Figure 6. Representative images from experiments simultaneously tracing both genioglossus (green) and left masseter (red) premotor neurons.
(A) Caudal brainstem at the level of MoXII, showing a rough spatial segregation between the two premotor populations in the IRt-c, with masseter premotor neurons more ventrally situated as compared to genioglossus premotor neurons. (B) Brainstem at the level between MoXII and MoVII, showing mostly genioglossus premotor neurons present in this region. (C) Brainstem at the level of MoVII, showing spatial intermingling of the two premotor populations. Axon collaterals crossing the midline are visible from both genioglossus and masseter premotor neurons. Genioglossus axon collaterals are visible extending into the central MoVII. (D) Labeling patterns at the level of MoV in dPrV, dRt (region just above dPrV), supra trigeminal nucleus (SupV), and inter-trigeminal region (IntV). Masseter premotor axon collaterals (red) extend into the contralateral MoV, while genioglossus premotor axon collaterals (green) extend into the Dig (arrows). Displayed side of the brainstem is indicated in each panel.