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 neuro nes and glial cells. Therefore, organotypic cultures of neocortex of n ewborn rats were used in the present study to examine whether neurones as well as glial cells expressed the gene. The slices were prepared a t birth and kept in culture for 7-13 days. Proenkephalin mRNA was visu alised by in situ hybridisation, while immunocytochemical staining for MAP-2 and GFAP was used to identify neurones and astroglial cells, re spectively. In the analysed slices, only neurones contained proenkepha lin mRNA. Activation of protein kinase C with tetradecanoylphorbol ace tate (1 mu mol/l) caused a strong increase in the number of neurones e xpressing proenkephalin mRNA. Our results indicate that a large number of neurones is able to express the proenkephalin gene under these con ditions. However, only a few of them have a basal expression which is strong enough to be detected with in situ hybridisation.