Fig. 1.

Key premotor areas identified by retrograde tracing from the deflector nasi (d. nasi). A: diagram of the experimental procedure. The deflector nasi was injected with N2c replication-competent rabies virus (CVS-N2c RV), and rats were perfused at primary, secondary, or tertiary time points. B: examples of labeling in the facial motor nucleus (7N) at primary, secondary, and tertiary time points. Motoneurons remain intact at all time points. C: reconstructions of labeled motoneurons and motoneuron dendrites in the facial motor nucleus. Cell bodies and dendritic fields were found in the dorsolateral part of 7N. Colors correspond to individual time points (colors in A). Top, primary labeled time points (grayscale); middle, secondary labeled time points (red-green); bottom, tertiary labeled time points (blues). D, dorsal; V, ventral; M, medial; L, lateral. D: example of premotor labeling in the retrofacial area at a 64-h time point in a sagittal section ~1.7 mm lateral of midline. Labeled cells are revealed in dark product, whereas structures are identified in a cytochrome oxidase (CO) stain. IRt, intermediate reticular nucleus; LRt, lateral reticular nucleus; 7n, facial tract. E: reconstructions of premotor labeling in the retrofacial area in 6 rats at secondary labeled time points. Left, reconstructions of labeled cells in a 200-µm-thick coronal slice at 10.7 mm caudal of bregma. Right, 10% maximum density contours in the same coronal slice. Secondary time points shown are 51 h (purple), 53 h (red), 61 h (orange), 64 h (yellow), 64 h (light green), and 67 h (green). Four of six contours (53, 64, 64, and 67) overlap in the nose retrofacial (nRF) region. Amb, nucleus ambiguus; IO, inferior olive; SpVI, Spinal trigeminal nucleus, pars interpolaris; Ve, vestibular nucleus. F: example of premotor labeling in the nose intermediate reticular (nIRt) area at a 64-h time point ~1.5 mm lateral of midline. Labeled cells are revealed in dark product, whereas structures are identified in a CO stain. Gi, gigantocellular reticular nucleus. G: reconstructions of premotor labeling in the caudal IRt/Gi area in 6 rats at secondary labeled time points. Left, reconstructions of labeled cells in a 200-µm-thick coronal slice at 11.5 mm caudal of bregma. Right, 10% maximum density contours in the same coronal slice. Secondary time points shown are 51 h (purple), 53 h (red), 61 h (orange), 64 h (yellow), 64 h (light green), and 67 h (green). Four of six contours overlap for 51, 61, 64, and 67 h in the caudal IRt/Gi area (nIRt). H: 3-dimensional display of a 2-component Gaussian mixture model fit to the high-density labeled area in 6 rats. Reconstructed cells are shown as small spheres. Centroids of the 2 labeled areas are shown as large black spheres. Three-sigma radius ellipsoids are shown in magenta. Two areas emerge from the fit: a more rostral area that we call the nRF area and a more caudal nose area on the border of Gi and IRt that we call the nIRt area. Centroids are located (rostral/caudal, M/L, D/V) at (−10.7 mm, 1.7 mm, 7.8 mm) for the retrofacial area and at (−11.5 mm, 1.5 mm, 7.7 mm) for the nIRt. Forty-five degree (left) and sagittal (right) projections of the data are displayed. 5N, trigeminal motor nucleus; I: diagram of proposed nose motion circuit based on the results of premotor labeling from the d. nasi muscle. Motoneurons located in the dorsolateral facial motor nucleus (7Ndl) send projections to the ipsilateral deflector nasi muscle and receive input from the ipsilateral nRF and nIRt premotor areas.