In vivo manganese-enhanced magnetic resonance imaging reveals connections and functional properties of the songbird vocal control system

Injection of manganese (Mn2+), a paramagnetic tract tracing agent and calcium analogue, into the high vocal center of starlings labeled within a few hours the nucleus robustus archistriatalis and area X as observed by in vivo magnetic resonance imaging. Structures highlighted by Mn2+ accumulation assumed the expected tri-dimensional shape of the nucleus robustus archistriatalis and area X as identified by classical histological or neurochemical methods. The volume of these nuclei could be accurately calculated by segmentation of the areas highlighted by Mn2+. Besides confirming previously established volumetric sex differences, Mn2+ uptake into these nuclei revealed new functional sex differences affecting Mn2+ transport. A faster transport was observed in males than in females and different relative amounts of Mn2+ were transported to nucleus robustus archistriatalis and area X in males as compared to females. This new in vivo approach, allowing repeated measures, opens new vistas to study the remarkable seasonal plasticity in size and activity of song-control nuclei and correlate neuronal activity with behavior. It also provides new insights on in vivo axonal transport and neuronal activity in song-control nuclei of oscines. (C) 2002 IBRO. Published by Elsevier Science Ltd. All rights reserved.