. Accordingly, it seems reasonable to propose that acupuncture attenuates relapse to drug-seeking behavior through inhibition of stress response. In this review, a brief description of stress in relapse to drug-seeking behavior and the effects of acupuncture were presented.

PGC-1α-FNDC5-BDNF signaling pathway in skeletal muscle confers resilience to stress in mice subjected to chronic social defeat

Skeletal muscle consumes two thirds of the body's energy and may play a role in stress-related disorders. Evidence suggests that the peroxisome proliferator-activated receptor γ coactivator α (PGC-1α)-fibronectin type III domain-containing 5 (FNDC5)-brain-derived neurotrophic factor (BDNF) signaling pathway in skeletal muscle plays a key role in conferring the beneficial effects of exercise. In this study, we aimed to determine whether this pathway contributes to the resilience or susceptibility of mice subjected to chronic social defeat stress (CSDS). BDNF-tropomyosin receptor kinase B (TrkB) and proBDNF-p75^NTR signaling in the medial prefrontal cortex and nucleus accumbens of susceptible but not resilient mice were significantly altered compared with the controls. Furthermore, the levels of PGC-1α, FNDC5, and BDNF, as well as the p-TrkB/TrkB ratio in the skeletal muscle of susceptible but not resilient mice, were significantly lower than those of the controls, but the levels of proBDNF and p75^NTR in the skeletal muscle of susceptible mice were significantly higher than those of the controls. Moreover, there were significant positive associations between social interaction test data and the expression of PGC-1α, FNDC5, and BDNF or the p-TrkB/TrkB ratio in skeletal muscle. These results suggest that the downregulation of the PGC-1α-FNDC5-BDNF signaling pathway in skeletal muscle contributes to resilience vs. susceptibility to CSDS. Therefore, alterations in this pathway in skeletal muscle may play a crucial role in mediating stress-related disorders.