Aplysia californica

Aplysia is a genus of gastropod molluscs that generally populate the subtropical and tropical tide zones.  The species vary in size from a few centimeters to up to 70 centimeters and can weigh up to 15.9 kg.  Aplysia often release an ink containing chemical deterrants when disturbed, the ink is dark purple in color and is used to defend the animal against predators.  Aplysia are often used as a model organism in neuroscience due to their distinctive giant neurons  (Moroz, 2011.)

Aplysia californica is a well-studied model organism commonly used in neurobiology and neuroscience.  Their central nervous system consists of around 20,000 neurons organized into nine ganglia (Kandel, 2001).  The neurons found in A. californica are so large because they are polyploidy; in fact the R2 neuron can contain up to 600,000 copies of the haploid genome (Moroz, 2011.)  Due to their large size and relatively small number, the neurons in A. californica have been used to study the molecular and cellular level development of learning and memory behaviors (Kandel, 2001.)

(Moroz, 2011)

A behavior often studied in A. californica is the gill withdrawal reflex.  The gill withdrawal reflex is a behavior in which the animal draws its gill and siphon to retract into its body in the presence of a tactile stimulus, like one it would receive from a predator.  This behavior was found to be sensitive to habituation, sensitization, and classical conditioning, which led to its further study as a model for learning and memory (Kandel, 2001.)

The forms of learning seen in A. californica are very similar to those seen in higher vertebrates.  The formation of memories requires two periods: a short-term phase and a long-term phase.  The short-term memory is converted into a long-term memory with repetition (Kandel, 2001.)

Other aspects of development in A. californica are also similar to those seen in higher vertebrates and humans.  The cellular mechanisms underlying synaptic plasticity and the intracellular signaling pathways in A. californica are similar to those seen in vertebrates (Moroz, 2011.)  There has also been a call for a complete sequence of the A. californica genome, as there has been increasing evidence suggesting it would be a useful model for several genomic studies (Moroz et al., 2006.)

References:

Kandel, E. R. (2001). Neuroscience – The molecular biology of memory storage: A dialogue between genes and synapses. [Review]. Science, 294(5544), 1030-1038.  PMID: 11691980

Moroz, L. L. (2011). Aplysia. [Editorial Material]. Current Biology, 21(2), R60-R61.  PMID: 21256433

Moroz, L. L., Edwards, J. R., Puthanveettil, S. V., Kohn, A. B., Hla, T., Heyland, A., . . . Kandel, E. R. (2006). Neuronal transcriptome of Aplysia: neuronal compartments and circuitry. [Article]. Cell, 127(7), 1453-1467. doi: 10.1016/j.cell.2006.09.052  PMID: 17190607

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