Neuronal Mechanosensitivity in the Gastrointestinal Tract

Abstract

The ability to sense differing stimuli in the gut and translate this to alter a number of physiological outcomes is reliant on the mechanosensory and transductive capacity of the intestine. Mechanosensitivity is conferred by both extrinsic and intrinsic pathways in the gut and includes non-neuronal elements. This review focuses on the neuronal mechanosensitive elements within the GI tract and describes their functional and neuroanatomical features. The primary intrinsic neuronal mechanotransductive elements within the gut are intrinsic primary afferent neurons (IPANs) and contribute to the largely autonomous adaptation of the gut to intraluminal stimuli, allowing for peristalsis but also other reflexes such as secretion and local blood flow. The extrinsic mechano-transductive pathways run in vagal, pelvic and splanchnic circuits and can convey both innocuous and noxious aspects of the intestinal environment to the central nervous system including, but not limited to, mechanical stimuli. The exquisite ability of the gastrointestinal tract to sense different types of physical deformation and respond accordingly is conferred in part by the varying types of sensory mechanotransductive terminals. Such distinctions are exemplified by the purported roles of Intraganglionic Laminar Ending (IGLE) and Intramuscular Arrays (IMA) in mechanical sensing. Sensory mechanosen-sitive terminals can be found in all layers of the intestine where they subserve different stimulus modalities or varying degrees of stimuli such as distension or stretch. Intensive effort is currently being focused on the role of sensory neuronal mechanotransductive pathways in various 'hypersensitivity' disorders such as irritable bowel syndrome. An understanding of the physiological, patho-physiological and pharmacological distinctions between such neuronal mechan-osensitive elements may bring substantive clinical pharmacotherapeutic benefit.