Paraventricular hypothalamic nucleus projects directly to the preBötzinger complex and is involved in regulation of respiration in mice

To probe the spatial distribution of respiratory-related nuclei throughout the whole brain, and to investigate the circuit and projection links between the paraventricular hypothalamic nucleus (PVN) and the preBötzinger complex (preBötC) in mice.

Using a retrograde tracing strategy from peripheral to central, pseudorabies viruses (PRV) were microinjected into the diaphragm of mice to retrogradely label the upstream inputs brain regions from spinal respiratory phrenic motor neurons. The anterograde non-transsynaptic tracing viruses (AAV2/9-EGFP) were microinjected into the PVN to label the downstream brain region of the PVN; And using the Cre/loxP gene expression strategy, Dio-EGFP and Retro-Cre viruses were injected in the PVN and preBötC, respectively, to validate the PVN-preBötC circuit and the projection relationship between the two.

The results of PRV-mediated retrograde tracing showed that PRV-EGFP-positive neurons were distributed in several brain regions such as PVN, preBötC, nucleus tractus solitarii (NTS), locus coeruleus (LC) and periaqueductal grey (PAG). Except for the medulla oblongata region, the PVN brain region had the highest percentage of PRV-EGFP-positive neurons (P<0.0001). After AAV2/9-EGFP viruses were injected in the PVN, green neurofibrils were observed in the preBötC brain region after viral infection; Dio-EGFP and Retro-Cre viruses were injected in the PVN and preBötC, respectively, and green neuronal cells were seen in the brain region of the PVN after viral infection.

PVN is an important upstream input nucleus of spinal respiratory phrenic motor neurons, and has the potential to regulate respiration through direct projections from PVN-preBötC circuit.