Currents contributing to decision making in neurons B31/B32 of Aplysia.
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.
Hurwitz
Itay
I
Leslie and Susan Gonda (Goldschmied) Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan, Israel.
Ophir
Amit
A
Korngreen
Alon
A
Koester
John
J
Susswein
Abraham J
AJ
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D000818:Animals; D001048:Aplysia / Q000166:cytology*; D001522:Behavior, Animal; D003198:Computer Simulation; D003657:Decision Making / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004553:Electric Conductivity; D004558:Electric Stimulation; D008124:Locomotion / Q000502:physiology* / Q000528:radiation effects; D008959:Models, Neurological; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D018721:Muscarinic Agonists / Q000494:pharmacology; D010095:Oxotremorine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D018721:Muscarinic Agonists; D026902:Potassium Channel Blockers; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D010095:Oxotremorine; D019789:Tetraethylammonium; D015761:4-Aminopyridine