Modulation of orexinergic neurons in the perifornical region of the hypothalamus impacts tongue motility and hypoglossal motor output in an inducible rodent model of hypoglossal motor neuron degeneration

Patients with motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS), often develop upper airway dysfunction due to degeneration of hypoglossal lower motor neurons (XII LMNs) that innervate the muscles of the tongue, including the genioglossus, which causes extensive tongue weakness. Current treatments for patients with MNDs are largely palliative, highlighting the critical need for therapies that preserve upper airway function. Using our established model of targeted XII LMN loss induced by intralingual injection of cholera toxin B conjugated to saporin (CTB-SAP), we have shown that a high-repetition/low-resistance tongue exercise paradigm mitigates XII axis deficits by increasing tongue motility (i.e., lick rate) and XII motor output. However, the underlying mechanism of exercise-induced plasticity remains unknown. Orexinergic (OX) neurons in the perifornical region of the hypothalamus (PeF) project to the XII nucleus that abundantly expresses orexin receptor 1 (OxR1) and 2 (OxR2) which, when activated, may enhance genioglossus activity and promote airway patency. Notably, brain derived neurotrophic factor (BDNF) and OX expression are reduced in the CNS and limb muscles in ALS and other MNDs. Aerobic and limb-based exercise has been shown to increase BDNF and OX expression, which improved functional outcomes in ALS patients and rodent models. Our preliminary data suggest that XII BDNF levels are increased with tongue exercise following XII LMN loss, but it remains unknown if tongue exercise also increases OX levels in the PeF or XII nucleus, or if OX activation increases XII BDNF levels to improve upper airway function following XII LMN loss. Our recent pilot data demonstrate decreased OxR1 levels in the XII nucleus following XII LMN loss that is subsequently increased by tongue exercise, raising the possibility that PeF activation contributes to mitigating XII axis deficits. Thus, we hypothesize that XII-projecting PeF OX neurons are key mediators of tongue exercise-induced XII axis plasticity and BDNF-dependent functional improvements following XII LMN loss. To begin testing this, we targeted PeF OX neurons using chemogenetic activation or silencing via nanoinjection of Gq- (n=2) or Gi-DREADDs (n=1-2), respectively, into the PeF of control and CTB-SAP adult male rats, and compared these groups to rats without DREADD manipulation (n=4-10). We then performed videofluoroscopic swallow studies and in vivo neurophysiology to assess the impact of PeF OX modulation on tongue motility and XII motor output. Our preliminary findings suggest that chemogenetic activation of the PeF increases, whereas inhibition decreases, lick rate and XII motor output in CTB-SAP rats. These results suggest that PeF OX neurons promote XII plasticity to improve XII axis function following XII LMN loss. Thus, XII-projecting PeF OX neurons may contribute to tongue exercise-induced XII plasticity, which will be directly tested in our future studies. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.