Functional brain stem circuits for control of nose motion

Abstract

Rodents shift their nose from side to side when they actively explore and lateralize odors in the space. This motor action is driven by a pair of muscles, the deflector nasi. We studied the premotor control of this motion. We used replication-competent rabies virus to transsynaptically label inputs to the deflector nasi muscle and find putative premotor labeling throughout the parvocellular, intermediate, and gigantocellular reticular formations, as well as the trigeminal nuclei, pontine reticular formation, midbrain reticular formation, red nucleus, and superior colliculus. Two areas with extensive labeling were analyzed for their impact on nose movement. One area is in the reticular formation caudal to the facial motor nucleus and is denoted the nose retrofacial area. The second is in the caudal part of the intermediate reticular region near the oscillator for whisking (the nose IRt). Functionally, we find that optogenetic activation of glutamatergic cells in both areas drives deflection of the nose. Ablation of cells in the nose retrofacial area, but not the nose IRt, impairs movement of the nose in response to the presentation of odorants but otherwise leaves movement unaffected. These data suggest that the nose retrofacial area is a conduit for a sensory-driven orofacial motor action. Furthermore, we find labeling of neurons that are immediately upstream of premotor neurons in the preBötzinger complex that presumably synchronizes a small, rhythmic component of nose motion to breathing. NEW & NOTEWORTHY We identify two previously undescribed premotor areas in the medulla that control deflection of the nose. This includes a pathway for directed motion of the nose in response to an odorant.

Analyzing the brainstem circuits for respiratory chemosensitivity in freely moving mice

“…Only a minority of neurons, 10% (4/39), encoded the magnitude of hypercapnia and a similar minority (13%; 5/39) were active and inhibited throughout the hypercapnic episode. Interestingly, we found a small number of sniff-activated neurons, which may be from the most rostral and ventral aspect of the retrofacial nucleus, which overlaps with the most caudal and dorsal aspect of the RTN ( Deschênes et al, 2016 ; Kurnikova et al, 2018 ).…”

Retracted: Rubral modulation of breathing

“…Thus, it might coordinate oromotor activity with breathing, according to the behavioural demands on the animal; for instance, by facilitating jaw opening during high activity to increase maximal airflow, hence ventilation. Injection of the deflator nasi muscle with rabies virus revealed trans‐synaptic labelling in the red nucleus and other mesencephalic zones in rats, suggesting a rubral contribution to modulation of nose movement during sensory odour exploratory behaviours (Kurnikova, Deschênes, & Kleinfeld, ).…”

“…the so‐called biphasic ventilatory response (BVR). The first phase, respiratory augmentation, is mediated alternatively via peripheral chemoreceptors (Teppema, ), because glomectomized cats manifest only respiratory inhibition in response to hypoxia (Millhorn, Eldridge, Kiley, & Waldrop, ), although others have underscored a more critical role for central structures in hypoxic ventilatory amplification (Funk & Gourine, ). The response to hypoxia varies with age; elimination of fetal breathing movements is observed in utero (Boddy, Dawes, Fisher, Pinter, & Robinson, ; Kobayashi, Lemke, & Greer, ; Martin, Murata, Petrie, & Parer, ), and the second phase of BVR is less marked in adults than in neonates.…”

Dynamics of odor sampling strategies in mice

“…Sniffing is one of a set of orofacial motor behaviors that includes, in addition to sniffing, breathing, whisker movements, nares movements and head positioning [ 15 ]. Circuits in the ventral medulla of the brainstem are likely to provide the coupled rhythmic motor control for the essential coordination of sniffing and whisking [ 15 – 18 ]. This renewed interest in the coordination of rodent orofacial motor behaviors has led to the development of novel technologies for measuring rodent breathing and sniffing [ 19 , 20 ], which are complementary to the method described here.…”