Catecholaminergic inputs to aromatase cells in the canary auditory forebrain.

The caudomedial nidopallium in songbirds is a specialized forebrain auditory region involved in the processing of species-typical vocalizations. It receives a prominent catecholaminergic projection with many fibers forming basket-like structures around non-immunoreactive cells. We investigated in male canaries the anatomical relationship between tyrosine hydroxylase and cells immunoreactive for the steroid metabolizing enzyme, aromatase, in the caudomedial nidopallium using double-label immunocytochemistry. Fibers immunoreactive for tyrosine hydroxylase established numerous close contacts with aromatase-immunoreactive cells and often encircled these cells to form basket-like structures. Aromatase containing cells in the caudomedial nidopallium are therefore a major target of catecholaminergic inputs in canary. Interactions between catecholaminergic systems and aromatase in the caudomedial nidopallium may provide one mechanism for the regulation of estrogens involved in song perception and memorization.