Increased M-calpain expression in the mesencephalon of patients with Parkinson's disease but not in other neurodegenerative disorders involving the mesencephalon: a role in nerve cell death?

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra and, to a lesser extent, the ventral tegmental area and catecholaminergic cell group A8. However, among these dopaminergic neurons, those expressing the calcium buffering protein calbindin are selectively preserved, suggesting that a rise in intracellular calcium concentrations may be involved in the cascade of events leading to nerve cell death in Parkinson's disease. We therefore analysed immunohistochemically the expression of the calcium-dependent protease calpain II (m-calpain) in the mesencephalon of patients with Parkinson's disease, progressive supranuclear palsy or striatonigral degeneration, where nigral dopaminergic neurons degenerate, and matched controls without nigral involvement. Calpain immunoreactivity was found in fibers and neuronal perikarya in the substantia nigra, the ventral tegmental area, catecholaminergic cell group A8 and the locus coeruleus. In patients with Parkinson's disease but not with the other neurodegenerative disorders, m-calpain immunoreactivity was detected in fibers with an abnormal morphology and in Lewy bodies. Sequential double staining revealed that most of these m-calpain-positive fibers and neuronal perikarya co-expressed tyrosine hydroxylase, indicating that most m-calpain neurons are catecholaminergic. Quantitative analysis of m-calpain staining in the substantia nigra and locus coeruleus revealed an increased density of fibers and neuronal perikarya in parkinsonian patients in both structures. These data suggest that increased calcium concentrations may be associated with nerve cell death in Parkinson's disease.