Fetal Ventral Mesencephalic Cells Research Articles

Past, present, and future of cell replacement therapy for parkinson's disease: a novel emphasis on host immune responses.

Parkinson's disease (PD) stands as the second most common neurodegenerative disorder after Alzheimer's disease, and its prevalence continues to rise with the aging global population. Central to the pathophysiology of PD is the specific degeneration of midbrain dopamine neurons (mDANs) in the substantia nigra. Consequently, cell replacement therapy (CRT) has emerged as a promising treatment approach, initially supported by various open-label clinical studies employing fetal ventral mesencephalic (fVM) cells. Despite the initial favorable results, fVM cell therapy has intrinsic and logistical limitations that hinder its transition to a standard treatment for PD. Recent efforts in the field of cell therapy have shifted its focus towards the utilization of human pluripotent stem cells, including human embryonic stem cells and induced pluripotent stem cells, to surmount existing challenges. However, regardless of the transplantable cell sources (e.g., xenogeneic, allogeneic, or autologous), the poor and variable survival of implanted dopamine cells remains a major obstacle. Emerging evidence highlights the pivotal role of host immune responses following transplantation in influencing the survival of implanted mDANs, underscoring an important area for further research. In this comprehensive review, building upon insights derived from previous fVM transplantation studies, we delve into the functional ramifications of host immune responses on the survival and efficacy of grafted dopamine cells. Furthermore, we explore potential strategic approaches to modulate the host immune response, ultimately aiming for optimal outcomes in future clinical applications of CRT for PD.

Co-Existence of tau and α-synuclein pathology in fetal graft tissue at autopsy: A case report

IntroductionTransplant of fetal ventral mesencephalic tissue into the striatum of Parkinson's disease (PD) patients has been performed to increase dopamine production and stimulate neuronal regeneration. Analysis of fetal graft tissue at autopsy has demonstrated 6 cases of α-synuclein pathology in PD patients, one case with both α-synuclein and tau pathology in a PD patient, and two cases of tau pathology within a Huntington's Disease patient. MethodsA 49 year old man with PD underwent bilateral fetal ventral mesencephalic cell transplants into the striatum. Autopsy at age 70 included immunohistochemical staining of host and graft tissue with antibodies to phosphorylated α-synuclein and phosphorylated tau protein. ResultsAutopsy confirmed the diagnosis of PD. Immunohistochemical staining of graft tissue demonstrated frequent neuronal perikaryal inclusions of phosphorylated α -synuclein and tau in the left graft only. ConclusionSpeculations on the formation of pathology include: 1) α-synuclein and tau pathology spread from host to the graft in a neuron-neuron manner. 2) The nature of the fetal cells themselves, or transplantation process, may render fetal tissue more susceptible to the spontaneous generation of pathology. 3) Factors within host environment caused native tau and α-synuclein in fetal tissue graft to become phosphorylated.

Anodal Transcranial Direct Current Stimulation Enhances Survival and Integration of Dopaminergic Cell Transplants in a Rat Parkinson Model.

Restorative therapy concepts, such as cell based therapies aim to restitute impaired neurotransmission in neurodegenerative diseases. New strategies to enhance grafted cell survival and integration are still needed to improve functional recovery. Anodal direct current stimulation (DCS) promotes neuronal activity and secretion of the trophic factor BDNF in the motor cortex. Transcranial DCS applied to the motor cortex transiently improves motor symptoms in Parkinson’s disease (PD) patients. In this proof-of-concept study, we combine cell based therapy and noninvasive neuromodulation to assess whether neurotrophic support via transcranial DCS would enhance the restitution of striatal neurotransmission by fetal dopaminergic transplants in a rat Parkinson model. Transcranial DCS was applied daily for 20 min on 14 consecutive days following striatal transplantation of fetal ventral mesencephalic (fVM) cells derived from transgenic rat embryos ubiquitously expressing GFP. Anodal but not cathodal transcranial DCS significantly enhanced graft survival and dopaminergic reinnervation of the surrounding striatal tissue relative to sham stimulation. Behavioral recovery was more pronounced following anodal transcranial DCS, and behavioral effects correlated with the degree of striatal innervation. Our results suggest anodal transcranial DCS may help advance cell-based restorative therapies in neurodegenerative diseases. In particular, such an assistive approach may be beneficial for the already established cell transplantation therapy in PD.

An Update on Human Stem Cell-Based Therapy in Parkinson's Disease.

CDATA[Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease and it is characterized by the progressive loss of dopaminergic neurons of the substantia nigra pars compacta (SNpc). Current pharmacological treatments for PD are only symptomatic and unfortunately there is still no cure for this disorder. Stem cell technology has become an attractive option to investigate and treat PD. Indeed, transplantation of fetal ventral mesencephalic cells into PD brains have provided proof of concept that cell replacement therapy can be beneficial for some patients, greatly improving their motor symptoms. However, ethical and practical aspects of tissue availability limit its widespread clinical use. Hence, the need of alternative cell sources are based on the use of different types of stem cells. Stem cell-based therapies can be beneficial by acting through several mechanisms such as cell replacement, trophic actions and modulation of inflammation. Here we review recent and current remarkable clinical studies involving stem cell-based therapy for PD and provide an overview of the different types of stem cells available nowadays, their main properties and how they are developing as a possible therapy for PD treatment.

Induced pluripotent stem cells and Parkinson's disease: modelling and treatment.

Many neurodegenerative disorders, such as Parkinson's disease (PD), are characterized by progressive neuronal loss in different regions of the central nervous system, contributing to brain dysfunction in the relevant patients. Stem cell therapy holds great promise for PD patients, including with foetal ventral mesencephalic cells, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). Moreover, stem cells can be used to model neurodegenerative diseases in order to screen potential medication and explore their mechanisms of disease. However, related ethical issues, immunological rejection and lack of canonical grafting protocols limit common clinical use of stem cells. iPSCs, derived from reprogrammed somatic cells, provide new hope for cell replacement therapy. In this review, recent development in stem cell treatment for PD, using hiPSCs, as well as the potential value of hiPSCs in modelling for PD, have been summarized for application of iPSCs technology to clinical translation for PD treatment.

Foetal Cell Transplantation for Parkinson's Disease: Focus on Graft-Induced Dyskinesia.

Transplantation of dopamine- (DA-) rich foetal ventral mesencephalic cells emerged as a promising therapy for Parkinson's disease (PD), as it allowed significant improvement of motor symptoms in several PD patients in open-label studies. However, double-blind clinical trials have been largely disappointing. The general agreement in the field is that the lack of standardization of tissue collection and preparation, together with the absence of postsurgical immunosuppression, played a key role in the failure of these studies. Moreover, a further complication that emerged in previous studies is the appearance of the so-called graft-induced dyskinesia (GID), in a subset of grafted patients, which resembles dyskinesia induced by L-DOPA but in the absence of medication. Preclinical evidence pointed to the serotonin neurons as possible players in the appearance of GID. In agreement, clinical investigations have shown that grafted tissue may contain a large number of serotonin neurons, in the order of half of the DA cells; moreover, the serotonin 5-HT1A receptor agonist buspirone has been found to produce significant dampening of GID in grafted patients. In this paper, we will review the recent preclinical and clinical studies focusing on cell transplantation for PD and on the mechanisms underlying GID.

Treating Parkinson's disease in the 21st century: Can stem cell transplantation compete?

The characteristic and selective degeneration of a unique population of cells—the nigrostriatal dopamine (DA) neurons—that occurs in Parkinson’s disease (PD) has made the condition an iconic target for cell replacement therapies. Indeed, transplantation of fetal ventral mesencephalic cells into the DA-deficient striatum was first trialled nearly 30 years ago, at a time when other treatments for the disease were less well developed. Over recent decades standard treatments for PD have advanced, and newer biological therapies are now emerging. In the 21st century, stem cell technology will have to compete alongside other sophisticated treatments, including deep brain stimulation and gene therapies. In this review we examine how stem cell–based transplantation therapies compare with these novel and emerging treatments in the management of this common condition. J. Comp. Neurol. 522:2802–2816, 2014.

The effect of striatal dopaminergic grafts on the neuronal activity in the substantia nigra pars reticulata and subthalamic nucleus in hemiparkinsonian rats

The electrophysiological correlates of parkinsonism in the basal ganglia have been well studied in patients with Parkinson's disease and animal models. Separately, striatal dopaminergic cell transplantation has shown promise in ameliorating parkinsonian motor symptoms. However, the effect of dopaminergic grafts on basal ganglia electrophysiology has not thoroughly been investigated. In this study, we transplanted murine foetal ventral mesencephalic cells into rats rendered hemiparkinsonian by 6-hydroxydopamine injection. Three months after transplantation, extracellular and local field potential recordings were taken under urethane anaesthesia from the substantia nigra pars reticulata and subthalamic nucleus along with cortical electroencephalograms and were compared to recordings from normal and hemiparkinsonian controls. Recordings from cortical slow-wave activity and global activation states were analysed separately. Rats with histologically confirmed xenografts showed behavioural improvement measured by counting apomorphine-induced rotations and with the extended body axis test. Firing rates in both nuclei were not significantly different between control and grafted groups. However, burst firing patterns in both nuclei in the slow-wave activity state were significantly reduced (P < 0.05) in rats with large surviving grafts, compared to hemiparkinsonian controls. The neuronal firing entropies and oscillations in both nuclei were restored to normal levels in the large-graft group. Electroencephalogram spike-triggered averages also showed normalization in the slow-wave activity state (P < 0.05). These results suggest that local continuous dopaminergic stimulation exerts a normalizing effect on the downstream parkinsonian basal ganglia firing patterns. This novel finding is relevant to future preclinical and clinical investigations of cell transplantation and the development of next-generation therapies for Parkinson's disease that ameliorate pathophysiological neural activity and provide optimal recovery of function.

Neuroprotection by Minocycline Caused by Direct and Specific Scavenging of Peroxynitrite

Minocycline prevents oxidative protein modifications and damage in disease models associated with inflammatory glial activation and oxidative stress. Although the drug has been assumed to act by preventing the up-regulation of proinflammatory enzymes, we probed here its direct chemical interaction with reactive oxygen species. The antibiotic did not react with superoxide or (•)NO radicals, but peroxynitrite (PON) was scavenged in the range of ∼1 μm minocycline and below. The interaction of pharmacologically relevant minocycline concentrations with PON was corroborated in several assay systems and significantly exceeded the efficacy of other antibiotics. Minocycline was degraded during the reaction with PON, and the resultant products lacked antioxidant properties. The antioxidant activity of minocycline extended to cellular systems, because it prevented neuronal mitochondrial DNA damage and glutathione depletion. Maintenance of neuronal viability under PON stress was shown to be solely dependent on direct chemical scavenging by minocycline. We chose α-synuclein (ASYN), known from Parkinsonian pathology as a biologically relevant target in chemical and cellular nitration reactions. Submicromolar concentrations of minocycline prevented tyrosine nitration of ASYN by PON. Mass spectrometric analysis revealed that minocycline impeded nitrations more effectively than methionine oxidations and dimerizations of ASYN, which are secondary reactions under PON stress. Thus, PON scavenging at low concentrations is a novel feature of minocycline and may help to explain its pharmacological activity.

Effects of GDNF pretreatment on function and survival of transplanted fetal ventral mesencephalic cells in the 6-OHDA rat model of Parkinson's disease

Transplantation of fetal dopaminergic (DA) neurons offers an experimental therapy for Parkinson's disease (PD). The low availability and the poor survival and integration of transplanted cells in the host brain are major obstacles in this approach. Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor with growth- and survival-promoting capabilities for developing DA neurons. In the present study, we examined whether pretreatment of ventral mesencephalic (VM) free-floating roller tube (FFRT) cultures with GDNF would improve graft survival and function. For that purpose organotypic cultures of E14 rat VM were grown for 2, 4 or 8 days in the absence (control) or presence of GDNF [10 ng/ml] and transplanted into the striatum of 6-hydroxydopamine-lesioned rats. While all groups of rats showed a significant reduction in d-amphetamine-induced rotations at 6 weeks posttransplantation a significantly improved graft function was observed only in the days in vitro (DIV) 4 GDNF pretreated group compared to the control group. In addition, no statistical significant differences between groups were found in the number of surviving tyrosine hydroxylase-immunoreactive (TH-ir) neurons assessed at 9 weeks posttransplantation. However, a tendency for higher TH-ir fiber outgrowth from the transplants in the GDNF pretreated groups as compared to corresponding controls was observed. Furthermore, GDNF pretreatment showed a tendency for a higher number of GIRK2 positive neurons in the grafts. In sum, our findings demonstrate that GDNF pretreatment was not disadvantageous for transplants of embryonic rat VM with the FFRT culture technique but only marginally improved graft survival and function.

Embryonic Stem Cell-Derived Pitx3-Enhanced Green Fluorescent Protein Midbrain Dopamine Neurons Survive Enrichment by Fluorescence-Activated Cell Sorting and Function in an Animal Model of Parkinson's Disease

Both fetal ventral mesencephalic (VM) and embryonic stem (ES) cell-derived dopamine neurons have been used successfully to correct behavioral responses in animal models of Parkinson's disease. However, grafts derived from fetal VM cells or from ES cells contain multiple cell types, and the majority of these cells are not dopamine neurons. Isolation of ES cell-derived dopamine neurons and subsequent transplantation would both elucidate the capacity of these neurons to provide functional input and also further explore an efficient and safer use of ES cells for the treatment of Parkinson's disease. Toward this goal, we used a Pitx3-enhanced green fluorescent protein (Pitx3-eGFP) knock-in mouse blastocyst-derived embryonic stem (mES) cell line and fluorescence-activated cell sorting (FACS) to select and purify midbrain dopamine neurons. Initially, the dopaminergic marker profile of intact Pitx3-eGFP mES cultures was evaluated after differentiation in vitro. eGFP expression overlapped closely with that of Pitx3, Nurr1, Engrailed-1, Lmx1a, tyrosine hydroxylase (TH), l-aromatic amino acid decarboxylase (AADC), and vesicular monoamine transporter 2 (VMAT2), demonstrating that these cells were of a midbrain dopamine neuron character. Furthermore, postmitotic Pitx3-eGFP(+) dopamine neurons, which constituted 2%-5% of all live cells in the culture after dissociation, could be highly enriched to >90% purity by FACS, and these isolated neurons were viable, extended neurites, and maintained a dopaminergic profile in vitro. Transplantation to 6-hydroxydopamine-lesioned rats showed that an enriched dopaminergic population could survive and restore both amphetamine- and apomorphine-induced functions, and the grafts contained large numbers of midbrain dopamine neurons, which innervated the host striatum. Disclosure of potential conflicts of interest is found at the end of this article.

How to improve the survival of the fetal ventral mesencephalic cell transplanted in Parkinson’s disease?

It has been extensively confirmed that fetal ventral mesencephalic cell (VMC) transplantation can ameliorate the symptoms of Parkinson's disease (PD). But there are still several problems to be resolved before the extensive clinical application of this technology. The major limitations are the poor survival of grafted dopamine (DA) neurons and restricted dopaminergic reinnervation of host striatum. Some attempts have been made to solve these problems including use of some trophic factor and co-transplantation with neural/paraneural origins. The purpose of this review is to overview advances of the means improving the survival of grafts and their current limitations.

Local effects of dexamethasone on immune reaction in neural transplantation

This study was performed to see whether local injection of dexamethasone may protect the neural grafts from immunological rejection and increase the successive rate of graft. Rats with unilateral 6-hydroxydopamine lesions of the mesostriatal dopamine pathway received fetal ventral mesencephalic (FVM) cells and dexamethasone in two regions of the striatum and showed significant ( P < 0.001) reduction in rotational asymmetry as compared to the non-immunosuppressed group. A significantly greater number of total TH-ir cells ( P < 0.001) and fewer number of total GFAP -ir cells ( P < 0.001) and inflammatory cells were observed in the striatum of animals in immunosuppressed group than those in non-immunosuppressed group. This results indicated that local injection of dexamethasone could not only reduce the immune rejection and increase the survival grafted cell but also avoid the side effects brought by long systemic administer of immunosuppressant.

Derivation of Functional Dopamine Neurons from Embryonic Stem Cells

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the selective degeneration of dopaminergic (DA) neurons in the substantia nigra of the midbrain. Pharmacological treatment of PD has been a prevailing strategy. However, it has some limitations because its effectiveness gradually decreases and side effects develop. As an alternative, cell transplantation therapy has been tried. Although transplantation of fetal ventral mesencephalic cells looks promising for the treatment of PD in some cases, ethical and technical problems in obtaining large numbers of human fetal brain tissues also lead to difficulty in its clinical application. Our recent studies showed that a high yield of DA neurons could be derived from embryonic stem (ES) cells and they efficiently induced behavioral recovery in a PD animal model. Here we summarize methods for generation of functional DA neurons from ES cells for application to PD models.

Pharmacologically active microcarriers releasing glial cell line – derived neurotrophic factor: Survival and differentiation of embryonic dopaminergic neurons after grafting in hemiparkinsonian rats

To improve the outcome of foetal dopaminergic cell transplantation for the treatment of Parkinson's disease, pharmacologically active microcarriers (PAM) were developed. PAM are able to convey cells on their surface and release a growth factor to improve cell survival, differentiation and integration after brain implantation. Lysozyme-releasing PAM were first produced and characterized. They served as a model system for the development of glial cell line-derived neurotrophic factor (GDNF)-releasing PAM conveying foetal ventral mesencephalic (FVM) cells. The effects of the intrastriatal implantation of this system were studied in hemiparkinsonian rats during a 6-week period. This study reports on the degradation of coated and non-coated PAM and the release of lysozyme and of biologically active GDNF for 42 days. Unloaded and GDNF-loaded PAM conveying FVM cells allowed a high improvement of the grafted cell survival and of fibre outgrowth, when compared to the cells transplanted alone. The animals receiving the PAM showed an earlier improvement in amphetamine-induced rotational behaviour compared to animals receiving FVM cells only; behaviour that appears to be more regular and stable with the GDNF-releasing PAM. The use of PAM to convey foetal cells is thus an efficient strategy for cell therapy in neurodegenerative diseases, as it allows improvement of cell survival and fibre outgrowth inducing a rapid recovery of behaviour using only low amounts of cells.

Erythropoietin and GDNF enhance ventral mesencephalic fiber outgrowth and capillary proliferation following neural transplantation in a rodent model of Parkinson's disease

Low dopaminergic cell survival and suboptimal fiber reinnervation are likely major contributing factors for the limited benefits of neural transplantation in Parkinson's disease (PD) patients. Glial cell lined-derived neurotrophic factor (GDNF) has been shown to enhance dopaminergic cell survival and fiber outgrowth of the graft site as well as promote behavioral recovery in rodent models of PD, while erythropoietin (EPO) can produce dopaminergic neuroprotective effects against 6-hydroxydopamine (6-OHDA) exposure on cultured neurons and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice. The aim of this study was to determine if fetal ventral mesencephalic (FVM) tissue exposed to hibernation media containing a combination of GDNF and EPO could enhance dopaminergic graft survival, striatal reinnervation and functional recovery in a 6-OHDA rodent model of PD. FVM tissue was dissected from 14-day-old rat fetuses and placed for 6 days in hibernation media alone, and in hibernation media that received either a daily administration of GDNF, EPO or a combination of GDNF and EPO. Following hibernation, FVM cells were transplanted as a single cell suspension into the striatum of unilateral 6-OHDA-lesioned rats. Rotational behavioral assessment revealed animals that received FVM tissue exposed to GDNF, EPO or the combination of both drugs had accelerated functional recovery. Immunohistochemical and stereological assessment revealed a significant increase in graft fiber density and angiogenesis into the graft when compared with control. These findings suggest that the hibernation of FVM tissue in a combination of GDNF and EPO can enhance graft efficacy and may have important implications for tissue preparation protocols for clinical neural transplantation in PD.

Porcine Fetal Ventral Mesencephalic Cells are Targets for Primed Xenoreactive Human T Cells

Xenotransplantation of porcine fetal ventral mesencephalic (pfVM) cells to overcome the dopamine shortage in the striatum of patients with Parkinson's disease seems a viable alternative to allotransplantion of human fetal donor tissue, especially because the latter is complicated by both practical and ethical issues. There is, however, little known about the xenospecific immune responses involved in such an intracerebral xenotransplantation. The aim of our study was to investigate whether (1) naive human peripheral blood mononuclear cells (PMBC) display cytotoxicity against pfVM cells of E28 pig fetuses, and (2) priming of human PBMC by xenogeneic antigen presenting cells (APC) modulates pfVM-directed cellular cytotoxicity. For this purpose fresh PMBC from nine individual donors were primed by incubation with either irradiated pfVM cells or porcine spleen cells (PSC) as APC in the presence of IL-2 for 1 week before assessing cytotoxicity in a 51Cr release assay. Also, direct NK reactivity and antibody-dependent cellular cytotoxicity (ADCC) of fresh PMBC against pfVM cells was assessed. No direct cytotoxicity of naive cells (either NK reactivity or ADCC) against pfVM cells could be determined. Only PMBC primed with PSC were capable of lysing pfVM cells. PBMC primed with pfVM cells did not show cytolytic capacity towards pfVM. Interestingly, large differences in xenospecific T-cell responses exist between individual donor PBMC. Thus, human T cells are capable of killing pfVM cells in a xenoreactive response, but only after priming by donor APC. The large interindividual differences between human donors in their xenoreactive response may influence patient selection for xenotransplantation and chances of graft survival for individual patients.

Effect of GDNF-releasing biodegradable microspheres on the function and the survival of intrastriatal fetal ventral mesencephalic cell grafts

The transplantation of fetal ventral mesencephalic (FVM) cell suspensions into the brain striatal system is an alternative approach for the treatment of Parkinson’s disease (PD). However, one objection to this procedure is the relatively poor survival of implanted cells. Attempts have been made to improve the survival of grafted dopaminergic neurons using glial cell line-derived neurotrophic factor (GDNF). Nevertheless, the clinical application of GDNF is limited, due to the difficulties in administering a protein to the brain tissue and due to the ubiquity of its receptor, thus leading to neurological side effects. A strategy to deliver GDNF in the brain based on the intracerebral implantation of biodegradable poly( d,l-lactic acid-co-glycolic acid) sustained release microspheres has been developed. Such microparticles can be easily implanted by sterotaxy in precise and functional areas of the brain without causing damage to the surrounding tissue. Moreover, the release profile of the GDNF-loaded microspheres showed a sustained release over 56 days of biologically active GDNF at clinically relevant doses. The present study shows that the implantation of GDNF-loaded microspheres at a distance to the site of FVM cells in the 6-hydroxydopamine-lesioned rat model of PD improves dopaminergic graft survival and function. Furthermore, the unloaded and the GDNF-loaded microspheres, when they are mixed with FVM cells, may provide a mechanical support and a 3D environment inducing differentiation and increased function of dopaminergic neurons. Taken together, these results show that GDNF microspheres represent an efficient delivery system for cell transplantation studies.

Nerve growth factor increases survival of dopaminergic graft, rescue nigral dopaminergic neurons and restores functional deficits in rat model of Parkinson's disease

In the present study, an attempt has been made to explore the neuroprotective and neurorescue effects of nerve growth factor (NGF) on grafted cells and on host nigral dopaminergic neurons, respectively. NGF was co-transplanted with fetal ventral mesencephalic cells (VMC) in the striatum of 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease (PD). In the other groups fetal VMC and NGF were transplanted alone. Twelve weeks post-transplantation, a significant restoration was observed in d-amphetamine induced rotations (stereotypy), spontaneous locomotor activity, striatal and nigral dopamine (DA) and 3,4-dihydroxy-phenyl acetic acid (DOPAC) levels in co-transplanted rats as compared to VMC alone transplanted rats. Higher number of surviving tyrosine hydroxylase immunoreactive (TH-ir) neurons and significantly increased fiber outgrowth from graft was evident in co-transplanted rats as compared to VMC alone transplanted rats. Further, a significant increase was also observed in substantia nigra TH-ir neurons count in co-transplanted rats, exhibiting a potential neuroprotective and neurorescue effects of NGF on nigrostriatal dopaminergic neurons. The results suggest that NGF at the time of transplantation exhibits neuroprotective effect on transplanted VMC as well as neurorescue effect on remaining host nigral dopaminergic neurons, leading to better functional restoration.

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.