MICROGLIA FROM THE DEVELOPING RAT MEDIAL SEPTAL AREA CAN AFFECT CHOLINERGIC AND GABAERGIC NEURONAL DIFFERENTIATION IN-VITRO

The normal development of the central nervous system is regulated by g lia. In this regard, we have reported that astrocytes, stimulated by e pidermal growth factor or transforming growth factor alpha, suppress t he biochemical differentiation of rat medial septal cholinergic neuron s ill vitro, as evidenced by a decrease in choline acetyltransferase a ctivity. In this study, we found that, in contrast to astrocytes, micr oglia enhance rather than suppress this aspect of cholinergic cell exp ression. When in excess, microglia can revert the effects of epidermal growth factor on the septal cholinergic neurons without altering the astroglial proliferative response to this growth factor. In the absenc e of growth factors or other glial cell types, microglia increase chol ine acetyltransferase activity above control levels and thus, may be a source of cholinergic differentiating activity. The increase in enzym e activity induced by microglia is rapid in onset, detected as early a s 2 h after their addition to the septal neurons and maintained up to six or seven days ill vitro. Furthermore, in the absence or presence o f other glial cell types, microglia also influence septal GABAergic ne urons by significantly increasing glutamate decarboxylase activity. As microglia affect neither septal cholinergic nor GABAergic neuronal ce ll survival, they appear to enhance the biochemical differentiation of these two neuronal cell types. Specific immunoneutralizing antibodies were used to identify the microglia-derived factors affecting these t wo neuronal types. In this regard, we found that the microglia-derived cholinergic differentiating activity is significantly suppressed by a ntibodies raised against interleukin-3. Furthermore, interleukin-3 was detected in both conditioned media and cell homogenates from septal n euronal-microglial co-cultures by western blotting. Finally, although basic fibroblast growth factor and interleukin-3 significantly increas e septal glutamate decarboxylase activity, neither appears to be impli cated in the GABAergic cell response to the microglia. In conclusion, these results demonstrate that microglia can enhance the biochemical d ifferentiation of developing cholinergic and GABAergic neurons in vitr o. Copyright (C) 1996 IBRO.