PT - JOURNAL ARTICLE AU - Wataru Yamamoto AU - Rafael Yuste TI - “Whole-body imaging of neural and muscle activity during behavior in <em>Hydra vulgaris</em>: effect of osmolarity on contraction bursts” AID - 10.1523/ENEURO.0539-19.2020 DP - 2020 Jul 22 TA - eneuro PG - ENEURO.0539-19.2020 4099 - http://www.eneuro.org/content/early/2020/07/22/ENEURO.0539-19.2020.short 4100 - http://www.eneuro.org/content/early/2020/07/22/ENEURO.0539-19.2020.full AB - The neural code relates the activity of the nervous system to the activity of the muscles to the generation of behavior. To decipher it, it would be ideal to comprehensively measure the activity of the entire nervous system and musculature in a behaving animal. As a step in this direction, we used the cnidarian Hydra vulgaris to explore how physiological and environmental conditions alters simple contractile behavior and its accompany neural and muscle activity. We used whole-body calcium imaging of neurons and muscle cells and studied the effect of temperature, media osmolarity, nutritional state and body size on contractile behavior.In mounted Hydra preparations, changes in temperature, nutrition state or body size did not have a major effect on neural or muscle activity, or on contractile behavior. But changes in media osmolarity systematically altered contractile behavior and foot detachments, increasing their frequency in hypo-osmolar media solutions and decreasing it in hyperosmolar media. Similar effects were seen in ectodermal, but not in endodermal muscle. Osmolarity also bidirectionally changed the activity of contraction burst neurons, but did not affect the network of rhythmic potential neurons in the ectoderm.These findings show osmolarity-dependent changes in the activity of contraction burst neurons and ectodermal muscle, consistent with the hypothesis that contraction burst neurons respond to media hypo-osmolarity, activating ectodermal muscle to generate contraction bursts. This dedicated circuit could serve as an excretory system to prevent osmotic injury. This work demonstrates the feasibility of studying an entire neuronal and muscle activity in a behaving animal.Significance Statement We imaged whole-body muscle and neuronal activity in Hydra in response to different physiological and environmental conditions. Osmolarity bidirectionally altered Hydra contractile behavior in a reflexive fashion. These changes were accompanied by specific changes in the activity of one neuronal circuit and one set of muscles. By providing a neurobiological mechanisms for a reflexive behavior in a cnidarian, this work is a step toward comprehensive deciphering of the mechanisms of animal behavior by measuring the activity of all neurons and muscle cells.