The distribution of tyrosine hydroxylase in the canary brain: demonstration of a specific and sexually dimorphic catecholaminergic innervation of thetelencephalic song control nuclei

Singing and the processing of auditory information related to song can be a ffected by experimental manipulations of catecholamine activity in the brai n of zebra finches, We investigated, by immunocytochemistry in the brain of male and female canaries, the distribution of tyrosine hydroxylase (TH), t he rate-limiting step in the synthesis of catecholamines. Fibers immunoreac tive for TH (TH-ir) were particularly abundant in the lobus parolfactorius, the paleostriatum primitivum, and the nucleus septalis lateralis. A high d ensity of TH-ir basketlike structures was observed in the caudomedial neost riatum, an area involved in song perception and recognition. In most males, a high density of TH-ir fibers outlined the telencephalic song control nuc lei including the high vocal center, the nucleus robustus archistriatalis, the nucleus interfascialis, the lateral and medial parts of the magnocellul ar nucleus of the anterior neostriatum, and area X of the lobus parolfactor ius. The higher density of fibers immunoreactive for TH in these nuclei, co mpared with the surrounding telencephalon, supports the notion that the mor phological evolution of the song control nuclei was accompanied by a neuroc hemical specialization. This specific innervation of the song control regio ns was, in general, not found in females. The specific presence of high den sities of TH-ir fibers in the song system of male canaries and the sex diff erence of this innervation provide anatomical evidence in support of the cl aim that dopamine and/or norepinephrine play important roles in the modulat ion of song learning and production.