CHARACTERIZATION OF A NEUROTROPHIC FACTOR PRODUCED BY CULTURED ASTROCYTES INVOLVED IN THE REGULATION OF SUBCORTICAL CHOLINERGIC NEURONS

When dissociated subcortical cells were cultured in the presence of conditioned medium of relatively differentiated astrocytes (ACM), a marked increase was observed in the expression of choline acetyltransferase (ChAT), an enzyme required for the synthesis of the neurotransmitter acetylcholine. Astrocytes from the target regions of subcortical neurons, the hippocampus and the cerebral cortex, produced neurotrophic factor consistently more than those derived from the nontarget region, the cerebellum. The production of cholinergic trophic activity was increased with the maturation of astrocytes. Even though, nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF) are known cholinergic trophic compounds produced by astrocytes in vitro, a large part of the neurotrophic activity in our ACM was not related to either of these 2 factors. This is because (i) ACM and NGF produced an additive effect on ChAT activity, (ii) only a small proportion of the cholinergic trophic activity in ACM was abolished by anti-NGF antibody, and (iii) treatment with CNTF had no effect on ChAT activity of basal forebrain cholinergic neurons. On the other hand, when cholinergic neurons are cultured on a preformed layer of astrocytes, addition of basic fibroblast growth factor (bFGF) failed to increase further the ChAT activity. Similarly the effects of ACM and bFGF were not additive. A large proportion of the cholinergic trophic activity in ACM was neutralized by anti-bFGF antibody. These findings would suggest that the trophic activity on septal cholinergic neurons in our ACM was due to bFGF or a bFGF-like compound.