Noradrenergic system of the zebra finch brain: immunocytochemical study of dopamine-beta-hydroxylase

Oscine birds are among the few animal groups that have vocal learning, and their brains contain a specialized system for song learning and production. We describe here the immunocytochemical distribution of dopamine-beta-hydroxylase (DBH), a noradrenergic marker, in the brain of an oscine, the zebra finch (Taeniopygia guttata). DBH-positive cells were seen in the locus coeruleus, the nucleus subcoeruleus ventralis, the nucleus of the solitary tract, and the caudolateral medulla. Immunoreactive fibers and varicosities had a much wider brain distribution. They were particularly abundant in the hippocampus, septum, hypothalamus, area ventralis of Tsai, and substantia nigra, where they formed dense pericellular arrangements. Significant immunoreactivity was observed in auditory nuclei, including the nucleus mesencephalicus lateralis pars dorsalis, the thalamic nucleus ovoidalis, field L, the shelf of the high vocal center (HVC), and the cup of the nucleus robustus archistriatalis (RA), as well as in song control nuclei, including the HVC, RA, the lateral magnocellular nucleus of the anterior neostriatum, and the dorsomedial nucleus (DM) of the intercollicular complex. Except for the DM, DBH immunoreactivity within song nuclei was comparable to that of surrounding tissues. Conspicuously negative were the lobus paraolfactorius, including song nucleus area X, and the paleostriatum. Our results are in agreement with previous studies of the noradrenergic system performed in nonoscines. More importantly, they provide direct evidence for a noradrenergic innervation of auditory and song control nuclei involved in song perception and production, supporting the notion that noradrenaline is involved in vocal communication and learning in oscines.