INDUCTION OF CIRCADIAN-RHYTHM OF FEEDING-ACTIVITY BY TESTOSTERONE IMPLANTATIONS IN ARRHYTHMIC JAPANESE-QUAIL MALES

Studies in vertebrates have shown that hormones can influence circadia n rhythms of behavior. We investigated whether testosterone could indu ce rhythmicity in arrhythmic Japanese quail, kept in DD. The animals u sed were 3 1/2-week-old castrated males from a line of quail selected for the lack of the circadian rhythm of feeding activity After 3 weeks in DD, 8 birds were implanted with an empty implant and 16 others wit h a testosterone implant. Two weeks later, the operation was repeated. After implantation, we noticed that 15 out of 16 testosterone-treated birds showed a circadian rhythm of feeding activity, in contrast to t he control birds, which remained arrhythmic. The clarity of this rhyth m increased significantly after each implantation. A positive correlat ion was found between the indexes of clarity of the rhythm (autocorrel ation coefficient ratio and area of the peak of spectrum) and the plas ma testosterone level The period of the induced free-running rhythm wa s identical to the specific value of the endogenous circadian rhythm i n immature quail. The circadian period showed a significant lengthenin g with the second implantation. This lengthening looks like the variat ion previously observed in maturing rhythmic or implanted quail. So, i t would appear that testosterone can act on rhythmicity on a: least tw o levels: by inducing the circadian rhythm and increasing its clarity and by modulating its period. To explain these results, several hypoth eses can be considered. First, the observed arrhythmy may be the conse quence of an internal desynchronization of oscillators, responsible fo r generating the circadian rhythm of feeding activity, and testosteron e could play a role in the coupling of these oscillators. Alternativel y we suggest that testosterone could act on the transcription of genes implicated in the control of the rhythmicity or may regulate by rapid signals L-he cellular rhythmic activity. The possible functional valu es of the enhancing of circadian rhythmicity by testosterone at differ ent stages of the bird's Life were discussed.