Reversibility of ganglioside effects on astrocyte morphology

The B-subunit of cholera toxin (BCT) induces a morphological change in cultured rat cerebral astrocytes from flat (epithelioid) to stellate (process-bearing). This stellation is reversed by the gangliosides GM1 and GD1a at concentrations of 10 microM or higher. Upon changing to a ganglioside-free medium, the flat astrocytes reacquire the stellate morphology within 3 hr, indicating that the antistellation effect of gangliosides is reversible. The possibility that this reversibility was due to a loss of exogenously acquired gangliosides from the cell membrane can be ruled out since pretreatment with GM1, but not GD1a, which does not bind BCT, results in an increased responsiveness to BCT, which was identical whether measured immediately after withdrawal of the ganglioside or 3 hr later. Asialo-GM1, which neither binds BCT nor reverses BCT-induced stellation by itself, prevents the return to stellation after withdrawal of the gangliosides. These data suggest that while gangliosides remain associated with the cell, their effect on astrocytes can change from opposing to permitting the stellate morphology.