Journal of Andrology
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Published-Ahead-of-Print September 20, 2006, DOI:10.2164/jandrol.106.000653

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Serotonin concentration, synthesis, cell origin and targets in the rat caput epididymis during sexual maturation and variations associated with adult mating status: Morphological and biochemical studies

Francisco Jiménez-Trejo , Miguel Tapia-Rodríguez , Daniel B.C. Queiroz , Patricia Padilla , Maria Christina W. Avellar , Patricia Rivas Manzano , Gabriel Manjarrez-Gutiérrez , and Gabriel Gutiérrez-Ospina *

* To whom correspondence should be addressed. E-mail: gabo{at}correo.biomedicas.unam.mx.

The caput epididymis of some mammals contains large quantities of serotonin whose origin, targets and physiological variations have been poorly studied. We then combined morphological and biochemical techniques to begin approaching these aspects of serotonin in the rat caput epididymis. Serotonin immunostaining was detected in mast, epithelial and neuroendocrine cells. Epithelial cells displayed immunoreactivity to 5HT 1A, 5HT2A and 5HT3 serotonin receptors. Endothelial and mast cells labeled positive for 5HT1B serotonin receptors and spermatozoa displayed 5HT2A and 5HT3 serotonin receptor immunoreactivity. Epithelial, endothelial and mast cells stained positive for serotonin transporters. Only epithelial cells showed tryptophan hydroxylase immunoreactivity; this enzyme catalyzes the limiting step in the serotonin synthetic pathway. In addition, Western blot analyses of caput homogenates documented the presence of two protein bands (approximately 51kDa and 48kDa) that were immunoreactive for tryptophan hydroxylase. Chromatographic analyses documented the presence of the activity of tryptophan hydroxylase in the caput, and showed that both its activity and serotonin availability increased with sexual maturation, and decreased following p-chloro-phenylalanine treatment; this agent inhibits tryptophan hydroxylase activity. Interestingly, serotonin concentration and tryptophan hydroxylase activity tended to be higher in breeding males than in those with no mating experience. We think that these results support the existence of a local serotoninergic system in the rat caput epididymis that might regulate some aspects of male reproductive function.


Key words: Epididymis • Fertility • Reproductive Tract • Sperm • 5-hydroxytryptamine • neuroendocrine cells • serotonin receptor • spermatozoa • tryptophan hydroxylase






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