For more than a century, two general forms of memory have been classified by their duration: short-term memory (STM), which is rapidly formed and can outlast training for minutes or hours, and long-term memory (LTM), which lasts from hours to days, weeks or even years. STM involves post-translational modifications of preexisting molecules that alters the efficiency of synaptic transmission. In contrast, LTM can be blocked by inhibitors of transcription or translation indicating that it is dependent on de novo gene expression. Proteins newly synthesized during memory consolidation may contribute to restructuring processes at the synapse and thereby alter the efficiency of synaptic transmission beyond the duration of short-term memory. Past efforts to identify memory-related genes have only been able to screen a small number of genes at any one time, making it difficult to determine just how many genes are involved in learning and memory and how they interact during memory formation.
Using cDNA array technology, a powerful technique that can screen thousands of genes at one time, Sebastiano Cavallaro and Velia D'Agata at ISN, with colleagues at the Blanchette Rockefeller Neuroscience Institute in the US, surveyed the learning-induced changes in gene expression during learning and memory (Cavallaro S., D'Agata V., Manickam P., Dufour F., Alkon D.L., Memory specific temporal profiles of gene expression in the hippocampus. Proc. Natl. Acad. Sci. USA, 99(25):16279-16284, 2002). After putting rats through a standard learning task, the researchers analyzed gene expression in hippocampal tissue from the rats at different time points after testing (1, 6, and 24 hours).
Learning altered 140 different genes, 110 of which were also altered at different times by the physical activity and stress of the learning task.
One gene that was not influenced by physical activity, Fibroblast Growth Factor (FGF)-18, was increased at all time points after the learning task.
Additionally, the researchers found that injecting FGF-18 into the rat's brain during testing significantly improved learning.
Although sure to be just the tip of the iceberg, these results indicate distinct temporal gene expression profiles associated with learning and memory. They could point researchers towards new molecular cascades and therapies which may improve successive stages of memory (e.g. learning, consolidation and long-term retention), under normal conditions as well as in disorders that affect cognitive functioning, such as Alzheimer's disease.
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