Octopamine integrates the status of internal energy supply into the formation of food-related memories

Abstract

The brain regulates food intake in response to internal energy demands and the availability of food. However, can internal energy storage influence the kind of memory that is formed? We show that the duration of starvation determines whether Drosophila melanogaster forms appetitive short-term or long-term memory. The internal glycogen storage in the muscles and fat tissue influences how long sucrose is remembered. Insulin-like signaling in octopaminergic reward neurons integrates internal energy storage into memory formation. In turn, octopamine suppresses the formation of long-term memory. Octopamine is not required for short-term memory, since octopamine-deficient mutants form appetitive short-term memory to sucrose and to other nutrients depending on the internal energy status. The reduced positive reinforcing effect of sucrose in the presence of high internal glycogen levels combined with the increased stability of food-related memories due to increased starvation periods might drive increased food intake.