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COMPUTATIONAL STUDY OF HERMISSENDA TYPE-B PHOTORECEPTORS. I: IONIC CURRENTS UNDERLYING CHANGES IN EXCITABILITY PRODUCED BY ONE-TRIAL CONDITIONING
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Y. Cai*; D.A. Baxter; T. Crow
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| Dept. Neurobiol. & Anat., Univ. Texas-Houston Med. Sch., Houston, TX, USA |
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One-trial conditioning in Hermissenda consists of pairing light with the application of 5-HT to the exposed but otherwise intact nervous system. Empirical studies have shown that one-trial conditioning increases the excitability of B photoreceptors (i.e., increase in mean firing frequency elicited by extrinsic current). 5-HT modulates several currents in B photoreceptors, including A current (IK,A), Ca2+-activated K+ current (IK,Ca), delayed rectifier (IK,V), sustained Ca2+ current (ICa,S), and a hyperpolarization-activated inward rectifier (IH). To examine the relative contribution of these currents to increased excitability, a computational model was developed. The model incorporates previously identified currents and included 6 compartments (e.g., soma and axonal compartments). To characterize excitability, the soma compartment was hyperpolarized to -60 mV, and average spike frequency elicited by a 6-sec, 0.2-nA depolarizing current was determined. Ionic conductances were altered individually and in combinations within limits observed experimentally. Reducing either IK,A or IK,Ca increased excitability up to 25-40%. Increasing IH increased excitability up to 60%. The effect of reducing IK,V was minimal, suggesting that this current may play a minor role in one-trial conditioning. Decreasing ICa,S decreased excitability up to 70%. However, combining changes in IK,A, IK,Ca, IH and ICa,S increased excitability from 60% to over 100%, which is comparable to that observed experimentally.
Supported by: NIH grant P01 NS38310
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Citation for this abstract:
Cai, Y., D.A. Baxter, and T. Crow (2001). Computational study of Hermissenda type-B photoreceptors. I. Ionic currents underlying changes in excitability produced by one-trial conditioning. Soc. Neurosci. Abstr. 27, 2532.
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