An increase in insulin is important for the acquisition conditioned taste aversion in Lymnaea

Neurobiol Learn Mem. 2014 Dec;116:132-8. doi: 10.1016/j.nlm.2014.10.006. Epub 2014 Oct 25.

Abstract

Conditioned taste aversion (CTA) in Lymnaea is brought about by pairing a sucrose solution (the conditioned stimulus, CS) with an electric shock (the unconditioned stimulus, US). Following repeated CS-US pairings, CTA occurs and it is consolidated into long-term memory (LTM). The best CTA is achieved, if snails are food-deprived for 1 day before training commences. With a longer period of food deprivation (5 days), learning and memory formation does not occur. It has been hypothesized that the levels of insulin in the central nervous system (CNS) are very important for CTA to occur. To test his hypothesis, we injected insulin directly into 5-day food-deprived snails. The injection of insulin, as expected, resulted in a decrease in hemolymph glucose concentration. Consistent with our hypothesis with insulin injection, learning and memory formation of CTA occurred. That is, the 'insulin spike' is more important than an increase in hemolymph glucose concentration for CTA-LTM. If we injected an insulin receptor antibody into the snails before the insulin injection, learning was formed but memory formation was not, which is consistent with our previous study. Therefore, a rise in the insulin concentration (i.e., insulin spike) in the CNS is considered to be a key determining factor in the process of CTA-LTM.

Keywords: Conditioned taste aversion; Deprivation; Glucose; Hemolymph; Insulin; Lymnaea; Motivation; Sucrose.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Avoidance Learning / drug effects*
  • Avoidance Learning / physiology
  • Conditioning, Classical / drug effects*
  • Conditioning, Classical / physiology
  • Food Deprivation / physiology
  • Glucose / analysis
  • Hemolymph / chemistry
  • Hypoglycemic Agents / pharmacology*
  • Insulin / pharmacology*
  • Lymnaea
  • Motivation / drug effects
  • Motivation / physiology
  • Taste / physiology*

Substances

  • Hypoglycemic Agents
  • Insulin
  • Glucose