Opioid-dependent growth of glial cultures: Suppression of astrocyte DNA synthesis by met-enkephalin

The action of met-enkephalin on the growth of astrocytes in mixed-glial cultures was examined. Primary, mixed-glial cultures were isolated from 1 day-old mouse cerebral hemispheres and continuously treated with either basal growth media (controls), 1 μM)met-enkephalin plus the opioid antagonist naloxone (3 μM), or naloxone alone (3 μM). Absolute numbers of neural cells were counted in unstained preparations, while combined [ 3H]-thymidine autoradiography and glial fibrillary acid protein (GFAP) immunocytochemistry was performed to identify specific changes in astrocytes. When compared to control and naloxone treated cultures, met-enkephalin caused a significant decrease in both total cell numbers, and in [ 3H--thymidine incorporation by GFAP-positive cells with flat morphology. These results indicate that met-enkephalin suppresses astrocyte growth in culture.