Intrastriatal injection of GDNF attenuates the effects of 6-hydroxydopamine

Computationally Guided Intracerebral Drug Delivery via Chronically Implanted Microdevices

Treatments for neurologic diseases are often limited in efficacy due to poor spatial and temporal control over their delivery. Intracerebral delivery partially overcomes this by directly infusing therapeutics to the brain. Brain structures, however, are nonuniform and irregularly shaped, precluding complete target coverage by a single bolus without significant off-target effects and possible toxicity. Nearly complete coverage is crucial for effective modulation of these structures. We present a framework with computational mapping algorithms for neural drug delivery (COMMAND) to guide multi-bolus targeting of brain structures that maximizes coverage and minimizes off-target leakage. Custom-fabricated chronic neural implants leverage rational fluidic design to achieve multi-bolus delivery in rodents through a single infusion of radioactive tracer (Cu-64). The resulting spatial distributions replicate computed spatial coverage with 5% error in vivo, as detected by positron emission tomography. COMMAND potentially enables accurate, efficacious targeting of discrete brain regions.

Focused ultrasound enhanced intranasal delivery of brain derived neurotrophic factor produces neurorestorative effects in a Parkinson's disease mouse model

Focused ultrasound-enhanced intranasal (IN + FUS) delivery is a noninvasive approach that utilizes the olfactory pathway to administer pharmacological agents directly to the brain, allowing for a more homogenous distribution in targeted locations compared to IN delivery alone. However, whether such a strategy has therapeutic values, especially in neurodegenerative disorders such as Parkinson’s disease (PD), remains to be established. Herein, we evaluated whether the expression of tyrosine hydroxylase (TH), the rate limiting enzyme in dopamine catalysis, could be enhanced by IN + FUS delivery of brain-derived neurotrophic factor (BDNF) in a toxin-based PD mouse model. Mice were put on the subacute dosing regimen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), producing bilateral degeneration of the nigrostriatal pathway consistent with early-stage PD. MPTP mice then received BDNF intranasally followed by multiple unilateral FUS-induced blood-brain barrier (BBB) openings in the left basal ganglia for three consecutive weeks. Subsequently, mice were survived for two months and were evaluated morphologically and behaviorally to determine the integrity of their nigrostriatal dopaminergic pathways. Mice receiving IN + FUS had significantly increased TH immunoreactivity in the treated hemisphere compared to the untreated hemisphere while mice receiving only FUS-induced BBB opening or no treatment at all did not show any differences. Additionally, behavioral changes were only observed in the IN + FUS treated mice, indicating improved motor control function in the treated hemisphere. These findings demonstrate the robustness of the method and potential of IN + FUS for the delivery of bioactive factors for treatment of neurodegenerative disorder.

Neuroprotective Surgical Strategies in Parkinson's Disease: Role of Preclinical Data

Although there have been many pharmacological agents considered to be neuroprotective therapy in Parkinson's disease (PD) patients, neurosurgical approaches aimed to neuroprotect or restore the degenerative nigrostriatal system have rarely been the focus of in depth reviews. Here, we explore the neuroprotective strategies involving invasive surgical approaches (NSI) using neurotoxic models 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), which have led to clinical trials. We focus on several NSI approaches, namely deep brain stimulation of the subthalamic nucleus, glial neurotrophic derived factor (GDNF) administration and cell grafting methods. Although most of these interventions have produced positive results in preclinical animal models, either from behavioral or histological studies, they have generally failed to pass randomized clinical trials to validate each approach. We argue that NSI are promising approaches for neurorestoration in PD, but preclinical studies should be planned carefully in order not only to detect benefits but also to detect potential adverse effects. Further, clinical trials should be designed to be able to detect and disentangle neuroprotection from symptomatic effects. In summary, our review study evaluates the pertinence of preclinical models to study NSI for PD and how this affects their efficacy when translated into clinical trials.

Grafting of Encapsulated Genetically Modified Cells Secreting GDNF into the Striatum of Parkinsonian Model Rats

In order to deliver glial cell line-derived neurotrophic factor (GDNF) into the brain, we have established a cell line that produces GDNF in a continuous fashion by genetic engineering. These cells were encapsulated and grafted into parkinsonian model rats that had received unilateral intrastriatal injection of 6-hydroxydopamine 2 weeks earlier. Neurochemical analysis showed that GDNF has been produced from the capsule for 6 months after grafting and histological analysis revealed good survival of GDNF-producing cells in the capsule 6 months after grafting. The density of nigrostriatal dopaminergic fibers in the striatum as well as the number of dopaminergic cell bodies in the substantia nigra recovered significantly after GDNF-producing cell grafting. These results suggest the possible application of GDNF-producing cell grafting for the treatment of Parkinson's disease.

Electrical stimulation of the dorsal columns of the spinal cord for Parkinson's disease

Spinal cord stimulation has been used for the treatment of chronic pain for decades. In 2009, our laboratory proposed, based on studies in rodents, that electrical stimulation of the dorsal columns of the spinal cord could become an effective treatment for motor symptoms associated with Parkinson's disease (PD). Since our initial report in rodents and a more recent study in primates, several clinical studies have now described beneficial effects of dorsal column stimulation in parkinsonian patients. In primates, we have shown that dorsal column stimulation activates multiple structures along the somatosensory pathway and desynchronizes the pathological cortico-striatal oscillations responsible for the manifestation of PD symptoms. Based on recent evidence, we argue that neurological disorders such as PD can be broadly classified as diseases emerging from abnormal neuronal timing, leading to pathological brain states, and that the spinal cord could be used as a "channel" to transmit therapeutic electrical signals to disrupt these abnormalities. © 2017 International Parkinson and Movement Disorder Society.

Viral vector delivery of neurotrophic factors for Parkinson's disease therapy

Parkinson's disease (PD) is a neurodegenerative disorder characterised by the progressive loss of midbrain dopaminergic neurons, which causes motor impairments. Current treatments involve dopamine replacement to address the disease symptoms rather than its cause. Factors that promote the survival of dopaminergic neurons have been proposed as novel therapies for PD. Several dopaminergic neurotrophic factors (NTFs) have been examined for their ability to protect and/or restore degenerating dopaminergic neurons, both in animal models and in clinical trials. These include glial cell line-derived neurotrophic factor, neurturin, cerebral dopamine neurotrophic factor and growth/differentiation factor 5. Delivery of these NTFs via injection or infusion to the brain raises several practical problems. A new delivery approach for NTFs involves the use of recombinant viral vectors to enable long-term expression of these factors in brain cells. Vectors used include those based on adenoviruses, adeno-associated viruses and lentiviruses. Here we review progress to date on the potential of each of these four NTFs as novel therapeutic strategies for PD, as well as the challenges that have arisen, from pre-clinical analysis to clinical trials. We conclude by discussing recently-developed approaches to optimise the delivery of NTF-carrying viral vectors to the brain.

Comparative study of the neurotrophic effects elicited by VEGF-B and GDNF in preclinical in vivo models of Parkinson's disease

Vascular endothelial growth factor B (VEGF-B) has recently been shown to be a promising novel neuroprotective agent for several neurodegenerative conditions. In the current study we extended previous work on neuroprotective potential for Parkinson's disease (PD) by testing an expanded dose range of VEGF-B (1 and 10 μg) and directly comparing both neuroprotective and neurorestorative effects of VEGF-B in progressive unilateral 6-hydroxydopamine (6-OHDA) PD models to a single dose of glial cell line-derived neurotrophic factor (GDNF, 10 μg), that has been established by several groups as a standard in both preclinical PD models. In the amphetamine-induced rotational tests the treatment with 1 and 10 μg VEGF-B resulted in significantly improved motor function of 6-OHDA-lesioned rats compared to vehicle-treated 6-OHDA-lesioned rats in the neuroprotection paradigm. Both doses of VEGF-B caused an increase in tyrosine hydroxylase (TH)-positive cell and fiber count in the substantia nigra (SN) and striatum in the neuroprotective experiment. The effect size was comparable to the effects seen with GDNF. In the neurorestoration paradigm, VEGF-B injection had no significant effect in either the behavioral or the immunohistochemical analyses, whereas GDNF injection significantly improved the amphetamine-induced rotational behavior and reduced TH-positive neuronal cell loss in the SN. We also present a strong positive correlation (p=1.9e-50) of the expression of VEGF-B with nuclear-encoded mitochondrial genes involved in fatty acid metabolism in rat midbrain, pointing to the mitochondria as a site of action of VEGF-B. GDNF showed a positive correlation with nuclear-encoded mitochondrial genes that was not nearly as strong (p=0.018). VEGF-B counteracted rotenone-induced reduction of (a) fatty acid transport protein 1 and 4 levels and (b) both Akt protein and phosphorylation levels in SH-SY5Y cells. We further verified VEGF-B expression in the human SN pars compacta of healthy controls and PD patients, in neuronal cells that show co-expression with neuromelanin. These results have demonstrated that VEGF-B has potential as a neuroprotective agent for PD therapy and should be further investigated.

Chronic infusion of CDNF prevents 6-OHDA-induced deficits in a rat model of Parkinson's disease

Cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) constitute a novel, evolutionarily conserved family of neurotrophic factors (NTF) expressed in vertebrates and invertebrates. The effects of two-week infusions of CDNF, MANF and glial cell line-derived neurotrophic factor (GDNF) were studied in a rat 6-hydroxydopamine (6-OHDA) hemiparkinsonian model. Degeneration of nigrostriatal dopamine nerve tract after toxin injection was assessed by measuring amphetamine-induced rotational behavior, and at the end of the experiment by quantifying tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) and TH-positive fibers in the striatum. The diffusion of the NTFs into the brain tissue following chronic infusion was also studied. Finally, we examined the transportation of intrastriatally injected (125)I-CDNF within the brain. The amphetamine-induced rotational behavior was gradually normalized in rats treated with CDNF for two weeks following the intrastriatal 6-OHDA injection. CDNF was also able to inhibit 6-OHDA-induced loss of TH-immunoreactive cells of the SNpc and TH-positive fibers in the striatum. MANF and GDNF had no statistically significant effect in any of the above measures. The volume of distribution for MANF in the striatum was significantly larger than that of GDNF after 3-day infusions. Both (125)I-CDNF and (125)I-GDNF were retrogradely transported from the striatum to the SN. No behavioral signs of toxicity were observed during treatment with the three NTFs. These results imply that CDNF may have potential as a neuroprotective or even neurorestorative therapy of PD.

Mesencephalic astrocyte-derived neurotrophic factor is neurorestorative in rat model of Parkinson's disease

Neurotrophic factors are promising candidates for the treatment of Parkinson's disease (PD). Mesencephalic astrocyte-derived neurotrophic factor (MANF) belongs to a novel evolutionarily conserved family of neurotrophic factors. We examined whether MANF has neuroprotective and neurorestorative effect in an experimental model of PD in rats. We also studied the distribution and transportation of intrastriatally injected MANF in the brain and compared it with glial cell line-derived neurotrophic factor (GDNF). Unilateral lesion of nigrostriatal dopaminergic system was induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). Amphetamine-induced turning behavior was monitored up to 12 weeks after the unilateral lesion. The local diffusion at the injection site and transportation profiles of intrastriatally injected MANF and GDNF were studied by immunohistochemical detection of the unlabeled growth factors as well as by autoradiographic and gamma counting detection of (125)I-labeled trophic factors. Intrastriatally injected MANF protected nigrostriatal dopaminergic nerves from 6-OHDA-induced degeneration as evaluated by counting tyrosine hydroxylase (TH)-positive cell bodies in the substantia nigra (SN) and TH-positive fibers in the striatum. More importantly, MANF also restored the function of the nigrostriatal dopaminergic system when administered either 6 h before or 4 weeks after 6-OHDA administration in the striatum. MANF was distributed throughout the striatum more readily than GDNF. The mechanism of MANF action differs from that of GDNF because intrastriatally injected (125)I-MANF was transported to the frontal cortex, whereas (125)I-GDNF was transported to the SN. Our results suggest that MANF is readily distributed throughout the striatum and has significant therapeutic potential for the treatment of PD.

The structure of the glial cell line-derived neurotrophic factor-coreceptor complex: insights into RET signaling and heparin binding

Glial cell line-derived neurotrophic factor (GDNF), a neuronal survival factor, binds its co-receptor GDNF family receptor alpha1 (GFR alpha 1) in a 2:2 ratio and signals through the receptor tyrosine kinase RET. We have solved the GDNF(2).GFR alpha 1(2) complex structure at 2.35 A resolution in the presence of a heparin mimic, sucrose octasulfate. The structure of our GDNF(2).GFR alpha 1(2) complex and the previously published artemin(2).GFR alpha 3(2) complex are unlike in three ways. First, we have experimentally identified residues that differ in the ligand-GFR alpha interface between the two structures, in particular ones that buttress the key conserved Arg(GFR alpha)-Glu(ligand)-Arg(GFR alpha) interaction. Second, the flexible GDNF ligand "finger" loops fit differently into the GFR alphas, which are rigid. Third, and we believe most importantly, the quaternary structure of the two tetramers is dissimilar, because the angle between the two GDNF monomers is different. This suggests that the RET-RET interaction differs in different ligand(2)-co-receptor(2)-RET(2) heterohexamer complexes. Consistent with this, we showed that GDNF(2).GFR alpha1(2) and artemin(2).GFR alpha 3(2) signal differently in a mitogen-activated protein kinase assay. Furthermore, we have shown by mutagenesis and enzyme-linked immunosorbent assays of RET phosphorylation that RET probably interacts with GFR alpha 1 residues Arg-190, Lys-194, Arg-197, Gln-198, Lys-202, Arg-257, Arg-259, Glu-323, and Asp-324 upon both domains 2 and 3. Interestingly, in our structure, sucrose octasulfate also binds to the Arg(190)-Lys(202) region in GFR alpha 1 domain 2. This may explain how GDNF.GFR alpha 1 can mediate cell adhesion and how heparin might inhibit GDNF signaling through RET.

GDNF therapy for Parkinson's disease

With an increase in the aging population, the incidence of Parkinson's disease (PD), a disabling neurodegenerative disorder mainly affecting motor function, will inevitably present a challenge to an already overburdened healthcare system. Current medical and surgical therapies offer symptomatic relief but do not provide a cure. Experimental studies suggest that GDNF has the ability to protect degenerating dopamine neurons in PD as well as promote regeneration of the nigrostriatal dopamine system. However, clinical trials of GDNF infusion to date remain inconclusive. This review will examine the experimental and clinical evidence of GDNF use in PD with particular focus on its potential as an effective therapy in the treatment of PD.

Continuous exposure to glial cell line-derived neurotrophic factor to mature dopaminergic transplants impairs the graft’s ability to improve spontaneous motor behavior in parkinsonian rats

Functional recovery following intrastriatal transplantation of fetal dopaminergic neurons in animal models of Parkinson's disease is, at least in part, dependent on the number of surviving dopaminergic neurons and the degree of graft-derived dopaminergic reinnervation of the host striatum. In the present study, we analyzed whether continuous exposure of glial cell line-derived neurotrophic factor (GDNF) to mature dopaminergic grafts could further boost the functional outcome of widespread intrastriatal dopaminergic grafts. Rats with dopamine-denervating lesions received multiple intrastriatal transplants of fetal dopaminergic cells and graft-induced behavioral effects were analyzed in drug-induced and spontaneous motor behaviors. At three months after grafting, animals received intrastriatal injections of recombinant lentiviral vectors encoding for either human GDNF or the green fluorescent protein. Continuous exposure of GDNF to the grafts did not boost the functional recovery beyond what was observed in the control animals. Rather, in some of the spontaneous motor behaviors, animals in the GDNF-group showed deterioration as compared with control animals, and this negative effect of GDNF was associated with a down-regulation of the tyrosine hydroxylase enzyme. Based on these and our earlier results, we propose that intrastriatal administration of GDNF at the time of or shortly after grafting is highly effective in initially promoting the cell survival and fiber outgrowth from the grafts. However, once the grafts are mature, GDNF's ability to boost dopaminergic neurotransmission follows the same dynamics as for the native nigral dopaminergic neurons, which appears to be dependent on the concentration of GDNF. Since rather low doses of glial cell line-derived neurotrophic factor at nanogram levels appear to saturate these effects, it may be critical to adjust GDNF levels using tightly regulated gene expression systems.

Dopaminergic innervation of forebrain by ventral mesencephalon in organotypic slice co-cultures: Effects of GDNF

Numerous studies have verified the ability of glial cell line-derived neurotrophic factor (GDNF) to protect or rescue neurons in models of Parkinson's disease. However, the role of GDNF in the development of dopaminergic (DA) neurons remains unclear. We investigated the hypothesis that GDNF is a target protein for the DA neurons of the mesencephalon forming the nigrostriatal pathway in an in vitro rat model. Organotypic slice cultures were prepared from tissue isolated from postnatal rat pups including but not limited to the substantia nigra (SN), striatum, and cerebral cortex. These cultures were maintained for up to 100 days in vitro. In the absence of exogenous GDNF, DA neurons from the SN grew into the striatum but not the cerebral cortex or hippocampus as determined by immunostaining for tyrosine hydroxylase. The addition of exogenous GDNF increased the survival of DA neurons and also enhanced the number of dopaminergic processes innervating the striatum. GDNF also induced DA innervation of the cerebral cortex but not hippocampus. In conclusion, our studies indicate that the normal pattern of innervation by DA neurons of the mesencephalon can be recapitulated with organotypic co-cultures and that this pattern can be altered by GDNF.

Sparing of behavior and basal extracellular dopamine after 6-hydroxydopamine lesions of the nigrostriatal pathway in rats exposed to a prelesion sensitizing regimen of amphetamine

Repeated administration of amphetamine leads to enduring augmentation of its behavioral-activating effects, enhanced dopamine (DA) release in striatal regions, and morphological changes in DA target neurons. Here we show that exposure to a 2-week escalating-dose regimen of amphetamine prevents behavioral asymmetries of forelimb use and spontaneous (drug-independent) turning behavior following unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway made 7-14 days after termination of amphetamine treatment (Experiments 1-3). Exposure to three nonescalating injections of amphetamine 7 days before 6-OHDA lesions had no effect (Experiment 2). Prelesion amphetamine treatment led to normalization of basal extracellular levels of striatal DA as measured by microdialysis on days 11-14 and 25-28 after lesioning (Experiment 3). However, there were no significant differences between treatment groups in postmortem tissue levels of DA and its metabolites, indicating a dissociation between the DA depletion and the extracellular levels of DA as measured by microdialysis. Finally, rats exposed to the escalating amphetamine regimen had reduced lesion-induced loss of TH-IR cells in the ipsilateral DA cell body regions (Experiment 3). Thus, prelesion exposure to the escalating doses of amphetamine may render the cells resistant to the consequences of damage after subsequent 6-OHDA lesions, possibly by accelerating the development of compensatory changes in the DA neurons that typically accompany behavioral recovery. The potential role of amphetamine-induced endogenous neurotrophic factors in the behavioral sparing and normalization of basal extracellular DA levels observed after subsequent 6-OHDA lesions is discussed.

Protective effects of intracerebral adenoviral-mediated GDNF gene transfer in a rat model of Parkinson's disease

This study focuses on the potential protective effects of intracerebral adeno-viral mediated glial cell line derived neurotrophic factor (GDNF) gene transfer in a rat model of Parkinson's disease (PD). Thirty-five SD rats were divided into three groups to receive perinigral injections of recombinant adenovirus encoding GDNF (Ad-GDNF), LacZ (Ad-LacZ) or PBS, respectively. One week later, an intrastriatal injection of 6-hydroxydopamine (6-OHDA) was administered to induce the progressive degeneration of dopaminergic neurons. Immunohistochemistry showed that GDNF treatment prior to neuronal damage could promote survival and morphological recovery of tyrosine hydroxylase (TH)-positive neurons in the midbrain. Approximately 70% of nigral TH-positive cells survived in the Ad-GDNF group, compared to approximately 30% for the Ad-LacZ or PBS control group. Histochemical analysis of monoamine levels in the striatum demonstrated that the dopamine content was higher for the Ad-GDNF group than the control groups. Similarly, Ad-GDNF treated animals showed improved apomorphine-induced rotational behavior. The exogenous GDNF gene was efficiently expressed in the brain as detected by ELISA. This work demonstrates that intracerebral adeno-viral mediated GDNF gene transfer can protect dopaminergic neurons in vivo from 6-OHDA-induced injuries. The approach used in this study could potentially be used therapeutically in patients with PD and further work is required to explore this idea in depth.

Structural determinants of heparan sulphate modulation of GDNF signalling

Glial cell line-derived neurotrophic factor (GDNF) has many functions including regulation of kidney morphogenesis and of neuron growth and survival in the enteric, sensory and central nervous systems. Reports of GDNF being used against Parkinson's disease in human patients have sparked intense clinical interest in GDNF signalling. We recently showed that GDNF signalling requires cell surface heparan sulphate glycosaminoglycans (Barnett et al., 2002, J. Cell Sci. 115, 4495-4503). Here we use exogenous modified heparins to determine those structural features required to inhibit GDNF signalling in ex vivo assays. 2-O-sulphate groups were found to impart high activity but were not absolute requirements for the inhibition of GDNF signalling. These findings may explain the similarities between the phenotypes of transgenic mice lacking GDNF and those lacking heparan sulphate 2-sulphotransferase, the enzyme responsible for achieving 2-O-sulphation of uronic acids in vivo.

Glial cell line-derived neurotrophic factor-supplemented hibernation of fetal ventral mesencephalic neurons for transplantation in Parkinson disease: long-term storage

OBJECT

Transplantation of fetal dopaminergic tissue is being investigated in animal models and clinical trials for its potential as a treatment for advanced Parkinson disease. At the same time, the availability of fetal tissue is limited, making its storage time prior to transplantation a key practical issue. Although it results in a smaller percentage of surviving cells. a longer storage time enables fetal tissue obtained over several days to be pooled for transplantation in a recipient. Glial cell line-derived neurotrophic factor (GDNF) has been shown to improve survival of human dopaminergic tissue that has been stored prior to transplantation. The objective of this study was to evaluate the effects on fetal dopaminergic tissue of GDNF-supplemented hibernation for extended periods of 6 to 15 days.

METHODS

The ventral mesencephalon (VM) was harvested in a total of 27 14-day-old rat fetuses, and three VMs were cultured immediately (fresh control group). The remaining 24 VMs were divided sagittally along the midline to yield 48 equal pieces of hemimesencephalon. Twenty-four pieces were stored with GDNF-supplemented hibernation medium for 6, 9, 12, or 15 days, and the 24 "partner" hemimesencephalon pieces were stored in control hibernation medium for the same periods of time. Tissue was cultured for 48 hours and processed for tyrosine hydroxylase (TH) immunoreactivity and double-stained with cresyl violet. Cell counts for all cultures and the percentage of TH-immunoreactive cells were obtained. The percentage of TH-immunoreactive cells for the fresh control group was 6.3 +/- 0.5%. The percentage of TH-immunoreactive cells in cultures derived from tissue stored in GDNF-supplemented medium was significantly increased at 6 and 9 days posthibernation compared with the fresh control group and the "partner" groups stored in hibernation medium only. No significant increase in the percentage of TH-immunoreactive cells was observed in the 12- and 15-day groups.

CONCLUSIONS

In this study the authors have demonstrated that fetal dopaminergic tissue can be safely stored for up to 9 days in GDNF-supplemented hibernation medium. Furthermore, the percentage of TH-immunoreactive cells is significantly increased after 6 and 9 days of storage in this medium, improving the yield of TH-immunoreactive cells prior to transplantation. These observations have practical clinical implications for collecting fetal dopaminergic cells and improving their survival after transplantation.

Radiation and regeneration: behavioral improvement and GDNF expression after Gamma Knife radiosurgery in the 6-OHDA rodent model of hemi-parkinsonism

BACKGROUND

Recent research has demonstrated that the adult mammalian CNS is capable of regeneration. This regeneration is often initiated as a response to thermal, chemical or mechanical injury. The effects of radiation on the mammalian CNS have also been found to aid in certain regeneration processes.

METHOD

In our project we examined the potential therapeutic value of radiation induced regeneration of diseased mammalian rat CNS. Eleven Sprague-Dawley rats with 6-hydroxy-dopamine (6-OHDA) induced hemi-parkinsonism were treated in the Leksell Gamma Knife using a single 4 mm collimator shot targeted to the ipsilateral (parkinsonian) caudate-putamen complex. A maximum dose of 140 Gy was used to create a necrotic lesion. Animals were tested behaviorally using the apomorphine-induced rotational behavior model before and up to 6 months after radiosurgery. Histochemical analysis was performed 2 weeks, 1 month and 4 months after radiosurgery. Histological sections were obtained and immunohistochemistry was performed for glial cell line derived neurotrophic factor (GDNF).

FINDINGS

The rotational behavior for 11/11 animals (100%) was found to initially worsen at 2 weeks and 4 weeks after radiosurgery before a statistically highly significant reduction in apomorphine induced rotations was observed at 2, 3, and 4 months after radiosurgery (83% reduction by month four; p < 0.0001). For 2/11 animals the rotational behavior almost disappeared indicating near-abolition of parkinsonian behavior. On histological examination, the lesions were easily identified as areas of necrosis about 4 mm in diameter. The region immediately adjacent to the lesion was found to have highly positive expression of GDNF indicating high activity in dopamine-regenerating processes.

INTERPRETATION

In this preliminary study we demonstrated that radiosurgical lesioning with the Gamma Knife into the striatum of hemi-parkinsonian animals resulted in significant behavioral improvement of signs of parkinsonism. Since GDNF expression is tightly linked to the dopaminergic system, we conclude that focused radiation is potentially capable of inducing regeneration of dopaminergic pathways in the adult CNS. Further studies with dose deescalation and molecular biological characterization of the regeneration cascades are necessary to gain access to potential clinical value of our observations.

Neurotrophic factors for the investigation and treatment of movement disorders

Neurotrophic factors (NFs) are proteins that enhance neuronal survival, differentiation, neurotransmitter function and resistance to neurotoxins and lesions. For these reasons the NFs are considered as a new potential therapeutic tool for the treatment of neurodegenerative disorders, a group of diseases that produce the most important cause for disability in the Western world. Some NFs prevent or even reverse the behavioral, biochemical, pharmacological and histological abnormalities observed in several in vitro and in vivo models of neurodegenerative disorders, namely Parkinson's disease. Several NFs have been investigated in primate models of neurological disorders and some of them have been used for patients with these diseases. The results so far obtained in humans have been disappointing for several reasons, including technical problems for delivery, unbearable side effects or lack of efficacy. Future approaches for the use of NFs in humans should include the following: (1) Investigation of the putative compounds in animal models more related to the pathophysiology of each disease, such as in genetic models of neurodegenerative diseases; (2) New methods of delivery including genetic engineering by viral vectors and administration through implantable devices; (3) More precise methods of continuous response evaluation, including the novel neuroimaging techniques; (4) Investigation of the effects of behavioral stimulation and conventional pharmacotherapy on the metabolism of NFs.

Signalling by glial cell line-derived neurotrophic factor (GDNF) requires heparan sulphate glycosaminoglycan

Glial cell line-derived neurotrophic factor, GDNF, is vital to the development and maintenance of neural tissues; it promotes survival of sympathetic, parasympathetic and spinal motor neurons during development, protects midbrain dopaminergic neurons from apoptosis well enough to be a promising treatment for Parkinson's disease, and controls renal and testicular development. Understanding how GDNF interacts with its target cells is therefore a priority in several fields. Here we show that GDNF requires glycosaminoglycans as well as the already-known components of its receptor complex, c-Ret and GFRalpha-1. Without glycosaminoglcyans, specifically heparan sulphate, c-Ret phosphorylation fails and GDNF cannot induce axonogenesis in neurons, in PC-12 cells, or scatter of epithelial cells. Furthermore, exogenous heparan sulphate inhibits rather than assists GDNF signalling. The involvement of heparan sulphates in GDNF signalling raises the possibility that modulation of heparan expression may modulate signalling by GDNF in vivo.

Glial cell line-derived neurotrophic factor-supplemented hibernation of fetal ventral mesencephalic neurons for transplantation in Parkinson disease: long-term storage

OBJECT

Investigation of fetal dopaminergic tissue transplantation is being conducted in animal models and clinical trials as a potential treatment for advanced Parkinson disease (PD). Because the availability of fetal tissue is limited, however, the duration of its storage prior to transplantation is a key practical issue. Longer storage times may enable fetal tissue obtained over several days to be pooled together for transplantation in a recipient. Glial cell line-derived neurotrophic factor (GDNF) has been shown to improve survival of stored human dopaminergic tissue prior to transplantation. The objective of this study was to evaluate GDNF-supplemented hibernation of fetal dopaminergic tissue for extended periods of 6 to 15 days.

METHODS

A total of 27 rat ventral mesencephalons (VMs) were obtained in gestation Day 14 rat fetuses, and three were cultured immediately (fresh-culture control group). The remaining 24 VMs were divided sagittally along the midline to form 48 equal pieces of hemimesencephalons. Twenty-four pieces were stored with GDNF-supplemented hibernation medium for 6, 9, 12, or 15 days, and the 24 "partner" hemimesencephalons were stored in control hibernation medium for the same periods of time. Tissue was cultured for 48 hours and processed for tyrosine hydroxylase (TH) immunoreactivity and cresyl violet. Cell counts for all cultures and percentage of TH-immunoreactive cells were obtained. The percentage of TH-positive cells for the fresh control group was 6.3 +/- 0.5%; that measured in cultures derived from tissue hibernated in GDNF-supplemented medium was significantly increased at 6 and 9 days posthibernation compared with the fresh-culture control group and the partner groups stored in hibernation medium only. No significant increase in percentage of TH-immunoreactive cells was observed in the 12- and 15-day hibernation groups.

CONCLUSIONS

In summary the authors found that fetal dopaminergic tissue can safely be stored up to 9 days in GDNF-supplemented hibernation medium. Furthermore the percentage of TH-immunoreactive cells is significantly increased after 6 and 9 days of storage in this medium, improving the yield of TH-positive cells prior to transplantation. These observations may have important clinical implications for collecting fetal dopaminergic cells and improving their survival after transplantation.

Neuroprotective and restorative effects of intrastriatal grafting of encapsulated GDNF-producing cells in a rat model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) has been shown to possess potent neurotrophic effects on dopaminergic (DA) neurons. We attempted the transplantation of encapsulated GDNF-producing cells to generate a stable supply of GDNF in the brain to promote neuroprotective and restorative effects for DA neurons. We established baby hamster kidney (BHK) cells and introduced GDNF cDNA to produce human GDNF (BHK-GDNF). These BHK-GDNF cells, or nontransfected BHK cells (BHK-Control), were encapsulated into hollow fibers, and the polymer encapsulated cells were unilaterally implanted into the striatum of adult rats, either before or after the administration of 6-hydroxydopamine into the same striatum. The encapsulated BHK-GDNF cells produced GDNF continuously in the striatum for up to 6 months. The rats that received a BHK-GDNF capsule showed a significant decrease in rotational behaviour compared to those that received a BHK-control capsule. Preservation of the nigrostriatal pathway was significantly greater in those that received a BHK-GDNF capsule than in those that received a BHK-control capsule. This indicates that encapsulated GDNF-producing cells can supply GDNF in a stable fashion and have protective and restorative effects on host DA neurons. Our results support a role for this grafting technique in the treatment of Parkinson's disease.

Emerging therapies in the pharmacological treatment of Parkinson's disease

The pharmacological management of Parkinson's disease is a complex and dynamic task; there is no one 'right' strategy indicating which drugs should be used at a particular stage of the disease. There are now many different drugs belonging to several classes that may be effective, and there are still differences of opinion among leading clinicians about the best course of treatment. This review focuses on drug therapy for the motor impairment in Parkinson's disease. Current and future research directions are summarised by taking inventory of recent and innovative areas of development in the field, representing each category with at least one of its featured treatments. The main research efforts are being directed towards delaying the use of levodopa or finding therapies to be used as adjunct to it, in order to postpone motor complications and, in particular, dyskinesias. One of the recent trends is early employment of dopamine agonists. Additional efforts are being directed towards protecting and restoring dopamine neurons. Novel therapies acting on non-dopaminergic systems are also being researched.

Intrastriatal injection of sonic hedgehog reduces behavioral impairment in a rat model of Parkinson's disease

Sonic hedgehog (Shh), a member of hedgehog (hh) family of signaling molecules, is necessary for normal axial patterning and cellular differentiation in the developing central nervous system. Shh also promotes the survival of fetal dopaminergic neurons and protects cultures of fetal midbrain dopaminergic neurons from the toxic effects of N-methyl-4-phenylpyridinium (MPP(+)), a neurotoxin that selectively injures nigral dopaminergic neurons. The mRNA expression of Shh and its putative receptor in the adult brain indicates an important role of Shh in the mature nervous system in addition to its roles during embryogenesis. In this study we examined the behavioral and anatomical effects of intrastriatal injection of singly myristoylated wild-type human Sonic hedgehog N-terminal fragment (Shh-M) in a rat model of Parkinson's disease (PD). Five groups of rats received a series of four intrastriatal injections of Shh-M (180 ng, 540 ng, or 4.275 microg per injection), glial cell line-derived neurotrophic factor (GDNF) (1 microg/injection), or vehicle on days 1, 3, 5, and 8. On day 4, the animals received an intrastriatal injection of 15 microg 6-hydroxydopamine (6-OHDA) free base. Intrastriatal administration of Shh (180 ng/injection) twice before and after a single intrastriatal injection of 6-OHDA reduced apomorphine- and amphetamine-induced rotation and forelimb akinesia and partially preserved dopaminergic axons in the striatum. This is the first demonstration in vivo that Shh reduces behavioral deficits induced by intrastriatal 6-OHDA lesion and suggests that Shh may be useful in the treatment of disorders that affect the nigrostriatal system, such as PD.

Adenoviral vector-mediated delivery of glial cell line-derived neurotrophic factor provides neuroprotection in the aged parkinsonian rat

1. The long-term delivery of neurotrophic factors to specific regions of the central nervous system via gene therapy offers a new strategy for the treatment of neurodegenerative disorders. 2. The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) is a potent dopaminergic (DA) trophic factor that ameliorates the behavioural and histological consequences of lesioning DA neurons in rodent and primate models of Parkinson's disease. 3. Glial cell line-derived neurotrophic factor gene therapy may have a potential use in the clinical treatment of Parkinson's disease. 4. We examined whether injection of an adenoviral vector encoding human GDNF preproprotein (Ad GDNF) could protect the rat nigrostriatal DA system from progressive neuronal degeneration. Because Parkinson's disease occurs primarily in the elderly population, we studied the effect of GDNF gene delivery in an aged rat model of Parkinson's disease. 5. In the aged (20 month) Fischer 344 rat, Ad GDNF was injected either near DA cell bodies in the substantia nigra (SN) or at the DA terminals in the striatum. One week following gene delivery, the neurotoxin 6-hydroxydopamine (6-OHDA) was injected unilaterally into the striatum to cause progressive degeneration of the DA neurons. 6. Injection of GDNF vector into either the striatum or the SN provided significant cell protection against 6-OHDA. However, only striatal injection of Ad GDNF protected against the development of behavioural and neurochemical changes that occur in the DA-depleted brain. 7. The results of this study are reviewed here and the behavioural and cellular effects of GDNF gene delivery into striatal versus mesencephalic sites are discussed.

Prospects for the treatment of Parkinson's disease using neurotrophic factors

Parkinson's disease (PD) is a debilitating neurodegenerative condition that is characterised by a progressive loss of dopaminergic neurones of the substantia nigra pars compacta (SNpc) and the presence of alpha-synuclein cytoplasmic inclusions (Lewy bodies). Cardinal symptoms include tremor, bradykinesia, and rigidity, although cognitive and autonomic disturbances are not uncommon. Pharmacological treatment targeting the dopaminergic network is relatively effective at ameliorating these symptoms, especially in the early stages of the disease, but none of these therapies are curative and they generate their own problems. As dopaminergic neuronal death in PD occurs in a gradual manner, it is amenable to treatments that can either protect remaining dopaminergic neurones or prevent death of those neurones that have begun to die. Use of neurotrophic factors is a potential candidate, as various factors have been shown to increase dopaminergic neuronal survival in culture and promote survival and axonal growth in animal models of PD. Glial cell line-derived neurotrophic factor (GDNF) is currently the most effective substance that has been intensively studied and shown to have a specific 'dopaminotrophic' effect. This review will therefore focus on studies that have investigated GDNF and discuss the potential for neurotrophic factor treatment in PD.

Glial cell line-derived neurotrophic factor (GDNF) gene delivery protects dopaminergic terminals from degeneration

Previously, we observed that injection of an adenoviral (Ad) vector expressing glial cell line-derived neurotrophic factor (GDNF) into the striatum, but not the substantia nigra (SN), prior to a partial 6-OHDA lesion protects dopaminergic (DA) neuronal function and prevents the development of behavioral impairment in the aged rat. This suggests that striatal injection of AdGDNF maintains nigrostriatal function either by protecting DA terminals or by stimulating axonal sprouting to the denervated striatum. To distinguish between these possible mechanisms, the present study examines the effect of GDNF gene delivery on molecular markers of DA terminals and neuronal sprouting in the aged (20 month) rat brain. AdGDNF or a control vector coding for beta-galactosidase (AdLacZ) was injected unilaterally into either the striatum or the SN. One week later, rats received a unilateral intrastriatal injection of 6-OHDA on the side of vector injection. Two weeks postlesion, rats injected with AdGDNF into either the striatum or the SN exhibited a reduction in the area of striatal denervation and increased binding of the DA transporter ligand [(125)I]IPCIT in the lesioned striatum compared to control animals. Furthermore, injections of AdGDNF into the striatum, but not the SN, increased levels of tyrosine hydroxylase mRNA in lesioned DA neurons in the SN and prevented the development of amphetamine-induced rotational asymmetry. In contrast, the level of T1 alpha-tubulin mRNA, a marker of neuronal sprouting, was not increased in lesioned DA neurons in the SN following injection of AdGDNF either into the striatum or into the SN. These results suggest that GDNF gene delivery prior to a partial lesion ameliorates damage caused by 6-OHDA in aged rats by inhibiting the degeneration of DA terminals rather than by inducing sprouting of nigrostriatal axons.

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.

Immunophilin ligands can prevent progressive dopaminergic degeneration in animal models of Parkinson's disease

Slowing or halting the progressive dopaminergic (DA) degeneration in Parkinson's disease (PD) would delay the onset and development of motor symptoms, prolong the efficacy of pharmacotherapies and decrease drug-induced side-effects. We tested the potential of two orally administered novel immunophilin ligands to protect against DA degeneration in two animal models of PD. First, in an MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model, we compared an immunophilin ligand (V-10,367) documented to bind the immunophilin FKBP12 with V-13,661, which does not bind FKBP12. Both molecules could prevent the loss of striatal DA innervation in a dose-dependent fashion during 10 days of oral administration. Second, to determine whether an immunophilin ligand can protect against progressive and slow DA degeneration typical of PD, an intrastriatal 6-hydroxydopamine-infusion rat model was utilized. Oral treatment with the FKBP12-binding immunophilin ligand began on the day of lesion and continued for 21 days. At this time point, post mortem analyses revealed that the treatment had prevented the progressive loss of DA innervation within the striatum and loss of DA neurons within the substantia nigra, related to functional outcome as measured by rotational behaviour. Notably, DA fibres extending into the area of striatal DA denervation were observed only in rats treated with the immunophilin ligand, indicating neuroprotection or sprouting of spared DA fibres. This is the first demonstration that immunophilin ligands can prevent a slow and progressive DA axonal degeneration and neuronal death in vivo. The effects of orally administered structurally related immunophilin ligands in acute and progressive models of DA degeneration are consistent with the idea that these compounds may have therapeutic value in PD.

Glial cell line-derived neurotrophic factor concentration dependently improves disability and motor activity in MPTP-treated common marmosets

Glial cell line-derived neurotrophic factor (GDNF) has previously reduced motor deficits and preserved nigral dopamine neurones in rhesus monkeys with a unilateral MPTP-induced lesion of substantia nigra. We now report on the ability of GDNF to reverse motor deficits induced by parenteral administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to common marmosets resulting in bilateral degeneration of the nigrostriatal pathway. Prior to GDNF administration, all MPTP-treated animals showed akinesia or bradykinesia, rigidity, postural instability and tremor. Intraventricular injection of GDNF (10, 100 or 500 microg) at 9 and 13 weeks post MPTP treatment resulted in a concentration dependent improvement in locomotor activity and motor disability which became significant after administration of 100 and 500 microg of GDNF. The most prominent improvements were in alertness, checking movements, and posture. It is concluded that intraventricular GDNF administration improves bilateral Parkinsonian motor disability following MPTP treatment and this may reflect an action of GDNF on remaining nigral dopaminergic neurones.

Recombinant adeno-associated virus vector expressing glial cell line-derived neurotrophic factor reduces ischemia-induced damage

To explore the potential of using the recombinant adeno-associated viral (rAAV) vector, expressing glial cell line-derived neurotrophic factor (GDNF) as the gene therapy for stroke, we injected rAAV vectors expressing GDNF (rAAV-GDNF) into the cortex of rats which had been experiencing transient bilateral common carotid artery ligation and right middle cerebral artery ligation for 90 min. GDNF levels in cortical tissues of rAAV-GDNF-injected animals were significantly higher than in the control animals injected with rAAV-expressing lacZ (rAAV-lacZ), indicating that rAAV can deliver and express the GDNF gene in cortical tissues. Triphenyltetrazolium chloride tissue stain analysis revealed that the rAAV-delivered GDNF gene could rescue the brain tissues from ischemia-induced injury. Cortical tissues which received rAAV-GDNF injections had both significantly smaller total volumes of infarction and smaller areas of infarction on each brain slice than those which were injected with rAAV-lacZ. An in situ labeling analysis demonstrated significantly less apoptotic cells in cortical tissues rescued by rAAV-GDNF, indicating prevention of apoptosis as the mechanism of cortical cell protection. Moreover, immunohistochemistry staining of Neu-N indicated that the rescued brain tissues contained the same number of Neu-N-positive neuronal cells as contralateral undamaged brain tissues. This provides strong evidence that cortical neuronal cells can be rescued by GDNF gene therapy. Indeed, these findings show that the rAAV is a potential delivery vector of GDNF gene for the therapy of stroke.

Fibroblast growth factor-2-producing fibroblasts protect the nigrostriatal dopaminergic system from 6-hydroxydopamine

We tested the hypothesis that fibroblasts, which had been genetically engineered to produce fibroblast growth factor-2 (FGF-2), can protect nigrostriatal dopaminergic neurons. Three groups of rats received either a burr hole only (n=5) or implantation of fibroblasts, which had been genetically engineered to produce beta-galactosidase (beta-gal) (n=8) or FGF-2 (n=8), at two sites in the right striatum. Two weeks later, the animals received an injection of 25 microg of 6-hydroxydopamine hydrobromide (6-OHDA) midway between the two implant sites. The group that received FGF-2-fibroblasts had significantly fewer apomorphine-induced rotations than the groups that received a burr hole only or beta-gal-fibroblasts at weeks 2 and 3 following lesioning with 6-OHDA. Testing for amphetamine-induced rotation revealed a mild reduction in rotation in the beta-gal-fibroblast group compared to the burr hole only group, but a striking attenuation of amphetamine-induced rotation in the FGF-2-fibroblast group. There was also preservation of TH-IR neurons on the lesioned side relative to both control groups. The size of the grafts and the gliosis surrounding the injection sites did not differ between the FGF-2-fibroblast and beta-gal-fibroblast groups. To further characterize the production of FGF-2 by the FGF-2-fibroblasts, we implanted FGF-2-fibroblasts and beta-gal-fibroblast into the striatum of rats but did not lesion the animals with 6-OHDA. The animals were then sacrificed at 1, 2 and 5 weeks following implantation. Prior to implantation the FGF-2 fibroblasts contained 148 ng/mg of FGF-2-immunoreactive (FGF-2-IR) material per mg of protein of cell lysate. After implantation FGF-2-IR material was noted in the grafts of FGF-2-fibroblasts, most conspicuously at 1 and 2 weeks following implantation. We also noted FGF-2-IR material in the nuclei of reactive astrocytes adjacent to the implants, and OX-42-immunoreactive (OX-42-IR) cells adjacent and occasionally within the implants. Our work indicates that fibroblasts genetically engineered to produce FGF-2 and implanted in the striatum can protect the nigrostriatal dopaminergic system and may be useful in the treatment of Parkinson's disease.

Glial cell line-derived neurotrophic factor (GDNF) as a defensive molecule for neurodegenerative disease: a tribute to the studies of antonia vernadakis on neuronal-glial interactions

Research stemming from interests in neuronal-glial interactions has led to the identification of a number of novel trophic factors, such as the dopaminergic neurotrophic factor glial cell line-derived neurotrophic factor (GDNF). Delivery of the GDNF gene to rat models of Parkinson's disease suggests a potential clinical use of GDNF gene therapy for humans with this disease. This review article briefly summarizes the history of GDNF and the effects of GDNF gene delivery prior to or after a lesion of the rat nigrostriatal system.

Delivery of a GDNF gene into the substantia nigra after a progressive 6-OHDA lesion maintains functional nigrostriatal connections

The effects of delivering GDNF via an adenoviral vector (AdGDNF) 1 week after lesioning dopaminergic neurons in the rat substantia nigra (SN) with 6-hydroxydopamine (6-OHDA) were examined. Rats were unilaterally lesioned by injection of 6-OHDA into the striatum, resulting in progressive degeneration of dopaminergic neurons in the SN. One week later, when substantial damage had already occurred, AdGDNF or a control vector harboring beta-galactosidase (AdLacZ) was injected into either the striatum or SN (3.2 x 10(7) PFU/microl in 2 microl). Rats were examined behaviorally with the amphetamine-induced rotation test and for forelimb use for weight-bearing movements. On day 30 postlesion, the extent of nigrostriatal tract degeneration was determined by injecting a retrograde tracer (FluoroGold) bilaterally into the lesioned striatum. Five days later, rats were sacrificed within 2 h of amphetamine injection to examine amphetamine-induced Fos expression in the striatum, a measure of dopaminergic-dependent function in target neurons. AdGDNF injection in the SN rescued dopaminergic neurons in the SN and increased the number of dopaminergic neurons that maintained a connection to the striatum, compared to rats injected with AdLacZ. Further support that these spared SN cells maintained functional connections to the striatum was evidenced by increased Fos expression in striatal target neurons and a decrease in amphetamine-induced rotation. In contrast to the effects observed in rats injected with AdGDNF in the SN, rats injected with AdGDNF in the striatum did not exhibit significant ameliorative effects. This study demonstrates that experimentally increasing levels of GDNF biosynthesis near the dopaminergic neuronal soma is effective in protecting the survival of these neurons and their function even when therapy is begun after 6-OHDA-induced degeneration has commenced. Thus, GDNF gene therapy may ameliorate the consequences of Parkinson's disease through rescuing compromised dopaminergic neurons.

The effect of intrastriatal single injection of GDNF on the nigrostriatal dopaminergic system in hemiparkinsonian rats: behavioral and histological studies using two different dosages

Glial cell line-derived neurotrophic factor (GDNF) is a member of the transforming growth factor-beta superfamily and acts as a neurotrophic factor for the nigrostriatal dopamine (DA) system. Although previous studies have shown that pretreatment with GDNF could prevent degenerative changes of nigrostriatal DA system by DA neurotoxin 6-hydroxydopamine (6-OHDA), it is not really known whether GDNF can induce recovery of nigrostriatal DA system after partial lesioning by 6-OHDA. Substantia nigra has been commonly chosen as injection site for GDNF but a limited number of studies have used striatum as injection site where neural transplantation is commonly performed. Unilateral intrastriatal administration of 6-OHDA was performed in Sprague-Dawley rats to create partial lesion of the nigrostriatal DA system. These hemiparkinsonian model rats received a 10- or 100-microg single injection of human recombinant GDNF into the same portion of the striatum 4 weeks after 6-OHDA treatment. Both animals that received a 10- or 100-microg single injection of GDNF showed decreased apomorphine-induced rotation at 2 weeks after injection. More potent and prolonged functional recovery was observed in animals receiving 100 microg of GDNF than in those receiving 10 microg of GDNF. Tyrosine hydroxylase (TH) immunocytochemistry revealed that TH positive DA fiber density in the striatum and the number of DA cell bodies in the substantia nigra were greater in animals receiving 10 or 100 microg of GDNF than those receiving saline. These immunocytochemical results have also shown that 100 microg of GDNF was more potent than 10 microg of GDNF. These morphological and functional results indicate that GDNF treatment 4 weeks after 6-OHDA lesioning could induce recovery of nigrostriatal DA system. Striatum was a good site for GDNF administration for hemiparkinsonian rats and a single injection of 100 microg of GDNF was more potent than 10 microg of GDNF.

Sequential administration of GDNF into the substantia nigra and striatum promotes dopamine neuron survival and axonal sprouting but not striatal reinnervation or functional recovery in the partial 6-OHDA lesion model

Glial cell line-derived neurotrophic factor (GDNF) has prominent survival-promoting effects on lesioned nigrostriatal dopamine neurons, but understanding of the conditions under which functional recovery can be obtained remains to be acquired. We report here the time course of nigrostriatal axon degeneration in the partial lesion model of Parkinson's disease and the morphological and functional effects of sequential administration of GDNF in the substantia nigra (SN) and striatum during the first 5 weeks postlesion. By 1 day postlesion, the nigrostriatal axons had retracted back to the level of the caudal globus pallidus. Over the next 6 days axonal retraction progressed down to the SN, and during the following 7 weeks 74% of tyrosine hydroxylase-positive (TH(+)) and 84% of retrogradely labeled nigral neurons were lost, with a more pronounced loss in the rostral part of the SN. GDNF administration protected 70 and 72% of the nigral TH(+) and retrogradely labeled cell bodies, respectively, but did not prevent the die-back of the lesioned nigrostriatal axons. Although clear signs of sprouting were observed close to the injection site in the striatum as well as in the globus pallidus, the overall DA innervation of the striatum [as measured by [(3)H]-N-[1-(2-benzo(b)thiopenyl)cyclohexyl]piperidine-binding autoradiography] was not improved by the GDNF treatment. Moreover, the lesion-induced deficits in forelimb akinesia and drug-induced rotation were not attenuated. We conclude that functional recovery in the partial lesion model depends not only on preservation of the nigral cell bodies, but more critically on the ability of GDNF to promote significant reinnervation of the denervated striatum.

In vivo protection of nigral dopamine neurons by lentiviral gene transfer of the novel GDNF-family member neublastin/artemin

The glial cell line-derived neurotrophic factor (GDNF)-family of neurotrophic factors consisted until recently of three members, GDNF, neurturin, and persephin. We describe here the cloning of a new GDNF-family member, neublastin (NBN), identical to artemin (ART), recently published (Baloh et al., 1998). Addition of NBN/ART to cultures of fetal mesencephalic dopamine (DA) neurons increased the number of surviving tyrosine hydroxylase (TH)-immunoreactive neurons by approximately 70%, similar to the maximal effect obtained with GDNF. To investigate the neuroprotective effects in vivo, lentiviral vectors carrying the cDNA for NBN/ART or GDNF were injected into the striatum and ventral midbrain. Three weeks after an intrastriatal 6-hydroxydopamine lesion only about 20% of the nigral DA neurons were left in the control group, while 80-90% of the DA neurons remained in the NBN/ART and GDNF treatment groups, and the striatal TH-immunoreactive innervation was partly spared. We conclude that NBN/ART, similarly to GDNF, is a potent neuroprotective factor for the nigrostriatal DA neurons in vivo.

Neurotrophic factors in neurodegenerative disorders: model of Parkinson's disease

Neurotrophic factors are compounds that enhance neuronal survival and differentiation. Most of these compounds exert their pharmacological actions on selective types of neurons, and therefore, are considered promising new therapeutic agents for the treatment of different neurodegenerative disorders characterized by selective degeneration of certain neuronal groups. Those compounds have been used in humans for several neurological disorders including amyotrophic lateral sclerosis--ciliary derived neurotrophic factor (CNTF) and brain derived neurotrophic factor (BDNF), Alzheimer's disease and peripheral neuropathy--nerve growth factor (NGF) and Parkinson's disease (PD)--glial derived neurotrophic factor (GDNF). In spite of well founded clinical experiments by previous experimental work in animal models some of these trials have been negative. For instance, animal models of PD have shown that several neurotrophic factors, including GDNF and other compounds, reduce apoptosis and increase resistance of dopamine neurons to neurotoxins in vitro. These compounds prevent or recover the damage to dopamine neurons of rodents and primates produced by chemical or mechanical acute lesions including 6-OH-DA, MPTP, methamphetamine and axotomy. The differences between the promising results obtained in experimental models and the lack of clinical results or excessive toxicity found in humans could be attributed to the following reasons: (a) Lack of relevance between the pathogenesis of the experimental lesion and the corresponding neurodegenerative disorder. (b) Poor correlation between results obtained in acute, self-limited, selective deficit produced to experimental animals and those available in more complex, chronic and progressive disorders involving patients. (c) Inadequate delivery of the active product to the target area in the human brain. (d) Poor information from acute experiments in animals which does not predict long-term effects of chronic infusion in humans. Further experimental work, therefore, is needed to transfer these neurotrophic factors to the clinic.

Differential effects of glial cell line-derived neurotrophic factor (GDNF) in the striatum and substantia nigra of the aged Parkinsonian rat

Injection of an adenoviral (Ad) vector encoding human glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic (DA) neurons in the substantia nigra (SN) of young rats. As Parkinson's disease occurs primarily in aged populations, we examined whether chronic biosynthesis of GDNF, achieved by adenovirus-mediated delivery of a GDNF gene (AdGDNF), can protect DA neurons and improve DA-dependent behavioral function in aged (20 months) rats with progressive 6-OHDA lesions of the nigrostriatal projection. Furthermore, the differential effects of injecting AdGDNF either near DA cell bodies in the SN or at DA terminals in the striatum were compared. AdGDNF or control vector was injected unilaterally into either the striatum or SN. One week later, rats received a unilateral intrastriatal injection of 6-OHDA on the same side as the vector injection. AdGDNF injection into either the striatum or SN significantly reduced the loss of FG labelled DA neurons 5 weeks after lesion (P </= 0.05). However, only striatal injections of AdGDNF protected against the development of behavioral deficits characteristic of unilateral DA depletion. Striatal AdGDNF injections also reduced tyrosine hydroxylase fiber loss and increased amphetamine-induced striatal Fos expression. These results demonstrate that increased levels of striatal, but not nigral, GDNF biosynthesis prevents DA neuronal loss and protects DA terminals from 6-OHDA-induced damage, thereby maintaining DA function in the aged rat.

New developments in the surgery for Parkinson's disease

Despite optimization of medical therapy, a large number of patients with Parkinson's disease continue to be disabled. For this group, alternate treatment strategies such as neurosurgical intervention can be considered. Recent advances in neurosurgical techniques and in understanding the pathophysiology of motor disturbances in PD have made surgery safer and more effective. Functional neurosurgical procedures to lesion or electrically modulate dysfunctional basal ganglia circuits or to protect or restore dopaminergic transmission are being increasingly used. These procedures are having a profound impact on the motor disturbances of PD and are producing important improvements in quality of life of patients.

Protection and regeneration of nigral dopaminergic neurons by neurturin or GDNF in a partial lesion model of Parkinson's disease after administration into the striatum or the lateral ventricle

Both glial cell line-derived neurotrophic factor (GDNF) and its recently discovered congener, neurturin (NTN), have been shown to exert neuroprotective effects on lesioned nigral dopamine (DA) neurons when administered at the level of the substantia nigra. In the present study, we have explored the relative in vivo potency of these two neurotrophic factors using two alternative routes of administration, into the striatum or the lateral ventricle, which may be more relevant in a clinical setting. In rats subjected to an intrastriatal (IS) 6-hydroxydopamine (6-OHDA) lesion, GDNF and NTN were injected every third day for 3 weeks starting on the day after the 6-OHDA injection. GDNF provided almost complete (90-92%) protection of the lesioned nigral DA neurons after both IS and intracerebroventricular (ICV) administration. NTN, by contrast, was only partially effective after IS injection (72% sparing) and totally ineffective after ICV injection. Although the trophic factor injections protected the nigral neurons from lesion-induced cell death, the level of expression of the phenotypic marker, tyrosine hydroxylase (TH), was markedly reduced in the rescued cell bodies. The extent of 6-OHDA-induced DA denervation in the striatum was unaffected by both types of treatment; consistent with this observation, the high rate of amphetamine-induced turning seen in the lesioned control animals was unaltered by either GDNF or NTN treatment. In the GDNF-treated animals, and to a lesser extent also after IS NTN treatment, prominent axonal sprouting was observed within the globus pallidus, at the level where the lesioned nigrostriatal axons are known to end at the time of onset of the neurotrophic factor treatment. The results show that GDNF is highly effective as a neuroprotective and axon growth-stimulating agent in the IS 6-OHDA lesion model after both IS and ICV administration. The lower efficacy of NTN after IS, and particularly ICV, administration may be explained by the poor solubility and diffusion properties at neutral pH.

Therapeutic potential of nerve growth factors in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative syndrome which primarily affects dopamine-producing neurons of the substantia nigra, resulting in poverty and slowness of movement, instability of gait and posture, and tremor at rest in individuals with the disease. While symptoms of the disease can be effectively managed for several years with available drugs, the syndrome is progressive and the efficacy of standard drugs wanes with time. One experimental approach to therapy is to use natural and synthetic molecules which promote survival and growth of dopaminergic neurons, so-called 'neurotrophic factors', to stabilise the diminishing population of dopaminergic neurons and stimulate compensation and growth in these cells. In this review, we examine the available evidence on 29 molecules with neurotrophic properties for dopaminergic neurons. The properties of these molecules provide ample reasons for optimism that a neurotrophic strategy can be developed that would provide a significant treatment option for patients with PD. While the search continues for even more specific, potent and long lasting agents, the single greatest challenge is the development of techniques for targeted delivery of these molecules.

Novel drugs for Parkinson's disease

Treatment options in PD have expanded remarkably in the past several years. Three new drugs were approved for use in the United States just within the 9 months preceding the preparation of this article. Several new compounds are in the pipeline. Nevertheless, the unmet needs of PD patients are readily apparent in any busy clinical practice. These needs can be posed as three deceivingly simple questions: 1. When and how should L-dopa be started? Despite the fact that L-dopa remains the mainstay of PD therapy after 30 years' time, lacking is a fundamental understanding of proper usage and avoidance of long-term complications. 2. What can be done about cognitive decline and dementia in PD? The current answer is nothing. Efforts are just beginning to fill this large void in knowledge and provide adequate treatment for this disabling problem. 3. How can PD be prevented? This question cannot be answered because the cause of PD remains uncertain. The dearth of substantive information available on this topic is evidenced in this article. The bulk of text appears under the heading Symptomatic Treatments, whereas only a few speculative comments can be offered under the heading Preventive Treatments. The paramount need for expanded resources and dedicated efforts to identify the causes and devise preventions must be met if advances in the treatment of PD are to be made in the twenty-first century.

GDNF protection against 6-OHDA-induced reductions in potassium-evoked overflow of striatal dopamine

Glial cell line-derived neurotrophic factor (GDNF), when administered before 6-hydroxydopamine (6-OHDA), has been shown to prevent the reduction in nigral dopamine (DA) levels and tyrosine hydroxylase-positive neurons normally observed after 6-OHDA lesions. The present study examined the ability of GDNF to prevent 6-OHDA-induced reductions in striatal DA release and reductions in striatal and nigral DA levels. GDNF (10 micrograms), or vehicle, was injected into the right nigra of anesthetized male Fischer-344 rats and was followed 6 hr later by intranigral 6-OHDA or saline. Three to four weeks later the animals were anesthetized with urethane and prepared for in vivo electrochemistry. Potassium-evoked overflow of DA was dramatically decreased in the right striatum of the vehicle + 6-OHDA-treated animals. GDNF appeared to prevent the reduction in evoked overflow of DA in the right striatum of the 6-OHDA-treated animals. However, in comparison with that in animals that received GDNF + saline, the overflow of DA was significantly reduced in the GDNF + 6-OHDA animals. Similarly, although nigral levels of DA were above normal in the GDNF + 6-OHDA-treated animals, they were below DA levels found in GDNF + saline-treated rats. Striatal DA levels were partially protected by GDNF. In animals examined 10-12 weeks after the GDNF and 6-OHDA treatments, the apparent protective ability of GDNF on the evoked overflow of DA in the striatum was diminished. Thus, although intranigral GDNF can prevent 6-OHDA-induced reductions in nigral DA levels, long-term protection of the evoked overflow of DA in the striatum is minimal.

Behavioral and cellular protection of rat dopaminergic neurons by an adenoviral vector encoding glial cell line-derived neurotrophic factor

Previously, we observed that an adenoviral (Ad) vector encoding human glial cell line-derived neurotrophic factor (GDNF), injected near the rat substantia nigra (SN), protects SN dopaminergic (DA) neuronal soma from 6-hydroxydopamine (6-OHDA)-induced degeneration. In the present study, the effects of Ad GDNF injected into the striatum, the site of DA nerve terminals, were assessed in the same lesion model. So that effects on cell survival could be assessed without relying on DA phenotypic markers, fluorogold (FG) was infused bilaterally into striatae to retrogradely label DA neurons. Ad GDNF or control treatment (Ad mGDNF, encoding a deletion mutant GDNF, Ad lacZ, vehicle, or no injection) was injected unilaterally into the striatum near one FG site. Progressive degeneration of DA neurons was initiated 7 days later by unilateral injection of 6-OHDA at this FG site. At 42 days after 6-OHDA, Ad GDNF prevented the death of 40% of susceptible DA neurons that projected to the lesion site. Ad GDNF prevented the development of behavioral asymmetries which depend on striatal dopamine, including limb use asymmetries during spontaneous movements along vertical surfaces and amphetamine-induced rotation. Both behavioral asymmetries were exhibited by control-treated, lesioned rats. Interestingly, these behavioral protections occurred in the absence of an increase in the density of DA nerve fibers in the striatum of Ad GDNF-treated rats. ELISA measurements of transgene proteins showed that nanogram quantities of GDNF and lacZ transgene were present in the striatum for 7 weeks, and picogram quantities of GDNF in the SN due to retrograde transport of vector and/or transgene protein. These studies demonstrate that Ad GDNF can sustain increased levels of biosynthesized GDNF in the terminal region of DA neurons for at least 7 weeks and that this GDNF slows the degeneration of DA neurons and prevents the appearance of dopamine dependent motor asymmetries in a rat model of Parkinson's disease (PD). GDNF gene therapy targeted to the striatum, a more surgically accessible site than the SN, may be clinically applicable to humans with PD.

Dopamine D1 and D2 receptor-mediated acute and long-lasting behavioral effects of glial cell line-derived neurotrophic factor administered into the striatum

To determine the differences in behavioral effects between intrastriatal and intracerebroventricular glial cell-derived neurotrophic factor (GDNF) administration, spontaneous locomotor activity was measured after intrastriatal or intracerebroventricular injection of GDNF (10 microg) in normal adult rats with implanted guide cannulae. In addition, the distribution of GDNF after intracerebral injection was studied immunohistochemically. Intrastriatal administration of GDNF significantly increased rearing behavior 3-4 h after injection. Increases in all three aspects of locomotor activity (motility, locomotion, and rearing) were most pronounced 3 days after intrastriatal injection, and they lasted for several days. This hyperactivity was blocked by the selective dopamine D1 receptor antagonist SCH22390 and by the selective D2 receptor antagonist raclopride at doses of the dopamine receptor antagonists, which by themselves did not affect spontaneous locomotor activity. These results suggest that GDNF has both acute and long-lasting pharmacological effects on dopamine neurons in adult animals and stimulates locomotor activity by activating both dopamine D1 and D2 receptors. On the other hand, intracerebroventricular administration of the same dose of GDNF failed to increase locomotor activity at any time during the test period (12 days). The immunohistochemical study demonstrated widespread distribution of GDNF in the entire body of the striatum within 24 h after intrastriatal injection. It also revealed deep penetration of GDNF from the ventricular space into the brain parenchyma after intracerebroventricular injection. GDNF-immunoreactive neuronal cell bodies were seen in the ipsilateral substantia nigra pars compacta most frequently 6 h after intrastriatal injection. The number of such cell bodies after intracerebroventricular administration, on the other hand, was much lower than that seen after intrastriatal administration. Taken together, these data suggest that intrastriatal administration of GDNF is an effective approach for affecting DA transmission. Long-lasting behavior effects are mediated via dopamine D1 and D2 receptors. Higher doses of GDNF would probably be needed using the intracerebroventricular route as compared to intraparenchymal delivery to exert effects on the nigrostriatal system in Parkinson's disease patients.

The role of neuronal growth factors in neurodegenerative disorders of the human brain

Recent evidence suggests that neurotrophic factors that promote the survival or differentiation of developing neurons may also protect mature neurons from neuronal atrophy in the degenerating human brain. Furthermore, it has been proposed that the pathogenesis of human neurodegenerative disorders may be due to an alteration in neurotrophic factor and/or trk receptor levels. The use of neurotrophic factors as therapeutic agents is a novel approach aimed at restoring and maintaining neuronal function in the central nervous system (CNS). Research is currently being undertaken to determine potential mechanisms to deliver neurotrophic factors to selectively vulnerable regions of the CNS. However, while there is widespread interest in the use of neurotrophic factors to prevent and/or reduce the neuronal cell loss and atrophy observed in neurodegenerative disorders, little research has been performed examining the expression and functional role of these factors in the normal and diseased human brain. This review will discuss recent studies and examine the role members of the nerve growth factor family (NGF, BDNF and NT-3) and trk receptors as well as additional growth factors (GDNF, TGF-alpha and IGF-I) may play in neurodegenerative disorders of the human brain.

Expression of the proto-oncogene Ret, a component of the GDNF receptor complex, persists in human substantia nigra neurons in Parkinson's disease

The proto-oncogene Ret, a membrane-associated receptor protein tyrosine kinase, has recently been shown to be a component of the glial cell line-derived neurotrophic factor (GDNF) receptor complex. GDNF has potent dopaminergic neurotrophic properties and has been suggested as a treatment for Parkinson's disease (PD). In this study, tissue sections of human substantia nigra (SN) from normal and PD cases were examined to determine the pattern of Ret expression in this region, and whether there was continued Ret expression in surviving dopaminergic neurons in PD cases. Using a polyclonal antibody to the amino terminal of Ret, immunoreactivity was localized in the SN to dopaminergic neurons. The antibody predominantly identified punctate deposits within cells. A similar pattern of immunoreactivity was observed in rat and monkey SN neurons. In neurologically normal cases, immunoreactivity was detected in many of the SN neurons. In all the PD cases studied, continued expression of Ret was observed in many of the surviving dopaminergic neurons. In certain cases, it was also detected on cells with the morphology of microglia. Ret expression by microglia was confirmed by immunoblot analysis on the human THP-1 macrophage type cell line. However, these cells did not express the mRNA for GDNFRalpha, the other component of the GDNF receptor complex.