Investigation of Mature BDNF and proBDNF Signaling in a Rat Photothrombotic Ischemic Model

Treatment with mature brain-derived neurotrophic factor (mBDNF) promotes functional recovery after ischemia in animal trials but the possible role of its precursor protein proBDNF and its receptors or the factors responsible for the conversion of proBDNF to mBDNF in ischemic stroke are not known. The main aim of this study was to characterize the time-dependent expression of genes and/or proteins related to BDNF processing and signaling after ischemia as well as the sensorimotor behavioral dysfunction in a photothrombotic ischemic model in rats. Characterization of different genes and proteins related to BDNF processing and signaling was performed using qPCR, immunoblotting and enzyme-linked immunosorbent assays. We showed in this study that some sensory and motor functional deficiencies appeared in the ischemic group at day 1 and persisted until day 14. Most changes in gene expression of BDNF and its processing enzymes occurred within the first 24 h in the ipsilateral cortex, but not in the contralateral cortex. At the protein level, proBDNF expression was increased at 6 h, mBDNF expression was increased between 15 h and 1 day while p75 receptor protein expression was increased between 6 h and 3 days in the ipsilateral cortex, but not in the contralateral cortex. Therefore, cerebral ischemia in rats led to the up-regulation of genes and/or proteins of BDNF, proBDNF and their processing enzymes and receptors in a time-dependent manner. We propose that the balance between BDNF and proBDNF and their associated proteins may play an important role in the pathogenesis and recovery from ischemia.     

Decreased Serum Levels of Mature Brain-Derived Neurotrophic Factor (BDNF), but Not Its Precursor proBDNF, in Patients with Major Depressive Disorder

Background

Meta-analyses have identified serum levels of brain-derived neurotrophic factor (BDNF) as a potential biomarker for major depressive disorder (MDD). However, at the time, commercially available human ELISA kits are unable to distinguish between proBDNF (precursor of BDNF) and mature BDNF because of limited BDNF antibody specificity. In this study, we examined whether serum levels of proBDNF, mature BDNF, and matrix metalloproteinase-9 (MMP-9), which converts proBDNF to mature BDNF, are altered in patients with MDD.

Methodology/Principal Findings

Sixty-nine patients with MDD and 78 age- and gender-matched healthy subjects were enrolled. Patients were evaluated using 17 items on the Structured Interview Guide for the Hamilton Depression Rating Scale. Cognitive impairment was evaluated using the CogState battery. Serum levels of proBDNF, mature BDNF, and MMP-9 were measured using ELISA kits. Serum levels of mature BDNF in patients with MDD were significantly lower than those of normal controls. In contrast, there was no difference in the serum levels of proBDNF and MMP-9 between patients and normal controls. While neither proBDNF nor mature BDNF serum levels was associated with clinical variables, there were significant correlations between MMP-9 serum levels and the severity of depression, quality of life scores, and social function scores in patients.

Conclusions/Significance

These findings suggest that mature BDNF may serve as a biomarker for MDD, and that MMP-9 may play a role in the pathophysiology of MDD. Further studies using larger sample sizes will be needed to investigate these results.     

Precursor form of brain-derived neurotrophic factor and mature brain-derived neurotrophic factor are decreased in the pre-clinical stages of Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) is critical for the function and survival of neurons that degenerate in the late stage of Alzheimer's disease (AD). There are two forms of BDNF, the BDNF precursor (proBDNF) and mature BDNF, in human brain. Previous studies have shown that BDNF mRNA and protein, including proBDNF, are dramatically decreased in end-stage AD brain. To determine whether this BDNF decrease is an early or late event during the progression of cognitive decline, we used western blotting to measure the relative amounts of BDNF proteins in the parietal cortex of subjects clinically classified with no cognitive impairment (NCI), mild cognitive impairment (MCI) or mild to moderate AD. We found that the amount of proBDNF decreased 21 and 30% in MCI and AD groups, respectively, as compared with NCI, consistent with our previous results of a 40% decrease in end-stage AD. Mature BDNF was reduced 34 and 62% in MCI and AD groups, respectively. Thus, the decrease in mature BDNF and proBDNF precedes the decline in choline acetyltransferase activity which occurs later in AD. Both proBDNF and mature BDNF levels were positively correlated with cognitive measures such as the Global Cognitive Score and the Mini Mental State Examination score. These results demonstrate that the reduction of both forms of BDNF occurs early in the course of AD and correlates with loss of cognitive function, suggesting that proBDNF and BDNF play a role in synaptic loss and cellular dysfunction underlying cognitive impairment in AD.     

The effects of chronic alcoholization on the expression of brain-derived neurotrophic factor and its receptors in the brains of mice genetically predisposed to depressive-like behavior

Brain-derived neurotropic factor (BDNF) plays an important role in mechanisms of depression. Precursor protein of this factor (proBDNF) can initiate apoptosis in the brain, while the mature form of BDNF is involved in neurogenesis. It is known that chronic alcoholization leads to the activation of apoptotic processes, neurodegeneration, brain injury, and cognitive dysfunction. In this work, we have studied the influence of long-term ethanol exposure on the proBDNF and BDNF protein levels, as well as on the expression of genes that encode these proteins in the brain structures of ASC mice with genetic predisposition to depressive-like behavior and in mice from parental nondepressive CBA strain. It was shown that chronic alcoholization results in a reduction of the BDNF level in the hippocampus and an increase in the amount of TrkB and p75 receptors in the frontal cortex of nondepressive CBA mice. At the same time, the long-term alcoholization of depressive ASC mice results in an increase of the proBDNF level in the frontal cortex and a reduction in the p75 protein level in the hippocampus. It has also been shown that, in depressive ASC mice, proBDNF and BDNF levels are significantly lower in the hippocampus and the frontal cortex compared with nondepressive CBA strain. However, no significant differences in the expression of genes encoding the studied proteins were observed. Thus, changes in the expression patterns of proBDNF, BDNF, and their receptors under the influence of alcoholization in the depressive ASC strain and nondepressive CBA strain mice are different.     

The effects of voluntary, involuntary, and forced exercises on brain-derived neurotrophic factor and motor function recovery: a rat brain ischemia model

Background

Stroke rehabilitation with different exercise paradigms has been investigated, but which one is more effective in facilitating motor recovery and up-regulating brain neurotrophic factor (BDNF) after brain ischemia would be interesting to clinicians and patients. Voluntary exercise, forced exercise, and involuntary muscle movement caused by functional electrical stimulation (FES) have been individually demonstrated effective as stroke rehabilitation intervention. The aim of this study was to investigate the effects of these three common interventions on brain BDNF changes and motor recovery levels using a rat ischemic stroke model.

Methodology/Principal Findings

One hundred and seventeen Sprague-Dawley rats were randomly distributed into four groups: Control (Con), Voluntary exercise of wheel running (V-Ex), Forced exercise of treadmill running (F-Ex), and Involuntary exercise of FES (I-Ex) with implanted electrodes placed in two hind limb muscles on the affected side to mimic gait-like walking pattern during stimulation. Ischemic stroke was induced in all rats with the middle cerebral artery occlusion/reperfusion model and fifty-seven rats had motor deficits after stroke. Twenty-four hours after reperfusion, rats were arranged to their intervention programs. De Ryck''s behavioral test was conducted daily during the 7-day intervention as an evaluation tool of motor recovery. Serum corticosterone concentration and BDNF levels in the hippocampus, striatum, and cortex were measured after the rats were sacrificed. V-Ex had significantly better motor recovery in the behavioral test. V-Ex also had significantly higher hippocampal BDNF concentration than F-Ex and Con. F-Ex had significantly higher serum corticosterone level than other groups.

Conclusion/Significance

Voluntary exercise is the most effective intervention in upregulating the hippocampal BDNF level, and facilitating motor recovery. Rats that exercised voluntarily also showed less corticosterone stress response than other groups. The results also suggested that the forced exercise group was the least preferred intervention with high stress, low brain BDNF levels and less motor recovery.     

NT-3 modulates BDNF and proBDNF levels in naïve and kindled rat hippocampus

Both mature and precursor forms of neurotrophins regulate nerve development, survival and plasticity. Brain-derived neurotrophic factor (BDNF) synthesis and secretion in turn are regulated by neuronal activity, such as epilepsy. Further, neurotrophins themselves are regulated by neurotrophin levels. Neurotrophin-3 (NT-3) and BDNF in particular can be co-expressed and each can regulate the levels of the other. This regulation is thought to be mediated through receptor tyrosine kinase (Trk) activity. It is not known whether this neurotrophin-neurotrophin interaction occurs in hippocampal tissue in vivo, or how it is influenced by neuronal activation. In this study, we explored the reciprocal influences of intraventricular infusions of NT-3 and BDNF in na?ve and kindled hippocampi of rats using Western blotting. We confirm that hippocampal kindling resulted in a significant increase in levels of BDNF both in cytochrome C (control) infused and NT-3 infused kindled rats. However, NT-3 infusion significantly reduced BDNF levels in both kindled and non-kindled hippocampi compared to their cytochrome C infused counterparts. These results are consistent with our earlier studies demonstrating lowered levels of TrkA and TrkC (NGF modulates BDNF levels via TrkA) following chronic NT-3 infusion. Although kindling led to an increase in BDNF, this was not accompanied by any detectable change in the levels of proBDNF. However, there was a significant increase in proBDNF following NT-3 infusions, suggesting NT-3 may reduce proBDNF processing. In contrast, neither NT-3 nor proNT-3 levels were affected by kindling or chronic BDNF infusions, consistent with down-regulation of TrkB by chronic BDNF infusion. Thus, modulation of BDNF by NT-3, likely mediated by Trk receptors, occurs in na?ve and kindled adult rat hippocampus.     

Circulating and brain BDNF levels in stroke rats. Relevance to clinical studies

Background

Whereas brain-derived neurotrophic factor (BDNF) levels are measured in the brain in animal models of stroke, neurotrophin levels in stroke patients are measured in plasma or serum samples. The present study was designed to investigate the meaning of circulating BDNF levels in stroke patients.

Methods and Results

Unilateral ischemic stroke was induced in rats by the injection of various numbers of microspheres into the carotid circulation in order to mimic the different degrees of stroke severity observed in stroke patients. Blood was serially collected from the jugular vein before and after (4 h, 24 h and 8 d) embolization and the whole brains were collected at 4, 24 h and 8 d post-embolization. Rats were then selected from their degree of embolization, so that the distribution of stroke severity in the rats at the different time points was large but similar. Using ELISA tests, BDNF levels were measured in plasma, serum and brain of selected rats. Whereas plasma and serum BDNF levels were not changed by stroke, stroke induced an increase in brain BDNF levels at 4 h and 24 h post-embolization, which was not correlated with stroke severity. Individual plasma BDNF levels did not correlate with brain levels at any time point after stroke but a positive correlation (r = 0.67) was observed between individual plasma BDNF levels and stroke severity at 4 h post-embolization.

Conclusion

Circulating BDNF levels do not mirror brain BDNF levels after stroke, and severe stroke is associated with high plasma BDNF in the very acute stage.     

Development of mature BDNF‐specific sandwich ELISA

Mature brain‐derived neurotrophic factor (mBDNF) plays a vital role in the nervous system, whereas proBDNF elicits neurodegeneration and neuronal apoptosis. Although current enzyme‐linked immunosorbent assay (ELISA) has been widely used to measure BDNF levels, it cannot differentiate mBDNF from proBDNF. As the function of proBDNF differs from mBDNF, it is necessary to establish an ELISA assay specific for the detection of mBDNF. Therefore, we aimed to establish a new mBDNF‐specific sandwich ELISA. In this study, we have screened and found a combination of antibodies for a sandwich ELISA. A monoclonal antibody and sheep anti‐BDNF were chosen as capture and detection antibody for sandwich ELISA respectively. The new ELISA showed no cross‐reactivity to human recombinant NT‐3, NT‐4, nerve growth factor and negligible cross‐reactivity (0.99–4.99%) for proBDNF compared to commercial ELISA kits (33.18–91.09%). The application of the new mBDNF ELISA was shown through the measurement of mBDNF levels in different brain regions of rats and in the brain of β‐site amyloid precursor protein cleaving enzyme 1 (BACE1)^?/? and WT mice and compared to western blot. Overall, this new ELISA will be useful for the measurement of mBDNF levels with high specificity.

     

Mature and precursor brain-derived neurotrophic factor have individual roles in the mouse olfactory bulb

Background

Sensory deprivation induces dramatic morphological and neurochemical changes in the olfactory bulb (OB) that are largely restricted to glomerular and granule layer interneurons. Mitral cells, pyramidal-like neurons, are resistant to sensory-deprivation-induced changes and are associated with the precursor to brain-derived neurotrophic factor (proBDNF); here, we investigate its unknown function in the adult mouse OB.

Principal Findings

As determined using brain-slice electrophysiology in a whole-cell configuration, brain-derived neurotrophic factor (BDNF), but not proBDNF, increased mitral cell excitability. BDNF increased mitral cell action potential firing frequency and decreased interspike interval in response to current injection. In a separate set of experiments, intranasal delivery of neurotrophic factors to awake, adult mice was performed to induce sustained interneuron neurochemical changes. ProBDNF, but not BDNF, increased activated-caspase 3 and reduced tyrosine hydroxylase immunoreactivity in OB glomerular interneurons. In a parallel set of experiments, short-term sensory deprivation produced by unilateral naris occlusion generated an identical phenotype.

Conclusions

Our results indicate that only mature BDNF increases mitral cell excitability whereas proBDNF remains ineffective. Our demonstration that proBDNF activates an apoptotic marker in vivo is the first for any proneurotrophin and establishes a role for proBDNF in a model of neuronal plasticity.     

ProBDNF collapses neurite outgrowth of primary neurons by activating RhoA

Background

Neurons extend their dendrites and axons to build functional neural circuits, which are regulated by both positive and negative signals during development. Brain-derived neurotrophic factor (BDNF) is a positive regulator for neurite outgrowth and neuronal survival but the functions of its precursor (proBDNF) are less characterized.

Methodology/Principal Findings

Here we show that proBDNF collapses neurite outgrowth in murine dorsal root ganglion (DRG) neurons and cortical neurons by activating RhoA via the p75 neurotrophin receptor (p75NTR). We demonstrated that the receptor proteins for proBDNF, p75NTR and sortilin, were highly expressed in cultured DRG or cortical neurons. ProBDNF caused a dramatic neurite collapse in a dose-dependent manner and this effect was about 500 fold more potent than myelin-associated glycoprotein. Neutralization of endogenous proBDNF by using antibodies enhanced neurite outgrowth in vitro and in vivo, but this effect was lost in p75NTR^−/− mice. The neurite outgrowth of cortical neurons from p75NTR deficient (p75NTR^−/−) mice was insensitive to proBDNF. There was a time-dependent reduction of length and number of filopodia in response to proBDNF which was accompanied with a polarized RhoA activation in growth cones. Moreover, proBDNF treatment of cortical neurons resulted in a time-dependent activation of RhoA but not Cdc42 and the effect was absent in p75NTR^−/− neurons. Rho kinase (ROCK) and the collapsin response mediator protein-2 (CRMP-2) were also involved in the proBDNF action.

Conclusions

proBDNF has an opposing role in neurite outgrowth to that of mature BDNF. Our observations suggest that proBDNF collapses neurites outgrowth and filopodial growth cones by activating RhoA through the p75NTR signaling pathway.     

Precursor of brain-derived neurotrophic factor (proBDNF) forms a complex with Huntingtin-associated protein-1 (HAP1) and sortilin that modulates proBDNF trafficking, degradation, and processing

proBDNF, a precursor of brain-derived neurotrophic factor (BDNF), is anterogradely transported and released from nerve terminals, but the mechanism underlying this process remains unclear. In this study, we report that proBDNF forms a complex with Huntingtin associated protein-1 (HAP1) and sortilin, which plays an important role in proBDNF intracellular trafficking and stabilization. The interaction of proBDNF with both HAP1A and sortilin in co-transfected HEK293 cells is confirmed by both fluorescence resonance energy transfer and co-immunoprecipitation. The frequent co-localization (>90%) of endogenous HAP1, sortilin, and proBDNF is also found in cultured cortical neurons. Mapping studies using GST pulldown and competition assays has defined the interacting region of HAP1 with proBDNF within amino acids 371-445 and the binding sequences of proBDNF to HAP1 between amino acids 65 and 90. Fluorescence recovery after photobleaching confirms the defective movement of proBDNF-containing vesicles in neurites of HAP1(-/-) neurons, which can be partially restored by reintroducing HAP1 cDNA into the neurons. However, the effect is significantly increased by simultaneously reintroducing both HAP1 and sortilin. proBDNF and HAP1 are highly co-localized with organelle markers for the Golgi network, microtubules, molecular motor, or endosomes in normal neurons, but this co-localization is reduced in HAP1(-/-) neurons. Co-immunoprecipitation and Western blot showed that sortilin stabilizes the proBDNF·HAP1 complex in co-transfected HEK293 cells, helping to prevent proBDNF degradation. Furthermore, the complex facilitates furin cleavage to release mature BDNF.     

Role of Brain-Derived Neurotrophic Factor in Beneficial Effects of Repetitive Transcranial Magnetic Stimulation for Upper Limb Hemiparesis after Stroke

Background

Repetitive transcranial magnetic stimulation (rTMS) can improve upper limb hemiparesis after stroke but the mechanism underlying its efficacy remains elusive. rTMS seems to alter brain-derived neurotrophic factor (BDNF) and such effect is influenced by BDNF gene polymorphism.

Objectives

To investigate the molecular effects of rTMS on serum levels of BDNF, its precursor proBDNF and matrix metalloproteinase-9 (MMP-9) in poststroke patients with upper limb hemiparesis.

Methods

Poststroke patients with upper limb hemiparesis were studied. Sixty-two patients underwent rehabilitation plus rTMS combination therapy and 33 patients underwent rehabilitation monotherapy without rTMS for 14 days at our hospital. One Hz rTMS was applied over the motor representation of the first dorsal interosseous muscle on the non-lesional hemisphere. Fugl-Meyer Assessment and Wolf Motor Function (WMFT) were used to evaluate motor function on the affected upper limb before and after intervention. Blood samples were collected for analysis of BDNF polymorphism and measurement of BDNF, proBDNF and MMP-9 levels.

Results

Two-week combination therapy increased BDNF and MMP-9 serum levels, but not serum proBDNF. Serum BDNF and MMP-9 levels did not correlate with motor function improvement, though baseline serum proBDNF levels correlated negatively and significantly with improvement in WMFT (ρ = -0.422, p = 0.002). The outcome of rTMS therapy was not altered by BDNF gene polymorphism.

Conclusions

The combination therapy of rehabilitation plus low-frequency rTMS seems to improve motor function in the affected limb, by activating BDNF processing. BDNF and its precursor proBDNF could be potentially suitable biomarkers for poststroke motor recovery.     

Effects of prenatal stress exposure on soluble Aβ and brain-derived neurotrophic factor signaling in male and female APPswe/PS1dE9 mice

Chronic stress and stress-related disorders, such as major depression (MD), have been shown to increase the risk for developing Alzheimer's disease (AD). Brain-derived neurotrophic factor (BDNF) has been postulated as a neurophysiological link between these illnesses. Our previous research has indicated that exposing the APPswe/PS1dE9 mouse model of AD to prenatal maternal stress (PS) induced a depressive-like phenotype, specifically in female mice. Considering the role of BDNF in depressive-like behavior and its interactions with amyloid-β (Aβ), our aim was to explore whether these mice would also exhibit alterations in soluble Aβ, mature BDNF (mBDNF), proBDNF, and the receptors TrkB and p75(NTR) in comparison to non-stressed animals. Our results demonstrate that female APPswe/PS1dE9 mice have higher levels of hippocampal proBDNF and soluble Aβ as compared to their male littermates. Additionally, a tendency was observed for PS to lower mBDNF protein levels in the hippocampus, but only in female mice, while receptor levels remained unaltered by sex or PS exposure. Given that female mice both have higher proBDNF and Aβ levels, these findings suggest an underlying role for BDNF signaling and Aβ production in the selective vulnerability of women for MD and AD development.     

BDNF variant linked to anxiety-related behaviors

Brain-derived neurotrophic factor (BDNF) is the most-abundant neurotrophin in the brain. In mammals, it is synthesized as a precursor called proBDNF, which is proteolytically cleaved to generate mature BDNF. The BDNF gene is located on chromosome 11p13, and a functional single nucleotide polymorphism (SNP) of this gene has been shown to produce a valine (Val)-to-methionine (Met) substitution in the proBDNF protein at codon 66 (Val66Met). Several papers suggest that this SNP is related to decreased hippocampal volume and hippocampus-mediated memory performance in humans. Recently, Chen et al. generated a variant BDNF mouse (BDNF(Met/Met)) that reproduces the phenotypic hallmarks in humans with a variant Met allele. In the behavioral analysis, BDNF(Met/Met) mice show increased anxiety-related behaviors. This mini-review examines the impact of Met substitution of proBDNF on anxiety-related behaviors.     

阻断NMDA受体可增强皮质酮对海马脑源性神经营养因子表达的抑制:cAMP反应元件结合蛋白的作用

高浓度的皮质酮可引起海马形态与功能的损伤,其中脑源性神经营养因子(brain-derived neurotrophic factor,BDNF) 表达的改变在海马形态与功能损伤中扮演重要角色。本实验的目的是观察单次皮下注射皮质酮后海马内BDNF-mRNA、前 体蛋白及成熟型蛋白表达的改变,并观察N-甲基-D-天冬氨酸(N-methyl-D-aspartate NMDA)受体阻滞剂MK801对皮质酮 作用的影响。实验结果显示,单次皮下注射皮质酮2 mg／kg,3 h后海马内BDNF mRNA、前体蛋白及成熟型蛋白的表达 均降低;MK801(0．1 mg／kg)对皮质酮的这一作用有增强效果。单独给予皮质酮或注射MK801 30 min后再给予皮质酮, 均能明显降低海马中cAMP反应元件结合蛋白(cAMP response element binding protein,CREB)的磷酸化水平,MK801与 皮质酮联用时CREB的磷酸化水平降低更为显著(与单独给予皮质酮相比,P<0．05)。实验结果提示,CREB磷酸化水平降 低可能是皮质酮引起海马BDNF表达减少的重要中间环节,阻断NMDA受体可加强皮质酮降低BDNF表达的效应。     

BDNF and Huntingtin protein modifications by manganese: implications for striatal medium spiny neuron pathology in manganese neurotoxicity

High levels of manganese (Mn) exposure decrease striatal medium spiny neuron (MSN) dendritic length and spine density, but the mechanism(s) are not known. The Huntingtin (HTT) gene has been functionally linked to cortical brain‐derived neurotrophic factor (BDNF) support of striatal MSNs via phosphorylation at serine 421. In Huntington's disease, pathogenic CAG repeat expansions of HTT decrease synthesis and disrupt transport of cortical–striatal BDNF, which may contribute to disease, and Mn is a putative environmental modifier of Huntington's disease pathology. Thus, we tested the hypothesis that changes in MSN dendritic morphology Mn due to exposure are associated with decreased BDNF levels and alterations in Htt protein. We report that BDNF levels are decreased in the striatum of Mn‐exposed non‐human primates and in the cerebral cortex and striatum of mice exposed to Mn. Furthermore, proBDNF and mature BDNF concentrations in primary cortical and hippocampal neuron cultures were decreased by exposure to Mn confirming the in vivo findings. Mn exposure decreased serine 421 phosphorylation of Htt in cortical and hippocampal neurons and increased total Htt levels. These data strongly support the hypothesis that Mn‐exposure‐related MSN pathology is associated with decreased BDNF trophic support via alterations in Htt.

     

耐力运动对增龄大鼠脑皮层突触可塑性的影响及相关调控机制*

目的:探讨规律性耐力运动对脑皮层增龄性老化适应性的作用与机制。方法:将三个不同年龄段的健康SPF级雄性Sprague-Dawley大鼠分为3月龄 (青年,n=20)、13月龄 (中年,n=24)和23月龄 (老年,n=24)组,每组又随机分为静息组和运动组;静息组三组静息,运动组三组实施10周递增负荷规律的中等强度耐力运动:运动方式为跑台运动(坡度0),运动强度从最大摄氧量(V·O2max) 60%～65%逐渐递增到70%～75%,运动时间为10周;取大鼠脑皮层,HE染色测试大鼠脑皮层增龄性形态学变化,检测BDNF和SOD的蛋白表达及突触素-1(SYN1)和CaMK IIα/AMPKα1/ mTOR通路等相关基因。结果:静息各组大鼠的脑皮层结构呈现年龄增龄性衰老变化,脑皮层SOD表达呈增龄性下降趋势,BDNF表达变化呈增龄性上升趋势,SYN1和CaMK IIα表达水平随增龄性趋势变化不大,AMPKα1和SirT2以及 IP3R、AKT1、mTOR mRNA表达水平随年龄变化呈现中年略上升而老年下降趋势;与静息各组大鼠相比,运动各组大鼠脑皮层神经细胞核排列紧密有序,显微镜下观察细胞核的数量明显增加,运动促进大鼠脑皮层SOD、BDNF和突触素SYN1表达水平增加,其中老年大鼠SOD、BDNF表达水平显著上调(P＜0.01),青年和老年大鼠SYN1表达水平显著上调(P＜0.05),运动上调中年和老年大鼠脑皮层CaMK IIα表达水平上调(P＜0.01),而对青年大鼠CaMK IIα表达水平却是下调(P＜0.01),运动可上调青年大鼠脑皮层的AMPKα1表达水平(P＜0.05),而对中年和老年大鼠AMPKα1的影响不显著,运动均可上调各年龄大鼠脑皮层的SirT2表达水平(P＜0.05),运动上调各年龄大鼠脑皮层的IP3R/AKT1/ mTOR表达水平,其中青年IP3R显著上调(P＜0.01),青年和中年mTOR显著上调(P＜0.01),老年mTOR也显著上调(P＜0.05)。结论:耐力运动通过上调BDNF的表达水平,调控CaMK IIα信号、激活AMPK信号通路和IP3R/AKT1/mTOR信号通路,改善脑皮层的突触可塑性。     

Role for brain-derived neurotrophic factor in learning and memory

In addition to its actions on neuronal survival and differentiation, brain-derived neurotrophic factor (BDNF) has a role in the regulation of synaptic strength. Long-term potentiation, a form of synaptic plasticity, is markedly impaired in BDNF mutant mice, but the changes were restored by the re-expression of BDNF. BDNF also influences the development of patterned connections and the growth and complexity of dendrites in the cerebral cortex. These results suggest a role for BDNF in learning and memory processes, since memory acquisition is considered to involve both short-term changes in electrical properties and long-term structural alterations in synapses. Memory acquisition is associated with an increase in BDNF mRNA and TrkB receptor activation in specific brain areas. Moreover, the pharmacologic and genetic deprivation of BDNF or its receptor TrkB results in severe impairment of learning and memory in mice, rats and chicks. The effect of BDNF on learning and memory may be linked to the modulation of NMDA and non-NMDA receptor functions as well as the expression of synaptic proteins required for exocytosis. Activation of the mitogen-associated protein kinase and/or phosphatidylinositol 3-kinase signaling pathways may be involved in BDNF-dependent learning and memory formation. It is concluded that BDNF/TrkB signaling plays an important role in learning and memory.     

Physical Exercise Reverses Cognitive Impairment in Rats Subjected to Experimental Hyperprolinemia

This study investigated whether physical exercise would reverse proline-induced performance deficits in water maze tasks, as well as its effects on brain-derived neurotrophic factor (BDNF) immunocontent and brain acetylcholinesterase (AChE) activity in Wistar rats. Proline administration followed partial time (6th–29th day of life) or full time (6th–60th day of life) protocols. Treadmill exercise was performed from 30th to 60th day of life, when behavioral testing was started. After that, animals were sacrificed for BDNF and AChE determination. Results show that proline impairs cognitive performance, decreases BDNF in cerebral cortex and hippocampus and increases AChE activity in hippocampus. All reported effects were prevented by exercise. These results suggest that cognitive, spatial learning/memory, deficits caused by hyperprolinemia may be associated, at least in part, to the decrease in BDNF levels and to the increase in AChE activity, as well as support the role of physical exercise as a potential neuroprotective strategy.     

Phase advance of the light-dark cycle perturbs diurnal rhythms of brain-derived neurotrophic factor and neurotrophin-3 protein levels, which reduces synaptophysin-positive presynaptic terminals in the cortex of juvenile rats

In adult rat brains, brain-derived neurotrophic factor (BDNF) rhythmically oscillates according to the light-dark cycle and exhibits unique functions in particular brain regions. However, little is known of this subject in juvenile rats. Here, we examined diurnal variation in BDNF and neurotrophin-3 (NT-3) levels in 14-day-old rats. BDNF levels were high in the dark phase and low in the light phase in a majority of brain regions. In contrast, NT-3 levels demonstrated an inverse phase relationship that was limited to the cerebral neocortex, including the visual cortex, and was most prominent on postnatal day 14. An 8-h phase advance of the light-dark cycle and sleep deprivation induced an increase in BDNF levels and a decrease in NT-3 levels in the neocortex, and the former treatment reduced synaptophysin expression and the numbers of synaptophysin-positive presynaptic terminals in cortical layer IV and caused abnormal BDNF and NT-3 rhythms 1 week after treatment. A similar reduction of synaptophysin expression was observed in the cortices of Bdnf gene-deficient mice and Ca(2+)-dependent activator protein for secretion 2 gene-deficient mice with abnormal free-running rhythm and autistic-like phenotypes. In the latter mice, no diurnal variation in BDNF levels was observed. These results indicate that regular rhythms of BDNF and NT-3 are essential for correct cortical network formation in juvenile rodents.