Characterization of respiratory neurons in the rostral ventrolateral medulla (PAm), an area critical for vocal production in songbirds

The avian nucleus Parambigualis (PAm) is an essential element of the song production and respiratory pathways, but little is known about this brainstem area. PAm projects to motor neurons in the spinal cord that control the inspiratory portion of the respiratory cycle. It has also been shown to project bilaterally to the control centers of the song production pathway, namely HVC, via an intermediate nucleus called Uvaeformis (Uva). It thus has potential roles in both interhemispheric coordination and feedback-dependent control of song production (Ashmore et al, 2008). The achieved goal of this study was to use techniques of electrophysiology, histology, and computer analysis to establish a baseline of knowledge about the individual neurons present in this respiratory nucleus. Surgeries were performed on anesthetized adult male zebra finches and an extracellular electrode was used to record from respiratory neurons within PAm. This study categorized 130 neurons in PAm based on their phase-locking to the respiratory cycle and found that the six primary subtypes are the same as those identified in mammalian respiratory neurons. The most common subtypes were Inspiratory- Augmenting and Pre-Inspiratory. Subsequent histological examination showed that there is no significant localization of any neuronal subtypes within PAm. Finally, several dual electrode surgeries were performed to obtain simultaneous PAm and contralateral HVC recordings. These surgeries suggest that PAm neurons exhibiting ascending projections constitute a very small amount (less than 5%) of the total neurons in this brainstem nucleus.