Serotonergic sprouting into transplanted C-6 gliomas is blocked by S-100 beta antisense gene

S-100 beta, a calcium binding protein produced by astrocytes, has been proposed to be a neuronotropic agent. In order to test the tropic effects of S-100 beta in vivo, the technique of cell transplantation was used. C6 glioma cells and C6 cells containing a S-100 beta antisense gene (C6AS) were transplanted into contralateral hippocampi. 5-HT immunoreactive, varicose fibers with a normal appearance penetrated into the glioma mass and were seen in high density around the C6 cell mass. However, 5-HT fibers with enlarged, abnormal varicosities were seen bordering C6AS tissue and were very rarely observed within the C6AS cell mass. Extracellular S-100 beta from normal C6 cells may function as a growth factor on sprouting serotonergic fibers.