Dendritic patterns and axonal projections of ocular dominance column neurons in area V1 of strabismic and normal macaque

Purpose. To determine: a) the shape of neurons in striate cortex of primates who have normal binocular vision and b) to compare their shape to that of neurons in primates who have infantile strabismus. Methods. Behavioral testing was performed to document that two strabismic macaque monkeys had the constellation of sensory and ocular motor deficits that characterize strabismus with onset in infancy. A double-labelling experiment was then carried out on the two strabismic monkeys and a normal monkey using the neuronal tracer BDA and the ODC label cytochrome oxidase. The axons and dendrites of individual neurons, the ODCs within which they resided, and the neighboring ODCs to which they connected were analyzed in tangential sections through layers 2, 3 and 4B. Results. Axonal projections from neurons were distributed as ellipses surrounding BDA injection sites in both normal and strabismic macaque. The long axis of the ellipses was oriented roughly orthogonal (± 30°)to rows of right and left eye ODCs. The ellipses had short/long axis ratios ∼0.50. Dendritic patterns in normal and strabismic macaque were less elliptical, with short/long axis ratios ∼0.75. The long axis of the dendritic ellipses was oriented randomly in normal primate. However, in one injection in a strabismic macaque the axes of ∼80% of dendritic ellipses were oriented parallel to the axonal projections, running orthogonal to the local boundaries of right and left eye ODC rows. No striking foveopetal/fugal biases were seen. Conclusion. The overall shape of axonal projections and dendritic patterns within V1 is similar in normal and strabismic primate. The distributions are elliptical, and for axons, run roughly orthogonal to rows of ODCs. The elliptical distributions do not conform to known rules of retinotopic anisotropy.