Pupil constriction evoked in vitro by stimulation of the oculomotor nerve in the turtle (Trachemys scripta elegans)

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Pupil constriction evoked in vitro by stimulation of the oculomotor nerve in the turtle (Trachemys scripta elegans)

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dc.contributor.author Dearworth, James R.
dc.contributor.author Brenner, J. E.
dc.contributor.author Blaum, J. F.
dc.contributor.author Littlefield, T. E.
dc.contributor.author Fink, D. A.
dc.contributor.author Romano, J. M.
dc.contributor.author Jones, M. S.
dc.date.accessioned 2010-05-04T14:27:02Z
dc.date.available 2010-05-04T14:27:02Z
dc.date.issued 2009
dc.identifier.citation Dearworth, J. R., et al. "Pupil constriction evoked in vitro by stimulation of the oculomotor nerve in the turtle (Trachemys scripta elegans)." Visual Neuroscience 26 (3): 309-318. en_US
dc.identifier.uri http://hdl.handle.net/10385/663
dc.description.abstract The pond turtle (Trachemys scripta elegans) exhibits a notably sluggish pupillary light reflex (PLR), with pupil constriction developing Over Several minutes following light onset. In the present study, we examined the dynamics of the efferent branch of the reflex in vitro using preparations consisting of either the isolated head or the enucleated eye Stimulation of the oculomotor nerve (nIII) using 100-Hz Current trains resulted in a maximal pupil constriction of 17.4% compared to 27.1% observed in the intact animal in response to light. When current amplitude was systematically increased front 1 to 400 mu A, mean response latency decreased front 64 to 45 ms, but this change was not statistically significant. Hill equations fitted to these responses indicated a current threshold of 3.8 mu A. Stimulation using single pulses evoked a smaller constriction (3.8%) with response latencies and threshold similar to that obtained using train stimulation. The response evoked by postganglionic stimulation of the ciliary nerve using 100-Hz trains was largely indistinguishable from that of train stimulation of nIII. However, application of single-pulse stimulation postganglionically resulted in smaller pupil constriction at all current levels relative to that of nIII stimulation, suggesting that there is amplification of efferent drive at the ganglion. Time constants for constrictions ranged front 88 to 154 ms with relaxations occurring more slowly at 174-361 ms. These values for timing from in vitro are much faster than the time constant 1.66 min obtained for the light response in the intact animal. The rapid dynamics of pupil constriction observed here suggest that the slow PLR of the turtle observed in vivo is not due to limitations of the efferent pathway. Rather, the sluggish response probably results from photoreceptive mechanisms or central processing. en_US
dc.publisher Visual Neuroscience en_US
dc.subject Turtle en_US
dc.subject Pupil en_US
dc.subject Oculomotor en_US
dc.subject In vitro en_US
dc.subject Time constant en_US
dc.title Pupil constriction evoked in vitro by stimulation of the oculomotor nerve in the turtle (Trachemys scripta elegans) en_US
dc.type Article en_US
dc.identifier.doi 10.1017/S0952523809090099

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