Immunoreactive calcium‐binding protein (calbindin‐D 28k ) in interneurons and trigeminothalamic neurons of the rat nucleus caudalis localized with peroxidase and immunogold methods

Calbindin‐D 28k is a highly abundant protein found in neurons in selected brain regions, including cells in sensory system of the brainstem. Because of its capacity to bind cytosolic ca ++ , calbindin‐D 28k is thought to contribute to the regulation of compartmental Ca ++ concentration in neurons. In this study of the rat spinal trigeminal nucleus, calbindin‐D 28k was localized with immunoperoxidase and immunogold methods. Results showed that immunoreactive calbindin‐D 28k neurons were widely distributed to all region of the nucleus, but were particularly numerous in the substantia gelatinosa. Some trigeminothalamic neurons that were identified by retrograde labeling of conjugated wheat‐ germ agglutinin with horseadish perosidase also contained calbindin‐D 28k immunoreactivity. Most of the calbindin‐D 28k labeling was found in cell bodies and dendrites. Axon terminal were rarely stainded. More discreate labeling with a gold conjugated second antibody showed that the predominant site of calbindin‐D 28k was the matrix of the cytoplasm. Gold label was also heavily associated with euchromatin within nuclei. These finding show that immunoreactive calbindin‐D 28k is localized to both interneurons and projecting neurons of the spinal trigeminal nucleus. Many of these cells are likely to receive glutamatergic afferent inputs, which may act in part by increasing Ca ++ and under some condition may protect neurons against glutamate‐induced excitotoxicity. We speculate that calbindin‐D 28k may function to regulate calcium concentration in spinal trigeminal neurons.