Up-regulation of ciliary neurotrophic factor receptor expression by GABAA receptors in undifferentiated neural progenitors of fetal mouse brain.

In this study, we evaluated the role of the GABA(A) receptor (GABA(A)R), expressed by undifferentiated neural progenitors isolated from fetal mouse neocortex, in the mechanisms relevant to self-replication and differentiation toward neuronal and astroglial lineages. Round spheres were formed with clusters of proliferating cells within 2-4 days during culture with epidermal growth factor (EGF), whereas the size of these clusters was drastically increased in proportion to increasing durations up to 10 days. Sustained exposure to the GABA(A)R agonist muscimol at 100 microM led to significant increases in the size of neurospheres cultured for 6-10 days, with increased proliferative activity and unchanged lactate dehydrogenase release in a manner sensitive to the GABA(A)R antagonist bicuculline. Muscimol also significantly increased the incorporation of 5-bromo-2'-deoxyuridine in neurospheres in a bicuculline-sensitive manner, whereas both high potassium and nifedipine significantly decreased the neurosphere area with increased numbers of apoptotic cells. Prior activation of GABA(A)R significantly promoted the subsequent expression of an astroglial marker protein in cells differentiated by ciliary neurotrophic factor (CNTF) toward an astroglial lineage after the removal of EGF, with a concomitant decrease in neuronal marker protein expression. In neurospheres with GABA(A)R activation, a significant and predominant increase was seen in mRNA expression of CNTF receptors. These results suggest that prior tonic activation of GABA(A)R may preferentially promote the differentiation by CNTF of neural progenitor cells toward an astroglial lineage through selective up-regulation of CNTF receptor expression in the developing mouse brain. (c) 2008 Wiley-Liss, Inc.