Glial expression of the proenkephalin gene in slice cultures of the subventricular zone.

The proenkephalin (PEnk) gene is expressed in rats in the neocortical subventricular zone (nSVZ) of the lateral ventricle during the first postnatal week, when precursors of astro- and oligoglial cells of the rat neocortex proliferate in this area. To study the expression of the gene in the glial precursors, slices containing the nSVZ were prepared from the brains of newborn and 7-day-old rats. After 1-5 d of cultivation, numerous cells that expressed PEnk mRNA were found in the nSVZ with in situ hybridization. Some of these cells coexpressed the glial fibrillary acidic protein (GFAP), indicating that they were of astroglial origin. Activation of protein kinase A with 8Br.cAMP strongly enhanced the number of cells that expressed the PEnk gene in slices prepared from the brains of newborn or 7-d-old rats. Also pituitary adenylate cyclase activating polypeptide (PACAP) proved to be effective. After stimulation with 8Br.cAMP or PACAP-38, PEnk mRNA-containing cells were found in the subventricular zone as well as in the adjacent area through which glial cells migrate on their way to the neocortex. It has therefore been concluded that protein kinase A may regulate the expression of the PEnk gene expression in glial precursors in the nSVZ.