Cyclic estrogenic fluctuation influences synaptic transmission of the medial vestibular nuclei in female rats

Abstract

Conclusion: The estrous cycle in female rats influences the basal synaptic responsiveness and plasticity of the medial vestibular nucleus (MVN) neurons through different levels of circulating 17β-estradiol (cE₂). Objective: The aim of this study was to verify, in the female rat, whether cyclic fluctuations of cE₂ influence long-term synaptic effects induced by high frequency afferent stimulation (HFS) in the MVN, since we found that HFS in the male rat induces fast long-term potentiation (fLTP), which depends on the neural synthesis of E₂ (nE₂) from testosterone (T). Methods: We analyzed the field potential (FP) evoked in the MVN by vestibular afferent stimulation, under basal conditions, and after HFS, in brainstem slices of female rats during high levels (proestrus, PE) and low levels (diestrus, DE) of cE₂. Selective blocking agents of converting T enzymes were used. Results: Unlike in the male rat, HFS induced three effects: fLTP through T conversion into E₂, and slow LTP (sLTP) and long-term depression (LTD), through T conversion into DHT. The occurrence of these effects depended on the estrous cycle phase: the frequency of fLTP was higher in DE, and those of sLTP and LTD were higher in PE. Conversely, the basal FP was also higher in PE than in DE.

Keywords::

• Estrous cycle
• long-term potentiation
• long-term depression
• high frequency stimulation
• vestibular field potential

Acknowledgments

This research was supported by the COMPAGNIA di San Paolo (Turin, PN 3941 SD/sd, 2008.2176). We wish to thank D. Bambagioni for outstanding technical assistance.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.