Differential calbindin-immunoreactivity in dopamine neurons projecting to the rat striatal complex

The calcium-binding protein calbindin-D-28K is an anatomical marker that ha s been associated with resistance to neurodegeneration and with the electro physiological characteristics of neurons. In this study, we compared the pr esence of calbindin in dopamine neurons projecting to three distinct functi onal regions of the striatal complex: the striatum, and the core and the sh ell of the nucleus accumbens. After iontophoretic injections of Fluoro-Gold in the dopaminergic terminal fields, the presence of tyrosine hydroxylase and calbindin were immunohistochemically assessed in the mesencephalon. It was found that the proportion of cells expressing calbindin was highest in the dopamine cells projecting to the core (72%), intermediate in the cells projecting to the shell (51%) and lowest in the cells projecting to the dor solateral striatum (2.6%), These results do not support the idea that calbi ndin is a sufficient condition to confer resistance to neurodegeneration be cause shell-projecting neurons seem the most resistant to it. The present d ata also raise the question of the role of calbindin in the differences in firing characteristics among dopamine neurons projecting to the striatal co mplex.