Specificity of gonadal hormone modulation of cholinergic enzymes in the avian syrinx.

The effectiveness of testosterone (T) and metabolites to increase activity of cholinergic enzymes in the androgen-sensitive syrinx of male zebra finches was assessed. Administration of aromatizable (T and androstenedione) or non-aromatizable (androsterone) androgens to castrates increased total activity of acetylcholinesterase (AChE) in the syrinx. Estradiol was ineffective in altering AChE activity. Results, when compared with behavioral data from the birds, support the hypothesis that expression of male reproductive behaviors requires peripheral target organ activation by androgens and central target area activation by both androgens and estrogens.