MPTP-treated Groups Research Articles

MPTP- Induced BALB/C Mice Recapitulate Compensatory Parkinson’s-Like Motor Features

This study aimed to assess motor responses and associated pathological changes caused by MPTP neurotoxicity in Balb/c mice. Male mice (13 weeks old, 25-30 g) were divided into four groups and received intraperitoneal injections of normal saline or different doses of MPTP-HCl for five consecutive days. Body weight was monitored, and behavioral tests were conducted. Histological examination with H&E staining was performed on the striatum and substantia nigra. Contrary to expectations, MPTP-treated mice showed increased locomotor activity in the open field test, covering a greater distance and exhibiting more rearing compared to control mice (p<0.05). The catalepsy test also showed lower catalepsy scores in the MPTP-treated group (p<0.05). However, the pole test did not indicate the presence of MPTP-induced bradykinesia (p>0.05). Similarly, the traction and hang tests showed no significant effects of MPTP on motor balance or muscle strength (p>0.05). Among the MPTP-treated groups, the 30 mg/kg MPTP-HCl group displayed the most severe pathological changes, including reactive gliosis, as observed in histological examination. In conclusion, the subacute MPTP mouse model used in this study did not exhibit noticeable motor deficits or significant weight loss in Balb/c mice, possibly due to subthreshold dopamine depletion compensatory mechanisms. This model could provide valuable insights into the compensatory mechanisms involved in Parkinson's disease.

TLR2 deficiency is beneficial at the late phase in MPTP-induced Parkinson’ disease mice

AimsParkinson's disease (PD) is a progressive neurodegenerative disorder. The etiology of PD is still elusive but neuroinflammation is proved to be an important contributor. Toll-like receptor 2 (TLR2) involves in the release of several inflammatory cytokines. Whether TLR2 serves as a mediator contributing to the damage of DA system in PD remain unclear. Main methodsTlr2 knockout (Tlr2−/−) and wild-type (WT) mice were treated with a subacute regimen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). At 3, 7 and 14 days after MPTP injection, the behavioral performance, including the Pole test, the Rotarod test, the Rearing test and the Wire hang test was evaluated. Moreover, the PD-like phenotypes, including dopaminergic degeneration, the activation of glial cells and the α-Syn expression were systematically analyzed in the nigrostriatal pathway. Finally, the composition of gut microbiota in the MPTP-treated groups were assessed. Key findingsTLR2 deficiency had no obvious impact on the dopaminergic injury at 3 and 7 days following MPTP administration. On the contrary, at 14 days post injection, TLR2 deficiency not only significantly attenuated motor deficits in the Pole test and the Rotarod test, and the nigrostriatal dopaminergic degeneration, but also mitigated α-Syn abnormality, astrocyte activation and neuroinflammation through the suppressed TLR2/MyD88/TRAF6/NF-κB signaling pathways. Additionally, the alteration of gut microbiota was also detected in the mutant mice. SignificanceThese findings highlight the neuroprotective effect of TLR2-pathways at the late phase in the MPTP-induced PD mouse model.

Decreased Mcl-1 protein level in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a well-known neurotoxicant that can selectively destroy dopaminergic neurons and MPTP-treated animals are often used as models for studying aspects of Parkinson’s disease (PD). While apoptosis has been suggested as a possible mechanism underlying MPTP-induced cell death and several apoptosis-associated proteins have been implicated in MPTP-animal models, relevant information regarding the possible involvement of Mcl-1 (myeloid cell leukemia 1) protein is missing. Mcl-l is an important member of the Bcl-2 family that is thought to be a highly regulated controller of cell death and survival. However, the expression level of Mcl-1 in response to MPTP-treatment has not been examined in any area of the brain previously. In the present study, an acute MPTP treatment regimen was utilized with male C57BL/6 mice (10 mg/kg i.p. injections, 4 times with 2 h intervals) and several protein markers were examined 24-h after the initial injection. Dramatic decreases in the immunoreactivities of tyrosine hydroxylase and dopamine transporters were observed. Western-blot analysis and immunocytochemical labeling demonstrated an MPTP-induced decrease in Mcl-1 protein levels in the striatum. In addition, the two proteins BAX and ERK, both of which are also involved in apoptosis signaling, were examined. While the total BAX levels showed no significant difference between the control and MPTP-treated groups, levels of phosphorylated ERK were significantly increased following MPTP-treatment. Since Mcl-1 is an anti-apoptotic protein, down-regulation of Mcl-1 following MPTP-treatment would be expected to lead to increased apoptotic activities processes, leading to increased neurodegeneration.

Proteomic profiling in MPTP monkey model for early Parkinson disease biomarker discovery

Identification of reliable and robust biomarkers is crucial to enable early diagnosis of Parkinson disease (PD) and monitoring disease progression. While imperfect, the slow, chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced non-human primate animal model system of parkinsonism is an abundant source of pre-motor or early stage PD biomarker discovery. Here, we present a study of a MPTP rhesus monkey model of PD that utilizes complementary quantitative iTRAQ-based proteomic, glycoproteomics and phosphoproteomics approaches. We compared the glycoprotein, non-glycoprotein, and phosphoprotein profiles in the putamen of asymptomatic and symptomatic MPTP-treated monkeys as well as saline injected controls. We identified 86 glycoproteins, 163 non-glycoproteins, and 71 phosphoproteins differentially expressed in the MPTP-treated groups. Functional analysis of the data sets inferred the biological processes and pathways that link to neurodegeneration in PD and related disorders. Several potential biomarkers identified in this study have already been translated for their usefulness in PD diagnosis in human subjects and further validation investigations are currently under way. In addition to providing potential early PD biomarkers, this comprehensive quantitative proteomic study may also shed insights regarding the mechanisms underlying early PD development. This article is part of a Special Issue entitled: Neuroproteomics: Applications in neuroscience and neurology.

Therapeutic Effects of Rapamycin on MPTP-Induced Parkinsonism in Mice

In neurodegenerative disorders such as Parkinson's disease (PD), autophagy is implicated in the process of dopaminergic neuron cell death. The α-synuclein protein is a major component of Lewy bodies and Lewy neurites, and mutations in α-synuclein have been implicated in the etiology of familial PD. The current work investigates the mechanisms underlying the therapeutic effects of the autophagy-stimulating antibiotic rapamycin in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Male C57BL/6 mice were treated with intravenous rapamycin or saline control for 7 days following MPTP administration. Immunohistochemistry and western blotting were used to detect alterations in the expression of PD biomarkers, including tyrosine hydroxylase (TH), and the level of autophagy was evaluated by the detection of both microtubule-associated protein light chain 3 (LC3) and α-Synuclein cleavage. In addition, levels of monoamine neurotransmitters were measured in the striatum using high performance liquid chromatography (HPLC). Immunohistochemistry using antibodies against TH indicated that the number of dopaminergic neurons in the substantia nigra following MPTP treatment was significantly higher in rapamycin-treated mice compared with saline-treated controls (p < 0.01). Levels of TH expression in the striatum were similar between the groups. α-synuclein Immunoreactivity was significantly decreased in rapamycin-treated mice compared with controls (p < 0.01). Immunoreactivity for LC3, however, was significantly higher in the rapamycin-treated animals than controls (p < 0.01). The concentrations of both striatal dopamine, and the dopamine metabolite DOPAC, were significantly decreased in both MPTP-treated groups compared with untreated controls. The loss of DOPAC was less severe in rapamycin-treated mice compared with saline-treated mice (p < 0.01) following MPTP treatment. These results demonstrate that treatment with rapamycin is able to prevent the loss of TH-positive neurons and to ameliorate the loss of DOPAC following MPTP treatment, likely via activation of autophagy/lysosome pathways. Thus, further investigation into the effectiveness of rapamycin administration in the treatment of PD is warranted.

Therapeutic Effects of Valproate Combined With Lithium Carbonate on MPTP-Induced Parkinsonism in Mice: Possible Mediation Through Enhanced Autophagy

ABSTRACTIn order to investigate the mechanisms and therapeutic effects of valproate combined with lithium carbonate on mouse model of Parkinson's disease (PD), male C57BL/6 mice were injected into intraperitoneal with valproate (20 μg/ml) combined with lithium carbonate (10 μg/ml) for 7 days following 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) (30 mg/kg) administration, and the effects on motor function were analyzed. Immunohistochemistry and Western blotting were used to detect alterations in the expression of PD biomarkers, including tyrosine hydroxylase (TH), and the level of autophagy was evaluated by the detection of microtubule-associated protein light chain 3 (LC3). In addition, the levels of monoamine neurotransmitters were measured in the striatum using high performance liquid chromatography (HPLC). After MPTP exposure, all groups manifested decreased rolling bar latency and spontaneous activity, in addition to increased pole-climbing time. The combined treatment group exhibited a recovery of rolling bar latency and pole-climbing time. The number of dopaminergic neurons in the substantia nigra following MPTP treatment was higher in the combined treatment group compared with the positive control group (p = .003). Immunoreactivity for LC3 was higher in the combined treatment group than in the controls (p = .003). The concentrations of both striatal dopamine and the dopamine metabolite dihydroxyphenyl acetic acid (DOPAC) were decreased in both MPTP-treated groups compared with the controls. The loss of DOPAC was less severe in the combined treatment group relative to the positive control group (p = .001). Therefore, we infer that valproate combined with lithium carbonate can rescue dopaminergic neurons and ameliorate the loss of DOPAC following MPTP treatment, likely via activation of autophagic/lysosomal pathways.

Targeting oxidative stress, mitochondrial dysfunction and neuroinflammatory signaling by selective cyclooxygenase (COX)-2 inhibitors mitigates MPTP-induced neurotoxicity in mice

Several studies have pointed towards the role of oxidative stress, mitochondrial dysfunction and neuroinflammation in Parkinson's disease (PD). The present study was focused on the possible neuroprotective effect of selective cyclooxygenase (COX)-2-inhibitors: valdecoxib and NS-398 in 1-methyl-4-phenyl-1,2,3,6-tertahydropyridine (MPTP)-induced neurotoxicity in mice. MPTP administration in dose of 40 mg/kg, i.p (four injections of 10mg/kg, i.p. at an interval of 1h each) significantly induced the Parkinson-like symptoms in mice as indicated by change in locomotor activity, inability to correct posture (bar test), and oxidative stress (increased levels of lipid peroxidation, nitrite concentration, and depletion of antioxidant enzyme). MPTP administration significantly impaired mitochondrial complex-I activity and redox activity, upregulated the caspase-3 and NF-κB levels as compared to vehicle group. Treatment with valdecoxib (5 or 10 mg/kg, p.o.) or NS-398 (5 or 10mg/kg, p.o.) for 7 days significantly reversed behavioral, biochemical, mitochondrial complex alterations as well as attenuated the induction of proinflammatory mediators in MPTP-treated groups. The findings of the present study substantiate the neuroprotective role of selective COX-2 inhibitors in ameliorating MPTP-induced neurodegeneration in mice and suggest the possible therapeutic potential of these drugs in the management of PD.

A new model to study compensatory mechanisms in MPTP-treated monkeys exhibiting recovery

The cardinal symptoms in Parkinson's disease (PD), akinesia, rigidity and tremor, are only observed when the striatal level of dopamine is decreased by 60-80%. During the preclinical phase of PD, compensatory mechanisms are probably involved in delaying the appearance of motor symptoms. In a MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkey model of PD, a spontaneous recovery has been reported after initial intoxication suggesting that compensatory mechanisms are activated in this model as well. Assuming that mechanisms are similar in these phenomena, the study of recovery in monkeys following MPTP intoxication may enable identification of compensatory mechanisms involved in the preclinical phase of PD. In order to maximize the temporal similarity between PD and the MPTP model, we assessed a new progressive monkey model in which spontaneous recovery is expressed systematically and to characterize it based on (1) its behavioural features, and (2) the presence of compensatory mechanisms revealed by an immunohistological approach comparing dopaminergic and serotoninergic innervation between monkeys either exhibiting behavioural recovery or stable motor symptoms. This immunohistological study focused on the substantia nigra, striatum and pallidum, and their anatomical and functional subdivisions: sensorimotor, associative and limbic. The behavioural analysis revealed that with progressive MPTP intoxication motor symptoms were initially expressed in all monkeys. Observable recovery from these symptoms occurred in all monkeys (7/7) within 3-5 weeks after the last MPTP injection, and most exhibited a full recovery. In contrast, acute intoxication induced stable motor symptoms. Despite this obvious behavioural difference, immunohistological methods revealed that the loss of dopaminergic cell bodies in substantia nigra was substantial and similar in both MPTP-treated groups. However, quantification of fibres revealed that recovered monkeys displayed more dopaminergic and serotoninergic fibres than those with stable motor symptoms in sensorimotor and associative territories of striatum and more dopaminergic fibres in internal pallidum. This study provides a new model of PD where all monkeys expressed functional recovery from motor symptoms despite a large dopaminergic neuronal loss. The immunohistological results suggest that both dopamine and serotonin could be implicated in the compensatory mechanisms.

Manganese does not alter the severe neurotoxicity of MPTP

We utilized a mice model of Parkinsonism: (1) to evaluate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity; and (2) to evaluate whether manganese (Mn) exposure can affect MPTP-induced neurotoxicity. A 2 x 3 experimental design (MPTP x+/- Mn) was as follows: SS, MPTP(-) x Mn(-); SLMn, MPTP(-) x low Mn(+); SHMn, MPTP(-) x high Mn(+); MpS, MPTP(+) x Mn(-); MpLMn, MPTP(+) x low Mn(+); MpHMn, MPTP(+) x high Mn(+). We administered MPTP (30 mg/kg per day) to male C57BL/6 mice intraperitoneally, once a day for 5 days. Subsequently, mice were treated with either 2 or 8 mg/kg of MnCl(2).4H(2)O intraperitoneally, once a day for 3 weeks. Blood and striatal Mn levels were elevated in the Mnexposed groups. The number of tyrosine hydroxylase (TH)-immunoreactive (ir) neurons in the substantia nigra pars compacta were decreased significantly in the MPTP-exposed groups. The densities of TH-ir axon terminals in caudate-putamen (CPU) were significantly decreased in the MPTP-treated groups. However, Mn treatment did not affect MPTP neurotoxicity. The densities of glial fibrillary acidic protein (GFAP)-ir astrocytes in the CPU or globus pallidus were significantly increased in the MPTP-treated groups. Concentrations of dopamine in the striatum were decreased significantly in the MPTP-exposed groups only, but Mn had no effect.

Effect of Manganese Exposure on MPTP Neurotoxicities

We used a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice model to evaluate whether manganese (Mn) exposure can affect MPTP-induced neurotoxicity. We randomly assigned adult male C57BL/6 mice ( n=5–7 per group) the following treatments: SO, Mn(−) × MPTP(−); MO, Mn(+) × MPTP(−); SM, Mn(−) × MPTP(+); MM, Mn(+) × MPTP(+). Mn (MnCl 2·4H 2O) was administered intraperitoneally at a dose of 2 mg/kg daily for 3 weeks. MPTP was then administered intraperitoneally at a dose of 30 mg/kg daily for 5 days in the SM and MM groups. Seven days after the last MPTP injection, the animals were sacrificed. Blood Mn levels were elevated in the Mn-exposed groups. Striatal Mn levels were not influenced by Mn treatment alone, however, they were decreased following MPTP. Tyrosine hydroxylase (TH)-immunoreactive (ir) neurons in the substantia nigra pars compacta (SNpc) were decreased significantly in the MPTP-exposed groups. Densities of TH- and dopamine transporter (DAT)-ir axon terminals in the caudate-putamen (CPU) were also decreased in the MPTP-treated groups. Furthermore, glial fibrillary acidic protein (GFAP)-ir astrocytes increased in the CPU with MPTP treatment. However, no effects were observed with Mn exposure. Concentrations of dopamine (DA), 3,4-dihydrophenyl acetic acid (DOPAC) and homovanillic acid (HVA) in the corpus striatum were also decreased significantly with MPTP treatment alone, but Mn had no effect. Thus, decreased dopaminergic activities with MPTP led to decreased DA and its metabolites. Significant hypertrophies of GFAP-ir astrocytes in the globus pallidus (GP) were observed in Mn-exposed groups, especially in the MM group. MPTP targeted dopaminergic systems whereas Mn neurotoxicities occurred in the GP. In conclusion, our data suggest that Mn does not potentiate the neurotoxicity of MPTP.

Acute and subchronic MPTP administration differentially affects striatal glutamate synaptic function

We previously reported that 1 month following unilateral loss (>95%) of striatal dopamine, there is an increase in striatal glutamate function as measured by in vivo microdialysis and quantitative immuno-gold electron microscopy (Meshul, C.K., et al., 1999, Neuroscience 88, 1–16). The goal of this study was to determine the effect of bilateral loss of striatal dopamine on striatal glutamate function following acute or subchronic administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to C57/B6J mice. Animals were administered either single injections (ip) of 30 mg/kg/day for 7 days (subchronically treated group) or 20 mg/kg × 4 doses every 2 h (acutely treated group) of the toxin or saline. One month following the first injection, there was a 44 and 65% loss in the relative density of tyrosine hydroxylase (TH) immunolabeling within the dorsolateral striatum in the subchronically and acutely MPTP-treated groups compared to the saline group, respectively. There was a decrease in the basal level of extracellular glutamate within the striatum in the subchronically MPTP-treated animals compared to an increase in the acutely treated group in relationship to the saline group. Ultrastructurally, only in the acutely MPTP-treated group was there a decrease in the density of glutamate immunolabeling within nerve terminals associated with an asymmetrical synaptic contact in the dorsolateral striatum compared to either the subchronic or saline groups. In addition, there was a decrease in the relative density of GluR-2/3 subunit immunolabeling within the dorsolateral striatum in the acute MPTP compared to the saline group. These data indicate that differences in striatal glutamate function appear to be associated with the dosing interval of MPTP administration and the variable loss of striatal TH immunolabeling.

Coenzyme Q 10 attenuates the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced loss of striatal dopamine and dopaminergic axons in aged mice

We investigated whether oral administration of coenzyme Q 10 (CoQ 10) could attenuate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in one-year-old mice. Four groups of one-year-old, male C57BL/6 mice received a either standard diet or a diet supplemented with CoQ 10 (200 mg/kg/day) for five weeks. After four weeks, one group that had received the standard diet and one group that had received the CoQ 10 supplemented diet were treated with MPTP. The four groups continued on their assigned diets for an additional week prior to sacrifice. Striatal dopamine concentrations were reduced in both groups treated with MPTP, but they were significantly higher (37%) in the group treated with CoQ 10 and MPTP than in the group treated with MPTP alone. The density of tyrosine hydroxylase immunoreactive (TH–IR) fibers in the caudal striatum was reduced in both MPTP-treated groups, but the density of TH–IR fibers was significantly (62%) greater in the group treated with CoQ 10 and MPTP than in the group treated with MPTP alone. Our results indicate that CoQ 10 can attenuate the MPTP-induced loss of striatal dopamine and dopaminergic axons in aged mice and suggest that CoQ 10 may be useful in the treatment of Parkinson's disease.

Metallothionein inducers protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity in mice.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a drug that induces parkinsonism in human and non-human primates. Free radicals are thought to be involved in its mechanism of action. Recently, the participation of metallothionein as scavenger of free radicals has been proposed. In this work, we studied the effect of metallothionein inducers in MPTP neurotoxic action. Male swiss albino mice were pretreated either with cadmium (1 mg/kg) or dexamethasone (5 mg/kg), two well-known inducers of metallothionein synthesis, and 5 hours later with an MPTP administration (30 mg/kg). Treatment schedule was repeated daily for either 3 or 5 consecutive days. All animals were killed 7 days after the last administration, and striatal dopamine and homovanillic acid contents were analyzed as an end-point of MPTP neurotoxicity. Striatal dopamine content of cadmium plus MPTP-treated animals (3-days) increased by 32%, and 48% (5-days) vs MPTP-alone animals. Dexamethasone plus MPTP-treated group also showed increased dopamine levels 28% (3-days) and 43% (5-days). MPTP treatment reduced striatal metallothionein concentration (49% vs control animals). Dexamethasone and cadmium increased metallothionein concentrations in MPTP-treated groups, by 77% and 82% respectively. Results suggest that metallothionein induction provide a significant resistance factor against the deleterious effect of MPTP.

Restoration of dopamine transporter density in the striatum of fetal ventral mesencephalon-grafted, but not sham-grafted, MPTP-treated parkinsonian monkeys

Transplantation of fetal dopamine neurons to the adult striatum potentially offers a means to reverse the striatal dopamine deficiency that characterizes Parkinson's disease. Many investigations in rodents have supported the hope that neural grafting may be a useful treatment for parkinsonism. However, clinical studies have generally produced more modest improvements in motor abnormalities than observed in lower species. It is possible that the number of fetal dopamine neurons that survive transplantation is insufficient to restore dopaminergic innervation of the large human striatum to a level where striking recovery is obtained. In fact, there has been no quantitative study of graft outgrowth to indicate what portion of the dopamine-depleted striatum might be reinnervated with present techniques. Furthermore, it has been speculated that regeneration of the host dopamine system in response to the implantation surgery may play an important role in the beneficial effects of neural grafting in primates. The present study used nine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys to investigate these issues. Sham implantation procedures produced no increase in either dopamine transporter density (measured by quantitative autoradiography) or tissue dopamine concentration (measured by HPLC) in the striatum of MPTP-treated monkeys. In sham-grafted and nonimplanted MPTP-treated monkeys, the striatal dopamine concentration was reduced by 99%, based on analysis of 16 sampled sites in the caudate nucleus and putamen of each monkey. No behavioral recovery was seen in the sham-grafted and nonimplanted MPTP-treated groups. In contrast, transplantation of fetal dopamine neurons to the caudate nucleus or putamen of MPTP-treated monkeys resulted in a significant elevation of dopamine transporter density and dopamine levels in the grafted striatal nucleus. Each grafted MPTP-treated monkey received ventral mesencephalon dopamine neurons from one donor harvested during putative neurogenesis. Donor ventral mesencephalon was divided equally and implanted into six sites either in the caudate nucleus or putamen. One graft site in each monkey was examined by dopamine transporter autoradiography. In sections in which graft fibers were present, a mean of one-third of the volume of the grafted nucleus was occupied by an elevated density of dopamine transporters. This increase in dopamine transporter density was defined to be at least 5-10% of the control density. However, full behavioral recovery was not observed in the grafted MPTP-treated group. These data provide no support for the hypothesis that regeneration of the host dopamine system occurs in response to a sham implantation procedure in severely parkinsonian monkeys. The current study illustrates the power of the applied techniques for delineating the relationship between the level of host dopamine depletion, the extent of graft-induced dopaminergic restoration, and behavioral recovery.

Restoration of dopamine transporter density in the striatum of fetal ventral mesencephalon-grafted, but not sham-grafted, MPTP-treated parkinsonian monkeys.

Transplantation of fetal dopamine neurons to the adult striatum potentially offers a means to reverse the striatal dopamine deficiency that characterizes Parkinson's disease. Many investigations in rodents have supported the hope that neural grafting may be a useful treatment for parkinsonism. However, clinical studies have generally produced more modest improvements in motor abnormalities than observed in lower species. It is possible that the number of fetal dopamine neurons that survive transplantation is insufficient to restore dopaminergic innervation of the large human striatum to a level where striking recovery is obtained. In fact, there has been no quantitative study of graft outgrowth to indicate what portion of the dopamine-depleted striatum might be reinnervated with present techniques. Furthermore, it has been speculated that regeneration of the host dopamine system in response to the implantation surgery may play an important role in the beneficial effects of neural grafting in primates. The present study used nine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys to investigate these issues. Sham implantation procedures produced no increase in either dopamine transporter density (measured by quantitative autoradiography) or tissue dopamine concentration (measured by HPLC) in the striatum of MPTP-treated monkeys. In sham-grafted and nonimplanted MPTP-treated monkeys, the striatal dopamine concentration was reduced by 99%, based on analysis of 16 sampled sites in the caudate nucleus and putamen of each monkey. No behavioral recovery was seen in the sham-grafted and nonimplanted MPTP-treated groups. In contrast, transplantation of fetal dopamine neurons to the caudate nucleus or putamen of MPTP-treated monkeys resulted in a significant elevation of dopamine transporter density and dopamine levels in the grafted striatal nucleus. Each grafted MPTP-treated monkey received ventral mesencephalon dopamine neurons from one donor harvested during putative neurogenesis. Donor ventral mesencephalon was divided equally and implanted into six sites either in the caudate nucleus or putamen. One graft site in each monkey was examined by dopamine transporter autoradiography. In sections in which graft fibers were present, a mean of one-third of the volume of the grafted nucleus was occupied by an elevated density of dopamine transporters. This increase in dopamine transporter density was defined to be at least 5-10% of the control density. However, full behavioral recovery was not observed in the grafted MPTP-treated group. These data provide no support for the hypothesis that regeneration of the host dopamine system occurs in response to a sham implantation procedure in severely parkinsonian monkeys. The current study illustrates the power of the applied techniques for delineating the relationship between the level of host dopamine depletion, the extent of graft-induced dopaminergic restoration, and behavioral recovery.

The dopamine D 1 receptor agonist SKF 38393 suppresses detrusor hyperreflexia in the monkey with parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

A pharmacological study using monkeys, in which parkinsonism was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was undertaken to elucidate the mechanism underlying urinary bladder dysfunctions in Parkinson's disease. Under ketamine anesthesia, cystometrograms showed that, in MPTP-treated monkeys, a contraction of the urinary bladder was induced with smaller bladder volume than that in normal monkeys. In MPTP-treated monkeys, subcutaneously injected SKF 38393, a dopamine D 1 receptor agonist, significantly increased the bladder volume and pressure thresholds for inducing the micturition reflex without affecting those in normal monkeys. In contrast, subcutaneous injections of quinpirole, a dopamine D 2 receptor agonist, and apomorphine, a dopamine D 1 and D 2 receptor agonist, slightly, but significantly reduced the volume threshold of the bladder for the micturition reflex in both normal and MPTP-treated groups. These results indicate that, in parkinsonism, the degeneration of dopaminergic neurons in the substantia nigra leads to the detrusor hyperreflexia, probably due to a failure of activation of dopamine D 1 receptors.