PubMed Health⌕ Search

Biomedical subjects

S Nusinowitz

Publications and source records attributed to S Nusinowitz.

17 recordsLinked to original sources
PubMed2001

The reelin pathway modulates the structure and function of retinal synaptic circuitry.

The formation of synaptic connections requires the coordination of specific guidance molecules and spontaneous neuronal activity. The visual system has provided a useful model for understanding the role of these cues in shaping the precise connections from the neural retina to the brain. Here, we demonstrate that two essential genes in the Reelin signaling pathway function during the patterning of synaptic connectivity in the retina. Physiological studies of mice deficient in either reelin or disabled-1 reveal an attenuation of rod-driven retinal responses. This defect is associated with a decrease in rod bipolar cell density and an abnormal distribution of processes in the inner plexiform layer. These results imply that, in addition to its essential role during neuronal migration, the Reelin pathway contributes to the formation of neuronal circuits in the central nervous system.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Deficiency of rds/peripherin causes photoreceptor death in mouse models of digenic and dominant retinitis pigmentosa.

Retinitis pigmentosa (RP) is a group of inherited blinding diseases caused by mutations in multiple genes including RDS. RDS encodes rds/peripherin (rds), a 36-kDa glycoprotein in the rims of rod and cone outer-segment (OS) discs. Rom1 is related to rds with similar membrane topology and the identical distribution in OS. In contrast to RDS, no mutations in ROM1 alone have been associated with retinal disease. However, an unusual digenic form of RP has been described. Affected individuals in several families were doubly heterozygous for a mutation in RDS causing a leucine 185 to proline substitution in rds (L185P) and a null mutation in ROM1. Neither mutation alone caused clinical abnormalities. Here, we generated transgenic/knockout mice that duplicate the amino acid substitutions and predicted levels of rds and rom1 in patients with RDS-mediated digenic and dominant RP. Photoreceptor degeneration in the mouse model of digenic RP was faster than in the wild-type and monogenic controls by histological, electroretinographic, and biochemical analysis. We observed a positive correlation between the rate of photoreceptor loss and the extent of OS disorganization in mice of several genotypes. Photoreceptor degeneration in RDS-mediated RP appears to be caused by a simple deficiency of rds and rom1. The critical threshold for the combined abundance of rds and rom1 is approximately 60% of wild type. Below this value, the extent of OS disorganization results in clinically significant photoreceptor degeneration.

Animals↗
PubMed2000

Maternal germ-line transmission of mutant mtDNAs from embryonic stem cell-derived chimeric mice.

We report a method for introducing mtDNA mutations into the mouse female germ line by means of embryonic stem (ES) cell cybrids. Mitochondria were recovered from the brain of a NZB mouse by fusion of synaptosomes to a mtDNA-deficient (rho degrees ) cell line. These cybrids were enucleated and the cytoplasts were electrofused to rhodamine-6G (R-6G)-treated female ES cells. The resulting ES cell cybrids permitted transmission of the NZB mtDNAs through the mouse maternal lineage for three generations. Similarly, mtDNAs from a partially respiratory-deficient chloramphenicol-resistant (CAP(R)) cell line also were introduced into female chimeric mice and were transmitted to the progeny. CAP(R) chimeric mice developed a variety of ocular abnormalities, including congenital cataracts, decreased retinal function, and hamaratomas of the optic nerve. The germ-line transmission of the CAP(R) mutation resulted in animals with growth retardation, myopathy, dilated cardiomyopathy, and perinatal or in utero lethality. Skeletal and heart muscle mitochondria of the CAP(R) mice were enlarged and atypical with inclusions. This mouse ES cell-cybrid approach now provides the means to generate a wide variety of mouse models of mitochondrial disease.

Animals↗
PubMed2000

A deletion in a photoreceptor-specific nuclear receptor mRNA causes retinal degeneration in the rd7 mouse.

The rd7 mouse, an animal model for hereditary retinal degeneration, has some characteristics similar to human flecked retinal disorders. Here we report the identification of a deletion in a photoreceptor-specific nuclear receptor (mPNR) mRNA that is responsible for hereditary retinal dysplasia and degeneration in the rd7 mouse. mPNR was isolated from a pool of photoreceptor-specific cDNAs originally created by subtractive hybridization of mRNAs from normal and photoreceptorless rd mouse retinas. Localization of the gene corresponding to mPNR to mouse Chr 9 near the rd7 locus made it a candidate for the site of the rd7 mutation. Northern analysis of total RNA isolated from rd7 mouse retinas revealed no detectable signal after hybridization with the mPNR cDNA probe. However, with reverse transcription-PCR, we were able to amplify different fragments of mPNR from rd7 retinal RNA and to sequence them directly. We found a 380-nt deletion in the coding region of the rd7 mPNR message that creates a frame shift and produces a premature stop codon. This deletion accounts for more than 32% of the normal protein and eliminates a portion of the DNA-binding domain. In addition, it may result in the rapid degradation of the rd7 mPNR message by the nonsense-mediated decay pathway, preventing the synthesis of the corresponding protein. Our findings demonstrate that mPNR expression is critical for the normal development and function of the photoreceptor cells.

Amino Acid Sequence↗
PubMed2000

Retinal degeneration but not obesity is observed in null mutants of the tubby-like protein 1 gene.

The tub gene is a member of a small, well conserved neuronal gene family of unknown function. Mutations within this gene lead to early-onset blindness and deafness, as well as late-onset obesity and insulin resistance. To test the hypothesis that mutations within other members of this gene family would lead to similar phenotypes as observed in tubby mice, and hence have similar functional properties, we have generated null mutants of the tubby-like protein ( Tulp ) 1 gene by homologous recombination. Similarly to tubby mice, Tulp1 (-/-)mice exhibit an early-onset retinal degeneration with a progressive, rapid loss of photoreceptors, further supporting the notion that previously identified mutations within the human TULP1 gene are indeed causative of retinitis pigmentosa. However, in contrast to tubby mice, Tulp1 (-/-)mice exhibited normal hearing ability and, surprisingly, normal body weight despite the fact that both TUB and TULP1 are expressed in the same neurons within the hypothalamus in areas known to be involved in feeding behavior and energy homeo stasis. However, TUB and TULP1 show a distinctly different staining pattern in the nucleus of these neurons, perhaps explaining the difference in body weight between the Tulp1 (-/-)and tubby mutant mice.

Animals↗
PubMed2000

Retinal degeneration 6 (rd6): a new mouse model for human retinitis punctata albescens.

PURPOSE: To characterize the genetics and phenotype of a new mouse mutant with retinal degeneration, rd6, that is associated with extensive, scattered, small white retinal dots seen ophthalmoscopically. METHODS: The phenotype was characterized using ophthalmoscopy, fundus photography, electroretinography, light microscopy, immunocytochemistry, and electron microscopy. Genetic characterization and linkage analysis studies were performed using standard methods. RESULTS: The inheritance pattern of rd6 is autosomal recessive. Linkage analysis mapped rd6 to mouse Chromosome 9 approximately 24 cM from the centromere, suggesting that the human homolog may be on chromosome 11q23. Ophthalmoscopic examination of mice homozygous for rd6 revealed discrete subretinal spots oriented in a regular pattern across the retina. The retinal spots appeared by 8 to 10 weeks of age and persisted through advanced stages of retinal degeneration. Histologic examination revealed large cells in the subretinal space, typically juxtaposed to the retinal pigment epithelium. The white dots seen on fundus examination corresponded both in distribution and size to these large cells. By 3 months of age, the cells were filled with membranous profiles, lipofuscin-like material, and pigment. These cells reacted strongly with an antibody directed against a mouse macrophage-associated antigen. Photoreceptor cells progressively degenerated with age, and an abnormal electroretinogram was initially detected between 1 and 2 months of age. CONCLUSIONS: The fundi of mice homozygous for rd6 exhibit phenotypic similarities to the human flecked retinal disorder retinitis punctata albescens. Thus, rd6/rd6 mice may be a model for understanding the etiology of this or similar disorders. The relationship between the aberrant subretinal cells and the concomitant photoreceptor degeneration remains to be established.

Animals↗
PubMed1999

Genetic and physical maps of the mouse rd3 locus; exclusion of the ortholog of USH2A.

The rd3 retinal degeneration gene was previously mapped 10 +/- 2.5 cM distal to Akp1 on mouse Chromosome (Chr) 1 (Chang et al., 1993), a region that may be homologous to the locus of the human USH2A gene, which carries mutations responsible for Usher IIa retinal degeneration/hearing loss syndrome. An intercross from an Rb(11, 13)4Bnr(rd3/rd3) x C57BL/6J mating was set up, 428 F2 meioses were analyzed, and the rd3 gene was placed between the markers D1MIT292/D1MIT209 and D1MIT510, a distance of 1.40 +/- 0.57 cM. These flanking markers and the mouse ortholog of USH2A (Mush2a) were mapped in the T31 mouse radiation hybrid (RH) panel, with the result that D1MIT292/D1MIT209 and D1MIT510 were 7.9 cR3000 apart ( approximately 800 kb), and Mush2a was > 30 cR3000 proximal to the pair, excluding it from the rd3 locus. A contig spanning the rd3 locus and consisting of 2 YACs and one BAC was generated, and Mush2a was absent from it, confirming its exclusion from the locus. Comparison of adjacent marker pairs in the Whitehead genetic map and our genetic map showed some discrepancies in order of markers and genetic distances. Comparison of our genetic map and the RH map showed some highly skewed relationships between genetic and physical distances.

Animals↗
PubMed1999

Control of transmission of vancomycin-resistant Enterococcus faecium in a long-term-care facility.

OBJECTIVES: To describe the investigation and control of transmission of vancomycin-resistant enterococci (VRE) in a residential long-term-care (LTC) setting. OUTBREAK INVESTIGATION: A strain of vancomycin-resistant Enterococcus faecium not previously isolated in Ontario colonized five residents of a 254-bed LTC facility in Toronto. The index case was identified when VRE was isolated from a urine culture taken after admission to a local hospital. Screening of rectal swabs from all 235 residents identified four others who were colonized with the same strain of E faecium. CONTROL MEASURES: Colonized residents were cohorted. VRE precautions were established as follows: gown and gloves for resident contact, restriction of contact between colonized and noncolonized residents, no sharing of personal equipment, and daily double-cleaning of residents' rooms and wheelchairs. OUTCOME: Two colonized residents died of causes unrelated to VRE. Although bacitracin therapy (75,000 units four times a day x 14 days) failed to eradicate carriage in two of three surviving residents, both cleared their carriage within 7 weeks. Repeat rectal swabs from 224 residents (91%) 2 months after isolation precautions were discontinued and from 125 residents (51%) 9 months later identified no new cases. Total cost of investigation and control was $12,061 (Canadian). CONCLUSION: VRE may be transmitted in LTC facilities, and colonized LTC residents could become important VRE reservoirs. Control of VRE transmission in LTC facilities can be achieved even with limited resources.

Aged↗
PubMed1999

Rod multifocal electroretinograms in mice.

PURPOSE: To test the feasibility of recording rod multifocal electroretinograms (ERGs) from the mouse eye. METHODS: Multifocal ERGs were recorded from normal mice (C57BL/6J) using an array of equal-sized hexagons. Local stimuli were blue (W47A), and the number of blank frames between successive flashes at the same location was fixed at 14 (minimum 200 msec between flashes). Flash and surround intensity, and the number of hexagons, were varied to optimize the stimulus conditions for the mouse, and alterations in adaptation level were used to assess cone intrusion. Local response isolation was evaluated by comparing multifocal responses to full-field ERGs and by mapping local defects in laser-treated mice. RESULTS: Rod multifocal ERGs, although small, were clearly recordable and well formed under many conditions. Decreasing flash intensity or the size of stimulus elements, and/or increasing the surround intensity or adaptation level, decreased local response amplitudes. At the dimmest flash intensity (-0.70 log scotopic trolands [scot td]/s) and the smallest stimulus element (2.9 degrees x 3.5 degrees), local responses were nondetectable. Comparisons with full-field ERGs supported the hypothesis that the local responses were not contaminated by contributions from dark-adapted retinal areas surrounding the multifocal display. With sufficiently bright (0.30 log scot td-s) and relatively large (5.6 degrees x 6.9 degrees) stimulus elements, multifocal responses clearly revealed local retinal defects created with laser treatment. CONCLUSIONS: Rod multifocal ERGs can be recorded from the mouse eye to provide topographical maps of retinal function that have sufficient spatial resolution to be of practical use. The technique will be useful in characterizing the natural history of regional loss in mouse models of human retinal disease and in evaluating some forms of interventional therapy.

Animals↗
PubMed1998

Rod photoresponses in 6-week and 4-month-old human infants.

Rod-only electroretinograms (ERGs) were recorded from 6-week and 4-month-old normal human infants. The leading edge of the rod a-wave was fitted with a model of the activation phase of phototransduction to provide estimates of S (a sensitivity parameter) and RmP3 (the maximum saturated photoreceptor response) at each of the investigated ages. Both S and RmP3 increased over the first postnatal months but followed different developmental time courses with S approaching adult-like values sooner than RmP3. The changes in S and RmP3 can be interpreted within the context of a model incorporating the combined effects of increased levels of rhodopsin and the changing structure of the rod outer segment during development.

Aging↗
PubMed1998

Leukocytoclastic vasculitis associated with clarithromycin.

OBJECTIVE: To report a possible case of leukocytoclastic vasculitis associated with clarithromycin therapy. CASE SUMMARY: An 83-year-old white woman was prescribed clarithromycin for pneumonia. Six days after her initial presentation, she developed lesions on her palms. Clarithromycin was discontinued at that time. The following day she developed purpuric eccymotic nonblanching lesions that primarily appeared on the lower extremities, buttocks, and abdomen. Colonoscopy revealed generalized erythema and edema of the bowel mucosa. Gastroscopy revealed duodenitis and gastritis, but no bleeding or ulceration. Skin biopsy of the lesions was compatible with leukocytoclastic vasculitis. Renal function was not affected, although hematuria was noted. All symptoms resolved after drug withdrawal and a short course of corticosteroids. DATA SOURCES: Searches were performed on MEDLINE, Embase, International Pharmaceutical Abstracts, and major adverse drug reaction databases to identify reports and articles discussing clarithromycin- and macrolide-induced leukocytoclastic vasculitis. DISCUSSION: Leukocytoclastic vasculitis is one category of drug hypersensitivity reactions characterized by distinctive patterns of perivascular inflammation. The case described here is consistent with the diagnosis of leukocytoclastic vasculitis, and is similar to the other single published case report associated with clarithromycin. CONCLUSIONS: Leukocytoclastic vasculitis induced by clarithromycin is a rare but serious potential adverse effect.

Aged↗
PubMed1997

Light reduction and the electroretinogram of preterm infants.

AIMS: To examine the effects of light on retinal development and function in preterm infants as measured by the electroretinogram (ERG). Secondary outcomes included visual acuity testing, the incidence of retinopathy of prematurity, and general wellbeing, reflected in feeding tolerance, rate of weight gain, and length of hospital stay. METHODS: Eligibility criteria for enrollment were birthweight < or = 1250 g and gestational age < or = 31 weeks. Sixty one infants were randomly allocated by 6 hours after birth to a control or treatment group which wore 97% light filtering goggles for a minimum of four weeks or until the infant reached 31 weeks postmenstrual age. RESULTS: There were no significant differences between the two groups in the numbers of electroretinograms performed at 36 weeks of postmenstrual age. Although the sample size was not large enough to exclude clinically important differences in secondary outcomes, no significant differences were observed between the groups in visual acuity testing at 4-6 months corrected age, incidence of retinopathy of prematurity, weight gain, or length of stay. CONCLUSION: These data support the safety and feasibility of this intervention. A much larger study will be needed to determine whether light reduction to the eyes of very low birthweight infants will reduce the incidence of retinopathy of prematurity or enhance general well-being.

Electroretinography↗
PubMed1995

Rod transduction parameters from the a wave of local receptor populations.

The analysis of electroretinogram a waves from locally stimulated populations of rods is complicated by the presence of scattered light within the eye. Scattered-light and cone contributions can be assessed after brief flashes of light designed to saturate only rods in the locally stimulated area. Subtracting the scattered-light and the cone responses from the local electroretinogram gives a pure rod a wave that can be fitted with models of photoreceptor activity. We demonstrate the feasibility of this technique by recording local rod a waves from a group of five normal subjects and by fitting the a waves with the rod model to derive transduction parameters. The local rod a waves are compared with expected responses derived from simulations in which the response of the entire retina to heterogeneous illumination is mimicked.

Adult↗
PubMed1995

Abnormal activation and inactivation mechanisms of rod transduction in patients with autosomal dominant retinitis pigmentosa and the pro-23-his mutation.

PURPOSE: The leading edge of the rod a-wave in normal human subjects can be fit with a computational model of the activation phase of transduction to provide parameters analogous to those obtained from individual photoreceptors. The authors extend this work to the kinetics of recovery after saturating flashes. METHODS: Electroretinograms were recorded from three patients with autosomal dominant retinitis pigmentosa and the pro-23-his rhodopsin mutation, two patients with rod monochromatism, and five normal subjects. Rod-only a-waves were obtained for a series of flashes ranging from 4.4 to 10.1 ln (1.9 to 4.4 log) scot td-sec. One set of parameters describing the activation process was derived from fits to the a-wave model. A double-flash paradigm was used to study inactivation mechanisms. The first flash was achromatic and varied in intensity (I(f)) from 6.1 to 13.9 ln (2.6 to 6.0 log) scot td-sec. The second flash was a short-wavelength probe held constant at 9.3 ln (4.0 log) scot td-sec. Cone components were elicited with a photopically matched long-wavelength stimulus and were computer subtracted. Recovery at each I(f) was followed by measuring the amplitude to the probe flash at various interstimulus intervals (ISI). The critical time (Tc) before the initiation of rod recovery was determined from the function relating relative rod amplitude to ISI. RESULTS: Recovery from activation was similar in normal subjects and in patients with rod monochromatism. Over a large range of I(f) above rod saturation, Tc increased in proportion to ln I(f). The mean slope of the function relating Tc to I(f) was 2.3 s/ln I(f) when I(f) varied between 11 and 13.9 ln scot td-sec. Patients with retinitis pigmentosa and the pro-23-his rhodopsin mutation had a decrease in the gain of activation. They also had significantly slower than normal recovery after high test flash intensities, such that the slope of the function relating Tc to ln I(f) was 12.1 seconds. CONCLUSION: Available data from other species imply that complete, transient activation of transducin (T saturation) occurs within or below the investigated range of flash intensities. Based on the slope of the delay function (delta Tc/ delta ln I(f)) above 11 ln scot td-sec, the authors hypothesize that the lifetime of activated rhodopsin (R) in normal human rods is approximately 2.3 seconds. In patients with the pro-23-his mutation, the gain of the activation mechanism is reduced and the reaction determining the delta Tc/ delta ln I(f) slope is markedly slowed. The activated species that exhibits this prolonged lifetime could be the mutant rhodopsin itself.

Adolescent↗