Different expression of brain-derived neurotrophic factor in the nucleus accumbens of alcohol-preferring (P) and -nonpreferring (NP) rats

Recent studies suggest that the gene that encodes brain-derived neurotrophic factor (BDNF) might be linked with vulnerability to alcohol abuse. We have now compared BDNF protein levels in several brain regions between alcohol-naive alcohol-preferring (P) and -nonpreferring (NP) rats using the enzyme-linked immunosorbent assay (ELISA) procedure. The results showed that BDNF levels in the nucleus accumbens of the P rats were significantly lower than those of the NP rats, suggesting that this innate difference may contribute to the disparate alcohol drinking behavior of the P and NP rats.     

Levels of brain-derived neurotrophic factor and neurotrophin-4 in lumbar motoneurons after low-thoracic spinal cord hemisection

Neuroplasticity represents a common phenomenon after spinal cord (SC) injury or deafferentation that compensates for the loss of modulatory inputs to the cord. Neurotrophins play a crucial role in cell survival and anatomical reorganization of damaged spinal cord, and are known to exert an activity-dependent modulation of neuroplasticity. Little is known about their role in the earliest plastic events, probably involving synaptic plasticity, which are responsible for the rapid recovery of hindlimb motility after hemisection, in the rat. In order to gain further insight, we evaluated the changes in BDNF and NT-4 expression by lumbar motoneurons after low-thoracic spinal cord hemisection. Early after lesion (30 min), the immunostaining density within lumbar motoneurons decreased markedly on both ipsilateral and contralateral sides of the spinal cord. This reduction was statistically significant and was then followed by a significant recovery along the experimental period (14 days), during which a substantial recovery of hindlimb motility was observed. Our data indicate that BDNF and NT-4 expression could be modulated by activity of spinal circuitry and further support putative involvement of the endogenous neurotrophins in mechanisms of spinal neuroplasticity.     

Prevention of endoplasmic reticulum stress-induced cell death by brain-derived neurotrophic factor in cultured cerebral cortical neurons

Brain-derived neurotrophic factor (BDNF), one of the neurotrophic factors acting in the central nervous system (CNS), prevents ordinary types of neuronal cell death induced by various stimulants. On the other hand, an accumulation of unfolded proteins in the endoplasmic reticulum (ER) leads to ER stress and then induces ER stress-mediated cell death. The ER stress-mediated cell death is distinctive because the caspase-12 activity plays a crucial role in the progression of cell death. We previously showed that nerve growth factor (NGF) attenuated ER stress-mediated cell death in non-neuronal PC12 cells. Here, we report that BDNF suppressed the ER stress-mediated cell death in tunicamycin (Tm)-treated cerebral cortical neurons. An analysis using a specific inhibitor of phosphatidylinositol 3-kinase (PI3-K), LY294002, revealed that BDNF prevented this cell death via the PI3-K signaling pathway. We found that the number of NeuN/TUNEL-double positive cells and the activity of caspase-3 suppressed by BDNF were increased by LY294002. We also discovered that LY294002 diminished the effect of BDNF on the activation of caspase-12, indicating that BDNF prevents ER stress-mediated cell death via a PI3-K-dependent mechanism by suppressing the activation of caspase-12 in cultured CNS neurons.     

Effect of propofol on brain-derived neurotrophic factor and tyrosine kinase receptor B in the hippocampus of aged rats with chronic cerebral ischemia

We intraperitoneally injected 10 and 50 mg/kg of propofol for 7 consecutive days to treat a rat model of chronic cerebral ischemia. A low-dose of propofol promoted the expression of brain-derived neurotrophic factor, tyrosine kinase receptor B, phosphorylated cAMP response element binding protein, and cAMP in the hippocampus of aged rats with chronic cerebral ischemia, but a high-dose of propofol inhibited their expression. Results indicated that the protective effect of propofol against cerebral ischemia in aged rats is related to changes in the expression of brain-derived neurotrophic factor and tyrosine kinase receptor B in the hippocampus, and that the cAMP-cAMP responsive element binding protein pathway is involved in the regulatory effect of propofol on brain-derived neurotrophic factor expression.     

侧脑室内注入脑源性神经营养因子对AD小鼠酪氨酸激酶B及内源性BDNF表达的影响

目的 探讨侧脑室内注入脑源性神经营养因子(BDNF)对APP/PS1双转基因阿尔茨海默病(AD)小鼠酪氨酸激酶B (TrkB)及内源性BDNF表达的影响. 方法 10只10月龄APP/PS1雄性小鼠按随机数字表法分为2组,实验组5只,双侧侧脑室内注入BDNF;磷酸盐缓冲液(PBS)组5只,双侧侧脑室内注入PBS,为阳性对照组;干预时间均为6周.同时选择5只同窝生10月龄野生型小鼠,不予任何处理,为阴性对照组.采用荧光免疫组化法观察小鼠皮层区β-淀粉样蛋白(Aβ)斑块形态学改变,硫磺素S法检测致密斑的数量,同时检测小鼠皮层区TrkB、BDNF蛋白表达的情况. 结果 (1)治疗前、后BDNF组Aβ斑块总数分别为(101.58±7.86)个、(102.83±8.22)个,与PBS组(97.23±1 1.62)个、(103.6±6.46)个比较差异均无统计学意义(t=0.695、-0.171,P=-0.509、0.869);治疗6周后BDNF组Aβ斑块直径缩小至(34.65±9.33)μm,TS+斑块数量减少至(51.70±4.18)个,与PBS组(46.17±10.16)μm、(58.85±7.55)个比较,差异均具有统计学意义(t=-2.401、-2.536,P=0.047、0.039);(2)治疗后BDNF组TrkB、BDNF蛋白表达明显增强. 结论 侧脑室内注入BDNF减少了Aβ致密斑的形成,使Aβ蛋白沉积导致的神经毒性作用减弱,从而促进皮层区TrkB表达增强,导致内源性BDNF表达增强,可在一定程度上延缓AD小鼠的病程.     

Synaptic and extrasynaptic localization of brain-derived neurotrophic factor and the tyrosine kinase B receptor in cultured hippocampal neurons

Brain-derived neurotrophic factor (BDNF) regulates synapses, but the distribution of BDNF and its receptor TrkB relative to the location of glutamatergic and gamma-aminobutyric acidergic (GABAergic) synapses is presently unknown. Immunocytochemistry was performed in primary hippocampal neuron cultures to determine whether BDNF and TrkB are preferentially localized to excitatory or inhibitory markers at 7, 14, and 21 days in vitro (DIV). Glutamatergic sites were localized with vesicular glutamate transporter type 1 (VGLUT1) as presynaptic marker and the NR1 subunit of the NMDA receptor and the GluR1 subunit of the AMPA receptor as receptor markers. GABAergic sites were labeled with the 65-kDa isoform of glutamic acid decarboxylase (GAD-65) as presynaptic marker and the gamma2 subunit of the GABAA receptor as receptor marker. During development, <30% of BDNF punctae and TrkB clusters were localized to glutamatergic and GABAergic markers. Because their rates of colocalization did not change from 7 to 21 DIV, this study details the distribution of BDNF and TrkB at 14 DIV. BDNF was preferentially colocalized with glutamatergic markers VGLUT1 and NR1 ( approximately 30% each). TrkB was also relatively highly colocalized with VGLUT1 and NR1 ( approximately 20% each) but was additionally highly colocalized with GABAergic markers GAD-65 ( approximately 20%) and gamma2 ( approximately 30%). NR1 clusters colocalized with BDNF puncta and TrkB clusters were mostly extrasynaptic, as were gamma2 clusters colocalized with TrkB clusters. These results show that, whereas most BDNF and TrkB protein is extrasynaptic, BDNF is preferentially associated with excitatory markers and that TrkB is associated equally with excitatory and inhibitory markers.     

Influence of ginsenoside on expression of brain-derived neurotrophic factor and receptor tyrosine kinase B in the medial septum of aged rats

BACKGROUND: It has been shown that ginsenoside, the effective component of ginseng, can enhance expression of choline acetyl transferase, as well as brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase B (TrkB), in cholinergic neurons of the basal forebrain. OBJECTIVE: To qualitatively and quantitatively verify the influence of ginsenoside on expression of BDNF and its receptor, TrkB, in the medial septum of aged rats, and to provide a molecular basis for clinical application. DESIGN, T...     

Effects of ginsenoside on brain-derived neurotrophic factor and tyrosine kinase B mRNA expression in the hippocampal formation of aged rats

BACKGROUND:There are a limited number of studies involving the effects of ginsenosides,the active component of ginseng,on expression of hippocampal TrkB mRNA in aged rats.OBJECTIVE:To observe expression of brain-derived neurotrophic factor(BDNF) and tyrosine kinase B (TrkB)mRNA in the hippocampal formation of aged rats,as well as changes after ginsenoside administrated.DESIGN,TIME AND SETTING:A randomized,controlled experiment was performed at the Department of Anatomy,College of Basic Medical Sciences,China Medical University in March 2005.MATERIALS:A total of 39 female,Wistar rats were randomly divided into 3 groups (n=13 each):young (3-5 months old),aged(27 months old),and ginsenoside group(received 25mg/kg/d ginsenoside in the drinking water between 17 and 27 months of age).METHODS:Following anesthesia,the rats were exsanguinated and perfused transcardially with chilled,heparinized,0.9% saline.The brains were removed and post-fixed in 40 g/L paraformaldehyde/phosphate buffer for 20 minutes,and further incubated in 30% sucrose/phosphate buffer overnight.MAIN OUTCOME MEASURES:In situ hybridization,immunohistochemistry,and image analysis were used to investigate expression of BDNF and Trk(B mRNA in the hippocampal formation.RESULTS:The expression levels of BDNF in the hippocampal CA3 and CA1 of aged rats was significantly less than the young group(t=2.879,1.814,1.984,P<0.05).BDNF expression was significantly greater in the dentate gyrus of the ginsenoside group,compared with the aging group(t=1.943,P<0.01).The expression of TrkB mRNA in the hippocampal CA3,CA1,and dentate gyrus of aged rats was less than the young group(t=3.540,3.629,17.905,P<0.01).TrkB mRNA expression in the CA3 region and dentate gyrus of the ginsenoside group was significantly greater compared with the aging group(t=1.293,3.386,P<0.05.0.01).CONCLUSION:BDNF and TrkB mRNA expression in the hippocampal formation were reduced in the aged group.However,ginsenosides can increase BDNF and TrkB mRNA expression in the hippocampal formation.     

Effects of ginsenoside on brain-derived neurotrophic factor and tyrosine kinase B mRNA expression in the hippocampal formation of aged rats*☆

BACKGROUND： There are a limited number of studies involving the effects of ginsenosides, the active component of ginseng, on expression of hippocampal TrkB mRNA in aged rats.
OBJECTIVE： To observe expression of brain-derived neurotrophic factor （BDNF） and tyrosine kinase B （TrkB） mRNA in the hippocampal formation of aged rats, as well as changes after ginsenoside administrated.
DESIGN, TIME AND SETTING： A randomized, controlled experiment was performed at the Department of Anatomy, College of Basic Medical Sciences, China Medical University in March 2005.
MATERIALS： A total of 39 female, Wistar rats were randomly divided into 3 groups （n = 13 each）： young （3-5 months old）, aged （27 months old）, and ginsenoside group （received 25mg/kg/d ginsenoside in the drinking water between 17 and 27 months of age）.
METHODS： Following anesthesia, the rats were exsanguinated and perfused transcardially with chilled, heparinized, 0.9% saline. The brains were removed and post-fixed in 40 g/L paraformaldehyde/phosphate buffer for 20 minutes, and further incubated in 30% sucrose/phosphate buffer overnight.
MAIN OUTCOME MEASURES： In situ hybridization, immunohistochemistry, and image analysis were used to investigate expression of BDNF and TrkB mRNA in the hippocampal formation. RESULTS： The expression levels of BDNF in the hippocampal CA3 and CA1 of aged rats was significantly less than the young group （t = 2.879, 1.814, 1.984, P 〈 0.05）. BDNF expression was significantly greater in the dentate gyrus of the ginsenoside group, compared with the aging group （t = 1.943, P 〈 0.01）. The expression of TrkB mRNA in the hippocampal CA3, CA1, and dentate gyrus of aged rats was less than the young group （t = 3.540, 3.629, 17.905, P 〈 0.01）. TrkB mRNA expression in the CA3 region and dentate gyrus of the ginsenoside group was significantly greater compared with the aging group （t = 1.293, 3.386, P 〈 0.05, 0.01 ）.
CONCLUSION： BDNF and TrkB mRNA expression in the hipp     

Influence of ginsenoside on expression of brain-derived neurotrophic factor and receptor tyrosine kinase B in the medial septum of aged rats★

BACKGROUND： It has beenshown that ginsenoside, the effective component of ginseng, can enhance expression of choline acetyl transferase, as well as brain-derived neurotrophic factor （BDNF） and its receptor tyrosine kinase B （TrkB）, in cholinergic neurons of the basal forebrain. OBJECTIVE： To qualitatively and quantitatively verify the influence of ginsenoside on expression of BDNF and its receptor, TrkB, in the medial septum of aged rats, and to provide a molecular basis for clinical application. DESIGN~ TIME AND SETTING： A contrast study, which was performed in the Department of Anatomy, China Medical University, and the Department of Anatomy, Shenyang Medical College between December 2005 and May 2007. MATERIALS： Thirty-five, healthy, female, Sprague Dawley rats were selected for this study. Ginsenoside （81% purity） was provided by Jilin Ji＇an Wantai Chinese Medicine Factory; anti-BDNF antibody, anti-TrkB antibody, and their kits were provided by Wuhan Boster Company. METHODS： A total of 35 rats were divided into three groups： young （four months old）, aging （26 months old）, and ginsenoside. Rats in the ginsenoside group were administered ginsenoside （25 mg/kg/d） between 17 months and 26 months. MAIN OUTCOME MEASURES： Immunohistochemistry and in situ hybridization were used to measure expression of BDNF and TrkB in the medial septum of aged rats, and the detected results were expressed as gray values. RESULTS： （1） Qualitative detection： using microscopy, degenerative neurons were visible in the medial septum in the aging group. However, neuronal morphology in the ginsenoside group was similar to neurons in the young group. （2） Quantitative detection： the mean gray value of BDNF-positive and TrkB-positive products in the aging group were significantly higher than in the young group （t = 3.346, 4.169, P 〈 0.01）; however, the mean gray value in the ginsenoside group was significantly lower than in the aging group （t = 2.432, 2.651, P 〈 0.01）. CONCLUS     

Memantine inhibits ethanol-induced NMDA receptor up-regulation in rat hippocampal neurons

The present study examined the effect of memantine, an uncompetitive NMDA receptor antagonist, on ethanol-induced NMDA receptor up-regulation. Primary glutamatergic rat hippocampal neurons were exposed to ethanol and memantine for 5 days. The ethanol-sensitive NMDA receptor subunits NR1, NR2A and NR2B were quantified by Western immunoblot analysis. Exposure to ethanol (50 mM) caused an increase in the levels of NR1 (137 +/- 11% of untreated control, P = 0.009), NR2A (128 +/- 14%, P = 0.022) and NR2B (136 +/- 19%, P = 0.012). Coincubation with memantine (10 microM) completely blocked the ethanol-induced up-regulation of NR1 (102 +/- 4%), NR2A (95 +/- 7%) and NR2B (105 +/- 13%). No effect of memantine on NR subunit expression was observable, except for NR2A, where a decrease (79 +/- 6%, P = 0.034) was noted. Neither ethanol nor memantine alone or in combination were toxic in the concentrations tested. These results may provide a molecular explanation for beneficial effects of memantine on ethanol-induced glutamatergic hyperexcitability reflected in the ethanol withdrawal syndrome and on the development of ethanol dependence.     

Effects of prenatal alcohol exposure on neural cells in mice

Pregnant DBA/1J mice were treated orally with 1.0 or 2.0 g/kg ethanol from days 11–17 of gestation to determine whether ethanol can perturb normal brain development. On gestational day 18 the fetuses were removed and fetal growth parameters were determined. The cerebrums from one group of fetuses were subsequently analyzed for cell number and protein content. The remaining cerebrums were assayed for their ability to grow in an in vitro cell culture system. Prenatal ethanol exposure decreased fetal body and brain weights and crown-rump length. The brain was particularly affected as indicated by a decreased brain: body wt ratio. The percentage of affected and marginally affected fetuses increased in a dose-dependent manner. While the number of cells/brain was unaffected, the number of cells/g cerebrum and the number of cells/mg cerebral protein was increased. Prenatal ethanol exposure decreased the ability of cerebral cells to grow in culture as demonstrated by the reduced plating efficiency and reduced colony size.The data from the present study suggest that ethanol induces a two-fold effect on mouse brain development. First, since the total number of cells/brain was not appreciably affected by prenatal ethanol treatment, it is possible that the reduction in brain size is due to a decreased amount of neuropil. This putative effect on the neuropil was manifested in vitro by decreased colony area. Second, the decreased plating efficiency of cells from brains of affected fetuses suggests that these cells are not functionally normal. These effects may be important in the pathogenesis of central nervous system anomalies associated with the Fetal Alcohol Syndrome.     

BDNF及其受体TrkB mRNA在脑缺血后适应大鼠模型中的表达变化

目的检测脑源性性神经营养因子(BDNF)及其受体酪氨酸激酶B(TrkB)在脑缺血后适应大鼠模型再灌注不同时间窗的表达,探讨BDNF/TrkB在脑缺血后适应中的作用。方法 Wistar大鼠随机分成对照组、缺血-再灌注组(IR)和缺血后适应组(IP),后两组根据再灌注时间的不同各分为6h、12h、24h、48h、72h 5个亚组。线栓法建立局灶性脑缺血-再灌注模型。TTC染色测定脑梗死体积,原位杂交法检测BDNF/TrkB mRNA的表达。结果 IP组大鼠梗死体积较IR组明显减小(P0.05)。IP组各时间点BDNF mRNA及TrkB mRNA表达较IR组均明显升高(P0.05)。结论脑缺血后适应能增加脑缺血-再灌注后BDNF及TrkB的表达,减轻脑梗死体积,BDNF/TrkB在脑缺血后适应后脑缺血-再灌注损伤中发挥了重要保护作用。     

Systemic ethanol administration elevates deoxycorticosterone levels and chronic ethanol exposure attenuates this response

Systemic ethanol administration is known to elevate levels of the GABAergic neuroactive steroid 3alpha,21-dihydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THDOC). 3alpha,5alpha-THDOC is synthesized from deoxycorticosterone (DOC) by metabolism in adrenals and brain. The present study investigated DOC levels in plasma and brain following ethanol administration to na?ve and ethanol-exposed rats. Rats were administered ethanol (2 g/kg, i.p.) or saline and DOC levels were measured in plasma and brain regions by radioimmunoassay. Chronic ethanol-exposed rats were administered an ethanol challenge (2 g/kg, i.p.) following 15 days of ethanol liquid diet consumption. Ethanol administration markedly increased DOC levels in plasma, cerebral cortex, hippocampus, hypothalamus, cerebellum, and olfactory tubercle of na?ve rats. Ethanol challenge produced an attenuated elevation of DOC in rat plasma and brain following chronic ethanol consumption for 2 weeks. These findings suggest that acute ethanol increases DOC levels in ethanol na?ve rats and chronic ethanol consumption induces tolerance to ethanol-induced increases in DOC levels.     

MK-801 prevents the increased NMDA-NR1 and NR2B subunits mRNA expression observed in the hippocampus of rats tolerant to diazepam

The chronic diazepam administration in rats has been show from our previous results, to produce an increased synaptic plasticity. Furthermore, this occurs with a concomitant over expression of the mRNA NR1 and NR2B N-methyl-D-aspartate receptor subunits. MK-801, a non-competitive antagonist of N-methyl-D-aspartate receptor, impairs both the development of conditioned tolerance to diazepam and the hippocampal long-term potentiation generation. In the present study, we have further investigated the hippocampal glutamatergic transmission in the development of tolerance to diazepam. Our results demonstrate that the development of tolerance to the hypolocomotive effect of diazepam, along with the increased hippocampal synaptic plasticity and the associated over expression of the mRNA NR1 and NR2B N-methyl-D-aspartate receptor subunits, were blocked by previous MK-801 administration. We suggest that the participation of hippocampal glutamatergic transmission is relevant to increased hippocampal synaptic plasticity, the latter being a neurobiological mechanism behind the development of the conditioned tolerance to diazepam.     

Brain-derived neurotrophic factor mRNA and protein in the piglet brainstem and effects of Intermittent Hypercapnic Hypoxia

Brain-derived neurotrophic factor (BDNF) is a neurotrophin essential for the development of normal respiratory rhythm and ventilatory control. Chronic exposure to Intermittent Hypercapnic Hypoxia (IHH) has been shown to alter ventilatory responses of piglets. This study investigated changes in BDNF distribution and expression in seven nuclei of the caudal medulla, from piglets exposed to IHH for 1, 2, 3, or 4 days before death, using non-radioactive in situ hybridisation (for mRNA) and immunohistochemistry (for protein). Compared to controls, BDNF mRNA was markedly increased across the entire medulla of the brainstem, after all durations of IHH (1-4 days). In contrast, BDNF protein expression increased after 1 day of exposure to IHH (p=0.003), but, thereafter, was not different to controls. Amongst individual nuclei, neurons of the dorsal motor nucleus of the vagus (DMNV) showed increased BDNF mRNA (p<0.01), but decreased protein expression (p=0.05) after all durations of IHH. In the ION, both mRNA and protein for BDNF were significantly increased after 1 day IHH (p<0.01 and p=0.001, respectively), but these increases were not sustained. This study is the first to investigate changes in BDNF expression in response to environmental challenges during postnatal development in the brainstem. Implications of the wide distribution of BDNF in the piglet caudal medulla and increased expression after IHH exposure are discussed, with particular reference to roles for BDNF-dependent neurons at this stage of development.     

Expression of brain-derived neurotrophic factor and tyrosine kinase B receptor proteins in glioneuronal tumors from patients with intractable epilepsy: colocalization with N-methyl-D-aspartic acid receptor

Recent evidence suggests that brain-derived neurotrophic factor (BDNF) and its tyrosine kinase B (TrkB) receptor, in addition to promoting neuronal survival and differentiation, modulates synaptic transmission by increasing N-methyl-D-aspartic acid receptor (NMDAR) activity. Overexpression of BDNF may, then, interfere with normal brain function, causing increased excitability. We have examined the immunohistochemical expression of BDNF, full-length TrkB receptor and the NMDAR subunit 1 and subunit 2A/B proteins (NMDAR1 and NMDAR2A/B) in glioneuronal tumors (gangliogliomas, GG, n = 40; dysembryoplastic neuroepithelial tumors, DNT, n = 15), from patients with chronic intractable epilepsy. The great majority of tumors studied were positive for all markers examined, supporting the high level of neurochemical differentiation of these lesions. BDNF and TrkB immunoreactivity (ir) was mainly observed in the neuronal component of the tumors. In GG, more than 90% of tumors contained very intense BDNF-ir ganglion cells. Double labeling confirmed the presence of BDNF-ir and TrkB-ir in neurons which contained NMDAR1. NMDAR2A/B intensely labeled abnormal neurons in both GG and DNT and co-localized with NMDAR1. The presence of BDNF and its receptor in the neuronal component of GG and DNT may suggest a role for this neurotrophin in the development of these lesions, preventing the death of abnormal neuronal cells. In addition, since these neurons contain both NMDAR1 and NMDAR2A/B subunits, the BDNF-TrkB pathway may also contribute through a modulation of glutamatergic transmission to the intrinsic epileptogenicity of glioneuronal tumors.     

The effect of 'binge' cocaine administration on the expression of cyclin-dependent kinase 5 and its activator p35 in various regions of rat brain

The present study was aimed at determining whether the administration of cocaine in 'binge' pattern regimen that evoked tolerance to the locomotor stimulant effects of cocaine also influenced the expression of cyclin-dependent kinase 5 (Cdk5) and its activator p35 in the amygdala, medial prefrontal cortex, nucleus accumbens septi and caudate-putamen. Western blot techniques revealed that acute and repeated 'binge' cocaine decreased expression of the Cdk5 protein in the amygdala. In the medial prefrontal cortex, only exposure to repeated 'binge' cocaine decreased the content of the Cdk5 protein. 'Binge' cocaine administration also altered the expression of Cdk5 activator p35 protein. In the amygdala, only repeated 'binge' cocaine decreased the expression of p35, while in the medial prefrontal cortex, a decrease was observed after acute and repeated 'binge' cocaine exposure. In neither the nucleus accumbens septi nor the caudate-putamen acute or repeated 'binge' cocaine modified the expression of Cdk5 and p35. The above data indicate that in contrast to sensitizing doses of cocaine, a single and repeated binge of cocaine, which evoked tolerance to its locomotor stimulant effects, decreases expression of Cdk5 and p35 and possibly decreases the efficacy of neurotransmission or induces brain plastic changes regulated by Cdk5 and its activator p35.     

Brain-derived neurotrophic factor reduces TrkB protein and mRNA in the normal retina and following optic nerve crush in adult rats

Brain-derived neurotrophic factor (BDNF) is a well-known retinal neuroprotectant, but its effectiveness is limited: higher doses do not yield increased cell survival, multiple applications are not additive, and long-term delivery does not reverse, ganglion cell death. These limitations might reflect either injury- or BDNF-induced retinal changes in TrkB, the high affinity tyrosine kinase receptor used by BDNF. Retinal levels of TrkB protein and mRNA were measured in rats following intravitreal application of BDNF alone, optic nerve crush alone, and both. Full-length receptor protein levels (TrkB.FL) were determined by Western blot analysis and mRNA (trkB.FL) levels were measured using RNAse protection assay (RPA). BDNF alone produced a rapid and prolonged decrease in normal retina TrkB.FL. Nerve crush also resulted in decreased TrkB.FL, but the reduction was not apparent before 2-week post-crush. BDNF applied at the time of the crush yielded reductions in TrkB.FL similar to that of BDNF alone. With respect to TrkB mRNA levels, injection of BDNF into normal eyes and optic nerve crush alone showed bell-shaped patterns of change: approximately 50% below normal at 24-h post-procedure, approximately 50% above normal at 3 days, normal at 7 days, and approximately 50% below normal at 2-week post-procedure. When BDNF and nerve crush were combined, trkB-FL levels reached 90% of normal 1-week post-crush/injection. The data suggest that the limitation of BDNF in promoting ganglion cell survival following optic nerve injury results, in part, due to drug-induced down-regulation of the full-length TrkB receptor needed to activate intracellular pathways.