284 REGULATION OF PROENKEPHALIN mRNA AND LEUCINE-ENKEPHALIN IN EXPLANTED RAT ADRENAL MEDULLAE

Impulse activity differentially regulates enkephalinergic and catecholaminergic (CA) transmitter phenotypic characteristics in rat adrenal medullae in vivo and in vitro (LaGarama, et al, Science 224:1102, 1984). Adult male rat adrenal medullae, grown as explants for 4 days, show a 50-fold rise in leu-enkephalin-like immunoreactivity (LEU) following a 2 day plateau period. To further characterize cellular mechanisms governing the rise in LEU, 2 1/2 day cultured medullae were treated with inhibitors of protein, RNA, and DNA synthesis. Cycloheximide completely prevented the rise in LEU, while Actinamycin-D prevented 50% of the increase. Cytosine arabinoside had no effect. To begin characterizing the molecular level of regulation, proenkephalin mRNA was measured in this culture system using a 918 base pair cDNA probe. Proenkephalin mRNA levels in 2 and 4 day explants revealed a striking increase in proenkephalin mRNA which preceded the rise in LEU and could be prevented by depolarization. These data suggest tht ongoing synthesis of both mRNA and protein is required to increase LEU. This culture system may permit characterization of the gencmic processes involved in transsynaptic regulation of CA and LEU in explanted adrenal medullary cells. (Supported by NIH Grants HL00756, NS10259 and HD12108).