Calretinin-immunoreactivity in organotypic cultures of the rat cerebral cortex: effects of serum deprivation.

Calretinin, a calcium-binding protein, is expressed in a specific set of interneurons in the adult rat cortex. Although its role in development is not known with any degree of certainty, evidence in support of a neuroprotective function has been forthcoming. To test this hypothesis, we submitted organotypic cultures (interphase technique) of 4- to 6-day-old rat brain slices to nutritive stress by serum deprivation for 1-3 weeks. Cultures were immunolabelled either with an antiserum against calretinin or with an antibody against MAP2 (the latter being used to assess neuronal cell number). In control (serum-enriched) cultures, the pattern of development of calretinin immunoreactivity mimicked that evinced in vivo with respect to layer- and cell-type specificity, but the maturation process was retarded by about 1 week. In the experimental group, cultures were incubated for 1 week in the presence of serum and then transferred to serum-free medium for an additional 2 weeks. Tissue was characterized by necrotic foci, a marked decrease in neuronal cell number and a further retardation in the course of development of the calretinin immunoreactivity pattern. The proportion of calretinin-immunoreactive cells to total number of viable neurons was 16% in serum-free cultures as against 9% in serum-enriched ones, suggesting that cells expressing the calcium-binding protein exhibit a greater tenacity for survival under conditions of nutritive stress, and thereby supporting the contention that calretinin acts in a neuroprotective capacity.