MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) damages dopaminergic neurons as seen in Parkinson disease. Here we show that after administration of MPTP to mice, there was a robust gliosis in the substantia nigra pars compacta associated with significant upregulation of inducible nitric oxide synthase (iNOS). These changes preceded or paralleled MPTP-induced dopaminergic neurodegeneration. We also show that mutant mice lacking the iNOS gene were significantly more resistant to MPTP than their wild-type littermates. This study demonstrates that iNOS is important in the MPTP neurotoxic process and indicates that inhibitors of iNOS may provide protective benefit in the treatment of Parkinson disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) damages dopaminergic neurons in the substantia nigra pars compacta (SNpc) as seen in Parkinson's disease. Here, we show that the proapoptotic protein Bax is highly expressed in the SNpc and that its ablation attenuates SNpc developmental neuronal apoptosis. In adult mice, there is an up-regulation of Bax in the SNpc after MPTP administration and a decrease in Bcl-2. These changes parallel MPTP-induced dopaminergic neurodegeneration. We also show that mutant mice lacking Bax are significantly more resistant to MPTP than their wild-type littermates. This study demonstrates that Bax plays a critical role in the MPTP neurotoxic process and suggests that targeting Bax may provide protective benefit in the treatment of Parkinson's disease. P arkinson's disease (PD) is a common neurodegenerative disorder whose cardinal clinical features include tremor, slowness of movement, stiffness, and postural instability (1). These disabling symptoms are primarily due to a profound deficit in striatal dopamine content that results from the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the consequent loss of their projecting nerve fibers in the striatum (2, 3). Although several approved drugs do alleviate PD symptoms, their chronic use often is associated with debilitating side effects (4), and none seem to dampen the progression of the disease. Moreover, the development of effective neuroprotective therapies is impeded by our limited knowledge of the mechanism by which SNpc dopaminergic neurons die in PD. Thus far, however, significant insights into the pathogenesis of PD have been achieved by the use of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which replicates in humans and nonhuman primates a severe and irreversible PD-like syndrome (5). In several mammalian species, MPTP reproduces most of the biochemical and pathological hallmarks of PD, including the dramatic degeneration of dopaminergic neurons (5).Mounting evidence indicates that highly regulated cell deathassociated molecular pathways could participate in the relentless demise of neurons in degenerative diseases (6, 7), including PD (8). In keeping with this, Bax (9) has emerged as a pro-cell death driving force within the central decision point constituted by the Bcl-2 family that modulates the activation of downstream effectors of cell death such as caspases (7). It is also clear that Bax is required for the death of several types of neurons in the peripheral and central nervous systems during both normal development and pathological situations (10-18). In light of its critical role within the programmed cell death machinery and its importance in neuronal death, Bax appears as a particularly appealing target for therapeutic interventions aimed at hampering neurodegeneration. Consistent with a potential pivotal role for Bax in SNpc neuronal death, here we show that Bax is highly expressed in the SNpc and that its ablation attenuates SNpc developmental neu...

Mutations in ␣-synuclein cause a form of familial Parkinson's disease (PD), and wild-type ␣-synuclein is a major component of the intraneuronal inclusions called Lewy bodies, a pathological hallmark of PD. These observations suggest a pathogenic role for ␣-synuclein in PD. Thus far, however, little is known about the importance of ␣-synuclein in the nigral dopaminergic pathway in either normal or pathological situations. Herein, we studied this question by assessing the expression of synuclein-1, the rodent homologue of human ␣-synuclein, in both normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In normal mice, detectable levels of synuclein mRNA and protein were seen in all brain regions studied and especially in ventral midbrain. In the latter, there was a dense synuclein-positive nerve fiber network, which predominated over the substantia nigra, and only few scattered synuclein-positive neurons. After a regimen of MPTP that kills dopaminergic neurons by apoptosis, synuclein mRNA and protein levels were increased significantly in midbrain extracts; the time course of these changes paralleled that of MPTP-induced dopaminergic neurodegeneration. In these MPTP-injected mice, there was also a dramatic increase in the number of synuclein-immunoreactive neurons exclusively in the substantia nigra pars compacta; all synuclein-positive neurons were tyrosine hydroxylasepositive, but none coexpressed apoptotic features. These data indicate that synuclein is highly expressed in the nigrostriatal pathway of normal mice and that it is up-regulated following MPTP-induced injury. Parkinson's disease (PD) is a common disabling neurodegenerative disorder that can present as both a familial and a nonfamilial (i.e., sporadic) condition (Fahn, 1988). Its cardinal clinical features include tremor, stiffness, and slowness of movement, all of which are attributed to the dramatic loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) (Fahn, 1988). Although the actual cause of PD remains unknown, a breakthrough on this question emerged from studies on the small brain-specific protein ␣-synuclein. The first clue linking ␣-synuclein to PD comes from the observation that point mutations in the ␣-synuclein gene cause an autosomal dominant parkinsonian syndrome almost indistinguishable from the prominent sporadic form of PD (Polymeropoulos et al., 1997;Kruger et al., 1998). The two missense mutations identified thus far result in a single amino acid substitution in ␣-synuclein protein, that is, an alanine being replaced by a hydrophobic residue threonine, at position 53, and proline, at position 30. Since the discovery of these mutations, data have been accumulated suggesting that both mutations may alter ␣-synuclein's normal intracellular distribution, enhance ␣-synuclein's propensity to interact with other intracellular proteins, and increase ␣-synuclein disposition to aggregate and consequently to form intraneuronal inclusions (Conway et al., 1998;El-Agnaf et al., 1998;Engelend...