TESTOSTERONE INCREASES THE RECRUITMENT AND OR SURVIVAL OF NEW HIGH VOCAL CENTER NEURONS IN ADULT FEMALE CANARIES/

New neurons are added to the high vocal center (HVC) of adult male and female canaries. Exogenous testosterone induces a marked increase in HVC size in adult female canaries, though the mechanisms responsible f or this increase remain unknown. To understand the mechanisms, we anal yzed the effects of testosterone on neuronal recruitment in the female HVC. Intact adult female canaries received Silastic implants that wer e empty or filled with testosterone. Birds in the short-survival group received the Silastic implant, followed by a single injection of [H-3 ]thymidine 2 days later, and were killed on the following day. Birds i n the long-survival group were injected once a day for 5 days with [3H ]thymidine and received the Silastic implant 20 and 40 days later. The se birds were killed 60 days after the first injection of [H-3]thymidi ne. The number of H-3-labeled ventricular zone cells above, rostral, o r caudal to HVC was not affected by the hormone treatment in the short -survival birds, suggesting that testosterone did not affect neuronal production. However, the number of H-3-labeled HVC neurons that projec ted to robust nucleus of the archistriatum (RA) in the long-survival b irds was three times greater in the hormone-treated than in the contro l group, though the total number of RA-projecting cells did not change significantly. Testosterone also induced an increase in the size of t he HVC cells that project to RA. Thus, these experiments suggest that testosterone affects the recruitment and/or survival of newly generate d RA-projecting HVC neurons but does not affect their production.