Linalool acts as a fast and reversible anesthetic inHydra

Abstract

15The ability to make transgenic Hydra lines has opened the door for quantitative in vivo studies of 16 Hydra regeneration and physiology. These studies commonly include excision, grafting and 17 transplantation experiments along with high-resolution imaging of live animals, which can be 18 challenging due to the animal's response to touch and light stimuli. While various anesthetics 19 have been used in Hydra studies over the years, they tend to be toxic over the course of a few 20 hours or their long-term effects on animal health have not been studied. Here we show that the 21 monoterpenoid linalool is a useful anesthetic for Hydra. Linalool is easy to use, non-toxic, fast 22 acting, and reversible. It has no detectable long-term effects on cell viability or cell proliferation. 23 We demonstrate that the same animal can be immobilized in linalool multiple times at intervals 24 of several hours for repeated imaging over 2-3 days. This uniquely allows for in vivo imaging of 25 dynamic processes such as head regeneration. We further directly compare linalool to currently 26 used anesthetics and show its superior performance. Because linalool, which is frequently 27 utilized in perfumes and cosmetic products, is also non-hazardous to humans, it will be a useful 28 tool for Hydra research in both research and teaching contexts. 29 30 31 112

Mapping the Whole-Body Muscle Activity of Hydra vulgaris

“…After each contraction burst, polyps passively relaxed into a resting posture as calcium levels decreased in both epitheliomuscular tissues (Figure 2A). In this posture, passive tissue forces are presumably minimized, as it was also observed in animals treated with the muscle relaxant linalool [35] (Figure S2E). From this passive resting posture, polyps could also exhibit a slow active elongation over hundreds of seconds, which involves calcium increases in the endodermal epithelium, presumably exerting circumferential forces on the gastric fluid to induce body elongation.…”