Immunohistochemical detection of the orexin system in the placenta of cats

The aim of the present study was to investigate the presence and distribution of cells containing orexin A (OXA), and orexin type 1 and 2 receptors (OX1R and OX2R, respectively) in the feline placenta by means of immunohistochemical technique. OXA was identified in several decidual and syncytiotrophoblastic cells present in the lamellar portion of the placenta. In the same placental structures, few decidual and syncytiotrophoblastic cells showed the presence of OX1R-like immunoreactivity. Characteristically, immunopositivity for OX2R, but not for OX1R, was evidenced in the cells of the glandular layer. The orexinic system was not expressed in the uterine structures that were not engaged by the chorion. Our results provide the first evidence of the presence of a placental orexinic system in a mammalian species. Orexin A and both OX1R and OX2R are unequally distributed within the cat placenta. Local OXA production and the presence of specific receptors, differentially expressed in the placental structures of the cat, suggest that the orexinic system may participate in placental growth and development as well as in the regulation of its steroidogenic capacity via endocrine, paracrine and/or autocrine mechanisms.