Avian prolactin (PRL) secretion is under stimulatory control by the PRL-releasing factor (PRF), vasoactive intestinal peptide (VIP). The neuroendocrine regulation of the avian reproductive system has been extensively studied in females. However, there are limited data in males. The aim of this study was to elucidate the VIPergic system and its relationship to PRL and testosterone (T) in the male native Thai chicken. The distributions of VIP-immunoreactive (-ir) neurons and fibers were determined by immunohistochemistry. Changes in VIP-ir neurons within the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) areas were compared across the reproductive stages. Plasma levels of PRL and T were determined by enzyme-linked immunosorbent assay and then compared across the reproductive stages. The results revealed that the highest accumulations of VIP-ir neurons were concentrated only within the IH-IN, and VIP-ir neurons were not detected within other hypothalamic nuclei. Within the IH-IN, VIP-ir neurons were low in premature and aging males and markedly increased in mature males. Changes in VIP-ir neurons within the IH-IN were directly mirrored with changes in PRL and T levels across the reproductive stages. These results suggested that VIP neurons in the IH-IN play a regulatory role in year-round reproductive activity in males. The present study also provides additional evidence that VIP is the PRF in non-seasonal, continuously breeding equatorial species.
Bibliographical noteFunding Information:
This work was supported by a grant funded under the Suranaree University of Technology (SUT) PhD Program (Contract number: SUT-PhD/08/2554), SUT, and the National Research University (NRU) Project of Thailand, Office of the Higher Education Commission. The authors would also like to thank the University Farm of Suranaree University of Technology for providing the chicken barns.
© 2016 Elsevier B.V.
- Vasoactive intestinal peptide