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The Journal of Neuroscience, September 3, 2003, 23(22):8020-8028

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Comparison of Hermissenda Type A and Type B Photoreceptors: Response to Light as a Function of Intensity and Duration

Ji Ling Mo and Kim T. Blackwell

School of Computational Sciences and Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia 22030

Hermissenda crassicornis is an invertebrate model used to study classical conditioning using light as the conditioned stimulus. The memory of the association is stored in type B photoreceptors, the output of which depends on interactions with type A photoreceptors. To understand the effect of classical conditioning on the output of type B photoreceptors in response to light, we measured the effect of light duration and intensity on membrane potential in both photoreceptor types of Hermissenda. The results show that, independent of light stimulus, the afterhyperpolarization is significantly greater in type A than in type B photoreceptors. In response to light, the generator potential (GP) rises linearly with an increase in either intensity or duration for both type A and type B photoreceptors. However, the difference between type A and type B photoreceptors depends on the time after light onset; the increase in peak GP with intensity is steeper in type A than type B, but by 14 sec after light onset, membrane potential is greater in type B than type A photoreceptors. Similarly, firing frequency increases with intensity and duration in both photoreceptor types but with a difference that is time dependent. During the first second after light onset, type A photoreceptors have a significantly higher firing frequency than type B photoreceptors; after this time, firing frequency is higher in type B than type A photoreceptors. Although membrane potential is correlated with firing frequency, this correlation is much lower in type A than type B photoreceptors, suggesting that some other conductance influences firing frequency in type A photoreceptors.

Key words: associative learning; photoreceptors; phototransduction; classical conditioning; generator potential; AHP

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Received Nov 26, 2002; revised July 10, 2003; accepted July 14, 2003.

This article has been cited by other articles:

				C. R. Butson and G. A. Clark Random Noise Paradoxically Improves Light-Intensity Encoding in Hermissenda Photoreceptor Network J Neurophysiol, January 1, 2008; 99(1): 146 - 154. [Abstract] [Full Text] [PDF]

				K. T. Blackwell Ionic Currents Underlying Difference in Light Response Between Type A and Type B Photoreceptors J Neurophysiol, May 1, 2006; 95(5): 3060 - 3072. [Abstract] [Full Text] [PDF]

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