The Journal of Neuroscience, August 15, 2001, 21(16):6440-6446
Chattering and Differential Signal Processing in Identified
Motion-Sensitive Neurons of Parallel Visual Pathways in the Chick
Tectum
Harald
Luksch1,
Harvey
J.
Karten2,
David
Kleinfeld3, and
Ralf
Wessel4
1 Institute of Biology II, Rheinisch-Westfälische
Technische Hochschule Aachen, 52074 Aachen, Germany, Departments
of 2 Neuroscience and 3 Physics, University of
California at San Diego, La Jolla, California 92093, and
4 Department of Physics, Washington University, St. Louis,
Missouri 63130
At least three identified cell types in the stratum griseum
centrale (SGC) of the chick optic tectum mediate separate pathways from
the retina to different subdivisions of the thalamic nucleus rotundus.
Two of these, SGC type I and type II, constitute the major direct
inputs to rotundal subdivisions that process various aspects of visual
information, e.g., motion and luminance changes. Here, we examined the
responses of these cell types to somatic current injection and synaptic
input. We used a brain slice preparation of the chick tectum and
applied whole-cell patch recordings, restricted electrical stimulation
of dendritic endings, and subsequent labeling with biocytin. Type I
neurons responded with regular sequences of bursts ("chattering")
to depolarizing current injection. Electrical stimulation of retinal
afferents evoked a sharp-onset EPSP/burst response that was blocked
with CNQX. The sharp-onset EPSP/burst response to synaptic stimulation
persisted when the soma was hyperpolarized, thus suggesting the
presence of dendritic spike generation. In contrast, the type II
neurons responded to depolarizing current injection solely with an
irregular sequence of individual spikes. Electrical stimulation of
retinal afferents led to slow and long-lasting EPSPs that gave rise to
one or several action potentials. In conclusion, the morphological
distinct SGC type I and II neurons also have different response
properties to retinal inputs. This difference is likely to have
functional significance for the differential processing of visual
information in the separate pathways from the retina to different
subdivisions of the thalamic nucleus rotundus.
Key words:
visual system; cellular physiology; optic tectum; whole-cell patch recording; synaptic stimulation; dendrites; motion
Copyright © 2001 Society for Neuroscience 0270-6474/01/21166440-07$05.00/0