GABA induces proliferation of immature cerebellar granule cells grown in vitro

The presence of GABA and its receptors early in rodent nervous system development has lead to speculation on the role of this transmitter system in neuroblast proliferation, migration and differentiation. We studied the effect of GABA and GABA agonists on immature cerebellar granule cell proliferation and survival. Cerebellar granule cell suspensions were obtained from 6-8-day-old rats and grown in culture for up to 7 days in serum-containing or serum-free medium. The addition of GABA (0.1-100 mu M) or muscimol (0.01-10 mu M) 2 h after inoculation and harvested 22 h later, lead to an increase in H-3-thymidine incorporation over control samples with the correspondent increase in granule cells number assayed 48 h later. The effect on cell proliferation exerted by GABA(A) agonists was blocked by MgCl2 and nifedipine, as well as by the chloride channel blocker, picrotoxin (50 mu M), and the GABA(A) receptor specific blocker, bicuculline (50 mu M). The increase on cell proliferation induced by GABA also was blocked by PD98059 (75 mu M), a specific inhibitor of the mitogen-activated protein kinase kinase (MAPKK). GABA(A) receptor-mediated proliferation was consistently seen in cells inoculated in serum-containing medium supplemented with 25 mM KCI but not seen in serum-free medium, with 5 mM or 25 mM KCl. The presence of serum did not enhance the survival off cerebellar granule cells grown for 7 days in either 5 mM or 25 mM KCl. Additionally, neither GABA nor muscimol applied from day 2 to day 7 in vitro affected cell survival in any culture condition. We conclude that GABA and GABA(A) receptor agonists influence granule cell proliferation but not survival and that this effect is mediated by a calcium influx via voltage-dependent calcium channel activation, with a subsequent activation of the MAPK cascade. (C) 1999 Elsevier Science B.V. All rights reserved.