Oestrogen is a known to act centrally as a modulator of autonomic function. Our previous study showed changes in oestrogen receptor (ER) subtype expression in the nucleus of the solitary tract (NTS), an area of the brainstem regulating autonomic reflexes, are associated with fluctuating plasma oestrogen levels during the oestrous cycle and after ovariectomy (OVX)1. GABA transmission in the NTS is critical for baroreflex control of blood pressure (BP) and as the promoter sequences for several receptors, receptor associated proteins, enzymes and transporters involved in GABA transmission include potential oestrogen response element consensus sites we analysed mRNA expression levels for these markers in the NTS of normal cycling and OVX female rats. Female Wistar rats (approx. 150g, n=6) fed a phytoestrogen free diet were subjected to OVX or sham-OVX under anaesthesia (isofluorane, 5% in O2). Radiotelemetry probes (DSI) were implanted to record from the left carotid artery. BP, heart rate and activity levels were recorded for 3 or 6 weeks post surgery, at which point rats were killed under the same anaesthetic conditions. Micropunches of NTS tissue were taken for reverse transcription of mRNA and analysis by real-time PCR. Percentage body weight gain after 6 weeks in OVX rats (45.48 ± 1.1%; mean ± SE) was significantly greater than in sham-OVX rats (28.68 ± 1.7%, p=0.01), although food intake between the two groups was consistent (approx 110-115g/animal/week). After 3 weeks increases in systolic (+3.4%) and mean (+5.3%) BP were evident in OVX rats compared to starting values. These increases continued to 6 weeks, becoming significantly different (+10.3%, p=0.05; +12.55%, p=0.05). No significant changes in BP were observed in control rats over 3 or 6 weeks. Real-time PCR for the GABA-A subunit mRNAs revealed significantly decreased expression for 4 of the 14 tested (alpha1; alpha 5; gamma3, delta) in OVX rats at both 3 and 6 weeks. Additionally, at 3 weeks a reduction in beta1 was seen, with a reduction in beta3 at 6 weeks. In contrast, mRNA for the epsilon subunit appeared up-regulated. Expression levels for the GABA-B receptor subtypes BR1 and BR2 showed significant reductions (p<0.05) in OVX after 6 weeks, as was the case for the GABA transporter GAT1 and the GABA receptor-associated protein GABARAP. In contrast the GABA synthesising enzyme GAD67 and the GABA receptor-associated protein like 1 GABARAPL1 were increased (p<0.05) in OVX after 3 weeks. The data are consistent with the hypothesis that circulating oestrogen acts on ERs in the NTS to modulate inhibitory GABAergic influences on autonomic reflexes controlling BP through affecting both GABA synthesis/release mechanisms and GABA receptor composition.