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2 (GFR
2) in the actions of the glucagon-like peptides on the murine intestine
1 Department of Physiology, University of Toronto, Toronto, Canada
2 Department of Physiology, University of Toronto, Toronto, Canada; Department of Medicine, University of Toronto, Toronto, Canada
* To whom correspondence should be addressed. E-mail: p.brubaker{at}utoronto.ca.
The intestinal glucagon-like peptides, GLP-1 and GLP-2 inhibit intestinal motility, while GLP-2 also stimulates growth of the intestinal mucosa. However, the mechanisms of action of these peptides in the intestine remain poorly characterized. To determine the role of the enteric nervous system in the actions of GLP-1 and GLP-2 on the intestine, the glial cell line-derived neurotropic factor family receptor
2 (GFR
2) knockout mouse was employed. The mice exhibited decreased cholinergic staining, as well as reduced mRNA transcripts for substance P-ergic excitatory motor neurons in the enteric nervous system (P<0.05). Examination of parameters of intestinal growth, including small and large intestinal weight, and small intestinal villus height, crypt depth and crypt cell proliferation, demonstrated no differences between wild-type and knockout mice in either basal or GLP-2-stimulated mucosal growth. Nonetheless, knockout mice exhibited reduced numbers of synaptophysin-positive enteroendocrine cells (P<0.05), as well as a markedly impaired basal gastrointestinal transit rate (P<0.05). Furthermore, acute administration of GLP-1 and GLP-2 significantly inhibited transit rates in wild-type mice (P<0.05-0.01), but had no effect in GFR
2 knockout mice. Despite these changes, expression of mRNA transcripts for the GLP receptors was not reduced in the ENS of knockout animals, suggesting that GLP-1 and -2 modulate intestinal transit through enhancement of inhibitory input to cholinergic/substance P-ergic excitatory motor neurons. Together, these findings demonstrate a role for GFR
2-expressing enteric neurons in the downstream signalling of the glucagon-like peptides to inhibit gastrointestinal motility, but not in intestinal growth.
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