Photorefractoriness in European starlings: Associated hypothalamic changes and the involvement of thyroid hormones and prolactin

✍ Scribed by Nicholls, T. J. ;Goldsmith, A. R. ;Dawson, A.

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 512 KB
• Volume: 232
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402320324

✦ Synopsis

Responsivity to photostimulation in previously photorefractory European starlings is caused by subjection to short daylengths and is characterized by a marked activation of the hypothalamus in terms of synthesis of gonadotropin releasing hormone. This active hypothalamic state is amplified for a time by a subsequent exposure to long days but is soon completely reversed as the birds become photorefractory again. This latter effect of long photoperiods and the concurrent secretion of prolactin are dependent on the presence of thyroid hormones. Conceivably, prolactin causes photorefractoriness by inhibition at a hypothalamic level.