Proliferation, morphologic and functional characteristics of alkylnitrosourea-induced astrocytoma cells and changes induced by nerve growth factor

Nerve growth factor (NGF) is a potent differentiation promoter of astrocytes. In response to treatment with NGF, astrocyte morphology changes and cells take on the end stage appearance of protoplasmic and fibrous astrocytes. Anaplastic astrocytoma cells also have been reported to respond with changes suggesting promotion of morphologic differentiation. In addition, astrocytoma cells have been reported to respond to NGF treatment by a reduction in growth. NGF has been shown to reduce the size of tumors in vivo and to control the growth of tumor cells in vitro. Because of these reverse transforming characteristics, NGF has been suggested as a treatment for astrocytomas. However, aside from these observations on tumors and tumor cells, little is known of the molecular mechanisms involved in NGF's action. There also is very little information available, outside of morphologic studies, on the effects of NGF on normal astrocytes. Therefore, the purpose of this dissertation was to examine and compare the action of NGF on neonatal astrocytes and anaplastic astrocytoma cells in vitro, and with respect to morphology, function and proliferation. Morphology was studied by determining the effects of NGF on cellular anatomy, characterized by formation of cytoplasmic processes and intermediate filaments. These areas were investigated by using light-microscopy as well as immunofluoresence. Function was studied by determining the effects of NGF on the uptake of glutamate (GLU) and {dollar}gamma{dollar}-aminobutyric acid (GABA), the major excitatory and inhibitory amino acid neurotransmitters, respectively. This area was investigated by use of {dollar}sp3{dollar}H-GLU and {dollar}sp3{dollar}H-GABA and scintillation analysis. Proliferation was studied by determining NGF induced changes in the cell cycle of these two cell populations. This was investigated by use of acridine orange flow cytometry.; NGF treatment of cell cultures in the presence of glutamate resulted in morphologic differentiation of astrocytoma cells from monotonous spindle shaped cells to cells resembling protoplasmic and fibrous astrocytes. NGF increased the intensity of glial fibrillary acidic protein with perinuclear, nuclear and nucleolar distributions. Amino acid neurotransmitter uptake was not adversely affected by NGF treatment. NGF was also found to significantly affect proliferation potential of astrocytoma cells by inducing a quiescent non-cycling subpopulation of cells.