BDNF and irritable bowel syndrome: In analogy with the CNS, in the ENS, BDNF is a target-derived growth factor involved in neuronal development and survival during ontogenesis [15,43,44], but may also act as an excitatory neurotransmitter/neuromodulator, and is involved in the rearrangement of enteric neuronal circuitries, both in physiological conditions and in disease states, such as IBS [23,25,29].