Changes in brain peptides associated with reproduction and energy homeostasis in photosensitive and photorefractory migratory redheaded buntings

- Annual changes in brain peptides in buntings under low-amplitude photoperiod cycle.
- Changes in GnRH-I are consistent with that of an absolute refractory species.
- NPY/VIP expressions are consistent with seasonal reproductive and metabolic changes.
- Proximity of perikarya and fibres suggests probable interaction between peptides.

Present study examined the expression of brain peptides associated with the reproduction and energy homeostasis (GnRH/GnIH, NPY/VIP), and assessed their possible functional association in the photosensitive (non-breeding, pre-breeding), photostimulated (breeding) and photorefractory (post-breeding) migratory redheaded buntings (Emberiza bruniceps), using double-labeled immunohistochemistry. Particularly, we measured immunoreactive (-ir) cell numbers, per cent cell area and cell optical density (OD) in the preoptic area (GnRH-I), midbrain (GnRH-II), paraventricular nucleus (GnIH), dorsomedial hypothalamus, DMH and infundibular complex, INc (NPY and VIP), and lateral septal organ (VIP) of buntings kept under natural photoperiods at the wintering latitude (26°55′N). There was a significant seasonal difference in GnRH-I, not GnRH-II, with reduced -ir cells in the photosensitive and photorefractory buntings, and notably with increased cell OD between the refractory and non-breeding states with no increase in testis size. Also, increased cell OD of GnIH neurons in non-breeding state indicated its role in the maintenance of small testes during the post-refractory period. Overall, seasonal changes in GnRH-I and GnIH were found consistent with their suggested roles in reproductive regulation of absolute photorefractory birds. Further, there was a significant seasonal change in cell OD of NPY neurons in DMH, not the INc. In contrast, VIP immunoreactivity was seasonally altered, with a significantly higher VIP-ir cells in breeding than the pre-breeding state. Finally, close proximity between perikarya with fibres suggested functional interactions between the GnRH and GnIH, and NPY and VIP. Thus, seasonal plasticity of brain peptides is perhaps the part of neural regulation of seasonal reproduction and associated energy homeostasis in migratory songbirds.