Responses of Photosensitive and Photorefractory Male White-crowned Sparrows (Zonotrichia leucophrys gambelii) to Synthetic Mammalian Luteinizing Hormone Releasing Hormone (Syn-LHRH)

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Abstract
To assess a possible role of the adenohypophysis in photorefractoriness, photosensitive and photorefractory adult male white-crowned sparrows (Zonotrichia leucophrys) were treated with single intravenous injections of 0, 0.5, 5, 20, 35, 50 or 500 ng of synthetic luteinizing hormone releasing hormone (Syn-LHRH) in 0.9% saline solution. Serial samples of plasma were taken immediately before and at 5, 20 and 60 min after injection. The plasma level of immunoreactive luteinizing hormone (irLH) was not altered by the injection of saline solution alone, or by 0.5 or 5 ng Syn-LHRH in either photosensitive or photorefractory birds. Treatment with 20, 35, 50 or 500 ng Syn-LHRH, however, elicited significant and approximately equal increases in plasma levels of irLH in both groups 5 min after injection. These responses are consistent with the hypothesis that the site of photorefractoriness is at a level higher than the adenohypophysis.

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