Biomedical subjects

J Neitz

Publications and source records attributed to J Neitz.

At least 19 recordsLinked to original sources

PubMed2001

Local cellular sources of apolipoprotein E in the human retina and retinal pigmented epithelium: implications for the process of drusen formation.

PURPOSE: The inheritance of specific apolipoprotein E allelles has been linked to atherosclerosis, Alzheimer disease, and, most recently, to the incidence of age-related macular degeneration. Apolipoprotein E is a common component of the extracellular plaques and deposits characteristic of these disorders, including drusen, which are a hallmark of age-related macular degeneration. Accordingly, we assessed the potential biosynthetic contribution of local ocular cell types to the apolipoprotein E found in drusen. METHODS: We measured apolipoprotein E mRNA levels in human donor tissues using a quantitative assay of apolipoprotein E transcription, and we localized apolipoprotein E protein to specific cell types and compartments in the neural retina, retinal pigmented epithelium, and choroid using laser scanning confocal immunofluorescence microscopy. RESULTS: Apolipoprotein E immunoreactivity is associated with photoreceptor outer segments, the retinal ganglion cell layer, the retinal pigmented epithelium basal cytoplasm and basal lamina, and with both collagenous layers of Bruch membrane. Apolipoprotein E appears to be a ubiquitous component of drusen, irrespective of clinical phenotype. It also accumulates in the cytoplasm of a subpopulation of retinal pigmented epithelial cells, many of which overlie or flank drusen. Mean levels of apolipoprotein E mRNA in the adult human retina are 45% and 150% of the levels measured in liver and adult brain, the two most abundant biosynthetic sources of apolipoprotein E. Apolipoprotein E mRNA levels are highest in the inner retina, and lowest in the outer retina where photoreceptors predominate. Significant levels of apolipoprotein E mRNA are also present in the retinal pigmented epithelium/choroid complex and in cultured human retinal pigmented epithelial cells. CONCLUSIONS: Apolipoprotein E protein is strategically located at the same anatomic locus where drusen are situated, and the retinal pigmented epithelium is the most likely local biosynthetic source of apolipoprotein E at that location. Age-related alteration of lipoprotein biosynthesis and/or processing at the level of the retinal pigmented epithelium and/or Bruch membrane may be a significant contributing factor in drusen formation and age-related macular degeneration pathogenesis.

Adult↗

PubMed2001

The uncommon retina of the common house mouse.

Unlike most mammals, most cones in house mouse retina express two opsins, one sensitive to UV-light, and another sensitive to middle-wavelengths. Is the mouse unique, having a single cone type that normally expresses two opsins? Or is the mouse a typical mammal having two cone types, but a species wide mutation results in co-expression of two opsins?

Animals↗

PubMed2001

Photopigment basis for dichromatic color vision in the horse.

Horses, like other ungulates, are active in the day, at dusk, dawn, and night; and, they have eyes designed to have both high sensitivity for vision in dim light and good visual acuity under higher light levels (Walls, 1942). Typically, daytime activity is associated with the presence of multiple cone classes and color-vision capacity (Jacobs, 1993). Previous studies in other ungulates, such as pigs, goats, cows, sheep and deer, have shown that they have two spectrally different cone types, and hence, at least the photopigment basis for dichromatic color vision (Neitz & Jacobs, 1989; Jacobs, Deegan II, Neitz, Murphy, Miller, & Marchinton, 1994; Jacobs, Deegan II, & Neitz, 1998). Here, electroretinogram flicker photometry was used to measure the spectral sensitivities of the cones in the domestic horse (Equus caballus). Two distinct spectral mechanisms were identified and are consistent with the presence of a short-wavelength-sensitive (S) and a middle-to-long-wavelength-sensitive (M/L) cone. The spectral sensitivity of the S cone was estimated to have a peak of 428 nm, while the M/L cone had a peak of 539 nm. These two cone types would provide the basis for dichromatic color vision consistent with recent results from behavioral testing of horses (Macuda & Timney, 1999; Macuda & Timney, 2000; Timney & Macuda, 2001). The spectral peak of the M/L cone photopigment measured here, in vivo, is similar to that obtained when the gene was sequenced, cloned, and expressed in vitro (Yokoyama & Radlwimmer, 1999). Of the ungulates that have been studied to date, all have the photopigment basis for dichromatic color vision; however, they differ considerably from one another in the spectral tuning of their cone pigments. These differences may represent adaptations to the different visual requirements of different species.

Adaptation, Physiological↗

PubMed2001

Differential recovery of retinal function after mitochondrial inhibition by methanol intoxication.

PURPOSE: The authors' laboratory has previously documented formate-induced retinal toxicity in a rodent model of methanol intoxication. These studies determined functional, bioenergetic, and structural recovery of the retina after methanol intoxication. METHODS: Rats were intoxicated with methanol, and retinal function was assessed by electroretinography 72 hours after the initial dose of methanol and after a 72-hour recovery period. Retinal energy metabolites, glutathione (GSH) concentrations, and histology were determined at the same time points. RESULTS: Both rod-dominated and UV-cone-mediated electroretinogram responses were profoundly attenuated in methanol-intoxicated rats. In rats allowed to recover from methanol intoxication, there was significant, although incomplete, recovery of rod-dominated retinal function. However, there was no demonstrable improvement in UV-cone-mediated responses. Retinal adenosine triphosphate (ATP), adenosine diphosphate (ADP), and GSH concentrations were significantly reduced after intoxication. Although retinal energy metabolites returned to control values after the recovery period, retinal GSH remained significantly depleted. Histopathologic changes were apparent in the photoreceptors after methanol intoxication, with evidence of inner segment swelling and mitochondrial disruption. In animals allowed to recover from methanol intoxication, there was no evidence of histopathology at the light microscopic level; however, ultrastructural studies revealed subtle photoreceptor mitochondrial alterations. CONCLUSIONS: These findings support the hypothesis that formate inhibits retinal mitochondrial function and increases oxidative stress. They also provide evidence for a differential sensitivity of photoreceptors to the cytotoxic actions of formic acid, with a partial recovery of rod-dominated responses and no recovery of UV-cone-mediated responses.

Adenosine Diphosphate↗

PubMed2000

Molecular genetics of color vision and color vision defects.

Color is an extremely important component of the information that we gather with our eyes. Most of us use color so automatically that we fail to appreciate how important it is in our daily activities. It serves as a nonlinguistic code that gives us instant information about the world around us. From observing color, for example, we can find the bee sting on an infant's arm even before it begins to swell by looking for the little spot where the infant's skin is red. We know when fruit is ripe; the ripe banana is yellow not green. We know when meat is cooked because it is no longer red. When watching a football game, we can instantly keep track of the players on opposing teams from the colors of their uniforms. Using color, we know from a distance which car is ours in the parking lot--it is the blue one--and whether we will need to stop at the distant traffic light, even at night, when we cannot see the relative positions of red and green lights.

Color Perception↗

PubMed2000

Flicker-photometric electroretinogram estimates of L:M cone photoreceptor ratio in men with photopigment spectra derived from genetics.

Relative proportions of long-wavelength-sensitive (L) to middle-wavelength-sensitive (M) cones were estimated by use of the flicker-photometric electroretinogram (ERG). It has been demonstrated that a major source of error in estimates of cone proportions from spectral luminosity functions is the known variation in the lambda(max) of the photopigments [Vision Res. 38, 1961 (1998)]. To correct for these errors, estimates of cone proportions were derived by use of individualized L-cone spectral sensitivity curves deduced from photopigment gene sequences from each subject. For some individuals this correction made a large difference in the estimated cone proportions compared with the value obtained when a fixed standard L cone was assumed. The largest discrepancy occurred in a man estimated to have 62% L cones (L:M ratio 1.6:1) when a standard L pigment was assumed but a value of 80% L cones (L:M ratio 4:1) when his individualized L-cone spectrum was used. From repeated measurements made with the ERG, it was determined that individual estimates of the relative L-to-M cone contributions, expressed as %L cones, are usually reliable within approximately 2%. The average L:M ratio for 15 male subjects was estimated at 2:1 (67% L cones). Previously, a large range of individual variability was reported for L:M ratios obtained from photometry. An unresolved issue concerns how much of the range might be attributed to error. Here efforts have been taken to markedly reduce measurement error. Nonetheless, a large range of individual differences persists. Estimated L:M ratios for individuals ranged from 0.6:1 to 12:1 (40% L to 92% L).

Adolescent↗

PubMed2000

Cone pigment gene expression in individual photoreceptors and the chromatic topography of the retina.

Human trichromatic vision is based on three classes of cones: L, M, and S (long-, middle-, and short-wavelength sensitive, respectively). Individuals can have more than one M and/or more than one L pigment gene on the X chromosome along with an S pigment gene on chromosome 7. In some people the X-linked pigment gene array can include polymorphic variants that encode multiple, spectrally distinct cone photopigment subtypes. A single-cell, polymerase chain reaction approach was used to examine visual pigment gene expression in individual human cone cells and identify them as L or M. The ratio of L:M pigment gene expression was assayed in homogenized retinal tissues taken from the same eyes. Results indicate that there is a close correspondence between the cone ratio determined from counting single cells and the L:M pigment mRNA ratio estimated from homogenized pieces of retina. The results also show that the different pigment genes in one array are often expressed at very different levels, giving rise to unequal numbers of L and M cones. Expression of only one photopigment gene was detected in each cone cell. However, individual males can have more than the classically described three spectrally distinct cone types in their retinas.

Adult↗

PubMed2000

Functional consequences of the relative numbers of L and M cones.

Direct imaging of the retina by adaptive optics allows assessment of the relative number of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in living human eyes. We examine the functional consequences of variation in the relative numbers of L and M cones (L/M cone ratio) for two observers whose ratios were measured by direct imaging. The L/M cone ratio for the two observers varied considerably, taking on values of 1.15 and 3.79. Two sets of functional data were collected: spectral sensitivity measured with the flicker electroretinogram (ERG) and the wavelength of unique yellow. A genetic analysis was used to determine L and M cone spectra appropriate for each observer. Rayleigh matches confirmed the use of these spectra. We determined the relative strength of L and M cone contributions to ERG spectral sensitivity by fitting the data with a weighted sum of L and M cone spectra. The relative strengths so determined (1.06 and 3.38) were close to the cone ratios established by direct imaging. Thus variation in L/M cone ratio is preserved at the sites tapped by the flicker ERG. The wavelength of unique yellow varied only slightly between the two observers (576.8 and 574.7 nm). This small variation indicates that neural factors play an important role in stabilizing unique yellow against variation in the L/M cone ratio.

Adult↗

PubMed1999

Trichromatic color vision with only two spectrally distinct photopigments.

Protanomaly is a common, X-linked abnormality of color vision. Like people with normal color vision, protanomalous observers are trichromatic, but their ability to discriminate colors in the red-green part of the spectrum is reduced because the photopigments that mediate discrimination in this range are abnormally similar. Whereas normal subjects have pigments whose wavelengths of peak sensitivity differ by about 30 nm, the peak wavelengths for protanomalous observers are thought to differ by only a few nanometers. We found, however, that although this difference occurred in some protanomalous subjects, others had pigments whose peak wavelengths were identical. Genetic and psychophysical results from the latter class indicated that limited red-green discrimination can be achieved with pigments that have the same peak wavelength sensitivity and that differ only in optical density. A single amino acid substitution was correlated with trichromacy in these subjects, suggesting that differences in pigment sequence may regulate the optical density of the cone.

Amino Acid Substitution↗

PubMed1999

Formate-induced inhibition of photoreceptor function in methanol intoxication.

Formic acid is the toxic metabolite responsible for the retinal and optic nerve toxicity produced in methanol intoxication. Previous studies in our laboratory have documented formate-induced retinal dysfunction and histopathology in a rodent model of methanol intoxication. The present studies define the time and concentration dependence of formate-induced retinal toxicity in methanol-intoxicated rats. Retinal function was assessed 24, 48, and 72 h after the initial dose of methanol by flicker electroretinographic measurements. Retinal histopathology was assessed at the same time intervals. Rod- and cone-mediated electroretinogram (ERG) responses were attenuated in a formate concentration- and time-dependent manner, and both retinal sensitivity and maximal responsiveness to light were diminished. Attenuation of UV-cone-mediated responses was temporally delayed in comparison to the functional deficits observed in the 15 Hz/510 nm responses, which have a rod-mediated component and occurred at significantly higher formate concentrations. Both 15 Hz/510 nm and UV-cone-mediated ERG responses were undetectable by 72 h; however, if light intensity was increased, a retinal ERG response could be recorded, indicating that photoreceptor function was profoundly attenuated, but not abolished, under these intoxication conditions. Functional changes preceded structural alterations. Histopathological changes were most pronounced in the outer retina with evidence of inner segment swelling, photoreceptor mitochondrial disruption, and the appearance of fragmented photoreceptor nuclei in the outer nuclear layer. The nature of both the functional and structural alterations observed are consistent with formate-induced inhibition of mitochondrial energy production, resulting in photoreceptor dysfunction and pathology.

Animals↗

PubMed1999

Vitronectin gene expression in the adult human retina.

PURPOSE: To determine whether vitronectin (Vn), a plasma protein and extracellular matrix molecule that is also a prominent constituent of drusen, is synthesized by cells in the adult human retina. METHODS: The distribution of Vn in the normal adult human retina was examined using antibodies to circulating plasma Vn and to the multimeric, heparin-binding form that is most prevalent in extravascular tissues. Evidence of Vn transcription by retinal cells was analyzed by in situ hybridization and also by reverse transcription of total RNA derived from dissociated human or mouse photoreceptors followed by amplification using polymerase chain reaction (RT-PCR). RESULTS: Cytoplasmic immunoreactivity for plasma Vn or multimeric Vn was detected in photoreceptors, in a subpopulation of neurons situated in the inner retina, and in vitreous hyalocytes. Extracellular labeling was limited primarily to Bruch's membrane and the retinal vasculature. At the transcriptional level, Vn mRNA was localized to both photoreceptors and ganglion cells by in situ hybridization. The in situ findings were corroborated by RT-PCR using total RNA from dissociated mouse or human photoreceptor cells. CONCLUSIONS: The results constitute the first evidence for Vn gene expression by adult neurons in the mammalian central nervous system. The identification of the photoreceptors as a cellular source of Vn suggests that these cells have the potential to make a biosynthetic contribution to the Vn that is found in drusen.

Adult↗

PubMed1998

Variations in cone populations for red-green color vision examined by analysis of mRNA.

In the central human retina, there are estimated to be nearly two L cone photoreceptors for each M cone. The extent to which this value varies across individuals is unclear and little is known about how the M:L cone ratio might change with retinal location. To address these questions, the ratio of M:L cone pigment mRNA was examined at different locations. For patches of central retina, the average M:L ratio was about 2:3 which decreased to about 1:3 for patches 40 degrees eccentric. There were also large individual differences among the 23 eyes examined. The extremes differed in central M:L mRNA ratio by a factor of > 3. The measured differences in mRNA ratio are proposed to reflect differences in photoreceptor ratio. Such variations provide unique opportunities for understanding how the neural circuitry for color vision is affected by changes in cone ratio.

Adolescent↗

PubMed1998

Molecular genetic detection of female carriers of protan defects.

Females heterozygous for congenital colour vision defects are of interest because they are believed to have cone photoreceptor ratios and cone photopigments that differ from normal. We describe a molecular genetic method to identify protan carriers that involves characterizing the genes that occur in the most upstream position in each of the X-chromosome photopigment gene arrays.

Base Sequence↗

PubMed1998

L-cone pigment genes expressed in normal colour vision.

To directly test the hypothesis that only two pigment genes are expressed from the X-chromosome array, we examined expressed M and L pigment gene sequences from > 100 male eye donors. In this sample, there were eight men who expressed high levels of more than one L pigment gene in addition to M pigment genes. The fact that these eyes expressed both L and M pigment genes at significant levels suggests they were from men with normal colour vision. We reject the hypothesis that only two pigment genes from one X-chromosome array can be expressed.

Amino Acid Sequence↗

PubMed1998

Spectra of human L cones.

Variations in the amino acid sequences of the human cone opsins give rise to spectrally variant subtypes of L and M cone pigments even in the population with normal color vision. In vitro mutagenesis studies have shown that a limited number of amino acid substitutions produce shifts in the wavelength sensitivity. Presented here are results comparing electrophysiological measurements of single human cones with the expressed cone pigment gene sequences from the same retina. In a sample of eight long-wavelength sensitive cone (L cone) spectra obtained from five donors the precise spectral sensitivities, measured in situ, of the two most commonly occurring spectral variants were determined. The peak sensitivity of the Lser180 cone was 563 nm while that of the Lala180 cone was 559 nm.

Base Sequence↗

PubMed1998

Relating color discrimination to photopigment genes in deutan observers.

Deutan observers are a heterogeneous group, varying nearly continuously from deuteranomalous trichromats with fine chromatic discrimination in the red/green range to deuteranopes who have none. We sought to relate chromatic discriminative ability among deutans measured psychophysically (phenotypes) to observers' separation between long-wave visual pigments inferred from visual pigment genes (genotypes). If middle-wave pigment genes are assumed not to be expressed in these deutan observers there is a clear relation between phenotype and genotype.

Color Perception↗

PubMed1998

Pigment gene expression in protan color vision defects.

We screened 150 male eye donors and identified four who did not have or express L pigment genes, consistent with each of them having a congenital protan color vision defect. One donor was identified as a protanope because he had and expressed a single X-chromosome photopigment gene that encoded an M pigment. Three were categorized as protanomalous because each expressed significant levels of genes specifying two spectrally different M pigments. The first gene in each of the protanomalous arrays was expressed the most and encoded an M pigment that differed in amino acid sequence from M pigments in color normal men.

Base Sequence↗

PubMed1998

M- and L-cones in early infancy: III. Comparison of genotypic and phenotypic markers of color vision in infants and adults.

Genetic analyses were performed on five male children (approximately 3 years), two suspect color-normals and three suspects for congenital color vision deficiencies. These classifications were based on visually-evoked potential (VEP) responses to M- and L-cone-isolating stimuli obtained in a previous study when each subject was either 4- or 8-weeks old. The present analyses were performed in a blind study to characterize the genotypes of these subjects. Four male adults with various color vision phenotypes were also tested as a control. DNA was isolated using a non-invasive technique followed by polymerase chain reaction (PCR) amplification and restriction enzyme analysis to examine the genomic DNA of each subject. The genetic analyses confirmed the VEP identification of two color defective infants, and were consistent with the diagnosis of two other infants as color normal. A third infant was predicted by VEP analysis to have a protan defect, but he did not have a gene array typically found in protan observers.

Child, Preschool↗