DISTINCT DEVELOPMENTAL PATTERNS OF EXPRESSION OF RAT ALPHA, ALPHA-5, GAMMA-2S, AND GAMMA-2L GAMMA-AMINOBUTYRIC ACIDA RECEPTOR SUBUNIT MESSENGER-RNAS INVIVO AND INVITRO

We have quantitated the alpha-1, alpha-5, gamma-2S, and gamma-2L gamma-aminobutyric acid(A) (GABA(A)) receptor subunit mRNAs in the maturing cerebellum in vivo and in cerebellar granule neurons differentiating in vitro. Absolute amounts of MRNA were measured by reverse transcription and competitive polymerase chain reaction (PCR) analysis with appropriate internal standards. The alpha-1, and gamma-2L mRNA content increased continuously during postnatal cerebellar maturation and their changes with time matched verv closely those of the cerebellar granule cells differentiating in vitro. The gamma-2s subunit mRNA showed a relatively constant pattern of expression both in vivo and in vitro, with comparable absolute concentrations in both developmental paradigms. The alpha-5 mRNA was initially high in vivo and decreased (eight-fold) to adult levels as postnatal cerebellar development progressed. In vitro the amount of alpha-5 GABA(A) receptor subunit mRNA was higher than in vivo at 3 days, increased by more than twofold by 8 days, and declined to approximately the initial values at 23 and 28 days in vitro. Collectively', the results indicate that the alpha-1, alpha-5, gamma-2S and gamma-2L GABA(A) receptor subunit mRNAs are regulated differentially in a temporal manner during in vivo and in vitro maturation. Moreover, a comparison of the ontogenetic profiles of the gamma-2S and gamma-2L mRNAs indicates that alternative splicing of the gamma-2S primary RNA transcript is regulated developmentally during postnatal maturation of the rat cerebellum.