Photoperiodic responses in bilaterally enucleated female white-crowned sparrows, Zonotrichia leucophrys gambelii

Abstract

The responses to long daily photophases (20L 4D) by bilaterally and unilaterally enucleated female white-crowned sparrows were studied in order to assess the role of extraretinal photoreceptors in the induction of the secretion of luteinizing hormone (LH), of growth of the ovary and oviduct, and of premigratory fat deposition. Photostimulation induced a marked increase in the concentration of LH in the plasma of both groups with maximum levels of 8.9 ng/ml of plasma in the bilateral enucleates and 6.9 ng/ml in the unilateral enucleates. Plasma levels of LH in the bilateral enucleates remained consistently higher than in the unilateral enucleates throughout the experimental period of 36 days and were higher than those attained by intact females treated similarly. Unilateral and bilateral enucleates showed typical photoperiodically induced fattening; however, the increase in weight in the bilateral enucleates began approximately 8 days later than in the unilateral enucleates. Extraretinal photoreceptors are clearly involved in the photoperiodic responses studied. The presence of eyes appears somehow to suppress the level of LH in the plasma.