Midbrain dopaminergic neurons (nuclei A8, A9, and A10): three-dimensional reconstruction in the rat.

The dopaminergic neurons in the midbrain of the rat are located in three cell groups: nucleus A8 cells in the retrorubral field, nucleus A9 cells in the substantia nigra, and nucleus A10 cells in the ventral tegmental area and related nuclei. The purpose of the present study was to map and quantify the midbrain dopaminergic neurons in two and three dimensions in the rat brain, using immunohistochemical staining and computer imaging techniques. The cells were identified with an antibody against tyrosine hydroxylase, and counted in six midbrain nuclei: the retrorubral field, substantia nigra pars compacta, substantia nigra pars reticulata, central linear nucleus, ventral tegmental area, and interfascicular nucleus. Outlines were traced around the perimeters of the coronal tissue sections, and the locations of all immunoreactive ventral midbrain cells were mapped. On one side of the brain there are approximately 1,300 nucleus A8 cells, 10,500 nucleus A9 cells, and 10,200 nucleus A10 cells. The 2- and 3-dimensional reconstructions illustrate the region-specific density of dopaminergic neurons throughout the midbrain cell complex, and provide a visual appreciation of the location and distribution of the three dopaminergic cell groups in relation to their position in the midbrain. Information about the number and location of midbrain dopaminergic neurons will be useful in conjunction with future studies that characterize these cells more specifically, for example, in terms of their co-transmitters, and afferent and efferent projections.