7,8-Dihydroxyflavone, a TrkB agonist, attenuates behavioral abnormalities and neurotoxicity in mice after administration of methamphetamine

The neuroprotective effects of caffeic acid phenethyl ester against methamphetamine-induced neurotoxicity

Methamphetamine (METH) is a highly abused substance on a global scale and has the capacity to elicit toxicity within the central nervous system. The neurotoxicity induced by METH encompasses neuronal degeneration and cellular demise within the substantia nigra-striatum and hippocampus. Caffeic acid phenethyl ester (CAPE), a constituent of propolis, is a diminutive compound that demonstrates antioxidative and anti-inflammatory characteristics. Numerous investigations have demonstrated the safeguarding effects of CAPE in various neurodegenerative ailments. Our hypothesis posits that CAPE may exert a neuroprotective influence on METH-induced neurotoxicity via specific mechanisms. In order to validate the hypothesis, a series of experimental techniques including behavioral tests, immunofluorescence labeling, RNA sequencing, and western blotting were employed to investigate the neurotoxic effects of METH and the potential protective effects of CAPE. The results of our study demonstrate that CAPE effectively ameliorates cognitive memory deficits and anxiety symptoms induced by METH in mice. Furthermore, CAPE has been observed to attenuate the upregulation of neurotoxicity-associated proteins that are induced by METH exposure and also reduced the loss of hippocampal neurons in mice. Moreover, transcriptomics analysis was conducted to determine alterations in gene expression within the hippocampus of mice. Subsequently, bioinformatics analysis was employed to investigate the divergent outcomes and identify potential key genes. Interferon-stimulated gene 15 (ISG15) was successfully identified and confirmed through RT-qPCR, western blotting, and immunofluorescence techniques. Our research findings unequivocally demonstrated the neuroprotective effect of CAPE against METH-induced neurotoxicity, with ISG15 may have an important role in the underlying protective mechanism. These results offer novel perspectives on the treatment of METH-induced neurotoxicity.

Methamphetamine induced neurotoxic diseases, molecular mechanism, and current treatment strategies

Methamphetamine (MA) is a extremely addictive psychostimulant drug with a significant abuse potential. Long-term MA exposure can induce neurotoxic effects through oxidative stress, mitochondrial functional impairment, endoplasmic reticulum stress, the activation of astrocytes and microglial cells, axonal transport barriers, autophagy, and apoptosis. However, the molecular and cellular mechanisms underlying MA-induced neurotoxicity remain unclear. MA abuse increases the chances of developing neurotoxic conditions such as Parkinson's disease (PD), Alzheimer's disease (AD) and other neurotoxic diseases. MA increases the risk of PD by increasing the expression of alpha-synuclein (ASYN). Furthermore, MA abuse is linked to high chances of developing AD and subsequent neurodegeneration due to biological variations in the brain region or genetic and epigenetic variations. To date, there is no Food and Drug Administration (FDA)-approved therapy for MA-induced neurotoxicity, although many studies are being conducted to develop effective therapeutic strategies. Most current studies are now focused on developing therapies to diminish the neurotoxic effects of MA, based on the underlying mechanism of neurotoxicity. This review article highlights current research on several therapeutic techniques targeting multiple pathways to reduce the neurotoxic effects of MA in the brain, as well as the putative mechanism of MA-induced 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.

Long-term effects of young-adult methamphetamine on dorsal raphe serotonin systems in mice: Role of brain-derived neurotrophic factor

To assess the long-term effects of chronic adolescent methamphetamine (METH) treatment on the serotonin system in the brain, we used serotonin-1A receptor (5-HT_1A) and serotonin transporter (SERT) autoradiography, and quantitative tryptophan-hydroxylase 2 (TPH2) immunohistochemistry in the raphe nuclei of mice. Because of the modulatory role of brain-derived neurotrophic factor (BDNF) on the serotonin system and the effects of METH, we included both BDNF heterozygous (HET) mice and wildtype (WT) controls. Male and female mice of both genotypes were treated with an escalating METH dose regimen from the age of 6-9 weeks. At least two weeks later, acute locomotor hyperactivity induced by a 5 mg/kg D-amphetamine challenge was significantly enhanced in METH-pretreated mice, showing long-term sensitisation. METH pretreatment caused a small, but significant decrease of 5-HT_1A receptor binding in the dorsal raphe nucleus (DRN) of males independent of genotype, but there were no changes in the median raphe nucleus (MRN) or in SERT binding density. METH treatment reduced the number of TPH2 positive cells in ventral subregions of the rostral and medial DRN independent of genotype. METH treatment selectively reduced DRN cell counts in BDNF HET mice compared to wildtype mice in medial and caudal ventrolateral subregions previously associated with panic-like behaviour. The data increase our understanding of the long-term and selective effects of METH on brain serotonin systems. These findings could be relevant for some of the psychosis-like symptoms associated with long-term METH use.

Psychoactive Drugs-From Chemical Structure to Oxidative Stress Related to Dopaminergic Neurotransmission. A Review

Nowadays, more and more young people want to experience illegal, psychoactive substances, without knowing the risks of exposure. Besides affecting social life, psychoactive substances also have an important effect on consumer health. We summarized and analyzed the published literature data with reference to the mechanism of free radical generation and the link between chemical structure and oxidative stress related to dopaminergic neurotransmission. This review presents data on the physicochemical properties, on the ability to cross the blood brain barrier, the chemical structure activity relationship (SAR), and possible mechanisms by which neuronal injuries occur due to oxidative stress as a result of drug abuse such as "bath salts", amphetamines, or cocaine. The mechanisms of action of ingested compounds or their metabolites involve intermediate steps in which free radicals are generated. The brain is strongly affected by the consumption of such substances, facilitating the induction of neurodegenerative diseases. It can be concluded that neurotoxicity is associated with drug abuse. Dependence and oxidative stress are linked to inhibition of neurogenesis and the onset of neuronal death. Understanding the pathological mechanisms following oxidative attack can be a starting point in the development of new therapeutic targets.

Evaluation of a TrkB agonist on spatial and motor learning in the Ube3a mouse model of Angelman syndrome

Angelman syndrome is a rare neurodevelopmental disorder caused by a mutation in the maternal allele of the gene Ube3a The primary symptoms of Angelman syndrome are severe cognitive deficits, impaired motor functions, and speech disabilities. Analogous phenotypes have been detected in young adult Ube3a mice. Here, we investigate cognitive phenotypes of Ube3a mice as compared to wild-type littermate controls at an older adult age. Water maze spatial learning, swim speed, and rotarod motor coordination and balance were impaired at 6 mo of age, as predicted. Based on previous findings of reduced brain-derived neurotrophic factor in Ube3a mice, a novel therapeutic target, the TrkB agonist 7,8-DHF, was interrogated. Semichronic daily treatment with 7,8-DHF, 5 mg/kg i.p., did not significantly improve the impairments in performance during the acquisition of the water maze hidden platform location in Ube3a mice, after training with either massed or spaced trials, and had no effect on the swim speed and rotarod deficits. Robust behavioral phenotypes in middle-aged Ube3a mice appear to result from continued motor decline. Our results suggest that motor deficits could offer useful outcome measures for preclinical testing of many pharmacological targets, with the goal of reducing symptoms in adults with Angelman syndrome.

7,8-Dihydroxyflavone alleviated the high-fat diet and alcohol-induced memory impairment: behavioral, biochemical and molecular evidence

RATIONALE

Alcoholism and obesity impart a deleterious impact on human health and affects the quality of life. Chronic consumption of alcohol and western diet has been reported to cause memory deficits. 7,8-dihydroxyflavone (7,8-DHF), a TrkB agonist, comprises antioxidant and anti-inflammatory properties in treating various neurological disorders.

OBJECTIVES

The current study was aimed to determine the protective effect and molecular mechanism of 7,8-DHF against alcohol and high-fat diet (HFD)-induced memory deficits in rats.

METHODS

The adult male Wistar rats were given alcohol (3-15%) and HFD ad libitum for 12 weeks in different experimental groups. 7,8-DHF (5 mg/kg) was intraperitoneally injected daily for the last 4 weeks (9th-12th week).

RESULTS

The alcohol and HFD administration caused cognitive impairment as evaluated through the Morris water maze (MWM) test in alcohol, HFD, and alcohol + HFD-fed animals. The last 4-week treatment of 7,8-DHF (5 mg/kg; i.p.) attenuated alcohol and HFD-induced memory loss. 7,8-DHF treatment also restored the glutathione (GSH) level along with attenuation of nitrite, malondialdehyde content (markers of oxidative and nitrosative stress), and reduction of the acetylcholinesterase activity in the hippocampus of alcohol and HFD-fed animals. Furthermore, the administration of 7,8-DHF caused downregulation of NF-κB, iNOS, and caspase-3 and upregulation of Nrf2, HO-1, and BDNF mRNA level in rat hippocampus.

CONCLUSION

7,8-DHF administration conferred beneficial effects against alcohol and HFD-induced memory deficit via its unique antioxidant, anti-inflammatory, anti-apoptotic potential, along with the activation of TrkB/BDNF signaling pathway in the hippocampus.

Targeting the Neuronal Activity of Prefrontal Cortex: New Directions for the Therapy of Depression

Depression is one of the prevalent psychiatric illnesses with a comprehensive performance such as low self-esteem, lack of motivation, anhedonia, poor appetite, low energy, and uncomfortableness without a specific cause. So far, the cause of depression is not very clear, but it is certain that many aspects of biological psychological and social environment are involved in the pathogenesis of depression. Recently, the prefrontal cortex (PFC) has been indicated to be a pivotal brain region in the pathogenesis of depression. And increasing evidence showed that the abnormal activity of the PFC neurons is linked with depressive symptoms. Unveiling the molecular and cellular, as well as the circuit properties of the PFC neurons will help to find out how abnormalities in PFC neuronal activity are associated with depressive disorders. In addition, concerning many antidepressant drugs, in this review, we concluded the effect of several antidepressants on PFC neuronal activity to better understand its association with depression.

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.

Recent Advances in the Early Intervention in Schizophrenia: Future Direction from Preclinical Findings

PURPOSE OF REVIEW

In the past decade, there has been increasing interest in the potential benefit of early intervention in schizophrenia. Patients with schizophrenia show cognitive impairment for several years preceding the onset of psychosis. The author discusses the recent topics on prevention of schizophrenia.

RECENT FINDINGS

Preclinical findings suggest that maternal immune activation (MIA) produces cognitive deficits as a prodromal symptom in juvenile offspring in rodents. Treatment with anti-inflammatory compounds, such as D-serine, 7,8-dihydroxyflavone (a TrkB agonist), sulforaphane (or its precursor glucoraphanin), and TPPU (1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea: a soluble epoxide hydrolase inhibitor), during adolescence might prevent the onset of behavioral abnormalities and parvalbumin immunoreactivity in the medial prefrontal cortex of adult offspring after MIA. Based on the role of inflammation and cognitive impairment in the prodromal state, early intervention using anti-inflammatory compounds (i.e., D-serine, sodium benzoate, TrkB agonist, Nrf2 agonist, soluble epoxide hydrolase inhibitor) may reduce the risk of subsequent transition to schizophrenia.

Dietary intake of glucoraphanin prevents the reduction of dopamine transporter in the mouse striatum after repeated administration of MPTP

Aims

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder. Although diet may influence the development of PD, the precise mechanisms underlying relationship between diet and PD pathology are unknown. Here, we examined whether dietary intake of glucoraphanin (GF), the precursor of a natural antioxidant sulforaphane in cruciferous vegetables, can affect the reduction of dopamine transporter (DAT) in the mouse striatum after repeated administration of MPTP (1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine).

Methods

Normal food pellet or 0.1% GF food pellet was given into male mice for 28 days from 8‐week‐old. Subsequently, saline (5 mL/kg × 3, 2‐hour interval) or MPTP (10 mg/kg × 3, 2‐hour interval) was injected into mice. Immunohistochemistry of DAT in the striatum was performed 7 days after MPTP injection.

Results

Repeated injections of MPTP significantly decreased the density of DAT‐immunoreactivity in the mouse striatum. In contrast, dietary intake of 0.1% GF food pellet significantly protected against MPTP‐induced reduction of DAT‐immunoreactivity in the striatum.

Conclusion

This study suggests that dietary intake of GF food pellet could prevent MPTP‐induced dopaminergic neurotoxicity in the striatum of adult mice. Therefore, dietary intake of GF‐rich cruciferous vegetables may have beneficial effects on prevention for development of PD.

Oxidative stress plays a role in the neurotoxicity of MPTP in the striatum. Dietary intake of glucoraphanin could prevent the MPTP‐induced neurotoxicity in mouse striatum. Dietary intake of glucoraphanin‐rich vegetables may have beneficial effects on prevention of Parkinson's disease.

7,8-Dihydroxyflavone blocks the development of behavioral sensitization to MDPV, but not to cocaine: Differential role of the BDNF-TrkB pathway

3,4-Methylenedioxypyrovalerone (MDPV) acts as a dopamine transporter blocker and exerts powerful psychostimulant effects. In this study we aimed to investigate the bidirectional cross-sensitization between MDPV and cocaine, as well as to evaluate the role of the BDNF-TrkB signaling pathway in the development of locomotor sensitization to both drugs. Mice were treated with MDPV (1.5 mg/kg) or cocaine (10 or 15 mg/kg) once daily for 5 days. After withdrawal (10 days), animals were challenged with cocaine (8 mg/kg) or MDPV (1 mg/kg). For biochemical determinations, MDPV (1.5 mg/kg) or cocaine (15 mg/kg) were administered acutely or repeatedly, and BDNF, D3R and G9a transcription levels as well as pro- and mature BDNF protein levels were determined. Our results demonstrate that repeated administration of MDPV or cocaine sensitizes to cocaine and MDPV locomotor effects. After an acute or a repeated exposure to MDPV, cortical mRNA BDNF levels were increased, while a decrease in mBDNF protein levels in the nucleus accumbens 2 h after repeated exposure was evidenced. Interestingly, such decline was involved in the development of locomotor sensitization, thus the pretreatment with 7,8-dihydroxyflavone (10 mg/kg), a TrkB agonist, blocked the development of sensitization to MDPV but not to cocaine, for which no changes in the BDNF-TrkB signaling pathway were observed at early withdrawal. In conclusion, a bidirectional cross-sensitization between MDPV and cocaine was evidenced. Our findings suggest that decreased BDNF-TrkB signaling has an important role in the behavioral sensitization to MDPV, pointing TrkB modulation as a target to prevent MDPV sensitization.

Hypothesis-driven investigations of diverse pharmacological targets in two mouse models of autism

Autism spectrum disorder is a neurodevelopmental syndrome diagnosed primarily by persistent deficits in social interactions and communication, unusual sensory reactivity, motor stereotypies, repetitive behaviors, and restricted interests. No FDA‐approved medical treatments exist for the diagnostic symptoms of autism. Here we interrogate multiple pharmacological targets in two distinct mouse models that incorporate well‐replicated autism‐relevant behavioral phenotypes. Compounds that modify inhibitory or excitatory neurotransmission were selected to address hypotheses based on previously published biological abnormalities in each model. Shank3B is a genetic model of a mutation found in autism and Phelan‐McDermid syndrome, in which deficits in excitatory neurotransmission and synaptic plasticity have been reported. BTBR is an inbred strain model of forms of idiopathic autism in which reduced inhibitory neurotransmission and excessive mTOR signaling have been reported. The GABA‐A receptor agonist gaboxadol significantly reduced repetitive self‐grooming in three independent cohorts of BTBR. The TrkB receptor agonist 7,8‐DHF improved spatial learning in Shank3B mice, and reversed aspects of social deficits in BTBR. CX546, a positive allosteric modulator of the glutamatergic AMPA receptor, and d‐cycloserine, a partial agonist of the glycine site on the glutamatergic NMDA receptor, did not rescue aberrant behaviors in Shank3B mice. The mTOR inhibitor rapamycin did not ameliorate social deficits or repetitive behavior in BTBR mice. Comparison of positive and negative pharmacological outcomes, on multiple phenotypes, evaluated for replicability across independent cohorts, enhances the translational value of mouse models of autism for therapeutic discovery. GABA agonists present opportunities for personalized interventions to treat components of autism spectrum disorder. Autism Res 2019, 12: 401–421 © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc.

Lay Summary

Many of the risk genes for autism impair synapses, the connections between nerve cells in the brain. A drug that reverses the synaptic effects of a mutation could offer a precision therapy. Combining pharmacological and behavioral therapies could reduce symptoms and improve the quality of life for people with autism. Here we report reductions in repetitive behavior by a GABA‐A receptor agonist, gaboxadol, and improvements in social and cognitive behaviors by a TrkB receptor agonist, in mouse models of autism.

Modulation of ERK1/2 and Akt Pathways Involved in the Neurotrophic Action of Caffeic Acid Alkyl Esters

Neurodegenerative diseases affect millions of human lives all over the world. The number of afflicted patients is rapidly growing, and disease-modifying agents are urgently needed. Caffeic acid, an important member of the hydroxycinnamic acid family of polyphenols, has considerable neurotrophic effects. We have previously shown how caffeate alkyl ester derivatives significantly promote survival and differentiation in neuronal cells. In this study, the mechanisms by which these ester derivatives exert their neurotrophic effects are examined. A series of eight caffeic acid esters with different alkyl chain lengths, ranging from methyl (CAF1) to dodecyl esters (CAF8), were synthesized and studied for their influence on neurotrophic signaling pathways. Caffeate esters did not induce tropomyosin-receptor kinase A (TrkA) phosphorylation, which was assessed by immunoblotting up to a concentration of 25 µM. NIH/3T3 cells overexpressing TrkA were generated to further examine phosphorylation of this receptor tyrosine kinase. None of the esters induced TrkA phosphorylation in these cells either. Assessment of the effect of caffeate derivatives on downstream neurotrophic pathways by immunoblotting showed that the most potent esters, decyl caffeate (CAF7) and dodecyl caffeate (CAF8) caused extracellular signal-regulated kinase (ERK1/2) and Akt serine threonine kinase phosphorylation in PC12 cells at 5 and 25 µM concentrations. In conclusion, this study shows that caffeate esters exert their neurotrophic action by modulation of ERK1/2 and Akt signaling pathways in neuronal cells, and further demonstrates the potential therapeutic implications of these derivatives for neurodegenerative diseases.

The Main Molecular Mechanisms Underlying Methamphetamine- Induced Neurotoxicity and Implications for Pharmacological Treatment

Methamphetamine (METH) is a popular new-type psychostimulant drug with complicated neurotoxicity. In spite of mounting evidence on METH-induced damage of neural cell, the accurate mechanism of toxic effect of the drug on central nervous system (CNS) has not yet been completely deciphered. Besides, effective treatment strategies toward METH neurotoxicity remain scarce and more efficacious drugs are to be developed. In this review, we summarize cellular and molecular bases that might contribute to METH-elicited neurotoxicity, which mainly include oxidative stress, excitotoxicity, and neuroinflammation. We also discuss some drugs that protect neural cells suffering from METH-induced neurotoxic consequences. We hope more in-depth investigations of exact details that how METH produces toxicity in CNS could be carried out in future and the development of new drugs as natural compounds and immunotherapies, including clinic trials, are expected.

YL-0919, a dual 5-HT1A partial agonist and SSRI, produces antidepressant- and anxiolytic-like effects in rats subjected to chronic unpredictable stress

YL-0919 has been identified as a novel dual 5-HT_1A partial agonist and serotonin reuptake inhibitor. In the current study, we demonstrated that YL-0919 produced prominent antidepressant-like and anxiolytic-like effects in a chronic unpredictable stress (CUS) rat model. Male SD rats were exposed to CUS for 5 weeks; YL-0919 (1.25 and 2.5 mg/kg) or a positive control fluoxetine (Flx, 10 mg/kg) was orally administered daily. YL-0919 or Flx treatment significantly increased the sucrose preference rate, the locomotor activity in an open field test (OFT), the latency to feed in a novelty-suppressed feeding test (NSFT), and both the percentage of time spent in the open arms and the number of entries into the open arms in an elevated plus-maze test. YL-0919 or Flx treatment significantly suppressed the serum levels of ACTH and corticosterone in CUS-exposed rats. Additionally, YL-0919 or Flx treatment significantly enhanced the levels of cAMP, the expression of phosphorylated cAMP response element-binding protein (pCREB) and brain-derived neurotrophic factor (BDNF) in the hippocampus of CUS-exposed rats. Similar to Flx, YL-0919 treatment significantly enhanced the dendritic complexity, and increased the number of dendritic nodes as well as the spine length and number of branch nodes in the hippocampal pyramidal neurons of CUS-exposed rats. Overall, our results reveal that YL-0919 suppresses the HPA axis and exerts antidepressant-like and anxiolytic-like effects in CUS-exposed rats, which are associated with the enhanced cAMP signaling and hippocampal dendritic complexity.

Pharmacotherapeutic agents in the treatment of methamphetamine dependence

INTRODUCTION

Methamphetamine use is a serious public health concern in many countries and is second to cannabis as the most widely abused illicit drug in the world. Effective management for methamphetamine dependence remains elusive and the large majority of methamphetamine users relapse following treatment. Areas covered: Progression in the understanding of the pharmacological basis of methamphetamine use has provided us with innovative opportunities to develop agents to treat dependence. The current review summarizes relevant literature on the neurobiological and clinical correlates associated with methamphetamine use. We then outline agents that have been explored for potential treatments in preclinical studies, human laboratory phase I and phase II trials over the last ten years. Expert opinion: No agent has demonstrated a broad and strong effect in achieving MA abstinence in Phase II trials. Agents with novel therapeutic targets appear promising. Advancement in MA treatment, including translation into practice, faces several clinical challenges.

Brain-derived Neurotrophic Factor (BDNF)-TrkB Signaling in Inflammation-related Depression and Potential Therapeutic Targets

Depression is the most prevalent and among the most debilitating of psychiatric disorders. The precise neurobiology of this illness is unknown. Several lines of evidence suggest that peripheral and central inflammation plays a role in depressive symptoms, and that anti-inflammatory drugs can improve depressive symptoms in patients with inflammation-related depression. Signaling via brain-derived neurotrophic factor (BDNF) and its receptor, tropomycin receptor kinase B (TrkB) plays a key role in the pathophysiology of depression and in the therapeutic mechanisms of antidepressants. A recent paper showed that lipopolysaccharide (LPS)-induced inflammation gave rise to depression-like phenotype by altering BDNF-TrkB signaling in the prefrontal cortex, hippocampus, and nucleus accumbens, areas thought to be involved in the antidepressant effects of TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF) and TrkB antagonist, ANA-12. Here we provide an overview of the tryptophan-kynurenine pathway and BDNF-TrkB signaling in the pathophysiology of inflammation-induced depression, and propose mechanistic actions for potential therapeutic agents. Additionally, the authors discuss the putative role of TrkB agonists and antagonists as novel therapeutic drugs for inflammation-related depression.

Adjunctive treatment of brexpiprazole with fluoxetine shows a rapid antidepressant effect in social defeat stress model: Role of BDNF-TrkB signaling

Addition of low doses of the atypical antipsychotic drug brexpiprazole with selective serotonin reuptake inhibitors (SSRIs) could promote antidepressant effect in patients with major depressive disorder although the precise mechanisms underlying the action of the combination are unknown. Combination of low dose of brexpiprazole (0.1 mg/kg) and SSRI fluoxetine (10 mg/kg) could promote a rapid antidepressant effect in social defeat stress model although brexpiprazole or fluoxetine alone did not show antidepressant effect. Furthermore, the combination significantly improved alterations in the brain-derived neurotrophic factor (BDNF) - TrkB signaling and dendritic spine density in the prefrontal cortex, hippocampus, and nucleus accumbens in the susceptible mice after social defeat stress. Interestingly, TrkB antagonist ANA-12 significantly blocked beneficial effects of combination of brexpiprazole and fluoxetine on depression-like phenotype. These results suggest that BDNF-TrkB signaling plays a role in the rapid antidepressant action of the combination of brexpiprazole and fluoxetine.

Intake of 7,8-Dihydroxyflavone During Juvenile and Adolescent Stages Prevents Onset of Psychosis in Adult Offspring After Maternal Immune Activation

Prenatal infection and subsequent abnormal neurodevelopment of offspring is involved in the etiology of schizophrenia. Brain-derived neurotrophic factor (BDNF) and its high affinity receptor, tropomyosin receptor kinase B (TrkB) signaling plays a key role in the neurodevelopment. Pregnant mice exposed to polyriboinosinic-polyribocytidylic acid [poly(I:C)] causes schizophrenia-like behavioral abnormalities in their offspring at adulthood. Here we found that the juvenile offspring of poly(I:C)-treated mice showed cognitive deficits, as well as reduced BDNF-TrkB signaling in the prefrontal cortex (PFC). Furthermore, the adult offspring of poly(I:C)-treated mice showed cognitive deficits, prepulse inhibition (PPI) deficits, reduced BDNF-TrkB signaling, immunoreactivity of parvalbumin (PV) and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) in the prelimbic (PrL) of medial PFC and CA1 of hippocampus. Supplementation of a TrkB agonist 7,8-dihydroxyflavone (1 mg/mL in drinking water) during juvenile and adolescent stages could prevent these behavioral abnormalities, reduced BDNF-TrkB signaling in PFC and CA1, and immunoreactivity of PV and PGC-1α in the PrL of medial PFC and CA1 in the adult offspring from poly(I:C)-treated mice. These findings suggest that early intervention by a TrkB agonist in subjects with ultra-high risk for psychosis may reduce the risk of subsequent transition to schizophrenia.

Depression-like phenotype by deletion of α7 nicotinic acetylcholine receptor: Role of BDNF-TrkB in nucleus accumbens

The α7 subtype of nicotinic acetylcholine receptor (nAChR) plays a role in the inflammation which is implicated in depression. This study was undertaken to examine the role of α7 nAChR in depression using α7 nAChR knock-out (KO) mice. Serum levels of tumor necrosis factor-α and interlukin-1β in KO mice were higher than wild-type mice, suggesting an inflammatory process in KO mice. α7 nAChR KO mice showed depression-like phenotype. Furthermore, KO mice showed increased brain-derived neurotrophic factor (BDNF) and its receptor TrkB signaling, as well as increased synaptogenesis and spine density in the nucleus accumbens (NAc), although BDNF-TrkB signaling and synaptogenesis were not altered in the prefrontal cortex and hippocampus. Systemic administration of the TrkB antagonist ANA-12, but not the TrkB agonist 7,8-dihydroxyflavone and the selective serotonin reuptake inhibitor fluoxetine, showed a rapid antidepressant effect in KO mice by normalizing increased synaptogenesis in the NAc. In addition, bilateral infusion of ANA-12 into NAc promoted a rapid antidepressant effect in KO mice by normalizing increased synaptogenesis in the NAc. These findings suggest that increased BDNF-TrkB signaling and synaptogenesis in the NAc by deletion of α7 nAChR plays a key role in depression.

Role of Keap1-Nrf2 signaling in depression and dietary intake of glucoraphanin confers stress resilience in mice

The transcription factor Keap1-Nrf2 system plays a key role in inflammation which is involved in depression. We found lower expression of Keap1 and Nrf2 proteins in the prefrontal cortex (PFC), CA3 and dentate gyrus (DG) of hippocampus in mice with depression-like phenotype compared to control mice. Serum levels of pro-inflammatory cytokines in Nrf2 knock-out (KO) mice were higher than those of wild-type mice, suggestive of enhanced inflammation in KO mice. Decreased brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-receptor-kinase B (TrkB) signaling in the PFC, CA3 and DG plays a role in the depression-like phenotype of Nrf2 KO mice. TrkB agonist 7,8-dihydroxyflavone, but not antagonist ANA-12, produced antidepressant effects in Nrf2 KO mice, by stimulating TrkB in the PFC, CA3 and DG. Pretreatment with Nrf2 activator sulforaphane (SFN) prevented the depression-like phenotype induced after repeated social defeat stress. Interestingly, dietary intake of 0.1% glucoraphanin (a precursor of SFN) containing food during juvenile and adolescent stages also prevented the depression-like phenotype evoked in adulthood, after repeated social defeat stress. These findings suggest that Keap1-Nrf2 system plays a key role in depression and that dietary intake of SFN-rich food during juvenile stages and adolescence can confer stress resilience in adulthood.

Prefrontal cortical BDNF: A regulatory key in cocaine- and food-reinforced behaviors

Brain-derived neurotrophic factor (BDNF) affects synaptic plasticity and neural structure and plays key roles in learning and memory processes. Recent evidence also points to important, yet complex, roles for BDNF in rodent models of cocaine abuse and addiction. Here we examine the role of prefrontal cortical (PFC) BDNF in reward-related decision making and behavioral sensitivity to, and responding for, cocaine. We focus on BDNF within the medial and orbital PFC, its regulation by cocaine during early postnatal development and in adulthood, and how BDNF in turn influences responding for drug reinforcement, including in reinstatement models. When relevant, we draw comparisons and contrasts with experiments using natural (food) reinforcers. We also summarize findings supporting, or refuting, the possibility that BDNF in the medial and orbital PFC regulate the development and maintenance of stimulus-response habits. Further investigation could assist in the development of novel treatment approaches for cocaine use disorders.

Update of neurotrophic factors in neurobiology of addiction and future directions

Drug addiction is a chronic brain disease and drugs of abuse cause long lasting neuroadaptations. Addiction is characterized by the loss of control over drug use despite harmful consequences, and high rates of relapse even after long periods of abstinence. Neurotrophic factors (NTFs) are well known for their actions on neuronal survival in the peripheral nervous system. Moreover, NTFs have been shown to be involved in synaptic plasticity in the brain. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are two of the most studied NTFs and both of them have been reported to increase craving when administered into the mesocorticolimbic dopaminergic system after drug self-administration. Here we review recent data on BDNF and GDNF functions in addiction-related behavior and discuss them in relation to previous findings. Finally, we give an insight into how new technologies could aid in further elucidating the role of these factors in drug addiction.

Natural polyphenols: Influence on membrane transporters

Accumulated evidence has focused on the use of natural polyphenolic compounds as nutraceuticals since they showed a wide range of bioactivities and exhibited protection against variety of age-related disorders. Polyphenols have variable potencies to interact, and hence alter the activities of various transporter proteins, many of them classified as anion transporting polypeptide-binding cassette transporters like multidrug resistance protein and p-glycoprotein. Some of the efflux transporters are, generally, linked with anticancer and antiviral drug resistance; in this context, polyphenols may be beneficial in modulating drug resistance by increasing the efficacy of anticancer and antiviral drugs. In addition, these effects were implicated to explain the influence of dietary polyphenols on drug efficacy as result of food-drug interactions. However, limited data are available about the influence of these components on uptake transporters. Therefore, the objective of this article is to review the potential efficacies of polyphenols in modulating the functional integrity of uptake transporter proteins, including those terminated the effect of neurotransmitters, and their possible influence in neuropharmacology.

Alterations in brain-derived neurotrophic factor (BDNF) and its precursor proBDNF in the brain regions of a learned helplessness rat model and the antidepressant effects of a TrkB agonist and antagonist

Role of brain-derived neurotrophic factor (BDNF)-TrkB signaling in a learned helplessness (LH) model of depression was investigated. LH rats showed a reduction of BDNF in the medial prefrontal cortex (mPFC), CA3, and dentate gyrus (DG) of the hippocampus, whereas LH rats showed an increase in BDNF in the nucleus accumbens (NAc). Furthermore, levels of proBDNF, a BDNF precursor, were higher in the mPFC, but lower in the NAc, of LH rats. A single bilateral infusion of a TrkB agonist 7,8-DHF, but not a TrkB antagonist ANA-12, into the infralimbic (IL) of mPFC, DG, and CA3, but not the prelimbic (PrL) of mPFC, exerted antidepressant effects in LH rats. In contrast, a single bilateral infusion of ANA-12, but not 7,8-DHF, into the core and shell of NAc exerted antidepressant-like effects in LH rats, with more potent effects observed for the NAc core than for NAc shell. Interestingly, a single administration of 7,8-DHF (10mg/kg, i.p.) significantly improved a decreased phosphorylation of TrkB in the mPFC, CA3, and DG of LH rats. Additionally, ANA-12 (0.5mg/kg, i.p.) significantly improved an increased phosphorylation of TrkB in the NAc of LH rats. In conclusion, these results suggest that LH causes depression-like behavior by altering BDNF in the brain regions, and that proBDNF-BDNF processing and transport may be altered in the mPFC-NAc circuit of LH rats. Therefore, TrkB agonists might exert antidepressant effects by stimulating TrkB in the IL, CA3, and DG, while TrkB antagonists might exert antidepressant effects by blocking TrkB in the NAc.

Comparison of ketamine, 7,8-dihydroxyflavone, and ANA-12 antidepressant effects in the social defeat stress model of depression

RATIONALE

Brain-derived neurotrophic factor (BDNF) and signaling at its receptor, tropomyosin-related kinase B (TrkB), are implicated in the rapid and long-lasting antidepressant effects of ketamine. Moreover, a TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF), and/or TrkB antagonist, ANA-12, shows antidepressant effects in animal models of depression.

OBJECTIVE

The objective of this study is to compare the influence of ketamine, 7,8-DHF, and ANA-12 on antidepressant activity in the social defeat stress model.

RESULTS

In the tail suspension and forced swimming tests, ketamine, 7,8-DHF, or ANA-12 markedly attenuated the increased immobility time in depressed mice compared with the vehicle-treated group. In the sucrose preference test, all drugs significantly improved the reduced preference in depressed mice at both 1 and 3 days after a single dose. Antidepressant effect of ketamine, but not 7,8-DHF or ANA-12, was still detectable 7 days after a single dose. Western blot analyses showed that ketamine, but not 7,8-DHF or ANA-12, markedly attenuated reduced levels of BDNF and postsynaptic density protein 95 (PSD-95) in the prefrontal cortex (PFC), dentate gyrus (DG), and CA3 of the hippocampus in depressed mice 8 days after a single dose. Furthermore, ketamine markedly increased reduced levels of GluA1 in the PFC and DG of depressed mice. In contrast, ketamine showed no effect against increased levels of BDNF, PSD-95, and GluA1 observed in the nucleus accumbens of depressed mice.

CONCLUSIONS

Compared with 7,8-DHF and ANA-12, ketamine is a longer-lasting antidepressant in the social defeat stress model, and synaptogenesis may be required for the mechanisms that promote sustained antidepressant effects of ketamine.

BDNF-Deficient Mice Show Reduced Psychosis-Related Behaviors Following Chronic Methamphetamine

BACKGROUND

One of the most devastating consequences of methamphetamine abuse is increased risk of psychosis. Brain-derived neurotrophic factor has been implicated in both psychosis and neuronal responses to methamphetamine. We therefore examined persistent psychosis-like behavioral effects of methamphetamine in brain-derived neurotrophic factor heterozygous mice.

METHODS

Mice were chronically treated with methamphetamine from 6 to 9 weeks of age, and locomotor hyperactivity to an acute D-amphetamine challenge was tested in photocell cages after a 2-week withdrawal period.

RESULTS

Methamphetamine-treated wild-type mice, but not brain-derived neurotrophic factor heterozygous mice, showed locomotor sensitization to acute 3mg/kg D-amphetamine. Qualitative analysis of exploration revealed tolerance to D-amphetamine effects on entropy in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice, but not wild-type mice.

CONCLUSIONS

Chronic methamphetamine exposure induces contrasting profiles of behavioral changes in wild-type and brain-derived neurotrophic factor heterozygous mice, with attenuation of behaviors relevant to psychosis in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice. This suggests that brain-derived neurotrophic factor signalling changes may contribute to development of psychosis in methamphetamine users.

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

Depression is a core symptom of methamphetamine (METH) withdrawal during the first several weeks of abstinence. However, the precise mechanisms underlying METH withdrawal symptoms remain unknown. Brain-derived neurotrophic factor (BDNF) and its specific receptor, tropomyosin-related kinase (TrkB), have a role the in pathophysiology of depression. In this study, we examined the role of BDNF-TrkB signaling in different brain regions of male mice with METH withdrawal symptoms. Repeated METH (3 mg kg(-1) per day for 5 days) administration to mice caused a long-lasting depression-like behavior including anhedonia. Western blot analysis showed that BDNF levels in the nucleus accumbens (NAc) of METH-treated mice were significantly higher than those of control mice whereas BDNF levels in other regions, including the prefrontal cortex and hippocampus, were not altered. METH-induced depression-like behavior, behavioral sensitization and dendritic changes in the NAc shell were improved by subsequent subchronic administration of TrkB antagonist ANA-12 (0.5 mg kg(-1) per day for 14 days), but not TrkB agonist 7,8-dihydroxyflavone (10 mg kg(-1) per day for 14 days). In vivo microdialysis showed that METH (1 mg kg(-1))-induced dopamine release in NAc shell of METH-treated mice was attenuated after subsequent subchronic ANA-12 administration. Interestingly, a single bilateral infusion of ANA-12 into the NAc shell, but not NAc core, showed a rapid and long-lasting therapeutic effect. However, ketamine and paroxetine had no effect. These findings suggest that increased BDNF-TrkB signaling in the NAc shell has an important role in the behavioral abnormalities after withdrawal from repeated METH administration, and that TrkB antagonists are potential therapeutic drugs for withdrawal symptoms in METH abusers.

R-ketamine: a rapid-onset and sustained antidepressant without psychotomimetic side effects

Although the efficacy of racemate ketamine, a rapid onset and sustained antidepressant, for patients with treatment-resistant depression was a serendipitous finding, clinical use of ketamine is limited, due to psychotomimetic side effects and abuse liability. Behavioral and side-effect evaluation tests were applied to compare the two stereoisomers of ketamine. To elucidate their potential therapeutic mechanisms, we examined the effects of these stereoisomers on brain-derived neurotrophic factor (BDNF)-TrkB signaling, and synaptogenesis in selected brain regions. In the social defeat stress and learned helplessness models of depression, R-ketamine showed a greater potency and longer-lasting antidepressant effect than S-ketamine (esketamine). Furthermore, R-ketamine induced a more potent beneficial effect on decreased dendritic spine density, BDNF-TrkB signaling and synaptogenesis in the prefrontal cortex (PFC), CA3 and dentate gyrus (DG) of the hippocampus from depressed mice compared with S-ketamine. However, neither stereoisomer affected these alterations in the nucleus accumbens of depressed mice. In behavioral tests for side effects, S-ketamine, but not R-ketamine, precipitated behavioral abnormalities, such as hyperlocomotion, prepulse inhibition deficits and rewarding effects. In addition, a single dose of S-ketamine, but not R-ketamine, caused a loss of parvalbumin (PV)-positive cells in the prelimbic region of the medial PFC and DG. These findings suggest that, unlike S-ketamine, R-ketamine can elicit a sustained antidepressant effect, mediated by increased BDNF-TrkB signaling and synaptogenesis in the PFC, DG and CA3. R-ketamine appears to be a potent, long-lasting and safe antidepressant, relative to S-ketamine, as R-ketamine appears to be free of psychotomimetic side effects and abuse liability.

Effects of sodium benzoate on pre-pulse inhibition deficits and hyperlocomotion in mice after administration of phencyclidine

OBJECTIVE

A recent clinical study demonstrated that sodium benzoate (SB), a prototype competitive d-amino acid oxidase inhibitor, was effective in the treatment of several symptoms, such as positive and negative symptoms, and cognitive impairment in medicated patients with schizophrenia. The objective of the study was to examine the effects of SB on behavioural abnormalities such as pre-pulse inhibition (PPI) deficits and hyperlocomotion in mice after a single administration of the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP).

METHODS

The effects of SB on behavioural abnormalities (PPI deficits and hyperlocomotion) in mice after PCP administration were examined. Furthermore, effects of SB on tissue levels of amino acids were also examined.

RESULTS

A single oral dose of SB (100, 300, or 1000 mg/kg) attenuated PPI deficits in mice after administration of PCP (3.0 mg/kg, s.c.) in a dose-dependent manner. In contrast, L-701,324 (10 mg/kg), an antagonist at the glycine site of the NMDA receptor, did not affect the effect of SB (1000 mg/kg) on PCP-induced PPI deficits. Furthermore, a single oral dose of SB (1000 mg/kg) significantly attenuated the hyperlocomotion in mice after administration of PCP (3.0 mg/kg, s.c.). However, a single oral dose of SB (1000 mg/kg) caused no changes to D-serine levels in plasma or in the frontal cortex, hippocampus, and striatum of these animals.

CONCLUSION

This study suggests that SB induced antipsychotic effects in the PCP model of schizophrenia, although it did not increase D-serine levels in the brain.

Antidepressant effects of TrkB ligands on depression-like behavior and dendritic changes in mice after inflammation

BACKGROUND

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase B (TrkB), signaling represent potential therapeutic targets for major depressive disorder. The purpose of this study is to examine whether TrkB ligands show antidepressant effects in an inflammation-induced model of depression.

METHODS

In this study, we examined the effects of TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) and TrkB antagonist ANA-12 on depression-like behavior and morphological changes in mice previously exposed to lipopolysaccharide (LPS). Protein levels of BDNF, phospho-TrkB (p-TrkB), and TrkB in the brain regions were also examined.

RESULTS

LPS caused a reduction of BDNF in the CA3 and dentate gyrus (DG) of the hippocampus and prefrontal cortex (PFC), whereas LPS increased BDNF in the nucleus accumbens (NAc). Dexamethason suppression tests showed hyperactivity of the hypothalamic-pituitary-adrenal axis in LPS-treated mice. Intraperitoneal (i.p.) administration of 7,8-DHF showed antidepressant effects on LPS-induced depression-like behavior, and i.p. pretreatment with ANA-12 blocked its antidepressant effects. Surprisingly, ANA-12 alone showed antidepressant-like effects on LPS-induced depression-like behavior. Furthermore, bilateral infusion of ANA-12 into the NAc showed antidepressant effects. Moreover, LPS caused a reduction of spine density in the CA3, DG, and PFC, whereas LPS increased spine density in the NAc. Interestingly, 7,8-DHF significantly attenuated LPS-induced reduction of p-TrkB and spine densities in the CA3, DG, and PFC, whereas ANA-12 significantly attenuated LPS-induced increases of p-TrkB and spine density in the NAc.

CONCLUSIONS

The results suggest that LPS-induced inflammation may cause depression-like behavior by altering BDNF and spine density in the CA3, DG, PFC, and NAc, which may be involved in the antidepressant effects of 7,8-DHF and ANA-12, respectively.

Protective effects of cholecystokinin-8 on methamphetamine-induced behavioral changes and dopaminergic neurodegeneration in mice

We investigated whether pretreatment with the neuropeptide cholecystokinin-8 affected methamphetamine (METH)-induced behavioral changes and dopaminergic neurodegeneration in male C57/BL6 mice. CCK-8 pretreatment alone had no effect on locomotion and stereotypic behavior and could not induce behavioral sensitization; however, it attenuated, in a dose-dependent manner, hyperlocomotion and behavioral sensitization induced by a low dose of METH (1mg/kg). CCK-8 attenuated METH-induced stereotypic behavior at a dose of 3mg/kg but not at 10mg/kg. CCK-8 pretreatment attenuated METH (10mg/kg)-induced hyperthermia, the decrease of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum, and TH in the substantia nigra. CCK-8 alone had no effect on rectal temperature, TH and DAT expression in the nigrostriatal region. In conclusion, our study demonstrated that pretreatment with CCK-8 inhibited changes typically induced by repeated exposure to METH, such as hyperlocomotion, behavioral sensitization, stereotypic behavior, and dopaminergic neurotoxicity. These findings make CCK-8 a potential therapeutic agent for the treatment of multiple symptoms associated with METH abuse.