Effects of learning on mTOR pathway gene expression in the brain of zebrafish (Danio rerio) of different ages.

Target of rapamycin (TOR) is a protein kinase involved in the modulation of mRNA translation and, therefore, in the regulation of protein synthesis. In neurons, the role of TOR is particularly important in the consolidation of long-term memory (LTM). One of the modulators of TOR is brain-derived neurotrophic factor (BDNF), which activates the TOR signaling pathway to promote protein synthesis, synapse strengthening, and the creation of new neural networks. We investigated the gene expression pattern of this pathway during memory consolidation in zebrafish of different ages. Our findings demonstrate that TOR activation in old animals occurs in the early phase of consolidation, and follows a pattern identical to that of BDNF expression. In younger animals, this increase in activation did not occur, and changes in BDNF expression were also not so remarkable. Furthermore, the expression of the main proteins regulated by the synthesis of TOR (i.e., 4EBP and p70S6K) remained identical to that of TOR in all age groups.