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Krasnow Institute > Monday Seminars > Abstracts Cellular Mechanisms of Associative Learning and Memory Avrama Blackwell Hermissenda crassicornis is a small, shell-less marine snail that can be classically conditioned to associate light (the conditioned stimulus) with turbulence (the unconditioned stimulus). The memory of the association is stored in the medial type B pho toreceptor, which both transduces the light stimulus, and receives direct inhibitory synaptic input from the statocyst, which transduces the turbulence. Input resistance is increased and voltage-and calcium-dependent potassium currents are reduced in B cells from animals trained with paired light and turbulence as compared to unpaired controls. These cellular changes are critically dependent on elevation of intracellular calcium, and subsequent activation of protein kinase C. Stimulation of the photore ceptor with light activates a cascade of biochemical reactions which results in (a) initiation of a light-induced current and (b) causes an increase in intracellular calcium concentration. I present a model of the biochemical reactions involved in phototransduction, including calcium dynamics in the photoreceptor. Mechanisms of calcium diffusion, buffering and light activated release from intracellular stores are included in the model. Mo del simulations are used to determine (1) the source of calcium in the soma, and (2) the identity of the ligand of the light- induced current? Planned extension of the model to include the turbulence signals will be used to address the question of why is there no long term reduction in potassium currents consequent to light alone. Either memory storage requires a non-linear combination of light-induced and turbulence induced calcium, or unique second messengers, contributed by light and turbulence are required for memory storage.
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