AUTORADIOGRAPHIC STUDIES OF RAT ASTROGLIAL CELL-PROLIFERATION INVITRO WITH AND WITHOUT TREATMENT WITH BASIC FIBROBLAST GROWTH-FACTOR

Using specific autoradiographic methods, cell cycle parameters of untreated and basic fibroblast growth factor (bFGF)-treated astroglial cells from newborn rats grown in primary culture were directly measured. The mode of proliferation was also analysed. In untreated cultures, S phase duration (T(S) = 6.9-13.1 h) and cell cycle time (T(C) = 10-18 h) can be modified by about a factor of 2 depending on the culture conditions (serum-supplemented or defined medium, thyroid hormone concentration). However, growth fraction (GF = 0.15) and the ratio T(S)/T(C) remain stable. With increasing days in vitro (DIV) (DIV 7-DIV 20), T(S) (7.8-10.6 h) and T(C) (10-21 h) are prolonged and GF (0.14-0.06) decreases, probably due to cell maturation. In general, astroglial cells proliferate exponentially with a GF < 1, but stop proliferating about 30-36 h after the last feeding, probably caused by exhaustion of the medium. However, after refeeding they continue to proliferate. As opposed to in vivo, no transition of non-proliferating cells into the GF occurs. After addition of bFGF, GF increases (e.g. GF at DIV 7 = 0.43), but T(S) and T(C) are not influenced at DIV 7 and 12. At DIV 20, bFGF additionally shortens T(S) and T(C), thereby producing values of T(S), T(C) and GF like 'younger' cultures. However, the revitalizing effect on 'mature' cells is only transitory. In general, bFGF leads to a single re-entry of G0 cells into the GF. Thereafter, bFGF does not affect the mode of proliferation.