The effects of systemic androgen treatment on androgen accumulation in song control regions of the adult female canary brain.

Systemic treatment of adult female canaries (Serinus canarius) with testosterone (T) induces song and increases the size of song control regions (SCRs) in the brain. We used autoradiographic techniques to determine whether systemic T treatment also changes the accumulation of tritiated T or its metabolites by SCR cells. T treatment did not change the proportion of T target cells in SCRs, nor did it change the degree of cellular accumulation of T or its metabolites. Neuronal density was not altered by T treatment in any SCR sampled. In HVc (caudal nucleus of the ventral hyperstriatum) and RA (robust nucleus of the archistriatum), cell size did not differ between T-treated and control females. However, systemic T did increase the mean sizes of labelled cells and of all cells sampled in MAN (magnocellular nucleus of the anterior neostriatum). The results support the hypothesis that the induction of song in female canaries by T relates to increases in the absolute numbers of neurons and of T target neurons in SCRs.