Photorefractoriness in Pinealectomized Harris' Sparrows

Abstract

Exposure to long daily photoperiods induces testicular growth in photosensitive passerine species and, if prolonged, inevitably causes testicular regression. The latter signals the onset of refractoriness which, under natural conditions, is not eliminated without the effect of short daily photoperiods (for reviews see Farner 1959, 1964, 1967; Farner and Follett 1966). Since the pineal body has an antigonadotropic function in the golden hamster (Reiter et al. 1966; Reiter 1967) and perhaps in the rat (Wurtman et al. 1959; Reiter et al. 1968), the possibility exists that this organ plays a role in refractoriness in photoperiodic passerine species. To test this possibility, we examined the effect of pinealectomy on testicular regression in photostimulated Harris' Sparrows (Zonotrichia querula) and on testicular quiescence in refractory Harris' Sparrows retained on long daily photoperiods. Birds captured with mist nets near Manhattan, Kansas, were housed, several per cage, in Hendryx breeding cages. Illumination was provided by fluorescent lamps at an intensity of at least 375 lux. Ambient temperature ranged between 180 and 240C. At autopsy, testes were removed and fixed for 5 days in AFA; after 5 additional days in 70 per cent ethanol, they were debrided and weighed on a torsion balance. Statistical analysis of testicular weights was by Student's t-test. The region of the pineal body was inspected microscopically to verify operational success. Harris' Sparrows captured between 17 December 1966 and 4 February 1967 were held on 8-hr daily photoperiods (08:30-16:30 CST) until 27 February 1967, when testicular growth was induced by lengthening the daily photoperiod to 20 hr (08:3004:30 CST). Twenty days later, i.e., near the end of the logarithmic growth phrase (Wilson 1968), pinealectomy or sham pinealectomy (for procedures see Donham 1968) was performed and the birds returned to long daily photoperiods. They were sacrificed 54 or 79 days postoperatively. The data in table 1 show that pinealectomy neither prevented testicular regression nor altered its course. Both pinealectomized and sham-pinealectomized Harris' TABLE 1. Failure of pinealectomy to prevent testicular regression in photostimulated Harris' Sparrows.