A computational study of the role of spike broadening in synaptic facilitation of Hermissenda.
Pavlovian conditioning in Hermissenda produces a decrease in voltage-dependent (I(K,A) and I(Ca)) and Ca2+-dependent (I(K,Ca)) currents, and an increase in the action potential (AP) duration in type B-photoreceptors. In addition, synaptic connections between B and A photoreceptors and B photoreceptor and type I interneurons are facilitated. The increase in AP duration, produced by decreasing one or more K+ currents, may account for synaptic facilitation. The present study examined this issue by using a mathematical model of the B-photoreceptor and the neurosimulator SNNAP. In the model, decreasing g(K,A) by 70% increased the duration of the AP in the terminal by 41% and Ca2+ influx by 30%. However, if the decrease in g(K,A) was combined with a decrease in g(Ca), similar to what has been reported experimentally, the Ca2+ influx decreased by 54%. Therefore, the concomitant change in I(Ca) counter-acted the broadening-induced increase in Ca2+ influx in the synaptic terminal. This result suggests that a spike-duration independent process must contribute to the synaptic facilitation observed following Pavlovian conditioning.
Flynn
Mark
M
Department of Neurobiology and Anatomy, The University of Texas-Houston Medical School, P.O. Box 20708, Houston, TX 77225, USA.
Cai
Yidao
Y
Baxter
Douglas A
DA
Crow
Terry
T
D000200:Action Potentials; D000818:Animals; D001369:Axons / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism*; D003214:Conditioning, Classical / Q000502:physiology; D005071:Evoked Potentials / Q000502:physiology; D007395:Interneurons / Q000502:physiology; D008433:Mathematics; D008959:Models, Neurological; D008962:Models, Theoretical; D008974:Mollusca; D018408:Patch-Clamp Techniques; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000648:ultrastructure; D015221:Potassium Channels / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000502:physiology*; D009435:Synaptic Transmission
D015220:Calcium Channels; D015221:Potassium Channels