Calbindin D-28k positive projection neurones and calretinin positive interneurones of the rat globus pallidus

Abstract

Immunohistochemistry for three calcium-binding proteins calbindin D-28k, calretinin, and parvalbumin revealed neuronal heterogeneity within the GP. Each neurone appeared to express either a single type of calcium binding protein or none at all. The co-localisation of calcium binding proteins was not observed. Combined immunohistochemistry and retrograde tract tracing using colloidal gold particles injected into the projection fields, the substantia nigra or subthalamic nucleus, revealed that projection neurones could be labelled with either calbindin or parvalbumin. These cells were of medium size (22 x 12 microm), multipolar and moderate varicose dendritic trees. In contrast, calretinin-positive neurones were never retrogradely labelled, even in regions where neuronal colloidal gold deposits were numerous. This, combined with their rarity (<1%) and small size (11 x 9 microm), suggests that calretinin may be a neurochemical marker for putative rat globus pallidus interneurones. Calcium-binding proteins are known to have unique buffering characteristics that may confer specific functional properties upon pallidal neurones. Indeed, differential calcium binding protein expression may underlie the electrophysiological heterogeneity observed in the rat globus pallidus.