Brain region specific alterations in the protein and mRNA levels of protein kinase A subunits in the post-mortem brain of teenage suicide victims.

Protein kinase A (PKA), a critical component of the adenylyl cyclase signaling system, phosphorylates crucial proteins and has been implicated in the pathophysiology of depression and suicide. The objective of the study was to examine if changes in PKA activity or in the protein and messenger RNA (mRNA) expression of any of its subunits are related to the pathophysiology of teenage suicide. We determined PKA activity and the protein and mRNA expression of different subunits of PKA in cytosol and membrane fractions obtained from the prefrontal cortex, (PFC) hippocampus, and nucleus accumbens (NA) of post-mortem brain from 17 teenage suicide victims and 17 nonpsychiatric control subjects. PKA activity was significantly decreased in the PFC but not the hippocampus of teenage suicide victims as compared with controls. However, the protein and mRNA expression of only two PKA subunits, that is, PKA RIalpha and PKA RIbeta, but not any other subunits were significantly decreased in both membrane and cytosol fractions of the PFC and protein expression of RIalpha and RIbeta in the NA of teenage suicide victims as compared to controls. A decrease in protein and mRNA expression of two specific PKA subunits may be associated with the pathogenesis of teenage suicide, and this decrease may be brain region specific, which may be related to the specific behavioral functions associated with these brain areas. Whether these changes in PKA subunits are related to suicidal behavior or are a result of suicide or are specific to suicide is not clear at this point.     

An AMPA receptor potentiator modulates hippocampal expression of BDNF: an in vivo study

AMPA receptor activation has been demonstrated to increase the neuronal expression of brain derived neurotrophic factor (BDNF). In the present study, we investigated the effect of a novel AMPA receptor potentiator (LY404187) and its active isomer (LY451646) on the expression of BDNF protein and mRNA, as well as TrkB mRNA in rat hippocampus. LY404187 administered for 7 days (1 mg/kg) significantly increased the number of BDNF immunopositive cells in the dentate gyrus, but not other hippocampal subfields. Chronic treatment (7 days) with LY451646 (0.5 mg/kg, comparable to 1 mg/kg of LY404187) increased the level of both BDNF and TrkB mRNA expression in the dentate gyrus, CA3 and CA4 of the hippocampus. However, chronic treatment with lower doses of LY451646 (0.125 and 0.25 mg/kg) decreased the level of BDNF and TrkB mRNA in hippocampus, whilst the highest used dose of LY451646 (1 mg/kg) had no effect on BDNF and TrkB mRNA in hippocampus. In contrast, acute treatment with LY451646 produced an increase in BDNF mRNA levels at doses of 0.125 and 0.25 mg/kg in the hippocampus (CA4, CA3 and dentate gyrus, but not in CA1). LY451646 at 0.5 mg/kg had no effect, but at 1.0 mg/kg decreased the level of BDNF mRNA in hippocampus. Acute treatment with LY451646 did not affect the TrkB receptor mRNA levels in hippocampus. Our results demonstrate that biarylpropylsulfonamide AMPA receptor potentiators are capable of modulating the expression of BDNF and TrkB mRNA in a dose- and time-dependent manner. The increase in both BDNF protein and mRNA expression in the dentate gyrus but not in CA1 indicates a specific role of AMPA receptors in the regulation of BDNF expression in this hippocampal subfield. The regulation of BDNF expression by biarylpropylsulfonamids such as LY451646 may have important therapeutical implications for this class of molecule in the treatment of depression and other CNS disorders.     

五味子乙素对慢性应激抑郁大鼠海马BDNF/TrkB/CREB通路的影响

目的 研究五味子乙素对慢性应激抑郁大鼠海马脑源性神经营养因子（BDNF）/酪氨酸激酶B（TrkB）/环磷腺苷效应元件结合蛋白（CREB）信号通路的影响。方法 40只SD大鼠随机选择10只作为对照组,其余大鼠采用慢性不可预知温和应激（chronic unpredictable mild stress,CUMS）结合孤养制备抑郁症模型,造模结束后随机分为3组：模型组、盐酸氟西汀（3 mg·kg^-1）组、五味子乙素（5 mg·kg^-1）组,每天ig给药1次,连续8周。分别于造模前、造模后及给药后进行旷场、悬尾、强迫游泳行为学实验;通过苏木素-伊红（HE）染色观察大鼠海马形态学改变;免疫组织化学染色（IHC）法观察大鼠海马BDNF蛋白表达;实时荧光定量PCR（qRT-PCR）法检测大鼠海马BDNF、TrkB、CREB mRNA相对表达量;Westernblotting检测大鼠海马BDNF、TrkB、CREB蛋白相对表达量。结果 与对照组比较,模型组大鼠旷场实验水平、垂直得分显著降低（P＜0.05）,悬尾不动时间和强迫游泳漂浮时间显著增加（P＜0.05）;HE染色结果显示海马神经元结构损伤,IHC结果显示海马BDNF表达明显降低;海马BDNF、TrkB、CREB mRNA及蛋白相对表达显著降低（P＜0.05）。与模型组比较,盐酸氟西汀及五味子乙素组大鼠水平、垂直得分显著增加（P＜0.05）,不动时间和漂浮时间显著减少（P＜0.05）;海马神经元结构明显复原,海马组织中BDNF染色明显增加;BDNF、TrkB、CREB mRNA和蛋白相对表达量显著增加（P＜0.05）。结论 五味子乙素可以改善慢性应激抑郁大鼠抑郁样行为、海马区神经元数量及形态,其机制可能与上调BDNF/TrkB/CREB信号通路有关。     

The delta-opioid receptor agonist (+)BW373U86 regulates BDNF mRNA expression in rats.

delta-Opioid receptor agonists have antidepressant-like effects in behavioral models of depression. Chronic administration of classical antidepressants upregulates mRNA expression of brain-derived neurotrophic factor (BDNF) and its high-affinity tyrosine kinase receptor, TrkB in the frontal cortex and hippocampus of rats. Increases in BDNF and TrkB levels are thought to be important for the therapeutic effects of these drugs. Therefore, we examined the ability of the delta-opioid receptor agonist (+)BW373U86 to regulate BDNF and TrkB mRNA expression in frontal cortex, hippocampus, as well as, basolateral amygdala, endopiriform nucleus, and primary olfactory cortex. At 3 h after a single administration of (+)BW373U86 animals were killed and BDNF and TrkB mRNA levels were examined by in situ hybridization. BDNF mRNA levels produced by (+)BW373U86 were compared to acute administration of the antidepressants desipramine and bupropion. A behaviorally antidepressant dose of 10 mg/kg (+)BW373U86 increased BDNF mRNA expression in all regions examined; a smaller dose of (+)BW373U86 (1 mg/kg) significantly increased BDNF mRNA expression only in frontal cortex. The delta-opioid receptor antagonist naltrindole blocked (+)BW373U86-mediated increases in BDNF mRNA expression. In addition, tolerance developed to increased BDNF mRNA expression with repeated injection, except in frontal cortex. Midazolam was administered to some animals to prevent the convulsions produced by (+)BW373U86, but midazolam did not block delta-opioid receptor-mediated increases in BDNF mRNA expression in frontal cortex, hippocampus, or amygdala. Unlike desipramine and bupropion, (+)BW373U86 upregulated BDNF mRNA expression acutely (within 3 h after a single administration). These data support the concept that delta-opioid receptor agonists may have antidepressant potential, and could be good targets for the development of faster-acting antidepressants.     

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.     

蝎毒注射液对阿尔茨海默病模型大鼠学习记忆能力及海马BDNF/TrkB表达的影响

目的：探讨蝎毒注射液（scorpion venom injection，SVI）对阿尔茨海默病（Alzheimer’s disease，AD）模型大鼠的学习记忆能力以及海马组织中脑源性神经营养因子（brain-derived neurotrophic factor，BDNF）和酪氨酸激酶受体B （tyrosine kinase receptor B，TrkB）表达的影响。方法： 36只智力正常的健康成年SD大鼠，每组12只，随机分为正常对照组、AD模型组与SVI治疗组。后两组采用双侧海马注射Aβ_25-35构建AD模型，SVI治疗组于造模后每日一次腹腔注射SVI，连续10 d。Morris水迷宫测试各组大鼠认知功能，之后取大鼠海马组织，RT-PCR法、免疫组化和Western Blot法分别检测海马组织中BDNF与TrkB的mRNA和蛋白表达情况。结果：与对照组相比，AD模型组大鼠认知能力降低，逃避潜伏期延长，空间探索次数减少，海马中BDNF、TrkB的mRNA和蛋白表达水平明显降低（P<0.05）。而与AD模型组相比，SVI治疗组大鼠的逃避潜伏期缩短，空间探索次数增加，海马中BDNF与TrkBmRNA和蛋白表达水平显著升高（P<0.05）。结论： SVI能够改善AD模型大鼠学习记忆能力，可能与激活脑内BDNF-TrkB信号通路、提高海马组织中BDNF和TrkB表达有关。     

Increased mRNA expression of alpha2A-adrenoceptors, serotonin receptors and mu-opioid receptors in the brains of suicide victims.

The development of new therapies for the treatment of psychiatric disorders requires an in-depth knowledge of the molecular bases underlying these pathologies, which remain largely unknown. Alterations in adrenoceptors, serotonin receptors, and other G protein-coupled receptors (GPCRs) have been associated with suicide and depression. However, to date, there is little information about mRNA expression of the GPCRs in the frontal cortex of suicide victims. Our goal was to study the expression in the brain of these receptors. For this purpose, we measured mRNA levels by RT-PCR. We found that the expressions of alpha2A-adrenoceptors, 5-HT1A, 5-HT2A serotonin receptors, and mu-opioid receptors were elevated in the post-mortem brains of these suicide victims with respect to matched controls. Moreover, in the case of alpha2A-adrenoceptors (the only for which these data were available), a significant correlation was observed between the level of mRNA and protein quantified in the brain of the same subjects, indicating that protein synthesis of this receptor was not influenced by post-translational regulatory mechanisms. In addition, the degree of adrenoceptor and 5-HT receptor expressions appeared to be correlated in the brains of suicide victims and control subjects. Alterations in the expression of adrenoceptors, serotonin, and opioid receptors indicate that these signaling proteins might be related to the etiopathology of suicidal and depressive behaviors. Alternatively, such changes may represent adaptive mechanisms to compensate for other as yet unknown alterations. The results also suggest that these receptors could share common regulatory mechanisms.     

Long-term down-regulation of BDNF mRNA in rat hippocampal CA1 subregion correlates with PTSD-like behavioural stress response

Brain-derived neurotrophic factor (BDNF) and its intracellular kinase-activating receptor TrkB, have been implicated in the neurobiological mechanisms underlying the clinical manifestations of PTSD, especially those related to synaptic efficacy and neural plasticity. BDNF interacts with components of the stress response such as corticosterone, and plays an important role in growth, maintenance and functioning of several neuronal systems. This study employed an animal model of PTSD to investigate the relationship between prevalence rates of distinct patterns of behavioural responses to predator stress, circulating levels of corticosterone and local levels of mRNA for BDNF, TrkB and two other neurotrophic factors in selected brain areas. Animals whose behaviour was extremely disrupted by exposure selectively displayed significant down-regulation of mRNA for BDNF and up-regulation of TrkB mRNA in the CA1 subregion of the hippocampus, compared to animals whose behaviour was minimally or partially affected and to unexposed controls. The response was consistent throughout the entire study only in CA1. The consistent long-term the BDNF down-regulation and TrkB up-regulation associated with extreme behavioural compromise may be associated with chronic stress-induced psychopathological processes, especially in the hippocampus. The corresponding changes in neural plasticity and synaptic functioning may mediate clinical manifestations of PTSD.     

Brain-derived neurotrophic factor/TrkB signaling in memory processes

Activity-dependent changes in synaptic strength are considered mechanisms underlying learning and memory. Brain-derived neurotrophic factor (BDNF) plays an important role in activity-dependent synaptic plasticity such as long-term potentiation. Recent experimental evidence supports the role of BDNF in memory processes: Memory acquisition and consolidation are associated with an increase in BDNF mRNA expression and the activation of its receptor TrkB. Genetic as well as pharmacologic deprivation of BDNF or TrkB impairs learning and memory. In a positively motivated radial arm maze test, activation of the TrkB/phosphatidylinositol-3 kinase (PI3-K) signaling pathway in the hippocampus is associated with consolidation of spatial memory through an activation of translational processes. In a negatively motivated passive avoidance test, mitogen-activated protein kinase (MAPK) is activated during acquisition of fear memory. Furthermore, recent findings suggest the importance of interaction between BDNF/TrkB signaling and NMDA receptors for spatial memory. A Src-family tyrosine kinase, Fyn plays a role in this interaction by linking TrkB with NR2B. These findings suggest that BDNF/TrkB signaling in the hippocampus plays a crucial role in learning and memory.     

The differential regulation of BDNF and TrkB levels in juvenile rats after four days of escitalopram and desipramine treatment

Major depressive disorder is a major health problem in adults and is now recognized as a substantial problem in children as well. Tricyclic antidepressants, including desipramine (DMI), are no better than placebo in treating childhood and adolescent depression, but are effective in treating adult depression. Several studies have suggested that normal BDNF (brain-derived neurotrophic factor) signaling is necessary for antidepressant drug action. Antidepressant drugs induce several plastic changes in the rodent brain which may be associated with changes in BDNF levels and/or with BDNF function. In the present study we report parallel measurements of BDNF mRNA and protein in the frontal cortex and hippocampus after four days of twice daily treatments with escitalopram, a selective serotonin reuptake inhibitor, and desipramine, a tricyclic antidepressant. Post-natal day 13, 21, 28 and adult rats were used in this study. TrkB (the primary receptor for BDNF) mRNA levels were also examined under the same treatment conditions. BDNF mRNA and protein levels, as well as TrkB mRNA levels, were increased significantly in post-natal day 13 pups after escitalopram treatment as compared to control, but desipramine failed to increase either BDNF or TrkB. The failure of desipramine to increase BDNF and TrkB levels in juvenile rats is consistent with the lack of efficacy of desipramine in children and adolescents. The serotonergic nervous system matures earlier than the noradrenergic system, which may explain why escitalopram, but not desipramine, increases BDNF and TrkB levels.     

Aberrant extracellular signal-regulated kinase (ERK) 5 signaling in hippocampus of suicide subjects.

Extracellular signal-regulated kinase 5 (ERK5), the newest member of the mitogen-activated protein (MAP) kinase family, is regulated differently than the other MAP kinases. Emerging evidence suggest the role of ERK5 signaling in promoting cell proliferation, differentiation, neuronal survival, and neuroprotection. The present study investigates whether suicide brain is associated with alterations in components of the ERK5 signaling cascade. In the prefrontal cortex (PFC) and hippocampus of suicide subjects (n=28) and nonpsychiatric control subjects (n=21), we examined the catalytic activities and protein levels of ERK5 and upstream MAP kinase kinase MEK5 in various subcellular fractions; mRNA levels of ERK5 in total RNA; and DNA-binding activity of myocyte enhancer factor (MEF)2C, a substrate of ERK5. In the hippocampus of suicide subjects, we observed that catalytic activity of ERK5 was decreased in cytosolic and nuclear fractions, whereas catalytic activity of MEK5 was decreased in the total fraction. Further, decreased mRNA and protein levels of ERK5, but no change in protein level of MEK5 were noted. A decrease in MEF2C-DNA-binding activity in the nuclear fraction was also observed. No significant alterations were noted in the PFC of suicide subjects. The observed changes were not related to a specific psychiatric diagnosis. Our findings of reduced activation and/or expression of ERK5 and MEK5, and reduced MEF2C-DNA-binding activity demonstrate abnormalities in ERK5 signaling in hippocampus of suicide subjects and suggest possible involvement of this aberrant signaling in pathogenic mechanisms of suicide.     

Effects of infrasound on hippocampus-dependent learning and memory in rats and some underlying mechanisms

To investigate the effect of infrasound on the hippocampus-dependent spatial learning and memory as well as its underlying mechanisms, we measured the changes of cognitive abilities, brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) signal transduction pathway and neurogenesis in the hippocampus of rats. The results showed that rats exposed to infrasound of 16 Hz at 130 dB for 14 days exhibited longer escape latency from day 2 and shortened time staying in the quadrant P in Morris water maze (MWM). It was found that mRNA and protein expression levels of hippocampal BDNF and TrkB were significantly decreased in real-time PCR and Western blot, and the number of BrdU-labeled cells in hippocampus was also reduced when compared to control. These results provided novel evidences that the infrasound of a certain exposure parameter can impair hippocampus-dependent learning and memory, in which the downregulation of the neuronal plasticity-related BDNF–TrkB signal pathway and less neurogenesis in hippocampus might be involved.     

Icariin isolated from Epimedium brevicornum Maxim attenuates learning and memory deficits induced by d-galactose in rats

The effects of icariin (ICA), a major constituent of flavonoids from the Chinese medical herb Epimedium brevicornum Maxim, on spatial memory performances and expressions of hippocampus brain-derived neurotrophic factor (BDNF) and tyrosine kinase TrkB (tropomyosin receptor kinase B) were investigated in d-galactose (d-gal)-treated rats. Subcutaneous injection of d-gal (500 mg/kg/d) for four months caused memory loss as detected by the Morris water maze, morphologic abnormalities of neurons in hippocampus region and the reduced expression of BDNF and TrkB were observed. ICA (60 mg/kg/d) given orally 1 h after subcutaneous injection of d-gal daily for 4 months markedly attenuated d-gal-induced rats behavioral dysfunction and neurodegeneration, as evidenced by shortened escape latency and searching distance and rescued morphologic abnormalities, and also elevated the mRNA levels and the protein expressions of BDNF and TrkB in hippocampus, as evidenced by quantitative real-time RT-PCR and Western blotting analysis. But ICA had no significant influence on normal rats which were not injected d-gal. These results clearly demonstrated that d-gal produced learning and memory deficits after chronic administration, and ICA can protect neuron from d-gal insults and improve the memory loss.     

Reduced potency of zinc to interact with NMDA receptors in hippocampal tissue of suicide victims

Zinc is involved in both psychopathology and treatment of depression. Since a considerable percentage of suicide victims had suffered from depression, we hypothesized that alteration in zinc homeostasis might occur in their brain tissue. We now report that zinc content is not altered in the hippocampal or cortical tissue of suicide victims (n = 10) compared to age-matched controls (n = 10). However, there is a statistically significant 26% decrease in the potency (increase in the IC(50) value) of zinc to inhibit [(3)H]MK-801 binding to NMDA receptors in the hippocampal but not cortical tissue of suicide subjects. The data represent the first demonstration that the alteration in zinc interaction with NMDA receptors may be involved in psychopathology underlying suicidal attempts.     

Tryptophan hydroxylase gene 218A/C polymorphism is not associated with depressed suicide

Abnormalities in functioning of the central serotonergic system are believed to be involved in the pathogenesis of depressive illness and suicidal behaviour. Recently, polymorphism in the tryptophan hydroxylase (TPH) gene has been studied for association with aggression, anger-related traits and suicidal behaviour, but the results are inconclusive. The present investigation was to determine whether there are differences in genotype and allele distribution of the TPH gene 218A/C polymorphism in post-mortem brain samples from 35 depressed suicide victims and 84 control subjects of the same ethnic background. A functional polymorphism in the promoter region of 5-HT transporter gene was also re-examined in this increased sample size. No significant difference in TPH gene 218A/C polymorphism between controls and depressed suicide victims was detected. This may suggest that the TPH gene has no significant effect on suicidality in depressed subjects. In a previous study on a smaller sample we found the frequency of the long allele of 5-HT transporter gene to be higher in depressed suicide victims. In this increased sample size, both the genotype and alleles of the 5-HT transporter gene were significantly associated with completed suicide. The frequency of the L/L genotype in depressed suicide victims was almost double of that found in control group (48.6 vs. 26.2%). The odds ratio for the L allele associated with depressed suicide was 2.1 (95% CI, 1.2-3.7). The relatively small sample size does not exclude the possibility of false-positive results and the finding needs replication.     

Influence of brain-derived neurotrophic factor (BDNF) on serotonin neurotransmission in the hippocampus of adult rodents

Whereas SSRIs produce rapid blockade of the serotonin transporter (SERT) in vitro and in vivo, the onset of an observable clinical effect takes longer to occur and a variety of pharmacological effects caused by antidepressants have been speculated to be involved either in initiating antidepressant effects and/or enhancing their effects on serotonergic transmission so as to cause clinical improvement. Among such secondary factors is increased activity of brain-derived neurotrophic factor (BDNF), which requires the Tropomyosine-related kinase B receptor (TrkB) for its effects. To begin an analysis of the influence of BDNF on serotonergic activity, we studied the acute effects of BDNF on SERT activity. A single BDNF injection (either intracerebroventricularly or directly into the CA3 region of hippocampus) decreased the signal amplitude and clearance rate produced by exogenously applied 5-HT compared to what was measured in control rats, shown using in vivo chronoamperometry. It also reduced the ability of a locally applied SSRI to block the clearance of 5-HT. In awake freely moving mice, acute intrahippocampal injection of BDNF decreased extracellular levels of 5-HT in the hippocampus, as measured using microdialysis. In addition, perfusion with BDNF decreased KCl-evoked elevations of 5-HT. These effects of BDNF were blocked by the non-selective antagonist of TrkB receptors, K252a. Overall, it may be inferred that in the hippocampus, through TrkB activation, a single injection of BDNF enhances SERT function. Such acute effects of BDNF would be expected to counter early effects of SSRIs, which might, in part, account for some delay in therapeutic effect.