Is this effect on the motivational phase really due to the non-genomic action of oestradiol? In order to test this idea, the researchers coupled the hormone with a molecule that is incapable of crossing cell membranes: bovine serum albumin. “We obtained the same result, which indicates that the effect on sexual motivation is initiated at the cellular membrane and not in the cell nucleus”, reveals Charlotte Cornil. The same hormone has therefore developed complementary mechanisms – Slow, genomic, and rapid, non-genomic – to regulate different components of sexual behavior. “Our observations suggest that the genomic mode of action serves to prepare the brain for the breeding season. It enables the nervous system to be set up such that it can react when required to do so”, explains the researcher. “The non-genomic mechanisms act as a switch that turns on the system when the environmental and social conditions are appropriate”, continues Charlotte Cornil.

What about the activity of aromatase?

Another line of research in the behavioral neuroendocrinology laboratory is the study of the control of aromatase. Here too, different studies have shown that in parallel with the genomic mechanisms which control the activation of this enzyme, the aromatase can be activated or inactivated a lot more rapidly by simple phosphorylation (addition of a phosphate group to a protein or small molecule). Continuing their collaboration with Gregory Ball, Charlotte Cornil and Catherine de Bournonville, a PhD student in the laboratory, wanted to know more about the rapid changes in aromatase activity that occur in vivo following sexual interactions in quail. “To ensure rapid changes in local oestradiol concentration, aromatase must also quickly change its activity”, specifies Charlotte Cornil.

Scientists dissected six aromatase-expressing cell populations in the brains of male quail which had been previously exposed to the sight of a female or that had copulated. “We noticed that aromatase activity drops rapidly after copulation but also after simple visual contact with the female”, indicates Charlotte Cornil. The results of this study have been published in the journal Psychoneuroendocrinology (2).

“We have not yet solved the mystery of this early drop in aromatase activity. But if we take into account our previous study, we can hypothesize that, as the rapid action of oestradiol affects sexual motivation but not performance, oestradiol needs to be rapidly synthesized in order to allow the animals to get closer to each other but is no longer required afterwards when other neurotransmitters take over, which might explain the drop in aromatase activity after just seeing the female”, explains the researcher.

A hormone that ressembles neurotransmitters

More and more studies tend to show that oestradiol is capable of rapid action. This is true to such a degree that scientists are asking the question as to whether this hormone should not be placed in the same category as “neurotransmitters” instead of continuing to consider it as a chemical messenger which exerts a long-term action (3). Indeed, while hormones are molecules secreted into the blood and act on distant targets, neurotransmitters are synthesized in the synapses where they act directly. The two studies mentioned here reinforce the idea that oestradiol, with its non-genomic action, behaves more like a neurotransmitter.

(2) Catherine de Bournonville, Molly J. Dickens, Gregory F. Ball, Jacques Balthazart, Charlotte A. Cornil. Dynamic changes in brain aromatase activity following sexual interactions in males: Where, when and why? Psychoneuroendocrinology (2012 – due to appear, doi: 10.1016/j.psyneuen.2012.09.001).
(3) Jacques Balthazart, Gregory F. Ball.  Is brain estradiol a hormone or a transmitter? Trends in Neurosciences 2006 • 29, 241-249. Read the article: Oestradiol, sex dan sun.