Compartmentalization of calbindin and parvalbumin in different parts of rat rubrospinal neurons

The distribution of calbindin-immunoreactive neurons in the red nucleus and the subcellular distribution of the calbindin and parvalbumin in tracer-identified rubrospinal neurons of the rat were studied. Only a fraction of the retrogradely labeled rubrospinal neurons was found to contain calbindin. They filled the caudal part of the red nucleus and also appeared sporadically along the ventro- medial border of the middle segment of the red nucleus. In addition to the somata, calbindin was also found in the dendritic arbors of tracer-identified rubrospinal neurons revealed by injecting the fluorescent dye Lucifer yellow into their cell bodies. The axons of rubrospinal neurons located in the caudal red nucleus were marked by performing anterograde tracing with fluorescent dextran tracer in freshly prepared brainstem slice. Parvalbumin was found to locate in swellings along these tracer-identified axons as well as at their cut ends. The results indicate that calbindin and parvalbumin are segregated to the soma- dendritic and axonal compartments of the rat rubrospinal neurons, respectively. This anatomical segregation suggests that they may have different functions in neurons