ON THE FORMATION OF EYE DOMINANCE STRIPES AND PATCHES IN THE DOUBLY-INNERVATED OPTIC TECTUM OF THE CHICK

By surgically dividing the region of the presumptive optic chiasm in chick embryos on the 3rd day of incubation (.apprx. stage 15), to induce substantial numbers of optic nerve fibers to grow aberrantly into the ipsilateral optic tract. Many of the visual centers that are normally innervated only by fibers from the contralateral retina received fibers from both eyes. The proportion of fibers going to each tectal lobe varied from case to case, but in about one-third of the animals the tectal lobes received approximately equal numbers of fibers from each eye. In animals that survived until embryonic days 17-19 (which is beyond the period of retinal ganglion cell death) labeling of the 2 eyes with WGA-HRP [wheat germ agglutinin-horseradish peroxidase] and [3H]proline respectively, revealed a pattern of sharply defined eye dominance stripes or patches in the stratum griseum et fibrosum superficiale (SGFS) of the optic tectum and in the ventral lateral geniculate nucleus. Less clearly segregated eye dominance zones were seen in the ectomammillary nucleus and the nucleus externus. The size and distribution of the stripes varied depending on the number of fibers projecting from each eye to a given tectal lobe; the minimum size was .apprx. 75 .mu.m, while the maximum was large enough to occupy almost the entire tectal lobe. In animals in which the tectal input from the 2 eyes was roughly equal, the stripes varied in width between 75 .mu.m and about one-third of the surface of the tectal lobe. The orientation of the stripes was consistently orthogonal to the direction of fiber ingrowth from the optic tract. From the earliest stages of optic fiber ingrowth, the fibers from the 2 eyes are completely intermixed in the stratum opticum (SO). On embryonic day 12, shortly after they have begun to penetrate into the SGFS, they are already segregated into stripes, although the stripe borders are very fuzzy. The fibers from the 2 eyes may overlap at this stage. The phase of stripe formation coincides with that of naturally occurring retinal ganglion cell death, and the 2 processes are probably interlinked.