Expression of the proenkephalin A gene in organotypic cultures of neocortex from newborn rats.
In rats, the proenkephalin A gene is expressed in proliferating cells of the neuroepithelial zone which later give rise to neocortical neurones and glial cells. Therefore, organotypic cultures of neocortex of newborn rats were used in the present study to examine whether neurones as well as glial cells expressed the gene. The slices were prepared at birth and kept in culture for 7-13 days. Proenkephalin mRNA was visualised by in situ hybridisation, while immunocytochemical staining for MAP-2 and GFAP was used to identify neurones and astroglial cells, respectively. In the analysed slices, only neurones contained proenkephalin mRNA. Activation of protein kinase C with tetradecanoylphorbol acetate (1 mumol/l) caused a strong increase in the number of neurones expressing proenkephalin mRNA. Our results indicate that a large number of neurones is able to express the proenkephalin gene under these conditions. However, only a few of them have a basal expression which is strong enough to be detected with in situ hybridisation.