Fruit flies are attractive organisms for the study of learning and memory. They are easy to maintain in the laboratory, even in mass culture, their generation time is short, and their nervous system is simple. Above all, the ease of producing mutants renders them suitable for the genetic dissection of the learning and memory processes. This holds true particularly for Drosophila melanogaster, the much-investigated object of classical genetics. In addition to the vast amount of information available about its genome, it lends itself readily to molecular genetic manipulations. Currently, there are half a dozen mutations known to affect conditioning in Drosophila. Importantly, the biochemical lesion in all those characterized so far is somehow related to cyclic adenosine monophosphate (cAMP) metabolism. The dunce strains have a crippled cAMP-specific phosphodiesterase (PDE-II), with consequentially elevated overall cAMP levels. There is strong evidence that the mutation is located in the structural gene of this enzyme. The rutabaga flies are impaired in a Ca2+/calmodulin-activated adenylate cyclase catalytic subunit, resulting in the overall cAMP levels slightly below normal. Behavior studies indicate that dunce, rutabaga, amnesiac, and probably cabbage are able to acquire a labile form of memory, but this rapidly wanes. Hence, they are regarded as memory mutants. In contrast, dopa decarboxylase deficient (Ddc) appears to be affected in the phase of acquisition rather than memory storage.
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