Sex differences in dopaminergic neurons of substantia nigra pars compacta of adult and aged rats: a histological and immunohistochemical study

ABSTRACT

Substantia nigra pars compacta [SNC] is the main source of dopaminergic [DA] input to the striatum. Parkinson's disease is a neurodegenerative disease affecting DA neurons in SNC, with a higher incidence in men. To study the effect of sex on the structure of DA neurons in adult and aged rat SNC. The brains of 22 adult [11 males and 11 females] and 22 aged [11 males and 11 females] albino rats were processed for histological and immunohistochemical examination of DA neurons in the right SNC. Golgi-Cox staining of adult male SNC neurons showed more varicosities and less extension of their dendrites than adult female SNC. Adult male SNC showed a nonsignificant increase in tyrosine hydroxylase-positive neurons than adult female SNC. Aging-related changes were more marked in aged male rats. Aged SNC showed decreased packing density of neurons, some of which appeared irregular and deeply stained. A reduction in Nissl staining was observed. Golgi-Cox staining showed a marked decrease in extension and branching of the dendrites with loss of spines. Ultrastructurally, accumulation of lipofuscin pigment, membranous whorls, dilated Golgi bodies, decreased rough endoplasmic reticulum, and destroyed cristae of mitochondria were observed. A significant reduction in tyrosine hydroxylase-positive neurons was evident in aged SNC. Sex differences in DA neurons of SNC were more apparent in aged rats, with more degenerative changes in the aged male group, which may underlie the predisposition of males to Parkinson's disease