TRANSFER CHARACTERISTICS OF X-LGN NEURONS IN CATS REARED WITH EARLY DISCORDANT BINOCULAR VISION. Cheng, Han, Yuzo M. Chino, Earl L. Smith III, Junji Hamamoto, Kazuyuki Yoshida. College of Optometry, University of Houston, 4901 Calhoun Blvd, Houston, TX 77204-6052.
APStracts 2:0212N, 1995.
SUMMARY AND CONCLUSIONS
1. The effects of early discordant binocular vision on the functional development of the cat lateral geniculate nucleus (LGN) were investigated by quantitatively comparing responses of individual LGN neurons with their direct retinal inputs. 2. Unilateral convergent strabismus (esotropia) was surgically induced in 11 kittens at the age of 3 weeks. After the animals had reached 9 months of age, extracellular microelectrode recordings were made from individual X-LGN units in laminae A and A 1 of anesthetized and paralyzed cats. Responses were measured for drifting sinusoidal gratings. Within-unit comparisons of LGN action potentials (LGN output) and S potentials (retinal input) were performed to determine the nature of signal transfer in the units driven by the deviating (N=42) or non-deviating eyes (N=29) of strabismic cats. The results were compared to similar data (N=29) obtained from 5 normal control cats. 3. The spatial resolution of many individual LGN units in strabismic cats was abnormally reduced relative to their retinal inputs. These differences were more pronounced in units that received inputs from the nasal retina of the contralateral eye. The resolution loss was closely associated with a dramatic decrease in the strength of the receptive field center mechanism of LGN units relative to their retinal inputs. Moreover, the efficiency of signal transfer for high spatial frequency stimuli, determined by the transfer ratio (response amplitude of LGN action potentials / amplitude of S potentials), was significantly lower in strabismic cats compared to normal controls. 4. In strabismic cats, contrast thresholds for the action potentials of individual LGN units were significantly higher than those determined for the S potentials. In normal cats, the input-output differences in contrast threshold were negligible. The observed contrast sensitivity loss was more pronounced for high spatial frequency stimuli. 5. The speed of signal transfer was significantly decreased in the LGNs of strabismic animals. The visual response latencies of many, but not all, X-LGN cells in the strabismic cats were abnormally long when compared to those in normal control units, while SP latencies were virtually the same for strabismic and normal cats. Abnormal latencies were prevalent in units that exhibited contrast threshold deficits, and were more severe among the units receiving input from the contralateral nasal retina. 6. The deficits in strabismic cats were found in the LGN units innervated by the deviating and non-deviating eyes. However, for the majority of response measures, the units innervated by the deviating eyes showed notably larger deficits. 7. We conclude that the fidelity of signal transfer from the retina to the LGN is significantly reduced in cats reared with discordant binocular visual experience. Thus, the adverse effects of early strabismus are not confined, at least in cats, to the visual cortex. 

Received 2 February 1995; accepted in final form 17 July 1995.
APS Manuscript Number J68-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 August 1995.