Calbindin D28k-containing neurons are restricted to the medial substantia nigra in humans

A controversy exists in the literature as to whether neurons containing the calcium binding protein calbindin-D28k are located within the human substantia nigra. The point of variance between reports, however, is not the anatomical distribution of these neurons, but rather the delineation of the dorsal border of the substantia nigra. It has been suggested that the dense substance P striatonigral innervation delimits the substantia nigra in the human. The aim of the present study is to re-examine the distribution of calbindin-D28k-positive neurons throughout the substantia nigra using substance P to delimit its borders. Although a few calbindin-D28k-positive neurons were found in the medial cell group of the substantia nigra, the vast majority of positive neurons were located in the adjacent A8 and A10 dopaminergic cell groups. This anatomical location of calbindin-D28k-positive neurons is consistent with previous reports, though our results indicate that when the striatonigral projection is used to define the substantia nigra, calbindin-D28k is not a notable feature of these neurons. This questions the neuroprotective role of this protein in Parkinson's disease.