INVESTIGATING POTENTIAL MECHANISMS OF CLOVE OIL (EUGENOL) IN MODEL CRUSTACEANS

Elizabeth Grau*, Alec Bradley, Danielle Cantrell, Samantha Eversole, Carolyn Grachen, Kaylee Hall, Danielle Hawthorne, Claire Kinmon, Paula Ortiz Guerrero, Bhavik Patel, Kaitlyn Samuels, Chinni Suryadevara, Gia Valdes, Samuel Wycoff, Kristin Weineck, Shannon Conlin, Andrew Ray, Leo Fleckenstein, Elena Piana and Robin Cooper

Department of Biology, University of Kentucky
Lexington, KY, USA 40506-0225
emgr242@g.uky.edu

Eugenol is used as topical anesthetic in mammals to remedy pain and to anesthetize fish for short periods. Eugenol was examined for its potential use on crustaceans. The exact mechanisms in the effects are still not fully understood. The effects of eugenol on neuronal activity in sensory and motor neurons in the Red Swamp crayfish (Procambarus clarkii), Blue crab (Callinectes sapidus) and Whiteleg shrimp (Litopenaeus vannamei) with electrophysiological recordings was examined. The neurogenic heart rate in the 3 species was also monitored along with behaviors and responsiveness to sensory stimuli while exposed to eugenol. The activity of the primary proprioceptive neurons was reduced at 200ppm and ceased at 400ppm for both crayfish (i.e., muscle receptor organ) and crab (i.e., leg PD organ) preparations when saline containing eugenol was directly applied to exposed sensory organs. Flushing out eugenol resulted in recovery in the preparations within 5 to 10 minutes. Administering eugenol to crayfish and crabs both systemically by injection and through exposure in their aquatic environment resulted in the animals becoming lethargic. Direct injection into the hemolymph was quicker to decrease reflexes and sensory perception but heart rate was still maintained. Eugenol at a circulating level of 400ppm decreased electromyogram activity in the claw muscle of crabs. Surprisingly, this study found no change in heart rate despite administering eugenol into the hemolymph to reach 400ppm in crabs or crayfish; however, heartrate decreased in shrimp. Excessive use of clove oil can result in overdose and cellular toxicity in humans. Overuse of topical eugenol or ingestion may silence neurons in mammals by the same mechanisms as in our model crustacean animals. The next focus is to determine the mechanism of action by intracellular recordings from neurons to support scant evidence of blocking voltage gated-sodium channels and thus decrease neuronal excitability.