Studies in the Visual System of the Cat. I. The Retinothalamic Pathway in Normal and Siamese Cats. II. The Vertical Horopter

Author: Cooper, Michael Lee

Year: 1979

Degree: Dissertation (Ph.D.)

Advisor: Pettigrew, John D.

Committee Members: Pettigrew, John D.; Allman, John Morgan; Brockes, Jeremy P.; Konishi, Masakazu; Van Essen, David C.

Option: Neurobiology

DOI: 10.7907/ra6s-ca04

Abstract

The naso-temporal division of the retinothalamic pathway was studied in normal and Siamese cats. One lateral geniculate nucleus (LGN) of each animal was filled with horseradish peroxidase (HRP) in order to visualize the retinothalamic ganglion cells over a wide area of retina. Whole-mounted retinae of normal animals showed clear vertical decussation lines between areas projecting ipsilaterally or contralaterally. The ipsilateral decussation was sharp and passed through the center of the area centralis; the contralateral decussation was somewhat less sharp, with scattered cells extending up to a few degrees into the temporal retina. However, in contrast to the findings in Stone's ('66) tract section material, no significant numbers of HRP-filled cells were found beyond a few degrees into the contralateral temporal retina.

In the Siamese cat retina there was no sharp vertical decussation line between areas sending axons ipsilaterally or contralaterally; rather there was overlap in the temporal retina between cell populations projecting to the two hemispheres. Thus there is no region of exclusive contralateral misprojection. extending 20° temporally from the zero azimuthal meridian; in fact, there is a smooth, gradient-like decrease in the percentage of retinothalamic cells misprojecting contralaterally as one proceeds into the temporal retina. Cell-size measurements indicated that the large (presumably Y-type) ganglion cells are more affected by the Siamese defect than the rest of the retinothalamic population. Use of the anterograde transport of tritiated amino acids confirmed the existence of bilateral projection to the LGN from the central temporal retina of Siamese cats.

The second part of this thesis was an attempt to determine the form of the vertical horopter in the cat and burrowing owl by electro-physiologically mapping the receptive field positions of binocular cortical neurons at various elevations along the zero azLmuthal meridian. Our recordings indicated that, in the alert, unparalyzed cat and owl, midline binocular units in the lower visual field have crossed receptive fields compared to the fixation point, while upper field cells have uncrossed receptive fields. It follows from our data that the vertical horopter is a straight line tilted away from the animal in both species, with the lower field horopter closer to the animal and the upper field horopter farther away.

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