Basic fibroblast growth factor promotes the survival of embryonic ventral mesencephalic dopaminergic neurons--I. Effects in vitro

Altered heparan sulfate metabolism during development triggers dopamine-dependent autistic-behaviours in models of lysosomal storage disorders

Lysosomal storage disorders characterized by altered metabolism of heparan sulfate, including Mucopolysaccharidosis (MPS) III and MPS-II, exhibit lysosomal dysfunctions leading to neurodegeneration and dementia in children. In lysosomal storage disorders, dementia is preceded by severe and therapy-resistant autistic-like symptoms of unknown cause. Using mouse and cellular models of MPS-IIIA, we discovered that autistic-like behaviours are due to increased proliferation of mesencephalic dopamine neurons originating during embryogenesis, which is not due to lysosomal dysfunction, but to altered HS function. Hyperdopaminergia and autistic-like behaviours are corrected by the dopamine D1-like receptor antagonist SCH-23390, providing a potential alternative strategy to the D2-like antagonist haloperidol that has only minimal therapeutic effects in MPS-IIIA. These findings identify embryonic dopaminergic neurodevelopmental defects due to altered function of HS leading to autistic-like behaviours in MPS-II and MPS-IIIA and support evidence showing that altered HS-related gene function is causative of autism.

The role of fibroblast growth factor 2 in drug addiction

Fibroblast growth factor 2 (FGF2) is a member of the FGF-family, which consists of 22 members, with four known FGF receptors (five in humans). Over the last 30 years, FGF2 has been extensively studied for its role in cell proliferation, differentiation, growth, survival and angiogenesis during development, as well as for its role in adult neurogenesis and regenerative plasticity. Over the past decade, FGF2 has been implicated in learning and memory, as well as in several neuropsychiatric disorders, including anxiety, stress, depression and drug addiction. In this review, we present accumulating evidence indicating the involvement of FGF2 in neuroadaptations caused by drugs of abuse, namely, amphetamine, cocaine, nicotine and alcohol. Moreover, evidence suggests that FGF2 is a positive regulator of alcohol and drug-related behaviors. Thus, although additional studies are yet required, we suggest that reducing FGF2 activity may provide a novel therapeutic approach for substance use disorders.

Effects of Passage Number and Differentiation Protocol on the Generation of Dopaminergic Neurons from Rat Bone Marrow-Derived Mesenchymal Stem Cells

Multiple studies have demonstrated the ability of mesenchymal stem cells (MSCs) to differentiate into dopamine-producing cells, in vitro and in vivo, indicating their potential to be used in the treatment of Parkinson’s disease (PD). However, there are discrepancies among studies regarding the optimal time (i.e., passage number) and method for dopaminergic induction, in vitro. In the current study, we compared the ability of early (P4) and later (P40) passaged bone marrow-derived MSCs to differentiate into dopaminergic neurons using two growth-factor-based approaches. A direct dopaminergic induction (DDI) was used to directly convert MSCs into dopaminergic neurons, and an indirect dopaminergic induction (IDI) was used to direct MSCs toward a neuronal lineage prior to terminal dopaminergic differentiation. Results indicate that both early and later passaged MSCs exhibited positive expression of neuronal and dopaminergic markers following either the DDI or IDI protocols. Additionally, both early and later passaged MSCs released dopamine and exhibited spontaneous neuronal activity following either the DDI or IDI. Still, P4 MSCs exhibited significantly higher spiking and bursting frequencies as compared to P40 MSCs. Findings from this study provide evidence that early passaged MSCs, which have undergone the DDI, are more efficient at generating dopaminergic-like cells in vitro, as compared to later passaged MSCs or MSCs that have undergone the IDI.

A Comparative Study of Preparation Techniques for Improving the Viability of Nigral Grafts using Vital Stains, in Vitro Cultures, and in Vivo Grafts

The intracerebral transplantation of embryonic dopaminergic nigral neurons, although relatively successful, leads to a fairly low yield of surviving cells. Many factors may influence the viability of dopaminergic grafts and one of these is the preparation of the tissue prior to transplantation. We have investigated the effects of different steps during the preparation and storage of embryonic rat nigral cell suspensions on their subsequent survival at a variety of different time points using a combination of techniques and studies. For studies concerned with the first 24 h we employed vital stains, in the period covering the next 7 days we used in vitro cultures, and in the long term experiment we used in vivo grafts. The results suggest that nigral cell suspensions may remain sufficiently viable for grafting for much longer periods than previously reported. In addition a number of parameters which affect cell survival have been characterised, including the age of the embryonic donor tissue, the use of proteolytic enzymes and the trituration procedure used during the preparation of the suspension. The optimal preparation technique, therefore, uses E13-E14 embryos with the dissected ventral mesencephalon being incubated in purified 0.1% trypsin solutions for 60 min and triturated using a flame polished Pasteur pipette. This may have important implications in improving intracerebral transplantation for Parkinson's disease.

Trophic Effect of Porcine Sertoli Cells on Rat and Human Ventral Mesencephalic Cells and Hnt Neurons in Vitro

The poor survival of embryonic dopaminergic (DA) neurons transplanted into patients with Parkinson's disease (PD) has encouraged researchers to search for new methods to affect the short- as well as long-term survival of these neurons after transplantation. In several previous rodent studies Sertoli cells increased survival of islet cells and chromaffin cells when cotransplanted in vivo. The aims of this study were to investigate whether porcine Sertoli cells had a positive effect on the survival and maturation of rat and human DA neurons, and whether the Sertoli cells had an effect on differentiation of neurons derived from a human teratocarcinoma cell line (hNT neurons). A significant increase of tyrosine hydroxylase (TH)-positive neurons of both rat and human ventral mesencephalic tissue was found when cocultured with Sertoli cells. Furthermore, there was a significantly increased soma size and neurite outgrowth of neurons in the coculture treated group. The Sertoli cell and hNT coculture also revealed an increased number of TH-positive cells. These results demonstrate that the wide variety of proteins and factors secreted by porcine Sertoli cells benefit the survival and maturation of embryonic DA neurons and suggest that cotransplantation of Sertoli cells and embryonic DA neurons may be useful for a cell transplantation therapy in PD.

Differential behavioral outcomes following neonatal versus fetal human retinal pigment epithelial cell striatal implants in parkinsonian rats

Following the failure of a Phase II clinical study evaluating human retinal pigment epithelial (hRPE) cell implants as a potential treatment option for Parkinson's disease, speculation has centered on implant function and survival as possible contributors to the therapeutic outcomes. We recently reported that neonatal hRPE cells, similar to hRPE cells used in the Phase II clinical study, produced short-lived in vitro and limited in vivo trophic factors, which supports that assumption. We hypothesize that the switch from fetal to neonatal hRPE cells, between the Phase I and the Phase II clinical trial may be partly responsible for the later negative outcomes. To investigate this hypothesis, we used two neonatal hRPE cell lots, prepared in a similar manner to neonatal hRPE cells used in the Phase II clinical study, and compared them to previously evaluated fetal hRPE cells for behavioral changes following unilateral striatal implantation in 6-hydroxydopamine-lesioned rats. The results showed that only fetal, not neonatal, hRPE cell implants, were able to improve behavioral outcomes following striatal implantation in the lesioned rats. These data suggest that fetal hRPE cells may be preferential to neonatal hRPE cells in restoring behavioral deficits.

A Subpopulation of Dopaminergic Neurons Coexpresses Serotonin in Ventral Mesencephalic Cultures But Not After Intrastriatal Transplantation in a Rat Model of Parkinson's Disease

Cell replacement therapy is a promising avenue into the investigation and treatment of Parkinson's disease (PD), and in some cases, significant long-term motor improvements have been demonstrated. The main source of donor tissue is the human fetal ventral mesencephalon (FVM), which consists of a mixed neuronal population, and its heterogeneity likely contributes to the inconsistent outcome observed in clinical trials. Therefore, detailed knowledge about the neuronal subpopulations in the VM seems essential for successful cell transplantation. Interestingly, it has been reported that some tyrosine hydroxylase-positive (TH+) neurons in the VM of adult rats and in cultured midbrain-derived neuroblasts coexpress additional neurotransmitters. Thus, the present study investigated, by means of colocalization analyses, the possible expression of GABA or serotonin in TH+ neurons. For that purpose, both fetal rat and human dissociated, organotypic and neurosphere FVM cultures as well as an animal model of PD were investigated. In dissociated rat FVM cultures, approximately 30% of the TH+ neurons coexpressed serotonin, while no colocalization with GABA was observed. Interestingly, coexpression of TH and serotonin was found to be dependent on the time in culture, the plating density, and the exposure to neurotrophic factors, that is, higher cell densities and treatment with brain-derived neurotrophic factor resulted in a significantly reduced coexpression rate. Notably, even though approximately 30% of the dopaminergic neurons in the donor tissue coexpressed serotonin, no colocalization could be detected in grafts 1 month after intrastriatal transplantation into hemiparkinsonian rats. In conclusion, a significant and susceptible subpopulation of dopaminergic neurons in FVM tissues coexpresses serotonin. This might have potential implications for the future selection and handling of cells prior to transplantation in PD.

Repair of spinal cord injury by implantation of bFGF-incorporated HEMA-MOETACL hydrogel in rats

There is no effective strategy for the treatment of spinal cord injury (SCI). An appropriate combination of hydrogel materials and neurotrophic factor therapy is currently thought to be a promising approach. In this study, we performed experiments to evaluate the synergic effect of implanting hydroxyl ethyl methacrylate [2-(methacryloyloxy)ethyl] trimethylammonium chloride (HEMA-MOETACL) hydrogel incorporated with basic fibroblast growth factor (bFGF) into the site of surgically induced SCI. Prior to implantation, the combined hydrogel was surrounded by an acellular vascular matrix. Sprague-Dawley rats underwent complete spinal cord transection at the T-9 level, followed by implantation of bFGF/HEMA-MOETACL 5 days after transection surgery. Our results showed that the bFGF/HEMA-MOETACL transplant provided a scaffold for the ingrowth of regenerating tissue eight weeks after implantation. Furthermore, this newly designed implant promoted both nerve tissue regeneration and functional recovery following SCI. These results indicate that HEMA-MOETACL hydrogel is a promising scaffold for intrathecal, localized and sustained delivery of bFGF to the injured spinal cord and provide evidence for the possibility that this approach may have clinical applications in the treatment of SCI.

Viability of olfactory ensheathing cells after hypoxia and serum deprivation: Implication for therapeutic transplantation

Olfactory ensheathing cells (OECs) represent glial cells supporting neuronal turnover in the olfactory system. In vitro, OECs promote axonal growth as a source of neurotrophic growth factors; in vivo, they produce myelin, promoting remyelination of damaged axons. Consequently, OEC transplantation appears to be a promising treatment for spinal cord injury, although the functional recovery is limited. This might be ascribed to the microenvironment at the lesion site, lacking growth factors (GFs), nutrients, and oxygen. To mimic this condition, we used an in vitro approach by growing primary neonatal mouse OECs under hypoxic conditions and/or serum deprivation. In addition, we compared OECs survival/proliferation with that of primary cultures of Schwann cells (SCs) and astrocytes under the same experimental conditions. Cultures were analyzed by immunocytochemistry, and cell viability was evaluated by MTT assay. Different GFs, such as NGF, bFGF, and GDNF, and their combination were used to rescue cells from serum and/or oxygen deprivation. We show that the cell types were differently sensitive to the tested stress conditions and that OECs were the most sensitive among them. Moreover, OEC viability was rescued by bFGF under serum-deprived or hypoxic condition but not under conditions of drastic serum deprivation and hypoxia. bFGF was effective also for the other cell types, whereas the effect of the other GFs was negligible. This model suggests that administration of bFGF might be considered useful to sustain cell survival/proliferation after transplantation of OECs either alone or in combination with other glial cell types.

Fibroblast growth factor-20 protects against dopamine neuron loss in vitro and provides functional protection in the 6-hydroxydopamine-lesioned rat model of Parkinson's disease

Fibroblast growth factor-20 (FGF-20) has been shown to protect dopaminergic neurons against a range of toxic insults in vitro, through activation of fibroblast growth factor receptor 1 (FGFR1). This study set out to examine whether FGF-20 also displayed protective efficacy in the unilateral, 6-hydroxydopamine (6-OHDA) lesion rat model of Parkinson's disease. Initial studies demonstrated that, in embryonic ventral mesencephalic (VM) cultures, FGFR1 was expressed on tyrosine hydroxylase (TH)-positive neurons and that, in line with previous data, FGF-20 (100 and 500 ng/ml) almost completely protected these TH-positive neurons against 6-OHDA-induced toxicity. Co-localisation of FGFR1 and TH staining was also demonstrated in the substantia nigra pars compacta (SNpc) of naïve adult rat brain. In animals subject to 6-OHDA lesion of the nigrostriatal tract, supra-nigral infusion of FGF-20 (2.5 μg/day) for 6 days post-lesion gave significant protection (∼40%) against the loss of TH-positive cells in the SNpc and the loss of striatal TH immunoreactivity. This protection of the nigrostriatal tract was accompanied by a significant preservation of gross locomotion and fine motor movements and reversal of apomorphine-induced contraversive rotations, although forelimb akinesia, assessed using cylinder test reaching, was not improved. These results support a role for FGF-20 in preserving dopamine neuron integrity and some aspects of motor function in a rodent model of Parkinson's disease (PD) and imply a potential neuroprotective role for FGF-20 in this disease.

Expression of tissue transglutaminase on primary olfactory ensheathing cells cultures exposed to stress conditions

Tissue transglutaminase (TG2), a multifunctional enzyme implicated in cellular proliferation and differentiation processes, plays a modulatory role in the cell response to stressors. Herein, we used olfactory ensheathing cells (OECs), representing an unusual population of glial cells to promote axonal regeneration and to provide trophic support, as well as to assess whether the effect of some Growth Factors (GFs), NGF, bFGF or GDNF, on TG2 overexpression induced by stress conditions, such as glutamate or lipopolysaccaride (LPS). Glial Fibrillary Acidic Protein (GFAP) and vimentin were used as markers of astroglial differentiation and cytoskeleton component, respectively. Glutamate or LPS treatment induced a particular increase of TG2 expression. A pre-treatment of the cells with the GFs restored the levels of the protein to that of untreated ones. Our results demonstrate that the treatment of OECs with the GFs was able to restore the OECs oxidative status as modified by stress, also counteracting TG2 overexpression. It suggests that, in OECs, TG2 modulation or inhibition induced by GFs might represent a therapeutic target to control the excitotoxicity and/or inflammation, which are involved in several acute and chronic brain diseases.

Strain difference in the up-regulation of FGF-2 protein following a neurotoxic lesion of the nigrostriatal pathway

Lesions of the nigrostriatal pathway are known to induce a compensatory up-regulation of various neurotrophic factors. In this study we examined protein content of basic fibroblast growth factor (FGF-2) in tissue samples taken from the ventral midbrain and striatum at two different time points following a neurotoxic lesion of the nigrostriatal pathway in two different rat strains, the outbred Sprague-Dawley (SD) and inbred F344 9 Brown Norway F1 hybrid (F344BNF1). Despite both rat strains having comparable lesions of the nigrostriatal pathway, we observed a difference in the temporal up-regulation of FGF-2 in ventral midbrain samples taken from the side ipsilateral to the lesion. Basic FGF was significantly upregulated in ventral midbrain in SD rats 1 week post-lesion while we did not observe an up-regulation of FGF-2 in the lesioned ventral midbrain of F344BNF1 at this same time point. However, both strains showed a significant up-regulation of FGF-2 in the lesioned ventral midbrain 3 weeks post-lesion. Sprague-Dawley rats also appeared to be more sensitive to the lesion in terms of up-regulating FGF-2 expression. The differences reported here suggest currently unknown genetic differences between these two strains may be important factors for regulating the compensatory release of neurotrophic factors, such as FGF-2, in response to a neurotoxic lesion of the nigrostriatal pathway.

Olfactory ensheathing cells represent an optimal substrate for hippocampal neurons: an in vitro study

Olfactory ensheathing cells (OECs) are cells that display Schwann cell or astrocyte-like properties. They are a source of growth factors and adhesion molecules which play a very important role as neuronal support enhancing cellular survival. Over the past 10 years, OECs have emerged as a leading reparative candidate, when transplanted into the injured spinal cord, having shown significant promise in the regeneration of spinal cord lesions. In this study we assessed the efficacy of OECs on the survival and neurite outgrowth of hippocampal neurons in vitro. Co-cultures of OECs and hippocampal of postnatal rats were successfully established and cells were immunocytochemically characterized. Some hippocampal cultures were added with growth factors, as bFGF, NGF and GDNF. Furthermore, conditioned medium from OECs cultures was used to feed some hippocampal neurons coverslips. Our results show that in co-cultures of hippocampal neurons and OECs the number of neurons and their neurite outgrowth were significantly increased in comparison with controls. Moreover, we showed that NGF and GDNF promoted a more positive effect in both neuronal survival and neurite outgrowth than bFGF. OEC-conditioned media stimulated both the neuronal survival and dense neurite outgrowth. These data indicate that OECs, as a source of growth factors, can promote the survival and the neurite outgrowth of hippocampal neurons in vitro and that bFGF, NGF and GDNF support them differently. Therefore, as OECs and their secreted growth factors appear to exert a neuroprotective effect for functional restoration and for neural plasticity in neurodegenerative disorders, they might be considered an approach for functional recovery.

Protection of dopamine neurons by bone marrow stromal cells

Transplantation of bone marrow stromal cells (BMSC) has recently been demonstrated to provide neuroprotection in animal models of brain injuries such as ischemia and trauma. The present study was undertaken to explore whether BMSC can promote the survival of dopamine (DA) neurons in neuronal insult models in vitro. We also examined whether BMSC can increase the survival rate of embryonic DA neurons grafted into the striatum of a rat model of Parkinson's disease (PD). Treatment with conditioned media derived from BMSC cultures was found to significantly prevent the death of DA neurons in in vitro cell injury models such as serum deprivation and exposure to the neurotoxin 6-OHDA. In a transplantation study, we also found that the survival of grafted DA cells was significantly enhanced by treating donor cells with the conditioned media at the steps of both cell dissociation and implantation. The results suggest that BMSC may secrete diffusible factors able to protect DA neurons against neuronal injuries. Indeed, BMSC expressed mRNA encoding brain-derived neurotrophic factor, fibroblast growth factor-2 and glial cell line-derived neurotrophic factor, all of which have previously been shown to exhibit potent neurotrophic effects on DA cells. Enzyme-linked immunosorbent assay revealed that the cells release these growth factors into culture media. The present data indicate that BMSC may be a potential donor source of cell-based regenerative therapy for PD where the progressive loss of the midbrain DA neurons takes place.

The physiological and pharmacological role of basic fibroblast growth factor in the dopaminergic nigrostriatal system

Basic fibroblast growth factor (FGF-2) is a physiological relevant neurotrophic factor in the nigrostriatal system and hence a promising candidate for the establishment of alternative therapeutic strategies in Parkinson's disease. FGF-2 and its high-affinity receptors (FGFR) display an expression in the developing, postnatal, and adult substantia nigra (SN) and in the striatum. Exogenous application promoted survival, neurite outgrowth and protection from neurotoxin-induced death of dopaminergic (DA) neurons both in vitro and in vivo. In animal models of Parkinson's disease, co-transplantation of fetal DA cells with FGF-2 expressing cells increased survival and functional integration of the grafted DA neurons resulting in improved behavioral performance. Analyzing the physiological function of the endogenous FGF-2 system during development and after neurotoxin-induced lesion revealed for the DA neurons of the SNpc a dependence on FGFR3 signaling during development. In addition, in the absence of FGF-2 an increased number of DA neurons was found, whereas enhanced levels of FGF-2 resulted in a reduced DA cell density. Following neurotoxin-induced lesion of DA neurons, FGF-2-deleted mice displayed a higher extent of DA neuron death whereas in FGF-2 overexpressing mice more DA neurons were protected. According to the data, FGF-2 seems to promote DA neuron survival via FGFR3 during development, whereas absence of this ligand could be compensated by other members of the FGF family. In contrast, in the adult organism, FGF-2 cannot be compensated by other factors under lesion conditions suggesting a central role for this molecule in the nigrostriatal system.

Olfactory ensheathing cells exert a trophic effect on the hypothalamic neurons in vitro

Olfactory ensheathing cells (OECs) constitute an usual population of glial cells sharing properties with both Schwann cells (SC) of peripheral nervous system (PNS) and astrocytes of the central nervous system (CNS). They express a high level of growth factors which play a very important role as neuronal support. Recent evidence in literature suggests that OECs may facilitate axonal regeneration in the injured nervous system. In this study, we developed an in vitro model to evaluate the neurotrophic effect of OECs on the survival and axonal outgrowth of hypothalamic neurons. Co-cultures of OECs and hypothalamus neuronal cells of postnatal rats were successfully established and cells were immunocytochemically characterized. Furthermore, some neuronal cultures were added with NGF, bFGF and GDNF to compare with the co-cultures. Our results indicate that in co-cultures of hypothalamic neurons and OECs, the number of neurons was significantly increased compared to control cultures exhibiting a dense axonal outgrowth. Moreover, we show that NGF promoted a major neuronal survival than bFGF and GDNF, while bFGF and GDNF exerted an evidence axonal and dendritic outgrowth compared to NGF. In conclusion, these data suggest that OECs have the capacity to promote the survival and axonal outgrowth of hypothalamic neurons in vitro and that bFGF, NGF and GDNF differentially support hypothalamic neurons promoting and enhancing the neuronal survival and outgrowth. Therefore, the OECs are a source of growth factors and might be considered a better approach for functional recovery and growth factors might exert a neuroprotective effect in neurodegenerative disorders.

Fibroblast growth factor (FGF)-2 and FGF receptor 3 are required for the development of the substantia nigra, and FGF-2 plays a crucial role for the rescue of dopaminergic neurons after 6-hydroxydopamine lesion

Basic fibroblast growth factor (FGF-2) is involved in the development and maintenance of the nervous system. Exogenous administration of FGF-2 increased dopaminergic (DA) graft survival in different animal models of Parkinson's disease. To study the physiological function of the endogenous FGF-2 system, we analyzed the nigrostriatal system of mice lacking FGF-2, mice overexpressing FGF-2, and FGF-receptor-3 (FGFR3)-deficient mice both after development and after 6-hydroxydopamine lesion. FGFR3-deficient mice (+/-) displayed a reduced number of DA neurons compared with the respective wild type. Whereas absence of FGF-2 led to significantly increased numbers of DA neurons, enhanced amount of the growth factor in mice overexpressing FGF-2 resulted in less tyrosine hydroxylase expression and a reduced DA cell density. The volumes of the substantia nigra were enlarged in both FGF-2(-/-) and in FGF-2 transgenic mice, suggesting an important role of FGF-2 for the establishment of the proper number of DA neurons and a normal sized substantia nigra during development. In a second set of experiments, the putative relevance of endogenous FGF-2 after neurotoxin application was investigated regarding the number of rescued DA neurons after partial 6-OHDA lesion. Interestingly, the results after lesion were directly opposed to the results after development: significantly less DA neurons survived in FGF-2(-/-) mice compared with wild-type mice. Together, the results indicate that FGFR3 is crucially involved in regulating the number of DA neurons. The lack of FGF-2 seems to be (over)compensated during development, but, after lesion, compensation mechanisms fail. The transgenic mice showed that endogenous FGF-2 protects DA neurons from 6-OHDA neurotoxicity.

Nucleofection is the most efficient nonviral transfection method for neuronal stem cells derived from ventral mesencephali with no changes in cell composition or dopaminergic fate

Neuronal progenitor cells (NPCs) play an important role in potential regenerative therapeutic strategies for neurodegenerative diseases, such as Parkinson disease. However, survival of transplanted cells is, as yet, limited, and the identification of grafted cells in situ remains difficult. The use of NPCs could be more effective with regard to a better survival and maturation when transfected with one or more neurotrophic factors. Therefore, we investigated the possibility of transfecting mesencephalic neuronal progenitors with different constructs carrying neurotrophic factors or the expression reporters enhanced green fluorescence protein (EGFP) and red fluorescent protein (DsRed). Different techniques for transfection were compared, and the highest transfection rate of up to 47% was achieved by nucleofection. Mesencephalic neuronal progenitors survived the transfection procedure; 6 hours after transfection, viability was approximately 40%, and the transfected cells differentiated into, for example, tyrosine hydroxylase-positive neurons. Within the group of transfected cells, many progenitors and several neurons were found. To provide the progenitor cells with a neurotrophic factor, different isoforms of fibroblast growth factor-2 were introduced. To follow the behavior of the transfected cells in vitro, functional tests such as the cell viability assay (water-soluble tetrazolium salt assay [WST-1]) and the cell proliferation assay (5-bromo-2'-deoxyuridine-enzyme-linked immunosorbent assay) were performed. In addition, these transfected NPCs were viable after transplantation, expressed tyrosine hydroxylase in vivo, and could easily be detected within the host striatum because of their EGFP expression. This study shows that genetic modification of neural progenitors could provide attractive perspectives for new therapeutic concepts in neurodegenerative diseases.

Schwann cell: A source of neurotrophic activity on cortical glutamatergic neurons in culture

Glial cells secrete numerous soluble molecules that enhance the development and the survival of different neuronal types cultured in vitro. Schwann cells (SC) play an important role as they are the source of different trophic substances and present a great neurotrophic activity. The aim of this study is to investigate the influence of postnatal SC on embryonic glutamatergic neurons. Co-cultures of SC from sciatic nerve of postnatal rats and neurons from rat embryonic cerebral cortex were successfully established, and cells were immunocytochemically characterized using mono and polyclonal antibodies as different glial and neuronal markers. Furthermore, some neuronal cultures were added with Nerve Growth Factor (NGF) and Insulin-like Growth Factor (IGF) to compare to co-cultures. Our results show that SC promote an increase in the number of glutamatergic cortical neurons; moreover, these neurons present an evidence of dense axonal and dendritic outgrowth even when were fed with conditioned medium obtained from SC cultures. In conclusion, our data suggest that substances produced by SC exert a positive effect on central neuron survival and differentiation as indicated by processes of elongation and that this activity is mediated by soluble factors. Therefore, it is possible to consider the SC as a source of growth factors and might be suitable for the development of a neuroprotective effect in neurodegenerative disorders.

New therapeutic approaches to Parkinson's disease including neural transplants

Parkinson's disease (PD) is a common neurodegenerative disorder of the brain and typically presents with a disorder of movement. The core pathological event underlying the condition is the loss of the dopaminergic nigrostriatal pathway with the formation of alpha-synuclein positive Lewy bodies. As a result, drugs that target the degenerating dopaminergic network within the brain work well at least in the early stages of the disease. Unfortunately, with time these therapies fail and produce their own unique side-effect profile, and this, coupled with the more diffuse pathological and clinical findings in advancing disease, has led to a search for more effective therapies. In this review, the authors will briefly discuss the emerging new drug therapies in PD before concentrating on a more detailed discussion on the state of cell therapies to cure PD.

Neuroinflammatory processes in Parkinson's disease

In Parkinson's disease (PD), post-mortem examination reveals a loss of dopaminergic (DA) neurons in the substantia nigra (SN) associated with a massive astrogliosis and the presence of activated microglial cells. Similarly, microglial activation has also been reported to be associated with the loss of DA neurons in animal models of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, annonacine and lipopolysaccharide (LPS). Recent evidence suggests that the disease may progress even when the initial cause of neuronal degeneration has disappeared, raising the possibility that toxic substances released by glial cells could be involved in the propagation of neuronal degeneration. Inhibition of the glial reaction and the inflammatory processes may thus represent a therapeutic target to reduce neuronal degeneration in PD.

Neuroprotective role of astrocytes in cerebral ischemia: focus on ischemic preconditioning

Following focal cerebral ischemia ("stroke") a complex and dynamic interaction of vascular cells, glial cells, and neurons determines the extent of the ensuing lesion. Traditionally, the focus has been on mechanisms of damage, while recently it has become clear that endogenous mechanisms of protection are equally important for the final outcome. Glial cells, in particular astrocytes, have always been viewed as supporters of neuronal function. Only recently a very active role for glial cells has been emerging in physiology and pathophysiology. Not surprisingly, then, specific protective pathways have been identified by which these cells can protect or even help to regenerate brain tissue after acute insults. However, as exemplified by the existence of the glial scar, which forms around lesioned brain tissue, is composed mainly of astrocytes and plays a key role in regeneration failure, it is an oversimplification to assign merely protective functions to astrocytes. The present review will discuss the role of astrocytes in ischemic brain injury with a focus on neuroprotection in general. In this context we will consider particularly the phenomenon of "ischemic tolerance," which is an experimental paradigm helpful in discriminating destructive from protective mechanisms after cerebral ischemia.

"In vitro" postnatal expression of 5-HT7 receptors in the rat hypothalamus: an immunohistochemical analysis

The neurotransmitter serotonin (5-HT) is involved in various physiological functions via multiple receptor subtypes. These have been classified in seven receptor families (5-HT1-7) on the basis of their structures and functional characteristics. In this study, we examined the expression of 5-HT7 receptors in the rat hypothalamic neurons cultured "in vitro" during postnatal development. Neuronal cultures were prepared from postnatal pups P2, P3 and P5, were treated with bFGF and processed by means of immunofluorescence technique using a polyclonal 5-HT7 receptor antibody. In P2, we found a low density of 5-HT7 labeled hypothalamic bFGF-treated neurons and no 5-HT7 immunolabeling in control cultures; in P3, a moderate number of bFGF-treated neurons were observed but they were not bright. No 5-HT7 immunolabeling was found in controls. In P5, a heavy labeling of small sized bipolar neurons was seen in bFGF-treated neurons, while in control cultures, few labeled neurons with a low stained density were observed. These results suggest that 5-HT7 receptors in hypothalamic neurons begin to appear at P5 and then could be involved in many physiological implications that are not exerted at P2 and P3. This indicates that 5-HT7 receptors have a potential significance in the rat hypothalamus during early postnatal development.

Fibroblast growth factor-20 promotes the differentiation of Nurr1-overexpressing neural stem cells into tyrosine hydroxylase-positive neurons

Stem cells are currently considered as alternative cell resources for restorative transplantation strategies in Parkinson's disease. However, the mechanisms that induce differentiation of a stem cell toward the dopaminergic phenotype are still partly unknown thus hampering the production of dopaminergic neurons from stem cells. In the past, FGF-20 has been found to promote the survival of ventral mesencephalic (VM) dopaminergic (DA) neurons in culture. We hereby provide evidence that FGF-20, a growth factor of the FGF family, is expressed in the adult and 6-OHDA-lesioned striatum and substantia nigra, but is not expressed by VM glia or DA neurons, suggesting that FGF-20 may work on DA neurons in a paracrine- or target-derived manner. We also found that co-culture of Nurr1-NSCs with Schwann cells overexpressing FGF-20 induced the acquisition of a neuronal morphology by the NSCs and the expression of tyrosine hydroxylase (TH) as assessed by immunocytochemistry, cell ELISA, and Western blot analysis. RT-PCR showed, that both, Schwann cells and Nurr1-NSCs (differentiated or not), expressed the FGF-1 receptor suggesting that both direct and indirect actions of FGF-20 are possible. We show that differentiated Nurr1 cells retained both neuronal morphology and TH expression after transplantation into the striatum of 6-OHDA-lesioned postnatal or adult rats, but that neuritogenesis was only observed after postnatal grafts. Thus, our results suggest that FGF-20 promotes the differentiation of Nurr1-NSCs into TH-positive neurons and that additional factors are required for the efficient differentiation of DA neurons in the adult brain.

Olfactory ensheathing cell transplantation restores functional deficits in rat model of Parkinson's disease: a cotransplantation approach with fetal ventral mesencephalic cells

Different strategies have been worked out to promote survival of transplanted fetal ventral mesencephalic cells (VMCs) using trophic and nontrophic support. Olfactory ensheathing cells (OECs) express high level of growth factors including NGF, bFGF, GDNF, and NT3, which are known to play important role in functional restoration or neurodegeneration. In the present investigation, an attempt has been made to study functional restoration in 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD) following cotransplantation of VMC and OECs (cultured from olfactory bulb, OB) in striatal region. The functional restoration was assessed using neurobehavioral, neurochemical, and immunohistochemical approach. At 12 weeks, post-transplantation, a significant recovery (P < 0.001) in D-amphetamine induced circling behavior (73%), and spontaneous locomotor activity (SLA, 81%) was evident in cotransplanted animals when compared with 6-OHDA-lesioned animals. A significant restoration (P < 0.001) in [3H]-spiperone binding (77%), dopamine (DA) (82%) and 3,4-dihydroxy phenyl acetic acid (DOPAC) level (75%) was observed in animals cotransplanted with OECs and VMC in comparison to lesioned animals. A significantly high expression and quantification of tyrosine hydroxylase (TH)-positive cells in cotransplanted animals further confirmed the supportive role of OECs in viability of transplanted dopaminergic cells, which in turn may be helping in functional restoration. This was further substantiated by our observation of enhanced TH immunoreactivity and differentiation in VMC cocultured with OECs under in vitro conditions as compared to VMC alone cultures. The results suggest that cotransplantation of OECs and VMC may be a better approach for functional restoration in 6-OHDA-induced rat model of Parkinson's disease.

Enhanced survival, reinnervation, and functional recovery of intrastriatal dopamine grafts co-transplanted with Schwann cells overexpressing high molecular weight FGF-2 isoforms

Dopaminergic (DA) micrografts were co-transplanted with Schwann cells (SC) overexpressing 18 kDa and 21/23 kDa FGF-2 into the caudate-putamen unit (CPu) of unilaterally 6-hydroxydopamine-lesioned rats. We report here that SC engineered to overexpress FGF-2 promoted DA-graft-induced restoration, whether co-transplanted at the same site or grafted at a second more distant site within the CPu. In addition, the 21/23 kDa FGF-2 isoforms resulted in a significantly better reinnervation and survival of dopaminergic micrografts when compared to the 18-kDa FGF-2 isoform. However, this effect was not that distinct on functional recovery due to, for example, ceiling effects. One main finding of this study was the influence of the gene promotor on DA survival, respectively, vector-mediated trophism. Therefore, comparisons in terms of survival between 18 kDa and higher molecular weight (HMW) FGF-2 are complicated in the mixed grafted experiments. Furthermore, the first demonstration of the presence of the 21/23 kDa FGF-2 isoforms in the nigrostriatal system and their potent neurotrophic in vivo activities, as shown in the present study, suggest (I) a physiological role of these proteins for dopaminergic neurons and (II) a restorative potential under normal as well as regenerative processes. However, FGF-2-mediated effects are more pronounced after co-transplantation with SC/DA cells mixed in one suspension at the same implantation side than in the side-by-side approach with a spatially and temporally separated transplantation of SC (day 1) and DA-cells (day 3). These findings indicate the necessity of direct contact between FGF-2 and DA-neurons, further elucidate the neurotrophic role of FGF-2 for DA-neurons and highlight the differential restorative potentials of its respective isoforms. We propose that administration of HMW FGF-2 may be used to improve function in the rat Parkinson's disease model.

Alterations in the expressions of mRNA for GDNF and its receptors in the ventral midbrain of rats exposed to subchronic phencyclidine

Phencyclidine (PCP) produces schizophrenia-like symptoms in normal humans. This suggests that the dysfunction of glutamatergic neurotransmission may play an important role in the pathology of schizophrenia. However, PCP also exerts its effect on the mesolimbic dopamine (DA) system and modulates DA function in the brain, the abnormality of which is proposed to be a main pathology of schizophrenia. Recently, glial cell-line derived neurotrophic factor (GDNF) has been shown to play a protective role for DA neurons against neurotoxic injuries and maintaining DA function in the brain. We hypothesized that subchronic PCP may alter the function of GDNF in the ventral midbrain, where DA cell bodies are localized. Male Wistar rats were injected intraperitoneally with PCP daily for 10 days at 5 or 10 mg/kg, and their brains were removed 24 h after the last injection. The expressions of GDNF and its receptor (GFRalpha-1 and c-ret) mRNAs in the substantia nigra compacta (SNC) and ventral tegmental area (VTA) were determined by non-radioactive in situ hybridization, and those of GDNF and c-ret mRNA were found to be increased after the PCP subchronic administration. No significant changes, however, were observed in the expressions of GFRalpha-1 and basic fibroblast growth factor. These results suggest that subchronic PCP may modulate the function of the GDNF system, which exerts a trophic action on DA neurons in the ventral midbrain.

Effect of glial cell line‐derived neurotrophic factor (GDNF) co‐transplantation with fetal ventral mesencephalic cells (VMC) on functional restoration in 6‐hydroxydopamine (6‐OHDA) lesioned rat model of Parkinson's disease: neurobehavioral, neurochemical and immunohistochemical studies

Among trophic factors already known, glial cell line-derived neurotrophic factor (GDNF) and other members of its family have potent and specific action on dopaminergic neurons. In the present investigation an attempt has been made to validate the role of GDNF co-transplantation with fetal ventral mesencephalic cells (VMC) on functional viability and restoration using neurobehavioral, neurochemical and immunohistochemical parameters at 6 weeks post-transplantation in 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease (PD). A significant restoration (P<0.01) in D-amphetamine induced rotations, spontaneous and apomorphine induced locomotor activity in rats co-transplanted with VMC and GDNF was observed as compared to VMC alone transplanted rats. Level of dopamine (DA), 3,4-dihydroxy-phenyl acetic acid (DOPAC) and dopamine D2 (DA-D2) receptors in the caudate putamen (CPu) were significantly (P<0.001) restored in co-transplanted group as compared to VMC transplanted or GDNF administered animals. The functional viability of transplanted VMC was confirmed by tyrosine hydroxylase (TH) expression and quantification of TH-positive cells by image analysis revealed a significant restoration in TH-IR fibers density as well as TH-IR neurons counts in co-transplanted animals over VMC transplanted animals. Results suggest that co-transplantation of VMC and GDNF may be a better approach towards functional restoration in 6-OHDA lesioned rat model of Parkinson's disease.

Gene therapy for experimental brain tumors using a xenogenic cell line engineered to secrete hIL-2

Local delivery of cytokines has been shown to have a potent anti-tumor activity against a wide range of malignant brain tumors. In this study, we examined the feasibility and efficacy of using a rat endothelial cell line (NTC-121) transfected with the human interleukin-2 (IL-2) gene in treating experimental murine CNS tumors. The NTC-121 cells were injected intracranially in C57BL/6 mice (N = 10/group) along with non-irradiated, non-transfected B16/F10 (wild type) melanoma cells. Sixty percent of mice treated with IL-2 (p < 0.001 vs. control) were long-term survivors (LTS) of > 120 days. Control animals that received only wild type cells had a median survival of 18 days (range 15-20). Histopathological examination of brains from animals sacrificed at different times showed no tumor growth in the non-irradiated NTC-121 group, moderate (1-2 mm) tumor growth in the irradiated group, and gross tumor invasion (>2 mm) and tissue necrosis in the control group. Moreover, animals treated with IL-2 showed an accumulation of CD8+ T cells around the site of the injected tumor. The use of a xenogenic cell line to deliver hIL-2 stimulates a strong immunologic cytotoxic anti-tumor response that leads to significant prolongation of survival in mice challenged with the B16/F10 intracranial melanoma tumor. Our findings demonstrate that the use of a xenogenic cell line can provide a potent vehicle for the delivery of gene therapy and may therefore represent a new approach for brain tumor therapy.

Sphingosine 1-phosphate induces the production of glial cell line-derived neurotrophic factor and cellular proliferation in astrocytes

Sphingosine 1-phosphate (S1P) is a platelet-derived bioactive sphingolipid that evokes a variety of biological responses. To understand the role of S1P in the central nervous system, we have examined the effect of S1P on the production of glial cell line-derived neurotrophic factor (GDNF) and growth regulation of cortical astrocytes from rat embryo. Moreover, we examined the possibility that the expression of GDNF is regulated differently in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) than in those from Wistar kyoto rats (WKY). The mRNA expression was quantitated by RT-PCR based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay. S1P induced the expression of GDNF mRNA and the production of GDNF protein in a dose-dependent manner in WKY astrocytes. Moreover, S1P increased cell numbers and induced the proliferation of astrocytes. In addition, the level of mRNA expression and protein production of GDNF was significantly lower in SHRSP than WKY astrocytes following exposure to S1P. These findings revealed that S1P augments GDNF protein production and cellular growth in astrocytes. Also, our results indicate that production in SHRSP astrocytes was attenuated in response to S1P compared with that observed in WKY. We conclude that S1P specifically triggers a cascade of events that regulate the production of GDNF and cell growth in astrocytes. Our results also suggest that the reduced expression of GDNF caused by S1P is a factor in the stroke proneness of SHRSP.

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.

Dynamic expression of bFGF and TGFbeta2 in glomus cell grafts of carotid body in rat model of Parkinson disease

To investigate the changes in the expression of basic fibroblast growth factor (bFGF) and transforming growth factor beta 2 (TGFbeta2) in glomus cell grafts of carotid body in the rat model of 6-hydroxydopamine-induced Parkinson disease, immunohistochemical staining of bFGF and TGFbeta2 in the sections of striate body was done on the 2nd, 4th and 12th week after transplantation. The results showed that on the 2nd week after transplantation, bFGF and TGFbeta2 were not detectable in the glumous cell grafts. On the 4th week after graft, bFGF and TGFbeta2 immunoreactivity was increased within the grafts and at the graft-host interface but was restricted only to astrocytes. In the striatum surrounding the graft, bFGF was expressed persistently, while TGFbeta2 showed transient expression. It was suggested that the transient expression of TGFbeta2 was likely due more to the trauma imposed by the graft procedure than to an intrinsic. The deficiency in astrocytic bFGF early after graft may be responsible for the poor survival of grafted glomus cells of carotid body.

Expression of voltage-dependent calcium channels in the embryonic rat midbrain

The diversity of expression of high-voltage activated voltage-dependent calcium channels (VDCC) was investigated with whole-cell voltage-clamp recordings from dissociated embryonic rat ventral mesencephalic cells over a 7-day culture period. Cell phenotype was identified post-recording by fluorescent immunocytochemistry as tyrosine hydroxylase positive (TH+) or glutamic acid decarboxylase positive (GAD+). Both TH+ and GAD+ cells displayed high-threshold calcium (Ca(2+)) currents activated by depolarisations positive to -60 mV. In both cell types, pharmacological dissection using selective VDCC inhibitors, omega-agatoxin IVA (Aga IVA), omega-conotoxin GVIA (GVIA) and nifedipine demonstrated the existence of P/Q-, N- and L-type VDCC, respectively. The remaining residual current could be blocked by cadmium. It was found that the contribution to the whole-cell current by the N-type channel was greater in TH+ cells than GAD+ cells at each time point examined, whilst the contribution to the whole-cell current by the L-type channel was greater in GAD+ cells than TH+ cells. However, over the 7-day culture period, the expression of VDCC types in both cell phenotypes changed in a similar fashion, with the contribution to the whole-cell current from the N-type current decreasing, and the contribution from the R-type current increasing. Our data could provide new insights into a range of neurodevelopmental mechanisms related to Ca(2+) homeostasis in developing mesencephalic neurons.

Models of repair mechanisms for future treatment modalities of Parkinson's disease

Parkinson's disease is one of the most likely neurological disorders to be fully treatable by drugs and new therapeutic modalities. The age-dependent and multifactorial nature of its pathogenesis allows for many strategies of intervention and repair. Most data indicate that the selectively vulnerable dopaminergic neurons in the substantia nigra of patients that have developed Parkinson's disease can be modified by protective and reparative therapies. First, the oxidative stress, protein abnormalities, and cellular inclusions typically seen could be dealt with by anti-oxidants, trophic factors, and proteolytic enhancements. Secondly, if the delay of degeneration is not sufficient, then immature dopamine neurons can be placed in the parkinsonian brain by transplantation. Such neurons can be derived from stem cell sources or even stimulated to repair from endogenous stem cells. Novel molecular and cellular treatments provide new tools to prevent and alleviate Parkinson's disease.

Temporal changes in the neurotrophic environment of the denervated striatum as determined by the survival and outgrowth of grafted fetal dopamine neurons

There is growing evidence that the neurotrophic environment of the denervated striatum may change with time following a lesion of the nigrostriatal pathway in young adult rats. To test this hypothesis, we implanted fetal dopamine grafts into the striatum at several different time points relative to the nigrostriatal pathway lesion and allowed the grafts to integrate with the host for a period of 1 month; subsequently, we observed the function and morphology of the dopamine grafts. Fetal grafts were implanted at the following time points relative to the lesion: 1 week before (-1 Week), at the same time (Week 0), 1 week after (1 Week), 4 weeks after (4 Weeks), or 12 weeks after (12 Weeks). Amphetamine-induced rotational behavior was assessed 4 weeks after grafting for all groups. Rotational scores indicate that grafts for the 1 Week group showed the greatest reversal of amphetamine-induced rotational behavior that was also significantly greater than the scores for the -1 Week group. Morphological analysis revealed that grafts in the Week 0, 1 Week and 4 Weeks groups showed a significantly larger area of tyrosine hydroxylase-positive (TH+) fiber outgrowth than in the -1 Week group, while fiber outgrowth for the 12 Weeks group was significantly lower than for the 1 Week group. Cell count analysis for TH+ neurons within the graft indicate a significantly greater number of TH+ neurons in grafts for the 1 Week group than in grafts for the -1 Week. The results of this study suggest that neurotoxic lesions may induce a compensatory increase in neurotrophic activity within the denervated striatum of young rats that is conducive to the survival and outgrowth of fetal dopamine grafts. These data also correlate well with reports that the expression of several specific dopaminergic neurotrophic factors within the striatum increase following a neurotoxic lesion of the nigrostriatal pathway in young adult rats.

Differential regulation of glial cell line-derived neurotrophic factor (GDNF) mRNA expression during hypoxia and reoxygenation in astrocytes isolated from stroke-prone spontaneously hypertensive rats

Glial cell line-derived neurotrophic factor (GDNF) plays several important roles in the survival and recovery of mature neurons during ischemia. We examined the possibility that the expression of GDNF mRNA and the release of GDNF protein are regulated differentially in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) compared with those from Wistar Kyoto rats (WKY) during hypoxia and reoxygenation (H/R) and after exposure to glutamate and hydrogen peroxide (H(2)O(2)). The mRNA expression was quantitated by reverse transcription-polymerase chain reaction (RT-PCR) based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real-time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay (ELISA). GDNF mRNA expression and GDNF protein release at normoxia were greater in SHRSP than in WKY astrocytes. During H/R, however, the mRNA expression and protein release tended to be reduced in SHRSP compared with WKY. Glutamate and H(2)O(2) induced the expression of GDNF mRNA and the release of GDNF protein in both WKY and SHRSP in a dose-dependent manner. Levels of GDNF mRNA and protein in SHRSP were significantly lower than in WKY. These findings indicate that GDNF production in SHRSP astrocytes was low in response to H/R, glutamate, and H(2)O(2), compared with that observed in WKY. We conclude that the attenuated production of GDNF in astrocytes is involved in neuronal vulnerability in SHRSP during H/R, as GDNF production, which is stimulated by glutamate and H(2)O(2), is closely related to the protective effect against H/R-mediated neurotoxicity.

The high molecular weight fibroblast growth factor-2 isoforms (21,000 mol. wt and 23,000 mol. wt) mediate neurotrophic activity on rat embryonic mesencephalic dopaminergic neurons in vitro

Basic fibroblast growth factor is expressed in different isoforms which display tissue and species specificity and are differentially regulated during development and after experimental interventions. The differential regulation of the fibroblast growth factor-2 isoforms may indicate specific activities and functions of these molecules. The characterization of fibroblast growth factor-2 effects, however, is almost exclusively based on studies including the 18,000 mol. wt isoform. It is not yet known whether the high molecular weight fibroblast growth factor-2 isoforms (21,000 mol. wt, 23,000 mol. wt) exert similar or distinct activities in the nervous system. In the present study, we investigated the effects of the high molecular weight isoforms on dissociated rat mesencephalic dopaminergic neurons. For this purpose, recombinant fibroblast growth factor-2 isoforms, prepared in a histidine expression system, were administered on dopaminergic neurons in vitro, and Schwann cells over-expressing the high molecular weight isoforms were co-cultured with dopaminergic neurons. This is the first demonstration to show that the high molecular weight isoforms mediate a neurotrophic activity. Exogenous high molecular weight fibroblast growth factor-2 isoforms stimulated the survival of embryonic mesencephalic dopaminergic neurons and protected them from 6-hydroxydopamine neurotoxicity. In addition, co-culture of dopaminergic neurons with high molecular weight fibroblast growth factor-2 over-expressing Schwann cells revealed an increased survival and neurite formation of the mesencephalic dopaminergic neurons. These results suggest that the high molecular weight fibroblast growth factor-2 isoforms may serve as a new tool for the treatment of Parkinson's disease.

Inhibition of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor expression reduces dopaminergic sprouting in the injured striatum

After striatal injury, sprouting dopaminergic fibres grow towards and intimately surround wound macrophages which, together with microglia, express the dopaminergic neurotrophic factors glial cell line-derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF). To evaluate the importance of these endogenously secreted neurotrophic factors in generating striatal peri-wound dopaminergic sprouting, the peri-wound expression of BDNF or GDNF was inhibited by intrastriatal infusion of antisense oligonucleotides for 2 weeks in mice. Knock-down of both BDNF and GDNF mRNA and protein levels in the wounded striatum were confirmed by in situ hybridization and enzyme-linked immunosorbent assay, respectively. Dopamine transporter immunohisto-chemistry revealed that inhibition of either BDNF or GDNF expression resulted in a marked decrease in the intensity of peri-wound sprouting. Quantification of this effect using [H3]-mazindol autoradiography confirmed that peri-wound sprouting was significantly reduced in mice receiving BDNF or GDNF antisense infusions whilst control infusions of buffered saline or sense oligonucleotides resulted in the pronounced peri-wound sprouting response normally associated with striatal injury. BDNF and GDNF thus appear to be important neurotrophic factors inducing dopaminergic sprouting after striatal injury.

Time course of apoptotic cell death within mesencephalic cell suspension grafts: implications for improving grafted dopamine neuron survival

The vast majority ( congruent with 90%) of embryonic mesencephalic dopamine (DA) neurons die following transplantation to the striatum. Recent reports indicate that at least a subpopulation of grafted cells undergo apoptotic cell death at early times following implantation. This study examines the temporal pattern and magnitude of apoptotic cell death following the implantation of mesencephalic cell suspension grafts. Two techniques, a modified terminal deoxynucleotide-mediated nucleotide end labeling (TUNEL) technique and cresyl violet staining, are used to assess apoptotic cell death by detection of its biochemical and morphological identifiers, respectively. Male, Fischer 344 rats were examined at 1, 4, 7, and 28 days following implantation of embryonic day 14 (E14) ventral mesencephalic cells to the DA-denervated striatum. Results indicate that the overwhelming majority of apoptotic cell death occurs within the first 7 days after transplantation. However, the impact of the apoptosis that occurs over the first week following grafting only appears to limit grafted tyrosine hydroxylase-immunoreactive (THir) neuron survival during the first 4 days. No significant differences between the survival rates of THir neurons at 4 days after grafting and at 28 days after grafting were found. Therefore, it appears that the critical interval during which an estimated 90% of grafted DA neurons die is during the first 4 days postimplantation and that a major contributor to this cell death is apoptosis.

Characterization of the dopamine defect in primary cultures of dopaminergic neurons from hypoxanthine phosphoribosyltransferase knockout mice

Lesch-Nyhan disease (LND) is an X-linked metabolic disorder caused by lack of activity of the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT) and characterized by hyperuricemia and debilitating neurological manifestations. The mechanisms underlying the neuropathology are not well understood and the principal neurochemical lesion characterized to date is a deficiency of the dopamine system in the basal ganglia. To facilitate the study of mechanism(s) by which HPRT deficiency causes the dopamine defect, we have compared the survival and dopamine phenotype of primary cultures of dopamine neurons derived from HPRT-deficient mice with the dopaminergic neurons from wild-type mice. The survival of dopaminergic neurons from both sources was promoted to an equal extent by glial cell line-derived neurotrophic factor (GDNF), a potent survival factor for dopamine neurons in vitro. Although the survival of the HPRT-deficient neurons was indistinguishable from that of cells derived from wild-type counterparts, the HPRT-deficient cells demonstrated a persistent deficiency of dopamine content and dopamine uptake with increasing neuritic differentiation, indicating that GDNF does not restore the normal phenotype in HPRT-deficient dopamine neurons despite its well-known protective and regenerative properties in several neurodegeneration models. Nevertheless, the demonstration that GDNF trophic support promotes the survival of these dopaminergic neurons will facilitate gaining a better understanding of the neuropathological mechanisms of LND by allowing a more extensive analysis of the cells central to the Lesch-Nyhan phenotype, the dopaminergic neurons of the basal ganglia.

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.

Dopamine cells in nigral grafts differentiate prior to implantation

The yield of surviving dopamine cells in nigral grafts is typically low. It is unclear whether the dopamine neurons that do survive are postmitotic at the time of implantation, or are precursor cells that differentiate into dopamine neurons following transplantation in the host brain. We have therefore compared the survival of dopamine neurons in grafts that have been labelled with BrdU at different times prior to or following implantation in order to identify those cells that undergo final cell division at each stage of the procedure. Seven groups of rats were prepared with unilateral nigrostriatal lesions. Three groups received nigral grafts derived from E14 embryos labelled with BrdU in utero on either E12, E13 or E14 days of embryonic age (the E14 injection made 2 h prior to preparation of the graft cell suspension). Three further groups received nigral grafts from untreated E14 embryos, and then dividing cells within the grafts were labelled by injection of BrdU into the host lateral ventricle, 2 h, 1 day or 2 days after implantation (equivalent to E14, E15 and E16 days of embryonic age). The control group received standard (unlabelled) E14 grafts. Five weeks after the transplantation surgery, the host brains were processed using double immunohistochemical techniques to detect tyrosine hydroxylase (TH)-positive neurons which had incorporated BrdU. In the grafts labelled with BrdU prior to implantation, there was an increasing proportion of double-labelled cells (out of the total TH-positive cells surviving in the grafts) with birth dates on E12, E13 and E14 (1%, 12% and 10% per day, respectively). By contrast, grafts labelled following implantation, although containing many dividing neurons, had very few of these BrdU-labelled cells expressing a dopaminergic phenotype; < 1% surviving TH-positive cells were double-labelled from the 2 h post-transplant injection, and < 0.1% from each subsequent injection. This suggests not only that the great majority of TH-positive neurons in nigral grafts were already differentiated at the time of implantation, but also that transplantation of E14 ventral mesencephalic tissue either kills dopaminergic precursors or (more likely in our opinion) prevents their differentiation into a dopaminergic phenotype. Precursor cells that would differentiate into dopaminergic neurons beyond E14 if left in situ in the intact ventral mesencephalon do not readily differentiate into mature dopamine neurons following transplantation. If we are to enhance yields of functional dopamine-rich transplants, then we must identify strategies both to protect predifferentiated dopamine neurons in the grafts and to promote differentiation of a dopaminergic phenotype in precursor cells that continue to divide within the grafts following transplantation into an adult host environment.

Early hypoxia modulates the phenotype of dopaminergic cells in rat di- and mesencephalic cell cultures and induces a higher vulnerability of non-dopaminergic neurons to a second hypoxic exposure

To investigate long-term effects of hypoxia on a cellular level, di- and mesencephalic cell cultures were exposed to hypoxia on in vitro day 2 (incubation in culture medium, pO2 = 10-20 mmHg, 24 h) and on in vitro day 13 (incubation in an electrolyte solution, pO2 = 10-20 mmHg, 8 h). The numbers of neuron-specific enolase immuno-reactive (NSE-IR) and tyrosine hydroxylase immuno-reactive (TH-IR) neurons and the levels of dopamine, its main metabolites and the spontaneous and potassium-stimulated DA release were determined on DIV 15. Hypoxia on DIV 2 did not affect the numbers of NSE-IR and TH-IR neurons, but increased the dopamine content and dopamine release by about 100% in both di-and mesencephalic cultures. In addition, this hypoxia increased the vulnerability of non-TH-IR neurons to the second hypoxic episode applied during more advanced stages of the culture development on DIV 13. On the contrary, hypoxia exposure did not affect the vulnerability of TH-IR cells.

Enhancement of graft survival and sensorimotor behavioral recovery in rats undergoing transplantation with dopaminergic cells exposed to glial cell line-derived neurotrophic factor

The goal of this study was to investigate the ability of fetal dopaminergic neurons to improve complex sensorimotor behavior.

The authors obtained ventral mesencephalic tissue from 14-day-old rat fetuses. The cells were exposed to glial cell line-derived neurotrophic factor (GDNF) prior to transplantation into rats with unilateral 6-hydroxydopamine lesions of the dopaminergic nigrostriatal pathway. Animals that received 400,000 cells exposed to GDNF demonstrated significant improvement in contralateral forelimb function and showed improvement in rotational behavior faster than animals that received cells not exposed to GDNF. Increasing the number of implanted cells to 800,000 exposed to GDNF did not result in any additional improvement in functional recovery.

As neural grafting procedures in the nervous system evolve and genetically engineered cells or stem cells replace fetal tissue, crucial questions about cell number and trophic regulation will need to be addressed. This study demonstrates that grafting of 400,000 cells exposed to GDNF before transplantation has a beneficial effect in the restoration of complex sensorimotor behavior.

Lack of effect of short-term depletion of plasma complement C3 on the survival of syngeneic dopaminergic neurons following grafting into the intact rat striatum

Metabolically compromised cells may be subject to complement-mediated cytotoxicity. The aim of this study was to clarify to what extent plasma complement C3 might contribute to the low survival (5-20%) of grafted dopaminergic neurons. The survival of intrastriatal cell suspension grafts of syngeneic dopaminergic, tyrosine hydroxylase (TH)-containing neurons was compared in rats subjected to short-term i.v. treatment with 1) cobra venom factor (CVF), or 2) placebo treatment. Depletion of plasma complement C3 by CVF was confirmed by crossed immunoelectrophoresis. With 159 +/- 37 (mean +/- SEM) TH-immunoreactive and 154 + /- 40 TH mRNA-expressing neurons in the CVF-treated rats (n = 9), and 117 +/- 34 TH-immunoreactive and 160 +/- 49 TH mRNA-expressing neurons in placebo rats (n = 6), the CVF treatment did not increase the survival of the grafted dopaminergic neurons. Similarly, CVF had no apparent effect on the astroglial, microglial, or oligodendroglial cell response within and around the graft. The data indicate that depletion of plasma complement C3 at the time of grafting has no effect on the long-term survival of syngeneic ventral mesencephalic dopaminergic neuronal grafts.

Excitotoxicity plays a role in the death of tyrosine hydroxylase- immunopositive nigral neurons cultured in serum-free medium

We studied the effects of different amino acid receptor antagonists and a calcium (Ca2+) channel blocker on the survival of embryonic tyrosine hydroxylase (TH)-immunopositive nigral neurons grown under serum-free culture conditions. Ventral mesencephalic neurons were cultivated for 2 or 7 days. Following serum withdrawal on day 2, some cultures were treated with different concentrations of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine hydrogen maleate (MK-801), the competitive NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid, the competitive kainate/quisqualate receptor antagonist 6,7-dinitroquinoxaline-2, 3-dione, and the Ca2+ channel blocker flunarizine. Treatment with MK-801 or flunarizine increased the survival of TH-positive neurons after serum deprivation. These findings suggest a possible role for excitotoxicity in dopaminergic cell death which can be prevented by blocking the NMDA receptor or by inhibiting Ca2+ entry through voltage-gated channels.