(A) Caudal brainstem at the level of the hypoglossal motor nucleus (MoXII), illustrating primary infection of the left MoXII, and extensive labeling in IRt-c, in the spinal trigeminal nucleus caudalis (SpVc), and sparse labeling in the nucleus of the solitary tract (NTS). (B) Brainstem between MoXII and MoVII showing extensive bilateral labeling in the IRt-r, with sparse labeling in the NTS, PCRt, Gi, and pre-Bötzinger complex (pre-BötC) below the nucleus ambiguus (NA). (C) Rostral brainstem at the level of MoVII, showing labeling in the IRt-r and extending into the PCRt. Additionally, bilateral labeling of the LPGi is visible (inset). Labeled premotor axon collaterals are visible invading the central MoVII (arrow). (D–G) Other groups of labeled premotor neurons in: the DCN (D); dPrV, dRt and PeriV (E); MesV (F); and dMRf (G). Genioglossus premotor labeling was weaker in the DCN and stronger in bilateral dMRf and LPGi as compared to masseter premotor labeling. Note the dense innervation of the anterior digastric motor nucleus (Dig) with premotor axons (E, arrow). Displayed side of the brainstem is indicated in each panel.