GM1 ganglioside partially rescues cultured dopaminergic neurons from MPP(+)-induced damage: dependence on initial damage and time of treatment

Ganglioside GM1 and the Central Nervous System

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

GM1 Oligosaccharide Efficacy in Parkinson's Disease: Protection against MPTP

Past evidence has shown that the exogenous administration of GM1 ganglioside slowed neuronal death in preclinical models of Parkinson's disease, a neurodegenerative disorder characterized by the progressive loss of dopamine-producing neurons: however, the physical and chemical properties of GM1 (i.e., amphiphilicity) limited its clinical application, as the crossing of the blood-brain barrier is denied. Recently, we demonstrated that the GM1 oligosaccharide head group (GM1-OS) is the GM1 bioactive portion that, interacting with the TrkA-NGF complex at the membrane surface, promotes the activation of a multivariate network of intracellular events regulating neuronal differentiation, protection, and reparation. Here, we evaluated the GM1-OS neuroprotective potential against the Parkinson's disease-linked neurotoxin MPTP, which destroys dopaminergic neurons by affecting mitochondrial bioenergetics and causing ROS overproduction. In dopaminergic and glutamatergic primary cultures, GM1-OS administration significantly increased neuronal survival, preserved neurite network, and reduced mitochondrial ROS production enhancing the mTOR/Akt/GSK3β pathway. These data highlight the neuroprotective efficacy of GM1-OS in parkinsonian models through the implementation of mitochondrial function and reduction in oxidative stress.

Protective Effect of GM1 Attenuates Hippocampus and Cortex Apoptosis After Ketamine Exposure in Neonatal Rat via PI3K/AKT/GSK3β Pathway

Ketamine is a widely used analgesic and anesthetic in obstetrics and pediatrics. Ketamine is known to promote neuronal death and cognitive dysfunction in the brains of humans and animals during development. Monosialotetrahexosyl ganglioside (GM1), a promoter of brain development, exerts neuroprotective effects in many neurological disease models. Here, we investigated the neuroprotective effect of GM1 and its potential underlying mechanism against ketamine-induced apoptosis of rats. Seven-day-old Sprague Dawley (SD) rats were randomly divided into the following four groups: (1) group C (control group: normal saline was injected intraperitoneally); (2) group K (ketamine); (3) group GM1 (GM1 was given before normal saline injection); and (4) GM1+K group (received GM1 30 min before continuous exposure to ketamine). Each group contained 15 rats, received six doses of ketamine (20 mg/kg), and was injected with saline every 90 min. The Morris water maze (MWM) test, the number of cortical and hippocampal cells, apoptosis, and AKT/GSK3β pathway were analyzed. To determine whether GM1 exerted its effect via the PI3K/AKT/GSK3β pathway, PC12 cells were incubated with LY294002, a PI3K inhibitor. We found that GM1 protected against ketamine-induced apoptosis in the hippocampus and cortex by reducing the expression of Bcl-2 and Caspase-3, and by increasing the expression of Bax. GM1 treatment increased the expression of p-AKT and p-GSK3β. However, the anti-apoptotic effect of GM1 was eliminated after inhibiting the phosphorylation of AKT. We showed that GM1 lessens ketamine-induced apoptosis in the hippocampus and cortex of young rats by regulating the PI3K/AKT/GSK3β pathway. Taken together, GM1 may be a potential preventive treatment for the neurotoxicity caused by continuous exposure to ketamine.

Ganglioside GM1 Targets Astrocytes to Stimulate Cerebral Energy Metabolism

Gangliosides are major constituents of the plasma membrane and are known to promote a number of physiological actions in the brain, including synaptic plasticity and neuroprotection. In particular, the ganglioside GM1 was found to have a wide range of preclinical and clinical benefits in brain diseases such as spinal cord injury, Huntington’s disease and Parkinson’s disease. However, little is known about the underlying cellular and molecular mechanisms of GM1 in the brain. In the present study, we show that GM1 exerts its actions through the promotion of glycolysis in astrocytes, which leads to glucose uptake and lactate release by these cells. In astrocytes, GM1 stimulates the expression of several genes involved in the regulation of glucose metabolism. GM1 also enhances neuronal mitochondrial activity and triggers the expression of neuroprotection genes when neurons are cultured in the presence of astrocytes. Finally, GM1 leads to a neuroprotective effect in astrocyte-neuron co-culture. Together, these data identify a previously unrecognized mechanism mediated by astrocytes by which GM1 exerts its metabolic and neuroprotective effects.

Gangliosides: Treatment Avenues in Neurodegenerative Disease

Gangliosides are cell membrane components, most abundantly in the central nervous system (CNS) where they exert among others neuro-protective and -restorative functions. Clinical development of ganglioside replacement therapy for several neurodegenerative diseases was impeded by the BSE crisis in Europe during the 1990s. Nowadays, gangliosides are produced bovine-free and new pre-clinical and clinical data justify a reevaluation of their therapeutic potential in neurodegenerative diseases. Clinical experience is greatest with monosialo-tetrahexosyl-ganglioside (GM1) in the treatment of stroke. Fourteen randomized controlled trials (RCTs) in overall >2,000 patients revealed no difference in survival, but consistently superior neurological outcomes vs. placebo. GM1 was shown to attenuate ischemic neuronal injuries in diabetes patients by suppression of ERK1/2 phosphorylation and reduction of stress to the endoplasmic reticulum. There is level-I evidence from 5 RCTs of a significantly faster recovery with GM1 vs. placebo in patients with acute and chronic spinal cord injury (SCI), disturbance of consciousness after subarachnoid hemorrhage, or craniocerebral injuries due to closed head trauma. In Parkinson's disease (PD), two RCTs provided evidence of GM1 to be superior to placebo in improving motor symptoms and long-term to result in a slower than expected symptom progression, suggesting disease-modifying potential. In Alzheimer's disease (AD), the role of gangliosides has been controversial, with some studies suggesting a "seeding" role for GM1 in amyloid β polymerization into toxic forms, and others more recently suggesting a rather protective role in vivo. In Huntington's disease (HD), no clinical trials have been conducted yet. However, low GM1 levels observed in HD cells were shown to increase cell susceptibility to apoptosis. Accordingly, treatment with GM1 increased survival of HD cells in vitro and consistently ameliorated pathological phenotypes in several murine HD models, with effects seen at molecular, cellular, and behavioral level. Given that in none of the clinical trials using GM1 any clinically relevant safety issues have occurred to date, current data supports expanding GM1 clinical research, particularly to conditions with high, unmet medical need.

GM1 ganglioside in Parkinson's disease: Pilot study of effects on dopamine transporter binding

OBJECTIVE

GM1 ganglioside has been suggested as a treatment for Parkinson's disease (PD), potentially having symptomatic and disease modifying effects. The current pilot imaging study was performed to examine effects of GM1 on dopamine transporter binding, as a surrogate measure of disease progression, studied longitudinally.

METHODS

Positron emission tomography (PET) imaging data were obtained from a subset of subjects enrolled in a delayed start clinical trial of GM1 in PD [1]: 15 Early-start (ES) subjects, 14 Delayed-start (DS) subjects, and 11 Comparison (standard-of-care) subjects. Treatment subjects were studied over a 2.5 year period while Comparison subjects were studied over 2 years. Dynamic PET scans were performed over 90 min following injection of [(11)C]methylphenidate. Regional values of binding potential (BPND) were analyzed for several striatal volumes of interest.

RESULTS

Clinical results for this subset of subjects were similar to those previously reported for the larger study group. ES subjects showed early symptomatic improvement and slow symptom progression over the study period. DS and Comparison subjects were initially on the same symptom progression trajectory but diverged once DS subjects received GM1 treatment. Imaging results showed significant slowing of BPND loss in several striatal regions in GM1-treated subjects and in some cases, an increased BPND in some striatal regions was detected after GM1 use.

INTERPRETATION

Results of this pilot imaging study provide additional data to suggest a potential disease modifying effect of GM1 on PD. These results need to be confirmed in a larger number of subjects.

Isolation and purification of monosialotetrahexosylgangliosides from pig brain by extraction and liquid chromatography

Monosialotetrahexosylganglioside (GM1), one of glycosphingolipids containing sialic acid, plays particularly important role in fighting against paralysis, dementia and other diseases caused by brain and nerve damage. In this work, a simple and highly efficient method with high yield was developed for isolation and purification of GM1 from pig brain. The method consisted of an extraction by chloroform-methanol-water and a two-step chromatographic separation by DEAE-Sepharose Fast Flow anion-exchange medium and Sephacryl S-100 HR size-exclusion medium. The purified GM1 was proved to be homogeneous and had a purity of >98.0% by high-performance anion-exchange and size-exclusion chromatography. The molecular weight was 30.0 kDa by high-performance size-exclusion chromatography and 1546.9 Da by electrospray ionization mass spectrometry. The chromogenic reaction by resorcinol-hydrochloric acid solution indicated that the purified GM1 showed a specific chromogenic reaction of sialic acid. Through this isolation and purification program, ~1.0 mg of pure GM1 could be captured from 500 g wet pig brain tissue and the yield of GM1 was around 0.022%, which was higher than the yields by other methods. The method may provide an alternative for isolation and purification of GM1 in other biological tissues.

A randomized, controlled, delayed start trial of GM1 ganglioside in treated Parkinson's disease patients

The present single center, double-blind, delayed start study was conducted to examine possible symptomatic and disease-modifying effects of GM1 ganglioside in Parkinson's disease (PD). Seventy-seven subjects with PD were randomly assigned to receive GM1 for 120 weeks (early-start group) or placebo for 24 weeks followed by GM1 for 96 weeks (delayed-start group). Washout evaluations occurred at 1 and 2 years after the end of treatment. Seventeen additional subjects who received standard-of-care were followed for comparative information about disease progression. Primary outcome was change from baseline Unified Parkinson's Disease Rating Scale (UPDRS) motor scores. At week 24, the early-start group had significant improvement in UPDRS motor scores vs. a significant worsening of scores in the delayed-start group. The early-start group also showed a sustained benefit vs. the delayed-start group at week 72 and at week 120. Both groups had significant symptom worsening during washout. This study provides evidence that GM1 use for 24 weeks was superior to placebo for improving motor symptoms and that extended GM1 use (up to 120 weeks) resulted in a lower than expected rate of symptom progression. The data from this small study suggest that GM1 may have symptomatic and potentially disease modifying effects on PD.

Trisialoganglioside GT1b induces in vivo degeneration of nigral dopaminergic neurons: role of microglia

We recently showed that trisialoganglioside (GT1b) induces cell death of dopaminergic neurons in rat mesencephalic cultures (Chung et al., Neuroreport 12:611-614, 2001). The present study examines the in vivo neurotoxic effects of GT1b on dopaminergic neurons in the substantia nigra (SN) of Sprague-Dawley rats. Seven days after GT1b injection into the SN, immunocytochemical staining of SN tissue revealed death of nigral neurons, including dopaminergic neurons. Additional immunostaining using OX-42 and OX-6 antibodies showed that GT1b-activated microglia were present in the SN where degeneration of nigral neurons was found. Western blot analysis and double-labeled immunohistochemistry showed that inducible nitric oxide synthase (iNOS) was expressed in the SN, where its levels were maximal at 8 h post-GT1b injection, and that iNOS was localized exclusively within microglia. GT1b-induced loss of dopaminergic neurons in the SN was partially inhibited by N(G)-nitro-L-arginine methyl ester hydrochloride, an NOS inhibitor. Our results indicate that in vivo neurotoxicity of GT1b against nigral dopaminergic neurons is at least in part mediated by nitric oxide released from activated microglia. Because GT1b exists abundantly in central nervous system neuronal membranes, our data support the hypothesis that immune-mediated events triggered by endogenous compounds such as GT1b could contribute to the initiation and/or the progression of dopaminergic neuronal cell death that occurs in Parkinson's disease.

Antioxidant compounds protect dopamine neurons from death due to oxidative stress in vitro

Using tissue culture models of oxidative stress caused by serum deprivation or MPTP/MPP+ toxicity, the present study establishes that the antioxidants epigallocatechin gallate, lazaroids U74389G and U83836E, reservatrol, MnTBAP, MCI 186, trolox, and melatonin protect 68-100% of dopamine (DA) neurons from cell death. In contrast, the nitric oxide inhibitor LY83583, the caspase inhibitors Z-VAD-FMK, Ac-DQMD-CHO and Z-DEVD-FMK, and the CDK-5 inhibitor, roscovotine were not neuroprotective, although death was often delayed by 1 day in vitro. We conclude that antioxidants are more effective at preventing cell death in vitro than are inhibitors at later stages in the death cascade.

GT1b ganglioside induces death of dopaminergic neurons in rat mesencephalic cultures

We examined neurotoxicity of GT1b against dopaminergic neurons in vitro. Cultures of mesencephalic cells deprived of serum underwent the loss of 19% of tyrosine hydroxylase immunopositive (TH-ip) neurons. In cultures deprived of serum, treatment with 10-30 microg/ml GT1b attenuated the number of TH-ip neurons by 26-69%, respectively, compared to non-treated cultures. Intriguingly, cultures deprived of serum were more vulnerable to GT1b-induced neurotoxicity. Application of 60 microg/ml GT1b to cultures grown in serum containing media resulted in the loss of 26% of TH-ip neurons, similar to that (28%) observed in serum-deprived cultures treated with 10 microg/ml GT1b. Moreover, in our cultures, absence of nitric oxide (NO) production after GT1b treatment was obvious. The present results strongly suggest direct neurotoxic actions of GT1b against dopaminergic neurons regardless of NO.

GM1 ganglioside in the treatment of Parkinson's disease

Since the early 1980s, numerous studies have been reported by laboratories around the world documenting the beneficial effects of GM1 ganglioside treatment on the damaged dopamine system in various animal and in vitro models. Based on the strength of these data, the first clinical studies designed to assess the efficacy and safety of chronic GM1 use in the treatment of Parkinson's disease were performed. In a double-blind placebo-controlled study, significant improvements in GM1-treated patients were demonstrated in clinical motor ratings, timed tests of motor function, activities of daily living, and some aspects of neuropsychological functioning. Patients who have elected to continue using GM1 in an open extension trial have either continued to improve over time or have shown initial functional improvements and their disease has remained stable (i.e., no symptom progression) after two years. These results suggest that long-term use of GM1 is safe and may work to partially reverse the degenerative process in established Parkinson's disease patients.

The effects of L-deprenyl treatment, alone and combined with GM1 ganglioside, on striatal dopamine content and substantia nigra pars compacta neurons

The present study examined the effects of GM1 ganglioside and the monoamine oxidase B (MAO-B) inhibitor L-deprenyl, alone and in combination, on striatal dopamine (DA) and DOPAC levels, and the density of tyrosine hydroxylase (TH) positive neurons in the substantia nigra pars compacta (SNc) of C57bl/6J mice following MPTP administration (20 mg/kg, s.c., twice daily for 5 days). GM1 treatment (30 mg/kg, i.p., daily for 3 weeks, beginning 24 h after the last MPTP injection) partially restored striatal DA levels and rescued SNc neurons. A high dose of L-deprenyl, inhibiting MAO-B activity, (10 mg/kg, i.p. every other day for 3 weeks beginning 3 days after the last MPTP injection) increased striatal DA content, but did not rescue TH-positive SNc neurons. A low dose of L-deprenyl (0.01 mg/kg, i.p. every other day for 3 weeks beginning 3 days after the last MPTP injection) had no effect on either striatal neurochemistry or the rescue of SNc TH-positive neurons. Co-administration of GM1 and high dose L-deprenyl caused a synergistic increase in striatal DA levels, above that obtained with either GM1 or high dose L-deprenyl alone. Co-administration of GM1 and low dose L-deprenyl was not only not synergistic, but caused GM1s effects to be antagonized. The results do not confirm previous findings that low dose L-deprenyl administration in vivo after MPTP can rescue SNc neurons. Given GM1's potential as an adjunct to present anti-parkinsonian medications which include L-deprenyl, it will be important to further investigate the interactions between these two potential therapies.

Melatonin rescues dopamine neurons from cell death in tissue culture models of oxidative stress

Dopamine (DA) neurons are uniquely vulnerable to damage and disease. Their loss in humans is associated with diseases of the aged, most notably, Parkinson's Disease (PD). There is now a great deal of evidence to suggest that the destruction of DA neurons in PD involves the accumulation of harmful oxygen free radicals. Since the antioxidant hormone, melatonin, is one of the most potent endogenous scavengers of these toxic radicals, we tested its ability to rescue DA neurons from damage/death in several laboratory models associated with oxidative stress. In the first model, cells were grown in low density on serum-free media. Under these conditions, nearly all cells died, presumably due to the lack of essential growth factors. Treatment with 250 microM melatonin rescued nearly all dying cells (100% tau+ neurons), including tyrosine hydroxylase immunopositive DA neurons, for at least 7 days following growth factor deprivation. This effect was dose and time dependent and was mimicked by other antioxidants such as 2-iodomelatonin and vitamin E. Similarly, in the second model of oxidative stress, 250 microM melatonn produced a near total recovery from the usual 50% loss of DA neurons caused by neurotoxic injury from 2.5 microM 1-methyl-4-phenylpyridine (MPP+). These results indicate that melatonin possesses the remarkable ability to rescue DA neurons from cell death in several experimental paradigms associated with oxidative stress.

Tyrosine hydroxylase and aromatic L-amino acid decarboxylase in mesencephalic cultures after MPP+: the consequences of treatment with GM1 ganglioside

Rat embryonic mesencephalic cultures were treated with the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+), and GM1 ganglioside added after the toxin. Twelve days after a 24-h exposure to MPP+, there was a significant decrement in tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AAAD) activities. In addition, TH mRNA was decreased, whereas AAAD mRNA was no different from control cultures. Adding GM1 to control unlesioned cultures had no effect on TH activity or mRNA. In contrast, GM1 modestly increased both the activity and mRNA for AAAD. In the MPP+-treated cultures, GM1 induced a partial recovery of TH and AAAD activity and increased mRNA for both above unlesioned control levels. Our studies demonstrate that GM1 upregulates the synthetic enzymes for dopamine in MPP+-lesioned embryonic mesencephalic cultures, and suggest that TH and AAAD respond differentially to the neurotoxin insult.

The effects of nerve growth factor and ganglioside GM1 on the anti-proliferative activity of cocaine in PC12 cells

The anti-proliferative activity of cocaine was determined in PC12 phenochromocytoma cells. The effects of nerve growth factor (NGF) and ganglioside GM1 (GM1) on the toxicity of this stimulant of abuse was examined over a period of 72 h. Cocaine (40 microM-320 microM) exhibited a dose-dependent inhibition of cellular proliferation as determined by 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) reduction. While NGF (100 ng/ml) and GM1 (100 microM) alone partially reversed the cocaine-induced inhibition of proliferation, the combination of NGF and GM1 afforded additional protection that was greater than that of either agent individually.

Ganglioside GM1 and GM3 in early human brain development: an immunocytochemical study

The distribution of GM1 and GM3 gangliosides in human brain development between gestational week (g.w.) 6 and 15 was demonstrated by an immunocytochemical approach using polyclonal anti-GM1 and anti-GM3 antibodies. The first appearance of GM1- and GM3-positive cells was recorded as early as in g.w.6. Both antibodies labeled the cells in the ventricular zone of the telencephalic wall, with radially oriented fibers toward the pial surface, which represent radial glia cells with glia fibers. The intensive GM3 immunoreactivity was also exhibited in proliferating cells in the ventricular zone between g.w.6 and 12. During the period from g.w. 12 to 15, characterized by a rapid multiplication of neurons and glia cells, an increased number of GM1- and GM3-positive cells was observed. Prominent GM1 ganglioside staining was observed at the surface of the cell bodies in the ventricular zone. Besides surface labeling in migrating cells, GM1 immunoreactivity was identified inside the soma in the regions of cortical plate and subplate. GM1 immunoreactivity was more pronounced on the membrane of neuronal cells migrating along radial glia fibers, especially at the contact site between neuronal and glial cells. The GM3 ganglioside was localized mostly inside the soma, showing a granular immunoreactivity pattern. Our observations confirm the presence of GM1 and GM3 gangliosides in neuronal and glial cells in early human brain development. The involvement, especially of GM1 ganglioside in glia-neuronal contacts during migration of neuroblasts to their final destination, as well as the presence of GM3 ganglioside in proliferative cells in the ventricular zone of the telencephalic wall was also recorded.

GM1 ganglioside rescues substantia nigra pars compacta neurons and increases dopamine synthesis in residual nigrostriatal dopaminergic neurons in MPTP-treated mice

GM1 ganglioside has been shown to stimulate recovery of the damaged dopamine system under a number of different circumstances. In addition to rescue of damaged dopamine neurons, the present study assessed the ability of GM1 to enhance the synthesis of dopamine in remaining nigrostriatal neurons following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure. There was a significantly greater accumulation of L-dopa 30 min after aromatic amino acid decarboxylase inhibition with NSD-1015 (100 mg/kg) and an increase in the ratio of L-dopa to dopamine in MPTP+GM1-treated mice than in mice that received only MPTP. This effect of GM1 on dopamine synthesis was dependent upon the degree of initial damage to the nigrostriatal dopamine system. That is, the GM1 effect on dopamine synthesis could not be demonstrated in mice with greater than 95% striatal dopamine loss and 75% substantia nigra dopamine neuron loss. These results suggest that in addition to previously reported effects of GM1 on rescue and repair of dopaminergic neurons, GM1 may also have the ability to enhance dopamine synthesis in residual dopaminergic neurons. Direct effects on dopamine neurochemistry may contribute to functional improvement seen after GM1 treatment in various models of parkinsonism.

Response of the damaged dopamine system to GM1 and semisynthetic gangliosides: effects of dose and extent of lesion

GM1 ganglioside, administered to young C57/B16J mice with moderate (approx 85%) 1-methyl-4-phenyl-1,2,3,6-terahydropyridine (MPTP)-induced striatal dopamine depletions, caused a dose-dependent increase in striatal dopamine levels. This effect was maximal between 7.0 and 30.0 mg/kg and was not apparent at higher and lower doses of GM1. GM1 ganglioside treatment had no effect on striatal dopamine levels in mice with more extensive lesions of the dopamine system (i.e. approx 93% loss of striatal dopamine). The semisynthetic ganglioside derivative LIGA 20, administered orally, also increased striatal dopamine levels in moderately lesioned animals, albeit at lower doses than GM1. LIGA 20 administration also resulted in increased striatal dopamine levels in animals with more extensive dopamine lesions, where GM1 had no effect. These results show that both GM1 and its semisynthetic derivative LIGA 20 can partially restore striatal dopamine levels in MPTP-treated mice and that LIGA 20 is more potent and not subject to the same dose-limiting effects as GM1.

Enhanced restoration of striatal dopamine concentrations by combined GM1 ganglioside and neurotrophic factor treatments

Intraperitoneal injection of GM1 ganglioside or intracerebroventricular infusion of basic fibroblast growth factor (FGF-2) or epidermal growth factor (EGF) partially restored dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the striatum of young MPTP-treated mice. Combined treatments of GM1 ganglioside with FGF-2 or EGF produced a greater restoration of striatal dopamine levels than treatments with GM1 or either of the neurotrophic factors alone. GM1 treatment, but not trophic factor treatments caused significant sparing of substantia nigra pars compacta (SNc) tyrosine hydroxylase (TH)-positive neurons. These results confirm previous findings that GM1 provides trophic support for damaged dopamine neurons and suggests that GM1, FGF-2, and EGF may also enhance dopaminergic function in residual neurons. The results also suggest that a potentially fruitful approach to treating degenerative disorders of the dopamine system may be the use of combined trophic factor therapies.

Purification of dopamine neurons by flow cytometry

The heterogeneity and preponderence of other cell types present in cultures has greatly impeded our ability to study dopamine neurons. In this report, we describe methods for isolating nearly pure dopamine neurons for study in culture. To do so, the lipid-soluble dye, 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (diI) was injected into the embryonic rat striata where it was taken up by nerve terminals and transported overnight back to the innervating perikarya in the ventral midbrain. Midbrain cells were then dissected, dissociated and separated on the basis of their (rhodamine) fluorescence by flow cytometry. Nearly all cells recovered as fluorescent positive (> 98%) were also immunoreactive for the dopamine specific enzyme tyrosine hydroxylase (80%-96%). Little contamination by other cells types was observed after labeling for specific neuronal and glial markers. Purified dopamine neurons continued to thrive and elaborate neuronal processes for at least 3 days in culture. Using this new model, it may now be possible to directly study the cellular and molecular processes regulating the survival and functioning of developing, injured and transplanted dopamine neurons.