Long-term potentiation in the rat medial vestibular nuclei depends on locally syntetised 17B-estradiol

In male rat brainstem slices, we investigated the involvement of locally synthesized 17-estradiol (E2) in the induction, in the medial vestibular nucleus (MVN), of long-term potentiation (LTP) by high-frequency stimulation (HFS) of the primary vestibular afferents. We demonstrated that the blockade of aromatase by letrozole or of E2 receptors (ER and ER) by ICI 182,780 prevented the HFS-induced LTP of the N1 wave of the evoked field potential (FP) without affecting baseline responses. Only prolonged afferent activation could induce low LTP. By contrast, HFS applied under a combined blockade of GABAA receptors and aromatase or ERs was still able to induce LTP, but it was significantly lower and slower. These findings demonstrate that E2 does not have a tonic influence on the activity of the MVN neurons and provide the first evidence of the crucial role played by local synthesis of E2 in inducing LTP. We suggest that the synthesis of E2 occurs following aromatase activation during HFS and facilitates the development of vestibular synaptic plasticity by influencing glutamate and GABA transmission