New Perspectives for the Use of Earthworms – Testing of Anesthetics

Anesthetic drugs have been tested for years on rats, rabbits, dogs, cats and monkeys, which may raise ethical concerns. Researchers do not always pay attention to the possibility of using techniques of anesthesia, analgesia or euthanasia in relation to invertebrate animals. It has previously been shown that earthworms meet the requirements of laboratory animals, and being a good alternative to the studies on vertebrates, may also be used as the first stage of testing anesthetics. The lethal concentrations of procaine and lidocaine for E. fetida and D. veneta were established using modified filter paper contact test. Using a modified method developed for testing anesthetics, mature earthworms (clitellate) of both species were used to check the effectiveness of lidocaine and procaine in safe immobilizing of earthworms. The reactions of earthworms in contact with anesthetics were different. The possibility of using a higher concentration range of procaine and lidocaine for E. fetida than for D. veneta, as E. fetida demonstrated a greater resistance to the stress caused by the action of chemical substances. The response to this stress varied and depended on the concentration used; however, higher concentrations of anesthetics caused rapid body movements and discharge of the coelomic fluid as well as morphological changes observed after 48 hours. Procaine was not effective in immobilizing earthworms, but lidocaine proved effective in reversibly immobilizing both species. For E. fetida, lidocaine in the concentrations of 1.4 and 1.6 at 95 and 90 min, respectively, resulted in a full immobilization of animals, which then survived following 24h and 48h of recovery. For D. veneta, lidocaine in the concentrations 1.3 and 1.4 during 40 min proved effective and safe to use, as all individuals survived following 24h and 48h of recovery.