Optogenetic Induction of Colonic Motility in Mice

Abstract

Strategies are needed to increase gastrointestinal transit without systemic pharmacologic agents. We investigated whether optogenetics, focal application of light to control enteric nervous system excitability, could be used to evoke propagating contractions and increase colonic transit in mice. We generated transgenic mice with Cre-mediated expression of light-sensitive channelrhodopsin-2 (ChR2) in calretinin neurons (CAL-ChR2 Cre+ mice); Cre- littermates served as controls. Colonic myenteric neurons were analyzed by immunohistochemistry, patch-clamp, and calcium imaging studies. Motility was assessed by mechanical, electrophysiological, and video recording invitro and by fecal output invivo. In isolated colons, focal light stimulation of calretinin enteric neurons evoked classic polarized motor reflexes (50/58 stimulations), followed by premature anterograde propagating contractions (39/58 stimulations). Light stimulation could evoke motility from sites along the entire colon. These effects were prevented by neural blockade with tetrodotoxin (n= 2), and did not occur in control mice (n= 5). Light stimulation of proximal colon increased the proportion of natural fecal pellets expelled over 15 minutes invitro (75% ± 17% vs 32% ± 8% for controls) (P < .05). Invivo, activation of wireless light-emitting diodes implanted onto the colon wall significantly increased hourly fecal pellet output in conscious, freely moving mice (4.2 ± 0.4 vs 1.3 ± 0.3 in controls) (P < .001). In studies of mice, we found that focal activation of a subset of enteric neurons can increase motility of the entire colon invitro, and fecal output invivo. Optogenetic control of enteric neurons might therefore be used to modify gut motility.