Aplysia gill and siphon withdrawal reflex

The Aplysia gill and siphon withdrawal reflex (GSWR) is an involuntary, defensive reflex of the sea hare Aplysia californica, a large shell-less sea snail or sea slug. This reflex causes the sea hare's delicate siphon and gill to be retracted when the animal is disturbed.Aplysia californica is used in neuroscience research for studies of the cellular basis of behavior including: habituation, dishabituation, and sensitization, because of the simplicity and relatively large size of the underlying neural circuitry.

Eric Kandel, recipient of the Nobel Prize in Physiology or Medicine in 2000 for his work with Aplysia californica, was involved in pioneering research into this reflex in the 1960s and 1970s.

Nonassociative learning is a change of the behavior of an animal due to an experience from specific kinds of stimuli. In contrast to associative learning the behavioral change is not caused by the animals learning that a particular temporal association occurs between the stimuli. There are three different forms of nonassociative learning examined in Aplysia: habituation, dishabituation and sensitization. Eric Kandel and colleagues were the first to demonstrate that Aplysia californica is capable of displaying both habituation and dishabituation.

Habituation in Aplysia californica is when a stimulus is repeatedly presented to an animal and there is a progressive decrease in response to that particular stimulus.

Dishabituation in Aplysia californica is when the animal is presented to another novel stimulus and a partial or complete restoration of a habituated response occurs.

Sensitization in Aplysia californica is the increase of a response due to the presentation of a novel, often noxious, stimulus.

A two-component reflex is triggered when a weak or moderate stimulus is applied to the siphon or the mantle shelf. These two components consist of two reflex acts, the siphon-withdrawal reflex and the gill-withdrawal reflex. Together they form a reflex pattern with short latency which protects the animals gill and siphon to potentially threatening stimuli.

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