Some sea stars have the ability to detach the arm when they are attacked by a predator, wounded in the arm, or subjected to inferior circumstances (pH, air supply, etc.). Japanese Asterias amurensis is known to have this ability of autotomy. The body fluids of scalded A. amurensis induced an arm autotomy of the intact A. amurensis by intracoelomic injection into an arm. This response is divided into two types, "slow autotomy" and "quick autotomy", according to the time taking to detach the arm. Bioassay-guided separation of lyophilized body fluids by size-exclusion column chromatography and repeated HPLC (ODS) gave an active fraction, which induced the "slow autotomy". A mixture of nicotinamide (NA) and N-methylquinolinic acid (NMQA) were assigned in this fraction as the inducers of the autotomy. NMQA is suggested to be the substrate of NMDA glutamate receptor, which has not yet been detected in sea stars. The "slow autotomy" is, therefore, induced by the stimulation of excitatory nerve system through an NMDA glutamate receptor and a pathway implicated with NA. On the other hand, the "quick autotomy" is induced by the above two pathways when the stimulation of an AMPA glutamate receptor and the other unidentified pathways are simultaneously occurred. SALMFamide S1 is suggested to be the substrate of the AMPA glutamate receptor.
