Shell damage leads to enhanced memory formation in Lymnaea

Abstract

Ecologically relevant stressors alter the ability of the pond snail, Lymnaea stagnalis, to form long-term memory (LTM). Here we show that an environmentally relevant stressor, shell damage, has a dramatic effect on the enhancement of LTM formation. Damage in the form of a shell clip 24h before operant conditioning training results in a single 0.5h training session (TS) to cause long-term memory (LTM) formation. Typically, in these snails two 0.5h TSs with a 1h interval between the sessions are required to cause LTM formation. We show here that even with a 72h interval between shell clip and training, memory enhancement still occurs. The stress associated with shell clip can be mitigated by an ongoing high Ca++ pond water environment, an injection of propranolol, and a DNA methylation blocker. However, use of an anesthetic (MgCl2) during the clip or intermittent exposure to the high Ca++ pond water environment does not mitigate the stress associated with the shell clip. Shell clip is also sufficient to cause juvenile snails, which neither learn nor form memory, to gain the capacity to form LTM. Together the experiments demonstrate that shell clipping is an environmentally relevant stressor that can cause enhancement of LTM formation.