Time-course and localization of transferrin receptor expression in the substantia nigra of 6-hydroxydopamine-induced parkinsonian rats

Abstract

Parkinson's disease is a neurodegenerative disease characterized by dopaminergic cell death in the substantia nigra. The cause of the cell death is, however, obscure. Recently, accumulation of iron in the parkinsonian substantia nigra and iron-catalysed free radical generation have been proposed as possible causes of nigral cell death. The transferrin receptor has been implicated as a possible mediator of this iron accumulation in the parkinsonian substantia nigra. The present study investigated the distribution of transferrin receptor-immunoreactive proteins and its co-localization with tyrosine hydroxylase in the normal rat substantia nigra and their expressions in the parkinsonian substantia nigra from three days to three months after 6-hydroxydopamine lesioning. Computer image analysis of the grey mean of transferrin receptor staining in the microvessels was also employed. The results showed that the transferrin receptor immunolabelling was localized in some neurons and glial cells in the normal substantia nigra pars compacta and pars reticulata, and that about 54% of tyrosine hydroxylase-positive cells were also stained with transferrin receptor. There was a decrease of tyrosine hydroxylase- and transferrin receptor-positive cells in the 6-hydroxydopamine-lesioned substantia nigra. The grey mean of transferrin receptor staining in microvessels in the lesioned substantia nigra was, however, not different from that in the control. It was concluded that transferrin receptors in neurons, glial cells and microvessels might not be responsible for iron accumulation in the parkinsonian substantia nigra. The loss of transferrin receptor-immunopositive cells might, however, partly be accounted for by the death of transferrin receptor-positive dopaminergic cells induced by 6-hydroxydopamine lesioning.