Currents contributing to decision making in neurons B31/B32 of Aplysia

Itay Hurwitz, Amit Ophir, Alon Korngreen, John Koester, Abraham J. Susswein

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Biophysical properties of neurons contributing to the ability of an animal to decide whether or not to respond were examined. B31/B32, two pairs of bilaterally symmetrical Aplysia neurons, are major participants in deciding to initiate a buccal motor program, the neural correlate of a consummatory feeding response. B31/B32 respond to an adequate stimulus after a delay, during which time additional stimuli influence the decision to respond. B31/B32 then respond with a ramp depolarization followed by a sustained soma depolarization and axon spiking that is the expression of a commitment to respond to food. Four currents contributing to decision making in B31/B32 were characterized, and their functional effects were determined, in current- and voltage-clamp experiments and with simulations. Inward currents arising from slow muscarinic transmission were characterized. These currents contribute to the B31/B32 depolarization. Their slow activation kinetics contribute to the delay preceding B31/B32 activity. After the delay, inward currents affect B31/B32 in the context of two endogenous inactivating outward currents: a delayed rectifier K+ current (IK-V) and an A-type K+ current (IK-A), as well as a high-threshold noninactivating outward current (I maintained). Hodgkin-Huxley kinetic analyses were performed on the outward currents. Simulations using equations from these analyses showed that IK-A and IK-A slow the ramp depolarization preceding the sustained depolarization. The three outward currents contribute to braking the B31/B32 depolarization and keeping the sustained depolarization at a constant voltage. The currents identified are sufficient to explain the properties of B31/B32 that play a role in generating the decision to feed.

Original languageEnglish
Pages (from-to)814-830
Number of pages17
JournalJournal of Neurophysiology
Issue number2
StatePublished - Feb 2008


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