Chemogenetic activation of the mid-cervical spinal neurons increases diaphragm activity post-cervical spinal cord injury (cSCI)

Respiratory insufficiencies are a common consequence of cSCI. The diaphragm is particularly prone to dysfunction post-injury due to the mid-cervical location of the phrenic motoneurons which innervate the diaphragm. Furthermore, recovery of diaphragm activation post-injury can be limited. Therefore, there is a need to develop novel methods that have the potential to improve diaphragm activation post-cSCI. Here we explored the use of an excitatory DREADD (i.e., designer receptor exclusively activated by design drugs) to increase diaphragm activation post-cSCI via excitation of phrenic motoneurons. Sprague Dawley rats (n = 7; females = 4) underwent bilateral intraspinal injections of an AAV vector encoding the excitatory DREADD, hM3D(Gq) (AAV9-hSyn-HA-hM3D(Gq)-mCherry; titer: 2.44x10 13 vg/mL) into the area of the phrenic nuclei. Animals were subsequently implanted with chronic indwelling diaphragm electrodes to record diaphragm electromyogram (EMG) activity before and after administration of the selective DREADD ligand, J60. Recordings were obtained under anesthesia at 3-days, 2-weeks, and 2-months following a unilateral, left C2 spinal cord hemisection. Administration of the J60 ligand resulted in robust, bilateral increases in diaphragm EMG output at all time points (REML mixed linear model; Main Effect of Treatment – Left hemidiaphragm p < 0.001; Right hemidiaphragm p = 0.002). In approximately 50% of trials post-cSCI we observed a near-complete restoration of diaphragm EMG activity from the paralyzed hemi-diaphragm (ipsilateral to site of injury). These proof-of-concept results indicate that chemogenetic methods can be used to activate the diaphragm after cSCI. 1R01NS139422-01 (DDF);R01HD052682-15 (DDF), K99NS133388-01A1 (SR), T32HG008958-07(ESB) This abstract was presented at the American Physiology Summit 2025 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.