The gonadal steroid oestrogen exerts an important modulatory influence upon the activity of multiple neuronal networks. In addition to classical genomic mechanisms of action through the two oestrogen receptors, ERα and ERβ, oestrogen also exerts poorly understood rapid non-genomic effects on neurones. We have examined whether the gonadotropin-releasing hormone (GnRH) neurones, which regulate fertility, are also influenced by oestrogen in a non-genomic manner. Using a transgenic mouse model in which GnRH neurones are tagged with GFP we undertook gramicidin, perforated-patch recordings of GnRH neurones in the acute brain slice preparation. Oestrogen (100 nM) was found to rapidly depolarize approximately 40 % of GnRH neurones. To evaluate whether rapid oestrogen actions may also occur in vivo, ovariectomised wild-type mice were given oestrogen (1-10 µg) and the phosphorylation status of cAMP response element-binding protein (CREB) examined within the GnRH neurones using immunocytochemistry. An increase in CREB phosphorylation within GnRH neurones was observed as soon as 15 min following oestrogen administration and found to be both time and dose dependent. Studies in both of the ER knockout mice were then undertaken to evaluate whether either of the classical ERs were involved in the rapid oestrogen actions upon GnRH neurones in vivo. Whereas the response was maintained in the ERα knockout mouse, the ability of oestrogen to phosphorylate CREB in GnRH neurones was blocked completely in the ERβ knockout mouse. Previous studies have established that GnRH neurones express only ERβ (Herbison & Pape, 2001). A final series of in vitro experiments demonstrated that oestrogen acts directly upon GnRH neurones to rapidly phosphorylate CREB and that oestrogen must pass through the cell membrane to achieve this effect. Together, these experiments demonstrate the presence of a functional ER involved in rapid oestrogen signalling within the GnRH neuronal phenotype and provide in vivo evidence for a role of ERβ in mediating non-genomic oestrogen signalling within the brain.

This work was supported by the BBSRC and EU.