Measurement of carotenoids in human and monkey retinas.
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Animals↗
Biomedical subjects
D M Snodderly
Publications and source records attributed to D M Snodderly.
Neural-vascular relationships in central retina of macaque monkeys (Macaca fascicularis).
The relationship of the vasculature to the neuronal layers was studied in whole-mounts and in sections of macaque retinas. Like other central nervous structures, primate retinas have local variations in vascularity that reflect local variations in metabolism, rather than simply tissue thickness or volume. A special feature of the retina is a dense vascular plexus in the nerve fiber layer, which is unmyelinated and hence must generate a substantial metabolic demand for ion pumping. Much of the retinal vasculature is laminated and located at specific layer boundaries. Throughout the central retina, two planes of capillaries bracket the inner nuclear layer to form a sclerad capillary network. In some regions, especially near the fovea, a second, more vitread network brackets the ganglion cell layer with another pair of capillary planes. Wherever the nerve fiber layer is thick, the vitread network becomes less planar and is multilayered. When surrounded by nerve fibers, capillaries tend to orient parallel to the fibers; when adjacent to ganglion cell bodies, the capillaries are less systematically oriented. At the border between the nerve fiber layer and the ganglion cell layer, rows of ganglion cells often interdigitate with nerve fiber bundles, resulting in local perturbations of capillary orientation. The volume of the sclerad capillary network is relatively constant at different locations, but the volume of the vitread network increases dramatically where the nerve fiber layer is thick. As a result, the vascularity of the retina is greatest in the peripapillary region near the optic disk, even though the total thickness of the peripapillary retina is comparable to the retinal thickness near the foveal crest. As many as 60-70% of the photons passing through the retina in the peripapillary region will encounter one or more capillaries before reaching a photoreceptor. Median capillary diameter increases with retinal depth from 4.5-4.7 microns in the nerve fiber layer to 5.0 microns at the sclerad border of the inner nuclear layer. Capillary diameter in the nerve fiber layer also increases near the optic disk.
Animals↗
Biological control of primate macular pigment. Biochemical and densitometric studies.
The amounts of zeaxanthin (Z) and lutein (L), the carotenoids constituting the primate macular pigment, were measured in the central retinas of monkeys (Saimiri sciureus and Macaca fascicularis). Two independent methods--reverse-phase high-performance liquid chromatography (HPLC) and microdensitometry--were used for analysis of the same set of retinas. Most of the measurements were made on retinas that had been fixed by glutaraldehyde-paraformaldehyde perfusion of the animal. Control experiments showed that this fixation did not interfere with the quantitative extraction and analysis of the carotenoids. The amount of macular pigment calculated from microdensitometry of the foveal region was proportional to the amount of pigment assayed by HPLC of the same retinal area, demonstrating that either method can be used reliably to rank the carotenoid content of aldehyde-fixed foveas. The optical density of pigment in the axial direction through the retina was higher than would be predicted if the pigment were randomly oriented. This is consistent with the idea that the nonrandom orientation of the dichroic macular pigment molecules found in previous studies contributes to increased optical filtering of the retinal image. Comparisons of the amounts of Z and L between the left and right eyes of the same monkey, within 1 mm of the foveal center, always showed excellent agreement (averaging a 5% difference for Z and 11% difference for L), whereas differences among individual monkeys were very large (up to fourfold for Z). These results indicate that the uptake and assimilation of the macular carotenoids are biologically regulated by selective mechanisms in primate retinas.
Animals↗
Distribution of individual macular pigment carotenoids in central retina of macaque and squirrel monkeys.
The spatial distribution of lutein (L) and zeaxanthin (Z), the structural isomers composing the macular pigment, was studied in the retinas of macaque monkeys (Macaca fascicularis) and squirrel monkeys (Saimiri sciureus). Spatial profiles of macular pigment optical density were obtained from retinal whole mounts. Then concentric annuli were microdissected from the fovea and adjacent regions of the same retinas. Each retinal segment was analyzed for carotenoids by high-performance liquid chromatography. Both L and Z reached their highest concentrations at the center of the fovea and declined monotonically with eccentricity for both primate species. This is inconsistent with a preferential association of L with rods. Macaque monkeys have a consistent pattern of more Z than L at the foveal center, like humans. Z declines more rapidly than L with eccentricity, so that L becomes dominant in the periphery. Squirrel monkeys (all male) showed striking individual differences. Some had more Z than L at the foveal center like macaques, but four of six had the reverse pattern, with more L than Z throughout the central retina. Individual differences among squirrel monkeys may be linked to their color vision polymorphisms. This suggests that a particular Z/L ratio in primate retinas may be associated with a specific cone phenotype, just as particular carotenoids are associated with specific cone types in vertebrates with cone oil droplets.
Animals↗
Retinal vasculature of the fovea of the squirrel monkey, Saimiri sciureus: three-dimensional architecture, visual screening, and relationships to the neuronal layers.
The retinal vasculature of the fovea of squirrel monkeys was studied in retinal whole mounts and in sections of the same retinas. At the center of the fovea there is an approximately circular avascular zone surrounded by a set of terminal capillaries in the inner nuclear layer. Within the foveal depression, four capillary planes that bear a precise relationship to the neuronal organization appear in a specific sequence with increasing eccentricity. The first plane to be established is the dominant, most voluminous one, located closest to the photoreceptors at the deep (sclerad) border of the inner nuclear layer. A second major plane appears next at the sclerad border of the ganglion cell layer. The two remaining, less voluminous planes occur at a slightly greater eccentricity. One of these, located at the shallow (vitread) border of the inner nuclear layer, often drains into the ganglion cell plane. The fourth plane is initially situated at the vitread border of the ganglion cell layer; with increasing eccentricity it moves into the nerve fiber layer. These capillaries are oriented like the nerve fibers with which they travel. Both the shallow inner nuclear and nerve fiber planes of capillaries show marked regional variations. The capillary planes are within or adjacent to regions of high cytochrome oxidase activity. The retinal vascular network is an unrecognized contributor to the optical filtering properties of the eye. In much of the central retina, a photon has a 40-50% chance of encountering one or more capillaries before it reaches a photoreceptor.
Animals↗
Structural and geometrical isomers of carotenoids in human plasma.
We have quantitatively analyzed human plasma for the following carotenoids: all-trans-lutein, all-trans-zeaxanthin, alpha-cryptoxanthin, beta-cryptoxanthin, the sum of all-trans-lycopene and its cis isomers, alpha-carotene and beta-carotene. In addition, we have tentatively identified and quantified 13-cis-lutein and 13-cis-zeaxanthin in human plasma. The latter two cis isomers are also apparent in samples of two common food items, spinach and corn meal. We have analyzed the ratios of all of the members of the beta, beta family of carotenoids (zeaxanthin, beta-cryptoxanthin and beta-carotene) to their corresponding beta, epsilon structural isomers (lutein, alpha-cryptoxanthin and alpha-carotene) in human plasma. There are marked differences in these ratios, with beta-carotene and beta-cryptoxanthin predominating in the carotene and monohydroxy-xanthophyll classes and lutein predominating in the dihydroxy-xanthophyll class. These differences could be attributable to dietary intake or to specific mechanisms in the way humans absorb and utilize these compounds.
Adult↗
Plasma carotenoids of monkeys (Macaca fascicularis and Saimiri sciureus) fed a nonpurified diet.
The major carotenoid pigments in the plasma and in a common, nonpurified diet of two species of monkeys (Macaca fascicularis and Saimiri sciureus) were measured. The xanthophylls, lutein, zeaxanthin, alpha-cryptoxanthin, and beta-cryptoxanthin, were the principal carotenoids in both the diet and the plasma. Lutein and zeaxanthin were abundant in the all-trans, the 9-cis, and the 13-cis geometrical isomers in the diet, but the 9-cis form was rarely measurable in plasma. However, the 13-cis isomers of lutein and zeaxanthin were found in higher proportions in plasma than in the diet. For both the monohydroxy-xanthophylls, alpha-cryptoxanthin and beta-cryptoxanthin, and the dihydroxy-xanthophylls, lutein and zeaxanthin, the beta, beta structural isomer (beta-cryptoxanthin or zeaxanthin) is less abundant than the beta, epsilon isomer in plasma than in the diet. These results indicate substantial specificity in the absorption or retention of closely related carotenoid isomers in primates. The proportions of different geometrical isomers of lutein and zeaxanthin in the plasma of both species of monkeys were nearly identical and were similar to human values. The hydrocarbon carotenoids, alpha-carotene, beta-carotene and lycopene were usually undetectable in monkey plasma. The monkeys appear to be like humans in their utilization of lutein and zeaxanthin but distinctly different in some other aspects of carotenoid utilization.
Animal Feed↗
Intensity coding in primate visual system.
The pupil reflex and the discharge of LGN cells of the awake macaque were measured under stimulus conditions that yielded evidence for wide-range intensity coding in human psychophysical experiments. Ganzfeld flashes of white light were delivered under dark-adapted conditions to the surgically immobilized eye of the monkey while the other eye was observed in the infrared. Three-sec flashes elicited a consensual pupil reflex that was graded from -8 to 0 log Lamberts (L), indicating that the optic nerve fibers are capable of coding at least an 8 log-unit range of light intensity. In the physiological experiments, shorter flashes (0.1-0.5 sec) but otherwise identical conditions elicited monotonically graded responses from one type of LGN cell over the photopic range of -5 to 0 log L. Responses from other types of LGN cells were also graded over wide ranges but had different thresholds and, in some cases, nonmonotonic intensity-response functions. Latency of the excitatory LGN responses decreased with increasing intensity according to a power function with slope of-0.08. The pupil reflex and the LGN cell excitatory responses approximate power functions of light intensity with exponents of 0.22 and 0.14-0.29 respectively. The range of intensity coding found for single LGN cells is the widest yet reported for diffuse stimuli.
Animals↗
Evaluation of a surgical method for immobilizing the eye of an alert monkey.
One eye of a macaque monkey was immobilized by severing the third, fourth, and sixth cranial nerves. The residual movements of the operated eye were measured by repeatedly mapping the position of a visual receptive field. Movements of several degrees were caused by contraction of the orbital musculature during the closure blink. The amount of movement was dramatically reduced by paralysis of the superficial orbital muscles with a local anesthetic. Side effects of surgical immobilization include increased risk of corneal clouding and eye infection. In one monkey intraocular pressure was lowered for several weeks. Regeneration of the severed nerves causes return of some voluntary movement of the eye, which is not coordinated with movements of the unoperated eye even after nine months postoperative survival. The suitability of this approach for studies on the visual nervous system is discussed.
Abducens Nerve↗
Responses of macaque lateral geniculate cells to luminance and color figures.
The spatial tuning of macaque lateral geniculate neurones was compared for luminance-based and color-based lines. Lines of various widths were flashed on and centered on the cell's receptive field, and the size of the increase or decrease in firing was noted. Luminance-based lines consisted of 0.7 log unit increments or decrements. Color-based lines consisted of shifts in wavelength with no change in luminance, e.g., from a red field to a green line on a red field. The cell fired most to intermediate widths of luminance-based lines, but to the widest pure-color lines.
Animals↗
Brightness contrast effects in monkey lateral geniculate nucleus.
Brightness contrast effects shown by single cells in the macaque's lateral geniculate nucleus were studied with black and white lines of various widths, consisting of either: (1) "simultaneous contrast" stimuli in which the line was produced by luminance changes in the flanking areas or (2) "successive contrast" stimuli in which the line itself changed in luminance. Line widths that gave optimal responses and response magnitudes themselves were similar for the two types of stimulus, except for the widest lines used (2 degrees). Thus, simultaneous brightness contrast is a primary determinant of the response of primate LGN cells but only within 2 degrees of the center of the receptive field. Neural processing up to this level cannot therefore explain the long distance effects of simultaneous brightness contrast in human perception.
Animals↗