The Journal of Neuroscience, April 1, 1998, 18(7):2673-2684
Direction Tuning of Individual Retinal Inputs to the Turtle
Accessory Optic System
Naoki
Kogo1,
Doris
McGartland
Rubio2, and
Michael
Ariel1
Departments of 1 Anatomy and Neurobiology and
2 Research Methodology, Saint Louis
University, Saint Louis, Missouri 63104
Neurons in turtle accessory optic system [basal optic nucleus
(BON)] were recorded to study convergence of retinal afferents, using
whole-cell patch electrodes in a reduced in vitro
brainstem preparation with the eyes attached. BON cells primarily
exhibit EPSPs from a contralateral retinal ganglion cell input and
generate an output of action potentials. Visual responses were evoked
by different directions of either full-field or local moving patterns. Direction tuning of action potentials was compared with that of EPSPs
detected by passing the membrane voltage through an AC amplifier and
window discriminator. This rough measure of retinal input indicated
that the direction tuning of the full-field excitatory input from the
retina matched that of the spike output for the same BON cell.
Using local patterns within the receptive fields of the BON cells, it
was estimated that one to four adjacent retinal inputs were being
stimulated. The direction tuning of these inputs had preferred
directions that were similar to that of the full-field spike output of
the cell, irrespective of where the small window was placed within the
receptive field. Because more than one retinal input may have been
stimulated by the small stimulus window, subsets of those EPSPs that
may represent responses of a single retinal afferent were identified
based on their amplitude and rise time. Again, the preferred direction
of those putative single retinal afferents matched the direction tuning
of the spike output of the BON cell. These findings are discussed in
terms of the formation of the retinal slip signal by the BON.
Key words:
EPSPs; basal optic nucleus; brainstem; synaptic
convergence; direction sensitivity; retinal slip
Copyright © 1998 Society for Neuroscience 0270-6474/98/1872673-12$05.00/0
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