GABAergic receptors in rostral ventrolateral medulla mediates the cardiovascular responses to activation of bed nucleus of the stria terminalis in the female rat

The bed nucleus of the stria terminalis (BST) is known to contain estrogen (E)- concentrating neurons. In addition, injections of E into BST have been reported to potentiate the sympathoinhibitory arterial pressure (AP) and heart rate (HR) responses elicited by glutamate (Glu) stimulation. In this study, the effect of GABA-A antagonist receptors, bicuculline methiodide (BMI), in the rostral ventrolateral medulla (RVLM) on the cardiovascular responses to Glu stimulation of BST (0.25 M; 20 nl) was investigated in the chloralose anaesthetized, ovariectomized (OVX; n = 6) or OVX+E treated (30 pg/ml plasma E, n = 7) female Wistar rats. Glu stimulation of the BST elicited decreases in AP (-28.1 ± 3.7 mmHg) and HR (-14.2 ± 3.5 bpm) in the OVX+E animals and in OVX only animals (AP, -22.48 ± 2.68 mmHg; HR, -12.2 ± 2.1 bpm). Microinjection of GABA-A receptor antagonist, BMI (1.0mM, 100nl) into the ipsilateral RVLM reversibly attenuates glutamate induced bradycardia and depressor responses to BST stimulation in both group of animals (OVX; n=6 AP,-8.03 ± 3.15 and HR,-5.8 ± 4.2) but in OVX+E animals only attenuates glutamate induced bradycardia but not depressor response (OVX+E;n=7 AP,-16.0 ± 2.4 and HR, -5.84 ± 2.0). These data suggest RVLM sympathetic premotor neurons contain GABA receptors, which mediate the sympathoinhibitory responses to stimulation of BST in OVX animals.