Long-Term Potentiation in the Rat Medial Vestibular Nuclei Depends on Locally Synthesized 17β-Estradiol

In male rat brainstem slices, we investigated the involvement of locally synthesized 17 beta-estradiol (E-2) 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 E-2 receptors (ER alpha and ER beta) 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. In contrast, HFS applied under a combined blockade of GABA(A) receptors and aromatase or ERs was still able to induce LTP, but it was significantly lower and slower. These findings demonstrate that E-2 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 E-2 in inducing LTP. We suggest that the synthesis of E-2 occurs after aromatase activation during HFS and facilitates the development of vestibular synaptic plasticity by influencing glutamate and GABA transmission.