Supratrigeminal Bilaterally Projecting Neurons Maintain Basal Tone and Enable Bilateral Phasic Activation of Jaw-Closing Muscles

Abstract

Anatomical studies have identified brainstem neurons that project bilaterally to left and right oromotor pools, which could potentially mediate bilateral muscle coordination. We use retrograde lentiviruses combined with a split-intein-mediated split-Cre-recombinase system in mice to isolate, characterize, and manipulate a population of neurons projecting to both the left and right jaw-closing trigeminal motoneurons. We find that these bilaterally projecting premotor neurons (BPNs) reside primarily in the supratrigeminal nucleus (SupV) and the parvicellular and intermediate reticular regions dorsal to the facial motor nucleus. These BPNs also project to multiple midbrain and brainstem targets implicated in orofacial sensorimotor control, and consist of a mix of glutamatergic, GABAergic, and glycinergic neurons, which can drive both excitatory and inhibitory inputs to trigeminal motoneurons when optogenetically activated in slice. Silencing BPNs with tetanus toxin light chain (TeNT) increases bilateral masseter activation during chewing, an effect driven by the expression of TeNT in SupV BPNs. Acute unilateral optogenetic inhibition of SupV BPNs identifies a group of tonically active neurons that function to lower masseter muscle tone, whereas unilateral optogenetic activation of SupV BPNs is sufficient to induce bilateral masseter activation both during resting state and during chewing. These results provide evidence for SupV BPNs in tonically modulating jawclosing muscle tone and in mediating bilateral jaw closing.

A craniofacial-specific monosynaptic circuit enables heightened affective pain

“…5a ). Retrograde-lentivirus infects axons and is transported back to cell bodies 36 , 37 . Ai65 is a Cre and Flp co-dependent tomato reporter 38 .…”

“…CANE-LV-Cre (titer, 5×10 8 ifu/ml; pLenti-hSynapsin-Cre-WPRE [Addgene Plasmid #86641]; CANE-LV envelope [Addgene Plasmid #86666]) and CANE-RV-mCherry (titer, 5×10 8 ifu/ml) were produced as previously described 12 . FuGB2-coated RG-LV-hSyn-FlpO and RG-LV-hSyn-DIO-FlpO were produced and concentrated as described previously 36 . pAAV-SynP-DIO-TVA-EGFP-RG (pAAV-SynP-DIO-sTpEpB) 28 was packaged in serotype AAV2/rh8 by the University of Pennsylvania Vector Core.…”

Parallel Inhibitory and Excitatory Trigemino-Facial Feedback Circuitry for Reflexive Vibrissa Movement

“…Motivated by a past study (Chiala et al, 1992), we found that parvalbumin (Pv) is expressed in excitatory (glutamatergic) SpVIr neurons. To determine whether Pv+ SpVIr cells represent the premotor neurons that project to both Po thalamus and extrinsic facial motoneurons, we employed a split-Cre system (Wang et al, 2012; Stanek et al, 2016). Specifically, we generated Pv-CreN knockin mice, and injected retrograde lentivirus that expressies CreC (RG-LV-CreC) in Po in Pv-CreN; Ai14 (Cre-dependent tdTomato reporter) double transgenic mice.…”

“…RG-LV-CreC and RG-LV-Cre were designed and produced as described (Stanek et al, 2016). AAV2/8-hSyn-Flex-TeLC-P2A-GFP was designed and produced as described (Zhang et al, 2015).…”

“…These data make use of a split-Cre strategy (Wang et al, 2012; Stanek et al, 2016). The starting substrate in all cases are mice that are engineered to express CreN in neurons that naturally express parvalbumin.…”