THYROID-HORMONE AND CONDITIONED MEDIUM EFFECTS ON ASTROGLIAL CELLS FROM HYPOTHYROID AND NORMAL RAT-BRAIN - FACTOR SECRETION, CELL-DIFFERENTIATION, AND PROLIFERATION

The effects of triiodothyronine (T-3) on cell morphology were examined in cerebral hemisphere and cerebellar astrocyte cultures obtained fro m normal and hypothyroid neonatal rats, T-3-treatment induced morpholo gical changes in astrocytes from cerebral hemispheres, This morphologi cal effect was produced earlier if astrocytes were treated with condit ioned medium obtained from cerebral hemisphere astrocyte cultures prev iously exposed to 50 nM T-3. T-3 or conditioned medium-treatment produ ced faster morphological changes in hypothyroid rat cerebral hemispher e astrocyte monolayers. Cerebellar astrocytes from normal brain did no t respond to thyroid hormone with morphological changes, but prolifera ted after T-3-treatment. However, hypothyroid cerebellar astrocyte cul tures exhibited morphological changes, differently than normal cells. We verified that T-3 may induce astrocyte secretion of factor(s) that promotes morphological differentiation in cerebral hemisphere astrogli al cultures and stimulates the proliferation of cerebellar astrocytes, Astrocytes obtained from hypothyroid animals were more sensitive to s ecreted factors than normal cells, These results emphasize the heterog eneity and the importance of glial cells to normal brain development a nd open new questions about thyroid hormone therapy in hypothyroidism. (C) 1995 Wiley-Liss, Inc.