Topographic distribution and quantitative analysis of retrograde-labelled cells in the substantia nigra following administration of fluoro gold in the caudate putamen nucleus.

The organization of the efferent projections of the substantia nigra following the injection of 0.4 microliters of 2% Fluoro Gold into the caudate-putamen nucleus of rats of both sexes was studied. After a survival period of 72 h, the greatest number of labelled cells was visualized in the substantia nigra, with lower numbers in adjacent structures (ventral tegmental area, zona incerta and medial lemniscus). The cells featured an intensely fluorescent gold-coloured soma and were varied in shape (round or oval); short sinuous projections arose out of them, corresponding to the dendrites and axons of the neurons. In the statistical study, no significant differences were observed between males and females. A similar pattern of distribution was found ranging from the rostral to the caudal regions of the substantia nigra, occupying the whole of the extent of the substantia nigra; this distribution was most predominant in the rostro-caudal transition of the pars compacta of the substantia nigra.