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Biomedical subjects

K Narfström

Publications and source records attributed to K Narfström.

At least 37 records · Page 2Linked to original sources
PubMed1992

Ultrastructural changes of the retina and the retinal pigment epithelium in Briard dogs with hereditary congenital night blindness and partial day blindness.

The offspring of two Briard dogs (brother and sister) with congenital, clinically stationary night blindness showed an aggravation of the disease with severe impairment of day vision in addition to night blindness. This ultrastructural study was performed on four such second generation puppies at the age of 4 months. The neuroretina and retinal pigment epithelium (RPE) from four locations were studied: the central area (immediately temporal to the optic disc); the centre of the tapetal area; the upper periphery (border of tapetal area); and the lower periphery (non-tapetal area). The RPE showed large inclusions, seemingly lipid in nature, mainly in the central and tapetal areas of the retina. Small, membrane bound, electron-dense inclusions were scattered in the RPE cytoplasm in all areas examined. The small inclusions were found to be less numerous in normal than in affected dogs and may be lysosomal in nature. Forty to fifty percent of the rod outer segments in the tapetal area showed disorientation of the disc membranes, whereas the corresponding figures were 20-40% in the central and lower peripheral areas and 6-25% in the upper peripheral area. No structural abnormalities were found in the rod inner segments or synaptic bodies. The cones were better preserved. The inner retina appeared normal. These electron microscopic findings seem to correspond to a previously published electrophysiologic evaluation, indicating a defective and delayed rod function (virtually no scotopic a- and b-waves), a better preserved cone function (photopic flicker responses present, although reduced) and impaired RPE activity (a prominent, slow negative potential of long latency at the site of the c-wave). It appears that these Briard dogs, showing structural changes of the rod outer segments in addition to pigment epithelial inclusions, mainly located in the posterior pole, comprise a pigment epitheliopathy and retinopathy morphologically different from other hereditary canine retinopathies that have been described earlier in the literature and different from animal models of congenital night blindness.

Animals↗
PubMed1992

Changes in the DC electroretinogram in Briard dogs with hereditary congenital night blindness and partial day blindness.

Five Briard dogs, 7-12 months old, with congenital night blindness and severely reduced day vision (offspring of a sister and brother with congenital and supposedly stationary night blindness but with normal or nearly normal day vision) and three normal control dogs were studied by means of direct current (DC) electroretinography in order to analyse fast and slow retinal and pigment epithelial (RPE) potentials. No definite a- and b-waves were seen in the affected dogs in the dark-adapted state, which indicates severely impaired rod function. All affected dogs responded to 30 Hz flickering light in the light-adapted state, although with an amplitude reduced by 50-70%. Thus, cone function was better preserved than rod function. The control dogs showed a small c-wave and a deep negative trough between the b- and c-waves, indicating that slow PIII from the Müller cells, as well as the photoreceptor potential, are very prominent. In the affected dogs, there was no c-wave, but from a stimulus intensity of 3 log U above the normal b-wave threshold, a slow negative potential appeared, the latency and peak time of which were very long, 5-7 and 11-15 sec, respectively. With increasing stimulus intensities, both parameters decreased substantially, whereas the amplitude increased to a maximum of 2400 microV. In the light-adapted state, the dog with the best day vision showed a negative potential of short duration (peak time about 0.2 sec), followed by a positive potential (peak time about 1.2 sec).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Photoreceptor degeneration and loss of immunoreactive GABA in the Abyssinian cat retina.

GABA (gamma-amino butyric acid) and its synthesizing enzyme, GAD (glutamate decarboxylase; EC 4.1.1.15) were localized in the retina of Abyssinian cats homozygous for a recessively inherited retinal degenerative disorder which in several respects is similar to the human disease, retinitis pigmentosa. Clinically normal mongrel cats and heterozygous Abyssinian cats were studied for comparison. The GABA and GAD immunoreactive neurons of the heterozygous or young homozygous (clinically unaffected animals) had the same distribution and morphology as normal mongrel European type cats. The neuronal GABA immunoreactivity in both the inner and outer parts of the retina gradually disappeared in the course of the disease, with little or no loss of GAD immunoreactive neurons. Early in the disease, the changes were most severe in patches in the mid periphery of the eye and then spread both centrally and peripherally. Loss of photoreceptors was a prerequisite for the loss of GABA immunoreactivity. The observations show that retinal changes are not limited to the photoreceptors. The GABA loss is not likely to be due to a loss of neurons, because of the persistence of GAD immunoreactive neurons.

Animal Husbandry↗
PubMed1991

Correlation of morphologic features of the iridocorneal angle to intraocular pressure in Samoyeds.

The iridocorneal angle of the left eye was investigated in 203 Samoyeds. Comparison was made of judgements of the width of the anterior opening of the ciliary cleft when performing gonioscopy with an objective method of estimation based on measurements on goniophotographs. Results indicated high degree of correlation. Various degrees of narrowness of the iridocorneal angle width were revealed and clinical glaucoma with total-angle closure was found in 6 of 203 dogs. The intraocular pressure was significantly (P less than 0.01) higher in eyes with closed iridocorneal angles than in eyes with any other width of the angle. Appearance of the structures of the iridocorneal angle, particularly the pigment bands, indicated extensive individual variation. In approximately 25% of the eyes, dysplasia of the pectinate ligaments of variable degree existed, indicating that this anomaly is common in the Samoyed breed. Significant difference was not evident in intraocular pressure in eyes with different degrees of dysplasia of the pectinate ligaments.

Animals↗
PubMed1989

Reduced level of interphotoreceptor retinoid-binding protein (IRBP), a possible cause for retinal degeneration in the Abyssinian cat.

Retinae of Abyssinian cats homozygous for a retinal degeneration gene, and normal controls, have been investigated using antibodies directed against opsin, transducin alpha (TD-alpha), S-antigen (48K protein), interphotoreceptor retinoid-binding protein (IRBP), and cone outer segments. IRBP-immunoreactivity (IR) is much reduced at stage 2 of the disease in affected retinae; later massive photoreceptor cell death occurs. In cats, at a late stage of the disease, the retina exhibits few S-antigen-IR cells in the peripheral part of the retina whereas, in the central part, some patches of cells exhibiting opsin-IR, TD-alpha-IR, and S-antigen-IR are present in remnants of the outer nuclear layer (ONL). No IRBP-IR is detectable at this stage. The form and size of the majority of these remaining cells, however, does not resemble that of normal photoreceptors. No, or only rudimentary, inner and outer segments are present; long bifurcating basal protrusions often occur. These cells, which could be remains of cone elements, are S-antigen immunoreactive. Double labelling for different retina-specific proteins reveals a co-localization of opsin, TD-alpha and S-antigen in some, but not all, remaining photoreceptor elements. Cells exhibiting opsin-IR also show TD-alpha-IR and S-antigen-IR located within the entire cell and its protrusions. In control retinae and retinae at early stages of the disease, immunoreactions are comparable with all antibodies used. However, TD-alpha-IR is less intensive in the photoreceptor terminals. S-antigen-IR cones are most frequently present in the peripheral retina. Reduction of IRBP at an early stage of the disease could be one of the factors leading to photoreceptor cell death at later stages.

Animals↗
PubMed1989

Rhodopsin levels and rod-mediated function in Abyssinian cats with hereditary retinal degeneration.

Abyssinian cats with different stages of a slowly progressive autosomal recessively-inherited retinal degeneration were studied with imaging fundus reflectometry (IFR) and electroretinography (ERG). Maps of the visual pigment distribution were made in an area of retina extending from the posterior pole to the midperiphery. Rhodopsin levels in the midperipheral retina of a 6-month-old affected cat (stage of suspected disease) were reduced about 20% relative to the mean normal value. The same cat, tested at 2.5 yr of age (now moderately advanced stage), showed a 60% reduction. A 3-yr-old affected cat (also moderately advanced) had a reduction in rhodopsin of about 60%. There was no measurable rhodopsin in a 7-yr-old affected cat (advanced stage). Rhodopsin regeneration kinetics at the different stages of disease were found to be similar to those of normal cats. The rod ERG b-wave threshold in the 6-month-old cat was elevated by 0.26 log units; at 2.5 yr of age, the threshold was elevated by 0.48 log units. A 0.34 log units threshold elevation was found in the 3-yr-old cat. There was no detectable ERG in the 7-yr-old cat. The relationship between the rod ERG threshold elevations and the rhodopsin levels was close to that expected if the dysfunction was caused by decreased quantal absorption.

Animals↗
PubMed1989

Morphological findings during retinal development and maturation in hereditary rod-cone degeneration in Abyssinian cats.

The sequence of structural changes involved in postnatal photoreceptor differentiation, maturation and early degeneration was studied in young Abyssinian cats and kittens with hereditary rod-cone degeneration and compared to maturation in normal controls. In affected cats the earliest change seen was disorientation of outer segment discs in the majority of the rods, while other rods appeared to develop and mature normally. Such disorientation of discs (at oblique angles or parallel to the longitudinal axis of the outer segment, or whorls of discs) is considered as 'immaturity', since controls also showed a substantial number of disoriented rod outer segment discs at this young age. At postnatal day 35 the difference between affected animals and controls was marked with a high frequency of immature appearing rod outer segment discs in affected animals, while all rod outer segment discs were adult-like and arranged in an orderly manner in controls. Cones seemed unaffected at this age. More severe changes in affected rod outer segments in the form of disintegration of discs (vacuolization and clumping of disc material, or formation of debris), which we consider to represent degeneration, were first observed at the time when retinal maturation normally occurs in the cat, i.e. 150 days postnatally. Subsequently a drop-out of rods was seen, primarily of rods with disoriented and disintegrated outer segment discs, followed by a slow, progressive degeneration of rods that had developed and matured normally. Cones appeared normal during the time of retinal development and maturation and it was not until the age of 2-3 years (Narfström and Nilsson, 1986, Incest. Ophthalmol, Vis. Sci. 27, 1569-76) that degenerative changes were seen also in cones.

Aging↗
PubMed1989

Retinal sensitivity in hereditary retinal degeneration in Abyssinian cats: electrophysiological similarities between man and cat.

The functional and electrophysiological similarities in the changes in the electroretinogram (ERG) of man and cat affected by hereditary retinal degenerative disease were studied. The results of a series of log intensity-amplitude studies in a group of young affected Abyssinian cats were fitted to the Naka-Rushton relationship by means of a mathematical package on the University of London mainframe. The analysis showed that the amplitude of the maximum dark-adapted b-wave was significantly reduced by the end of the period studied but that the value of k, a variable inversely equivalent to retinal sensitivity, was only slightly reduced by the retinal degenerative process. The electrophysiological findings thus are similar to those found in cases of human diffuse dominantly inherited retinitis pigmentosa.

Animals↗
PubMed1989

The Briard dog: a new animal model of congenital stationary night blindness.

Congenital stationary night blindness (CSNB), apparently inherited in an autosomal recessive manner, was observed in a litter of Briard dogs in Sweden. Of nine litter mates five had nyctalopia. The results of different clinical tests, including electroretinography (ERG), were compared with the results found in four human cases of CSNB, three of which were most probably associated with autosomal recessive inheritance and one with X-linked inheritance. The congenital and stationary nature of the disease, ophthalmoscopically normal appearing fundi, and recordable but reduced photopic flicker responses were some of the similarities found between canine and human cases. The single-flash ERG response was abnormal in the humans as well as in the affected Briards. However, the human cases showed a "negative' ERG, whereas in the Briards both the a and b waves were extremely reduced and present only at a photopic level. Cases similar to these Briards have been described also in man, where rhodopsin concentration and regeneration were found to be normal, suggesting a disturbed transduction mechanism. It thus appears that the Briard dog may become a valuable model of human CSNB.

Animals↗
PubMed1989

Postnatal development of photoreceptor proteins in mutant mice and Abyssinian cats with retinal degeneration.

Using immunocytochemical techniques, development of opsin, transducin alpha and S-antigen in photoreceptor cells of the mice homozygous or heterozygous for the rd or rds genes has been found to be similar to that of control animals during the first postnatal week. Even though the absolute amounts of these proteins are low (eg. opsin in the rds retina) or decrease in the postnatal period (as in the rd retina), we can demonstrate their persistence during the entire degeneration process. In fact, the content of the proteins in the photoreceptor perikarya actually appear to be higher after postnatal day 11 in all mutants studied. Thus, one of the major manifestations of the mutant retinae is a loss of polarity of the photoreceptor cells at the time of ROS degeneration without a loss in the ability to synthesize these important proteins of the visual cycle. This correlates well with the apparent defect in IRBP secretion and its intracellular accumulation in mutant photoreceptor cells as previously observed (van Veen et al. 1986). In the Abyssinian cat model for progressive retinal atrophy, the development an cellular distribution of all the proteins studied are similar in affected and control retinae until the beginning of stage 2 of the disease. At this time, outer segments begin to degenerate and immunoreactivity increases in the photoreceptor perikarya. The IRBP content of the retina declines markedly at stage 2, preceding extensive loss of photoreceptors.

Aging↗
PubMed1988

Hereditary retinal degeneration in the Abyssinian cat: developmental studies using clinical electroretinography.

Electroretinography was performed in 10 Abyssinian cats, homozygous for a hereditary retinal degenerative disease but still with an ophthalmoscopically normal retina, and in 11 mixed-breed controls, all between the ages of 8 and 104 weeks. A significant reduction of maximum dark-adapted b-wave amplitude was found in affected kittens as young as 8-16 weeks when compared with controls, although there was no major difference in dark-adapted b-wave threshold or implicit time for the b-wave between affected and controls. For cats 33-104 weeks, similar results were obtained except for the b-wave threshold, which was elevated 2.5 log units in one of the affected cats. No significant difference in 30-Hz cone flicker responses were found between affected and controls at any age studied. In the time period 17-32 weeks affected Abyssinian kittens could not be differentiated from controls by means of the electroretinogram. The significant reduction in scotopic b-wave maximum amplitudes in young affected kittens (8-16 weeks) in conjunction with normal thresholds suggests an early drop-out of rods. It is clear that affected kittens can be differentiated electrophysiologically from controls long before there are ophthalmoscopic signs of retinal disease.

Aging↗
PubMed1988

Accumulation of glial fibrillary acidic protein in Müller radial glia during retinal degeneration.

Müller radial glia accumulate glial fibrillary acid protein (GFAP) in response to retinal injuries. We have studied the changes in cellular localization of GFAP in genetically caused retinal dystrophy in strains of cat and mouse: Abyssinian cats with progressive retinal dystrophy, and mice homo- and heterozygous for the retinal degeneration (rd) and retinal degeneration slow (rds) genes. The following observations were made: (1) Glial fibrillary acid protein-immunoreactive (GFAP-IR) radial Müller glia are present in normal cat and mouse retinae. (2) There is a general increase with age in numbers of GFAP-IR radial Müller glia, and other GFAP-IR elements in the retina of cat and mice with hereditary retinal dystrophy. (3) The increase in GFAP-accumulating Müller cells seems to proceed from peripheral to central retina in both cats and mice. This might reflect the direction of photoreceptor degeneration, which proceeds in the same direction in the retinal dystrophic cat and in mice bearing the rds gene. However, in the rd mouse photoreceptor degeneration proceeds from central to peripheral retina, indicating that GFAP accumulation is not a local direct effect of photoreceptor damage. (4) Comparing the different mutant mouse strains, there seem to be qualitative differences in the distribution of GFAP-IR elements. The numbers of tangential elements and fibrillary tangles in the inner plexiform and nuclear layers are highest in the +/+ rds/rds retina, followed by the +/+ rds/+, whereas such elements appear to be more scarce in rd/rd rds/rds, followed by the rd/rd +/+ and +/+ +/+ retinae.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Hereditary rod-cone degeneration in a strain of Abyssinian cats.

The retinal disease found in this strain of Abyssinian cats is a heritable disorder, primarily affecting the photoreceptors. The retina is, in most cases, ophthalmoscopically normal until the age of 1.5-2 years. The retinal changes that then appear are slowly progressive and lead to a generalized retinal atrophy in another 2-4 years. It is obvious that this cat retinal degeneration shows many similarities to human Retinitis Pigmentosa. Just as in RP the midperiphery/periphery is most severely affected at the earlier stages, and with progression of disease alterations become generalized, the central retina being the best preserved area until the very late stage. Rods are affected prior to cones, but later in the disease there is an involvement of both rods and cones. Also, the disease process is slow, starting off from an ophthalmoscopically normal appearing retina. This strain of Abyssinian cats, affected by the presently described retinal disease, therefore has the potential of becoming a new animal model in the study of hereditary visual cell disease processes.

Animals↗
PubMed1986

Progressive retinal atrophy in the Abyssinian cat. Electron microscopy.

Seven adult Abyssinian cats at different stages of a recessively inherited retinal degenerative disease (progressive retinal atrophy) were studied ultrastructurally. At the stage of early disease, in 2-yr-old cats, disorganized and vesiculated discs were found in less than half of the rod outer segments in the periphery, while similar changes were seen in the central retina only infrequently or in patches. Cones appeared normal in all areas of the retina at the early stage. With progression of disease, the lesions were more advanced in all areas of the retina, and involved both rods and cones, with the most severe alterations found in the midperiphery. At the advanced stage, in a 6-yr-old cat, both rods and cones were lost, the inner nuclear layer thus being separated from the pigment epithelium by Müller cell processes and a few remaining outer plexiform processes only. Remnants of photoreceptor outer and inner segments, macrophages, and what appeared to be displaced photoreceptor cell nuclei could be found occasionally in the subretinal space, however. Clumps of pigment granules were often observed in the photoreceptor layer in the non-tapetal fundus. The pigment epithelium remained morphologically intact as a single layer of uninterrupted cells throughout the disease process, as did tapetal cells and choriocapillaris. There was no difference in the severity of disease between the peripheral tapetal and non-tapetal fundus. In the inner retina, only minor alterations were observed. These changes appeared at a later time than photoreceptor degeneration, and were considered secondary to the latter.

Animals↗
PubMed1985

Hereditary retinal degeneration in the Abyssinian cat: correlation of ophthalmoscopic and electroretinographic findings.

Ophthalmoscopic and electroretinographic (ERG) findings were correlated in a group of Abyssinian cats affected by a slowly progressive and hereditary retinal degenerative disease. According to ophthalmoscopic findings the disease was divided into stages. At stage 1 and 2 retinal changes were minor; showing a gray discoloration most often in the peripheral and midperipheral tapetal fundus. At stage 3 discoloration was generalized and there was marked vascular attenuation. A generalized retinal atrophy was found at stage 4. ERG recordings showed an abnormally depressed stimulus response curve for the b-wave at stage 1 of disease when 30-Hz cone flicker responses were indistinguishable from normal. With progression of disease there was a successive decrease of a- and b-wave amplitudes before there was a significant reduction also of the c-wave amplitude (first seen at stage 3). The ERG was nonrecordable at stage 4. These findings suggest that the photoreceptors are affected primarily by the disease, before there is a functional involvement also of the pigment epithelium. The rod system seems to be affected early in the disease as compared with the cone system. A staging of the disease by ophthalmoscopy correlated more to the function of the rods than to that of the cones.

Animals↗
PubMed1985

Progressive retinal atrophy in the Abyssinian cat. Clinical characteristics.

Ninety-four cases of a hereditary retinal degeneration in household Abyssinian cats were found in Sweden, mainly during a 3-year period. The disease was investigated by ophthalmoscopy, fluorescein angiography, electroretinography, and light microscopy. A bilateral retinopathy was usually first seen in affected cats at the age of 1.5-2 years. Fluorescein angiography did not demonstrate abnormalities of etiological significance to the disease process. A reduction mainly of a- and b-wave amplitudes in the ERG indicated a generalized photoreceptor disease. Light microscopy showed that the photoreceptor layer was primarily affected, while other retinal layers were mainly normal. The midperipheral and peripheral retina was affected more severely than the retina of the posterior pole until late stages of disease, when there was a generalized loss of photoreceptors. The clinical and laboratory findings suggest that PRA in these Abyssinian cats is a heritable photoreceptor degenerative disease with a fairly slow rate of progression.

Animals↗
PubMed1983

Accumulation of taurine in the nasal mucosa and the olfactory bulb.

Using whole-body autoradiography of 14C-taurine in mice we have observed a high concentration in the nasal mucosa followed by accumulation in the olfactory bulb at longer survival times. When 14C-taurine was administered in the nasal cavity unilaterally, a high accumulation was observed in the ipsilateral olfactory bulb.

Animals↗