Neuroscience 2000 Abstract
| Presentation Number: | 636.16 |
|---|---|
| Abstract Title: | Dendritic excitability sets the limit of speed sensitivity in motion sensitive neurons of chick tectum. |
| Authors: |
Wessel, R.*1
; Karten, H. J.2
; Kleinfeld, D.1
; Luksch, H.3
1Department of Physics, University of California at San Diego, La Jolla, CA 2Neuroscience, University of California at San Diego, La Jolla, CA 3Inst. Biology II, Aachen, Germany |
| Primary Theme and Topics | F. Sensory Systems |
| Secondary Theme and Topics | C. Excitable Membranes and Synaptic Transmission<br />- 31. Excitatory postsynaptic mechanisms |
| Session: |
636. Subcortical visual pathways: other Poster |
| Presentation Time: | Wednesday, November 8, 2000 11:00 AM-12:00 PM |
| Location: | Hall G-J |
| Keywords: | Vision, Dendrite, Channel, Tectum |
Neurons in the deep layers of the avian optic tectum (SGC) respond preferentially to small moving objects with a limit of speed sensitivity beyond 30 deg/s (Troje and Frost, SFN Abstract 24:642.9, 1998). We studied the circuit comprised of anatomically defined SGC type I cells and their presynaptic small retinal ganglion cells with respect to their ability for motion detection using a slice preparation. Type I SGC cells responded with one or multiple bursts (chattering) to depolarizing somatic current injection. Electrical stimulation of the retinal ganglion cell axons caused an EPSP/spike response in the SGC I soma with a sharp onset. Direct electrical stimulation of the SGC I dendrites caused a response in the soma similar in shape to synaptic stimulation. The sharp onset response to dendritic stimulation persisted when the soma was hyperpolarized below -100 mV, but was abolished in saline containing 1 μM TTX. The duration of the sharp onset response increased when Ca2+ in the saline was replaced with Ba2+. When two separate groups of retinal ganglion cell axons were stimulated electrically at different times, the second pulse caused a full response for an interval down to 23 ± 12 ms, but the response was completely abolished for intervals below this value. If the stimulation of a bottlebrush dendritic ending caused a graded depolarization (EPSP) in the soma with somatic spike generation, then we would expect that stimulating more bottlebrush dendritic endings would generate a larger EPSP and thus a larger firing rate. However, as a result of voltage gated dendritic conductances, the response to simultaneous, i.e., interval of less than 23 ms, stimulation at two different locations is similar to the response to one pulse stimulation at one location. Together with the anatomical organization of the retino-tectal pathway, this result predicts the limit of speed sensitivity to approximately 50 deg/s, a value close to the in-vivo observation.
Supported by DFG Lu 622 2-1 to H.L., and NSF IBN-9604799 to R.W..
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2000 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2000. Online.
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