Calcium-binding proteins in the chick Edinger Westphal nucleus.

It has been suggested that the calcium-binding proteins, parvalbumin and calbindin-D28K, are involved in the control of intracellular calcium levels but their exact functions are unknown. Immunoreactivity for parvalbumin has been associated with rapidly firing cells, while calbindin has been implicated in protecting neurons from excitotoxicity. Since the chick Edinger Westphal nucleus contains two populations of neurons with different firing patterns, parvalbumin and calbindin immunoreactivities were examined in the Edinger Westphal nuclei of posthatch chicks to determine whether a particular subpopulation of neurons is associated with either protein. Moderate levels of parvalbumin immunoreactivity were found consistently associated with repetitively firing neurons in the lateral Edinger Westphal nucleus. In contrast, medial neurons expressed much lower levels of parvalbumin immunoreactivity. Many medial neurons were negative for parvalbumin although occasionally a few medial neurons stained as strongly as lateral neurons. Definitive calbindin immunoreactivity was absent from Edinger Westphal nuclei despite robust staining of cells in other parts of the brainstem and in control sections of cerebellum.