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Open Access Research article

Oxidative-stress induced increase in circulating fatty acids does not contribute to phospholipase A2-dependent appetitive long-term memory failure in the pond snail Lymnaea stagnalis

Emily Beaulieu1, Julie Ioffe1, Shawn N Watson1, Petra M Hermann1 and Willem C Wildering12*

Author Affiliations

1 Department of Biological Sciences, Faculty of Science, University of Calgary, Calgary, Alberta T2N 1N4, Canada

2 Department of Physiology and Pharmacology, Faculty of Medicine, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada

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BMC Neuroscience 2014, 15:56  doi:10.1186/1471-2202-15-56

Published: 1 May 2014

Abstract

Background

Reactive oxygen species (ROS) are essential for normal physiological functioning of the brain. However, uncompensated increase in ROS levels may results in oxidative stress. Phospholipase A2 (PLA2) is one of the key players activated by elevated ROS levels resulting in the hydrolysis of various products from the plasmamembrane such as peroxidized fatty acids. Free fatty acids (FFAs) and fatty acid metabolites are often implicated to the genesis of cognitive impairment. Previously we have shown that age-, and experimentally induced oxidative stress causes PLA2-dependent long-term memory (LTM) failure in an aversive operant conditioning model in Lymnaea stagnalis. In the present study, we investigate the effects of experimentally induced oxidative stress and the role of elevated levels of circulating FFAs on LTM function using a non-aversive appetitive classical conditioning paradigm.

Results

We show that intracoelomic injection of exogenous PLA2 or pro-oxidant induced PLA2 activation negatively affects LTM performance in our learning paradigm. In addition, we show that experimental induction of oxidative stress causes significant temporal changes in circulating FFA levels. Importantly, the time of training coincides with the peak of this change in lipid metabolism. However, intracoelomic injection with exogenous arachidonic acid, one of the main FFAs released by PLA2, does not affect LTM function. Moreover, sequestrating circulating FFAs with the aid of bovine serum albumin does not rescue pro-oxidant induced appetitive LTM failure.

Conclusions

Our data substantiates previous evidence linking lipid peroxidation and PLA2 activation to age- and oxidative stress-related cognitive impairment, neuronal dysfunction and disease. In addition however, our data indicate that lipid peroxidation induced increased levels of circulating (per)oxidized FFAs are not a factor in oxidative stress induced LTM impairment.

Keywords:
Cognitive impairment; Lipid peroxidation; Classical conditioning; Invertebrate; Phospholipase A2; Arachidonic acid; Mollusc; Oxidative stress; Free fatty acid