Opposite long-term synaptic effects of 17beta-estradiol and 5apha-dyidrotestosterone and localization of their receptors in the medial vestibular nucleus of rats

In brainstem slices of male rats we examined in single neurons of the medial vestibular nucleus (MVN) the effect of exogenous administration of estrogenic (17beta-estradiol, E2) and androgenic (5alpha-dyidrotestosterone, DHT) steroids on the synaptic response to vestibular afferent stimulation. By whole cell patch clamp recordings we showed that E2 induced synaptic long-term potentiation (LTP) that was cancelled by the subsequent administration of DHT. Conversely, DHT induced synaptic long-term depression (LTD) that was partially reversed by E2. The electrophysiological findings were supported by immunohistochemical analysis showing the presence of estrogen (ER: alpha and beta) and androgen receptors (AR) in the MVN neurons. We found that a large number of neurons were immunoreactive for ERalpha, ERbeta, and AR and most of them co-localized ERβ and AR. We also showed the presence of P450-aromatase (ARO) in the MVN neurons, clearly proving that E2.can be locally synthesised in the MVN. On the whole, these results demonstrate a role of estrogenic and androgenic signals in modulating vestibular synaptic plasticity and suggest that the enhancement or depression of vestibular synaptic response may depend on the local conversion of T into E2 or DHT.