Sperm cannot smell

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Fragrances play no role for sperm

Sperm are directed by certain attractants on their way to the egg, but this has nothing to do with smelling. The so-called "lily-of-the-valley phenomenon", according to which fragrances influence the journey of sperm, is based on a laboratory phenomenon, according to the current result of a team of researchers from the Bonn foundation Caesare and the Research Center Jülich.

The previous assumption that sperm are guided by fragrances on their way to the egg cell has been refuted. Researchers from the Caesar Foundation (center of advanced european studies and research) in Bonn, together with scientists from Forschungszentrum Jülich, found that sperm have no olfactory signaling pathway, but are guided by a hormonal attractant during their journey - progesterone.

Lily of the valley phenomenon just a laboratory phenomenon The so-called "lily of the valley phenomenon" has long been considered a relatively accepted theory for the control of sperm on their way to the egg. In 2003, German and American scientists published a study in the journal Science, according to which a component of the lily-of-the-valley scent lures the sperm towards the egg cell. The Bonn scientists Caesare Foundation (associated with the Max Planck Society) did not want to follow this theory. Especially since no lily of the valley fragrance or any other "fragrance found in the female genital tract" that supports this theory has been explained by Dr. Timo Strünker from the Molecular Neurosensory Department at the Caesare Foundation opposite the “dpa” news agency. Last year, the Caesare researchers presented an alternative model according to which the hormone progesterone, as a chemical guide, directs the sperm towards the egg. Now the researchers, together with scientists from Forschungszentrum Jülich, have shown that the lily of the valley smell has a similar effect on sperm as progesterone, but this can only be achieved in the laboratory, since a concentration that is 1000 times higher than that of the hormone is required. The "lily of the valley phenomenon" is based on "on a laboratory artefact", there is no olfactory signaling pathway in sperm, the scientists report.

Sperm controlled by chemical attractants From previous studies it was already known that the egg cells support the sperm on their way by releasing certain attractants that influence the swimming movement of the sperm. The theory that fragrances serve as a guide for the sperm contrasted with the model of control by the female sex hormone progesterone. Now the researchers around Dr. Timo Strünker demonstrated that the effect of progesterone on the so-called "CatSper ion channels (cation channels of sperm)" is responsible for the control of the sperm. Although the lily-of-the-valley fragrance "Bourgeonal" shows a comparable effect on the "CatSper ion channels" as progesterone, the fragrance does not occur in the female genital tract and only works from a concentration 1,000 times higher than progesterone, according to the current results of the researchers . Calcium can flow into the sperm via the CatSper channels, which are only found in sperm, whereupon they adjust their swimming direction. Men who have functional disorders of the CatSper channels due to a genetic defect are sterile.

Pill for the man? Since the lily of the valley fragrance cannot be found in the female genital tract and only with an overdose can a comparable effect to that of progesterone, the "lily of the valley phenomenon" is only a laboratory phenomenon in the opinion of the Caesare researchers. "Sperm do not function like olfactory cells in the nose," emphasized study leader Dr. Timo Strünker told the “dpa” news agency. Instead, the sperm perceive “the chemical milieu in the fallopian tube” via the CatSper channels and can “find the egg cell”, the neuroscientists report. According to this, the sperm use the CatSper channels on their arduous journey to the egg cell in order to orient themselves again and again on the basis of various “chemical signs”. However, it has not yet been clarified why the spermatozoa react so little picky to different substances such as lily of the valley or menthol. In future studies, the scientists want to concentrate on identifying other attractants in the fallopian tube that, in addition to progesterone, determine the control of the sperm. According to the Caesare researchers, the discoveries are "also medically significant" because they could enable the development of new contraceptives (pill for men) "if the effects of female factors on the CatSper channels could be disrupted." ( fp)

Image: Thommy Weiss / pixelio.de

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