Impaired behavioural flexibility and memory in mice lacking GDNF family receptor alpha2

The glial cell line-derived neurotrophic factor (GDNF) family receptor GFRalpha2 is the binding receptor for neurturin (NRTN). The main biological responses of GFRalpha2 are mediated via the Ret receptor tyrosine kinase, although it may also signal independently of Ret via the neural cell adhesion molecule NCAM. GFRalpha2 is expressed in many neurons of both the central and peripheral nervous system. Mice lacking GFRalpha2 receptors do not exhibit any gross defects in the central nervous system structure. However, they display profound deficits in the parasympathetic and enteric nervous system, accompanied by significant reduction in body weight after weaning. Here we present the results of behavioural analysis of the GFRalpha2-knockout mice. The knockout mice did not differ from wild-type mice in basic tests of motor and exploratory activity. However, differences were established in several memory tasks. The knockout mice were not impaired in the acquisition of spatial escape strategy. However, the deficit in flexibility in establishing a new strategy was revealed during reversal learning with the platform in the opposite quadrant of the pool. Furthermore, the knockout mice displayed significant impairment in contextual fear conditioning and conditioned taste aversion tests of memory. The results suggest that GFRalpha2 signalling plays a role in the development or maintenance of cognitive abilities that help in solving complex learning tasks.     

Increased extracellular dopamine concentrations and FosB/DeltaFosB expression in striatal brain areas of heterozygous GDNF knockout mice

Glial cell line-derived neurotrophic factor (GDNF) has been shown to be involved in the maintenance of striatal dopaminergic neurons. To study whether reduced levels of endogenous GDNF affect the striatal dopaminergic transmission we estimated the basal extracellular levels of dopamine in vivo, the basal expression of FosB-related proteins in striatal brain areas as well as the effects of acute and repeated cocaine on locomotor activity and dopamine output in mice lacking one GDNF allele (heterozygous GDNF+/- mice). As expected the striatal GDNF protein content was found to be smaller in the GDNF+/- mice than in their wild-type littermates. Unexpectedly the extracellular dopamine concentration in the GDNF+/- mice in the dorsal striatum (CPu) was 2.0-fold, and in the nucleus accumbens (NAc) 1.6-fold the concentration found in the wild-type littermates. Also FosB/DeltaFosB-like immunoreactivity was found to be elevated in the CPu as well as in the core and in the shell of NAc of the GDNF+/- mice as compared with the wild-type mice. This suggests chronic postsynaptic activation of these brain areas and is in line with elevated extracellular dopamine concentrations. Cocaine's effects acutely and after repeated treatment on locomotor activity were similar in the GDNF+/- and the wild-type mice. Neither did cocaine's acute effects on dopamine output differ between the mice of the two strains. Our findings demonstrate that reduced levels of endogenous GDNF induce alterations in dorsal striatal and accumbal dopaminergic transmission, and stress the importance of endogenous GDNF in the regulation of the dopaminergic neurons.     

Neuronal GDNF Expression in the Adult Rat Nervous System Identified By In Situ Hybridization

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor which has been purified on the basis of its ability to promote the survival of dopaminergic neurons in vitro. GDNF has subsequently been cloned and its sequence shown to be distantly related to transforming growth factor-β (TGF-β). To identify GDNF expressing cells in the adult rat brain, in situ hybridization using a digoxygenin (DIG)-labelled riboprobe has been performed. Our results show that GDNF mRNA is mainly expressed in neurons and that its synthesis is not restricted to dopaminergic areas. It is widely expressed in the cortex, the hippocampus, the striatum, the substantia nigra, the thalamus, the cerebellum and the spinal cord. Neuronal GDNF expression varies among brain regions as determined by the intensity of the in situ signal. Double labelling of the substantia nigra using tyrosine hydroxylase immunohistochemistry, associated with GDNF in situ hybridization, show that the majority of dopaminergic neurons express GDNF. The widespread expression of GDNF throughout the adult brain suggests that its administration in Parkinson's disease should be restricted to the altered structures, in order to avoid possible deleterious side effects.     

男性慢性精神分裂症患者血清脑源性神经营养因子和胶质源性神经营养因子水平及认知功能的对照研究

目的:探讨慢性精神分裂症患者血清脑源性神经营养因子(BDNF)、胶质源性神经营养因子水平(GDNF)和神经认知功能的变化及它们之间关系。方法:入组慢性精神分裂症患者57例和正常对照39名。采用阳性与阴性症状量表(PANSS)评估患者的精神症状。使用酶联免疫吸附法检测血清BDNF、GDNF蛋白水平,采用数字划消测验、连线测验(TMT)、WMS-III空间广度测验(WMS-III SST)、定步调连续加法任务测验(PASAT)、Stroop测验、木块图评估神经认知功能。结果:患者组血清BDNF水平低于对照组,差异有统计学意义(t=9.112,P0.01),患者组血清GDNF与对照组相比差异无统计学意义(t=1.513,P0.05)。患者组数字划消测验、TMT-A、TMT-B、Stroop测验、木块图、WMS-III SST逆行分、PASAT成绩均差于对照组(P0.05)。患者组血清BDNF水平与PANSS阳性症状分、数字划消测验中的错误个数呈负相关(分别为r=-0.295,P=0.026;r=-0.262,P=0.049),血清GDNF水平与Stroop色词干扰测验分呈正相关(r=0.263,P=0.048)。结论:慢性稳定期的精神分裂症患者仍存在广泛的神经认知损害。BDNF可能是精神分裂症的一种素质性标记,可能参与了患者的注意障碍。     

Activation of cell-survival signal Akt by GDNF in normal rat brain

Glial cell line-derived neurotrophic factor (GDNF) activates protein kinase Akt/PKB by phosphorylation (p-Akt) which plays key roles in cell survival. In the current study, we investigated a temporal expression of p-Akt by immunohistochemical analysis after a topical application of GDNF to normal cerebral hemisphere of rats. Although p-Akt immunoreactivity was weakly present in the sham control neural cells, GDNF application greatly enhanced it at 3 h, which lasted until 1 day. These results indicate that p-Akt is expressed in neuronal cells under physiological conditions, and that topical application of GDNF greatly enhanced the phosphorylation of Akt in normal rat brain.     

神经细胞黏附分子在GDNF保护大鼠多巴胺能神经元中的作用

目的研究神经细胞黏附分子(neural cell adhesion molecule,NCAM)在胶质细胞系源性神经营养因子(glial cell line-derived neurotrophic factor,GDNF)保护帕金森(Parkinson's disease,PD)模型大鼠受损多巴胺(dopamine,DA)能神经元中的作用。方法右侧纹状体内立体定位注射6-羟多巴胺(6-OHDA)制备早期PD模型,而后分为4组:对照组(同侧黑质内注射PBS)、NCAM组(同侧黑质内仅注射anti-NCAM抗体)、GDNF组(同侧黑质内注射GDNF)、NCAM阻断组(同侧黑质内注射anti-NCAM抗体30min后注射GDNF),采用免疫组织化学染色技术和免疫印迹技术,观察各组酪氨酸羟化酶(tyrosine hydroxylase,TH)的表达变化。结果GDNF组黑质致密部TH阳性神经元数目及表达的量明显多于PBS组,差别有统计学意义;NCAM阻断组与GDNF组相比,该处TH阳性神经元数目及表达的量明显减少,差别有统计学意义。结论NCAM参与了GDNF保护DA能神经元的作用。     

Dopamine D3 receptor-preferring agonists induce neurotrophic effects on mesencephalic dopamine neurons

Anti-parkinsonian agents, pramipexole (PPX) and ropinirole (ROP), have been reported to possess neuroprotective properties, both in vitro and in vivo. The mechanisms underlying neuroprotection afforded by the D3-preferring receptor agonists remain poorly understood. The present study demonstrates that incubation of primary mesencephalic cultures with PPX and ROP or the conditioned medium from PPX- or ROP-treated primary cultures induced a marked increase in the number of dopamine (DA) neurons in the cultures. Similar effects can be observed after incubating with the conditioned medium derived from PPX- and ROP-treated substantia nigra astroglia. Meanwhile, PPX and ROP can protect the primary cells from insult of 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Furthermore, the neurotrophic effects of PPX and ROP on mesencephalic dopamine neurons could be significantly blocked by D3 receptor antagonist, but not by D2 receptor antagonist. Moreover, we found that the levels of glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) in the conditioned medium of mesencephalic cultures treated with PPX and ROP were significantly increased. Blocking GDNF and BDNF with the neutralizing antibodies, the neurotrophic effects of PPX and ROP were greatly diminished. These results suggest that D3 dopamine receptor-preferring agonists, PPX and ROP, exert neurotrophic effects on cultured DA neurons by modulating the production of endogenous GDNF and BDNF, which may participate in their neuroprotection.     

Neural progenitor cells engineered to secrete GDNF show enhanced survival, neuronal differentiation and improve cognitive function following traumatic brain injury

We sought to evaluate the potential of C17.2 neural progenitor cells (NPCs) engineered to secrete glial cell line-derived neurotrophic factor (GDNF) to survive, differentiate and promote functional recovery following engraftment into the brains of adult male Sprague-Dawley rats subjected to lateral fluid percussion brain injury. First, we demonstrated continued cortical expression of GDNF receptor components (GFRalpha-1, c-Ret), suggesting that GDNF could have a physiological effect in the immediate post-traumatic period. Second, we demonstrated that GDNF over-expression reduced apoptotic NPC death in vitro. Finally, we demonstrated that GDNF over-expression improved survival, promoted neuronal differentiation of GDNF-NPCs at 6 weeks, as compared with untransduced (MT) C17.2 cells, following transplantation into the perilesional cortex of rats at 24 h post-injury, and that brain-injured animals receiving GDNF-C17.2 transplants showed improved learning compared with those receiving vehicle or MT-C17.2 cells. Our results suggest that transplantation of GDNF-expressing NPCs in the acute post-traumatic period promotes graft survival, migration, neuronal differentiation and improves cognitive outcome following traumatic brain injury.     

大鼠胶质细胞源性神经营养因子的基因克隆及其在大肠杆菌中的表达

用逆转录一聚合酶链反应（ＲＴ－ＰＣＲ）以大鼠纹体总ＲＮＡ为模板，扩增了大鼠胶质细胞源性神经营养因子（ｒＧＤＮＦ）成熟序列的ｃＤＮＡ片段，将此ｃＤＮＡ克隆到载体ｐＧＥＭ－Ｔ中，对重组质粒进行限制酶切分析和序列测定，确定为含ｒＧＤＮＦｃＤＮＡ的重组质粒，将该ｒＧＤＮＦｃＤＮＡ重组到融合表达载体ｐＧＥＸ－１λＴ内，在大肠杆菌中较高的表达。     

Association of the GDNF gene with depression and heroin dependence,but not schizophrenia,in a Chinese population

The association of seven GDNF tag SNPs with depression, heroin dependence (HD) and schizophrenia was evaluated in Chinese. An increased risk of HD and depression was associated with rs2910709 T/T genotype and rs884344 C allele, respectively, suggesting GDNF is a novel susceptibility gene for depression and HD.     

Overexpression of GDNF induces and maintains hyperinnervation of muscle fibers and multiple end-plate formation

This study examined the role of glial cell line-derived neurotrophic factor (GDNF) in synaptic plasticity at the developing neuromuscular junction. Transgenic mice overexpressing GDNF in skeletal muscle under the myosin light chain-1 promoter were isolated. Northern blot and ELISA at 6 weeks of age indicated that GDNF mRNA and protein levels were elevated threefold in the lateral gastrocnemius muscle (LGM) of the GDNF-transgenic animals. Histochemical examination of LGM tissue sections at 6 weeks of age revealed a 70% increase in the number of cholinesterase-positive end plates without changes in end-plate area. Multiple end plates on a single muscle fiber were also observed, in addition to multiple axonal processes terminating on individual end plates. No change in the number of spinal motoneurons, overall LGM size, or muscle type composition was observed. Finally, overexpression of GDNF in muscle caused hypertrophy of neuronal somata in dorsal root ganglia without affecting their number. These findings demonstrate that overexpression of a single neurotrophic factor in skeletal muscle induces multiple end-plate formation and maintains hyperinnervation well beyond the normal developmental period. We suggest that GDNF, a muscle-derived motoneuron neurotrophic factor, serves an important role in the regulation of synaptic plasticity in the developing and adult neuromuscular junction.     

稳定表达GDNF基因的骨髓基质干细胞对多巴胺能神经元的作用

目的 制备胶质细胞源性神经生长因子(GDNF)基因修饰的骨髓基质干细胞(MSCs)，观察其对多巴胺能神经元的作用，探索治疗帕金森氏病的新途径。方法 应用逆转录聚合酶链反应(RT-PCR)方法从新生小鼠大脑皮层细胞克隆出GDNF cDNA片断，以pEGFP-C1为载体导入MSCs，制备稳定表达GDNF基因的MSCs工程细胞，采用联合培养的技术通过倒置显微镜和免疫组织化学的方法观察MSCs和GDNF基因修饰的MSCs工程细胞与多巴胺能神经元之间的相互作用。结果 MSCs和GDNF基因修饰的MSCs工程细胞均能促进多巴胺能神经元的存活和生长，MSCs工程细胞作用更强。结论 成功构建了GDNF基因修饰的MSCs工程细胞，该细胞对多巴胺能神经元有明显营养保护作用，在帕金森病治疗中可能有重要价值。     

腺病毒介导的GDNF基因转移体外表达及生物学活性研究

为利用重组腺病毒介导的胶质细胞源性神经营养因子（GDNF）基因转移治疗帕金森病（PD）提供依据。方法：采用免疫组化、RT－PCR及ELISA定量分析观察人GDNF腺病毒（Ad-GDNF)在大鼠星形胶质 PC12细胞的表达,通过观察病毒直接感染及病毒感染的PC12细胞上清对中脑原代培养细胞中的TH阳性细胞（DA能神经元）生存能力和形态分化的影响来验证其生物学活性。结果Ad-GDNF在星形胶质细胞、PC12细胞及大鼠中脑原代培养细胞均可有效表达,其表达产物对中脑DNA能神经元的生存和形态分化均有显著的促进作用。结论：腺病毒介导的GDNF基因转移可在体外有效表达,且表达产物具有生物学活性,提示该手段在PD治疗方面具有良好的应用前景。     

GDNF partially protects grafted fetal dopaminergic neurons against 6-hydroxydopamine neurotoxicity

Rats were given unilateral 6-hydroxydopamine (6-OHDA) lesions and subsequently received transplants of fetal ventral mesencephalic tissue into the denervated striatum. Four weeks later transplanted animals were tested for graft-mediated reduction of amphetamine-induced rotational behavior. Subsequently, transplanted animals received an intrastriatal injection of either GDNF (10 microg) or citrate buffer into a site lateral to the transplant, and then 6 h later received an injection of either 4.0 microg of 6-OHDA, 8.0 microg of 6-OHDA, or vehicle using the same stereotaxic coordinates that were used for the GDNF/citrate buffer injection. Animals were re-tested for amphetamine-induced rotational behavior 2 weeks later. Histological analysis revealed a significant reduction in the number of cell bodies immunostained for tyrosine hydroxylase (TH+) within the transplant for those animals pretreated with an intrastriatal injection of citrate buffer and subsequently given either dose of 6-OHDA. Transplanted animals pretreated with GDNF and subsequently administered 8.0 microg of 6-OHDA showed a significant reduction of TH+ neurons within the transplant compared to controls, however TH+ cell counts for this group remained significantly higher than the TH+ cell counts for the group of animals receiving the same dose of 6-OHDA but pretreated with citrate buffer. GDNF pretreatment completely protected TH+ cell bodies against 4.0 microg of 6-OHDA. Rotational scores indicated that GDNF provided only partial protection against 6-OHDA neurotoxicity in terms of transplant function. For both groups of transplanted animals receiving GDNF pretreatment and 6-OHDA injections, amphetamine-induced rotational scores dropped below the scores for animals pretreated with citrate buffer but remained significantly higher than the scores for transplanted animals that were not injected with 6-OHDA. Both histological and behavioral measures indicate GDNF partially protects integrated transplants against neurotoxic insult.     

无抽搐电休克对胶质源性神经营养因子的影响

目的：探讨无抽搐电休克治疗（MECT）对难治性抑郁症患者血清胶质源性神经营养因子（GDNF）的影响。方法：16例难治性抑郁症患者经MECT和40例抑郁症患者抗抑郁治疗前后分别检测血清GDNF浓度，并与30名正常者对照比较。结果：MECT及抗抑郁治疗前，难治性抑郁症组和抑郁症组血清GDNF浓度低于对照组（P〈0.01）。难治性抑郁症组中对MECT有效的患者血清GDNF浓度显著高于治疗前（P〈0.05）;而对MECT无效的患者血清GDNF浓度与治疗前相比差异无显著性。经抗抑郁药治疗8周，抑郁症组患者血清GDNF浓度也显著增高（P〈0.01）。结论：GDNF可能在MECT和抗抑郁药治疗中起了一定的作用。     

Neurotrophic factors： from neurodevelopmental regulators to novel therapies for Parkinson＇s disease

Neuroprotection and neuroregeneration are two of the most promising disease-modifying ther- apies for the incurable and widespread Parkinson＇s disease. In Parkinson＇s disease, progressive degeneration of nigrostriatal dopaminergic neurons causes debilitating motor symptoms. Neurotrophic factors play important regulatory roles in the development, survival and maintenance of specific neuronal populations. These factors have the potential to slow down, halt or reverse the loss of nigrostriatal dopaminergic neurons in Parkinsoffs disease. Several neurotrophic fac- tors have been investigated in this regard. This review article discusses the neurodevelopmental roles and therapeutic potential of three dopaminergic neurotrophic factors： glial cell line-derived neurotrophic factor, neurturin and growth/differentiation factor 5.     

Ex vivo and in vitro studies of transgene expression in rat astrocytes transduced with lentiviral vectors.

Implantation of cells genetically modified to express therapeutic genes into the brain has been proposed as a potential treatment for neurodegenerative diseases. In the current study embryonic rat-derived astrocytes were cultured and transduced with a lentiviral vector expressing the reporter gene green fluorescent protein (GFP) and subsequently grafted into the adult rat brain. The proportion of GFP expressing cells was stable, albeit small (1%), at all survival times, up to 6 weeks, the longest time point studied. In parallel in vitro studies, the astrocytes were lentivirally transduced to express either one of the two isoforms of glutamate decarboxylase (GAD(65) or GAD(67)) or glial cell line-derived neurotrophic factor (GDNF). When transducing 293T cells with the two GAD vectors, released GABA could be measured using high-performance liquid chromatography. Further studies of rat astrocytes transduced with the same vectors resulted in a level of GAD activity about 10 times higher than the activity of an intact rat striatum. One hundred thousand astrocytes transduced with LV-GDNF released approximately 27 ng of GDNF per hour. Thus, taken together, our observations provide support for the use of rat astrocytes in ex vivo gene transfer of these proteins in animal models of CNS disorders, e.g., Parkinson's disease or epilepsy.     

Variations in glial cell line-derived neurotrophic factor release from biodegradable nerve conduits modify the rate of functional motor recovery after rat primary nerve repairs

Accelerating axonal regeneration to shorten the delay of reinnervation and improve functional recovery after a peripheral nerve lesion is a clinical demand and an experimental challenge. We developed a resorbable nerve conduit (NC) for controlled release of glial cell line-derived neurotrophic factor (GDNF) with the aim of assessing motor functional recovery according to the release kinetics of this factor in a short gap model. Different types of resorbable NCs were manufactured from a collagen tube and multiple coating layers of poly(lactide-coglycolide), varying in poly(lactide-coglycolide) type and coating thickness to afford three distinct release kinetics of the neurotrophic factor. GDNF release was quantified in vitro. End-to-end suture and GDNF-free NC served as controls. Thirty-five Wistar rats underwent surgery. Motor recovery was followed from 1 to 12 weeks after surgery by video gait analysis. Morphometrical data were obtained at mid-tube level and distal to the NC. NCs were completely resorbed within 3 months with minimal inflammation. GDNF induced a threefold overgrowth of fibers at mid-tube level. However, the number of fibers was similar in the distal segment of all groups. The speed of recovery was inversely proportional to the number of fibers at the NC level but the level of recovery was similar for all groups at 3 months. The resorbable conduits proved their ability to modulate axonal regrowth through controlled release of GDNF. In relation to the dose delivered, GDNF strikingly multiplied the number of myelinated fibers within the NC but this increase was not positively correlated with the return of motor function in this model.     

Delayed infusion of GDNF promotes recovery of motor function in the partial lesion model of Parkinson's disease

Here we studied the effects of glial cell line-derived neurotrophic factor (GDNF) in a rat model that represents the symptomatic stages of Parkinson's disease. GDNF was infused starting 2 weeks after an intrastriatal 6-hydroxydopamine (6-OHDA) lesion in order to halt the ongoing degeneration of the nigrostriatal dopaminergic neurons. GDNF or vehicle was infused in the striatum or the lateral ventricle via an osmotic minipump over a total 4-week period (2-6 weeks postlesion). Motor function was evaluated by the stepping, paw reaching and drug-induced motor asymmetry tests before the pump infusion was initiated, and was repeated once during (5 weeks postlesion) and twice after the withdrawal of the minipumps (7 and 11 weeks postlesion). We found that within two weeks following the lesion approximately 40% of the nigral TH-positive neurons were lost. In the vehicle infusion groups there was an additional 20% cell loss between 2 and 12 weeks after the lesion. This latter cell loss occurred mainly in the caudal part of the SN whereas the cell loss in the rostral SN was almost complete within the first two weeks. Ventricular GDNF infusion completely blocked the late degenerating neurons in the caudal SN and had long lasting behavioural effects on the stepping test and amphetamine rotation, extending to 6 weeks after withdrawal of the factor. Striatal infusion affected the motor behaviour transiently during the infusion period but the motor performance of these animals returned to baseline upon cessation of the GDNF delivery, and the delayed nigral cell loss was marginally affected. We conclude that intraventricular GDNF can successfully block the already initiated degenerative process in the substantia nigra, and that the effects achieved via the striatal route, when GDNF is given acutely after the lesion, diminish as the fibre terminal degeneration proceeds.