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Aplysia
''Aplysia'' is a genus of medium-sized to extremely large sea slugs, specifically sea hares, which are one clade of large sea slugs, marine gastropod mollusks. The general description of sea hares can be found in the article on the superfamily Aplysioidea.
These benthic herbivorous creatures can become rather large compared with most other mollusks. They graze in tidal and subtidal zones of tropical waters, mostly in the Indo-Pacific Ocean (23 species); but they can also be found in the Atlantic Ocean (12 species), with a few species occurring in the Mediterranean.
''Aplysia'' species, when threatened, frequently release clouds of ink, it is believed in order to blind the attacker (though they are in fact considered edible by relatively few species). Following the lead of Eric R. Kandel, the genus has been studied as a model organism by neurobiologists, because its siphon-withdrawal response, as studied in ''Aplysia californica'', is mediated by electrical synapses, which allow several neurons to fire synchronously (Kandel et al., 2000). (See : Aplysia gill and siphon withdrawal reflex) This quick neural response is necessary for a speedy reaction to danger by the animal. Aplysia has only about 20,000 neurons, making it a favorite subject for investigation by neuroscientists. Also, the 'tongue' on the underside is controlled by only two neurons, which allowed complete mapping of the innervation network to be carried out.
==Long term memory==
In neurons that mediate several forms of long-term memory in ''Aplysia'', the DNA repair enzyme poly ADP ribose polymerase 1 (PARP-1) is activated. In virtually all eukaryotic cells tested, the addition of polyADP-ribosyl groups to proteins (polyADP-ribosylation) occurs as a response to DNA damage. Thus the finding of activation of PARP-1 during learning and its requirement for long-term memory was surprising. Cohen-Aromon et al.〔 suggested that fast and transient decondensation of chromatin structure by polyADP-ribosylation enables the transcription needed to form long-term memory without strand-breaks in DNA. Subsequent to these findings in ''Aplysia'', further research was done with mice and it was found that polyADP-ribosylation is also required for long-term memory formation in mammals.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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