HABITUATION, SENSITIZATION AND THE EFFECT OF SEROTONIN ON THE EYESTALK WITHDRAWAL REFLEX OF CANCER-MAGISTER

1. 1. The eyestalk withdrawal reflex in Cancer magister habituated to repeated tapping of the dorsal carapace during a first session of 50 taps when taps were repeated at 15 sec intervals. 2. 2. During subsequent sessions, crabs either continue to habituate or may become sensitized. 3. 3. The withdrawal twitches of sensitized crabs became tonic and the eyes often did not return to the fully elevated position between taps. 4. 4. Despite previous response history, systemically injected serotonin prior to a 4th test session caused all withdrawal twitches to become fast phasic, and most responses consisted of multiple twitches. 5. 5. The haemolymph glucose levels of all crabs tested became elevated, indicative of a serotonin/ hyperglycemic hormone-induced stressed state; however, the level of eye withdrawal was not correlated to the haemolymph glucose levels. © 1990.