Maintenance of glial plasticity with aging in C-6 glial cells and normal astrocytes in culture: Responsiveness to opioid peptides

In this study we used as glial cell models, early and late passage C‐6 glial cells, 2B clone, and advanced passages of glial cells derived from aged mouse cerebral hemispheres (MACH) to examine responsiveness to opioids. We have previously reported that early passage C‐6 glial cells, 2B clone, are bipotential and can be geared toward oligodendrocyte or astrocytic expression, whereas late passage C‐6 glial cells are astrocytic. In addition, MACH cultures have been previously characterized and consist of astrocytes type 1 and 2, some oligodendrocytes, and few glial precursors. In this study, early passage (17–20) and late passage (106–108) C‐6 glial cells or MACH cells of passages 16–19 were grown from plating time until harvesting, day 7 or 8, in DMEM + 10% FBS in the presence or absence of opioid peptides, Leu‐enkephalin (10−8 to 10−10 M) or its synthetic analog, dalargin (Tyr‐D‐Ala‐Gly‐Phe‐Leu‐Arg; 10−8 to 10−10 M). We examined for the activities of glutamine synthetase (GS) and cyclic nucleotide phosphohydrolase (CNP), enzyme markers for astrocytes and oligodendrocytes, respectively. We found that CNP activity was markedly increased in the early passage following opioid treatment, indicative of a shift to oligodendrocytic expression. In the late passage cells, already committed to astrocytic expression, opioid treatment enhanced GS activity suggesting that astrocytes respond to opioids. GS activity was markedly increased in MACH cultures grown in the presence of opioids with no changes in CNP. Thus, type 1 astrocytes, the predominant glial type in MACH cultures, responded to opioids. We conclude from these findings derived from two different glial models that regulation of astrocytes by microenvironmental signals appears to be maintained with aging. © 1993 Wiley‐Liss, Inc.