title: Feedback from luminosity horizontal cells mediates depolarizing responses of chromaticity horizontal cells in the Xenopus retina.
abstract: It has been proposed that the depolarizing responses of chromaticity horizontal cells (C-HCs) to red light depend on a feedback signal from luminosity horizontal cells (L-HCs) to short-wavelength-sensitive cones in the retinas of lower vertebrates. In this regard we studied the C-HCs of the Xenopus retina. C-HCs and L-HCs were identified by physiological criteria and then injected with neurobiotin. The retina then was incubated with peanut agglutinin, which stains red-but not blue-sensitive cones. Electron microscopic examination revealed that L-HCs contact all cone classes, whereas C-HCs contact only blue-sensitive cones. Simultaneous recordings from C-HC/L-HC pairs established that when the L-HC was saturated by a steady bright red light, C-HCs alone responded to a superimposed blue stimulus. In response to red test flashes, the C-HC response was delayed by approximately 30 msec with respect to the L-HC response. Isolated HCs of both subtypes were examined by whole-cell patch clamp. Both responded to kainate with sustained inward currents and to quisqualate or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) with desensitizing currents from a negative holding potential; i.e., both have AMPA-type glutamate receptors. gamma-Aminobutyric acid or glycine opened a chloride channel in the L-HC, whereas the C-HC was unresponsive to either inhibitory amino acid. Since glycine has been shown to abolish selectively the depolarizing response of the C-HC, this finding and other pharmacological data strongly implicate the L-HC in the underlying circuit. Moreover, because the C-HC does not respond to gamma-aminobutyric acid, the neurotransmitter of the L-HC, by elimination, a feedback synapse from L-HC to blue cone is the most plausible mechanism for the creation of depolarizing responses in C-HCs.
authors.affiliation: Department of Ophthalmology, New York University Medical Center, NY 10016, USA.
authors.forename: P
authors.initials: P
authors.lastname: Witkovsky
authors.forename: R
authors.initials: R
authors.lastname: Gabriel
authors.forename: D
authors.initials: D
authors.lastname: Krizaj
authors.forename: A
authors.initials: A
authors.lastname: Akopian
mesh_terms: D000818:Animals; D002450:Cell Communication / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology; D005074:Evoked Potentials, Visual / Q000502:physiology* / Q000528:radiation effects; D005246:Feedback; D005998:Glycine / Q000494:pharmacology; D008027:Light; D008297:Male; D009474:Neurons / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques; D017470:Receptors, Glutamate / Q000378:metabolism; D012160:Retina / Q000166:cytology* / Q000502:physiology* / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology; D014981:Xenopus; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D017470:Receptors, Glutamate; D003035:Cobalt; D005680:gamma-Aminobutyric Acid; D005998:Glycine