Recovery of photosensitivity in photorefractory starlings is not prevented by testosterone treatment.

Groups of photorefractory intact and castrated male starlings were implanted with three 30-mm Silastic capsules containing testosterone or with empty capsules and transferred to short (8-hr) daylengths. In the castrated birds given empty capsules plasma luteinizing hormone (LH) rose from basal levels after 20-30 days and reached a high plateau level at about 40 days; this return of a "castration response" indicates a quite rapid recovery of photosensitivity under short days. Half of these birds were transferred to long (18-hr) day-lengths after 56 days but no further significant increase in plasma LH was noted as a consequence. In fact, levels of the hormone soon declined markedly as the birds became photorefractory. In the castrates implanted with testosterone, LH remained very low throughout the period of short-day treatment. After 56 days the capsules were removed and half the birds were transferred to 18-hr photoperiods. In these, the LH levels rose markedly for the first 21 days and then declined as the birds became photorefractory. In the remaining castrates retained on 8-hr photoperiods, plasma levels of the gonadotrophin increased somewhat more slowly becoming maximal only after about 30 days, and refractoriness did not ensue. All intact birds retained small and undeveloped testes during the 56-day period of subjection to short days, i.e., testosterone did not induced gonadal growth. After this time capsules were removed and all of the birds were transferred to 18-hr day-lengths. The testes grew and reached a similar maximal size in all birds, though more slowly in those which had been implanted with testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)