The gastrointestinal tract is unique among all other organs of the body for its ability to exhibit a vast repertoire of functions which occur independently from the central nervous system (CNS). Hence, transport of luminal content, secretion and absorption of ions, water, and nutrients, blood flow, defensive mechanisms against pathogens and elimination of waste and/or noxious substances are under refined regulation of a dense intrinsic innervation referred to as enteric nervous system (ENS – the third division of the autonomic nervous system according to classic categorization proposed by Langley in 1905). Notably, the ENS formed by many different specialized subtypes of neurons and glial cells (reminiscent of CNS astrocytes), shares many common features with the CNS leading enteric neuroscientists to define it as “the brain of the gut” or the mammalian “second brain”. In the ENS, reflexes are triggered by local sensory inputs with the integrative ability of processing signals / stimuli from the smooth muscle and mucosa to determine the appropriate response of the gut. There are several distinct features of enteric neurons which contribute to their ability to regulate gastrointestinal functions. These are: their neurochemistry, their axonal projections in oral or anal directions, their interactions through synaptic transmission and the pronounced modulation by non-neuronal mediators. Nowadays more than 50 bioactive substances have been identified as putative transmitters, neuromodulators and mediators from immune competent cells and the list is still growing.
In addition to maintaining and regulating gut physiology and luminal homeostasis, there are a number of functional, inflammatory and structural gut disorders which are associated with malfunctions of the ENS. Thus, inflammatory conditions are associated with defined alterations in the neurobiology of the ENS. By functional imaging and other sophisticated methodological approaches that allow recordings of human ENS in health and disease, it has been possible to characterize the neurophysiology and neuropharmacology of the human ENS. Alterations in ENS reflex circuits are linked to gut dysfunctions observed in patients with various disorders spanning from common conditions such as irritable bowel syndrome or functional dyspepsia to the most severe forms of gut dysmotility, i.e. chronic intestinal pseudo-obstruction. This symposium is aimed at enhancing interest of the neuroscientist community on the multifunctional role of the ENS / second brain playing in concert with a wide array of specialized cells integrating signals that are involved in the space-temporal control of digestive activity. Also, the putative mechanisms leading to ENS derangement and disease will be highlighted along with most recent pharmacological impact of one major systems such as that provided by the opioids.