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Published-Ahead-of-Print September 20, 2006, DOI:10.2164/jandrol.106.000653
Journal of Andrology, Vol. 28, No. 1, January/February 2007
Copyright © American Society of Andrology
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{dagger}, PATRICIA PADILLA*, MARIA CHRISTINA W. AVELLAR{dagger}, PATRICIA RIVAS MANZANO{ddagger}, GABRIEL MANJARREZ-GUTIÉRREZ§ AND GABRIEL GUTIÉRREZ-OSPINA*

From the * Department of Cell Biology and Physiology, Biomedical Research Institute, National Autonomous University of Mexico, Mexico City, Mexico; the {dagger} Department of Pharmacology, Section of Experimental Endocrinology, Universidade Federal de São Paulo-Escola Paulista de Medicina, São Paulo, Brazil; the {ddagger} Department of Reproductive Biology, Faculty of Sciences, National Autonomous University of Mexico, Mexico City, Mexico; and the § Unit of Medical Investigation in Neurological Diseases, XXI Century National Medical Center, Mexican Institute of Social Security, Mexico City, Mexico.

Correspondence to: Dr. Gabriel Gutiérrez-Ospina, Department of Cell Biology and Physiology, National Autonomous University of Mexico, Ciudad Universitaria, Mexico City, 04510 (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 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 5HT1A, 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 2 protein bands (~51 kd and ~48 kd) that were immunoreactive for tryptophan hydroxylase. Chromatographic analyses documented the presence of tryptophan hydroxylase in the caput, and showed that both its activity and serotonin availability increased with sexual maturation and decreased following p-chlorophenylalanine treatment, an inhibitor of 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: 5-hydroxytryptamine, tryptophan hydroxylase, neuroendocrine cells, male reproduction, serotonin receptor, spermatozoa







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