Time dependent amelioration against ischemic brain damage by glial cell line-derived neurotrophic factor after transient middle cerebral artery occlusion in rat

MSCs overexpressing GDNF restores brain structure and neurological function in rats with intracerebral hemorrhage

Mesenchymal stem cells (MSCs) have been applied in transplantation to treat intracerebral hemorrhage (ICH) but with limited efficacy. Accumulated evidence has shown that glial cell-derived neurotrophic factor (GDNF) plays a crucial part in neuronal protection and functional recovery of the brain after ICH; however, GDNF has difficulty crossing the blood-brain barrier, which limits its application. In this study, we investigated the influences of MSCs overexpressing GDNF (MSCs/GDNF) on the brain structure as well as gait of rats after ICH and explored the possible mechanisms. We found that cell transplantation could reverse the neurological dysfunction and brain damage caused by ICH to a certain extent, and MSCs/GDNF transplantation was superior to MSCs transplantation. Moreover, Transplantation of MSCs overexpressing GDNF effectively reduced the volume of bleeding foci and increased the level of glucose uptake in rats with ICH, which could be related to improving mitochondrial quality. Furthermore, GDNF produced by transplanted MSCs/GDNF further inhibited neuroinflammation, improved mitochondrial quality and function, promoted angiogenesis and the survival of neurons and oligodendrocytes, and enhanced synaptic plasticity in ICH rats when compared with simple MSC transplantation. Overall, our data indicate that GDNF overexpression heightens the curative effect of MSC implantation in treating rats following ICH.

Sigma-1 receptor activation alleviates blood-brain barrier disruption post cerebral ischemia stroke by stimulating the GDNF-GFRα1-RET pathway

Blood-brain barrier (BBB) disruption is one of the most important pathological manifestations of ischemic stroke. Reducing BBB collapse is effective in alleviating brain parenchymal injury and cognitive dysfunction. Our previous study reported that Sigma-1 receptor (Sig-1R) activation in cerebral microvascular endothelial cells (CMECs) ameliorated BBB impairment, but the detailed mechanism remains unclear. In this study, we investigated Sig-1R activation as a BBB integrity promoter via many post ischemic stroke pathways. Sig-1R activation in BBB-associated astrocytes can increase glia-derived neurotrophic factor (GDNF) secretion in bilateral common carotid artery occlusion (BCCAO) mice. Upregulated GDNF activates its receptors in CMECs to promote BBB integrity, and activated Sig-1R in CMECs facilitates this process. In vitro experiments have found that Sig-1R activation in CMECs promotes the interaction between the GDNF α1 receptor and transduction rearrangement gene, increasing PI3K-AKT-junction protein signaling pathway expression. Sig-1R activation could be an effective therapeutic method for preventing BBB damage in ischemic stroke and other neurological conditions.

Early Transplantation of Human Cranial Bone-derived Mesenchymal Stem Cells Enhances Functional Recovery in Ischemic Stroke Model Rats

We analyzed the cell characteristics, neuroprotective, and transplantation effects of human cranial bone-derived mesenchymal stem cells (hcMSCs) in ischemic stroke model rats compared with human iliac bone-derived mesenchymal stem cells (hiMSCs). The expressions of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) as neurotrophic factors were analyzed in both MSCs. hiMSCs or hcMSCs were intravenously administered into ischemic stroke model rats at 3 or 24 h after middle cerebral artery occlusion (MCAO) and neurological function was evaluated. The survival rate of neuroblastoma × glioma hybrid cells (NG108-15) after 3 or 24 h oxidative or inflammatory stress and the neuroprotective effects of hiMSCs or hcMSCs-conditioned medium (CM) on 3 or 24 h oxidative or inflammatory stress-exposed NG108-15 cells were analyzed. The expressions of BDNF and VEGF were higher in hcMSCs than in hiMSCs. hcMSCs transplantation at 3 h after MCAO resulted in significant functional recovery compared with that in the hiMSCs or control group. The survival rate of stress-exposed NG108-15 was lower after 24 h stress than after 3 h stress. The survival rates of NG108-15 cells cultured with hcMSCs-CM after 3 h oxidative or inflammatory stress were significantly higher than in the control group. Our results suggest that hcMSCs transplantation in the early stage of ischemic stroke suppresses the damage of residual nerve cells and leads to functional recovery through the strong expressions of neurotrophic factors. This is the first report demonstrating a functional recovery effect after ischemic stroke following hcMSCs transplantation.

Impact of Auditory Integration Therapy (AIT) on the Plasma Levels of Human Glial Cell Line-Derived Neurotrophic Factor (GDNF) in Autism Spectrum Disorder

Neurotrophic factors, including the glial cell line-derived neurotrophic factor (GDNF), are of importance for synaptic plasticity regulation, intended as the synapses' ability to strengthen or weaken their responses to differences in neuronal activity. Such plasticity is essential for sensory processing, which has been shown to be impaired in autism spectrum disorder (ASD). This study is the first to investigate the impact of auditory integration therapy (AIT) of sensory processing abnormalities in autism on plasma GDNF levels. Fifteen ASD children, aged between 5 and 12 years, were enrolled and underwent the present research study. AIT was performed throughout 10 days with a 30-min session twice a day. Before and after AIT, Childhood Autism Rating Scale (CARS), Social Responsiveness Scale (SRS), and Short Sensory Profile (SSP) scores were calculated, and plasma GDNF levels were assayed by an EIA test. A substantial decline in autistic behavior was observed after AIT in the scaling parameters used. Median plasma GDNF level was 52.142 pg/ml before AIT. This level greatly increased immediately after AIT to 242.05 pg/ml (P < 0.001). The levels were depressed to 154.00 pg/ml and 125.594 pg/ml 1 month and 3 months later, respectively, but they were still significantly higher compared with the levels before the treatment (P = 0.001, P = 0.01, respectively). There was an improvement in the measures of autism severity as an effect of AIT which induced the up-regulation of GDNF in plasma. Further research, on a large scale, is needed to evaluate if the cognitive improvement of ASD children after AIT is related or not connected to the up-regulation of GDNF.

Promoting neuroregeneration after perinatal arterial ischemic stroke: neurotrophic factors and mesenchymal stem cells

Newborns suffering from perinatal arterial ischemic stroke (PAIS) are at risk of neurodevelopmental problems. Current treatment options for PAIS are limited and mainly focus on supportive care, as presentation of PAIS is beyond the time window of current treatment strategies. Therefore, recent focus has shifted to interventions that stimulate regeneration of damaged brain tissue. From animal models, it is known that the brain increases its neurogenic capability after ischemic injury, by promoting neural cell proliferation and differentiation. However, neurogenesis is not maintained at the long term, which consequently impedes full repair leading to adverse consequences later in life. Boosting neuroregeneration of the newborn brain using treatment with neurotrophic factors and/or mesenchymal stem cells (MSCs) may be promising novel therapeutic strategies to improve neurological prospects and quality of life of infants with PAIS. This review focuses on effectiveness of neurotrophic growth factors, including erythropoietin, brain-derived neurotrophic factor, vascular endothelial growth factor, glial-derived neurotrophic factor, and MSC therapy, in both experimental neonatal stroke studies and first clinical trials for neonatal ischemic brain injury.

The protein and mRNA expression levels of glial cell line-derived neurotrophic factor in post stroke depression and major depressive disorder

Previous studies have indicated that the level of glial cell line-derived neurotrophic factor (GDNF) may be correlated with stroke and depression. Here, we investigated whether GDNF can be a discriminant indicator for post stroke depression (PSD). 159 participants were divided into four groups: PSD, stroke without depression (Non-PSD), major depressive disorder (MDD) and normal control (NC) group, and the protein and mRNA expression levels of GDNF in serum were measured. The results showed that only MDD group had statistical difference in protein and mRNA levels compared with the other three groups (Bonferroni test, P < 0.05). The results of receiver operating curve (ROC) analysis supported GDNF as general distinguishing models in PSD and MDD groups with the area under the curve (AUC) at 0.797 (P < 0.001) and 0.831 (P < 0.001) respectively. In addition, the Spearman analysis demonstrated that the GDNF protein level negatively correlated with the value of Hamilton depression rating scale (HAMD) in PSD patients (correlation coefficient = -0.328, P = 0.047). Together, these findings suggest the protein and mRNA expression levels of GDNF decreased in patients with depression. GDNF may serve as a potential biomarker for differential diagnosis of PSD from MDD patients.

Transplantation of Fetal Kidney Cells: Neuroprotection and Neuroregeneration

Various trophic factors in the transforming growth factor-β (TGF-β) superfamily have been reported to have neuroprotective and neuroregenerative effects. Intracerebral administration of glial cell line-derived neurotrophic factor (GDNF) or bone morphogenetic proteins (BMPs), both members of the TGF-β family, reduce ischemia- or 6-hydroxydopamine (6-OHDA)-induced injury in adult rat brain. Because BMPs and GDNF are highly expressed in fetal kidney cells, transplantation of fetal kidney tissue could serve as a cellular reservoir for such molecules and protect against neuronal injury induced by ischemia, neurotoxins, or reactive oxygen species. In this review, we discuss preclinical evidence for the efficacy of fetal kidney cell transplantation in neuroprotection and regeneration models.

Neuroprotective effects of GDNF-expressing human amniotic fluid cells

Brain injury continues to be one of the leading causes of disability worldwide. Despite decades of research, there is currently no pharmacologically effective treatment for preventing neuronal loss and repairing the brain. As a result, novel therapeutic approaches, such as cell-based therapies, are being actively pursued to repair tissue damage and restore neurological function after injury. In this study, we examined the neuroprotective potential of amniotic fluid (AF) single cell clones, engineered to secrete glial cell derived neurotrophic factor (AF-GDNF), both in vitro and in a surgically induced model of brain injury. Our results show that pre-treatment with GDNF significantly increases cell survival in cultures of AF cells or cortical neurons exposed to hydrogen peroxide. Since improving the efficacy of cell transplantation depends on enhanced graft cell survival, we investigated whether AF-GDNF cells seeded on polyglycolic acid (PGA) scaffolds could enhance graft survival following implantation into the lesion cavity. Encouragingly, the AF-GDNF cells survived longer than control AF cells in serum-free conditions and continued to secrete GDNF both in vitro and following implantation into the injured motor cortex. AF-GDNF implantation in the acute period following injury was sufficient to activate the MAPK/ERK signaling pathway in host neural cells in the peri-lesion area, potentially boosting endogenous neuroprotective pathways. These results were complemented with promising trends in beam walk tasks in AF-GDNF/PGA animals during the 7 day timeframe. Further investigation is required to determine whether significant behavioural improvement can be achieved at a longer timeframe.

Transfection of the glial cell line-derived neurotrophic factor gene promotes neuronal differentiation

Glial cell line-derived neurotrophic factor recombinant adenovirus vector-transfected bone marrow mesenchymal stem cells were induced to differentiate into neuron-like cells using inductive medium containing retinoic acid and epidermal growth factor. Cell viability, microtubule-associated protein 2-positive cell ratio, and the expression levels of glial cell line-derived neurotrophic factor, nerve growth factor and growth-associated protein-43 protein in the supernatant were significantly higher in glial cell line-derived neurotrophic factor/bone marrow mesenchymal stem cells compared with empty virus plasmid-transfected bone marrow mesenchymal stem cells. Furthermore, microtubule-associated protein 2, glial cell line-derived neurotrophic factor, nerve growth factor and growth-associated protein-43 mRNA levels in cell pellets were statistically higher in glial cell line-derived neurotrophic factor/bone marrow mesenchymal stem cells compared with empty virus plasmid-transfected bone marrow mesenchymal stem cells. These results suggest that glial cell line-derived neurotrophic factor/bone marrow mesenchymal stem cells have a higher rate of induction into neuron-like cells, and this enhanced differentiation into neuron-like cells may be associated with up-regulated expression of glial cell line-derived neurotrophic factor, nerve growth factor and growth-associated protein-43.

Tissue regeneration in stroke: cellular and trophic mechanisms

Stroke is a leading cause of morbidity in the developed world and results in chronic disability in many cases. The literature related to the critical factors that regulate tissue self-regeneration in stroke is still limited, which restricts effective therapy. However, optimism in this area has been provided by recent research. The mechanisms involved in tissue regeneration and the mode of the participation of stem/progenitor cells and soluble protein neurotrophic factors in this process may yield a more complete understanding of the nature of stroke. This review summarizes the current understanding of both cellular and humoral issues with a particular emphasis on how these issues contribute to tissue regeneration in stroke.

Oral Administration of Royal Jelly Facilitates mRNA Expression of Glial Cell Line-Derived Neurotrophic Factor and Neurofilament H in the Hippocampus of the Adult Mouse Brain

Royal jelly (RJ) is known to have a variety of biological activities toward various types of cells and tissues of animal models, but nothing is known about its effect on brain functions. Hence, we examined the effect of oral administration of RJ on the mRNA expression of various neurotrophic factors, their receptors, and neural cell markers in the mouse brain. Our results revealed that RJ selectively facilitates the mRNA expression of glial cell line-derived neurotrophic factor (GDNF), a potent neurotrophic factor acting in the brain, and neurofilament H, a specific marker predominantly found in neuronal axons, in the adult mouse hippocampus. These observations suggest that RJ shows neurotrophic effects on the mature brain via stimulation of GDNF production, and that enhanced expression of neurofilament H mRNA is involved in events subsequently caused by GDNF. RJ may play neurotrophic and/or neuroprotective roles in the adult brain through GDNF.

Effects of GDNF-loaded injectable gelatin-based hydrogels on endogenous neural progenitor cell migration

Brain repair following disease and injury is very limited due to difficulties in recruiting and mobilizing stem cells towards the lesion. More importantly, there is a lack of structural and trophic support to maintain viability of the limited stem/progenitor cells present. This study investigates the effectiveness of an injectable gelatin-based hydrogel in attracting neural progenitor cells (NPCs) from the subventricular zone (SVZ) towards the implant. Glial cell-line-derived neurotrophic factor (GDNF) encapsulated within the hydrogel and porosity within the hydrogel prevents glial scar formation. By directly targeting the hydrogel implant towards the SVZ, neuroblasts can actively migrate towards and along the implant tract. Significantly more doublecortin (DCX)-positive neuroblasts surround implants at 7 d post-implantation (dpi) compared with lesion alone controls, an effect that is enhanced when GDNF is incorporated into the hydrogels. Neuroblasts are not observed at the implant boundary at 21 dpi, indicating that neuroblast migration has halted, and neuroblasts have either matured or have not survived. The development of an injectable gelatin-based hydrogel has significant implications for the treatment of some neurodegenerative diseases and brain injuries. The ability of GDNF and porosity to effectively prevent glial scar formation will allow better integration and interaction between the implant and surrounding neural tissue.

Combination stroke therapy in the mouse with blood-brain barrier penetrating IgG-GDNF and IgG-TNF decoy receptor fusion proteins

Stroke therapy may be optimized by combination therapy with both a neuroprotective neurotrophin and an anti-inflammatory agent. In the present work, the model neurotrophin is glial cell line-derived neurotrophic factor (GDNF), and the model anti-inflammatory agent is the type II tumor necrosis factor receptor (TNFR) decoy receptor. Both the GDNF and the TNFR are large molecules that do not cross the blood-brain barrier (BBB), which is intact in the early hours after stroke when neural rescue is still possible. The GDNF and the TNFR decoy receptor were re-engineered for BBB transport as IgG fusion proteins, wherein the GDNF or the TNFR are fused to the heavy chain of a chimeric monoclonal antibody (MAb) against the mouse transferrin receptor (TfR), and these fusion proteins are designated cTfRMAb-GDNF and cTfRMAb-TNFR, respectively. Mice were treated intravenously with (a) saline, (b) GDNF alone, (c) the cTfRMAb-GDNF fusion protein alone, or (d) the combined cTfRMAb-GDNF and cTfRMAb-TNFR fusion proteins, following a 1-h reversible middle cerebral artery occlusion (MCAO). The cTfRMAb-GDNF fusion protein alone caused a significant 25% and 30% reduction in hemispheric and cortical stroke volumes. Combined treatment with the cTfRMAb-GDNF and cTfRMAb-TNFR fusion proteins caused a significant 54%, 69% and 30% reduction in hemispheric, cortical and subcortical stroke volumes. Conversely, intravenous GDNF had no therapeutic effect. In conclusion, combination treatment with BBB penetrating IgG-GDNF and IgG-TNFR fusion proteins enhances the therapeutic effect of single treatment with the IgG-GDNF fusion protein following delayed intravenous administration in acute stroke.

Neuroprotection by GDNF in the ischemic brain

The glial cell line-derived neurotrophic factor (GDNF) was first identified as a survival factor for midbrain dopaminergic neurons, but additional studies provided evidences for a role as a trophic factor for other neurons of the central and peripheral nervous systems. GDNF regulates cellular activity through interaction with glycosyl-phosphatidylinositol-anchored cell surface receptors, GDNF family receptor-α1, which might signal through the transmembrane Ret tyrosine receptors or the neural cell adhesion molecule, to promote cell survival, neurite outgrowth, and synaptogenesis. The neuroprotective effect of exogenous GDNF has been shown in different experimental models of focal and global brain ischemia, by local administration of the trophic factor, using viral vectors carrying the GDNF gene and by transplantation of GDNF-expressing cells. These different strategies and the mechanisms contributing to neuroprotection by GDNF are discussed in this review. Importantly, neuroprotection by GDNF was observed even when administered after the ischemic injury.

Growth factors and neuropathic pain

A treatment for neuropathic pain is an important unmet medical need because this pain often is refractory to many medical interventions. An important element in the development of neuropathic pain is a dysfunction in the activity of peripheral nerves. Because neurotrophic factors affect nerve development and maintenance, modulating the activity of these factors can alter neuronal pathophysiology and produce a disease-modifying effect. Blocking the activity of nerve growth factor or enhancing the activity of either glial-derived neurotrophic factor or artemin has shown potential for normalizing neuronal activity and attenuating signs of neuropathic pain in animal models and clinical studies. This article discusses the role of these factors in neuropathic pain and the implications for the development of novel therapeutics.

Neuroprotective effects of bone marrow stem cells overexpressing glial cell line-derived neurotrophic factor on rats with intracerebral hemorrhage and neurons exposed to hypoxia/reoxygenation

BACKGROUND

Intracerebral hemorrhage (ICH) represents at least 15% of all strokes in the Western population and a considerably higher proportion at 50% to 60% in the Oriental population.

OBJECTIVE

To investigate whether administration of bone marrow stem cells (BMSCs) overexpressing glial cell line-derived neurotrophic factor (GDNF) provides more efficient neuroprotection for rats with ICH and neurons exposed to hypoxia/reoxygenation.

METHODS

Primary rat BMSCs were transfected with rat GDNF gene using virus vector (GDNF/BMSCs) and blank virus plasmid (BVP/BMSCs). Primary rat cortical neurons of rats were exposed to hypoxia and then reoxygenated with GDNF/BMSCs (GDNF/BMSCs group) or BVP/BMSCs (BMSCs group) treatment for 12 hours and 1, 2, 3, and 5 days. Hoechst 33258 staining was used to evaluate apoptosis. GDNF/BMSCs, BVP/BMSCs, and saline (GDNF/BMSCs, BMSCs, and control groups) were injected into the right striatum 3 days after rat ICH induced by injecting collagenase. Modified neurological severity scores and hematoxylin and eosin staining were performed to evaluate neurological function and lesion volume at 1 and 2 weeks after transplantation. Immunostaining was used to observe differentiation of grafted cells (neurofilament-200 for neurons, glial fibrillary acidic protein for astrocytes). The GDNF level and apoptosis were evaluated by Western blotting and terminal deoxynucleotidyl transferase dUTP nick-end labeling, respectively.

RESULTS

The GDNF/BMSCs group had significantly lowered apoptosis compared with the BMSCs group at the given time. The GDNF/BMSCs group had significantly improved functional deficits and reduced lesion volume compared with the BMSCs group. Stable GDNF expression in the GDNF/BMSCs group was detected at the given time in the host brain. The neurofilament-positive grafted cells in the GDNF/BMSCs group were more numerous than in the BMSCs group. The GDNF/BMSCs group had significantly decreased apoptotic cells compared with the BMSCs group.

CONCLUSION

These results suggest that GDNF/BMSCs provide better neuroprotection for rats with ICH and neurons exposed to hypoxia/reoxygenation.

Premarin improves outcomes of spinal cord injury in male rats through stimulating both angiogenesis and neurogenesis

OBJECTIVE

To ascertain whether Premarin improves spinal cord injury outcomes in male rats by stimulating both angiogenesis and neurogenesis.

DESIGN

Chi Mei Medical Center research laboratory.

SUBJECTS

Male Sprague-Dawley rats 240-258 g.

INTERVENTIONS

Anesthetized rats, after the onset of spinal cord injury, were divided into two groups and given the vehicle solution (1 mL/kg of body weight) or Premarin (1 mg/kg of body weight). Saline or Premarin solutions were administered intravenously and immediately after spinal cord injury.

MEASUREMENTS AND MAIN RESULTS

Premarin (an estrogen sulfate) causes attenuation of spinal cord injury-induced spinal cord infarction and hind limb locomotor dysfunction. Spinal cord injury-induced apoptosis as well as activated inflammation was also significantly Premarin-reduced. In injured spinal cord, angiogenesis, neurogenesis, and production of an antiinflammatory cytokine were all Premarin therapy-promoted.

CONCLUSIONS

Our results indicate that Premarin therapy may protect against spinal cord apoptosis after spinal cord injury through mechanisms stimulating both angiogenesis and neurogenesis in male rats.

Astrocytic endogenous glial cell derived neurotrophic factor production is enhanced by bone marrow stromal cell transplantation in the ischemic boundary zone after stroke in adult rats

Bone marrow stromal cells (BMSCs) facilitate functional recovery in rats after focal ischemic attack. Growing evidence suggests that the secretion of various bioactive factors underlies BMSCs' beneficial effects. This study investigates the expression of glial cell derived neurotrophic factor (GDNF) in the ischemic hemisphere with or without BMSC administration. Adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by an injection of 3 x 10(6) BMSCs (n = 11) or phosphate-buffered saline (n = 10) into the tail vein 24 h later. Animals were sacrificed seven days later. Single and double immunohistochemical staining was performed to measure GDNF, Ki67, doublecortin, and glial fibrillary acidic protein expression as well as the number of apoptotic cells along the ischemic boundary zone (IBZ) and/or in the subventricular zone (SVZ). BMSC treatment significantly increased GDNF expression and decreased the number of apoptotic cells in the IBZ (P < 0.05). GDNF expression was colocalized with GFAP. Meanwhile, BMSCs increased the number of Ki-67 positive cells and the density of DCX positive migrating neuroblasts (P < 0.05). GDNF expression was significantly increased in single astrocytes collected from animals treated with BMSCs, and in astrocytes cocultured with BMSCs after OGD (P < 0.05). Our data suggest that BMSCs increase GDNF levels in the ischemic hemisphere; the major source of GDNF protein is reactive astrocytes. We propose that the increase of GDNF in response to BMSC administration creates a hospitable environment for local cellular repair as well as for migrating neuroblasts from the SVZ, and thus contributes to the functional improvement.

Delayed administration of glial cell line-derived neurotrophic factor (GDNF) protects retinal ganglion cells in a pig model of acute retinal ischemia

This study investigates whether intravitreal administration of glial cell line-derived neurotrophic factor (GDNF) enhances survival of NeuN positive retinal cells in a porcine model of retinal ischemia. 16 pigs were subjected to an ischemic insult where intraocular pressure was maintained at 5 mmHg below mean arterial blood pressure for 2 h. The mean IOP during the ischemic insult was 79.5 mmHg (s.e.m. 2.1 mmHg, n = 15). Three days after the insult the pigs received an intravitreal injection of GDNF microspheres or blank microspheres. The pigs were evaluated by way of multifocal electroretinography (mfERG), quantification of NeuN positive cells and evaluation of the degree of retinal perivasculitis and inflammation 6 weeks after the insult. In the post-injection eyes (days 14, 28 and 42), the ratios of the iN1 and the iP2 amplitudes were 0.10 (95% CI: 0.05-0.15) and 0.09 (95% CI: 0.04-0.16) in eyes treated with blank microspheres, and 0.24 (95% CI: 0.18-0.32) and 0.23 (95% CI: 0.15-0.33) in eyes treated with GDNF microspheres. These differences were statistically significant (P < 0.05). The number of NeuN positive cells in the area of the visual streak area was significantly higher in eyes injected with GDNF microspheres compared to eyes injected with blank microspheres. In eyes injected with GDNF microspheres the ganglion cell count was 9.5/field (s.e.m.: 2.1, n = 8), in eyes injected with blank microspheres it was 3.5/field (s.e.m.: 1.2, n = 7). This difference was statistically significant (P < 0.05). There was also a significant difference (P < 0.01) in the degree of perivasculiitis between GDNF treated eyes (median perivasculitis score 1.5) and blank treated eyes (median perivasculitis score 3.0). In conclusion, injection of GDNF microspheres 3 days after an ischemic insult results in functional and morphological rescue of NeuN positive cells in a porcine model of acute ocular ischemia.

Neuroprotective effect of grafting GDNF gene-modified neural stem cells on cerebral ischemia in rats

Previous studies indicated the beneficial effects of glial cell line-derived neurotrophic factor (GDNF) and transplanted neural stem cells (NSCs) on stroke. Here, we explored whether transplantation of neural stem cells (NSCs) modified by GDNF gene provides a better therapeutic effect than native NSCs after stroke. Primary rat NSCs were transfected with GDNF plasmid (GDNF/NSCs, labeled by green fluorescent protein from AdEasy-1, GFP). Adult rats were subjected to two-hour middle cerebral artery occlusion and reperfusion, followed by infusion of NSCs (labeled with5-bromo-2'-deoxyuridine before infusion, BrdU), GDNF/NSCs and saline at 3 days after reperfusion (NSCs group, GDNF/NSCs group, control group), respectively. All rats were sacrificed at 1, 2, 3, 5, and 7 weeks after reperfusion. Modified Neurological Severity Scores (mNSS) test and H and E staining were respectively performed to evaluate neurological function and lesion volume. Immunohistochemistry was used to identify implanted cells and observe the expressions of Synaptophysin (Syp) and postsynaptic density-95 (PSD-95) and caspase-3. TdT-mediated dUTP-biotin nick-end labeling (TUNEL) was employed to observe apoptotic cells. Western blotting was used to detect brain-derived neurotrophic factor (BDNF) and NT-3 protein expression. Significant recovery of mNSS was found in GDNF/NSCs rats at 2 and 3 weeks after reperfusion compared with NSCs rats. Lesion volume in the NSCs and GDNF/NSCs groups was reduced significantly compared with control group. The number of NSCs in the GDNF/NSCs group was significantly increased in comparison with NSCs group. Moreover, Syp-immunoreactive product at 2 and 3 weeks after reperfusion and PSD-95 immunoreactive product in the GDNF/NSCs group were significantly increased compared with NSCs group. In contrast, caspase-3 positive cells and TUNEL-positive cells in the GDNF/NSCs group were significantly decreased compared with NSCs group. Significant increase of BDNF protein in the GDNF/NSCs and NSCs groups was observed compared to the control group at different time points of reperfusion, and GDNF/NSCs grafting significantly increased BDNF protein expression compared to NSCs grafting. In addition, significant increase of NT-3 protein in GDNF/NSCs and NSCs groups was detected only at 1 week of reperfusion compared to control group. The results demonstrate that grafting NSCs modified by GDNF gene provides better neuroprotection for stroke than NSCs grafting alone.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

Infusion of human umbilical cord blood cells ameliorates hind limb dysfunction in experimental spinal cord injury through anti-inflammatory, vasculogenic and neurotrophic mechanisms

BACKGROUND

Human umbilical cord blood cells (HUCBCs) were used to investigate the mechanisms underlying the beneficial effects of cord blood cells in spinal cord injury (SCI).

METHODS

Rats were divided into three groups: (1) sham operation (laminectomy only); (2) Laminectomy+SCI+human adult peripheral blood mononucleocytes (PBMCs) (5 x 10(6)/0.3 mL); and (3) Laminectomy+SCi+HUCBCs (5 x 10(6)/0.3 mL). SCI was induced by compressing the spinal cord for 1 minute with an aneurysm clip calibrated to 55 g closing pressure. HUCBCs were infused immediately after SCI via the tail vein. Behavioral function tests measuring the maximal angle at which an animal could hold onto the inclined plane were conducted on days 1, 4 and 7 after SCI. Serum levels of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10, were assayed. Furthermore, to determine if glial cell line-derived neurotrophic factor (GDNF) or vascular endothelial growth factor (VEGF) could be detected in the spinal cord injured area after systemic HUCBC infusion, analysis of these two molecules was conducted by immunofluorescence.

RESULTS

Systemic HUCBC infusion significantly attenuated SCI-induced hind limb dysfunction. The serum IL-10 levels were increased, but TNF-alpha levels were decreased after HUCBC infusion. Both VEGF and GDNF could be detected in the injured spinal cord after transplantation of HUCBC, but not PBMC, cells.

CONCLUSION

Our results demonstrate that HUCBC therapy may be beneficial for the recovery of SCI-induced hind limb dysfunction by increasing serum levels of IL-10, VEGF and GDNF in SCI rats.

Human umbilical cord blood-derived CD34+ cells can be used as a prophylactic agent for experimental heatstroke

We attempted to assess the prophylactic effect of human umbilical cord blood-derived CD34(+) cells in experimental heatstroke. Anesthetized rats, 1 day before heat stress, were divided into 2 major groups and given CD34(-) cells (defined by 1 x 10(6) human cord blood lymphocytes and monocytes that contained <0.2% CD34(+) cells) or CD34(+) cells (defined by 1 x 10(6) human cord blood lymphocytes and monocytes that contained >95% CD34(+) cells). They were exposed to ambient temperature of 43 degrees C for 70 min to induce heatstroke. When the CD34(-) cells-treated or untreated rats underwent heat stress, their survival time values were found to be 20-24 min. Pretreatment with CD34(+) cells significantly increased survival time (123-351 min). As compared with normothermic controls, all CD34(-) cells-treated heatstroke animals displayed hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. However, these heatstroke reactions all were significantly suppressed by CD34(+) cells pretreatment. In addition, the levels of interleukin-10 in plasma and glial cell line-derived neurotrophic factors in brain were all significantly increased after CD34(+) cell administration during heatstroke. Our data indicate that human umbilical cord-derived CD34(+) cells can be used as a prophylactic agent for experimental heatstroke.

HUMAN UMBILICAL CORD BLOOD-DERIVED CD34+ CELLS MAY ATTENUATE SPINAL CORD INJURY BY STIMULATING VASCULAR ENDOTHELIAL AND NEUROTROPHIC FACTORS

Human umbilical cord blood-derived CD34(+) cells were used to elucidate the mechanisms underlying the beneficial effects exerted by cord blood cells in spinal cord injury (SCI). Rats were divided into four groups: (1) sham operation (laminectomy only); (2) laminectomy + SCI + CD34(-) cells (5 x 10(5) human cord blood lymphocytes and monocytes that contained <0.2% CD34(+) cells); (3) laminectomy + SCI + CD34(+) cells (5 x 10(5) human cord blood lymphocytes and monocytes that contained approximately 95% CD34(+) cells); and (4) laminectomy + SCI + saline (0.3 mL). Spinal cord injury was induced by compressing the spinal cord for 1 min with an aneurysm clip calibrated to a closing pressure of 55 g. CD34 cells or saline was administered immediately after SCI via the tail vein. Behavioral tests of motor function measured by maximal angle an animal could hold to the inclined plane were conducted at days 1 to 7 after SCI. The triphenyltetrazolium chloride staining and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling assay were also conducted after SCI to evaluate spinal cord infarction and apoptosis, respectively. To elucidate whether glial cell line-derived neurotrophic factor (GDNF) or vascular endothelial growth factor (VEGF) can be secreted in spinal cord-injured area by the i.v. transplanted CD34(+) cells, analysis of spinal cord homogenate supernatants by specific enzyme-linked immunosorbent assay for GDNF or immunofluorescence for VEGF was conducted. It was found that systemic administration of CD34(+), but not CD34(-), cells significantly attenuated the SCI-induced hind limb dysfunction and spinal cord infarction and apoptosis. Both GDNF and VEGF could be detected in the injured spinal cord after transplantation of CD34(+), but not CD34(-), cells. The results indicate that CD34(+) cell therapy may be beneficial in reversing the SCI-induced spinal cord infarction and apoptosis and hindlimb dysfunction by stimulating the production of both VEGF and GDNF in a spinal cord compression model.

Intravenous administration of glial cell line-derived neurotrophic factor gene-modified human mesenchymal stem cells protects against injury in a cerebral ischemia model in the adult rat

Intravenous administration of human mesenchymal stem cells (hMSCs) prepared from adult bone marrow has been reported to ameliorate functional deficits after cerebral artery occlusion in rats. Several hypotheses to account for these therapeutic effects have been suggested, and current thinking is that neuroprotection rather than neurogenesis is responsible. To enhance the therapeutic benefits of hMSCs potentially, we transfected hMSCs with the glial cell line-derived neurotrophic factor (GDNF) gene using a fiber-mutant F/RGD adenovirus vector and investigated whether GDNF gene-modified hMSCs (GDNF-hMSCs) could contribute to functional recovery in a rat permanent middle cerebral artery occlusion (MCAO) model. We induced MCAO by using intraluminal vascular occlusion, and GDNF-hMSCs were intravenously infused into the rats 3 hr later. MRI and behavioral analyses revealed that rats receiving GDNF-hMSCs or hMSCs exhibited increased recovery from ischemia compared with the control group, but the effect was greater in the GDNF-hMSC group. Thus, these results suggest that intravenous administration of hMSCs transfected with the GDNF gene using a fiber-mutant adenovirus vector may be useful in the cerebral ischemia and may represent a new strategy for the treatment of stroke.

Progress in the identification of stroke-related genes: emerging new possibilities to develop concepts in stroke therapy

Stroke is a very complex disease influenced by many risk factors: genetic, environmental and comorbidities, such as hypertension, diabetes mellitus, obesity and having had a previous stroke. Neuroprotective therapies that have been found to be successful in laboratory animals have failed to produce the same benefits in clinical trials. Currently, a re-analysis of the clinical trial failures is underway and new therapeutic approaches using the growing knowledge from neurogenesis and neuroinflammation studies, combined with the information from gene expression studies, are taking place. This review focuses on possible ways to identify therapeutic targets using the new discoveries in neuroinflammation and intrinsic regenerative mechanisms of the brain. Molecular events associated with ischaemia trigger an environment for inflammation. Within the ischaemic region and its penumbra, a battery of chemokines and cytokines are released, which have both detrimental and beneficial effects, depending on the specific timepoint after injury and the current activation status of microglia/macrophages. Preventive therapies and treatments for stroke may be established by identifying the genes that are responsible for the induction of those phenotypic changes of microglia/macrophages that switch them to become players in tissue repair and regeneration processes. To aid in the establishment of new target sources for novel therapeutic agents, animal stroke models should closely mimic stroke in humans. To do so, these models should take into account the various risk factors for stroke. For example, hypertensive animals have a more vulnerable blood-brain barrier that in turn may trigger a greater degree of damage after stroke. Furthermore, in aged animals an accelerated astrocytic and microglial reaction has been observed and the regenerative capacity of aged brains is not as high as young brains. Improvements in animal models may also help to ensure better success rates of potential therapies in clinical studies. Inflammation in the brain is a double-edged sword--characterised by the deleterious effect of nerve cell damage and nerve cell death, as well as the beneficial influence on regeneration. The major challenge to develop successful stroke therapies is to broaden the knowledge regarding the underlying pathologic processes and the intrinsic mechanisms of the brain to drive regenerative and plasticity-related changes. On this basis, new concepts can be created leading to better stroke therapy.

The neuroprotective effect of glial cell line-derived neurotrophic factor in fibrin glue against chronic focal cerebral ischemia in conscious rats

Glial cell line-derived neurotrophic factor (GDNF) is a transforming growth factor-beta which has shown beneficial effects in rats after acute focal cerebral ischemia (FCI). To study the effects of GDNF on chronic FCI injury in conscious rats, we used fibrin glue (GDNF-fibrin glue) and fibrin glue free (GDNF-only)-GDNF topically applied to the ischemic brain after right middle cerebral artery (MCA) ligation. Infarct brain volume and functional motor deficits were measured before and after FCI injury. After FCI injury induced by right MCA ligation, rats were randomly assigned to one of four treatment groups: (a) sham, (b) control, (c) topically applied GDNF (1 mug)-only, and (d) topically applied GDNF (1 mug)-fibrin glue. The degree of ischemic brain injury was estimated by infarct volume of right MCA territory at 4 weeks after occlusion. The functional motor deficits were quantified with rotarod test and grasping power test once a week. Topically applied GDNF-fibrin glue at infarct brain tissue after 4 weeks FCI injury significantly reduced the total infarct volume by 44.3% and 36%, respectively, compared to that of control group and GDNF-only group. The mean latencies for rats to stay on the rotarod were 55.0%, 50.3%, and 92.2% (P < 0.05 vs. control group and GDNF-only group) of baseline, respectively, in the control, GDNF-only, and GDNF-fibrin glue groups at the end of the 1st week after FCI injury but 75.3%, 67.3%, and 106.6% (P < 0.05 vs. control group and GDNF-only group) of baseline at the end of the 4th week after FCI injury. The mean values of grasping power were 78.7%, 71.7%, and 101.2% (P < 0.05 vs. control group and GDNF-only group) of baseline, respectively, in the control, GDNF-only, and GDNF-fibrin glue groups at the end of 1st week after FCI injury but 89.6%, 97.6%, and 120.7% (P < 0.05 vs. control group) of baseline at the end of 4th week after FCI injury. These results indicate that GDNF-fibrin glue not only reduced the total infarct volume after FCI injury but can also improve motor deficits after FCI injury. We concluded GDNF-fibrin glue could facilitate delivery of GDNF to the damaged brain tissue with subsequent reduction of ischemic brain injury accompanied by enhancing functional recovery in rats with chronic FCI injury.

Mesenchymal stem cells that produce neurotrophic factors reduce ischemic damage in the rat middle cerebral artery occlusion model

Mesenchymal stem cells (MSC) were reported to ameliorate functional deficits after stroke in rats, with some of this improvement possibly resulting from the action of cytokines secreted by these cells. To enhance such cytokine effects, we previously transfected the telomerized human MSC with the BDNF gene using a fiber-mutant adenovirus vector and reported that such treatment contributed to improved ischemic recovery in a rat transient middle cerebral artery occlusion (MCAO) model. In the present study, we investigated whether other cytokines in addition to BDNF, i.e., GDNF, CNTF, or NT3, might have a similar or greater effect in this model. Rats that received MSC-BDNF (P < 0.05) or MSC-GDNF (P < 0.05) showed significantly more functional recovery as demonstrated by improved behavioral test results and reduced ischemic damage on MRI than did control rats 7 and 14 days following MCAO. On the other hand, rats that received MSC-CNTF or MSC-NT3 showed neither functional recovery nor ischemic damage reduction compared to control rats. Thus, MSC transfected with the BDNF or GDNF gene resulted in improved function and reduced ischemic damage in a rat model of MCAO. These data suggest that gene-modified cell therapy may be a useful approach for the treatment of stroke.

Anti-monocyte chemoattractant protein-1 gene therapy protects against focal brain ischemia in hypertensive rats

Monocyte chemoattractant protein-1 (MCP-1) is expressed in the ischemic cortex after focal brain ischemia and appears to exacerbate ischemic damage. The authors examined the effect of gene transfer of dominant negative MCP-1, called 7ND, 90 minutes after induction of focal brain ischemia in hypertensive rats. Adenoviral vectors encoding mutant MCP-1 (Ad7ND; n = 11), or Escherichia coli beta-galactosidase (AdlacZ; n = 17) as control were injected into the lateral ventricle of male spontaneously hypertensive rats. Both AdlacZ (n = 12) and Ad7ND (n = 6) administration provided transgene expression as early as 6 hours after injection and the expression further increased on day 1, followed by a sustained detection on day 5. Five days after ischemia, infarct volume (75 +/- 13 mm, n = 5, mean +/- SD) significantly reduced to 72% of control (104 +/- 22 mm3, n = 5, P < 0.05) by 7ND gene transfer. Numbers of leukocytes in the vessels (48.3 +/- 32.9/cm2) and macrophage/monocyte infiltration (475.2 +/- 125.5/mm2) of the infarct area in the Ad7ND group were significantly less than those measured in the AdlacZ group (143.8 +/- 72.1/cm2 and 671.8 +/- 125.5/mm2, P < 0.05, respectively). In summary, the postischemic gene transfer of dominant negative MCP-1 attenuated the infarct volume and infiltration of inflammatory cells, suggesting potential usefulness of the anti-MCP-1 gene therapy.

Stroke and TGF-beta proteins: glial cell line-derived neurotrophic factor and bone morphogenetic protein

Recent studies have indicated that proteins in the transforming growth factor-beta superfamily alter damage induced by various neuronal injuries. Of these proteins, glial cell line-derived neurotrophic factor (GDNF) and bone morphogenetic protein-7 (BMP-7) have unique protective and regenerative effects in stroke animals. Delivery of GDNF or BMP-7 to brain tissue reduced cerebral infarction and improved motor functions in stroke animals. Pretreatment with these factors reduced caspase-3 activity and DNA fragmentation in the ischemic brain region, suggesting that antiapoptotic effects are involved. Beside the protective effects, BMP-7 given after stroke improves locomotor function. These regenerative effects of BMP-7 may involve the enhancement of dendritic growth and remodeling. In this review, we illustrate the neuroprotective and neuroregenerative properties of GDNF and BMP-7 and emphasize their therapeutic potential for stroke.

Neuregulin-1 is neuroprotective and attenuates inflammatory responses induced by ischemic stroke

Recent work from our laboratory demonstrated that the expression neuregulin-1 in neurons was induced in the ischemic penumbra by focal stroke in the rat. Here, we show that a single intravascular injection of neuregulin-1beta (approximately 2.5 ng/kg) reduced cortical infarct volume by >98% when given immediately before middle cereral artery occlusion. Subcortical infarct volume was reduced by approximately 40%. Analysis of DNA fragmentation in brain tissues indicated that neuregulin-1 blocked apoptosis in cortical neurons in the penumbra. Neuregulin-1 prevented macrophage/microglial infiltration and astrocytic activation following focal ischemia. The neuroprotective effect of neuregulin-1 was also associated with a suppression of interleukin-1beta mRNA levels. These data suggest that neuregulin-1 protects neurons from delayed, ischemia-induced apoptotic cell death in the cortex by inhibiting pro-inflammatory responses. Neuregulins represent a novel, potent neuroprotective strategy that has potential therapeutic value in treating individuals after acute ischemic stroke.

Neurotrophic factors as novel therapeutics for neuropathic pain

Neuropathic pain is a chronic condition that is caused by injury to the nervous system. Unlike acute pain, which is protective, neuropathic pain persists and serves no useful purpose, and severely affects quality of life. However, present therapies have modest efficacy in most patients, are palliative rather than curative, and their side effects represent significant limitations. Tremendous progress has been made over the past decade in our understanding of the biology of pain sensory neurons. The recent discovery that neurotrophic factors play an important role in neuropathic pain indicates that these pathways could serve as novel intervention points for therapy. Moreover, neurotrophic factors have the potential to address the underlying pathophysiology of neuropathic pain, thereby halting or reversing the disease process.

Intravenous TAT-GDNF is protective after focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

Delivery of therapeutic proteins into tissues and across the blood-brain barrier is severely limited by their size and biochemical properties. The 11-amino acid human immunodeficiency virus TAT protein transduction domain is able to cross cell membranes and the blood-brain barrier, even when coupled with larger peptides. The present studies were done to evaluate whether TAT-glial line-derived neurotrophic factor (GDNF) fusion protein is protective in focal cerebral ischemia.

METHODS

Anesthetized male C57BL/6j mice were submitted to intraluminal thread occlusion of the middle cerebral artery. Reperfusion was initiated 30 minutes later by thread retraction. Laser Doppler flow was monitored during the experiments. TAT-GDNF, TAT-GFP (0.6 nmol each), or vehicle was intravenously applied over 10 minutes immediately after reperfusion. After 3 days (30 minutes of ischemia), animals were reanesthetized and decapitated. Brain injury was evaluated by histochemical stainings.

RESULTS

Immunocytochemical experiments confirmed the presence of TAT-GDNF protein in the brains of fusion protein-treated nonischemic control animals 3 to 4 hours after TAT fusion protein delivery. TAT-GDNF significantly reduced the number of caspase-3-immunoreactive and DNA-fragmented cells and increased the number of viable neurons in the striatum, where disseminated tissue injury was observed, compared with TAT-GFP- or vehicle-treated animals.

CONCLUSIONS

Our results demonstrate that TAT fusion proteins are powerful tools for the treatment of focal ischemia when delivered both before and after an ischemic insult. This approach may be of clinical interest because such fusion proteins can be intravenously applied and reach the ischemic brain regions. This approach may therefore offer new perspectives for future strategies in stroke therapy.

Protection against ischemic brain damage by GDNF affecting cell survival and death signals

Neuroprotective effects of glial cell line-derived neurotrophic factor (GDNF) on cell survival and death signals were investigated after 90 min of transient middle cerebral artery occlusion (MCAO) in rats. Immunoreactivities of phosphorylated Akt (p-Akt), cleaved caspase-9 (c-cas9), and -3 (c-cas3) increased after the reperfusion in the penumbra in vehicle group with peaks at 3 h, 8 h, and 1 day, respectively. Topical application of GDNF (6.8 micrograms/9 microliters) on brain surface potentiated and prolonged p-Akt activation, but suppressed activation of the caspases, and reduced the number of terminal deoxynucleotidyl transferase-mediated dUDP-biotin in situ nick labeling (TUNEL) positive cells. These results suggest that GDNF plays a protective role against ischemic injury by controlling the balance between Akt pathway and caspase cascades.

Therapeutic time window of adenovirus-mediated GDNF gene transfer after transient middle cerebral artery occlusion in rat

The time dependent influence of adenovirus-mediated glial cell line-derived neurotrophic factor (GDNF) gene (Ad-GDNF) was examined after 90 min of transient middle cerebral artery occlusion (MCAO) in rats. Treatment with Ad-GDNF significantly reduced the infarct volume when immediately administered after the reperfusion, but became insignificant when administered at 1 h after the reperfusion as were the cases treated with vehicle- and adenoviral vector containing the E. coli lacZ gene (Ad-LacZ)-treated groups. The protective effect of GDNF was related to the significant reduction of the number of TUNEL positive cells as well as immunohistochemical positive cells for active caspase-3 but not -9. These results showed that exogenous GDNF gene transfer successfully reduced the infarct size in a time-dependant manner by suppressing active caspase-3 but not active caspase-9. However, the therapeutic time window was shorter than the effect of GDNF protein itself previously reported.

Protective effects of glial cell line-derived neurotrophic factor in ischemic brain injury

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to have trophic activity on dopaminergic neurons. Recent studies indicate that GDNF can protect the cerebral hemispheres from damage induced by middle cerebral arterial ligation. We found that such neuroprotective effects are mediated through specific GDNF receptor alpha-1 (GFRalpha1). Animals with a deficiency in GFRalpha-1 have less GDNF-induced neuroprotection. Ischemia also enhances nitric oxide synthase (NOS) activity, which can be attenuated by GDNF. These.data suggest that GDNF can protect against ischemic injury through a GFRalpha-1/NOS mechanism. We also found that the receptor for GDNF, GFRalpha1, and its signaling moiety c-Ret were upregulated, starting immediately after ischemia. This upregulation suggests that activation of an endogenous neuroprotective mechanism occurs so that responsiveness of GDNF can be enhanced at very early stages during ischemia.