Semiquantitative analysis of the expression of GABA-A receptor subunits inthe developing embryonic chick brain stem

The expression levels of seven types of gamma-aminobutyric acid-A (GABA-A) receptor subunits (alpha1, beta2, beta3, beta4, gamma1, gamma2, and gamma4) were quantified in the embryonic chick brain stem at 2 to 20d of incubatio n (E2 to E20) and just after hatching. The expression level of mRNA was mea sured by using semiquantitative reverse transcription-polymerase chain reac tion (RT-PCR), When property regions were amplified, two products were obse rved for each of the beta2, beta4, and gamma2 subunits because of alternati ve splicing. These were named beta 2S and beta 2L, beta 4S and beta 4L, and gamma 2S and gamma 2L for shorter and longer fragments, respectively. Tran scripts of alpha1, beta 2L, beta 2S, beta3, beta 4L, beta 4S, gamma1, and g amma 2S subunits were first detected from E2 to E5 brain stems. The express ion level of each subunit increased gradually with development and reached a plateau at E9 to E12. In contrast, a delay occurred in the appearance of both the gamma4 and gamma 2L subunjts, which were not detected until E8 to E10. The absence of gamma4 and/or gamma 2L subunits may explain differences in the pharmacological characteristics of GABA-A receptors at the early st ages of development.