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Biomedical subjects

I Perlman

Publications and source records attributed to I Perlman.

At least 55 records · Page 3Linked to original sources
PubMed1986

CNS oxygen toxicity in the rat: role of ambient illumination.

The effect of ambient illumination on sensitivity to CNS oxygen toxicity was studied in awake male rats. Continuous recording of the EEG was obtained with chronically implanted cortical electrodes. The appearance of the electrical discharges in the EEG was used as an end point for CNS oxygen toxicity. It was found that sensitivity to CNS oxygen toxicity was inversely related to the level of ambient light illumination. The latent period for appearance of the electrical discharges was significantly shorter in darkness than in light over most of the oxygen pressures. Rats with severely depressed retinal function were as sensitive to oxygen at high pressure as normal rats in darkness, demonstrating the importance of visual input in the modulation of sensitivity to CNS oxygen toxicity.

Animals↗
PubMed1986

Clerkship site and duration: do they influence student performance?

At the School of Medicine of the State University of New York at Stony Brook, the surgical clerkship became mandatory in 1976. From the academic years 1976 through 1979, it was a 6-week program. Since the fall of 1979, it has been a 12-week program. Students have been divided among the University Center (the University Hospital and the Northport Veterans Administration Medical Center), two voluntary hospitals, and two county hospitals. This retrospective study was conducted to determine if duration of clinical site influenced student performance. Students taking the longer clerkship scored significantly higher on National Board examinations, oral examinations, and evaluations of clinical performance than did students in the shorter clerkship. Statistical analysis revealed no significant differences in the performance among students at different clinical campuses. Positive relationships were found between National Board scores versus oral examination scores, National Board scores versus clinical performance grades, and oral examinations versus clinical grades.

Academic Medical Centers↗
PubMed1986

Light damage in the developing retina of the albino rat: an electroretinographic study.

The albino rat retina is severely damaged by exposure to bright light. The degree of damage depends upon the intensity of the exposure and its duration. In the present study, electroretinographic (ERG) responses were measured in rats exposed at different ages during the period of retinal development to 24 hr of bright light and then transferred to darkness for about 2 months. The ERG data indicated that if the bright-light exposure was done prior to 20 days of age, the retina was resistant to the light damage, and the dark-adapted ERG responses measured later were normal. In rats older than 20 days, light damage increased with age until, in rats exposed to light at age 30 days, the ERG was unrecordable. Further experiments showed that light exposure did damage the 15-day-old rat retina; however, complete recovery was attained within 15 days postexposure.

Aging↗
PubMed1985

Chromatic and spatial information processing by red cones and L-type horizontal cells in the turtle retina.

Flash sensitivities to red (694 nm) and green (546 nm) light were measured intracellularly from red cones and L-type horizontal cells in the turtle retina. The horizontal cells' sensitivity to short wavelength light was significantly larger than expected from the model where horizontal cells receive input mainly from red cones. The red cone responses to chromatic stimuli were strongly dependent upon the flash colour and size. Increasing the spot size reduced the sensitivity to green relative to red and augmented the differences in kinetics between the response to red light and that evoked by green light. It was concluded that L-type horizontal cells received a short wavelength input in addition to the input from red cones. This additional green input coupled with the negative feedback pathway from horizontal cells onto red cones determined the differential spatial properties of the red cone responses to red and green test flashes.

Animals↗
PubMed1985

Retinal function of the diabetic retina after argon laser photocoagulation assessed electroretinographically.

Electroretinographic (ERG) responses were measured in diabetic patients before, during, and after panretinal photocoagulation treatment with argon laser. The laser applications reduced considerably the amplitudes of the a and b waves of the ERG. Moreover, the relationship between the amplitude of the b wave and that of the a wave was severely affected, resulting in ERG responses of abnormal pattern. The b waves were smaller than expected from the a waves. These findings indicated that the photocoagulation treatment not only destroyed the retinal areas directly illuminated by the laser beam, but also affected the functional integrity of adjacent areas. These additional effects resulted in subnormal signal transmission from the photoreceptors to the proximal retina.

Adult↗
PubMed1985

Mixing of color signals by turtle cone photoreceptors.

The direct mixing of red and green cone signals in the outer plexiform layer of the turtle retina was studied by using intracellular recordings from red cone photoreceptors. Cone photoresponses were a function of the wavelength of the photons that stimulated them, even when small-diameter stimuli were used. The intensity response curves measured with red and green test flashes had different shapes. The kinetics of approximately equal amplitude red and green responses also differed. To quantify the short wavelength input onto red cones, differential chromatic adaptation was used. The relative sensitivity of the red cone to red and green test flashes was a function of the color and intensity of the background illumination; red backgrounds decreased relative red sensitivity, and green backgrounds increased relative red sensitivity. The spectral sensitivity of the additional short wavelength input onto red cones was determined by using differential chromatic adaptation, and was found to peak approximately 550 nm. We conclude that red cones receive an additional excitatory input from green cones (and possibly blue cones). A model of the cone mosaic suggests that approximately 50% of the red cone response (linear range) to a dim green test flash arises from neighboring green cones.

Animals↗
PubMed1984

Single unit activity in the auditory cortex and the medial geniculate body of the rhesus monkey: behavioral modulation.

Three Rhesus monkeys were trained to respond to a given auditory signal, the nature of which could be predicted from a preceding visual stimulus. The activity of 28 units in the auditory cortex and 53 units in the Medial Geniculate Body (MGB) of the monkey was recorded during task-performance conditions, as well as in the non-performance conditions. The activity of about one third of the cortical and MGB units was independent of the behaving status of the animal. In other units, the response to an auditory signal delivered during task-performance conditions as compared to the response recorded during non-performance periods was either augmented or attenuated. Furthermore, it was found that the spontaneous activity of most of the MGB and cortical units was continuously affected by either an excitatory or an inhibitory input, activated by the behavioral state. The temporal characteristics of behavioral modulation were studied by computing an amplification curve for all MGB units characterized by a 'through stimulus excitation' type of response. Analysis of these curves together with the behavioral effect on the spontaneous activity allows the suggestion of possible mechanisms by which the behavioral state of the monkey modulates the activity in the thalamocortical segment of the auditory system.

Animals↗
PubMed1984

Direct excitatory interactions between cones of different spectral types in the turtle retina.

Cone linear sensitivities to red and green stimuli were measured intracellularly in the dark- and light-adapted turtle retina. Test flashes of small diameter were used to minimize horizontal cell feedback. Light adaptation was achieved with either green or red background illumination. The ratio of cone sensitivities to red and green light depended on the color of the background light and differed from the ratio measured in the dark. Electron microscope studies of Golgi-stained turtle cones revealed direct synaptic connections between red and green cones mediated by cone telodendria. These data indicate that the red cone photoresponse is not univariant as has been previously supposed and suggest that mixing of signals from different spectral classes of cones can occur via direct excitatory connections between cones.

Animals↗
PubMed1984

Light adaptation in luminosity horizontal cells in the turtle retina. Role of cellular coupling.

Intracellular recordings were made from L-type horizontal cells in the retina of the turtle Clemmys caspica. The test flashes covered a retinal area smaller than the receptive field of the impaled cells. Increment responses were compared between two states of light adaptation that were equal in intensity but differed in spatial pattern. The peak amplitude of the response to a dim test flash was larger when measured during large-field background compared to the one obtained during small-field one. It is suggested that this phenomenon of surround enhancement is due to the cellular coupling between neighboring horizontal cells.

Adaptation, Ocular↗
PubMed1984

Retinal function in high refractive error assessed electroretinographically.

The retinal function of patients with high refractive error was studied electroretinographically. Thirty-one hypermetropic patients, 7 myopic patients, and 7 patients with either unilateral or bilateral aphakia participated in the study. The ERG responses were measured in the light- and dark-adapted states. It was found that myopic eyes were characterised by subnormal amplitude but normal pattern, expressed by normal relationship between the b-wave amplitude and the a-wave amplitude. In aphakia the ERG responses were of normal amplitude and pattern. However, the hypermetropic patients could be divided into 3 groups. One group included subjects with a subnormal b-wave to a-wave relationship. The second group was characterised by a normal b- to a-wave relationship, while patients belonging to the third group exhibited supernormal b-wave to a-wave relationship. This classification of hypermetropic subjects did not correlate with the axial length of the eye or the refraction of the ocular media.

Adolescent↗
PubMed1984

Night blindness and liver cirrhosis as late complications of jejunoileal bypass surgery for morbid obesity.

A patient underwent end-to-side jejunoileostomy for morbid obesity, and 3 years later an end-to-end jejunoileostomy with ileotransversostomy was performed. Nine years later she presented with night blindness, severe diarrhea and mild jaundice and was found to have malabsorption with vitamin A and K deficiencies as well as asymptomatic liver cirrhosis. Her shunt was removed, and a gastric partition was performed. The night blindness and abnormal prothrombin time were corrected by the administration of vitamins A and K. This case demonstrates that complications may appear many years after jejunoileal bypass surgery, and therefore, the patients should remain under strict medical supervision indefinitely.

Female↗
PubMed1983

Night vision in a case of vitamin A deficiency due to malabsorption.

Night vision was tested electroretinographically and psychophysically in a vitamin A deficient patient before and after therapy. Vitamin A deficiency resulted from malabsorption due to a jeujunoileal bypass operation. Before therapy the patient had severely reduced cone and rod function. After the reversal operation, accompanied by 5 injections of a total of 500,000 units of vitamin A, complete recovery of cone and rod functions was observed within 7 months. Shortly after therapy rod sensitivity reached the normal level, while the time course of rod adaptation remained slower than normal and the dark-adapted electroretinographic (ERG) responses were subnormal. At later stages the ERG responses reached normal amplitudes but rod adaptation stayed slow. Only after 7 months did night vision reach the normal level with regard to the time course of rod adaptation, rod sensitivity, and ERG responses.

Dark Adaptation↗
PubMed1983

Relationship between the amplitudes of the b wave and the a wave as a useful index for evaluating the electroretinogram.

The present methods for the assessment of the electroretinogram (ERG) make the exchange of data between laboratories difficult owing to differences in photostimulation and recording techniques. In this study it is suggested that in addition to present techniques the b wave to a wave relationship may be a useful index for evaluating the ERG. The ERG responses evoked by relatively bright flashes are recorded in the dark-adapted state. A plot of the b wave amplitude as a function of the a wave amplitude describes the functional integrity of the retina. A normally functioning retina should elicit an ERG response that fits the normal curve regardless of the apparatus used for ERG recording. The only constraint is the use of full-field illumination. This method is based on physiological considerations regarding the origin of the ERG components. Such a method will facilitate data exchange between centres and can also be used for clinical assessment of the retina.

Dark Adaptation↗
PubMed1982

Visual defects in the uninjured eye of patients with unilateral eye injury.

We have examined the electroretinographic responses, the psychophysically determined course of dark adaptation and/or the scotopic and photopic (static) perimetric profile of the uninjured eyes of 11 patients with unilateral intraocular foreign bodies. Most of the patients showed subnormal ERG amplitudes over a range of light intensities, and subnormal light sensitivity in isolated retinal areas. The data suggest that eyes not directly injured by a unilateral traumatic ocular episode may show visual defects.

Adolescent↗
PubMed1981

The relationship between visual sensitivity and rhodopsin density in retinitis pigmentosa.

Rhodopsin density and absolute threshold were determined in 11 patients with retinitis pigmentosa (RP) and nine normal subjects. In eight patients with familial histories suggesting recessive inheritance, the retinal areas studied showed marked decrease in sensitivity which was related to rhodopsin loss, probably via a log-linear relationship. The other three patients showed absolute thresholds that were linearly related to rhodopsin density, suggesting that sensitivity loss was determined by the decrease in quantal absorption resulting from rhodopsin loss. The results indicate that RP patients can be classified into two categories according to the effects of rhodopsin loss on rod sensitivity. These categories may correspond to different genetic groups. Furthermore, this differentiation may, in fact, reflect different underlying disease mechanisms.

Adolescent↗