The management of
visceral pain is a major clinical problem in patients affected by
gastrointestinal disorders. The poor knowledge about
pain chronicization mechanisms prompted us to study the functional and morphological alterations of the gut and nervous system in the animal model of persistent
visceral pain caused by
2,4-dinitrobenzenesulfonic acid (
DNBS). This agent, injected intrarectally, induced a colonic
inflammation peaking on day 3 and remitting progressively from day 7. In concomitance with bowel
inflammation, the animals developed visceral
hypersensitivity, which persisted after
colitis remission for up to three months. On day 14, the administration of
pain-relieving drugs (injected intraperitoneally and intrathecally) revealed a mixed nociceptive, inflammatory and
neuropathic pain originating from both the peripheral and central nervous system. At this time point, the colonic histological analysis highlighted a partial restitution of the tunica mucosa, transmural
collagen deposition, infiltration of mast cells and eosinophils, and upregulation of
substance P (SP)-positive nerve fibers, which were surrounded by eosinophils and MHC-II-positive macrophages. A significant activation of microglia and astrocytes was observed in the dorsal and ventral horns of spinal cord. These results suggest that the persistence of
visceral pain induced by
colitis results from maladaptive plasticity of the enteric, peripheral and central nervous systems.