Telencephalic aromatase but not a song circuit in a sub-oscine passerine, the golden-collared manakin (Manacus vitellinus)

In oscine passerines, the telencephalon expresses high levels of the estrog en synthetic enzyme aromatase. in contrast, forebrain aromatase is limited to low levels at discrete limbic loci in non-passerines. The function of fo rebrain aromatase in oscines is unknown, however, estrogen-sensitive elemen ts of the telencephalic song circuit tan oscine characteristic) may be infl uenced by local aromatization. Very few studies have investigated the neuro endocrine characteristics of sub-oscine passerines. Species of this passeri ne sub-order are taxonomically similar to oscines, but do not appear to lea rn how to sing as oscines, and show no evidence of a song circuit. The neur al expression of aromatase in these birds is unknown. We asked whether the golden-collared manakin, a sub-oscine, (a) showed evidence of a song circui t, and (b) expressed aromatase in the telencephalon at high levels like the zebra finch (oscine passerine) or at low levels like the quail (non-passer ine), Nissl stains and immunocytochemistry for microtubule associated prote ins showed no evidence of a song circuit in manakins of either sex, whereas both techniques delineate all song nuclei in the zebra finch. However, bio chemical and immunocytochemical measures reveal that in the manakin, severa l telencephalic loci, including the hippocampus, caudomedial neostriatum, n ucleus taeniae, and the lateral neostriatum express aromatase. Assays run i n parallel show low to undetectable levels of aromatase in the telencephalo n of the quail (nonpasserine) and abundant levels in the zebra finch (oscin e passerine), suggesting a dissociation between the presence of a song circ uit and forebrain aromatase expression in this sub-oscine. These data sugge st that forebrain aromatase may have evolved in sub-oscine songbirds before the evolution of a song circuit and singing behavior in oscines. Alternati vely, forebrain aromatase may serve functions distinct from singing behavio r. Copyright (C) 2000 S. Karger AG. Basel.