The Naso-Temporal Division of the Monkey’s Retina JONATHAN STONE. JONATHAN LEICESTER AND S. MURRAY SHERMAN* Department of Physiology, John Curtin School of Medical Research, Australian National Untversity, Canberra ABSTRACT By sectioning one optic tract in each of four monkeys, and studying the distribution within each pair of retinas of the ganglion cells which remained after the affected ganglion cells had undergone retrograde degenera- tion, a description was obtained of the areas of a retina from which ganglion cells project to the ipsilateral and contralateral sides of the brain. Confirming previous work, ganglion cells in temporal retina were observed to project to the ipsilateral side. and cells in nasal retina to the contralateral side. It was noted, however, that ipsi- and contralaterally projecting areas of retina overlap along a vertically-oriented median strip, which is about 1 wide, and is centred on the fovea. Within this strip ipsi- and contralaterally projecting cells intermingle. Some functional implications of this result are discussed. Each retina of the monkey projects to removed by suction (fig. 1) allowing visu- both ipsi- and contralateral sides of the alization of the optic nerve, chiasm and brain (Polyak, ’57; Kupfer, ’63; van Buren, tract. A hook was passed under the tract ’63). Specifically, the ganglion cells located and pulled upwards, dividing it. Surgery in the area of retina nasal to the fovea send was performed in adult or young adult their axons to the contralateral optic tract, (2-year-old) monkeys. and cells located temporal to the fovea Following survival times of 6 to 12 send their axons to the ipsilateral optic months the monkeys were anaesthetized tract. This study is an attempt to define and perfused through the heart with 0.9% the border between ipsi- and contralater- saline followed by 10% formol-saline. Two ally projecting areas of retina. Evidence is animals were, before perfusion, placed in presented that the borders of these two a stereotaxic apparatus, paralyzed by in- areas run vertically across the fovea and travenous injection of gallamine triethio- that the two areas overlap to a small but dide (Flaxedil) and artificially respired. significant degree. As in the cat (Stone, Their fundi were photographed using a ’661, a median strip of ouerlap can be de- Zeiss fundus camera, and the optic disc scribed within which ganglion cells which and fovea of each retina were projected project to ipsi- and contralateral optic onto a frontal 1 metre tangent screen, tracts intermingle. The strip runs vertically using techniques described previously in the retina, passing across the fovea. In (Bishop, Henry and Smith, ’71). Following the monkeys used (Macacca irus) its width perfusion the eyes of each animal were ranged from 150-250 pm. This corre- enucleated and the brain removed. The sponds to approximately 1 O of visual angle. eyes of the two animals whose fundi had been photographed were placed in saline METHODS and photographed with eyeball gently in- The experimental approach was basic- flated. These photographs allowed estima- ally that used for the cat (Stone, ’66 >. Four tion of the radii of curvature of the cornea monkeys (Macncca irus) were used. In and eyeball and of the length of the eye- each one optic tract was sectioned by ball. The opened fundus of each of these aseptic surgery under pentobarbitone an- 1 Present address: Suite 20A, “Murray Place,” 127 aesthesia. The approach was through the Burwood Road, Burwood, 2134 N.S.W. temporal bone, with the animal lying on 2 Present address: Department of Physiology, School of Medicine, University of Virginia, Charlottesville, its side. The tip of the temporal lobe was Virginia. J. COMP NEUR,150 333-348. 333 3 34 J. STONE, J. LEICESTER AND S. M. SHERMAN Fig. 1 Ventral surface of brain of tract-sectioned monkey. The dotted line marks the surgical approach, through the right temporal lobe. The arrow points to the peripheral stump of the right optic tract. four eyes was subsequently photographed the peripheral pieces were also mounted (fig. 10). and stained. The staining technique was a Methylene blue-stained whole mounts of modification of that described previously the retinas were prepared as follows. Each (Stone, '65, '66) for retinal whole mounts. eye was cut around so that the anterior It is somewhat simpler than the earlier part (lens, ciliary body, iris and cornea) techniques, and has proved entirely re- was separated from the posterior, fundal liable. The preparations have now lasted part. The anterior part was discarded and two years without deterioration, and ap- the posterior half placed in 10% formol- pear likely to last indefinitely. Each piece saline for two days. The posterior half of of retina was dissected free of the choroid. each eye was then cut into appropriate In the central piece the optic nerve was pieces. Particular attention was given to cut with the tip of a scalpel blade passed the central piece, which was always cut between retina and choroid. Each piece of to include the optic disc and the fovea, but retina was cleaned as completely as pos- NASO-TEMPORAL DIVISION OF MONKEY RETINA 335 sible of pieces of choroid clinging to its by placing for three minutes in each of outer surface and of the vitreous humour the following solutions : 90% alcohol, attached to its inner surface. The piece was absolute alcohol (2 changes) and xylol then laid, fibre layer uppermost, on a (2 changes). gelatinized glass slide and processed 5. Depex was used for mounting. through the follow.ing steps : This sequence is equally effective for 1. Each preparation (i.e., each piece of staining cat and rabbit retina; we com- retina spread on a gelatinized glass slide) monly processed a piece of cat retina im- was placed in hot (60°C) formalin vapour mediately before the monkey retinas, to for two hours, so that the retina stuck check for defective solutions. firmly on the slide. The remaining steps were done at room temperature. RESULTS 2. The preparation was washed briefly Optic tract sections in distilled water, and then stained by lay- ing the retina “face-down’’ over a small Figure 1 shows the appearance of the Petrie dish brimming with 0.2% methylene ventral surface o€ the brain of one tract- blue. This face-down contact of retina with sectioned subject. The arrow follows the stain minimized the precipitation of par- surgical approach through the temporal ticles of stain onto the retinal surface. lobe and points to the stump of the Three minutes staining time at room tem- severed optic tract. Essentially identical perature reliably gave an appropriate depth controls of the tract section were obtained of stain, but this can be monitored under in the other animals. a microscope. 3. Excess stain was wiped off and the Normal retina stain was fixed in 5% ammonium molyb- In the normal monkey retina, seen in a date (3 minutes). whole mount preparation (fig. 2), the 4. The preparation was washed in dis- foveola is a circular area about 500 pm in tilled water, then dehydrated and cleared diameter, which is surrounded by densely Fig. 2 Foveal area of the right retina of a normal Macncca irus seen in a methylene blue- stained whole mount. The pale circle in the centre of the field is the foveola, i.e. the area free of ganglion and bipolar cells. The ganglion cells form a continuous layer, several deep, surrounding the foveola. The paths of axon bundles and of small blood vessels are apparent as faint streaks and loops. The arrow points to the optic disc. 336 J. STONE, J. LEICESTER AND S. M. SHERMAN packed ganglion cells (see also fig. 10 in Figure 5 shows, at still higher power, Stone, ’65). Pale streaks are apparent areas of the ganglion cell layer at the running across the surfacc of the ganglion junction of normal and degenerated areas. cell layer and revealing the pattern of Figure 5A shows an area at the upper fibre bundles around the foveola (cf. fig. margin of the foveola (labelled F) of the 162 in Poliak, ’57). The streaks mark the right retina shown in figures 3A and 4A. paths of fibre bundles. They appear be- Figure 5B shows an area at the lower cause the fibre bundles limit access of the margin of the foveola of the left retina stain to the underlying ganglion cells. The shown in figures 3B and 4B. In each of more tortuous pale lines are the paths of figures 5A and 5B a sharp gradient in superficial blood vessels. ganglion cell density is apparent. Many cell bodies are nevertheless apparent in areas The retinal distributions of ipsi- and lacking ganglion cells; their significance contralaterally projecting ganglion is considered further below. cells: basic observations Figures 6 and 7 show the whole mounts Confirming previous observations in obtained from two other animals. In each monkey and man (Gartner, ’51; Kupfer, eye the line dividing normal and degener- ’63; van Buren, ’63) ganglion cells in the ated retinal areas could be traced for 2 to temporal half of the retina ipsilateral to the 3 mm above and below the fovea. Because tract section and in the nasal half of the the line is formed by ganglion cells it be- contralateral retina underwent retrograde comes less distinct towards the retinal degeneration. Figure 3A shows at low periphery, as the density of ganglion cells power the appearance of a methylene blue decreases. stained whole mount of the right (ipsilat- The overlap eral) pztina of one monkey, six months In micrographs such as figures 3, 4, following section of the right optic tract. 6 and 7 it is reasonably straightforward to Up on the figure is “up” on the retina and delineate the areas of retina which contain left on the figure is “temporal” on the ipsi- and contralaterally projecting gan- retina; i.e.