Concha-Miranda M, Tang W, Hartmann K, Brecht M

The identity and location of vocalization pattern generating (VPG) circuits in mammals is debated. Based on physiological experiments, investigators suggested anterior brainstem circuits in the reticular formation, and anatomic evidence suggested the nucleus retroambiguus (NRA) in the posterior brainstem, or combinations of these sites as the putative mammalian VPG. Additionally, vocalization loudness is a critical factor in acoustic communication. However, many of the underlying neuronal mechanisms are still unknown. Here, we evoked calls by stimulation of the periaqueductal gray in anesthetized male rats, performed a large-scale mapping of vocalization-related activity using the activity marker c-fos, and high-density recordings of brainstem circuits using Neuropixels probes. Both c-fos expression and recording of vocalization-related activity point to a participation of the NRA in vocalization. More important, among our recorded structures, we found that the NRA is the only brainstem area showing a strong correlation between unit activity and call intensity. In addition, we observed functionally diverse patterns of vocalization-related activity in a set of regions around NRA. Dorsal to NRA, we observed activity specific to the beginning and end of vocalizations in the posterior level of the medullary reticular nucleus, dorsal part, whereas medial and lateral to the NRA, we observed activity related to call initiation. No clear vocalization-related activity was observed at anterior brainstem sites. Our findings suggest a set of functionally heterogeneous regions around the NRA contribute to vocal pattern generation in rats.

J Neurosci. 42 (44) 8252-8261 (2022)