Behavioral and Transcriptional Effects of Short or Prolonged Fasting on the Memory Performances of Lymnaea stagnalis

Abstract

Introduction: The Garcia effect, a solid learning paradigm, was used to investigate the molecular and behavioral effects induced by different lengths of fasting on the cognitive functions in the pond snail Lymnaea stagnalis, a valid model system Methods: Three experimental groups were used: Moderately hungry snails, food-deprived for 1 day (D1 snails), severely hungry snails (D5 snails), fasting for 5 days, and satiated snails with ad libitum access to food (AL snails). In the Garcia effect, a single pairing of an appetitive stimulus with a heat stressor results in a learned taste-specific negative hedonic shift. D5 snails were injected with bovine insulin and D1 snails with the insulin receptor antibody (Ab). As a control group, AL snails were injected with saline. Gene expression analyses were performed by Real-time PCR in snails’ central nervous system (CNS). Results: AL snails are ‘average learners’, D1 snails are the best performers, whereas the D5 ones do not show the Garcia effect. Severely fasting snails injected with insulin 3h before the training procedure, show the Garcia effect, whereas injecting 1-day fasting snails with insulin receptor Ab blocks their ability to express memory. The differences in memory performances are associated with changes in the expression levels of selected targets involved in neuronal plasticity, energy homeostasis, and stress response. Discussion: Our results suggest that short-term fasting creates an optimal internal state in L. stagnalis’ CNS, allowing a spike in insulin release and an upregulation of genes involved in neuroplasticity. Long-term fasting, instead, upregulates genes involved in energy homeostasis and animal survival.

Identification of Putative Molecules for Adiponectin and Adiponectin Receptor and Their Roles in Learning and Memory in Lymnaea stagnalis

“…Insulin-like peptides in the brain are strongly involved in the learning and memory mechanisms of Lymnaea [ 7 , 8 , 9 , 10 ]. For example, in long-term memory formation following a conditioned taste aversion (CTA) protocol [ 9 ], molluscan insulin-related peptides (MIPs) are up-regulated at the mRNA level in the Lymnaea central nervous system (CNS) [ 11 ], and MIPs enhance the neural transmission efficacy at a synapse in the CTA neural circuit [ 12 ].…”

LPS-Induced Garcia Effect and Its Pharmacological Regulation Mediated by Acetylsalicylic Acid: Behavioral and Transcriptional Evidence

“…We recently demonstrated—for the first time in an invertebrate model organism—that Lymnaea is capable of forming a unique type of conditioned taste aversion known as the “Garcia effect” [ 21 , 22 , 23 , 24 , 25 , 26 ]. To induce a Garcia effect, a single pairing of a novel appetitive stimulus followed by nausea or sickness even hours later is sufficient to establish an LTM that causes a long-lasting avoidance of that food [ 24 , 25 , 27 ].…”