Background: Gut dysmotility is common after ischemic stroke, but the mechanism underlying this response is unknown. Under homeostasis, gut motility is regulated by the neurons of the enteric nervous system (ENS) that control contractile/relaxation activity of muscle cells in the gut wall. More recently, studies of gut inflammation revealed interactions of macrophages with enteric neurons are also involved in modulating gut motility. However, whether post-stroke gut dysmotility is mediated by direct signalling to the ENS or indirectly via inflammatory macrophages is unknown.
Methods and Results: We examined these hypotheses by using a clinically relevant permanent intraluminal mid-cerebral artery occlusion (pMCAO) experimental model of stroke. At 24h post-stroke, we performed in vivo and ex vivo gut motility assays, flow cytometry, immunofluorescence, and transcriptomic analysis. Stroke-induced gut dysmotility was associated with recruitment of muscularis macrophages (MMs) into the gastrointestinal tract, and redistribution of MMs away from myenteric ganglia. The pMCAO model caused changes in gene expression in MMs consistent with an altered phenotype. While the size of myenteric ganglia after stroke was not altered, myenteric neurons from post-pMCAO mice showed a reduction in neuronal nitric oxide synthase (nNOS) expression, and this response was associated with enhanced intestinal smooth muscle contraction ex vivo. Finally, chemical sympathectomy with 6-hydroxydopamine prevented the loss of myenteric nNOS expression and stroke-induced slowed gut transit.
Conclusions: Our findings demonstrate that activation of the sympathetic nervous system after stroke is associated with reduced nNOS expression in myenteric neurons, resulting in impaired smooth muscle relaxation and dysregulation of gut transit.