Mesencephalic human neural progenitor cells transplanted into the neonatal hemiparkinsonian rat striatum differentiate into neurons and improve motor behaviour

Neural stem cell transplantation is a promising strategy for the treatment of neurodegenerative diseases. To evaluate the differentiation potential of human neural progenitor cells (hNPCs) as a prerequisite for clinical trials, we intracerebrally transplanted in vitro expanded fetal mesencephalic hNPCs into hemiparkinsonian rats. On postnatal day one (P1), 17 animals underwent a unilateral intraventricular 6-hydroxydopamine injection into the right lateral ventricle. At P3, animals (n = 10) received about 100,000 hNPCs (1 microL) in the right striatum. Five weeks after birth, animals underwent behaviour tests prior to fixation, followed by immunohistochemistry on brain slices for human nuclei, glial fibrillary acidic protein, S100beta, neuronal nuclei antigen, neuron-specific enolase and tyrosine hydroxylase. Compared with the apomorphine-induced rotations in the lesioned-only group (7.4 +/- 0.5 min(-1)), lesioned and successfully transplanted animals (0.3 +/- 0.1 min(-1)) showed a significant therapeutic improvement. Additionally, in the cylinder test, the lesioned-only animals preferred to use the ipsilateral forepaw. Conversely, the lesioned and transplanted animals showed no significant side bias similar to untreated control animals. Transplanted human nuclei-immunoreactive cells were found to survive and migrate up to 2000 microm into the host parenchyma, many containing the pan-neuronal markers neuronal nuclei antigen and neuron-specific enolase. In the striatum, tyrosine hydroxylase-immunoreactive somata were also found, indicating a dopaminergic differentiation capacity of transplanted hNPCs in vivo. However, the relative number of tyrosine hydroxylase-immunoreactive neurons in vivo seemed to be lower than in corresponding in vitro differentiation. To minimize donor tissue necessary for transplantation, further investigations will aim to enhance dopaminergic differentiation of transplanted cells in vivo.

Increased cell suspension concentration augments the survival rate of grafted tyrosine hydroxylase immunoreactive neurons

The poor survival rate (5-20%) of grafted embryonic dopamine (DA) neurons is one of the primary factors preventing cell replacement from becoming a viable treatment for Parkinson's disease. Previous studies have demonstrated that graft volume impacts grafted DA neuron survival, indicating that transplant parameters influence survival rates. However, the effects of mesencephalic cell concentration on grafted DA neuron survival have not been investigated. The current study compares the survival rates of DA neurons in grafts of varying concentrations. Mesencephalic cell suspensions derived from E14 Fisher 344 rat pups were concentrated to 25,000, 50,000, 100,000 and 200,000 cells/microl and transplanted into two 0.5 microl sites in the 6-OHDA-denervated rat striatum. Animals were sacrificed 10 days and 6 weeks post-transplantation for histochemical analysis of striatal grafts. The absolute number of DA neurons per graft increased proportionally to the total number of cells transplanted. However, our results show that the 200,000 cells/microl group exhibited significantly higher survival rates (5.48+/-0.83%) compared to the 25,000 cells/microl (2.81+/-0.39%) and 50,000 cells/microl (3.36+/-0.51%) groups (p=0.02 and 0.03, respectively). Soma size of grafted DA neurons in the 200,000 cells/microl group was significantly larger than that of the 25,000 cells/microl (p<0.0001) and 50,000 cells/microl groups (p=0.004). In conclusion, increasing the concentration of mesencephalic cells prior to transplantation, augments the survival and functionality of grafted DA neurons. These data have the potential to identify optimal transplantation parameters that can be applied to procedures utilizing stem cells, neural progenitors, and primary mesencephalic cells.

The functional impact of the intrastriatal dopamine neuron grafts in parkinsonian rats is reduced with advancing disease

Clinical trials involving intrastriatal transplants of human embryonic mesencephalic tissue have provided proof-of-principle that nigral dopamine (DA) neurons can survive and functionally integrate into the host neural circuitry. However, the degree of graft-induced symptomatic relief differs significantly between the patients. This variability has led to investigations aimed at identifying factors that could affect the clinical outcome. The extent and pattern of dopaminergic denervation in the brain may be one of the major determinants of the functional outcome after intrastriatal DA cell grafts. Here, we report that in animals subjected to an intrastriatal 6-hydroxydopamine lesion of the striatal dopaminergic afferent, the integrity of the host dopaminergic innervation outside the areas innervated by the graft is critical for optimal function of DA neurons placed in the striatum. Established graft-induced functional recovery, as assessed in the stepping and cylinder tests, was compromised in animals in which the dopaminergic lesion was extended to include also the medial and ventral striatum as well as the cortical and limbic DA projections. Poor clinical outcome after transplantation may, thus, at least in part, be caused by dopaminergic denervation in areas outside the graft-innervated territories, and similarly beneficial effects initially observed in patients may regress if the degeneration of the host extrastriatal DA projection systems proceeds with advancing disease. This would have two implications: first, patients with advanced disease involving the ventral striatum and/or nonstriatal DA projections would be unlikely to respond well to intrastriatal DA grafts and, second, to retain the full benefit of the grafts, progression of the disease should be avoided by, for example, combining cell therapy with a neuroprotective approach.

Effects of ex vivo transduction of mesencephalic reaggregates with bcl-2 on grafted dopamine neuron survival

Survival rates of dopamine (DA) neurons grafted to the denervated striatum are extremely poor (5-20%). Gene transfer of survival promoting factors, such as the anti-apoptotic protein bcl-2, to mesencephalic DA neurons prior to transplantation (ex vivo transduction) offers a novel approach to increase graft survival. However, specific criteria to assess the efficacy of various vectors must be adhered to in order to reasonably predict successful gene transfer with appropriate timing and levels of protein expression. Cell culture results utilizing three different herpes simplex virus (HSV) vectors to deliver the reporter beta-galactosidase gene (lacZ) indicate that transduction of mesencephalic cells with a helper virus-free HSV amplicon (HF HSV-TH9lac) that harbors the 9-kb tyrosine hydroxylase (TH) promoter to drive lacZ gene expression elicits the transduction of the highest percentage (approximately 50%) of TH-immunoreactive (THir) neurons without significant cytotoxic effects. This transduction efficiency and limited cytotoxicity was superior to that observed following transduction with helper virus-containing HSV (HC HSVlac) and helper virus-free HSV amplicons (HF HSVlac) expressing lacZ under the transcriptional control of the HSV immediate-early 4/5 gene promoter. Subsequently, we assessed the ability of HSV-TH9lac and the bcl-2 expressing HSV-TH9bcl-2 amplicon to transduce mesencephalic reaggregates. Although an increase in bcl-2 and beta-galactosidase protein was induced by transduction, amplicon-mediated overexpression of bcl-2 did not lead to an increase in grafted THir neuron number. Even with highly efficient viral vector-mediated transduction, our results demonstrate that ex vivo gene transfer of bcl-2 to mesencephalic reaggregates is ineffective in increasing grafted DA neuron survival.

The importance of A9 dopaminergic neurons in mediating the functional benefits of fetal ventral mesencephalon transplants and levodopa-induced dyskinesias

Intrastriatal transplantation of fetal ventral mesencephalon (VM) tissue provides the potential to alleviate motor symptoms of Parkinson's disease (PD) and levodopa-induced dyskinesia (LID). However, the degree of recovery varies among individuals with an incidence of "off-phase", graft-induced dyskinesia (GID) in some patients. We hypothesised that this variability is due to the heterogeneous nature of dopaminergic neurons in the transplant. We therefore investigated this in the unilateral 6-hydroxydopamine-lesioned rat model of PD. These animals were primed to develop LID and then transplanted with fetal VM into the caudal aspects of the striatum. No GID was observed but in a significant number of animals the transplants ameliorated LID. There was a correlation between the degree of behavioural and LID recovery with the number of A9 dopaminergic neurons in the transplant, based on their expression of a G-protein-coupled inward rectifying current potassium channel (Girk2). Furthermore, we showed that LID development is related to an abnormal expression profile of cyclin-dependent kinase 5 (Cdk5) and dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) in the striatum and that intrastriatal VM transplants normalised both Cdk5 expression and DARPP-32 phosphorylation in animals exhibiting functional improvement. These results suggest that an A9 dopaminergic neuron-enriched transplant may be the key to an effective PD cell replacement therapy through normalisation of the altered striatal expression of Cdk5/DARPP-32.

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.

Graft placement and uneven pattern of reinnervation in the striatum is important for development of graft-induced dyskinesia

In two recent double-blind clinical trials of fetal ventral mesencephalic cell transplants into the striatum in patients with Parkinson's disease (PD), a significant proportion of the grafted patients developed dyskinetic side effects, which were not seen in the sham operated patients. Comparison between dyskinetic and non-dyskinetic grafted patients in one of the trials suggested that an uneven pattern of striatal reinnervation might be the leading cause of the dyskinesias. Here, we studied the importance of graft placement for the development of dyskinesias in parkinsonian rats. Abnormal involuntary movements resembling peak-dose dyskinesias seen in PD patients were induced by daily injections of L-DOPA for 6 weeks. The dyskinetic animals received about 130.000 fetal ventral mesencephalic cells as single grafts placement in the rostral or the caudal aspect of the head of striatum. The results show that grafts placed in the caudal, but not the rostral, part are effective in reducing the L-DOPA-induced limb and orolingual dyskinesia, predominantly seen as hyperkinesia. The same grafts, however, also induced a new type of dyskinetic behavior after activation with amphetamine, which were not seen in non-grafted lesion controls. The severity of these abnormal involuntary movements was significantly correlated with a higher graft-derived dopaminergic reinnervation in the caudal aspect of the head of striatum relative to the rostral part. The results indicate that graft-induced dyskinesias in PD patients may be linked to single, small graft deposits that provide an uneven, patchy reinnervation of the putamen.

Survival of rat or mouse ventral mesencephalon neurons after cotransplantation with rat sertoli cells in the mouse striatum

Transplanting cells across species (xenotransplantation) for the treatment of Parkinson's disease has been considered an option to alleviate ethical concerns and shortage of tissues. However, using this approach leads to decreased cell survival; the xenografted cells are often rejected. Sertoli cells (SCs) are testis-derived cells that provide immunological protection to developing germ cells and can enhance survival of both allografted and xenografted cells. It is not clear whether these cells will maintain their immunosuppressive support of cografted cells if they are transplanted across species. In this study, we investigated the immune modulatory capacity of SCs and the feasibility of xenografting these cells alone or with allografted and xenografted neural tissue. Transplanting xenografts of rat SCs into the mouse striatum with either rat or mouse ventral mesencephalon prevented astrocytic infiltration of the graft site, although all transplants showed activated microglia within the core of the graft. Surviving tyrosine hydroxylase-positive neurons were observed in all conditions, but the size of the grafts was small at best. SCs were found at 1 and 2 weeks posttransplant. However, few SCs were found at 2 months posttransplant. Further investigation is under way to characterize the immune capabilities of SCs in a xenogeneic environment.

Long-term assessment of striatal dopamine transporters in parkinsonian patients with intrastriatal embryonic mesencephalic grafts

PURPOSE

Single-photon emission computed tomography (SPECT) of striatal dopamine transporters (DAT) has been used to demonstrate presynaptic dopaminergic dysfunction and to monitor the progression of Parkinson's disease. In parkinsonian patients who were implanted with embryonic mesencephalic tissue in the striatum, positron emission tomography (PET) has shown an increase in striatal [(18)F]dopa uptake as an indicator of graft survival and striatal reinnervation. The aim of this study was to investigate two patients who had undergone bilateral intrastriatal transplantation of human embryonic mesencephalic tissue using SPECT and the (123)I-labelled DAT ligand N-(3-iodopropen-2-yl)-2beta-carbomethoxy-3beta-(4-chlorophenyl) tropane (IPT).

METHODS

Two patients were subjected to [(123)I]IPT SPECT according to a standardised protocol prospectively and repeatedly up to 8 years after transplantation.

RESULTS

From baseline to year 3 after transplantation, mean striatal DAT availability increased by a mean of 61% (93% and 29% in patients 1 and 2, respectively). It then remained relatively stable up to 8 years in patient 2, but increased further by another 77% of baseline values in patient 1. Clinically, both patients experienced a moderate improvement in motor performance but developed moderate (patient 2) to severe (patient 1) off-medication dyskinesias.

CONCLUSION

Our data indicate that DAT imaging using IPT and SPECT can be used to demonstrate graft survival following dopaminergic tissue implantation. Because SPECT with DAT ligands is widely available in the routine clinical setting, this methodology may be a useful alternative to [(18)F]dopa PET for repeated scanning of grafted parkinsonian patients. The relevance of the long-term increase in DAT binding for the development of off-medication dyskinesias remains to be elucidated further.

Focal not widespread grafts induce novel dyskinetic behavior in parkinsonian rats

Dyskinesias are a common consequence of dopaminergic therapy in patients with Parkinson's disease. Little is known about the influence of cellular replacement strategies upon drug-induced dyskinesias. In the current study, we employed parkinsonian rats to test whether the distribution of dopamine neuron grafts could differentially alter striatal circuitry and levodopa-induced dyskinesias. Specifically, we compared behavioral and neurochemical consequences of dopamine reinnervation restricted to a focal region of the striatum to innervation encompassing the majority of the striatum by distributing the same number of cells into single locus or multiple locations. Both the single-site and widespread grafts reduced pregraft dyskinesias and normalized FosB/DeltaFosB in the dorsal two-thirds of the lateral striatum. However, single-site DA graft recipients developed a robust, novel forelimb-facial stereotypy and upregulated FosB/DeltaFosB expression in the ventrolateral striatum, an area associated with movements of tongue and forelimbs. The onset of forelimb-facial stereotypy correlated with measures of increased graft function.

Strengths and Limitations of the Neurosphere Culture System

After the initial reports of free-floating cultures of neural stem cells termed neurospheres (1,2), a wide array of studies using this promising culture system emerged. In theory, this was a near-perfect system for large-scale production of neural cells for use in cell replacement therapies and to assay for and characterize neural stem cells. More than a decade later, after rigorous scrutiny and ample experimental testing of the neurosphere culture system, it has become apparent that the culture system suffers from several disadvantages, and its usefulness is limited for several applications. Nevertheless, the bulk of high-quality research produced over the last decade has also shown that under the right circumstances and for the appropriate purposes, neurospheres hold up to their initial promise. This article discusses the pros and cons of the neurosphere culture system regarding its three major applications: as an assay for neural stem cells, as a model system for neurogenesis and neural development, and for expansion of neural stem cells for transplantation purposes.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.

Effects of intranigral vs intrastriatal fetal mesencephalic neural grafts on motor behavior disorders in a rat Parkinson model

BACKGROUND

Numerous experimental and clinical studies have shown that intrastriatal fetal mesencephalic grafts grow, survive, and reinnervate host brain tissue, resulting in partial recovery of motor deficits. In addition, pharmacological evidence indicates that these grafts increase dopamine secretion in lesioned brain. However, to date, no grafting method has completely restored the nigrostriatal pathway, and there is no consensus on optimal graft numbers or locations. This study compared outcomes with multiple striatal grafts vs a single intranigral graft in a rat model of Parkinson disease.

METHODS

Forty-one female Wistar rats weighing 200 to 250 g were used. First, baseline rotational behavior testing with amphetamine injection was done to identify each animal's dominant nigrostriatal pathway (left vs right hemisphere). Some rats then received a unilateral intranigral injection of 6-hydroxydopamine (4 microL [8 microg]) to produce the Parkinson model lesion, and rotational testing was repeated. One group of the lesioned rats received a single intranigral injection of suspended fetal ventral mesencephalic cells (n = 11), and another received multiple intrastriatal grafts of the same type (n = 11).

RESULTS

Both grafted groups showed significant improvement on rotational testing with amphetamine and apomorphine at 6 weeks "postgrafting" (P < .001 for "postlesioning" vs postgrafting results in each of the 2 groups); however, the animals with multiple intrastriatal grafts showed complete recovery from motor asymmetry, whereas the rats with single intranigral grafts showed only partial improvement.

CONCLUSION

The findings indicate that multiple intrastriatal grafts result in significantly greater functional improvement than single intranigral grafts in this rat Parkinson model.

The Corridor Task: A simple test of lateralised response selection sensitive to unilateral dopamine deafferentation and graft-derived dopamine replacement in the striatum

In this experiment, we report a novel drug-free behavioural test of lateralised neglect which is sensitive to unilateral dopamine-denervating lesions and subsequent graft-derived striatal dopamine replacement. For the task, white plastic lids containing sugar pellets were placed along the left and right sides of the floor of a long narrow corridor at regular intervals. Hungry female Sprague-Dawley rats were placed individually into the corridor where they were allowed to make up to 20 pellet retrievals. The number of retrievals each rat made from its left and right sides was counted. Complete mesencephalic or partial nigrostriatal lesions were induced by injection of 6-hydroxydopamine into the medial forebrain bundle or striatum, respectively. Both lesions induced a pronounced ipsilateral retrieval bias in the task. Five weeks after lesion surgery, half of the rats from each lesion group were given E14 ventral mesencephalic cell suspension transplants into the denervated striatum, and were then re-tested in the Corridor Task 5 and 10 weeks later. There was no amelioration of the side bias in rats with medial forebrain bundle lesions. In contrast, in nigrostriatal-lesioned rats, the graft significantly reduced the lesion-induced ipsilateral bias. We conclude that the Corridor Task is a sensitive test of lateralised sensorimotor response selection, and is suitable for assessing deficits and recovery associated with lesions and grafts within the nigrostriatal system.

Purified mouse dopamine neurons thrive and function after transplantation into brain but require novel glial factors for survival in culture

Cell replacement therapy in Parkinson's disease depends on a reliable source of purified dopamine (DA) neurons (PDN) and the identification of factors relevant to their survival. Our goal was to genetically tag and purify by flow cytometry embryonic midbrain DA neurons from a transgenic mouse line carrying 11 kb of human tyrosine hydroxylase promoter driving expression of the enhanced green fluorescent protein(GFP) for studies in vivo and in vitro. A 99% purification of GFP+ cells was achieved. When transplanted into 6-hydroxydopamine-treated rat striatum, PDN survived, became well-integrated and produced recovery from amphetamine-induced motor behaviors. However, when grown in culture, PDN died within days of plating. No known growth factors prevented PDN death as did incubation with novel factors in glia/glial-conditioned media. We conclude that GFP-tagged DA neurons can be purified to homogeneity and can survive and function when grown with glial factors in vitro or after transplantation in vivo.

Factors affecting the clinical outcome after neural transplantation in Parkinson's disease

Intrastriatal grafts of embryonic mesencephalic tissue can survive in the brains of patients with Parkinson's disease, but the degree of symptomatic relief is highly variable and some cases develop troublesome dyskinesias. Here we explored, using clinical assessment and 18F-dopa and 11C-raclopride PET, factors which may influence the functional outcome after transplantation. We observed increased 18F-dopa uptake in the grafted putamen, signifying continued survival of the transplanted dopaminergic neurons, in parallel with a progressive reduction of 18F-dopa uptake in non-grafted regions for the whole patient group. The patients with the best functional outcome after transplantation exhibited no dopaminergic denervation in areas outside the grafted areas either preoperatively or at 1 or 2 years post-operatively. In contrast, patients with no or modest clinical benefit showed reduction of 18F-dopa in ventral striatum prior to or following transplantation, which may have limited graft-induced improvement. We obtained no evidence that dyskinesias were caused by abnormal dopamine (DA) release from the grafts. As has been observed for intrinsic dopaminergic neurons, there was a significant correlation between 18F-dopa uptake and methamphetamine-induced change of 11C-raclopride binding (as a measure of DA release) in the putamen containing the graft. Furthermore, we observed no correlation between 11C-raclopride binding in anterior, posterior or entire putamen under basal conditions or after methamphetamine, and dyskinesia severity scores in the contralateral side of the body. Withdrawal of immunosuppression at 29 months after transplantation caused no reduction of 18F-dopa uptake or worsening of UPDRS motor score, indicating continued survival and function of the graft. However, patients showed increased dyskinesia scores, which might have been caused either by growth of the graft or worsening of a low-grade inflammation around the graft. These findings indicate that poor outcome after transplantation is associated with progressive dopaminergic denervation in areas outside the grafts, a process which may have started already before surgery. Also, that the development of dyskinesias after transplantation is not associated with excessive DA release from the grafts. Finally, our data provide evidence that long-term immunosuppression can be withdrawn without interfering with graft survival or the motor recovery induced by transplantation.

Evidence for dopaminergic re-innervation by embryonic allografts in an optimized rat model of the Parkinsonian variant of multiple system atrophy

Embryonic transplantation has been considered as an alternative treatment strategy for drug resistant parkinsonian symptoms in multiple system atrophy. So far our group has created a number of animal models of striatonigral degeneration, the core pathology underlying progressive Parkinsonism associated with multiple system atrophy, as testbed for neurorestaurative and neuroprotective approaches. Using embryonic allografts of either nigral, striatal, or combined nigro-striatal tissue we were able to consistently show graft survival in a denervated and lesioned striatum as well as improvement of rotational behaviour. However, due to severe lesions of the striatum and the chosen time window of 3-6 weeks between lesion and grafting, severe gliosis led to demarcation of the graft and prevented re-innervation of the remaining adult striatum. The aim of the present study was to modify our "double toxin-double lesion" rat model by reducing the dose of quinolinic acid injected into the striatum from 150 to 75 nmol and shortening the interval between lesion and grafting to 1-2 weeks. Injection of 75 nmol quinolinic acid still led to a significant reduction of DARPP-32 positive neurons and volume in the striatum. Analysis of embryonic mesencephalic grafts revealed survival of dopaminergic neurons and outgrowth of fibres re-innervating the adult striatum. Rotation behaviour was improved in the graft group. Considering embryonic transplantation a possible future antiparkinson therapeutic intervention in multiple system atrophy patients our data stress the necessity of optimal patient selection, i.e. early stage disease with limited striatal dysfunction.

Cell type analysis of functional fetal dopamine cell suspension transplants in the striatum and substantia nigra of patients with Parkinson's disease

We report the first post-mortem analysis of two patients with Parkinson's disease who received fetal midbrain transplants as a cell suspension in the striatum, and in one case also in the substantia nigra. These patients had a favourable clinical evolution and positive 18F-fluorodopa PET scans and did not develop motor complications. The surviving transplanted dopamine neurons were positively identified with phenotypic markers of normal control human substantia nigra (n = 3), such as tyrosine hydroxylase, G-protein-coupled inward rectifying current potassium channel type 2 (Girk2) and calbindin. The grafts restored the cell type that provides specific dopaminergic innervation to the most affected striatal regions in the parkinsonian brain. Such transplants were able to densely reinnervate the host putamen with new dopamine fibres. The patients received only 6 months of standard immune suppression, yet by post-mortem analysis 3-4 years after surgery the transplants appeared only mildly immunogenic to the host brain, by analysis of microglial CD45 and CD68 markers. This study demonstrates that, using these methods, dopamine neuronal replacement cell therapy can be beneficial for patients with advanced disease, and that changing technical approaches could have a favourable impact on efficacy and adverse events following neural transplantation.

Functional properties and synaptic integration of genetically labelled dopaminergic neurons in intrastriatal grafts

Intrastriatal grafts of fetal ventral mesencephalic tissue, rich in dopaminergic neurons, can reverse symptoms in Parkinson's disease. For development of effective cell replacement therapy, other sources of dopaminergic neurons, e.g. derived from stem cells, are needed. However, the electrophysiological properties grafted cells need to have in order to induce substantial functional recovery are poorly defined. It has not been possible to prospectively identify and record from dopaminergic neurons in fetal transplants. Here we used transgenic mice expressing green fluorescent protein under control of the rat tyrosine hydroxylase promoter for whole-cell patch-clamp recordings of endogenous and grafted dopaminergic neurons. We transplanted ventral mesencephalic tissue from E12.5 transgenic mice into striatum of neonatal rats with or without lesions of the nigrostriatal dopamine system. The transplanted cells exhibited intrinsic electrophysiological properties typical of substantia nigra dopaminergic neurons, i.e. broad action potentials, inward rectifying currents with characteristic 'sag', and spontaneous action potentials. The grafted dopaminergic neurons also received functional excitatory and inhibitory synaptic inputs from the host brain, as shown by the presence of both spontaneous and stimulation-evoked excitatory and inhibitory postsynaptic currents. Occurrence of spontaneous excitatory and inhibitory currents was lower, and of spontaneous action potentials was higher, in neurons placed in the dopamine-depleted striatum than of those in the intact striatum. Our findings define specific electrophysiological characteristics of transplanted fetal dopaminergic neurons, and we provide the first direct evidence of functional synaptic integration of these neurons into host neural circuitries.

Dissociation between short-term increased graft survival and long-term functional improvements in Parkinsonian rats overexpressing glial cell line-derived neurotrophic factor

The present study was designed to analyse whether continuous overexpression of glial cell line-derived neurotrophic factor (GDNF) in the striatum by a recombinant lentiviral vector can provide improved cell survival and additional long-term functional benefits after transplantation of fetal ventral mesencephalic cells in Parkinsonian rats. A four-site intrastriatal 6-hydroxydopamine lesion resulted in an 80-90% depletion of nigral dopamine cells and striatal fiber innervation, leading to stable motor impairments. Histological analysis performed at 4 weeks after grafting into the GDNF-overexpressing striatum revealed a twofold increase in the number of surviving tyrosine hydroxylase (TH)-positive cells, as compared with grafts placed in control (green fluorescent protein-overexpressing) animals. However, in animals that were allowed to survive for 6 months, the numbers of surviving TH-positive cells in the grafts were equal in both groups, suggesting that the cells initially protected at 4 weeks failed to survive despite the continued presence of GDNF. Although cell survival was similar in both grafted groups, the TH-positive fiber innervation density was lower in the GDNF-treated grafted animals (30% of normal) compared with animals with control grafts (55% of normal). The vesicular monoamine transporter-2-positive fiber density in the striatum, by contrast, was equal in both groups, suggesting that long-term GDNF overexpression induced a selective down-regulation of TH in the grafted dopamine neurons. Behavioral analysis in the long-term grafted animals showed that the control grafted animals improved their performance in spontaneous motor behaviors to approximately 50% of normal, whereas the GDNF treatment did not provide any additional recovery.

Restorative potential of dopaminergic grafts in presence of antioxidants in rat model of Parkinson's disease

Free radical mediated damage has been reported to contribute significantly towards low survival (5-10%) of grafted dopaminergic neurons, post transplantation. In the present study, an attempt has been made to explore the neuroprotective potential of the combination of two major antioxidants ascorbic acid (AA) and glutathione (GSH) on ventral mesencephalic cells (VMC) and nigral dopamine (DA) neurons when co-transplanted together with VMC in rat model of Parkinson's disease (PD). GSH and AA have been reported to act co-operatively in the conditions of oxidative stress thereby helping in maintaining the cellular GSH/GSSG redox status. Functional recovery was assessed 12 weeks post transplantation, where a significant restoration (p<0.001) in d-amphetamine induced circling behavior (62%), spontaneous locomotor activity (SLA; 64%), dopamine-D2 receptor binding (63%), dopamine (65%) and 3,4-dihydroxy phenyl acetic acid (DOPAC) level (64%) was observed in co-transplanted animals as compared to lesioned and VMC alone grafted rats. VMC and GSH+AA co-transplanted animals exhibited a significantly higher surviving TH-immunoreactive (TH-ir) neurons number (p<0.01), TH-ir fibers outgrowth (p<0.05) in striatal graft and TH-ir neurons in substantia nigra pars compacta (SNpc) (p<0.01), as compared to VMC alone transplanted rats. An attempt was made to further confirm our in vivo observations through in vitro experiments where following in vitro exposure to 6-OHDA, a higher cell survival (p<0.01), TH-ir cell counts (p<0.001) and DA and DOPAC levels (p<0.01) were also observed in 8-day-old VMC culture in presence of GSH+AA as compared to VMC cultured in absence of antioxidants. The results suggest that GSH+AA when co-transplanted with VMC provide higher restoration probably by increasing the survival of grafted VMC and simultaneously supporting nigral TH-immunopositive neurons in rat model of PD.

Co-transplantation of carotid body and ventral mesencephalic cells as an alternative approach towards functional restoration in 6-hydroxydopamine-lesioned rats: implications for Parkinson's disease

Exogenous administration of various neurotrophic factors has been shown to protect neurons in animal model of Parkinson's disease (PD). Several attempts are being made to search a tissue source simultaneously expressing many of these neurotrophic factors. Carotid body (CB) contains oxygen-sensitive glomus cells rich in dopamine (DA) and expresses glial cell line-derived neurotrophic factor, brain-derived neurotrophic factor and neurotrophin-3. We have attempted to study the functional restoration following co-transplantation of CB cells and ventral mesencephalic cells (VMC) in a 6-hydroxydopamine-lesioned rat model of PD. A significant recovery (p < 0.001) in d-amphetamine-induced circling behavior (80%) and spontaneous locomotor activity (85%) was evident in co-transplanted animals at 12 weeks post-transplantation as compared to lesioned animals. Similarly, a significant (p < 0.001) restoration was observed in DA-D(2) receptor binding (77%), striatal DA (87%) and 3,4-dihydroxyphenylacetic acid (DOPAC) (85%) levels and nigral DA (75%) and DOPAC (74%) levels. Functional recovery was accompanied by tyrosine hydroxylase (TH) expression and quantification of TH-positive cells by image analysis revealed a significant restoration in TH-immunoreactive (IR) fiber density in striatum, as well as TH-IR neurons in substantia nigra pars compacta in co-transplanted animals over VMC-transplanted animals. The result suggests that co-transplantation of CB cells along with VMC provides better and long-term functional restoration in the rat model of PD, possibly by supporting the survival of newly grafted cells as well as remaining host DA neurons.