Currents Contributing to Decision Making in Neurons B31/B32 of Aplysia

• Published in: Journal of neurophysiology Vol. 99; no. 2; pp. 814 - 830
• Main Authors: Hurwitz, Itay, Ophir, Amit, Korngreen, Alon, Koester, John, Susswein, Abraham J
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.02.2008
• Subjects: 4-Aminopyridine - pharmacology; Action Potentials - drug effects; Action Potentials - physiology; Action Potentials - radiation effects; Animals; Aplysia; Aplysia - cytology; Behavior, Animal; Computer Simulation; Decision Making - physiology; Dose-Response Relationship, Radiation; Drug Interactions; Electric Conductivity; Electric Stimulation; Locomotion - physiology; Locomotion - radiation effects; Marine; Models, Neurological; Motor Neurons - drug effects; Motor Neurons - physiology; Motor Neurons - radiation effects; Muscarinic Agonists - pharmacology; Oxotremorine - pharmacology; Patch-Clamp Techniques; Potassium Channel Blockers - pharmacology; Sodium Channel Blockers - pharmacology; Tetraethylammonium - pharmacology; Tetrodotoxin - pharmacology; Time Factors
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00972.2007

1 Leslie and Susan Gonda (Goldschmied) Multidisciplinary Brain Research Center, 2 Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel; and 3 Center for Neurobiology and Behavior and 4 Department of Psychiatry, Columbia University, New York, New York Submitted 28 August 2007; accepted in final form 18 November 2007 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 ( I K-V ) and an A-type K + current ( I K-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 I K-V and I K-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. Address for reprint requests and other correspondence: A. J. Susswein, Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, 52 900, Israel (E-mail: avy{at}mail.biu.ac.il )