Ji-chun Zhang

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.

R (-)-ketamine shows greater potency and longer lasting antidepressant effects than S (+)-ketamine.

The N-methyl-D-aspartate (NMDA) receptor antagonist ketamine is one of the most attractive antidepressants for treatment-resistant major depressive disorder (MDD). Ketamine (or RS (±)-ketamine) is a racemic mixture containing equal parts of R (-)-ketamine and S (+)-ketamine. In this study, we examined the effects of R- and S-ketamine on depression-like behavior in juvenile mice after neonatal dexamethasone (DEX) exposure. In the tail suspension test (TST) and forced swimming test (FST), both isomers of ketamine significantly attenuated the increase in immobility time, seen in DEX-treated juvenile mice at 27 and 29 h respectively, after ketamine injections. In the 1% sucrose preference test (SPT), both isomers significantly attenuated the reduced preference for 1% sucrose consumption in DEX-treated juvenile mice, 48 h after a ketamine injection. Interestingly, when immobility times were tested by the TST and FST at day 7, R-ketamine, but not S-ketamine, significantly lowered the increases in immobility seen in DEX-treated juvenile mice. This study shows that a single dose of R-ketamine produced rapid and long-lasting antidepressant effects in juvenile mice exposed neonatally to DEX. Therefore, R-ketamine appears to be a potent and safe antidepressant relative to S-ketamine, since R-ketamine may be free of psychotomimetic side effects.

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.

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.

Targeting of NMDA Receptors in the Treatment of Major Depression

Major depressive disorder (MDD) is a common, recurrent mental illness that affects millions of people worldwide. Accumulating evidence suggests that the N-methyl-D-aspartate (NMDA) receptor, a subtype of glutamate receptors, plays an important role in the neurobiology and treatment of this disease. Currently, the non-competitive NMDA receptor antagonist ketamine is considered as one of the most attractive candidate drugs in therapy of treatment-resistant depression. A recent study demonstrated ketamines rapid antidepressant activity in patients with treatment-resistant MDD and bipolar disorder. The response rate for ketamine ranged from 25% to 85% at 24 hours post-infusion and from 14% to 70% at 72 hours post-infusion, with generally mild adverse effects. Based on the role of the NMDA receptor in depression, a number of therapeutic drugs which interact with this receptor have been developed. In this article, we reviewed recent findings concerning the role of glutamatergic signaling in the neurobiology of MDD and potential, novel therapeutic drugs, such as ketamine, memantine, AZD6765, traxoprodil, MK-0657, GLYX-13, NRX-1047, D-cycloserine, sarcosine, all of which target this system.

Effects of Brilliant Blue G on Serum Tumor Necrosis Factor-α Levels and Depression-like Behavior in Mice after Lipopolysaccharide Administration.

Objective Accumulating evidence suggests that inflammation plays a role in the pathophysiology of major depression. The adenosine triphosphate (ATP)-sensitive P2X7 receptor (P2X7R) plays a crucial role in microglial activation caused by inflammation. The dye brilliant blue G (BBG) is a P2X7R antagonist. This study examined whether BBG shows antidepressant effects in an inflammation-induced model of depression. Methods We examined the effects of BBG (12.5, 25, or 50 mg/kg) on serum tumor necrosis factor-α (TNF-α) levels after administering the bacterial endotoxin lipopolysaccharide (LPS; 0.5 mg/kg) and the effects of BBG (50 mg/kg) on depression-like behavior in the tail-suspension test (TST) and forced swimming test (FST). Results Pretreatment with BBG (12.5, 25, or 50 mg/kg) significantly blocked the increase in serum TNF-α levels after a single dose of LPS (0.5 mg/kg). Furthermore, BBG (50 mg/kg) significantly attenuated the increase in immobility time in the TST and FST after LPS (0.5 mg/kg) administration. Conclusion The results suggest that BBG has anti-inflammatory and antidepressant effects in mice after LPS administration. Therefore, P2X7R antagonists are potential therapeutic drugs for inflammation-related major depression.

Loss of parvalbumin-immunoreactivity in mouse brain regions after repeated intermittent administration of esketamine, but not R-ketamine

Clinical use of the rapid antidepressant drug ketamine is limited, due to psychotomimetic side effects. R-ketamine appears to be a potent, long-lasting and safer antidepressant, relative to S-ketamine (esketamine), since it is free of psychotomimetic side effects. Repeated, intermittent administration of esketamine (10mg/kg, once per week for 8-weeks), but not R-ketamine, caused loss of parvalbumin (PV)-immunoreactivity in the medial prefrontal cortex and hippocampus of mouse brains, regions associated with psychosis. This study suggests that repeated intermittent use of R-ketamine is safer than esketamine in the treatment 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.

Role of the NMDA receptor in cognitive deficits, anxiety and depressive-like behavior in juvenile and adult mice after neonatal dexamethasone exposure.

Postnatal dexamethasone (DEX) therapy has been used to treat or prevent chronic lung disease after premature births. However, there are many reports of long-term negative neurodevelopmental sequelae following this treatment. In contrast, hydrocortisone (HYD), which has fewer neurodevelopment adverse effects, is used as an alternative for DEX. In this study, we report that neonatal DEX exposure (days 1-3) caused alterations of amino acids affecting N-methyl-d-aspartate (NMDA) receptor neurotransmission in mouse brains. Neonatal DEX, but not HYD, exposure (days 1-3) significantly decreased the GluN2B subunit of NMDA receptor in the hippocampus at juvenile and adult stages. Mice treated with DEX showed cognitive deficits, as well as anxiety and depressive-like behavior at juvenile and adult stages. In contrast, mice treated with HYD (days 1-3) showed no behavioral abnormalities at these stages. In the DEX suppression test, plasma levels of corticosterone in mice exposed neonatally to DEX and HYD were significantly higher at juvenile, but not adult stages. Pretreatment with Ro 63-1908, an antagonist at GluN2B subunit, 30min before each injection of DEX, prevented cognitive deficits, as well as anxiety and depressive-like behavior in juvenile and adult mice. Interestingly, subsequent repeated (days 29-33) administration of Ro 63-1908 or L701324, an antagonist of the glycine modulatory site on the NMDA receptor, significantly suppressed behavioral abnormalities in juvenile and adult mice after neonatal DEX exposure. These results indicate that neonatal DEX, but not HYD, exposure produced behavioral abnormalities in juvenile and adult mice by altering glutamatergic neurotransmission via the NMDA receptor. The NMDA receptor antagonists may prevent or treat these DEX-induced neonatal behavioral abnormalities in later life.

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.