Photoperiodic regulation of reproduction in birds

Birds time their activities in synchronization with daily and provided by changes in day length (=photoperiod). Photoreceptor cells in an avian brain are localized in three independent neural structures, the retina of eyes, pineal gland and hypothalamus. Dee localised particularly in the paraventricular organ (PVO) and lateral septal area (LSO) of hypothalamus are implicated in regulation of photoperiod induced reproductive response. DBPs relay the photoperiodic information to the tuberalis thyroid hormone stimulating (TSH) expressing cells. The TSH mediated signalling mediates the photoperiod induced gonadotropins releasing hormone (GnRH) release from the pre optic area (POA). In addition to the GnRH, other neurohormones including the neuropeptides Y (NPY), vasoactive intestinal peptide (VIP), and the neurosteroids, especially the brain derived testosterone contribute to regulation of the overt reproductive response and behaviour in seasonal breeding avian species. Here, we br hormone variations of the hypothalamus in the regulation of seasonal physiology, particularly in the long species.