Neuro-oestradiol, a two-speed sexual hormone

Oestradiol, which  controls sexual behavior and is known to act in the long-term, has also been shown to be able to act rapidly, much like a neuro-transmitter. In a study published in the Journal of Neuroscience, researchers at the University of Liege have demonstrated that this rapid action has a direct effect on the motivational phase of the sexual behavior of male quail but not on copulation. Thus, the “long-term” mode of action serves to prepare the brain for the breeding season. It makes it possible to set up the nervous system so that it will be ready to react when required to do so. The “short-term” mechanism acts like a switch that turns on the system when the environmental and social conditions are favorable.
Classified as a female hormone due to its high circulating concentration in females, oestradiol (or estradiol, E2) is a form of oestrogen. However, this steroid hormone is also present in males and plays an important role in reproduction. Ironically, in spite of the high concentration of the hormone in females, oestradiol is produced from testosterone which is typically considered as a male hormone. An enzyme known as aromatase transforms testosterone into oestradiol in both the ovaries and testicles as well as in many other tissues including the brain.

Although oestrogens are generally perceived as being associated with reproduction, they have different effects and act in numerous tissues in humans and animals. They notably play a role in bone and mammary tissue, growth, skin-flexibility, cognitive functions such as memory, neuro-protection and even hormone-dependent cancers.

Synchronising reproduction and season

In the male, oestrogens produced in the brain (sometimes called “neuro-oestrogens”) are involved in the control of sexual behaviour. “They act through genomic mechanisms by binding to intracellular receptors and interacting with the DNA of cells in order to modulate the transcription of target genes”, explains Charlotte Cornil, Research associate at the F.R.S.-FNRS in the Behavioral Neuroendocrinology Laboratory of Prof. Jacques Balthazart, at GIGA-Neurosciences of the University of Liege. This type of action produces effects on sexual behavior within a relatively long time-frame. “The behavioral effects appear after several days”, explains Charlotte Cornil. “This type of action is perfectly in line with the role commonly ascribed to oestrogens in the synchronization of sexual behaviour with the appropriate season”, continues the researcher.  Indeed, animal reproduction is generally controlled so that the youngs are born at the time of year that is the most favorable for their survival and growth. The environmental stimuli make this control possible and constitute signals for organisms. “For example, light affects the growth of the gonads and therefore the secretion of testosterone. This is followed by an increase in the brain production of oestradiol which itself acts on the nervous system”, indicates Charlotte Cornil. So, to summarize: seasonal variations lead to variations in the secretion of testosterone upon which the production of oestrogens depends and which in turn has an effect on sexual behavior!

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