GABA_A α₁ and α₂ receptor subunit expression in rostral ventrolateral medulla in nonpregnant and pregnant rats

Pregnancy results in attenuated baroreflex mediated sympathoexcitatory responses which may be due to potentiation of γ-aminobutyric acid (GABA) inhibition in the rostral ventrolateral medulla (RVLM). The major metabolite of progesterone, 3α-hydroxy-dihydroprogesterone (3α-OH-DHP), which is elevated in pregnancy, is a potent neurosteroid positive modulator of GABA_A receptors, and sensitivity of GABA_A receptors to 3α-OH-DHP is dependent on the receptor subunit composition. The purpose of this study was to evaluate the GABA_A α₁ and α₂ receptor subunit mRNA and protein expression in the RVLM of nonpregnant and late term pregnant rats. Micropunches of RVLM were collected from nonpregnant and late term pregnant rats and the expression levels of GABA_A α₁ and α₂ receptor subunits were analyzed using quantitative competitive reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblot techniques. The competitive RT-PCR analysis allows comparison of expression levels between different mRNA, and the mRNA expression level of GABA_A α₁ was several hundred fold greater than GABA_A α₂ in both groups. However, this relative distribution of GABA_A α₁ and α₂ receptor subunits protein or mRNA expression was not altered in late term pregnant compared to nonpregnant rats. These data demonstrate, that within the RVLM of both nonpregnant and late term pregnant rats, the relative expression levels of GABA_A α_1,2 receptor subunits favor GABA_A receptors susceptible to positive modulation by progesterone metabolites.