Computer imaging and immunohistochemical staining techniques were used to determine which midbrain dopaminergic (DA) cells are spared in Parkinson's disease (PD), and in animals treated with the DA neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and whether the spared cells contain the calcium-binding protein, calbindin-D28k (CaBP). The PD patients had more than 55% fewer midbrain DA neurons than age-matched normal subjects. The cell loss occurred within the combined substantia nigra and retrorubral area (greater than 61%; DA nuclei A9 and A8, respectively), and the ventral tegmental area (greater than 42%; DA nucleus A10). The cell loss was greatest within the ventral portion of the nucleus A9. A similar pattern of DA cell loss was observed in MPTP-treated Macaca fascicularis monkeys. The CaBP-containing cells were located specifically in the cell regions spared by PD and by MPTP-treatment in both monkeys and C57BL/6 mice. These data suggest that PD and MPTP both destroy the same population of midbrain DA neurons within nuclei A8, A9, and A10, and that perhaps CaBP protects the DA neurons from cell death caused by both PD and MPTP.

Midbrain Dopaminergic Cell Loss in Parkinson's Disease and MPTP‐Induced Parkinsonism: Sparing of Calbindin‐D25k—Containing Cells

MPTP mechanisms of neurotoxicity and their implications for Parkinson's disease

Oxidative stress in mitochondria: its relationship to cellular Ca2+ homeostasis, cell death, proliferation, and differentiation.

The molecular mechanisms mediating degeneration of midbrain dopamine neurons in Parkinson's disease (PD) are poorly understood. Here, we provide evidence to support a role for the involvement of the calcium-dependent proteases, calpains, in the loss of dopamine neurons in a mouse model of PD. We show that administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) evokes an increase in calpain-mediated proteolysis in nigral dopamine neurons in vivo. Inhibition of calpain proteolysis using either a calpain inhibitor (MDL-28170) or adenovirus-mediated overexpression of the endogenous calpain inhibitor protein, calpastatin, significantly attenuated MPTP-induced loss of nigral dopamine neurons. Commensurate with this neuroprotection, MPTP-induced locomotor deficits were abolished, and markers of striatal postsynaptic activity were normalized in calpain inhibitor-treated mice. However, behavioral improvements in MPTP-treated, calpain inhibited mice did not correlate with restored levels of striatal dopamine. These results suggest that protection against nigral neuron degeneration in PD may be sufficient to facilitate normalized locomotor activity without necessitating striatal reinnervation. Immunohistochemical analyses of postmortem midbrain tissues from human PD cases also displayed evidence of increased calpain-related proteolytic activity that was not evident in age-matched control subjects. Taken together, our findings provide a potentially novel correlation between calpain proteolytic activity in an MPTP model of PD and the etiology of neuronal loss in PD in humans.

https://www.jneurosci.org/content/jneuro/23/10/4081.full.pdf

Inhibition of calpains prevents neuronal and behavioral deficits in an MPTP mouse model of Parkinson's disease.

The identification of 6-hydroxydopamine (6-OHDA) and N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as dopaminergic neurotoxins that can induce parkinsonism in humans and animals has contributed to a better understanding of Parkinson's disease (PD). Although the involvement of similar neurotoxins has been implicated in PD, the etiology of the disease remains obscure. However, the recently described pathology of PD supports the view for a state of oxidative stress in the substantia nigra (SN), resulting as a consequence of the selective accumulation of iron in SN zona compacta and within the melanized dopamine neurons. Whether iron is directly involved cannot be ascertained. Nevertheless, the biochemical changes due to oxidative stress resulting from tissue iron overload (siderosis) are similar to those now being identified in parkinsonian SN. These include the reduction of mitochondrial electron transport, complex I and III activities, glutathione peroxidase activity, glutathione (GSH) ascorbate, calcium-binding protein, and superoxide dismutase and increase of basal lipid peroxidation and deposition of iron. The participation of iron-induced oxygen free radicals in the process of nigrostriatal dopamine neuron degeneration is strengthened by recent studies in which the neurotoxicity of 6-OHDA has been linked to the release of iron from its binding sites in ferritin. This is further supported by experiments with the prototype iron chelator, desferrioxamine (Desferal), a free-radical inhibitor, which protects against 6-OHDA-induced lesions in the rat. Indeed, intranigral iron injection in rats produces a selective lesioning of dopamine neurons, resulting in a behavioral and biochemical parkinsonism.

James M. Wright

Papers

The mechanism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity: role of intracellular calcium.