Identification and connections of inspiratory premotor neurons in songbirds and budgerigar

Abstract

Recordings of extracellular unit activity in the ventrolateral medulla and of electromyographic activity in either the M. scalenus, a principal inspiratory muscle, or the abdominal expiratory muscles, were used to identify inspiratory related (IR) neurons. IR neurons extended from levels caudal to the obex through the caudal level of the descending vestibular nucleus. This distribution was found to correspond to that of a subset of cells retrogradely labeled from injections of neuronal tracers into the upper thoracic spinal cord, where motoneurons innervating the M. scalenus were located by retrograde transport. Injections of biotinylated dextran amine at the recording sites resulted in projections to the spinal cord and brainstem. Bulbospinal axons traveled in the lateral funiculus, predominantly contralaterally, and terminated in relation to the dendrites and cell bodies of motoneurons innervating the M. scalenus. Brainstem nuclei receiving projections from injections at IR loci included the retroambigualis, tracheosyringeal motor nucleus, ventrolateral nucleus of the rostral medulla, infraolivaris superior, ventrolateral parabrachial nucleus, and the dorsomedial nucleus of the intercollicular complex. In the finches, there were also bilateral projections to nucleus uvaeformis of the posterior thalamus. The spinal and brainstem projections are similar to those found in pigeon (Reinke and Wild, [1997] J. Comp. Neurol. 379:347-362), and probably mediate the intricate coordination of the vocal (syringeal) and respiratory systems for the control of vocalization. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals.

Linked Control of Syllable Sequence and Phonology in Birdsong

“…Together with anatomical and stimulation studies suggesting that RA and its downstream targets can influence syllable sequence via projections to the forebrain (Vates et al, 1997; Reinke and Wild, 1998; Striedter and Vu, 1998; Ashmore et al, 2005; Ashmore et al, 2008; Roberts et al, 2008), these data support a model in which both sequence and phonology are controlled by interactions between descending and ascending circuits, rather than by individual nuclei dedicated to the control of sequence or phonology alone.…”

“…8, dotted line) or indirect projections from RA’s targets in the brainstem (Fig. 8, dashed line) to forebrain motor centers (Vates et al, 1997; Reinke and Wild, 1998; Striedter and Vu, 1998; Roberts et al, 2008). …”

“…RA sends projections to brainstem motor nuclei retroambigualis (RAm) and paraambigualis (PAm), which innervate the respiratory musculature, and to the tracheosyringeal portion of the twelfth motor nucleus (nXIIts), which innervates the muscles of the syrinx (vocal organ). A recurrent motor pathway (dashed line) indirectly connects respiratory nucleus paraambigualis back to HVC (Reinke and Wild, 1998; Striedter and Vu, 1998) via a network of midbrain and thalamic nuclei (not shown). Additionally, RA sends a reciprocal projection (dotted line) back to HVC (Roberts et al, 2008).…”

Avian nucleus retroambigualis: Cell types and projections to other respiratory‐vocal nuclei in the brain of the zebra finch (Taeniopygia guttata)

“…Using either iontophoresis or air pressure (supplied by a Picospritzer: General Valve, Fairfield, NJ), injections of a variety of different tracers [i) unconjugated cholera toxin B-chain (CTB, 1% in 0.1 M PBS; List Biological Laboratories, Campbell, CA); ii) 10% BDA in PBS; iii) 5% aqueous Fast Blue (Polysciences, Warrington, PA); iv) dextran-Alexa 488 or 594 (Invitrogen)] were made via glass micropipettes (pulled and broken back to yield tip sizes of 10–20 µm internal diameter) into the upper thoracic spinal cord (n = 6), the tracheosyringeal motor nucleus (XIIts, either uni- or bilaterally; n = 7), nucleus parambigualis (PAm; Wild, 1993a; Reinke and Wild, 1998), the ventrolateral nucleus of the rostral medulla (RVL, n = 2; Wild, 1993b), the dorsomedial nucleus of the intercollicular complex (DM, n = 2; Wild et al, 1997), or the cervical vagus nerve (n = 4). Injections in DM were made at loci at which electrical stimulation (100 pps, biphasic, 0.5 msec pulses, 10–20 µA) drove calling (Wild et al, 1997).…”

Central Contributions to Acoustic Variation in Birdsong

“…(c) The song system is composed of a direct motor pathway consisting of nuclei HVC and RA and an anterior forebrain pathway (AFP) containing Area X, the medial portion of the dorsolateral thalamus (DLM) and lMAN. RA sends projections to motor neurons in the tracheosyringeal portion of the twelfth motor nucleus (nXIIts), which innervates the muscles of the syrinx, and to motor nuclei retroambigualis (RAm) and paraambigualis (PAm), which innervate the respiratory musculature (Vicario and Nottebohm, 1988; Wild, 1993; Reinke and Wild, 1998). …”