Some melatonin functions in mammals are exerted through MT1 and MT2 receptors. However, there are no reports of their presence in the reproductive tract of the ram, a seasonal species. Thus, we have investigated their existence in the ram testis, epididymis, accessory glands and ductus deferens. Real-time polymerase chain reaction (qPCR) revealed higher levels of m-RNA for both receptors in the testis, ampulla, seminal vesicles, and vas deferens, than in the other organs of the reproductive tract (p < 0.05). Western blot analyses showed protein bands compatible with the MT1 in the testis and cauda epididymis, and for the MT2 in the cauda epididymis and deferent duct. Immunohistochemistry analyses revealed the presence of MT1 receptors in spermatogonias, spermatocytes, and spermatids, and MT2 receptors in the newly-formed spermatozoa in the testis, whereas both receptors were located in the epithelial cells of the ampulla, seminal vesicles, and ductus deferens. Indirect immunofluorescence showed significant differences in the immunolocation of both receptors in spermatozoa during their transit in the epididymis. In conclusion, it was demonstrated that melatonin receptors are present in the ram reproductive tract. These results open the way for new studies on the molecular mechanism of melatonin and the biological significance of its receptors.

We tested the hypothesis that sheep breed can influence the sperm quality and seminal plasma (SP) composition and investigated any potential relationship between SP proteins and antioxidant enzyme activities (AO) with sperm quality. Ejaculates from twelve rams of three breeds were obtained during the rainy season at high altitudes, and sperm quality was automatically evaluated (CASA-Hamilton Thorne). The AO of superoxide dismutase, glutathione peroxide and glutathione reductase (GR) in SP was evaluated and total proteins were separated by SDS-PAGE. Comparative analyses of semen quality parameters between breeds revealed that Creole and Hampshire breeds had a higher sperm quality compared with Romney Marsh (p<0.05), although no difference in AO was found. GR activity was negatively correlated (p<0.05) with several kinematic variables and positively (p<0.05) with morphological abnormalities. The highest SP protein concentration was found in semen collected from Hampshire males compared with that from Creole and Romney Marsh (p<0.05). SDS-PAGE analysis showed the presence of 32 protein bands in SP with molecular weights between 334 and 10 kDa. Differences (p<0.05) between breeds in bands of 43, 25, 22 and 20 kDa were observed. These results evidence a relationship between the protective effect of the antioxidant enzyme system in SP of three ram types under high altitude and tropical conditions and semen quality. Our findings also suggest that the identified proteins might play an important role in sperm physiology and quality.

The aim of this study was to determine whether polymorphisms of the melatonin receptor 1A (MTNR1A) gene influence the age at first mating in autumn-born ram-lambs and influence the out-of-season sexual activity of adult rams. In experiment 1, 24 Rasa Aragonesa ram-lambs born in September were genotyped for their RsaI and MnlI allelic variants of the MTNR1A gene, and the date of their first mounting with ejaculation after a period of semen collection training was documented. In experiment 2, the reproductive behavior, testicle size, and plasma testosterone concentrations of 18 adult rams (6 rams for each RsaI genotype) were recorded at the beginning (March) and end (May) of the seasonal anestrus.

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