A flavonol present in cocoa [(−)epicatechin] enhances snail memory

Abstract

SUMMARYDietary consumption of flavonoids (plant phytochemicals) may improve memory and neuro-cognitive performance, though the mechanism is poorly understood. Previous work has assessed cognitive effects in vertebrates; here we assess the suitability of Lymnaea stagnalis as an invertebrate model to elucidate the effects of flavonoids on cognition. (-)Epicatechin (epi) is a flavonoid present in cocoa, green tea and red wine. We studied its effects on basic snail behaviours (aerial respiration and locomotion), long-term memory (LTM) formation and memory extinction of operantly conditioned aerial respiratory behaviour. We found no significant effect of epi exposure (15mgl -1 ) on either locomotion or aerial respiration. However, when snails were operantly conditioned in epi for a single 0.5h training session, which typically results in memory lasting ~3h, they formed LTM lasting at least 24h. Snails exposed to epi also showed significantly increased resistance to extinction, consistent with the hypothesis that epi induces a more persistent LTM. Thus training in epi facilitates LTM formation and results in a more persistent and stronger memory. Previous work has indicated that memory-enhancing stressors (predator kairomones and KCl) act via sensory input from the osphradium and are dependent on a serotonergic (5-HT) signalling pathway. Here we found that the effects of epi on LTM were independent of osphradial input and 5-HT, demonstrating that an alternative mechanism of memory enhancement exists in L. stagnalis. Our data are consistent with the notion that dietary sources of epi can improve cognitive abilities, and that L. stagnalis is a suitable model with which to elucidate neuronal mechanisms.

Black tea differs from green tea: it suppresses long-term memory formation inLymnaea

“…Using this procedure GT was shown to enhance or to reverse a blockade of LTM formation [13–15]. Here we found (Figure 2) that training in the 1:14 BT blocked LTM formation.…”

“…a 24 h memory) two 0.5h training sessions separated by a 1h interval are necessary. The W- strain has been used extensively in our laboratory and is the same strain used in the previous experiments testing the effects of Epi and Epi-containing foods on cognition in Lymnaea [2,13–16]. In this strain a single 0.5h TS does not result in LTM formation.…”

“…Previously we showed that a natural food substance, Epi, that is present in a number of foods was able to enhance LTM formation if the snail was trained in Epi-PW or was placed in Epi-PW during the consolidation period following training in PW [13–15,19]. More recently we showed that LTM enhancement also occurs when snails are trained in food substances (e.g.…”

A flavonol, epicatechin, reverses the suppressive effects of a stressor on LTM formation

“…Exposing snails to epicatechin significantly enhanced the ability of snails to form LTM (Fruson et al, 2012). The epicatechinenhanced LTM formed faster, persisted longer, and was more resistant to extinction.…”

“…A comprehensive summary of which ecologically relevant stressors significantly alter LTM formation can be found in two recent reviews (Lukowiak et al, 2014). It has also been shown that a flavonoid, epicatechin, found in dark chocolate, green tea and red wine (Kühnau, 1976;Matsuoka et al, 1995;Galliet al, 2002;Youdim et al, 2002) enhances LTM formation in Lymnaea (Fruson et al, 2012). However, the enhancement brought about by epicatechin occurs via a different mechanism than that brought about by predator detection (Il-Han et al, 2010;Fruson et al, 2012).…”