GABA_A receptor subunit mRNA expression in cultured embryonic and adult human dorsal root ganglion neurons

Previous studies have demonstrated significant pharmacological differences between the GABA_A receptors expressed by neurons cultured from embryonic and adult human dorsal root ganglia (DRG). GABA_A receptors of both embryonic and adult neurons are potentiated by diazepam and low concentrations of pentobarbital, and are activated by high concentrations of pentobarbital. However, in contrast to the GABA responses of embryonic neurons, the GABA responses of adult neurons are insensitive to both bicuculline and picrotoxin. We performed RT-PCR using subunit specific primer pairs, followed by Southern blot analysis with a third specific primer, to determine the pattern of subunit mRNA expression in cultures of embryonic and adult human DRG neurons. α2 and β3 mRNA were expressed in all embryonic and adult cultures, while β2 mRNA was present in all adult cultures but none of the embryonic cultures. Transcripts expressed by at least half of both embryonic and adult cultures were α3, α5, γ2S, γ3, ε, θ, and ρ1. Transcripts for γ1 and δ were expressed in most adult cultures, but only a single embryonic culture. α4 mRNA was expressed by a single embryonic culture and π mRNA was expressed by a single adult culture. We found no evidence for expression of α1, α6, β1, γ2L or ρ2 transcripts. Changes in receptor subunit composition may underlie the novel pharmacological properties of GABA _A receptor responses in adult cells. However, post-translational modification of a known subunit or the expression of a novel subunit may also contribute to the unique pharmacology of these neurons.