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GRK 1482 Jahrbuch 2011-2014

Abstract In the gastrointestinal tract the enteric nervous system (ENS), an au- tonomous neuronal network, controls all gut functions independently from the central nervous system. Our hypothesis is that neurons of the ENS, which is strategically located in the gut wall, between blood vessels and epithelial cells function as peripheral osmoreceptors, car- rying responsibility for monitoring and regulating osmotic pressure changes in the gut, similar to central osmoreceptive neurons which are capable of osmosensation and crucial for systemic osmoregula- tion. Introduction The cells of our body are surrounded by the ext- racellular fluid (ECF) whose osmolality is in equi- librium with plasma osmolality that is a measure of the body‘s electrolyte-water balance. Loss or gain of water or electrolytes results in changes in ECF osmolality; this could lead to changes in cell volume and intracellular ionic strength which can affect the physical integrity of cells and tissues in critical manner [1]. Fortunately, Mother Nature has equipped us with specialized homeostatic con- trolmechanisms. The regulation of osmolality is achieved through a negative feedback regulation of thirst, diuresis, salt appetite and natriuresis which is driven by a sensory system capable of detecting changes in osmolality and to trigger the appropria- te responses [2]. Neurons regulating these reflexes are located in the central and in the peripheral ner- vous system. While central osmoregulation is well studied, data on peripheral osmoreceptors are very few: peripheral osmoreceptors have been identified and characterized in dorsal root ganglia innervating the liver [3]. The gastrointestinal tract anyway is the first loca- tion where osmotic changes take place: after wa- ter or food intake the luminal and consequently the blood osmolality undergo profound changes. Within the gut wall, so directly between the lumen and the intestinal blood vessel there is the enteric nervous system (ENS) that autonomously cont- rols absorption, secretion and blood flow among the other functions [4]. Enteric neurons have been already shown to be involved in the control of the glucose homeostasis [5]. Our hypothesis is that the neurons of the ENS, strategically located in the gut wall close to blood vessels and epithelial cells are responsible to de- tect and provide the adequate response to osmotic changes. PhD FELLOWS Page 56 | GRK Progress Report 2011-2014 Philip Graf (Dipl. Biol) Human Biology PhD 13/2 Osmosensitivity in the enteric nervous system

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