What's hot: the enhancing effects of thermal stress on long-term memory formation in Lymnaea stagnalis

Abstract

SUMMARYThe pond snail, Lymnaea stagnalis, naturally inhabits slow flowing, shallow and stagnant environments in the northern temperate zone. Consequently, it will experience wide temperature fluctuations dependent on prevailing weather conditions. We hypothesize that periods of warming act as a thermal stressor to alter memory formation. Snails were exposed to an acute 1 h period of 30°C pond water and we determined how memory formation following operant conditioning of aerial respiration was affected. In the snails used here (Dutch strain), a single 0.5 h training session (TS) results in intermediate-term (3 h) but not long-term memory (LTM). Applying the thermal stressor during training caused memory enhancement (i.e. LTM lasting 24 h). However, the breathing rate also increased in warm water, which might explain the enhanced memory. Therefore, we applied the thermal stressor (1 h at 30°C) up to 4 h before or 1 h after training. This did not alter baseline breathing rate during the period when snails would experience training. However, the thermal stressor whether experienced prior to or following the single TS, resulted in an enhanced memory that persisted up to 48 h (i.e. LTM). We conclude that memory enhancement is due to the stress associated with the thermal stimulus.

Heat stress enhances LTM formation inLymnaea: role of HSPs and DNA methylation

“…That is, the number of attempted openings in MT was significantly lower than that in TS1. Thus, we confirmed the previous findings of Teskey et al (2012) regarding enhancement of LTM formation by the heat stressor.…”

“…We first confirmed that we could replicate the data previously obtained (Teskey et al, 2012) showing that the 1 h heat stress at 30°C caused an enhancement of LTM formation in the W-strain of snails ( Fig. 1).…”

“…In the first procedure, snails received a single 0.5 h training session (TS1; Sangha et al, 2003;Parvez et al, 2005;Orr and Lukowiak, 2008;Teskey et al, 2012) and then a memory test session (MT) was performed 24 h after the TS1. In the second procedure, snails received two 0.5 h training sessions separated by a 1 h interval (i.e.…”

“…Conversely, a heat stressor (30°C for 1 h) enhances LTM formation in Lymnaea (Teskey et al, 2012). That is, snails experiencing the heat stressor formed LTM following a single 0.5 h training session, while LTM was not formed in control experiments (i.e.…”

“…Heat is assumed to be a stressor in Lymnaea as many important behavioural, physiological and immunological processes in Lymnaea are temperature dependent (Teskey et al, 2012). It has been demonstrated that laboratory-reared Lymnaea prefer temperatures of around 20°C for optimal growth and mortality (Vaughn, 1953;McDonald, 1969).…”