Heterogeneous distribution of neurons containing calbindin D-28k and/or parvalbumin in the rat red nucleus.

The cellular localization of calbindin D-28k (CB) and parvalbumin (PV) in the red nucleus of the rat was studied by means of double-immunohistochemical techniques applied to single sections. Neurons displaying immunoreactivity for either CB or PV were found throughout the rostrocaudal extent of the red nucleus, but PV neurons predominate in the rostral two-thirds and CB neurons in the caudal two-thirds of the nucleus. Likewise, there was a clear but not absolute segregation of the two types of neurons along the dorsoventral axis; PV and CB neurons were largely confined to the dorsolateral and ventromedial sectors of the nucleus, respectively. Most CB neurons were large (> 30 microns), whereas large and medium-sized (15-30 microns) PV neurons were equally abundant. Additionally, some large and medium-sized neurons displaying immunoreactivity for both PV and CB were encountered in the ventromedial sector of the red nucleus. The present study reveals that, in contrast to previous beliefs, the red nucleus is composed of a neuronal population that is chemically highly heterogeneous.