Figure 2. Representative images of labeled jaw premotor neurons after ΔG-RV injection into the left masseter muscle.

(A) Caudal brainstem showed labeling primarily in the caudal intermediate reticular formation (IRt-c) and medullary reticular formation (MdRt). (B) Rostral brainstem at the level of the facial motor nucleus (MoVII) showed extensive labeling in the rostral IRt (IRt-r) and some labeling in the gigantocellular (Gi) and parvocellular (PCRt) reticular formation. Insets, labeled neurons in the spinal trigeminal nucleus oralis (SpVo) and the lateral paragigantocellular nucleus (LPGi). This region of the brainstem contained extensive axon collaterals crossing the midline. (C–H) Labeling of other premotor neuron groups including: the deep cerebellar nuclei (DCN, C); the dorsal principal trigeminal sensory nucleus (dPrV, D); the motor trigeminal nucleus (MoV, primary infection) and surrounding trigeminal regions (collectively, PeriV) (E); the mesencephalic sensory nucleus (MesV), which extended from MoV to dorsal to the periaqueductal grey (PAG) (F); the dorsal midbrain reticular formation (dMRf, G); and the red nucleus (RN, H). Displayed side of the brainstem is indicated in each panel. Stereotaxic maps for this and all subsequent figures were obtained from the Allen Brain Institute website: www.brain-map.org.

DOI: http://dx.doi.org/10.7554/eLife.02511.006

Figure 2—figure supplement 1. The masseter premotor circuit contains more LPGi neurons in old pups.

(A) Schematic illustrating monosynaptic rabies-mediated tracing of the masseter premotor circuit in older pups (P8→P15 tracing). Rabies containing mCherry (red) was injected into the left masseter of P8 Chat-Cre::RGΦT pups; brainstem samples were obtained at P15. (B–E) Stereotypic labeling of the P15 masseter premotor circuit. (B) Premotor neurons were similarly observed in the rostral IRt and PCRt, but an increased number of neurons in the LPGi was observed in P8→P15 tracing (arrow; compare to Figure 2B, inset). Other labeling included: the MdRt (C); MesV (D); and the region surrounding MoV (E). (F) The number of LPGi neurons connected to masseter motoneurons increases during development. The ratio of LPGi neurons to primary motoneurons labeled in MoV was calculated for each sample. n = 3 mice per group, all values are averages ± SEM.

DOI: http://dx.doi.org/10.7554/eLife.02511.007