DEVELOPMENT OF PROENKEPHALIN GENE-EXPRESSION IN RAT NEOCORTEX - A NONRADIOACTIVE IN-SITU HYBRIDIZATION STUDY

Products of the proenkephalin gene are not only neurotransmitters but may also influence brain development. The ontogeny of the expression o f the proenkephalin gene in neocortex was studied in embryonic and pos tnatal rats with in situ hybridization. At embryonic day 14, the proli ferating cells in the ventricular zone strongly expressed the gene. Th ereafter, the expression decreased and was hardly detectable up to emb ryonic day 21. At the day of birth and during the subsequent week, pro liferating cells in the subventricular zone were labelled. The express ion of the proenkephalin gene in proliferating neuronal and glial prog enitors indicates that gene products may affect proliferation and/or c ommitment. In the neocortex, cells which strongly expressed the gene w ere first seen at postnatal day 7 in the outer part of the neocortex. Seven days later, a second band of positive cells had appeared in the inner part of the cortex, i.e. the adult pattern of distribution had b een established. Thus, in rat neocortex the expression of the proenkep halin gene developed in an outside-first, inside-last mode.