Developmental changes in GABA_A receptor subunit composition within the gonadotrophin-releasing hormone-1 neuronal system

It is becoming increasingly evident that GABA plays an important role in the regulation of gonadotrophin-releasing hormone (GnRH)-1 neurones via the GABA_A receptor. The aim of the present study was to characterise expression of the GABA_A receptor within the GnRH-1 system across development. The expression pattern of five GABA_A α subunits and one GABA_A β subunit was first examined within individual GnRH-1 neurones by the polymerase chain reaction. A significant increase in the expression of GABA_A α₂ and a significant decrease in the expression of GABA_A α₆ over time were found. Of the other subunits examined, two (α₁ and α₃) showed no differences in expression and two (α₄ and β₃) showed variable low incidence of expression. Given the reciprocal relationship of α₂ and α₆ expression, we hypothesised that there is a developmental switch in the expression of these subunits in GnRH-1 neurones. To investigate this hypothesis, single- and double-label immunocytochemistry for GABA_A α₂ and α₆ and GnRH-1 was performed in tissue from ages E12.5 to adulthood, as well as in nasal explants. We show that GABA_A α₂ and α₆ are present in the GnRH-1 neuronal system both in vivo and in vitro and that the levels of expression are altered as a function of age.