Optogenetic Tractography for anatomo-functional characterization of cortico-subcortical neural circuits in non-human primates.

Dissecting neural circuitry in non-human primates (NHP) is crucial to identify potential neuromodulation anatomical targets for the treatment of pharmacoresistant neuropsychiatric diseases by electrical neuromodulation. How targets of deep brain stimulation (DBS) and cortical targets of transcranial magnetic stimulation (TMS) compare and might complement one another is an important question. Combining optogenetics and tractography may enable anatomo-functional characterization of large brain cortico-subcortical neural pathways. For the proof-of-concept this approach was used in the NHP brain to characterize the motor cortico-subthalamic pathway (m_CSP) which might be involved in DBS action mechanism in Parkinson's disease (PD). Rabies-G-pseudotyped and Rabies-G-VSVg-pseudotyped EIAV lentiviral vectors encoding the opsin ChR2 gene were stereotaxically injected into the subthalamic nucleus (STN) and were retrogradely transported to the layer of the motor cortex projecting to STN. A precise anatomical mapping of this pathway was then performed using histology-guided high angular resolution MRI tractography guiding accurately cortical photostimulation of m_CSP origins. Photoexcitation of m_CSP axon terminals or m_CSP cortical origins modified the spikes distribution for photosensitive STN neurons firing rate in non-equivalent ways. Optogenetic tractography might help design preclinical neuromodulation studies in NHP models of neuropsychiatric disease choosing the most appropriate target for the tested hypothesis.

Implication of the JNK pathway in a rat model of Huntington's disease.

Huntington's disease (HD) is a neurodegenerative disorder resulting from the expansion of a glutamine repeat (polyQ) in the N-terminus of the huntingtin (htt) protein. Expression of polyQ-containing proteins has been previously shown to induce various cellular stress responses. Among these, activation of the c-Jun N-terminal kinase (JNK) cascade has been observed in cellular models of HD. However, the implication of the JNK pathway has not previously been evaluated in the striatum of HD animal models. Here we report that the JNK pathway participates in HD pathology in a rat model of the disease. Increased phosphorylation of the JNK target c-Jun was observed as early as 4 weeks and persisted for 13 weeks after lentiviral-mediated expression of htt171-82Q. In order to assess the importance of this pathway in HD pathology, JNK inhibitors including dominant-negative mutants of upstream kinases (ASK1(K709R), MEKK1(D1369A)), a c-Jun mutant (Delta169c-Jun) and the active domain of the scaffold protein JIP-1/IBI (IBI-JBD) were tested for their ability to mitigate the effect of htt171-82Q. The overexpression of MEKK1(D1369A) and JIP-1/IBI reduced the polyQ-related loss of DARPP-32 expression, while the other inhibitors had no effect. In all cases, the formation of EM48-positive htt inclusions and P-c-Jun immunoreactivity were unaltered. These results suggest that JNK activation is involved in HD and that blockade of this pathway may be of benefit in counteracting HD-related neurotoxicity.

Perseverative behavior underlying attentional set-shifting deficits in rats chronically treated with the neurotoxin 3-nitropropionic acid.

Huntington's disease (HD) is generally considered a prototypic motor disorder, but cognitive deficits are also prominent features of the disease. Systemic administration of the mitochondrial toxin 3-nitropropionic acid (3NP) has been proposed to be a phenotypic model of HD in rats and nonhuman primates. In this study, we investigated the effect of 5 days continuous subcutaneous infusion of 3NP on motor and cognitive abilities in Lewis rats. Intoxicated animals developed a motor syndrome consisting of bradykinesia as well as gait abnormalities and dystonic hindlimbs. Results from learning tasks showed that these rats: (1) did not exhibit learning deficits per se in our discrimination task but showed impairments in inhibiting behavioral responses when a transfer of learning (to new stimuli) or a transfer of response (new position of the lever) was required; (2) showed a marked tendency to persevere in choosing the compartment they previously visited in a T maze, thus leading to a clear retardation in learning a reinforced alternation task; and (3) did not show any memory deficit when a delay was introduced. Six months later, histological analyses showed severe neurodegeneration within the lateral striatum accompanied by apparent cell loss in the ventral pallidum and entopedoncular nucleus. We suggest that the 3NP rat model of basal ganglia neurodegeneration may provide a useful model for studying certain fundamental aspects of the physiopathology of HD and for evaluating the functional efficacy of new therapeutic strategies.

A short cytoplasmic domain of the amyloid precursor protein induces apoptosis in vitro and in vivo.

The amyloid precursor protein presents several cleavage sites leading to the release of its entire C-terminal domain into the cytoplasm. During apoptosis, this C-terminal domain can be cleaved at amino acid 664 by caspases 3, 6, and 8 and can thus generate two peptides N- and C-terminal to amino acid 664 (C31). Recently, it was shown that the C31 induces apoptosis after transfection into N2A and 293 T cell lines. We have analyzed here, by internalization into neurons, the physiological consequences of the entire C-terminal domain (APP-Cter) and of its membrane proximal sequence corresponding to the N-terminal peptide unmasked after caspase cleavage. We find that whereas micromolar concentrations of APP-Cter are harmless, the peptide extending from the membrane (amino acid 649) to the caspase cleavage site (amino acid 664) in the same range of concentrations induces DNA fragmentation, cleavage of actin at a caspase-sensitive site, and activates caspase 3. A mutated version of this sequence (tyrosine 653 replaced by an aspartate) abolishes the effect in vitro and in vivo. Taken together, this report suggests the existence of a new mechanism contributing to Alzheimer's Disease-associated cell death.

Major strain differences in response to chronic systemic administration of the mitochondrial toxin 3-nitropropionic acid in rats: implications for neuroprotection studies.

Chronic systemic treatment with 3-nitropropionic acid in rats produces persistent dystonia and bradykinesia, and striatal lesions reminiscent of Huntington's disease. However, the interpretation of results obtained with this model are complicated by a heterogeneous distribution of the response to a given toxic dose of 3-nitropropionic acid: approximately half of the animals develop selective striatal lesions, which in certain cases are associated with extrastriatal lesions, and the other half are apparently spared. Thus, the chronic 3-nitropropionic acid lesion model can be difficult for neuroprotection studies in which a consistent response to neurotoxic treatment is prerequisite. We hypothesized that some of the variability in the model was related to the use of Sprague-Dawley rats, since inter-individual variability in response to various stressful conditions has been described previously in this rat strain. We therefore compared 3-nitropropionic acid toxicity in rat strains known to be highly (Fisher 344) or poorly (Lewis) responsive to stress and compared the distribution of responses to that of Sprague-Dawley rats. In a protocol of intraperitoneal injection, toxicity of 3-nitropropionic acid was highest in Fisher rats, intermediate in Sprague-Dawley rats and lowest in Lewis rats. In addition, survival curves showed a more heterogeneous response to 3-nitropropionic acid toxicity in Sprague-Dawley rats than that observed in Lewis and Fisher rats. These differences between Sprague-Dawley and Lewis rats were confirmed in a protocol of subcutaneous 3-nitropropionic acid intoxication using osmotic minipumps, where doses up to 36-45mg/kg per day for five days were necessary to induce striatal lesions in Lewis rats as compared to 12-14mg/kg per day for five days in Sprague-Dawley rats. The selectivity of the striatum to lesions, and homogeneous progression of symptoms and neurodegeneration, were more consistently observed in Lewis as compared to Sprague-Dawley rats. These results suggest that vulnerability to 3-nitropropionic acid may depend on genetic factors, which could also influence the physiological response to stress. The present findings also establish an improved model of progressive striatal degeneration in the rat adapted for the testing of new neuroprotective strategies.

Restoration of cognitive and motor functions by ciliary neurotrophic factor in a primate model of Huntington's disease.

Huntington's disease (HD) is an inherited disorder characterized by cognitive impairments, motor deficits, and progressive dementia. These symptoms result from progressive neurodegenerative changes mainly affecting the neostriatum. This pathology is fatal in 10 to 20 years and there is currently no treatment for HD. Early in the course of the disease, initial clinical manifestations are due to striatal neuronal dysfunction, which is later followed by massive neuronal death. A major therapeutic objective is therefore to reverse striatal dysfunction prior to cell death. Using a primate model reproducing the clinical features and the progressive neuronal degeneration typical of HD, we tested the therapeutic effects of direct intrastriatal infusion of ciliary neurotrophic factor (CNTF). To achieve a continuous delivery of CNTF over the full period of evaluation, we took advantage of the macroencapsulation technique. Baby hamster kidney (BHK) cells previously engineered to produce human CNTF were encapsulated into semipermeable membranes and implanted bilaterally into striata. We show here that intracerebral delivery of low doses of CNTF at the onset of symptoms not only protects neurons from degeneration but also restores neostriatal functions. CNTF-treated primates recovered, in particular, cognitive and motor functions dependent on the anatomofunctional integrity of frontostriatal pathways that were distinctively altered in this HD model. These results support the hypothesis that CNTF infusion into the striatum of HD patients not only could block the degeneration of neurons but also alleviated motor and cognitive symptoms associated with persistent neuronal dysfunction.

Early N-acetylaspartate depletion is a marker of neuronal dysfunction in rats and primates chronically treated with the mitochondrial toxin 3-nitropropionic acid.

N-acetylaspartate (NAA) quantification by 1H-magnetic resonance spectroscopy has been commonly used to assess in vivo neuronal loss in neurodegenerative disorders. Here. the authors used ex vivo and in vivo 1H-magnetic resonance spectroscopy in rat and primate models of progressive striatal degeneration induced by the mitochondrial toxin 3-nitropropionate (3NP) to determine whether early NAA depletions could also be associated with neuronal dysfunction. In rats that were treated for 3 days with 3NP and had motor symptoms, the authors found a significant decrease in NAA concentrations, specifically restricted to the striatum. No cell loss or dying cells were found at this stage in these animals. After 5 days of 3NP treatment, a further decrease in striatal NAA concentrations was observed in association with the occurrence of dying neurons in the dorsolateral striatum. In 3NP-treated primates, a similar striatal-selective and early decrease in NAA concentrations was observed after only a few weeks of neurotoxic treatment, without any sign of ongoing cell death. This early decrease in striatal NAA was partially reversed after 4 weeks of 3NP withdrawal. These results demonstrate that early NAA depletions reflect a reversible state of neuronal dysfunction preceding cell degeneration and suggest that in vivo quantification of NAA 1H-magnetic resonance spectroscopy may become a valuable tool for assessing early neuronal dysfunction and the effects of potential neuroprotective therapies in neurodegenerative disorders.

MPTP induces alpha-synuclein aggregation in the substantia nigra of baboons.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity reproduces many of the features of Parkinson's disease (PD). alpha-Synuclein has been identified as a prominent component of the Lewy body (LB), the pathological hallmark of PD. MPTP-treated primates have been reported to develop intraneuronal inclusions but not true Lewy bodies. We administered MPTP to baboons and used a monoclonal alpha-synuclein antibody to define the relationship between neuronal degeneration and alpha-synuclein immunoreactivity in the substantia nigra. MPTP-induced neuronal degeneration was associated with the redistribution of alpha-synuclein from its normal synaptic location to aggregates in degenerating neuronal cell bodies. alpha-Synuclein aggregation induced by MPTP models the early stages of Lewy body formation and may be a fundamental step in the evolution of neuronal degeneration in PD.

Replicating Huntington's disease phenotype in experimental animals.

Huntington's disease (HD) is an inherited, autosomal dominant, neurodegenerative disorder characterized by involuntary choreiform movements, cognitive decline and a progressive neuronal degeneration primarily affecting the striatum. There is at present no effective therapy against this disorder. The gene responsible for the disease (IT15) has been cloned and the molecular defect identified as an expanded polyglutamine tract in the N-terminal region of a protein of unknown function, named huntingtin (The Huntington's Disease Collaborative Research Group, 1993. Cell 72, 971-983). An intense, search for the cell pathology attached to this molecular defect is currently under way [see Sharp and Ross (1996, Neurobiol. Dis. 3, 3-15) for review]. Huntingtin interacts with a number of proteins, some of which have well identified functions, and it has thus been suggested that alterations in glycolysis, vesicle trafficking or apoptosis play a role in the physiopathology of HD. On the other hand data derived from positron emission tomography (PET), magnetic resonance spectroscopy and post-mortem biochemical evidence for a defect in succinate oxidation have suggested the implication of a primary impairment of mitochondrial energy metabolism. All these hypotheses are not necessarily to be opposed and recent findings indicate that the HD mutation could possibly directly alter mitochondrial functions which would in turn activate apoptotic pathways. To test this mitochondrial hypothesis, we studied the effects in rodents and non-human primates of a chronic blockade of succinate oxidation by systemic administration of the mitochondrial toxin 3-nitropropionic acid (3NP). Extensive behavioural and neuropathological evaluations showed that a partial but prolonged energy impairment induced by 3NP is sufficient to replicate most of the clinical and pathophysiological hallmarks of HD, including spontaneous choreiform and dystonic movements, frontal-type cognitive deficits, and progressive heterogeneous striatal degeneration at least partially by apoptosis. 3NP produces the preferential degeneration of the medium-sized spiny GABAergic neurons with a relative sparing of interneurons and afferents, as was observed in HD striatum. The present manuscript reviews the different aspects of this neurotoxic treatment in rodents and non-human primates, and its interest as a phenotypic model of HD to understand the degenerative process of HD and test new therapeutic strategies.

Serial 1H-NMR spectroscopy study of metabolic impairment in primates chronically treated with the succinate dehydrogenase inhibitor 3-nitropropionic acid.

Previous studies in primates have shown that chronic systemic administration of the succinate dehydrogenase (SDH) inhibitor, 3-nitropropionic acid (3NP), replicates most of the motor, cognitive, and histopathological features of Huntington's disease. In the present study, serial 1H-NMR spectroscopy (1H-MRS) assessment of striatal and occipital cortex concentrations of N-acetylaspartate, phosphocreatine/creatine, choline, and lactate, were obtained every 2-weeks during the entire course of a chronic 3NP treatment in baboons. A region-selective increase in lactate was detected in the striatum of the 3NP-treated animals, either immediately before or in conjunction with a lesion in the dorsolateral putamen detected by T2-MR imaging. Absolute 1H-MRS quantitation demonstrated a progressive and region-specific decrease in striatal N-acetylaspartate, creatine, and choline, occuring as early as 3 weeks before the first detection of lactate. These results demonstrate that 1H-MRS can be used to monitor early stages of brain metabolic impairment. In addition, given that 3NP-induced SDH inhibition following systemic injection similarly affects all brain regions, the striatal selective decreases in N-acetylaspartate or creatine concentrations are not simply related to the level of mitochondrial impairment but to a preferential vulnerability of the striatum to 3NP-induced toxicity.

Increased nitrotyrosine immunoreactivity in substantia nigra neurons in MPTP treated baboons is blocked by inhibition of neuronal nitric oxide synthase.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces clinical, biochemical and neuropathologic changes reminiscent of those which occur in idiopathic Parkinson's disease. 7-Nitroindazole (7-NI) is a relatively selective inhibitor of the neuronal isoform of nitric oxide synthase. We previously demonstrated that administration of 7-NI is effective in blocking MPTP toxicity in both mice and baboons. This was suggested to be due to inhibition of the generation of peroxynitrite which can nitrate tyrosines. In the present study we found increased 3-nitrotyrosine immunoreactivity in the substantia nigra of MPTP treated baboons, which was blocked by coadministration of 7-NI. These findings provide further evidence that peroxynitrite may play a role in MPTP induced parkinsonism in baboons.

The amyloid precursor protein interacts with Go heterotrimeric protein within a cell compartment specialized in signal transduction.

The function of the beta-amyloid protein precursor (betaAPP), a transmembrane molecule involved in Alzheimer pathologies, is poorly understood. We recently reported the presence of a fraction of betaAPP in cholesterol and sphingoglycolipid-enriched microdomains (CSEM), a caveolae-like compartment specialized in signal transduction. To investigate whether betaAPP actually interferes with cell signaling, we reexamined the interaction between betaAPP and Go GTPase. In strong contrast with results obtained with reconstituted phospholipid vesicles (Okamoto et al., 1995), we find that incubating total neuronal membranes with 22C11, an antibody that recognizes an N-terminal betaAPP epitope, reduces high-affinity Go GTPase activity. This inhibition is specific of Galphao and is reproduced, in the absence of 22C11, by the addition of the betaAPP C-terminal domain but not by two distinct mutated betaAPP C-terminal domains that do not bind Galphao. This inhibition of Galphao GTPase activity by either 22C11 or wild-type betaAPP cytoplasmic domain suggests that intracellular interactions between betaAPP and Galphao could be regulated by extracellular signals. To verify whether this interaction is preserved in CSEM, we first used biochemical, immunocytochemical, and ultrastructural techniques to unambiguously confirm the colocalization of Galphao and betaAPP in CSEM. We show that inhibition of basal Galphao GTPase activity also occurs within CSEM and correlates with the coimmunoprecipitation of Galphao and betaAPP. The regulation of Galphao GTPase activity by betaAPP in a compartment specialized in signaling may have important consequences for our understanding of the physiopathological functions of betaAPP.

Fetal striatal allografts reverse cognitive deficits in a primate model of Huntington disease.

Substitutive therapy using fetal striatal grafts in animal models of Huntington disease (HD) have already demonstrated obvious beneficial effects on motor indices. Using a new phenotypic model of HD recently designed in primates, we demonstrate here complete and persistent recovery in a frontal-type cognitive task two to five months after intrastriatal allografting. The striatal allografts also reduce the occurrence of dystonia, a major abnormal movement associated with HD. These results show the capacity of fetal neurons to provide a renewed substrate for both cognitive and motor systems in the lesioned adult brain. They also support the use of neural transplantation as a potential therapy for HD.

Partial inhibition of brain succinate dehydrogenase by 3-nitropropionic acid is sufficient to initiate striatal degeneration in rat.

Chronic inhibition of succinate dehydrogenase (SDH) by systemic injection of the selective inhibitor 3-nitropropionic acid (3NP) has been used as an animal model for Huntington's disease (HD). However, the mechanisms by which 3NP produces lesions in the striatum are not fully characterized. A quantitative histochemical method was developed to study the level of regional SDH inhibition resulting from intraperitoneal injection of 3NP or chronic intoxication using osmotic pumps. The results showed that (a) 3NP was an irreversible SDH inhibitor in vivo, (b) the level of SDH inhibition in the striatum (the brain region most vulnerable to 3NP) was similar to that observed in other brain regions not affected by the toxin, such as the cerebral cortex, and (c) the neurotoxic threshold of SDH inhibition in the brain was 50-60% of control levels. The present study demonstrates that the selective degeneration in the striatum observed after chronic 3NP administration cannot be ascribed to a preferential inhibition of SDH in this particular brain region. This work also suggests that the partial decrease in the activity of the respiratory chain complex II-III reported in HD patients may be sufficient to induce the selective striatal degeneration observed in this disorder.

Riluzole protects from motor deficits and striatal degeneration produced by systemic 3-nitropropionic acid intoxication in rats.

The putative neuroprotective effect of riluzole was investigated in a rat model of progressive striatal neurodegeneration induced by prolonged treatment (three weeks, intraperitoneal) with 3-nitropropionic acid, an irreversible inhibitor of succinate dehydrogenase. Quantitative analysis of motor behaviour indicated a significant protective effect (60%) of riluzole (8 mg/kg/day) on 3-nitropropionic acid-induced motor deficits as assessed using two independent motor tests. Furthermore, quantitative analysis of 3-nitropropionic acid-induced lesions indicated a significant 84% decrease in the volume of striatal damage produced by 3-nitropropionic acid, the neuroprotective effect apparently being more pronounced in the posterior striatum and pallidum. In addition, it was checked that this neuroprotective effect of riluzole against systemic 3-nitropropionic acid did not result from a decreased bioavailability of the neurotoxin or a direct action of riluzole on 3-nitropropionic acid-induced inhibition of succinate dehydrogenase. We found that riluzole significantly decreased by 48% the size of striatal lesions produced by stereotaxic intrastriatal injection of malonate, a reversible succinate dehydrogenase inhibitor. Furthermore, the inhibition of cortical and striatal succinate dehydrogenase activity induced by systemic 3-nitropropionic acid was left unchanged by riluzole administration. The present results, consistent with a beneficial effect of riluzole in amyotrophic lateral sclerosis, suggest that this compound may be useful in the treatment of chronic neurodegenerative diseases.

Riluzole reduces incidence of abnormal movements but not striatal cell death in a primate model of progressive striatal degeneration.

Riluzole has been shown recently to increase life expectancy in patients with amyotrophic lateral sclerosis. A number of experimental studies also suggest that this compound may be a neuroprotectant. We have investigated in baboons whether riluzole would protect striatal neurons from a prolonged 3-nitropropionic acid (3NP) treatment and ameliorate the associated motor symptoms. In animals receiving 3NP and the solvent of riluzole, 12 weeks of high-dose 3NP treatment resulted in the appearance of persistent leg dystonia and significant increases in the incidence of three categories of abnormal movements and in the dyskinesia index in the apomorphine test (0.5 mg/kg i.m.). Quantitative assessment of these behavioral deficits using a video movement analysis system demonstrated a significant decrease in locomotor activity and peak tangential velocity in 3NP-treated animals compared to controls. Histological analysis showed the presence of severe, bilateral, striatal lesions, localized in both caudate and putamen. Cotreatment with riluzole (4 mg/kg i.p., twice daily) significantly reduced the dyskinesia index (-35%, P < 0.02) in the apomorphine test. In the quantitative behavioral analysis, riluzole significantly ameliorated the decrease in peak tangential velocity (P < 0.02) but not the decrease in locomotor activity observed after 3NP. Comparative histological analysis of the two groups of treated animals did not demonstrate a clear neuroprotective effect of riluzole. The present study suggests that one potential therapeutic interest for riluzole in neurodegenerative disorders may reside in the reduction of motor symptoms associated with striatal lesions.

Quantifiable bradykinesia, gait abnormalities and Huntington's disease-like striatal lesions in rats chronically treated with 3-nitropropionic acid.

Impairment in energy metabolism is thought to be involved in the aetiology of Huntington's disease. In line with this hypothesis, chronic systemic administration of the mitochondrial toxin 3-nitropropionic acid to rats and monkeys produces selective striatal lesions similar to Huntington's disease. The present study examined whether rats treated with varying regimen of 3-nitropropionic acid could present motor abnormalities reminiscent of Huntington's disease symptomatology, correlated with Huntington's disease specific striatal symptomatology. Subacute 3-nitropropionic acid treatment (15 mg/kg per day intraperitoneally for 10 days) produced dramatic motor symptoms associated with extensive neuronal loss and gliosis in the lateral striatum as well as severe hippocampal degeneration in 50% of the cases. In contrast, chronic 3-nitropropionic acid treatment (10 mg/kg per day subcutaneously for one month) led to more subtle excitotoxic-like lesions, selective for the dorsolateral striatum and more closely resembling Huntington's disease striatal pathology. Animals with these Huntington's disease-like lesions showed spontaneous motor symptoms including mild dystonia, bradykinesia and gait abnormalities, which were barely detectable on visual inspection but could be readily identified and quantified by computerized video analysis. In these chronic animals, the degree of striatal neuronal loss was significantly correlated with the severity of spontaneous motor abnormalities, as is the case in Huntington's disease. The present study demonstrates that chronic low-dose 3-nitropropionic acid treatment in rats results in a valuable model of both the histological features and motor deficits which occur in Huntington's disease. Despite the interanimal variability in terms of response to 3-nitropropionic acid treatment, this rat model may be particularly useful for evaluating the functional benefits of new therapeutic strategies for Huntington's disease, particularly those aiming to reduce the severity of motor symptoms.

In vivo modulation of benzodiazepine receptor function after inhibition of endogenous gamma-aminobutyyric acid synthesis.

The influence of decreased endogenous gamma-aminobutyric acid (GABA) concentration on benzodiazepine receptor function was studied in the brain of living baboons. Positron emission tomography and the radiotracer [11C]flumazenil combined with electroencephalography were used to determine the pharmacological properties of two bezodiazepine receptors agonists, diazepam and bretazenil, in baboons pre-treated or not with DL-allylglycine (an inhibitor of GABA synthesis). Our results show that, in vivo, DL-allylglycine reduces the affinity of benzodiazepine receptors for their agonists without altering the intrinsic capability of agonists to allosterically modulate GABAergic transmission.

Inhibition of neuronal nitric oxide synthase prevents MPTP-induced parkinsonism in baboons.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces clinical, biochemical and neuropathologic changes reminiscent of those which occur in idiopathic Parkinson's disease. 7-Nitroindazole (7-NI) is a relatively selective inhibitor of the neuronal isoform of nitric oxide synthase (NOS) that blocks MPTP neurotoxicity in mice. We now show that 7-NI protects against profound striatal dopamine depletions and loss of tyrosine hydroxylase-positive neurons in the substantia nigra in MPTP-treated baboons. Furthermore, 7-NI protected against MPTP-induced motor and frontal-type cognitive deficits. These results strongly implicate a role of nitric oxide in MPTP neurotoxicity and suggest that inhibitors of neuronal NOS might be useful in treating Parkinson's disease.