Patterns and biological significance of steroidal hormone metabolism in birds

Role of testosterone in stimulating seasonal changes in a potential avian chemosignal

Songbird preen oil contains volatile and semivolatile compounds that may contain information about species, sex, individual identity, and season. We examined the relationship between testosterone (T) and the amounts of preen oil volatile and semivolatile compounds in wild and captive dark-eyed juncos (Junco hyemalis). In wild males and females, we observed an increase in volatile compound relative concentration early in the breeding season. This increase mirrored previously described seasonal elevation in T levels in wild males and females, suggesting a positive relationship between hormone levels and preen gland secretions, and a possible role for these secretions in signaling receptivity. In females, the greatest relative concentrations of most compounds were observed close to egg laying, a time when steroid hormones are high and also the only time that females respond to an injection of gonadotropin-releasing hormone with a short-term increase in T. In a study of captive juncos held on short days, we asked whether the seasonal increases observed in the wild could be induced with experimental elevation of T alone. We found that exogenous T stimulated the production of some volatile compounds in non-breeding individuals of both sexes. However, of the 15 compounds known to increase during the breeding season, only four showed an increase in relative concentration in birds that received T implants. Our results suggest that testosterone levels likely interact with other seasonally induced physiological changes to affect volatile compound amounts in preen oil.

Effect of a vasotocin analog on singing behavior in the canary

Groups of juvenile and 1-year-old male canaries were treated briefly with the vasotocin (VT) analog desGly(NH2)9d(CH2)5-[Tyr(Me)2,Thr4, Orn8]VT (dGVTA) during four time intervals between September and February. The canaries received subcutaneously testosterone-containing silastic implants at the start of the VT analog treatment to assure that despite age and season differences the birds would all have comparable plasma levels of testosterone. The VT analog was administered subcutaneously (0.7 micrograms/100 microliters) during the first 3 days (3 injections daily) of chronic testosterone treatment. Observations on the singing behavior were carried out between Day 8 and Day 30 after implantation of the testosterone-filled silastic tubing. The short-term administration of the VT analog influenced the amount of singing behavior during a 30-min observation interval measured 1 to 4 weeks later. Despite age differences the effect of dGVTA held and seemed more related to season than to age. The song duration (seconds of song/30 min) was affected in a dual mode. In early autumn the VT analog enhanced song duration of testosterone-primed canaries, but the same VT analog decreased song duration in the period November/January. These results suggest that the neuropeptide VT is implicated in control of seasonal changes in singing behavior.

Performance of two male broiler breeder strains raised and maintained on various constant photoschedules

The purpose of the present study was to examine the interaction of constant photoschedules and genetic background on performance of male broiler breeders. Day-old cockerels from two BW strains were placed on litter floors in light-controlled chambers. Light treatments (LT) (60 lx) consisted of 2, 4, 8, 16, and 24 h light/day. At 9 wk of age, birds were individually caged and evaluated biweekly for semen production. Venous blood samples were collected at 16, 32, 48, and 64 wk of age. Data for testes weight, histology, and morphometry were obtained at 64 wk. Age at first semen production showed a cubic response in the levels of LT with earliest semen production from 4 and 8 h light (187.0 and 188.2 days, respectively). The BW was linear in the levels of LT within week; average BW was generally greater for birds on short LT than for birds on longer LT. Semen concentration was also linear in the levels of LT within week; increased semen concentration occurred with short LT. Changes in semen weight and spermatozoa count per ejaculate across the levels of LT differed for strain. A larger percentage of males produced semen in the less than or equal to 8 h LT than in the 16 or 24 h LT. Plasma testosterone was lower at 16 wk compared with later ages, and a positive linear relationship existed between testosterone level and hours of light. There was a cubic LT effect for testes weight per BW with larger values for less than or equal to 8 h LT compared with 16 or 24 h LT.

The distribution and plasticity of [3H]vasopressin-labelled specific binding sites in the canary brain

[3H]Vasopressin was used to detect and to quantitate specific binding sites with in vitro receptor autoradiography in the canary brain. A discrete regional distribution of [3H]vasopressin-labelled binding sites was observed. A high density of specific binding sites was present in the medial posterior hypothalamic nucleus, the superficial layer of the optic tectum, the area ventralis of Tsai (AVT), the nucleus pretectalis, the habenula, the nucleus of Darkschewitch and the nucleus interstitialis. A low density occurred in the nucleus robustus archistriatalis of female birds. However, after testosterone treatment the density of the sites in this area as well as in the AVT increased 2-fold. [3H]Vasopressin binding was displaced to the same extent by excess vasopressin as well as by vasotocin. Moreover, the [3H]vasopressin-labelled brain regions are innervated by immunoreactive vasotocin fibers and terminals. It seems likely therefore that the labelled sites represent putative vasotocin receptors.