Oestrogen plays a key role in a great variety of actions in the nervous system, either through classical or alternative pathways (Nadal et al. 2001). Classical pathways are initiated after binding to classical oestrogen receptors ERα or ERβ, which translocate from the cytoplasm to the nucleus acting there as transcription factors. Conversely, alternative pathways are initiated at the plasma membrane and cytoplasm, via binding to classical or nonclassical oestrogen receptors.

Using isolated ciliary ganglion neurons from humanely killed chick embryos and Ca²⁺ imaging, we have demonstrated that 17β-oestradiol rapidly reduces Ca²⁺ influx through the plasma membrane. This effect was not reproduced by oestradiol conjugated to bovine serum albumin (E2-BSA), which does not cross the plasma membrane. This indicated an intracellular action of 17β-oestradiol. The existence of ERα in cytoplasm was demonstrated by immunostaining and its involvement by the abolishment of the 17β-oestradiol action by the pure antioestrogen ICI 182, 780. The PI3-kinase inhibitor wortmannin and the NOS inhibitor L-NAME, both completely blocked oestradiol effect. The gonadal hormone action was reproduced by 8Br-cGMP and abolished in the presence of the PKG inhibitor KT5823. Remarkably, the PKA inhibitor KT5820 was without effect.

Our study clearly indicates that 17β-oestradiol can regulate Ca²⁺ influx via PI3-Kinase, NOS and PKG after activation of cytoplasmic ER. The present work provides a novel molecular mechanism used by oestrogens to control neuronal Ca²⁺ signalling.

This work is funded by by Grants from Instituto de Salud Carlos III (00/1082) and Ministerio de Ciencia y Tecnologia (BFI2002-01469).