Abstract
In avian species, gonadal differentiation not only depends on genetic information, but on the trophic action of numerous sex-determining factors and neuronal survival. Vasoactive Intestinal Peptide (VIP) participates in several functions, including sexual behavior, and has a neuroendocrine effect on the gonads. In gonadal tissue, VIP function is regulated via G-protein-coupled receptors and is mainly exerted through the VIP receptor type I (VIPR-I). In domestic hens, the VIP intercellular signal regulates the expression of enzymes that promote steroid production, such as progesterone and androgen in preovulatory follicles. In order to determine the sites of VIP synthesis and to compare it with VIPR-I localization during gonadal morphogenesis, pre and post-hatching left and right ovaries, as well as testicles were used. The patterns of VIP and VIPR-I localization were analyzed with immunohistochemistry techniques. From the 12th day of incubation, VIP distribution was observed in celomic epithelium, in testis and right and left ovaries. Moreover, VIP immunostaining was detected in the ovarian cortex in pregranulosa cells and shortly after, a gradient of VIP was seen from the cortex to the medulla. In the right ovary, the cortex is not found because it degenerates early in development. In ovarian and testicular medulla VIP was found in interstitial steroidogenic cumuli and in abundant nerve fibers. VIPergic fibers were more evident in ovaries than in testicles. In post-hatching left ovaries, VIP was found in the granulosa sheet and in some oocytes of immature follicles. In postnatal stages of males, VIP immunostaining was found in Leydig cells and spermatogonia. VIPR-I was observed in testicular and ovarian cortex and some epithelial cells during embryogenesis. In the ovary, VIPR-I was localized in the cytoplasm of granulosa cells and oocytes. In post-hatching females, up to the 7th day of incubation, VIPR-I immunostaining was detected mainly in the cortex, in oocytes and the granulosa sheet of developing follicles and in neuronal somas and nerve fibers. In embryonic stages of testis, VIPR-I was detected in Leydig cells and nerve fibers. Throughout maturation, VIPR-I was found in spermatogonia, Leydig cells and nerve fibers localized between the spermatic chords. With the findings of our work, we propose a regulatory action of VIP and VIPR-I on gonadal development. In the granulosa sheet of developing follicles it could be acting in a paracrine way, promoting oocyte maturation. We propose that VIP acts as a modulator of gonadal differentiation and steroidogenic activity. We thank to Verónica Rodríguez Mata for her technical assistance and Pablo G Hofmann Salcedo for reviewed the manuscript. Supported by DGAPA IN 207905. Supported by DGAPA IN206 007 (poster)
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