Dopaminergic cells of the carotid body: physiological significance and possible therapeutic applications in Parkinson's disease

Protection and Repair of the Nigrostriatal Pathway with Stem-Cell-Derived Carotid Body Glomus Cell Transplants in Chronic MPTP Parkinsonian Model

Antiparkinsonian carotid body (CB) cell therapy has been proven to be effective in rodent and nonhuman primate models of Parkinson’s disease (PD), exerting trophic protection and restoration of the dopaminergic nigrostriatal pathway. These neurotrophic actions are mediated through the release of high levels of glial-cell-line-derived neurotrophic factor (GDNF) by the CB transplant. Pilot clinical trials have also shown that CB autotransplantation can improve motor symptoms in PD patients, although its effectiveness is affected by the scarcity of the grafted tissue. Here, we analyzed the antiparkinsonian efficacy of in vitro-expanded CB dopaminergic glomus cells. Intrastriatal xenografts of rat CB neurospheres were shown to protect nigral neurons from degeneration in a chronic MPTP mouse PD model. In addition, grafts performed at the end of the neurotoxic treatment resulted in the repair of striatal dopaminergic terminals through axonal sprouting. Interestingly, both neuroprotective and reparative effects induced by in vitro-expanded CB cells were similar to those previously reported by the use of CB transplants. This action could be explained because stem-cell-derived CB neurospheres produce similar amounts of GDNF compared to native CB tissue. This study provides the first evidence that in vitro-expanded CB cells could be a clinical option for cell therapy in PD.

History and Recent Progress in Carotid Body Studies

This chapter describes the history of the carotid body (CB) and the subsequent research on its structure and function. The chronological development of ideas about its anatomical structure as a ganglion, the first descriptions of its glandular nature as a ball of highly vascular tissue (glomus), the discovery of its neural crest origin and relevant embryological views as a true paraganglion toward a more conclusive understanding of its sensory nature as a chemoreceptor for chemical changes in blood have been consistently demonstrated. The knowledge of the CB neurochemistry, physiology and pathophysiology has progressed immensely in the past century and a large and compelling body of evidence for the presence of a neurogenic niche in the CB has accumulated over the last two decades, thus underlying its function and possibility for the development of cell replacement therapies.

Carotid Body and Cell Therapy

During the past decade, the carotid body (CB) has been considered an innovative therapeutic target for the treatment of certain cardiorespiratory and metabolic diseases most of which are sympathetically mediated. It has recently been revealed that CB stem cells provide new target sites for the development of promising cell-based therapies. Specifically, generation of CB progenitors in vitro which can differentiate into functionally active glomus cells may be a useful procedure to produce the cell mass required for replacement cell therapy. Due to their dopaminergic nature, adult glomus cells can be used for an intrastriatal grafting in neurodegenerative brain disorders including Parkinson's disease. The beneficial effect of throphic factors such as glial cell-derived neurotrophic factor synergistically released by the transplanted cells then enables the transplant to survive. Likewise, intracerebral administration of CB cell aggregates or dispersed cells has been tested for the treatment of an experimental model of stroke. The systematic clinical applicability of CB autotransplants following glomectomy in humans is under investigation. In such autotransplantation studies, cell aggregates from unilaterally resected CB might be used as autografts. In addition, stem cells could offer an opportunity for tissue expansion and might settle the issue of small number of glomus cells available for transplantation.

GPER and IGF-1R mediate the anti-inflammatory effect of genistein against lipopolysaccharide (LPS)-induced nigrostriatal injury in rats

Neuroinflammation plays an important role in the pathogenesis of Parkinson's disease (PD). Genistein is an estrogen-like phytoestrogen that can exert biological effects via the crosstalk of estrogen receptor and insulin-like growth factor 1 receptor (IGF-1R). The present study aimed to evaluate the involvement of G protein-coupled estrogen receptor (GPER) and IGF-1R in the anti-inflammatory effects of genistein against lipopolysaccharide (LPS)-induced nigrostriatal injury in ovariectomized rats. Our results showed that genistein treatment could ameliorate the apomorphine-induced rotational behavior in LPS-induced inflammatory PD rat model. Genistein attenuated LPS-induced decrease of the contents of dopamine (DA) and its metabolites in striatum as well as the loss of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra (SN) of the lesioned side, which could be blocked by GPER antagonist G15 or IGF-1R antagonist JB1. Meanwhile, G15 or JB1 could attenuate the anti-inflammatory effects of genistein in LPS-induced microglial activation and production of tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Moreover, genistein could inhibit the LPS-induced phosphorylation of p38, JNK, ERK and IκB in the lesioned side of SN and these effects could also be blocked by G15 or JB1. Taken together, our data provide the first evidence that genistein can inhibit the increase of microglia and protect dopaminergic neurons at least in part via GPER and IGF-1R signaling pathways in ovariectomized PD rat model.

Hypoxia-Associated Changes in Striatal Tonic Dopamine Release: Real-Time in vivo Measurements With a Novel Voltammetry Technique

Introduction

Striatal tonic dopamine increases rapidly during global cerebral hypoxia. This phenomenon has previously been studied using microdialysis techniques which have relatively poor spatio-temporal resolution. In this study, we measured changes in tonic dopamine during hypoxia (death) in real time with high spatio-temporal resolution using novel multiple cyclic square wave voltammetry (MCSWV) and conventional fast scan cyclic voltammetry (FSCV) techniques.

Methods

MCSWV and FSCV were used to measure dopamine release at baseline and during hypoxia induced by euthanasia, with and without prior alpha-methyl-p-tyrosine (AMPT) treatment, in urethane anesthetized male Sprague-Dawley rats.

Results

Baseline tonic dopamine levels were found to be 274.1 ± 49.4 nM (n = 5; mean ± SEM). Following intracardiac urethane injection, the tonic levels increased to a peak concentration of 1753.8 ± 95.7 nM within 3.6 ± 0.6 min (n = 5), followed by a decline to 50.7 ± 21.5 nM (n = 4) at 20 min. AMPT pre-treatment significantly reduced this dopamine peak to 677.9 ± 185.7 nM (n = 3). FSCV showed a significantly higher (p = 0.0079) peak dopamine release of 6430.4 ± 1805.7 nM (n = 5) during euthanasia-induced cerebral hypoxia.

Conclusion

MCSWV is a novel tool to study rapid changes in tonic dopamine release in vivo during hypoxia. We found a 6-fold increase in peak dopamine levels during hypoxia which was attenuated with AMPT pre-treatment. These changes are much lower compared to those found with microdialysis. This could be due to improved estimation of baseline tonic dopamine with MCSWV. Higher dopamine response measured with FSCV could be due to an increased oxidation current from electroactive interferents.

Implantation of glial cell line-derived neurotrophic factor-expressing adipose tissue-derived stromal cells in a rat Parkinson's disease model

In previous studies, the effects of glial cell line-derived neurotrophic factor (GDNF) expressing adipose tissue-derived stromal cells (ADSCs) on Parkinson's disease (PD) models have been studied but have not been elucidated. The present study aims to investigate this phenomenon and trace their differentiation in vivo. In our study, ADSCs were harvested from adult Sprague-Dawley rats, then genetically modified into GDNF-expressing system by lentivirus. The secretion of GDNF from the transduced cells was titrated by enzyme-linked immunosorbent assay (ELISA). Cellular differentiation in vitro was observed after induction. To examine survival and differentiation in vivo, they were injected into the striatum of 6-hydroxydopamine-lesioned rats, whose apomorphine-induced rotations were examined 2, 7, 14 and 21d after grafting. It's found that GDNF-expressing ADSCs can differentiate into neuron-like cells in vitro. Moreover, engrafted GDNF-expressing ADSCs survived at least 90 days post-grafting and differentiated into dopaminergic neuron-like cells. Most importantly, these cells drastically improved the clinical symptoms of PD rats. In conclusion, ADSCs can be efficiently engineered by lentivirus system and deliver a therapeutic level of the transgene to target tissues. GDNF-ADSCs can improve behavior phenotype in the rat PD model. Moreover, ADSCs is a more readily available source of dopaminergic neurons, though a more effective procedure needs to be developed to enrich the number of differentiation.

Influence of propofol on isolated neonatal rat carotid body glomus cell response to hypoxia and hypercapnia

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The intravenous anaesthetic propofol acts directly on carotid body glomus cells to inhibit their response to hypoxia.

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Propofol acts via novel mechanisms, as we excluded action via its known target receptors (nicotinic, GABA-ergic, or K+ channel).

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Inhibition of the hypoxic response is clinically relevant in anaesthesia.

In humans the intravenous anaesthetic propofol depresses ventilatory responses to hypoxia and CO₂. Animal studies suggest that this may in part be due to inhibition of synaptic transmission between chemoreceptor glomus cells of the carotid body and the afferent carotid sinus nerve. It is however unknown if propofol can also act directly on the glomus cell. Here we report that propofol can indeed inhibit intracellular Ca²⁺ responses to hypoxia and hypercapnia in isolated rat glomus cells. Neither this propofol effect, nor the glomus cell response to hypoxia in the absence of propofol, were influenced by GABA receptor activation (using GABA, muscimol and baclofen) or inhibition (using bicuculline and 5-aminovaleric acid). Suggesting that these effects of propofol are not mediated through GABA receptors. Propofol inhibited calcium responses to nicotine in glomus cells but the nicotinic antagonists vecuronium and methyllycaconitine did not inhibit calcium responses to hypoxia. TASK channel activity was not altered by propofol. The glomus cell Ca²⁺ response to depolarisation with 30 mM K⁺ was however modestly inhibited by propofol. In summary we conclude that propofol does have a direct effect upon hypoxia signalling in isolated type-1 cells and that this may be partially due to its ability to inhibit voltage gated Ca²⁺_v channels. We also note that propofol has the capacity to supress glomus cell excitation via nicotinic receptors and may therefore also interfere with paracrine/autocrine cholinergic signalling in the intact organ. The effects of propofol on chemoreceptor function are however clearly complex and require further investigation.

Glucocorticoid receptor is involved in the neuroprotective effect of ginsenoside Rg1 against inflammation-induced dopaminergic neuronal degeneration in substantia nigra

Accumulating clinical and experimental evidence suggests that chronic neuroinflammation is associated with dopaminergic neuronal death in Parkinson's disease (PD). Ginsenoside Rg1, the most active components of ginseng, possesses a variety of biological effects on the central nervous system, cardiovascular system and immune system. The present study aimed to evaluate the protective effects of ginsenoside Rg1 on lipopolysaccharide (LPS)-induced microglia activation and dopaminergic neuronal degeneration in rat substantia nigra (SN) and its potential mechanisms. Treatment with Rg1 could ameliorate the apomorphine-induced rotational behavior in LPS-lesioned rats. GR antagonist RU486 partly abolished the protective effect of Rg1. Rg1 treatment significantly attenuated LPS-induced loss of tyrosin hydroxlase (TH) positive neurons in substantial nigra par compacta (SNpc) and decreased content of dopamine (DA) and its metabolites in striatum of the lesioned side. Meanwhile, Rg1 significantly inhibited LPS-induced microglial activation and production of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and nitric oxide (NO). These effects were abolished by co-treatment with RU486. In addition, Rg1 treatment significantly inhibited the LPS-induced phosphorylation of IκB, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) in the lesioned side of substantial nigra. These effect could be also partly blocked by RU486. Taken together, these data indicate that Rg1 has protective effects on mesencephalic dopaminergic neurons from LPS-induced microglia inflammation. GR signaling pathway might be involved in the anti-inflammatory effect of Rg1.

Stem cells and regenerative therapies for Parkinson's disease

Currently the mainstay of Parkinson's disease (PD) therapy is the pharmacological replacement of the loss of the dopaminergic nigrostriatal pathway using drugs such as dopamine agonists and levodopa. Whilst these drugs effectively ameliorate some of the motor features of PD, they do not improve many of the nonmotor features that arise secondary to pathology outside of this system, nor do they slow the progressive neurodegeneration that is a characteristic of the disease. Regenerative therapies for PD seek to fill this therapeutic gap, with cell transplantation being the most explored approach to date. A number of different cell sources have been used in this therapeutic approach, but to date, the most successful has been the use of fetal ventral mesencephalic (VM) tissue that contains within it the developing nigral dopaminergic cells. Cell transplantation for PD was pioneered in the 1980-1990s, with several successful open-label trials of fetal VM transplantation in patients with relatively advanced PD. Whilst these findings were not replicated in two subsequent double-blind sham-surgery controlled trials, there were reasons to explain this outside of the one drawn at the time that these therapies are ineffective. Indeed all these studies have provided evidence that following the transplantation of fetal VM tissue, dopaminergic cells can survive long term, produce dopamine, and bring about clinical improvements in younger patients over many years. The use of fetal tissue, irrespective of its true efficacy, will never become a widely available therapy for PD for a host of practical and ethical reasons, and thus much work has been put in recently to exploring the utility of stem cells as a source of nigral dopaminergic neurons. In this respect, the advent of embryonic stem cell and induced pluripotent cells has heralded a new era in cell therapy for PD, and several groups have now demonstrated that these cells can form dopaminergic neurons which improve functional deficits in animal models of PD. Whilst encouraging, problems with respect to the immunogenicity and tumorigenicity of these cells means that they will need to be used in the clinic cautiously. Other regenerative therapies in PD have been tried over the years and include the use of trophic factors. This has primarily involved glial cell line-derived neurotrophic factor (GDNF) and again has produced mixed clinical effects, and in order to try and resolve this, a new trial of intraputamenal GDNF is now being planned. In addition, a new trial for platelet derived growth factor as a treatment for PD has just completed recruitment, and PYM50028 (Cogane) an oral agent shown in animal models to reduce the effects of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) lesioning by the induction of growth factors is currently under investigation in a multicentre Phase II trial. Overall, there are a number of promising new regenerative therapies being developed and tested in PD, although the true long-term efficacy of any of these in large numbers of patients is still not known.

Phosphodiesterase 7 inhibition preserves dopaminergic neurons in cellular and rodent models of Parkinson disease

Background

Phosphodiesterase 7 plays a major role in down-regulation of protein kinase A activity by hydrolyzing cAMP in many cell types. This cyclic nucleotide plays a key role in signal transduction in a wide variety of cellular responses. In the brain, cAMP has been implicated in learning, memory processes and other brain functions.

Methodology/Principal Findings

Here we show a novel function of phosphodiesterase 7 inhibition on nigrostriatal dopaminergic neuronal death. We found that S14, a heterocyclic small molecule inhibitor of phosphodiesterase 7, conferred significant neuronal protection against different insults both in the human dopaminergic cell line SH-SY5Y and in primary rat mesencephalic cultures. S14 treatment also reduced microglial activation, protected dopaminergic neurons and improved motor function in the lipopolysaccharide rat model of Parkinson disease. Finally, S14 neuroprotective effects were reversed by blocking the cAMP signaling pathways that operate through cAMP-dependent protein kinase A.

Conclusions/Significance

Our findings demonstrate that phosphodiesterase 7 inhibition can protect dopaminergic neurons against different insults, and they provide support for the therapeutic potential of phosphodiesterase 7 inhibitors in the treatment of neurodegenerative disorders, particularly Parkinson disease.

Ginsenoside Rg1 protects dopaminergic neurons in a rat model of Parkinson's disease through the IGF-I receptor signalling pathway

BACKGROUND AND PURPOSE

We have shown that ginsenoside Rg1 is a novel class of potent phytoestrogen and activates insulin-like growth factor-I receptor (IGF-IR) signalling pathway in human breast cancer MCF-7 cells. The present study tested the hypothesis that the neuroprotective actions of Rg1 involved activation of the IGF-IR signalling pathway in a rat model of Parkinson's disease, induced by 6-hydroxydopamine (6-OHDA).

EXPERIMENTAL APPROACH

Ovariectomized rats were infused unilaterally with 6-OHDA into the medial forebrain bundle to lesion the nigrostriatal dopamine pathway and treated with Rg1 (1.5 h after 6-OHDA injections) in the absence or presence of the IGF-IR antagonist JB-1 (1 h before Rg1 injections). The rotational behaviour induced by apomorphine and the dopamine content in the striatum were studied. Protein and gene expression of tyrosine hydroxylase, dopamine transporter and Bcl-2 in the substantia nigra were also determined.

KEY RESULTS

Rg1 treatment ameliorated the rotational behaviour induced by apomorphine in our model of nigrostriatal injury. This effect was partly blocked by JB-1. 6-OHDA significantly decreased the dopamine content of the striatum and treatment with Rg1 reversed this decrease. Treatment with Rg1 of 6-OHDA-lesioned rats reduced neurotoxicity, as measured by tyrosine hydroxylase, dopamine transporter and Bcl-2 protein and gene level in the substantia nigra. These effects were abolished by JB-1.

CONCLUSIONS AND IMPLICATIONS

These data provide the first evidence that Rg1 has neuroprotective effects on dopaminergic neurons in the 6-OHDA model of nigrostriatal injury and its actions might involve activation of the IGF-IR signalling pathway.

Cells therapy for Parkinson's disease--so close and so far away

One of the strategies of treating Parkinson's disease (PD) is the replacement of lost neurons in the substantia nigra with healthy dapamingergic cells. Potential sources for cells range from autologous grafts of dopamine secreting cells, fetal ventral mesencephalon tissue, to various stem cell types. Over the past quarter century, many experimental replacement therapies have been tried on PD animal models as well as human patients, yet none resulted in satisfactory outcomes that warrant wide applications. Recent progress in stem cell biology has shown that nuclear transfer embryonic stem cells (ntES) or induced pluripotent stem cells (iPS) derived cells can be used to successfully treat rodent PD models, thus solving the problem of immunorejection and paving the way for future autologous transplantations for treating PD. Meanwhile, however, post mortem analysis of patients who received fetal brain cell transplantation revealed that implanted cells are prone to degeneration just like endogenous neurons in the same pathological area, indicating long-term efficacy of cell therapy of PD needs to overcome the degenerating environment in the brain. A better understanding of neurodegeneration in the midbrain appeared to be a necessary step in developing new cell therapies in Parkinson's disease. It is likely that future cell replacement will focus on not only ameliorating symptoms of the disease but also trying to slow the progression of the disease by either neuroprotection or restoring the micro-environment in the midbrain.

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.

Modification of the number and phenotype of striatal dopaminergic cells by carotid body graft

In non-human primates, striatal tyrosine hydroxylase-immunoreactive (TH-ir) cells are increased in number after dopamine depletion and in response to trophic factor delivery. As carotid body cells contain the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF), we evaluated the number, morphology and neurochemistry of these TH-ir cells, in the anterior and posterior striatum of five monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which received a graft of carotid body cell aggregates (CBCA) (n = 3) or sham surgery (n = 2), and six MPTP-monkeys that were sacrificed 6 months and 3 years after the last MPTP dose [MPTP I (n = 3) and MPTP II (n = 3), respectively]. Three intact monkeys served as controls. A disability rating scale was used for the assessment of parkinsonism in all lesioned animals, both before and after surgery. For the neurochemical examination, tissue sections were double-labelled with antibodies to TH, dopamine transporter, dopa decarboxylase-67, vesicular monoamine transporter 2, glutamic acid decarboxylase -67, calbindin, parvalbumin, calretinin, neuronal nitric oxide synthase and GDNF. Only animals receiving CBCA graft showed a moderate but significant recovery of parkinsonism that persisted 12 months after the graft. The grafted striatum contained the greatest TH-ir cell density (120.4 +/- 10.3 cells/100 mm2), while the control striatum displayed the lowest (15.4 +/- 6.8 cells/100 mm2), and MPTP I, MPTP II and sham-operated monkeys showed a similar intermediate value (66.1 +/- 6.2, 58.3 +/- 17.2 and 57.7 +/- 7.0 cells/100 mm2, respectively). In addition, in the post-commissural striatum, only CBCA graft induced a significant increase in the TH-ir cell density compared to control animals (47.9 +/- 15.9 and 7.9 +/- 3.2, respectively). Phenotypically, TH-ir cells were striatal dopaminergic interneurons. However, in the grafted animals, the phenotype was different from that in control, MPTP and sham-operated monkeys, with the appearance of TH/GDNF-ir cells and the emergence of two TH-ir subpopulations of different size as the two main differentiating features. Our data confirm and extend previous studies demonstrating that striatal CBCA grafts produce a long-lasting motor recovery of MPTP-monkeys along with an increase in the number and phenotype changes of the striatal TH-ir interneurons, probably by the action of the trophic factors contained in carotid body cells. The increased number of striatal TH-ir cells observed in the grafted striatum may contribute to the improvement of parkinsonism observed after the graft.

Transplantation of bone marrow stromal cells containing the neurturin gene in rat model of Parkinson's disease

The experiment was to evaluate the therapeutic benefit of transplanted bone marrow stromal cells (BMSCs) transfected with a kind of neurotrophic factor gene, neurturin (NTN) gene, in treating the rat model of Parkinson's disease (PD). The 6-OHDA-lesioned rats were assigned to one of three groups, those receiving BMSCs transfected with NTN gene, those receiving untransfected BMSCs containing a void plasmid and those receiving phosphate buffer solution (PBS). Treatments were injected into the right striatum (6-OHDA-lesioned side). One to six months post-transplantation, apomorphine-induced rotational behavior was observed. One month after transplantation, green fluorescent protein (GFP)/NTN, GFP/glial fibrillary acidic protein (GFAP), GFP/neuron specific enolase (NSE) and GFP/tyrosine hydroxylase (TH) fluorescence determinations of brain sections were carried out. One to six months after transplantation, brain sections containing striatum and substantia nigra were stained for TH. In situ hybridization and Western blots were used to determine NTN mRNA and protein concentration, respectively, in affected brain regions. High performance liquid chromatography (HPLC) was used to measure the dopamine (DA) content in the lesioned striatum 1 and 3 month(s) post-transplantation. The results were shown that: in the first 3 months after transplantation, the number of rotations was lower in NTN-transplant group than the void vector group, and during 1-6 months post-transplantation, the number of rotations was lower in both transplant groups than that in the PBS group (P<0.05). One month after transplantation, we detected GFP/NTN-, GFP/GFAP- and GFP/NSE-labeled cells in the transplantation area of the NTN-transplanted group, but no obvious GFP/TH labeled cells were found. Quantitative analysis of TH-positive cells 1 to 6 months after transplantation indicated that there were no significant differences between groups in survival rates of TH-positive neurons in the lesioned substantia nigra (P>0.05). In situ hybridization and Western blot identified NTN mRNA and protein expression in the transplantation area of the NTN-transplanted group. After transplantation of NTN-expressing cells, DA content in the lesioned striatum was significantly higher in the transgenic group than that in the void vector group or the PBS group (P<0.05). The overall therapeutic effects of the NTN-transplanted group were superior to those of the void plasmid group and the PBS group. The mechanisms by which transgenic therapy treats PD might involve functional enhancement of residual dopaminergic neurons by NTN, which significantly reduces the number of rotations in animals, but not increase the numbers of existing dopaminergic neurons.

Selective glial cell line-derived neurotrophic factor production in adult dopaminergic carotid body cells in situ and after intrastriatal transplantation

Glial cell line-derived neurotrophic factor (GDNF) exerts a notable protective effect on dopaminergic neurons in rodent and primate models of Parkinson's disease (PD). The clinical applicability of this therapy is, however, hampered by the need of a durable and stable GDNF source allowing the safe and continuous delivery of the trophic factor into the brain parenchyma. Intrastriatal carotid body (CB) autografting is a neuroprotective therapy potentially useful in PD. It induces long-term recovery of parkinsonian animals through a trophic effect on nigrostriatal neurons and causes amelioration of symptoms in some PD patients. Moreover, the adult rodent CB has been shown to express GDNF. Here we show, using heterozygous GDNF/lacZ knock-out mice, that unexpectedly CB dopaminergic glomus, or type I, cells are the source of CB GDNF. Among the neural or paraneural cells tested, glomus cells are those that synthesize and release the highest amount of GDNF in the adult rodent (as measured by standard and in situ ELISA). Furthermore, GDNF expression by glomus cells is maintained after intrastriatal grafting and in CB of aged and parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated animals. Thus, glomus cells appear to be prototypical abundant sources of GDNF, ideally suited to be used as biological pumps for the endogenous delivery of trophic factors in PD and other neurodegenerative diseases.

Transplantation of carotid body cells in the treatment of neurological disorders

Laboratory and clinical studies have shown that intracerebral transplantation of carotid body (CB) cells ameliorate Parkinsonian deficits. The recent clinical study by Arjona and colleagues indicated that CB autograft transplantation is a relatively simple, safe, and viable treatment for PD patients. In particular, Espejo and colleagues demonstrated that the therapeutic efficacy of intracerebral transplantation of the CB in PD was likely obtained through secretion of neurotrophic factors rather than the local release of dopamine, which suggests it possible and reasonable to extend the use of the CB as an efficacious graft source for neural transplantation. Thus, we transplanted CB cell suspensions into the ischemic penumbra within 1h after stroke surgery. The results revealed that CB transplantation also significantly reduced stroke-induced behavioral deficits and cerebral infarction. In this review, we focus on summarizing the physiological properties of the CB related to transplantation, describing briefly possible mechanisms responsible for the effect of CB transplantation, and introducing recent studies of the CB as a donor source for neural transplantation.

Challenges in Parkinson's disease: restoration of the nigrostriatal dopamine system is not enough

Levodopa remains the most effective treatment for Parkinson's disease (PD). However, the drug is complicated by a wide range of adverse effects, most notably motor fluctuations and dyskinesias. Long-acting dopamine agonists are associated with a reduced incidence of these complications and modern surgical approaches and pharmacological methods of providing more continuous dopaminergic stimulation have a substantial ameliorative effect on these problems. Despite these advances, disease progression remains unaffected. For this reason there has been much enthusiasm for cellular therapies designed to replace degenerating nigrostriatal dopaminergic neurons. However, recent fetal transplant trials have failed to show expected benefit and have been complicated by medication dyskinesias". Even if successful, such treatment may be predestined to provide no better outcome than available treatments given current medical and surgical experience that emphasises the increasingly critical role of "non-dopaminergic" symptoms to quality of life in late-stage PD. Knowledge of the widespread, multisystem nature of the neurodegeneration that accounts for these problems suggests that restoration of the nigrostriatal dopamine system should not be the ultimate goal of future research.

The cellular repair of the brain in Parkinson's disease—past, present and future

Damage to the central nervous system was once considered irreparable. However, there is now growing optimism that neural transplant therapies may one day enable complete circuit reconstruction and thus functional benefit for patients with neurodegenerative conditions such as Parkinson's disease (PD), and perhaps even those with more widespread damage such as stroke patients. Indeed, since the late 1980s hundreds of patients with Parkinson's disease have received allografts of dopamine-rich embryonic human neural tissue. The grafted tissue has been shown to survive and ameliorate many of the symptoms of the disease, both in the clinical setting and in animal models of the disease. However, practical problems associated with tissue procurement and storage, and ethical concerns over using aborted human fetal tissue have fuelled a search for alternative sources of suitable material for grafting. In particular, stem cells and xenogeneic embryonic dopamine-rich neural tissue are being explored, both of which bring their own practical and ethical dilemmas. Here we review the progress made in neural transplantation, both in the laboratory and in the clinic with particular attention to the development of stem cell and xenogeneic tissue based therapy.

Autotransplantation of human carotid body cell aggregates for treatment of Parkinson's disease

OBJECTIVE

In this study, we assessed the feasibility of autotransplantation of carotid body (CB) cell aggregates into the striatum for the treatment of patients with Parkinson's disease (PD).

METHODS

Six patients with advanced PD underwent bilateral autotransplantation of CB cell aggregates into the striatum. They were evaluated clinically preoperatively and for 18 months after surgery according to the recommendations of the Core Assessment Program for Intracerebral Transplantation.

RESULTS

No major complications or adverse events resulted from the cell implantation or surgical procedures. During the course of the study, there was no significant aggravation of dyskinesia or decline in cognitive function in any of the patients. Five of the six patients who underwent transplantation manifested a measurable degree of clinical improvement evidenced by standardized clinical rating scales for PD. A decrease in the blinded Unified Parkinson's Disease Rating Scale Part III in the "off" state, the main measure of transplant efficacy in our study, was found to be maximal (between 26 and 74%) at 6 months after surgery. At 1 year, clear reductions in the blinded Unified Parkinson's Disease Rating Scale Part III were maintained in three patients (24, 38, and 52%, respectively). Modest improvement was seen in two patients (13 and 17%), and the sole patient who showed no improvement had the most fibrosis in the CB. The age of the patient and the state of the CB tissue were adversely correlated with clinical improvement after CB autotransplantation.

CONCLUSION

This pilot study indicates that CB autograft transplantation is a relatively simple, safe, and viable therapeutical approach for the treatment of patients with advanced PD. More studies are needed to optimize the procedure and to assess its general applicability for the treatment of patients with PD.

Trophic restoration of the nigrostriatal dopaminergic pathway in long-term carotid body-grafted parkinsonian rats

We studied the mechanisms underlying long-term functional recovery of hemiparkinsonian rats grafted intrastriatally with carotid body (CB) cell aggregates. Amelioration of their motor syndrome is a result of the trophic actions of these grafts on the remaining ipsilateral substantia nigra neurons rather than of the release of dopamine from the CB grafts. The grafts maintain a stable morphological appearance and differentiated cell phenotype for the duration of the life of the host. Adult CB expresses high levels of glial cell line-derived neurotrophic factor (GDNF) and the multicomponent GDNF receptor complex. These properties may contribute to the trophic actions of the CB transplants on nigrostriatal neurons and to their extraordinary longevity. We show that CB glomus cells, although highly dopaminergic, are protected from dopamine-mediated oxidative damage because of the absence of the high-affinity dopamine transporter. Thus, intrastriatal CB grafts are uniquely suited for long-term delivery of trophic factors capable of promoting restoration of the nigrostriatal pathway.