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

J Neurophysiol. 2008 Feb;99(2):814-30. doi: 10.1152/jn.00972.2007. Epub 2007 Nov 21.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Action Potentials / radiation effects
  • Animals
  • Aplysia / cytology*
  • Behavior, Animal
  • Computer Simulation
  • Decision Making / physiology*
  • Dose-Response Relationship, Radiation
  • Drug Interactions
  • Electric Conductivity
  • Electric Stimulation*
  • Locomotion / physiology*
  • Locomotion / radiation effects
  • 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

Substances

  • Muscarinic Agonists
  • Potassium Channel Blockers
  • Sodium Channel Blockers
  • Tetrodotoxin
  • Oxotremorine
  • Tetraethylammonium
  • 4-Aminopyridine