Agonist-evoked Ca²⁺ signaling in enteric glia drives neural programs that regulate intestinal motility in mice

Gastrointestinal motility is regulated by enteric neural circuitry that includes enteric neurons and glia. Enteric glia monitor synaptic activity and exhibit responses to neurotransmitters that are encoded by intracellular calcium (Ca²⁺) signaling. What role evoked glial responses play in the neural regulation of gut motility is unknown. We tested how evoking Ca²⁺ signaling in enteric glia affects the neural control of intestinal motility.

We used a novel chemogenetic mouse model that expresses the designer receptor hM3Dq under the transcriptional control of the glial fibrillary acidic protein (GFAP) promoter (GFAP::hM3Dq mice) to selectively trigger glial Ca²⁺ signaling. We used in situ Ca²⁺ imaging and immunohistochemistry to validate this model and assessed gut motility by measuring pellet output and composition, colonic bead expulsion time, small intestinal transit time, total gut transit time, colonic migrating motor complex (CMMC) recordings and muscle tension recordings.

hM3Dq receptor expression is confined to GFAP-positive enteric glia in the intestines of GFAP::hM3Dq mice. In these mice, application of the hM3Dq agonist clozapine-N-oxide (CNO) selectively triggers intracellular Ca²⁺ responses in enteric glia. Glial activation drove neurogenic contractions in the ileum and colon but had no effect on neurogenic relaxations. CNO enhanced the amplitude and frequency of CMMCs in ex vivo preparations of the colon and CNO increased colonic motility in vivo. CNO had no effect on the composition of fecal matter, small intestinal transit or whole gut transit.

Glial excitability encoded by intracellular Ca²⁺ signaling functions to modulate excitatory enteric circuits. Selectively triggering glial Ca²⁺ signaling might be a novel strategy to improve gut function in motility disorders.