Immunocytochemical characterization of neuron-rich rat brain primary cultures: calbindin D28K as marker of a neuronal subpopulation.

The function in neurons of the vitamin D-dependent calcium ion-binding-protein of 28 kDa mol. wt., calbindin D28K, is unknown. In order to find a simple system for studying the function of this protein, neuron-rich primary cultures derived from brains of 16-day-old rat embryos were analyzed for the presence of calbindin D28K by immunocytochemical mono- and double-labelling techniques. The studies were carried out between the 5th and 23rd day after seeding. In contrast to the neuronal marker neuron-specific enolase which was found in nearly all cells in the culture, calbindin D28K was expressed only in a subpopulation of neurons. Calbindin D28K-positive cells were intensely stained in their cell bodies and were also stained in their processes. Astroglial cells identified by the presence of the processes. Astroglial cells identified by the presence of the specific marker glial fibrillary acidic protein did not express calbindin D28K. Therefore, calbindin D28K is a useful marker for defining a neuronal subpopulation in neuron-rich primary cultures. Such cultures may be employed as a tool in searching for function(s) of calbindin D28K.