Testosterone treatment blocks the termination of the gonadal photorefractory condition in white-throated sparrows maintained on short days

Testosterone was administered to photorefractory white-throated sparrows via intraperitoneal Silastic capsules to determine the effects of gonadal steroids on the termination of the gonadal photorefractory condition during exposure to short days (LD 8:16). Control birds exposed to short days terminated the refractory state, but birds treated with testosterone failed to respond to subsequent photostimulation when circulating levels of testosterone were maintained at about 30 ng/ml. Maintenance of plasma testosterone levels at about 4 ng/ml prevented the termination of the refractory condition in four out of six birds exposed to short days. In another experiment, sexually mature sparrows were transferred from LD 16:8 to LD 8:16 for 10 weeks and were treated with testosterone during the exposure to short days. Subsequent long-day photostimulation failed to maintain testicular function in these birds. In sharp contrast, when photosensitive (i.e., non-photorefractory) sparrows with regressed testes were treated with similar amounts of testosterone during a 10-week period of short-day exposure, subsequent photostimulation maintained testicular function. These results indicate that recovery from the gonadal photorefractory condition which normally occurs during exposure to short days can be blocked if circulating testosterone levels are elevated.