Enteric neuroplasticity evoked by inflammation

Neuroplastic changes in the enteric nervous system (ENS) may be observed in physiological states, such as development and aging, or occur as a consequence of different pathological conditions, ranging from enteric neuropathies (e.g., Hirschsprung's disease) to intestinal (e.g., inflammatory bowel disease) or extra-intestinal diseases (e.g., Parkinson's disease). Studying ENS plasticity may help to elucidate the pathophysiology of several diseases and have a bearing on the development of new pharmacological interventions. In the present review, we would like to focus on neuronal plasticity evoked by gastrointestinal inflammation occurring in inflammatory bowel disease and in a subset of patients with severe derangement of gut motility due to an enteric neuropathy characterized by an inflammatory infiltrate of the enteric plexuses. Major features of neuroplasticity within the enteric microenvironment encompass structural abnormalities ranging from nerve re-arrangement (e.g., hypertrophy and hyperplasia) to degeneration and loss of enteric ganglion cells; altered synthesis, content and release of neurotransmitters as well as up- or down-regulation of receptor systems; gastrointestinal dysfunction characterized by sensory-motor and secretory impairment of the gut. Interestingly, neuronal changes may also occur in segments of the gastrointestinal tract remote from the site of the original inflammation, e.g. the ileum may show neuroplastic changes during colitis. Sometimes, the inflamed site may even be outside the gut. Among potential mechanisms underlying ENS plasticity, neurotrophins and enteric glia deserve special attention. A better comprehension of ENS plasticity during inflammation could be instrumental to develop new therapeutic options for patients with IBD and inflammatory enteric neuropathies.