Binocular competition does not regulate retinogeniculate arbor size in fetal monkey.

Area of Science:

• Neuroscience
• Developmental Biology
• Ophthalmology

Background:

• Binocular interactions shape axonal arbors in the retinogeniculate pathway.
• Previous studies suggested eye interactions regulate retinal projections in fetal monkeys, but structural evidence was lacking.

Purpose of the Study:

• To investigate if prenatal enucleation affects the structural refinement of retinal arbors in macaque monkeys.
• To determine if the expanded projection from the remaining eye is due to structural changes in retinal fibers.

Main Methods:

• Quantified morphologic properties (branch points, arborization length, side branches) of individual retinal fibers in prenatal enucleated and normal macaque monkeys.
• Used DiI crystal labeling of optic tract fibers and visualized via confocal microscopy.
• Analyzed fibers innervating both magnocellular and parvocellular segments of the dorsal lateral geniculate nucleus.

Main Results:

• No significant differences in branch points, arborization length, or side branches were found between prenatal enucleates and normal monkeys.
• Retinal arbors from the remaining eye showed wide distribution in the dorsal lateral geniculate nucleus, occupying territories of the enucleated eye.
• These findings suggest structural integrity of individual retinal arbors is maintained despite prenatal enucleation.

Conclusions:

• The expanded projection of the remaining eye is likely due to the survival of retinal fibers that would normally be eliminated by ganglion cell death.
• Prenatal enucleation does not induce structural modifications in the axonal arbors of the remaining retinal fibers.
• This study clarifies the mechanisms behind compensatory axonal arborization in the developing visual system.