Immature granule neurons from cerebella of different ages exhibit distinct developmental potentials.

Cultured cerebellar granule neurons exhibit different developmental potentials in culture dependent on cerebellar age at plating. In cultures prepared at postnatal days (P)2-6, when all granule neurons reside in the external germinal layer (EGL) in vivo, levels of the GABA(A) receptor beta2 and gamma2 subunit mRNAs are constant. In contrast, in cultures prepared at P8-10, when neurons have begun to migrate into the internal granule cell layer (IGL), the mRNAs increase several-fold in a pattern mimicking that found in vivo. To determine the relationship between neuronal differentiation in culture and potential to express GABA(A) receptor beta2 and gamma2 subunit transcripts in the mature pattern, neuronal maturity in P6 and P10 cultures was compared. Bromodeoxyuridine labeling studies demonstrated that P10 as well as P6 cultures contained neurons only from the EGL. Moreover, the maturation of cultured P10 and P6 neurons appeared virtually identical. Cells dissociated at both ages expressed mRNAs encoding the EGL markers MATH-1 and TAG-1. The MATH-1 transcript disappeared from cultures maintained 4 days when expression of the GABA(A) receptor alpha6 subunit, a marker of mature cells, was initiated. Thus, although cultured P6 and P10 granule neurons exhibit the same maturation markers, P10 neurons presumably have been modulated by environmental cues specifying increases in GABA(A) receptor beta2 and gamma2 subunit expression. This possibility is supported by the finding that extracts of dissociated P10 cells but not P6 cells induce increases in GABA(A) receptor subunit expression in P6 cultures.