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

Disruption of the NMDA receptor GluN2A subunit abolishes inflammation-induced depression

Recent reports have demonstrated that lipopolysaccharide (LPS)-induced depressive-like behaviour is mediated via NMDA receptor. In this study, we further investigated the role of GluN2 A subunit of NMDA receptor in synaptic processes in the prefrontal cortex (PFC) and hippocampus of GluN2 A knockout (KO) mice in LPS-induced depressive-like behavior. Our data suggest that LPS-treated mice, lacking GluN2 A subunit, did not exhibit depressive-like behaviour. This was accompanied by unaltered levels of IL-6 and significant changes in neuroplasticity markers and glutamate receptor subunits composition in PFC and hippocampus. In particular, an immune challenge in GluN2 A KO mice resulted in unchanged PSA-NCAM levels and proBDNF increase in both brain structures as well as in increase in BDNF levels in hippocampus. Furthermore, the absence of GluN2 A resulted in increased levels of all NCAM isoforms in PFC upon LPS which was followed with a decrease in GluN1 and GluN2B subunits. The levels of AMPA receptor subunits (GluA1, GluA3, and GluA4) in the hippocampus of GluN2 A mice were unaltered upon the treatment and abundantly present in the PFC of KO mice. These results indicate that the GluN2 A subunit is critical in neuroinflammation-related depression, that its absence abolishes LPS-induced depressive phenotype, sustains PSA-NCAM levels, increases proBDNF signalling in the PFC and hippocampus and potentiates synaptic stabilization through NCAM in the PFC upon an immune challenge.

Synapse-selective rapid potentiation of hippocampal synaptic transmission by 7,8-dihydroxyflavone

AIM

The identification of 7,8-dihydroxyflavone (DHF) as a small molecule agonist for tropomyosin-related kinase B (TrkB) facilitated understanding of the role of TrkB signaling in regulating higher brain functions. DHF can penetrate the blood-brain barrier after systemic administration and changes the performance of cognitive and emotional behavioral tasks. However, it is poorly understood how DHF modulates neuronal functions at cellular levels. Aiming to understand the cellular basis underlying DHF-induced modifications of the brain functions, we examined the effects of DHF on the hippocampal excitatory synaptic transmission.

METHODS

Field excitatory postsynaptic potentials were recorded using hippocampal slices prepared from adult male mice. Effects of bath-applied DHF on the synaptic efficacy were examined.

RESULTS

We found that DHF induced robust synaptic potentiation at the mossy fiber to CA3 synapse. DHF had minimal effects at other hippocampal excitatory synapses or at immature mossy fiber synapse in juvenile mice. The TrkB receptor blockers K252a and ANA-12 did not affect the DHF-induced synaptic potentiation. Drug screening revealed that relatively low concentrations of 2-aminoethoxydiphenylborane blocked the DHF-induced synaptic potentiation.

CONCLUSION

Our results demonstrate that DHF selectively potentiates hippocampal mossy fiber synaptic transmission via a TrkB receptor-independent mechanism. This novel neuromodulatory effect of DHF may influence higher brain functions by itself or together with the activation of the TrkB receptor. The rapid induction of the potentiation implies its potential importance in the acute behavioral effects of DHF.

Neurotrophic factors and neuroplasticity pathways in the pathophysiology and treatment of depression

Depression is a major health problem with a high prevalence and a heavy socioeconomic burden in western societies. It is associated with atrophy and impaired functioning of cortico-limbic regions involved in mood and emotion regulation. It has been suggested that alterations in neurotrophins underlie impaired neuroplasticity, which may be causally related to the development and course of depression. Accordingly, mounting evidence suggests that antidepressant treatment may exert its beneficial effects by enhancing trophic signaling on neuronal and synaptic plasticity. However, current antidepressants still show a delayed onset of action, as well as lack of efficacy. Hence, a deeper understanding of the molecular and cellular mechanisms involved in the pathophysiology of depression, as well as in the action of antidepressants, might provide further insight to drive the development of novel fast-acting and more effective therapies. Here, we summarize the current literature on the involvement of neurotrophic factors in the pathophysiology and treatment of depression. Further, we advocate that future development of antidepressants should be based on the neurotrophin theory.

Val66Met polymorphism association with serum BDNF and inflammatory biomarkers in major depression

OBJECTIVES

Current evidence supports participation of neurotrophic and inflammatory factors in the pathogenesis of major depressive disorder (MDD). Some studies reported an association between the Val66Met polymorphism (rs6265) of brain-derived neurotrophic factor (BDNF) gene with MDD and peripheral BDNF levels. However, no previous studies have examined the association of this polymorphism with inflammation. The present study assessed the association of the Val66Met polymorphism with serum levels of BDNF and inflammatory markers among depressed outpatients.

METHODS

All participants (n = 73) met DSM-IV criteria for a unipolar depressive episode. The serum levels of BDNF and inflammatory biomarkers (IL-2, IL-4, IL-6, IL-10, TNF-α and IFN-γ) were compared between individuals presenting with at least one Met allele (Met-carriers) and those homozygous for the Val allele.

RESULTS

In our sample (84.9% female, mean age 52.4 ± 10.3 years), 24.7% (n = 18) were Met-carriers. After Bonferroni correction, the Met allele was significantly associated with higher BDNF and lower TNF-α. These associations persisted after adjusting for potential confounders.

CONCLUSIONS

The pattern of low BDNF and high inflammation in MDD may be influenced by the Val66Met polymorphism. The association of a polymorphism in the BDNF gene with inflammatory markers in addition to BDNF levels suggests an interaction between these systems.

(2R,6R)-Hydroxynorketamine is not essential for the antidepressant actions of (R)-ketamine in mice

(R,S)-Ketamine has rapid and sustained antidepressant effects in depressed patients. Although the metabolism of (R,S)-ketamine to (2 R,6 R)-hydroxynorketamine (HNK), a metabolite of (R)-ketamine, has been reported to be essential for its antidepressant effects, recent evidence suggests otherwise. The present study investigated the role of the metabolism of (R)-ketamine to (2 R,6 R)-HNK in the antidepressant actions of (R)-ketamine. Antidepressant effects were evaluated using the forced swimming test in the lipopolysaccharide (LPS)-induced inflammation model of mice and the tail suspension test in naive mice. To prevent the metabolism of (R)-ketamine to (2 R,6 R)-HNK, mice were pretreated with cytochrome P450 (CYP) inhibitors. The concentrations of (R)-ketamine, (R)-norketamine, and (2 R,6 R)-HNK in plasma, brain, and cerebrospinal fluid (CSF) samples were determined using enantioselective liquid chromatography-tandem mass spectrometry. The concentrations of (R)-norketamine and (2 R,6 R)-HNK in plasma, brain, and CSF samples after administration of (R)-norketamine (10 mg/kg) and (2 R,6 R)-HNK (10 mg/kg), respectively, were higher than those generated after administration of (R)-ketamine (10 mg/kg). Nonetheless, while (R)-ketamine attenuated, neither (R)-norketamine nor (2 R,6 R)-HNK significantly altered immobility times of LPS-treated mice. Treatment with CYP inhibitors prior to administration of (R)-ketamine increased the plasma levels of (R)-ketamine, while generation of (2 R,6 R)-HNK was almost completely blocked. (R)-Ketamine exerted the antidepressant effects at a lower dose in the presence of CYP inhibitors than in their absence, which is consistent with exposure levels of (R)-ketamine but not (2 R,6 R)-HNK. These results indicate that metabolism to (2 R,6 R)-HNK is not necessary for the antidepressant effects of (R)-ketamine and that unmetabolized (R)-ketamine itself may be responsible for its antidepressant actions.

No Sex-Specific Differences in the Acute Antidepressant Actions of (R)-Ketamine in an Inflammation Model

BACKGROUND

Although previous reports suggest sex-specific differences in the antidepressant actions of (R,S)-ketamine, these differences in the antidepressant actions of (R)-ketamine, which is more potent than (S)-ketamine, are unknown.

METHODS

Saline or (R)-ketamine was administered 23 hours post lipopolysaccharide administration to adult male or female mice. Subsequently, antidepressant effects were assessed using a forced swimming test. Furthermore, the concentration of (R)-ketamine and its 2 major metabolites, (R)-norketamine and (2R,6R)-hydroxynorketamine, was measured in the plasma and brain after the administration of (R)-ketamine in the mice.

RESULTS

(R)-ketamine (10 mg/kg) significantly attenuated the increased immobility time of forced swimming test in the lipopolysaccharide-treated mice. There were no sex-specific differences in the concentrations of (R)-ketamine and its 2 metabolites in the plasma and brain.

CONCLUSIONS

These findings showed no sex-specific differences in terms of the acute antidepressant effects and pharmacokinetic profile of (R)-ketamine.

Deletion of serine racemase confers D-serine -dependent resilience to chronic social defeat stress

The N-methyl-D-aspartate receptor (NMDAR) plays a key role in the pathophysiology of depression. Serine racemase (SRR, encoded by Srr) converts L-serine to D-serine, an endogenous co-agonist at the glycine site of the NMDAR. Knock-out (KO) of Srr did not alter behavioral signs of depression compared with wild-type (WT) mice as evaluated by locomotion, tail suspension, forced swimming, and 1% sucrose preference tests. However, chronic social defeat stress (CSDS: 10 days) caused a depression-like phenotype as measured by these same tests in WT mice but not in Srr KO mice, suggesting that decreased D-serine co-agonist activity confers resilience against CSDS. In WT mice, CSDS decreased brain-derived neurotrophic factor (BDNF) expression and phosphorylation/activation of its receptor TrkB in prefrontal cortex (PFC), dentate gyrus (DG), and the CA3 region of the hippocampus, but increased BDNF and phosphorylated TrkB in the nucleus accumbens (NAc). Conversely, CSDS did not alter BDNF or TrkB phosphorylation in any brain region of Srr KO mice. Administration of D-serine through drinking water (600 mg/L for 20 days) 10 days prior to and during CSDS restored the depression-like phenotype in Srr KO mice. These findings suggest that reducing brain D-serine may improve stress resilience, thereby reducing depression risk.

Protective effects of 7,8-dihydroxyflavone on neuropathological and neurochemical changes in a mouse model of Alzheimer's disease

Interest in brain-derived neurotrophic factor (BDNF) was greatly enhanced when it was recognized that its expression is reduced in neurodegenerative disorders, especially in Alzheimer's disease (AD). BDNF signaling through the TrkB receptor has a central role in promoting synaptic transmission, synaptogenesis, and facilitating synaptic plasticity making the BDNF-TrkB signaling pathway an attractive candidate for targeted therapies. Here we investigated the early effect of the small molecule TrkB agonist, 7,8 dihydroxyflavone (7,8-DHF), on AD-related pathology, dendritic arborization, synaptic density, and neurochemical changes in the 5xFAD mouse model of AD. We treated 5xFAD mice with 7,8-DHF for 2 months beginning at 1 month of age. We found that, in this model of AD, 7,8-DHF treatment decreased cortical Aβ plaque deposition and protected cortical neurons against reduced dendritic arbor complexity but had no significant impact on the density of dendritic spines. In addition 7,8-DHF treatment protected against hippocampal increase in the level of choline-containing compounds and glutamate loss, but had no significant impact on hippocampal neurogenesis.

The TrkB agonist 7,8-dihydroxyflavone changes the structural dynamics of neocortical pyramidal neurons and improves object recognition in mice

BDNF and its receptor TrkB have important roles in neurodevelopment, neural plasticity, learning, and memory. Alterations in TrkB expression have been described in different CNS disorders. Therefore, drugs interacting with TrkB, specially agonists, are promising therapeutic tools. Among them, the recently described 7,8-dihydroxyflavone (DHF), an orally bioactive compound, has been successfully tested in animal models of these diseases. Recent studies have shown the influence of this drug on the structure of pyramidal neurons, specifically on dendritic spine density. However, there is no information yet on how DHF may alter the structural dynamics of these neurons (i.e., real-time study of the addition/elimination of dendritic spines and axonal boutons). To gain knowledge on these effects of DHF, we have performed a real-time analysis of spine and axonal dynamics in pyramidal neurons of barrel cortex, using cranial windows and 2-photon microscopy during a chronic oral treatment with this drug. After confirming TrkB expression in these neurons, we found that DHF increased the gain rates of spines and axonal boutons, as well as improved object recognition memory. These results help to understand how the activation of the BDNF-TrkB system can improve basic behavioral tasks through changes in the structural dynamics of pyramidal neurons. Moreover, they highlight DHF as a promising therapeutic vector for certain brain disorders in which this system is altered.

Design, Synthesis and Evaluation of Oxazaborine Inhibitors of the NLRP3 Inflammasome

The NLRP3 inflammasome is an important regulator of the sterile inflammatory response, and its activation by host-derived sterile molecules leads to the intracellular activation of caspase-1, processing of the pro-inflammatory cytokines interleukin-1β (IL-1β)/IL-18, and pyroptotic cell death. Inappropriate activation of NLRP3 drives a chronic inflammatory response and is implicated in several non-communicable diseases, including gout, atherosclerosis, type II diabetes and Alzheimer's disease. In this study, we report the design, synthesis and biological evaluation of novel boron compounds (NBCs) as NLRP3 inflammasome inhibitors. Structure-activity relationships (SAR) show that 4-fluoro substituents on the phenyl rings retain NLRP3 inhibitory activity, whereas more steric and lipophilic substituents diminish activity. Loss of inhibitory activity is also observed if the CCl3 group on the oxazaborine ring is replaced by a CF3 group. These findings provide additional understanding of the NBC series and will aid in the development of these NLRP3 inhibitors as tool compounds or therapeutic candidates for sterile inflammatory diseases.

Advances in the Preclinical Study of Some Flavonoids as Potential Antidepressant Agents

Flavonoids are phenolic compounds found commonly in plants that protect them against the negative effects of environmental insults. These secondary metabolites have been widely studied in preclinical research because of their biological effects, particularly as antioxidant agents. Diverse flavonoids have been studied to explore their potential therapeutic effects in the treatment of disorders of the central nervous system, including anxiety and depression. The present review discusses advances in the study of some flavonoids as potential antidepressant agents. We describe their behavioral, physiological, and neurochemical effects and the apparent mechanism of action of their preclinical antidepressant-like effects. Natural flavonoids produce antidepressant-like effects in validated behavioral models of depression. The mechanism of action of these effects includes the activation of serotonergic, dopaminergic, noradrenergic, and γ-aminobutyric acid-ergic neurotransmitter systems and an increase in the production of neural factors, including brain-derived neurotrophic factor and nerve growth factor. Additionally, alterations in the function of tropomyosin receptor kinase B and activity of the enzyme monoamine oxidase A have been reported. In conclusion, preclinical research supports the potential antidepressant effects of some natural flavonoids, which opens new possibilities of evaluating these substances to develop complementary therapeutic alternatives that could ameliorate symptoms of depressive disorders in humans.

The Dopamine Receptor D3 Regulates Lipopolysaccharide-Induced Depressive-Like Behavior in Mice

BACKGROUND

The altered expression and function of dopamine receptor D3 (D3R) in patients and animal models have been correlated with depression disease severity. However, the morphological alterations and biological effects of D3R in the brain after inflammation-induced depressive-like behavior remain elusive.

METHODS

In the present study, we ascertained the changes of D3R expression in the brain regions after depressive-like behavior induced by peripheral administration of lipopolysaccharide (LPS). Protein levels of proinflammatory cytokines, brain-derived neurotrophic factor (BDNF), and extracellular signal-regulated kinase (ERK1/2)-cAMP-response element-binding protein (CREB) signaling pathway after activation or inhibition of D3R in the brain of depressive mice were also investigated.

RESULTS

LPS caused a significant reduction of D3R in the ventral tegmental area (VTA), medial prefrontal cortex (mPFC), and nucleus accumbens (NAc), which are areas related to the mesolimbic dopaminergic system. Pretreatment with pramipexole (PPX), a preferential D3R agonist, showed antidepressant effects on LPS-induced depression-like behavior through preventing changes in LPS-induced proinflammatory cytokines (tumour necrosis factor-α, interleukin-1β, and interleukin-6), BDNF, and ERK1/2-CREB signaling pathway in the VTA and NAc. In opposition, treatment with a D3R selective antagonist NGB 2904 alone made mice susceptible to depression-like effects and caused changes in accordance with the LPS-induced alterations in proinflammatory cytokines, BDNF, and the ERK1/2-CREB signaling pathway in the mPFC and NAc.

CONCLUSIONS

These findings provide a relevant mechanism for D3R in LPS-induced depressive-like behavior via its mediation of proinflammatory cytokines and potential cross-effects between BDNF and the ERK1/2-CREB signaling pathway.

Dihydromyricetin exerts a rapid antidepressant-like effect in association with enhancement of BDNF expression and inhibition of neuroinflammation

RATIONALE

Major depressive disorder (MDD) is a highly prevalent illness that affects large populations across the world, and increasing evidence suggests that neuroinflammation and levels of brain-derived neurotrophic factor (BDNF) are closely related to depression. Dihydromyricetin (DHM) is a kind of flavonoid natural product that has been reported to display multiple pharmacological effects, including anti-inflammatory and anti-oxidative properties, and these may contribute to ameliorate MDD.

OBJECTIVE

This study investigated the effect of DHM on depression-related phenotypes in various experimental animal models.

METHODS

The antidepressant-like effect of DHM was validated via depression-related behavioral tests in naïve male C57BL/6 mice, as well as in the acute lipopolysaccharide-induced mouse model of depression. The chronic unpredicted mild stress (CUMS) mouse model of depression was also used to assess the rapid antidepressant-like effect of DHM by tail suspension test (TST), forced swimming test (FST), locomotor activity, and sucrose preference test (SPT). The expression of BDNF and inflammatory factors were determined through Western blotting and enzyme-linked immunosorbent assay, respectively.

RESULTS

DHM reduced immobility time in the TST and FST both in mice and the acute LPS-induced mouse model of depression. Seven days of DHM treatment ameliorated depression-related behaviors induced by CUMS, whereas similar treatment with the typical antidepressant venlafaxine did not. DHM activated the ERK1/2-CREB pathway and increased glycogen synthase kinase-3 beta (GSK-3β) phosphorylation at ser-9, with upregulation of BDNF expression, in both hippocampal tissues and cultured hippocampal cells.

CONCLUSION

The present data indicate that DHM exerts a more rapid antidepressant-like effect than does a typical antidepressant, in association with enhancement of BDNF expression and inhibition of neuroinflammation.

Adolescent Corticosterone and TrkB Pharmaco-Manipulations Sex-Dependently Impact Instrumental Reversal Learning Later in Life

Early-life trauma can increase the risk for, and severity of, several psychiatric illnesses. These include drug use disorders, and some correlations appear to be stronger in women. Understanding the long-term consequences of developmental stressor or stress hormone exposure and possible sex differences is critically important. So-called “reversal learning” tasks are commonly used in rodents to model cognitive deficits in stress- and addiction-related illnesses in humans. Here, we exposed mice to the primary stress hormone corticosterone (CORT) during early adolescence (postnatal days 31–42), then tested behavioral flexibility in adulthood using an instrumental reversal learning task. CORT-exposed female, but not male, mice developed perseverative errors. Despite resilience to subchronic CORT exposure, males developed reversal performance impairments following exposure to physical stressors. Administration of a putative tyrosine kinase receptor B (trkB) agonist, 7,8-dihydroxyflavone (7,8-DHF), during adolescence blocked CORT-induced errors in females and improved performance in males. Conversely, blockade of trkB by ANA-12 impaired performance. These data suggest that trkB-based interventions could have certain protective benefits in the context of early-life stressor exposure. We consider the implications of our findings in an extended “Discussion” section.

Aerobic exercise and a BDNF-mimetic therapy rescue learning and memory in a mouse model of Down syndrome

Down syndrome (DS) is caused by the triplication of human chromosome 21 and represents the most frequent genetic cause of intellectual disability. The trisomic Ts65Dn mouse model of DS shows synaptic deficits and reproduces the essential cognitive disabilities of the human syndrome. Aerobic exercise improved various neurophysiological dysfunctions in Ts65Dn mice, including hippocampal synaptic deficits, by promoting synaptogenesis and neurotransmission at glutamatergic terminals. Most importantly, the same intervention also prompted the recovery of hippocampal adult neurogenesis and synaptic plasticity and restored cognitive performance in trisomic mice. Additionally, the expression of brain-derived neurotrophic factor (BDNF) was markedly decreased in the hippocampus of patients with DS. Since the positive effect of exercise was paralleled by increased BDNF expression in trisomic mice, we investigated the effectiveness of a BDNF-mimetic treatment with 7,8-dihydroxyflavone at alleviating intellectual disabilities in the DS model. Pharmacological stimulation of BDNF signaling rescued synaptic plasticity and memory deficits in Ts65Dn mice. Based on our findings, Ts65Dn mice benefit from interventions aimed at promoting brain plasticity, and we provide evidence that BDNF signaling represents a potentially new pharmacological target for treatments aimed at rescuing cognitive disabilities in patients with DS.

Regulation of actions and habits by ventral hippocampal trkB and adolescent corticosteroid exposure

In humans and rodents, stress promotes habit-based behaviors that can interfere with action-outcome decision-making. Further, developmental stressor exposure confers long-term habit biases across rodent-primate species. Despite these homologies, mechanisms remain unclear. We first report that exposure to the primary glucocorticoid corticosterone (CORT) in adolescent mice recapitulates multiple neurobehavioral consequences of stressor exposure, including long-lasting biases towards habit-based responding in a food-reinforced operant conditioning task. In both adolescents and adults, CORT also caused a shift in the balance between full-length tyrosine kinase receptor B (trkB) and a truncated form of this neurotrophin receptor, favoring the inactive form throughout multiple corticolimbic brain regions. In adolescents, phosphorylation of the trkB substrate extracellular signal-regulated kinase 42/44 (ERK42/44) in the ventral hippocampus was also diminished, a long-term effect that persisted for at least 12 wk. Administration of the trkB agonist 7,8-dihydroxyflavone (7,8-DHF) during adolescence at doses that stimulated ERK42/44 corrected long-lasting corticosterone-induced behavioral abnormalities. Meanwhile, viral-mediated overexpression of truncated trkB in the ventral hippocampus reduced local ERK42/44 phosphorylation and was sufficient to induce habit-based and depression-like behaviors. Together, our findings indicate that ventral hippocampal trkB is essential to goal-directed action selection, countering habit-based behavior otherwise facilitated by developmental stress hormone exposure. They also reveal an early-life sensitive period during which trkB-ERK42/44 tone determines long-term behavioral outcomes.

Antidiabetic drug glyburide modulates depressive-like behavior comorbid with insulin resistance

Background

Abundant reports indicated that depression was often comorbid with type 2 diabetes and even metabolic syndrome. Considering they might share common biological origins, it was tentatively attributed to the chronic cytokine-mediated inflammatory response which was induced by dysregulation of HPA axis and overactivation of innate immunity. However, the exact mechanisms remain obscure. Herein, we mainly focused on the function of the NLRP3 inflammasome to investigate this issue.

Methods

Male C57BL/6 mice were subjected to 12 weeks of chronic unpredictable mild stress (CUMS), some of which were injected with glyburide or fluoxetine. After CUMS procedure, behavioral and metabolic tests were carried out. In order to evaluate the systemic inflammation associated with inflammasome activation, IL-1β and inflammasome components in hippocampi and pancreases, as well as corticosterone and IL-1β in serum were detected separately. Moreover, immunostaining was performed to assess morphologic characteristics of pancreases.

Results

In the present study, we found that 12 weeks’ chronic stress resulted in depressive-like behavior comorbid with insulin resistance. Furthermore, antidiabetic drug glyburide, an inhibitor of the NLRP3 inflammasome, was discovered to be effective in preventing the experimental comorbidity. In brief, it improved behavioral performance, ameliorated insulin intolerance as well as insulin signaling in the hippocampus possibly through inhibiting NLRP3 inflammasome activation by suppressing the expression of TXNIP.

Conclusions

All these evidence supported our hypothesis that chronic stress led to comorbidity of depressive-like behavior and insulin resistance via long-term mild inflammation. More importantly, based on the beneficial effects of blocking the activation of the NLRP3 inflammasome, we provided a potential therapeutic target for clinical comorbidity and a new strategy for management of both diabetes and depression.

Increased EphA4-ephexin1 signaling in the medial prefrontal cortex plays a role in depression-like phenotype

Accumulating evidence suggests a role of the ephrin receptor EphA4 and the downstream protein ephexin1 in synaptic plasticity, which is implicated in depression. We examined whether EphA4–ephexin1 signaling plays a role in the pathophysiology of depression, and the antidepressant-like effect of EphA4 inhibitor rhynchophylline. We found increased ratios of p-EphA4/EphA4 and p-ephexin1/ephexin1 in the prefrontal cortex (PFC) and hippocampus but not in the nucleus accumbens (NAc), of susceptible mice after social defeat stress. Furthermore, the p-EphA4/EphA4 ratio was higher in the parietal cortex of depressed patients compared with controls. Systemic administration of rhynchophylline, produced a rapid antidepressant-like effect in a social defeat stress model by inhibiting EphA4–ephexin1 signaling and activating brain-derived neurotrophic factor-TrkB signaling in the PFC and hippocampus. Pretreatment with rhynchophylline before each social defeat stress could prevent the onset of the depression-like phenotype after repeated social defeat stress. Overexpression of EphA4 in the medial PFC owing to infection with an EphA4 adeno-associated virus caused the depression-like phenotype 3 weeks later and rhynchophylline had a rapid antidepressant-like effect in these mice. These findings suggest that increased EphA4–ephexin1 signaling in the PFC plays a role in the pathophysiology of depression.

Antidepressant-like effects and cognitive enhancement of Schisandra chinensis in chronic unpredictable mild stress mice and its related mechanism

The aim of this study was to evaluate whether Schisandra chinensis extract (SCE) administration influences chronic unpredictable mild stress (CUMS)-induced depression and cognitive impairment, and explores underlying mechanisms. Sucrose preference test (SPT) and forced swimming test (FST) were used for assessing depressive symptoms, and Y-maze, Morris water maze were used for evaluating cognition processes. The results showed that CUMS (4 weeks) was effective in producing both depression and memory deficits in mice. Additionally, CUMS exposure significantly decreased brain derived neurotrophic factor (BDNF) levels in hippocampus as indicated by ELISA, immunohistochemistry and immunofluorescence assays, accompanied by down-regulated tyrosine kinase receptor B (TrkB)/cAMP-response element binding protein (CREB)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3 kinase (PI3K)/ protein kinase B (AKT)/ glycogen synthase kinase-3β (GSK-3β) signaling pathways. Chronic administration of SCE (600 or 1200 mg/kg, i.g.) significantly prevented all these CUMS-induced behavioral and biochemical alterations. It suggested that SCE could improve the depression-like emotional status and associated cognitive deficits in CUMS mice, which might be mediated by regulation of BDNF levels in hippocampus, as well as up-regulating of TrkB/CREB/ERK and PI3K/AKT/GSK-3β pathways.

Inhibition of TrkB at the nucleus accumbens, using ANA-12, regulates basal and stress-induced orexin A expression within the mesolimbic system and affects anxiety, sociability and motivation

Repeated stress exposure can lead to the development of anxiety and mood disorders. An emerging biological substrate of depression and associated pathology is the nucleus accumbens (NAc), which through interactions with limbic, cognitive and motor circuits can regulate a variety of stress responses. Within these circuits, orexin neurons are involved in arousal and stress adaptability, effects proposed mediated via brain-derived neurotrophic factor signaling. This study tested the hypotheses that 1) repeated exposure to heterotypic stress alters social ability and preference and passive avoidant behaviors, 2) TrkB receptors at the NAc shell regulates stress-induced behavioral responses and orexin expression within the mesocorticolimbic system. Our findings indicate that ANA-12 (0.25 μg/0.5 μl) enhanced sociability during the social interaction test, although treatment had no effect on social preference. The development of conditioned place preference, and fear retention in the passive avoidance test were also facilitated by ANA-12. Biochemical assessments on brain tissues collected within 2 h of a forced swim exposure revealed that ANA-12 increased orexin A immunoreactivity (ir) in the hypothalamic perifornical area, while expression was reduced in the ventral portion of the hippocampal CA1 layer, irrespective of the stress condition. This contrasts changes at the VTA characterized by elevated versus reduced orexin A-ir in ANA-12-treated stress and non-stress rats, respectively. Colocalized orexin A- and tyrosine hydroxylase (TH)-ir at the VTA supports a different temporal expression post stress, TH-ir being unaffected 9 days post stress. These findings support a role for TrkB receptors in regulating basal and stress-induced social, cognitive and motivational behavior, and modulatory actions of BDNF, via TrkB signaling, on orexin A signaling upon stress exposure.

Alterations in the inflammatory cytokines and brain-derived neurotrophic factor contribute to depression-like phenotype after spared nerve injury: improvement by ketamine

Although pain is frequently accompanied with depression, little is known about the risk factors contributing to individual differences to the comorbidity of pain and depression. In this study, we examined whether cytokines and brain-derived neurotrophic factor (BDNF) might contribute to the individual differences in the development of neuropathic pain-induced depression. Rats were randomly subjected to spared nerved ligation (SNI) or sham surgery. The SNI rats were divided into two groups by the data from depression-related behavioral tests. Rats with depression-like phenotype displayed higher levels of pro-inflammatory cytokines (e.g., interleukin (IL)-1β, IL-6) as well as imbalance of pro/anti-inflammatory cytokines compared with rats without depression-like phenotype and sham-operated rats. Levels of BDNF in the prefrontal cortex of rats with depression-like phenotype were lower than those of rats without depression-like phenotype and sham-operated rats. A single dose of ketamine ameliorated depression-like behaviors in the rats with depression-like phenotype. Interestingly, higher serum levels of IL-1β and IL-6 in the rat with depression-like phenotype were normalized after a single dose of ketamine. These findings suggest that alterations in the inflammatory cytokines and BDNF might contribute to neuropathic pain-induced depression, and that serum cytokines may be predictable biomarkers for ketamine’s antidepressant actions.

Blockade of interleukin-6 receptor in the periphery promotes rapid and sustained antidepressant actions: a possible role of gut-microbiota-brain axis

Depression is a common, severe and chronic psychiatric disease. Although the currently available antidepressants have been used in the treatment of depression, their beneficial effects are limited. Accumulating evidence suggests that pro-inflammatory cytokines such as interleukin-6 (IL-6) have an important role in the pathogenesis of depression. This study was undertaken to examine whether anti-mouse IL-6 receptor antibody (MR16-1) induces antidepressant effects in a social defeat stress model. Intravenous injection of MR16-1 induced rapid-onset and long-lasting antidepressant effects in susceptible mice after social defeat stress through its anti-inflammatory actions. In contrast, intracerebroventricular injection of MR16-1 induced no antidepressant effects in susceptible mice. Furthermore, treatment with MR16-1 could significantly normalize alterations in the expression of synaptic proteins (postsynaptic density protein 95 and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor 1) and dendritic spine density in the brain regions of susceptible mice. Gut microbiota analysis using 16S ribosomal RNA gene sequencing showed that MR16-1 significantly improved decreased Firmicutes/Bacteroidetes ratio in susceptible mice. It also significantly improved decreased levels of Oscillospira in susceptible mice. These findings suggest that peripheral IL-6 has a key role in the pathogenesis of depression and that the blockade of IL-6 receptor in the periphery might have rapid-onset and long-lasting antidepressant effects by normalizing the altered composition of gut microbiota in susceptible mice after social defeat stress. Therefore, the blockade of IL-6 receptor in the periphery shows promise as a novel therapeutic approach for depressed patients with higher IL-6 blood levels.

Hippocampal CysLT1R knockdown or blockade represses LPS-induced depressive behaviors and neuroinflammatory response in mice

Evidence suggests that neuroinflammation is involved in depression and that the cysteinyl leukotriene receptor 1 (CysLT₁R) plays a potential pathophysiological role in several types of CNS disorders. Our previous study has shown that knockdown of hippocampal CysLT₁R in mice prevents the depressive-like phenotype and neuroinflammation induced by chronic mild stress (CMS). Here, we examined the effects of hippocampal CysLT₁R knockdown and CysLT₁R blockade on LPS-induced depressive-like behavior in mice. We found that injection of LPS (0.5 mg/kg, ip) caused marked increase in hippocampal CysLT₁R expression, which was reversed by pretreatment with fluoxetine (20 mg·kg^-1·d^-1 for 7 d, ig). Knockdown of hippocampal CysLT₁R or blockade of CysLT₁R by pretreatment with pranlukast (0.5 mg/kg, ip) significantly suppressed LPS-induced depressive behaviors, as evidenced by decreases in mouse immobility time in the forced swimming test (FST) and tail suspension test (TST) and latency to feed in the novelty-suppressed feeding (NSF) test. Moreover, both CysLT₁R knockdown and CysLT₁R blockade markedly prevented LPS-induced neuroinflammation, as shown by the suppressed activation of microglia and NF-κB signaling as well as the hippocampal levels of TNF-α and IL-1β in mice. Our results suggest that CysLT₁R may be involved in LPS-induced depressive-like behaviors and neuroinflammation, and that downregulation of CysLT₁R could be a novel and potential therapeutic strategy for the treatment of depression, at least partially due to its role in neuroinflammation.

Depressive-Like Behaviors Are Regulated by NOX1/NADPH Oxidase by Redox Modification of NMDA Receptor 1

Involvement of reactive oxygen species (ROS) has been suggested in the development of psychiatric disorders. NOX1 is a nonphagocytic form of NADPH oxidase whose expression in the nervous system is negligible compared with other NOX isoforms. However, NOX1-derived ROS increase inflammatory pain and tolerance to opioid analgesia. To clarify the role of NOX1 in the brain, we examined depressive-like behaviors in mice deficient in Nox1 (Nox1^-/Y). Depressive-like behaviors induced by chronic social defeat stress or administration of corticosterone (CORT) were significantly ameliorated in Nox1^-/Y Generation of ROS was significantly elevated in the prefrontal cortex (PFC) of mice administrated with CORT, while NOX1 mRNA was upregulated only in the ventral tegmental area (VTA) among brain areas responsible for emotional behaviors. Delivery of miRNA against NOX1 to VTA restored CORT-induced depressive-like behaviors in wild-type (WT) littermates. Administration of CORT to WT, but not to Nox1^-/Y, significantly reduced transcript levels of brain-derived neurotrophic factor (bdnf), with a concomitant increase in DNA methylation of the promoter regions in bdnf Delivery of miRNA against NOX1 to VTA restored the level of BDNF mRNA in WT PFC. Redox proteome analyses demonstrated that NMDA receptor 1 (NR1) was among the molecules redox regulated by NOX1. In cultured cortical neurons, hydrogen peroxide significantly suppressed NMDA-induced upregulation of BDNF transcripts in NR1-expressing cells but not in cells harboring mutant NR1 (C744A). Together, these findings suggest a key role of NOX1 in depressive-like behaviors through NR1-mediated epigenetic modification of bdnf in the mesoprefrontal projection.SIGNIFICANCE STATEMENT NADPH oxidase is a source of reactive oxygen species (ROS) that have been implicated in the pathogenesis of various neurological disorders. We presently showed the involvement of a nonphagocytic type of NADPH oxidase, NOX1, in major depressive disorders, including behavioral, biochemical, and anatomical changes in mice. The oxidation of NR1 by NOX1-derived ROS was demonstrated in prefrontal cortex (PFC), which may be causally linked to the downregulation of BDNF, promoting depressive-like behaviors. Given that NOX1 is upregulated only in VTA but not in PFC, mesocortical projections appear to play a crucial role in NOX1-dependent depressive-like behaviors. Our study is the first to present the potential molecular mechanism underlying the development of major depression through the NOX1-induced oxidation of NR1 and epigenetic modification of bdnf.

Using the BITOLA system to identify candidate molecules in the interaction between oral lichen planus and depression

Exacerbations of oral lichen planus (OLP) have been linked to the periods of psychological stress, anxiety and depression. The specific mechanism of the interaction is unclear. The aim of this study was to explore the candidate genes or molecules that play important roles in the interaction between OLP and depression. The BITOLA system was used to search all intermediate concepts relevant to the "Gene or Gene Product" for OLP and depression, and the gene expression data and tissue-specific gene data along with manual checking were then employed to filter the intermediate concepts. Finally, two genes (NCAM1, neural cell adhesion molecule 1; CD4, CD4 molecule) passed the follow-up inspection. By using the text mining can formulate a new hypothesis: NCAM1 and CD4 were identified as involved or potentially involved in the interaction between OLP and depression. These results offer a new clue for the experimenters and hold promise for developing innovative therapeutic strategies for these two diseases.

Increased Levels of C1q in the Prefrontal Cortex of Adult Offspring after Maternal Immune Activation: Prevention by 7,8-Dihydroxyflavone

Objective

Prenatal infection is implicated in the etiology of schizophrenia. The objective of this paper is to study the role of complement protein C1q in the psychosis of adult offspring after maternal immune activation (MIA). In addition, effect of 7,8-dihydroxyflavone (7,8-DHF: a tropomyosin receptor kinase B [TrkB] agonist) was also examined.

Methods

Western blot analysis of C1q in the brain regions from adult offspring after prenatal poly(I:C) (5.0 mg/kg/day from E12 to E17) exposure was performed. 7,8-DHF or vehicle was given from 4 to 8-weeks old.

Results

Expression of C1q in the prefrontal cortex (PFC) of adult offspring from poly(I:C)-treated pregnant mice was significantly higher than that of control group. Early treatment with 7,8-DHF during juvenile and adolescent stages could prevent an increase of C1q in the PFC of adult offspring after MIA.

Conclusion

Therefore, it is likely that increased C1q expression in the frontal cortex may play a role in the behavioral abnormalities of adult offspring after MIA. Furthermore, supplementation with a TrkB agonist such as 7,8-DHF during the prodromal stage may have prophylactic effects on the behavioral abnormalities after MIA.

Antidepressant effects of combination of brexpiprazole and fluoxetine on depression-like behavior and dendritic changes in mice after inflammation

RATIONALE

Addition of low doses of atypical antipsychotic drugs with selective serotonin reuptake inhibitors (SSRIs) could promote a rapid antidepressant effect in treatment-resistant patients with major depression. Brexpiprazole, a new atypical antipsychotic drug, has been used as adjunctive therapy for the treatment of major depression.

OBJECTIVES

The present study was undertaken to examine whether brexpiprazole could augment antidepressant effects of the SSRI fluoxetine in an inflammation model of depression.

METHODS

We examined the effects of fluoxetine (10 mg/kg), brexpiprazole (0.1 mg/kg), or the combination of the two drugs on depression-like behavior, alterations in the brain-derived neurotrophic factor (BDNF) - TrkB signaling, and dendritic spine density in selected brain regions after administration of lipopolysaccharide (LPS) (0.5 mg/kg).

RESULTS

Combination of brexpiprazole and fluoxetine promoted a rapid antidepressant effect in inflammation model although brexpipazole or fluoxetine alone did not show antidepressant effect. Furthermore, the combination significantly improved LPS-induced alterations in the BDNF - TrkB signaling and dendritic spine density in the prefrontal cortex, CA3 and dentate gyrus, and nucleus accumbens.

CONCLUSIONS

These results suggest that add-on of brexpiprazole to fluoxetine can produce a rapid antidepressant effect in the LPS inflammation model of depression, indicating that adjunctive therapy of brexpiprazole to SSRIs could produce a rapid antidepressant effect in depressed patients with inflammation.

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.

Ocular Nerve Growth Factor Administration Modulates Brain-derived Neurotrophic Factor Signaling in Prefrontal Cortex of Healthy and Diabetic Rats

AIMS

Nerve growth factor (NGF) eyedrops (ed-NGF) activate brain neurons, stimulate growth factors, including brain-derived neurotrophic factor (BDNF), and exert neuroprotection in the forebrain of streptozotocin-induced diabetic rats (STZ rats). In this study, the effects of ed-NGF on BDNF signaling in the prefrontal cortex (PFC) were explored in healthy and STZ-diabetic rats, in which cortical neuronal and axonal loss, and altered circulating BDNF associated with depressive phenotype are also described.

METHODS

STZ and healthy (CTR) adult rats received ed-NGF twice a day for 2 weeks. Depressive phenotype was identified by force swimming test (FST). Proteins extracted from PFC were processed for ELISA and Western blot analyses to measure the expression of BDNF, proBDNF, and their receptors and intracellular signals.

RESULTS

ed-NGF treatment modulates BDNF pathway in PFC and normalizes the STZ-induced BDNF alterations by stimulating TRK-mediated survival mechanism. A decreased latency in FST was also found in STZ rats, while no change was observed comparing CTR + NGF and STZ + NGF with CTR.

CONCLUSION

The present data confirm the capacity of ed-NGF treatment to affect brain neurons and lead to brain damage recovery by activating protective and remodeling pathways triggered by BDNF. We suggest that the ed-NGF-induced changes in BDNF signaling might influence the manifestation of depressive phenotype in diabetic rats.

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.

Regional differences in the expression of brain-derived neurotrophic factor (BDNF) pro-peptide, proBDNF and preproBDNF in the brain confer stress resilience

Using learned helplessness (LH) model of depression, we measured protein expression of brain-derived neurotrophic factor (BDNF) pro-peptide, BDNF precursors (proBDNF and preproBDNF) in the brain regions of LH (susceptible) and non-LH rats (resilience). Expression of preproBDNF, proBDNF and BDNF pro-peptide in the medial prefrontal cortex of LH rats, but not non-LH rats, was significantly higher than control rats, although expression of these proteins in the nucleus accumbens of LH rats was significantly lower than control rats. This study suggests that regional differences in conversion of BDNF precursors into BDNF and BDNF pro-peptide by proteolytic cleavage may contribute to stress resilience.

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.

Antidepressant effects of TBE-31 and MCE-1, the novel Nrf2 activators, in an inflammation model of depression

The Nuclear factor (erythroid 2-derived)-like 2 (Nrf2) plays a key role in inflammation which is implicated in the pathophysiology of depression. The Nrf2 activators have antidepressant effects in animal models of depression. The present study was undertaken to examine whether TBE-31 [(±)-(4bS,8aR,10aS)-10a-ethynyl-4b,8,8-trimethyl-3,7-dioxo-3,4b,7,8,8a,9,10,10a-octahydrophenanthrene-2,6-dicarbonitrile] and MCE-1 [(±)-3-ethynyl-3-methyl-6-oxocyclohexa-1,4-dienecarbonitrile], the novel Nrf2 activators, could show antidepressant effects in inflammation model of depression. We found that TBE-31 and MCE-1 significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, in a concentration dependent manner. The Nrf2 siRNA, but not negative control of siRNA, significantly blocked the potentiating effects of TBE-31 and MCE-1 on neurite outgrowth in PC12 cells. Furthermore, oral administration of TBE-31 or MCE-1 significantly attenuated an increase in serum levels of tumor necrosis factor-α (TNF-α) after administration of lipopolysaccharide (LPS: 0.5mg/kg). In the tail-suspension test and forced swimming test, oral administration of TBE-31 or MCE-1 significantly attenuated an increase in the immobility time after LPS (0.5mg/kg) administration. These findings suggest that the novel Nrf2 activators such as TBE-31 and MCE-1 might be potential therapeutic drugs for inflammation-related depression.

7,8-Dihydroxyflavone reverses the depressive symptoms in mouse chronic mild stress

7,8-Dihydroxyflavone (7,8-DHF) is a naturally-occurring flavone which possesses good bioavailability. Due to its ability to cross the blood-brain barrier, previous studies have demonstrated that 7,8-DHF was a potent tropomyosin-related kinase B (TrkB) agonist, and produced antidepressant-like effects in mouse forced swimming test and tail suspension test. However, it has not been evaluated in chronic mild stress (CMS), a classical depression model modulating the processes of major depression in human. In the present study, we not only evaluated the depressive-like behaviors, but also measured the key proteins of TrkB signaling in mice exposed to CMS. Our results firstly found that long term but not single injection of 7,8-DHF restored the depressive-like behaviors in sucrose preference test and novelty suppressed feeding test. In addition, 7,8-DHF not only increased TrkB phosphorylation and brain-derived neurotrophic factor (BDNF) levels, but also activated the expression of TrkB downstream synaptic proteins such as PSD95 and synaptophysin. Furthermore, the TrkB antagonist K252a blocked the antidepressant-like effects of 7,8-DHF. In summary, the present results demonstrated that chronic 7,8-DHF treatment exerted significant antidepressant-like effects, which were likely attributed to regulating TrkB signaling and thus promoting synaptic protein expression.

Prophylactic effects of sulforaphane on depression-like behavior and dendritic changes in mice after inflammation

Inflammation plays a role in the pathophysiology of depression. Sulforaphane (SFN), an isothiocyanate compound derived from broccoli, is a potent activator of the NF-E2-related factor-2 (Nrf2), which plays a role in inflammation. In this study, we examined whether the prevention effects of SFN in lipopolysaccharide (LPS) induced depression-like behavior in mice. Pretreatment with SFN significantly blocked an increase in the serum tumor necrosis factor-α (TNF-α) level and an increase in microglial activation of brain regions after a single administration of LPS (0.5 mg/kg). Furthermore, SFN significantly potentiated increased serum levels of IL-10 after LPS administration. In the tail-suspension test and forced swimming test, SFN significantly attenuated an increase of the immobility time after LPS administration. In addition, SFN significantly recovered to control levels for LPS-induced alterations in the proteins such as brain-derived neurotrophic factor, postsynaptic density protein 95 and AMPA receptor 1 (GluA1) and dendritic spine density in the brain regions. Finally, dietary intake of 0.1% glucoraphanin (a glucosinolate precursor of SFN) food during the juvenile and adolescence could prevent the onset of LPS-induced depression-like behaviors and dendritic spine changes in the brain regions at adulthood. In conclusion, these findings suggest that dietary intake of SFN-rich broccoli sprout has prophylactic effects on inflammation-related depressive symptoms. Therefore, supplementation of SFN-rich broccoli sprout could be prophylactic vegetable to prevent or minimize the relapse by inflammation in the remission state of depressed patients.

Rapid and Sustained Antidepressant Action of the mGlu2/3 Receptor Antagonist MGS0039 in the Social Defeat Stress Model: Comparison with Ketamine

BACKGROUND

Similar to the N-methyl-D-aspartate receptor antagonist ketamine, the metabotropic glutamate 2/3 receptor antagonist, MGS0039, shows antidepressant effects. However, there are no reports comparing these 2 compounds in the social defeat stress model of depression.

METHODS

We examined the effects of MGS0039 (1 mg/kg) and ketamine (10 mg/kg) on depression-like behavior in susceptible mice after repeated social defeat stress. Protein levels of brain-derived neurotrophic factor, TrkB, phospho-TrkB, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (GluA1), postsynaptic density protein 95, and dendritic spine density in selected brain regions were measured.

RESULTS

In the tail suspension and forced swimming tests, both MGS0039 and ketamine significantly attenuated the increased immobility time observed in susceptible mice, compared with vehicle-treated animals, 1 or 2 days after a single dose of drug. In the sucrose preference test, both compounds significantly improved the reduced preference typically seen in susceptible mice at 3 to 7 days after a single dose of drug. Western-blot analyses showed that similar to ketamine, MGS0039 significantly attenuated the reduced brain-derived neurotrophic factor, phospho-TrkB/TrkB ratio, GluA1 and postsynaptic density protein 95 seen in the prefrontal cortex, dentate gyrus, and CA3 of the hippocampus from susceptible mice, 8 days after a single dose. Again, in a similar manner to ketamine, MGS0039 significantly attenuated the reduction of spine density in the prelimbic regions of the medial prefrontal cortex, dentate gyrus, and CA3 of the hippocampus, but not infralimbic regions of the medial prefrontal cortex and CA1, in susceptible mice 8 days after a single dose. In contrast, neither drug elicited an effect on altered brain-derived neurotrophic factor-TrkB signaling, GluA1, and postsynaptic density protein 95 levels and did not increase spine density observed in the nucleus accumbens of susceptible mice.

CONCLUSIONS

Similar to ketamine, MGS0039 shows rapid and sustained antidepressant effects in the social defeat stress model. Long-lasting synaptogenesis in the prelimbic regions of medial prefrontal cortex, dentate gyrus, and CA3 might be implicated in this sustained antidepressant effect.

The interactive effects of ketamine and magnesium upon depressive-like pathology

Approximately one-third of patients with major depressive disorders (MDDs) are resistant to current treatment methods, and the majority of cases relapse at some point during therapy. This has resulted in novel treatments being adopted, including subanesthetic doses of ketamine, which affects aberrant neuroplastic circuits, glutamatergic signaling, and the production of brain-derived neurotrophic factor. Ketamine rapidly relieves depressive symptoms in treatment-resistant major depressive disorder patients with effects that last for up to 2 weeks even after a single administration. However, it is also a drug with an abusive potential and can have marked side effects. Hence, this study aimed at enhancing the antidepressant-like effects of ketamine (allowing for lower dosing regimens) by coadministering magnesium hydroaspartate (Mg(2+) normally affects the same receptors as ketamine) and also assessed whether an Mg(2+)-deficient diet would modify the impact of ketamine. It was found that a single 15 mg/kg dose of ketamine did indeed induce rapid antidepressant-like effects in the forced swim test but did not affect brain levels of the brain-derived neurotrophic factor. Contrary to our hypothesis, magnesium administration or deficiency did not influence the impact of ketamine on these outcomes. Thus, these data do not support the use of magnesium as an adjunct agent and instead suggest that further research involving other antidepressant and animal models is required to confirm the present findings.

7,8-Dihydroxyflavone, a Tropomyosin-Kinase Related Receptor B Agonist, Produces Fast-Onset Antidepressant-Like Effects in Rats Exposed to Chronic Mild Stress

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) and its specific receptor, tropomyosin-related kinase (TrkB), play important roles in treating depression. In this experiment, we examined whether 7,8-dihydroxyflavone, a novel potent TrkB agonist, could reverse the behavioral and biochemical abnormalities induced by the chronic mild stress (CMS) paradigm in rats.

METHODS

SD rats were exposed to a battery of stressors for 56 days. 7,8-dihydroxyflavone (5 and 20 mg/kg) were administered intraperitoneally during the last 28 days of the CMS paradigm. Rats were tested in sucrose consumption test (SCT), forced-swimming test (FST) and elevated T-maze (ETM). Serum corticosterone levels and hippocampal BDNF levels of the rats were measured.

RESULTS

Four-week CMS on the rats induced their depression-like behavior in SCT. The CMS-reduced sucrose consumption was reversed starting from 7 days after the 7,8-dihydroxyflavone (20 mg/kg) treatment and remained across the subsequent treatment regime. 7,8-dihydroxyflavone, when given at 5 mg/kg for 3 weeks, reduced the immobility time in the FST in the CMS-subjected rats. Additionally, the 4-week treatment with 7,8-dihydroxyflavone (20 mg/kg) attenuated the CMS-induced increase in anxiety-like behavior in the ETM. For the CMS-subjected rats, 7,8-dihydroxyflavone treatment dose-dependently reduced their serum corticosterone levels but increased their hippocampal BDNF levels only at 5 mg/kg.

CONCLUSION

7,8-dihydroxyflavone was beneficial for both depression and anxiety-like behaviors, and may exert fast-onset antidepressant effects. This provides a new insight into the pharmacological management of 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.

A small molecule TrkB/TrkC neurotrophin receptor co-activator with distinctive effects on neuronal survival and process outgrowth

Neurotrophin (NT) receptors are coupled to numerous signaling networks that play critical roles in neuronal survival and plasticity. Several non-peptide small molecule ligands have recently been reported that bind to and activate specific tropomyosin-receptor kinase (Trk) NT receptors, stimulate their downstream signaling, and cause biologic effects similar to, though not completely overlapping, those of the native NT ligands. Here, in silico screening, coupled with low-throughput neuronal survival screening, identified a compound, LM22B-10, that, unlike prior small molecule Trk ligands, binds to and activates TrkB as well as TrkC. LM22B-10 increased cell survival and strongly accelerated neurite outgrowth, superseding the effects of brain-derived neurotrophic factor (BDNF), NT-3 or the two combined. Additionally, unlike the NTs, LM22B-10 supported substantial early neurite outgrowth in the presence of inhibiting glycoproteins. Examination of the mechanisms of these actions suggested contributions of the activation of both Trks and differential interactions with p75(NTR), as well as a requirement for involvement of the Trk extracellular domain. In aged mice, LM22B-10 activated hippocampal and striatal TrkB and TrkC, and their downstream signaling, and increased hippocampal dendritic spine density. Thus, LM22B-10 may constitute a new tool for the study of TrkB and TrkC signaling and their interactions with p75(NTR), and provides groundwork for the development of ligands that stimulate unique combinations of Trk receptors and activity patterns for application to selected neuronal populations and deficits present in various disease states.