PROJECTIONS OF THE DORSOMEDIAL NUCLEUS OF THE INTERCOLLICULAR COMPLEX(DM) IN RELATION TO RESPIRATORY-VOCAL NUCLEI IN THE BRAIN-STEM OF PIGEON (COLUMBA-LIVIA) AND ZEBRA FINCH (TAENIOPYGIA-GUTTATA)

Injections of neuronal tracers were made into the dorsomedial nucleus of the intercollicular complex (DM) of pigeons and zebra finches in or der to investigate the projections of this nucleus which has long been implicated in respiratory-vocal control. Despite the fact that pigeon s are nonsongbirds and zebra finches are songbirds, the projections we re very similar in both species. Most descended throughout the brainst em, taking ventral and dorsal trajectories, which merged in the medull a. Those descending ventrally terminated upon the ventrolateral parabr achial nucleus (PBv1), the nucleus infraolivaris superior, a nucleus o f the rostral ventrolateral medulla (RVL), and the nucleus retroambigu alis (RAm). Those taking a dorsal trajectory via the occipitomesenceph alic tract terminated in the tracheosyringeal part of the hypoglossal nucleus (XIIts), the suprahypoglossal region, and nucleus retroambigua lis. There were also substantial projections throughout an are extendi ng between XIIts and RVL rostrally, and XIIts and RAm caudally. Neuron s throughout this are, which include inspiratory premotor neurons at l evels straddling the obex and expiratory premotor neurons more caudall y (in RAm), were retrogradely labeled from spinal injections. The DM p rojections were predominantly ipsilateral, but there were distinct con tralateral projections to all the homologous nuclei in both species. A ll but the projections to PBv1 and XIIts were reciprocal. In summary, the projections of DM suggest that it is able to influence all the key motor and premotor nuclei involved in patterned respiratory-vocal act ivity. J. Comp. Neurol. 377:392-413, 1997. (C) 1997 Wiley-Liss, Inc.