Age-related Localization and Expression of Orexin A and its Receptor 1 in Dromedary Camel Testis

Background: The orexin (OX) is a hypothalamic neuropeptide that exists in two forms, orexin A (OXA) and orexin B (OXB), which bind two receptors (OX1 and OX2). While orexin B shows selectivity for OX2, OXA is potent at both receptors. Orexins are also reported in other mammalian organs where they undergo many regulatory functions. However, their detection in the dromedary camel reproductive organs remains to be revealed. Methods: We investigated the immunoreactivity of orexin OXA and OX1 in the testis of young (6-12 month), pre-pubertal (2-3 years) and adult (6-15 years) dromedary camels. We also studied the relative expression of hypocretin neuropeptide precursor (HCRT) in the testicular tissue of these age groups. Result: Positive immunoreactions of OXA and OX1 were shown in both the tubules and interstitium of dromedary camel testis in the young animals. While positive OXA and OX1 immune-labeling was detected in the spermatogonia, Sertoli cells and Leydig cells in all ages, adult camels also showed positive OXA and OX1 signals in the primary spermatocytes, spermatozoa and interstitial blood vessels. In testes at pre-pubertal and adult stages, spermatogenic cells, Sertoli cells and Leydig cells showed stronger OXA and OX1 reactions than in young camels. Real time PCR analysis also revealed that HCRT was expressed in the testis of dromedary camels with minimal expression in young camels. In conclusion, the current study provides the first evidence for the presence of OXA and OX1 in the testis of adult and younger dromedary camels. Before puberty, the binding of OXA and OX1 in the camel testis might be important for development and proliferation of spermatogenic cells, Sertoli cells and Leydig cells; in adult animals they may play a role in steroidogenesis and spermatogenesis.