Projections of the dorsomedial nucleus of the intercollicular complex (DM) in relation to respiratory-vocal nuclei in the brainstem of pigeon (Columba livia) and zebra finch (Taeniopygia guttata)

Abstract

Injections of neuronal tracers were made into the dorsomedial nucleus of the intercollicular complex (DM) of pigeons and zebra finches in order to investigate the projections of this nucleus which has long been implicated in respiratory-vocal control. Despite the fact that pigeons are nonsongbirds and zebra finches are songbirds, the projections were very similar in both species. Most descended throughout the brainstem, taking ventral and dorsal trajectories, which merged in the medulla. Those descending ventrally terminated upon the ventrolateral parabrachial nucleus (PBvl), the nucleus infraolivaris superior, a nucleus of the rostral ventrolateral medulla (RVL), and the nucleus retroambigualis (RAm). Those taking a dorsal trajectory via the occipitomesencephalic tract terminated in the tracheosyringeal part of the hypoglossal nucleus (XIIts), the suprahypoglossal region, and nucleus retroambigualis. There were also substantial projections throughout an arc extending between XIIts and RVL rostrally, and XIIts and RAm caudally. Neurons throughout this arc, which include inspiratory premotor neurons at levels straddling the obex and expiratory premotor neurons more caudally (in RAm), were retrogradely labeled from spinal injections. The DM projections were predominantly ipsilateral, but there were distinct contralateral projections to all the homologous nuclei in both species. All but the projections to PBvl 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 activity.

Rudimentary substrates for vocal learning in a suboscine

“…We further conducted tract-tracing studies to test whether the arcopallium's RA-like area connects to the midbrain and medulla vocal-motor and respiratory nuclei in phoebes. A lipophilic carbocyanine dye, DiIC 12 , was injected into the GRIK1-rich, RA-like region in phoebes (Fig. 4).…”

“…We used tract tracers, carbocyanines dye, DiIC 12 , injecting into (A) the GRIK1-rich, RA-like area in the arcopallium of phoebes; (B) dorsal Nd in the midbrain; and (C) retroambigulias (RAm) in the brainstem. Anaesthesia was first induced with intramuscular injection of Nembutal (1:5) and maintained by 1-1.5% isofluorane.…”

“…In non-vocal-learners, the vocal pathway is thought to consist solely of midbrain and brainstem nuclei [9][10][11] . One of the neuroanatomical missing links for vocal learning to occur is thus the lack of projections from the telencephalon directly to vocal/respiratory neurons in the brainstem 12,13 . In non-vocal-learners, the forebrain nucleus Ai (intermediate arcopallium) has been considered most comparable to song nucleus RA (robust nucleus of arcopallium) in oscines, as Ai has motor-related projections to midbrain/hindbrain 14 .…”

Differential expression of glutamate receptors in avian neural pathways for learned vocalization

“…If this is correct, then the mechanisms of how such differential expression in vocal nuclei evolved require explanation. We propose an explanation that we call the vocal connectional evolution hypothesis: To date, in vocal nonlearners, no cerebral motor connections have been found to project to brainstem vocal nuclei (nXIIts and DM; Wild, 1997;Wild et al, 1997). However, vocal nonlearners have differential glutamate receptor expression in noncerebral vocal nuclei.…”

Temporal Structure in Zebra Finch Song: Implications for Motor Coding

“…These nuclei have a complex network of interconnections (Wild et al, 1997;Sturdy et al, 2003) and are responsible for the production of the discrete unlearned vocalizations known as calls (Simpson and Vicario, 1990). It may be here that song is organized into discrete motor gestures at the syllable or subsyllable level.…”