GDNF is a major component of trophic activity in DA-depleted striatum for survival and neurite extension of DAergic neurons

Extracts from dopamine (DA)-depleted striatal tissue (lesion extract) and from intact striatal tissue (intact extract) were prepared, and trophic activities in these extracts were evaluated using survival and neurite extension of DAergic neurons as indices. Levels of brain-derived neurotrophic factor (BDNF), basic fibroblast growth factor (bFGF), glial cell-line derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) in extracts were measured using enzyme-linked immunosorbent assay (ELISA). The lesion extract exhibited a stronger trophic activity on survival and neurite extension of DAergic neurons than intact extract. In lesion extract, bFGF was slightly and GDNF was significantly increased, while BDNF and NT-3 were the same level in each extract. The peak increase of bFGF and GDNF was during 2 to 3 weeks after DA depletion. Trophic activity of extract was strongly attenuated after immunoprecipitation of GDNF and partly attenuated after immunoprecipitation of bFGF. In parallel immunohistological study, no significant variations were found for striatal microtubule-associated protein-2 (MAP-2)- nor OX-41-immunoreactive cells, while the number of strongly labeled glial fibrillary acidic protein (GFAP)-immunoreactive cells were increased in DA-depleted striatum, suggesting reactive gliosis. Data suggest that bFGF is a minor, while GDNF is a major component of trophic activity for DAergic neurons in DA-depleted striatum, and increased bFGF and GDNF levels may be mediated partly by reactive gliosis.     

Glial cell line‐derived neurotrophic factor is a key neurotrophin in the postnatal enteric nervous system

Background The enteric nervous system (ENS) continues its structural and functional growth after birth, with formation of ganglia and the innervation of growing smooth muscle. However, little is known about factors in the postnatal intestine that influence these processes. Methods We examined the presence and potential role of glial cell line‐derived nerve growth factor (GDNF) in the rat postnatal ENS using neonatal tissue, primary co‐cultures of the myenteric plexus, smooth muscle, and glial cells as well as cell lines of smooth muscle or glial cells. Key Results Western blot analysis showed that GDNF and its co‐receptors rearranged during transfection (RET) and GDNF family receptor alpha‐1 were expressed in the muscle layer of the neonatal and adult rat intestine. Immunohistochemistry localized the receptors for GDNF to myenteric neurons, while GDNF was localized to smooth muscle cells. In a co‐culture model, GDNF but not nerve growth factor, brain derived neurotrophic factor or neurotrophin‐3 significantly increased neuronal survival and more than doubled the numbers of neurites in vitro. RT‐PCR, qPCR, Western blotting, ELISA, and immunocytochemistry as well as bioassays of neuronal survival and of RET phosphorylation all identified intestinal smooth muscle as the source of GDNF in vitro. GDNF also induced morphological changes in the structure and organization of neurons and axons, causing marked aggregation of neuronal cell bodies and collinear development of axons. As well, GDNF (50–150 ng mL^?1) significantly increased [³H]‐choline uptake and stimulated [³H]‐acetylcholine release. Conclusions & Inferences We conclude that GDNF derived from intestinal smooth muscle cells is a key factor influencing the structural and functional development of postnatal myenteric neurons.     

Implantation of bioactive growth factor-secreting rods enhances fetal dopaminergic graft survival, outgrowth density, and functional recovery in a rat model of Parkinson's disease

One of the drawbacks with fetal ventral mesencephalic (VM) grafts in Parkinson's disease is the limited outgrowth into the host striatum. In order to enhance graft outgrowth, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) were administered by implantation of bioactive rods to the lateral part of the striatum to support grafted fetal VM implanted to the medial portion of the striatum. The polymer-based bioactive rods allow for a local secretion of neurotrophic factors over a time period of approximately 2 weeks. Moreover, glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta1 (TGFbeta1) were administered using the same technique. Concomitant administration of GDNF and TGFbeta1 was achieved by insertion of one GDNF and one TGFbeta1 rod. This was performed to investigate possible additive effects between GDNF and TGFbeta1. Rotational behavior, outgrowth from and nerve fiber density within the VM graft, and the number of TH-positive cells were studied. Functional compensation by reduction of rotational behavior was significantly enhanced in animals carrying bFGF and GDNF rods in comparison with animals carrying only VM graft. EGF and bFGF significantly increased the innervation density. Moreover, the nerve fiber density within the grafts was significantly enhanced by bFGF. Cell counts showed that a significantly higher number of TH-positive neurons was found in grafts treated with bFGF than that found in GDNF-treated grafts. An additive effect of TGFbeta1 and GDNF was not detectable. These results suggest that bioactive rods is a useful tool to deliver neurotrophic factors into the brain, and since bFGF was a potent factor concerning both functional, immunohistochemical and cell survival results, it might be of interest to use bFGF-secreting rods for enhancing the overall outcome of VM grafts into patients suffering from Parkinson's disease.     

成年骨髓间质干细胞体外诱导分化成神经细胞研究

目的：探索成年骨髓间质干细胞（ABMMSC）诱导分化为神经细胞（神经元和神经胶质细胞）的可行性，为ABMMSC在神经科学领域内的应用提供 参考。方法：以成年犬ABMMSC为实验对象，利用碱性成纤维细胞生长因子（bFGF）、表皮生长因子（FGF）、维甲酸（RA）、脑源性神经营养因子（BDNF）、胶质细胞系源性神经营养因子（GDNF）等作为增殖及分化诱导因子，采用两步法进行增殖培养，分化诱导；免疫细胞化学法进行细胞性质鉴定。结果：加入bFGF、EGF后增殖培养48h，换液、去除非粘附细胞，再增殖培养72h ,可见细胞分裂相（成纤维细胞样细胞）和簇样克隆形成（中小型细胞）。加入RA、BDNF、GDNF诱导3d，部分细胞有神经元特异性烯醇酶（NSE）、胶质纤维酸性蛋白（GFAP）成分表达；第10d可见有神经元、神经胶质形态样细胞形成。经细胞成分（NSE、GFAP）鉴定证实为神经元、神经胶质细胞。结论：ABMSC在体外培养条件下，经过bFGF、EGF、RA、BDNF、GDNF等因子的“程序性”作用，可以向神经元、神经胶质前体细胞及其终末细胞方向分化。     

Anterograde axonal transport of internalized GDNF in sensory and motor neurons

Endogenous glial cell line-derived neurotrophic factor (GDNF) has been shown to be anterogradely transported in sensory and motor neurons which do not express detectable levels of GDNF mRNA. The source of the anterograde axonal GDNF in these neurons has remained unclear. Here we show that radiolabeled GDNF is internalized by dorsal root ganglion (DRG) and hypoglossal motor neurons at their cell bodies and/or their dendrites and that a mechanism exists to transport the internalized GDNF anterogradely in their axons. Since adjacent glial cells express GDNF mRNA, these data support the concept that Schwann cell- or oligodendrocyte-derived GDNF is taken up by DRG and motor neurons, respectively, and transported anterogradely along the axons for release from terminals, resulting in neuronal transcytosis.     

Trophic factor secreting kidney cell lines: in vitro characterization and functional effects following transplantation in ischemic rats

Several kidney cell lines were investigated for their ability to produce glial cell line-derived neurotrophic factor (GDNF). Cell line-conditioned medium was analyzed using ELISA and two cell lines were identified which produce GDNF in physiologically active concentrations. ELISA analyses revealed that conditioned medium from these two cell lines also contained PDGF, bFGF, TGFβ1 and TGFβ2. Both of these cell lines were then transplanted into the striatal penumbra of rats, 1 h following middle cerebral artery occlusion. Behavioral testing revealed that both cell lines reduced the deficit associated with cerebral ischemia and reduced the infarct volume relative to controls. Reduction of infarct volume was likely achieved by the action of GDNF and/or other growth factors produced by the cells.     

Changing responsiveness of developing midbrain dopaminergic neurons for extracellular growth factors

Numerous purified growth factors as well as yet-unidentified neurotrophic activities within mesencephalic glia support the survival of dopaminergic neurons. To further characterize the functional role of these multiple growth factor influences in dopaminergic cell development, various purified growth factors as well as mesencephalic glial-conditioned medium (CM) were screened for effects on dopaminergic cell survival and glial numbers in serum-free low density cultures of the dissociated embryonic day (E) 15 and E17 rat mesencephalon. In E15 mesencephalic cultures, dopaminergic cell survival increased with brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), transforming growth factor α (TGFα), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor-BB (PDGF-BB), and interleukin-6 (IL-6). bFGF, TGFα, PDGF, and IL-6 also stimulated glial proliferation as demonstrated by autoradiographic labeling for ³H-thymidine. Moreover, CM derived from the mesencephalic glial cell line Mes42 completely prevented the death of E15 dopaminergic neurons within the initial days of cultivation. In E17 mesencephalic cultures, survival-promoting effects on dopaminergic neurons were present with BDNF, GDNF, and bFGF. TGFα, IGF-1, PDGF-BB, and IL-6 stimulated glial proliferation but did not affect dopaminergic cell survival. Similarly, mesencephalic glial-CM completely failed to support the survival of E17 dopaminergic neurons. These observations demonstrate that during embryonic development, dopaminergic cell survival sequentially depends on distinct sets of growth factors. The concomitant loss of sensitivity of developing dopaminergic neurons for mesencephalic glial-CM as well as TGFα, IGF-1, PDGF-BB, and IL-6 further provides evidence that these growth factors indirectly affect early dopaminergic neurons through glial-mediated processes and suggests a crucial role of glia during the initial stages of neuronal development. J. Neurosci. Res. 51:508–516, 1998. © 1998 Wiley-Liss, Inc.     

Glial cell line-derived neurotrophic factor stimulates the morphological differentiation of cultured ventral mesencephalic calbindin- and calretinin-expressing neurons

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for mesencephalic dopaminergic neurons. Subpopulations of these neurons express the calcium-binding proteins calbindin (CB) and calretinin (CR). Understanding the specific effects of GDNF on these neurons is important for the development of an optimal cell replacement therapy for Parkinson's disease. To investigate the effects of GDNF on the morphological complexity of mesencephalic tyrosine hydroxylase (TH)-immunoreactive (-ir), CB-ir, and CR-ir neurons, dissociated cultures of embryonic (E14) rat ventral mesencephalon were prepared. Chronic administration of GDNF (10 ng/ml) for 7 days promoted the survival of TH-ir and CB-ir neurons but did not alter the density of CR-ir neurons. Total fiber length/neuron and number of branching points/neuron of CB-ir and CR-ir cells were significantly increased after GDNF treatment (2x for CB-ir cells and 1.4x and 1.7x, respectively, for CR-ir cells), which resulted in a significantly larger size of neurite field/neuron (2.9x and 1.5x for CB-ir and CR-ir neurons, respectively). The number of primary neurites/neuron of CB-ir neurons was found to be 1.5x larger, while no difference could be detected for CR-ir cells. Assessment of the effects of GDNF on TH-ir neurons unveiled a similar outcome with an increased total fiber length/neuron (1.5x), an increased number of primary neurites/neuron (1.6x), and a twofold larger size of neurite field/neuron. In conclusion, our findings recognize GDNF as a neurotrophic factor that stimulates the morphological differentiation of ventral mesencephalic CB-ir and CR-ir neurons.     

Glial cell line-derived neurotrophic factor augments midbrain dopaminergic circuits in vivo

Recently, a novel glial cell line-derived neurotrophic factor (GDNF) has been identified, cloned, and shown to have potent survival- and growth-promoting activity on fetal rat midbrain dopaminergic neurons in cell culture. In this study, we document marked and long-lasting effects on adult rat midbrain dopaminergic neurons in vivo after intracranial administration. A single injection of this factor into the substantia nigra elicited a dose-dependent increase in both spontaneous and amphetamine-induced motor activity, and a decrease in food consumption, lasting 7–10 days. Using immunocytochemistry, we found sprouting of tyrosine hydroxylase-positive neurites towards the injection site, and increased tyrosine hydroxylase immunoreactivity of the ipsilateral striatum was produced by GDNF. There was also a marked and dose-dependent increase in dopamine turnover in the substantia nigra and striatum, and in ipsilateral dopamine levels in the substantia nigra. Little or no effects of GDNF were seen on norepinephrine or serotonin levels. The neurochemical changes on dopaminergic afferents persist for at least 3 weeks after a single intracranial injection of 10 μg. Taken together, these data suggest that this glial cell line-derived factor has a potent influence on adult rat dopamine neurons and may have a potentially important role as a trophic factor for these neurons.     

The neurotrophic effects of fibroblast growth factors on dopaminergic neurons in vitro are mediated by mesencephalic glia

Neurotrophic support is generally believed to result from a direct action of growth factors on developing neurons. However, there is increasing evidence that growth factors can indirectly affect neuronal development by glial-mediated processes. To investigate a possible role of glia in mediating neurotrophic effects on dopaminergic neurons, four purified growth factors were screened for dual effects on the survival and differentiation of dopaminergic neurons and on the proliferation of mesencephalic glial cells in vitro. Dissociated embryonic day 14.5 rat mesencephalon was grown at low cell density without serum, conditions under which both glial growth and neuronal survival are not optimal. Treatment of these cultures with acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF) increased the number of surviving tyrosine hydroxylase-immunoreactive (TH-IR) neurons by 90-110% [corrected] at 8 d in vitro in a dose-dependent manner. The effects of these factors were not additive. High-affinity dopamine uptake was increased by bFGF, but not by aFGF. Length of TH-IR neurites was not affected by either aFGF or bFGF. Both growth factors induced proliferation of mesencephalic astrocytes as demonstrated by autoradiographic labeling with 3H-thymidine combined with immunocytochemistry for glial fibrillary acidic protein (GFAP). In contrast, platelet-derived growth factor (PDGF) and interleukin-1 had no effect on the survival or differentiation of dopaminergic neurons or the proliferation of mesencephalic astrocytes. Inhibition of glial proliferation abolished the neurotrophic effects exerted by aFGF or bFGF on dopaminergic neurons. Moreover, conditioned medium derived from mesencephalic glial cultures replated in the virtual absence of neurons also contained neurotrophic activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of neurotrophic factors in psychostimulant-induced behavioral and neuronal plasticity

Several neurotrophic factors influence the development, maintenance and survival of dopaminergic neurons in the mammalian central nervous system (CNS), including neurotrophin-3 (NT-3), brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and glial derived neurotrophic factor (GDNF). This review focuses on the role of these neurotrophic factors in psychostimulant-induced behavioral sensitization, a form of dopamine-mediated neuronal plasticity that models aspects of paranoid schizophrenia as well as drug craving among psychostimulant addicts. Whereas NT-3, CNTF and bFGF appear to play a positive role in psychostimulant-induced behavioral sensitization, GDNF inhibits this form of behavioral plasticity. The role of BDNF in behavioral sensitization, however, remains elusive. While it has been shown that neurotrophic factors can influence the behavioral, structural and biochemical phenomena related to psychostimulant-induced neuronal plasticity, it is unclear which neurotrophic factors are important physiologically and which have purely pharmacological effects. In either case, examining the role of neurotrophic factors in behavioral sensitization may enhance our understanding of the mechanisms underlying the development of paranoid psychosis and drug craving and lead to the development of novel pharmacological treatments for these disorders.     

重组大鼠质粒pEGFP-GDNF的构建及真核细胞转染

目的　构建携带大鼠胶质细胞源性神经营养因子(GDNF)基因的真核细胞表达载体,为应用GDNF进行如帕金森综合征之类的神经元退化性疾病的基因治疗打基础。方法　采用RT- PCR方法从大鼠胎脑组织总RNA中扩增出该基因的c DNA序列,并克隆到增强型绿色荧光蛋白(EGFP)报告基因的真核表达载体p EGFP- C1中,对重组质粒p EGFP- GDNF进一步鉴定。采用电转及阳离子脂质体将重组质粒p EGFP- GDNF转染至SH- SY5 Y细胞。结果　大鼠GDNF c DNA已正确地克隆到真核表达载体p EGFP- C1中,而构建成重组大鼠质粒p EGFP-GDNF。GDNF基因可稳定表达在细胞中。结论　真核细胞表达载体p EGFP- GDNF以及表达GDNF工程细胞SH-SY5 Y的成功构建,为进一步开展GDNF基因治疗PD等中枢神经系统疾病奠定了基础。     

成年大鼠骨髓基质干细胞诱导分化为神经元样细胞不同方法比较的研究

目的 研究成年大鼠骨髓基质干细胞(BMSCs)诱导分化为神经元样细胞不同的方法，寻找它向神经细胞分化的最佳条件。方法 取纯度较高的BMSCs，通过不同的神经营养因子诱导法和抗氧化剂诱导法，进行抗巢蛋白(nestin)、神经元特异烯醇化酶(NSE)、神经胶质纤维酸性蛋白(GFAP)、酪氨酸羟化酶(TH)免疫细胞化学染色，观察相应的阳性细胞数。结果 诱导第3天A组(EGF：表皮生长因子，bFGF：碱性成纤维细胞生长因子，RA：全反式维甲酸)，B组(GDNF：胶质细胞系源性神经营养因子，BDNF：脑源性神经营养因子)，C组(EGF，bFGF，GDNF，BDNF和RA)的Nestin阳性细胞数较多，其中以C组最多，而D组(抗氧化剂)Nestin阳性细胞数少于前三组。A，B，C组的NSE，GFAP染色阳性细胞数较D组少，但D组有部分细胞发生死亡。诱导第7天A，B，C组的NSE，GFAP阳性细胞数较第3天时明显增多，C组最多，B组其次，Nestin阳性细胞数比例较第3天时明显减少。而D组的NSE，GFAP阳性细胞数少于其第3天时；C组诱导成神经细胞比例较高，阴性对照组和空白对照组极少或无阳性细胞。此外，神经营养因子诱导法生成神经样细胞的比例都多于胶质样细胞。结论 抗氧化剂诱导法分化诱导快，而神经营养因子诱导法分化诱导效率高，诱导后细胞生长状态明显好于前者，各种神经营养因子联合作用影响BMSCs的增殖和分化。     

Effects of polychlorinated biphenyls (PCBs) on expression of neurotrophic factors in C6 glial cells in culture

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that affect nervous system function. Glial cells are among the first lines of defense in the nervous system and are involved in activities, including production of neurotrophic factors, which maintain an environment optimally suited for neuronal function. In this study, we investigated the effects of a commercial mixture of PCBs, Aroclor 1254 (A1254), on neurotrophic factor secretion by C6 cells in culture. C6 cells were exposed to medium containing 10 ppm A1254, 0.1% dimethyl sulfoxide (DMSO=vehicle), or normal culture medium. Glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) protein were measured by enzyme-linked immunosorbant assay. GDNF mRNA was measured by real-time RT-PCR. The role of protein kinase C (PKC) signaling in A1254 effects was investigated using bisindolylmaleimide, a PKC antagonist. Exposure to A1254 increased NGF (8.8x10(-5)+/-8.2x10(-6)pg NGF/cell) and GDNF (1.0x10(-4)+/-6.7x10(-6)pg GDNF/cell) secretion compared to DMSO treated controls (5.0x10(-5)+/-7.5x10(-6)pg NGF/cell and 6.2x10(-5)+/-3.1x10(-6)pg GDNF/cell). The effect of A1254 was long-lived, as GDNF secretion was elevated following 5 days of exposure (4.1x10(-5)+/-1.7x10(-6)pg GDNF/cell in A1254 exposed cells vs. 2.9x10(-5)+/-2.3x10(-6)pg GDNF/cell in DMSO exposed cells). GDNF mRNA expression was also elevated following exposure to A1254 (1.14+/-0.07 gene expression units in A1254 exposed cells vs. 0.8+/-0.07 gene expression units in DMSO exposed cells). Bisindolylmaleimide was able to block the effects of A1254 on GDNF secretion. Thus, one potential mechanism by which PCBs may alter nervous system function is via disruption of neurotrophic factor expression by glial cells. The observation that neurotrophic factor expression was increased following exposure to PCB may suggest that glial cells increase expression of neuroprotective genes following exposure to potentially damaging agents such as PCBs.     

Bone mesenchymal stromal cells stimulate neurite outgrowth of spinal neurons by secreting neurotrophic factors

It has been demonstrated that bone mesenchymal stromal cells (BMSCs) stimulate neurite outgrowth from dorsal root ganglion (DRG) neurons. The present in vitro study tested the hypothesis that BMSCs stimulate the neurite outgrowth from spinal neurons by secreting neurotrophic factors. Spinal neurons were cocultured with BMSCs, fibroblasts and control medium in a non-contact system. Neurite outgrowth of spinal neurons cocultured with BMSCs was significantly greater than the neurite outgrowth observed in neurons cultured with control medium or with fibroblasts. In addition, BMSC-conditioned medium increased the length of neurites from spinal neurons compared to those of neurons cultured in the control medium or in the fibroblasts-conditioned medium. BMSCs expressed brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). The concentrations of BDNF and GDNF in BMSC-conditioned medium were 132±12 and 70±6 pg ml(-1), respectively. The addition of anti-BDNF and anti-GDNF antibodies to BMSC-conditioned medium partially blocked the neurite-promoting effect of the BMSC-conditioned medium. In conclusion, our results demonstrate that BMSCs promote neurite outgrowth in spinal neurons by secreting soluble factors. The neurite-promoting effect of BMSCs is partially mediated by BDNF and GDNF.     

Retinal ganglion cell survival and neurite regeneration in vitro after cell death period are dependent upon target derived trophic factor and retinal glial factor(s)

Retinal ganglion cells (RGCs) obtained from the rat retina after the cell death period were maintained in vitro by target derived retinal ganglion cell neurotrophic factor (RGNF). However, only 15% of surviving RGCs expressed neurites. On the other hand, when the culture was supplemented with retinal glia conditioned medium, nearly 80% of surviving RGCs expressed neurites which were longer than two cell diameter. Expression of neurites is not due to the presence of laminin in the glial conditioned medium as laminin coated substratum had no significant effect on the neurite growth from mature RGCs in the absence of glial factors.     

Basic fibroblast growth factor (bFGF) and rat C6 glioma cells: regulation of expression, absence of release, and response to exogenous bFGF

Basic fibroblast growth factor (bFGF) is a potent mitogen for several types of cells, including glial cells, which also seem to express bFGF. We have used rat C6 glioma cells as a model system to study the expression and release of bFGF by glioma cells, as well as the effects of exogenous bFGF on these cells. We have shown that C6 cells express 18 kD bFGF and several higher molecular weight immunoreactive forms. The expression of bFGF could be induced by a factor present in fetal calf serum. Subsequent to its initial appearance, bFGF is regulated in a cell density-dependent manner. Neither bFGF-like immunoreactive material, nor bFGF-like neurotrophic activity were found to be released by C6 cells. Exogenously applied bFGF changed C6 cell morphology similar to cyclic AMP induced alterations but had no significant influence on C6 cell proliferation and biochemical differentiation. From these results we conclude that bFGF in C6 cells might act as an endogenous (not autocrine) mitogen. Possible roles for bFGF in glial cells are discussed.     

神经递质、神经营养因子对海马干细胞分化影响的研究

目的 探讨脑源性神经营养因子（BDNF）、胶质源性神经营养因子（GDNF）、谷氨酸及γ-氨基丁酸（GABA）对大鼠海马干细胞分化的影响。方法对大鼠海马干细胞进行体外培养，培养液中加入不同剂量的BDNF、GDNF、谷氨酸及GABA．应用免疫荧光方法观察，并计算微管相关蛋白（MAP-2ab）及胶质纤维酸性蛋白（GFAP）阳性细胞率。结果在神经干细胞分化的第7、14天，与对照组比，BDNF、GDNF、谷氨酸及GABA剂量依赖性地增加表达MAP-2ab阳性细胞率（P〈0．05）；而对GFAP表达主要是抑制性的。且随分化时间及BDNF、GDNF、谷氨酸及GABA的浓度不同而不同。结论BDNF、GDNF、谷氨酸和GABA均可明显促进神经干细胞分化为神经元，且GDNF的作用大于BDNF。谷氨酸和GABA作用最佳浓度可能需随分化时间的不同而进行调整。     

Glial cell line-derived neurotrophic factor in the rat pituitary gland

The presence of glial cell line-derived neurotrophic factor (GDNF) is described within specific regions of the adult rat pituitary gland. Immune staining methods revealed a small number of GDNF-immunopositive cells in the anterior lobe, and in areas of the neural lobe, while no immunoreactive endocrine cells were observed in the intermediate lobe. In the neural lobe, immunofluorescence methods were also used to demonstrate that GDNF and glial fibrillary acidic protein (GFAP) are co-localized in the glial cells (pituicytes) of the neural lobe. GDNF was not co-localized with neurofilament (NF) in nerve fibers of the neural lobe, suggesting that it is not present in axonal fibers. Measurements of GDNF content in separated anterior and neurointermediate lobes were also performed, using an enzyme-linked immunoassay (ELISA). Values for GDNF were slightly higher in the neurointermediate lobe than those obtained for the anterior lobe. The presence of GDNF in areas of the pituitary is discussed in the context of its possible function to support and maintain hypothalamic innervation, as well as a potential autocrine factor within endocrine cells.