When oestradiol moves into second gear

In addition to these delayed effects caused by the genomic action of oestradiol, this hormone also acts faster by taking a non-genomic route. “This mode of action does not involve the modulation of the expression of genes”, specifies Charlotte Cornil. “Here oestradiol interacts with membrane receptors located on the cell surface and triggers rapid changes in cell function”. As an example, this type of action by oestradiol in neurones causes a variation in the frequency of action potentials, that is to say, their firing rate. 

Charlotte Cornil and Aurore Seredynski, a PhD student in the laboratory, in collaboration with Gregory Ball of the Johns Hopkins University of Baltimore (Maryland, USA), wanted to know if the rapid mode of action of oestradiol (by the non-genomic route) had an effect on the sexual behavior of Japanese quail, which is the laboratory’s preferred model.

“Sexual behavior can be divided into two main phases”, continues Charlotte Cornil. “The first, called the appetitive or motivational phase, includes the approach and courtship behavior which allows partners to get closer to each other. The second phase, the consummatory phase, is the behavioral sequence during which the partners copulate”. While the consummatory phase is easy to assess, the motivational phase is measured by the frequency of contractions of the cloacal gland of the male quail. Birds do not have external genitalia. The sperm is transferred from the male to the female when the animals place their cloacae (posterior orifices) in contact. The frequency of the cloacal contractions in response to the sight of a female is one of the signs of sexual motivation in the male used in the laboratory setting.

A dichotomous effect on sexual behavior

“We administered a treatment directly into the 3rd cerebral ventricle of male birds. Some animals received an aromatase inhibitor combined or not with oestradiol”, explains Charlotte Cornil. The results of this study which was published in the Journal of Neuroscience (1) reveal that the treatment was rapidly followed by an effect on sexual motivation but had no effect on the consummatory phase. 

Individuals who had received the aromatase inhibitor alone showed a remarkable drop in the frequency of contraction of the cloacal gland in response to the presentation of a female while those treated with the inhibitor and oestradiol showed a frequency of contraction similar to that of the control individuals. However, in both cases, the treatment did not influence the copulation of individuals. “This was a real surprise, we expected to observe effects on both phases because they are very much connected”, indicates the scientist. Supplementary tests confirmed these results.

(1) Aurore L. Seredynski,  Jacques Balthazart, Virginie J. Christophe, Gregory F. Ball, Charlotte A. Cornil. Neuroestrogens Rapidly Regulate Sexual Motivation But Not Performance. The Journal of Neuroscience, January 2, 2013 • 33(1):164 –174.