CYTOARCHITECTURAL DISTRIBUTION OF CALCIUM-BINDING PROTEINS IN MIDBRAIN DOPAMINERGIC REGIONS OF RATS AND HUMANS

The present study compares the distribution of three calcium binding p roteins, calbindin-D-28k, calretinin, and parvalbumin, in the midbrain tegmentum of rats and humans. In order to compare the distributions o f these proteins directly, the cytoarchitecture of this region was eva luated by using immunohistochemistry for tyrosine hydroxylase and subs tance P in serial sections in both transverse and horizontal planes. T here was a high degree of homology in the cytoarchitecture of the thre e main dopaminergic regions identified. The A8 group was localised in the retrorubral fields, which extended rostrally into the midbrain ret icular fields in the human. The A9 group corresponded to the substanti a nigra, which was delimited by its dense substance P innervation. The heterogeneous A10 group, situated along the dorsal border as well as medial to the A9 group, comprised multiple nuclei. The distribution of calcium binding proteins was similar in both species, although a larg er proportion of neurons contained these proteins in the rat. Calbindi n-D-28k was localised in neurons within A8 and A10 nuclei and within t he caudomedial A9 region (and rostrolateral A9 in the rat only). Calre tinin was localised in similar regions. In contrast, neurons containin g parvalbumin were concentrated in the substantia nigra pars reticulat a. The results suggest that few dopaminergic neurons receiving striata l input in the substantia nigra contain calcium binding proteins; rath er, the nondopaminergic nigral neurons contain parvalbumin. Interestin gly, dopaminergic neurons are more numerous in humans, whereas nondopa minergic neurons predominate in rats, which suggests that functional d ifferences may exist between rats and humans. (C) 1996 Wiley-Liss, Inc .