Aplysia californica is a model organism for determining the molecular basis of memory. In this system identified synaptic changes have been closely linked to behavioral memories. Long-term sensitization and long-term synaptic changes between sensory neurons and motor neurons require both gene expression followed by translational control of the newly expressed mRNAs. One important mechanism for translational control is mediated through the target of rapamycin (TOR) and one mechanism downstream of TOR is the translational control of mRNAs containing a 5' terminal oligopyrimidine tract (5'TOP) sequence in their mRNA transcript. These include all ribosomal proteins, elongation factors and a few other translational regulators. TOR regulation of 5'TOP mRNAs in vertebrates is thought to be due to TOR dependent removal of the translational repression mediated by the 5'TOP sequence. Here, we show that this mechanism is similar in Aplysia, whereby Aplysia 5'TOP mRNAs are repressed under basal conditions and this repression is removed by serotonin in a rapamycin-sensitive manner. (C) 2010 Elsevier Inc. All rights reserved.