Abstract
The expression levels of seven types of gamma-aminobutyric acid-A (GABA-A) receptor subunits (α1, β2, β3, β4, γ1, γ2, and γ4) were quantified in the embryonic chick brain stem at 2 to 20 d of incubation (E2 to E20) and just after hatching. The expression level of mRNA was measured by using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). When property regions were amplified, two products were observed for each of the β2, β4, and γ2 subunits because of alternative splicing. These were named β2S and β2L, β4S and β4L, and γ2S and γ2L for shorter and longer fragments, respectively. Transcripts of α1, β2L, β2S, β3, β4L, β4S, γ1, and γ2S subunits were first detected from E2 to E5 brain stems. The expression 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 γ4 and γ2L subunits, which were not detected until E8 to E10. The absence of γ4 and/or γ2L subunits may explain differences in the pharmacological characteristics of GABA-A receptors at the early stages of development.
