Biomedical subjects

D Czepita

Publications and source records attributed to D Czepita.

At least 19 recordsLinked to original sources

PubMed2001

[Current state of knowledge on the subject of astigmatism etiopathogenesis].

PURPOSE: To present current state of knowledge on the subject of astigmatism etiopathogenesis. MATERIAL AND METHODS: A review of contemporary literature concerning pathomechanism of astigmatism. RESULTS: The optical, morphological and functional changes taking place in the visual pathway during the astigmatism are described. Special attention was focused on the functional modifications in the neuronal system of Brodmann's 17th area. The frequency of occurrence as well as the forms of astigmatism among children and adults are characterized. The results of papers indicating environmental and genetic reasons of astigmatism as well as the possible pathomechanism of astigmatism creation are presented. The necessity of astigmatism treatment before the end of visual cortex plasticity has been pointed out. The attitude towards some surgical methods of astigmatism treatment is expressed.

Adult↗

PubMed2000

[Epidemiology of myopia].

The present state of knowledge on the epidemiology of myopia is discussed. The history of myopia investigations is described. The prevalence of myopia in different ages, races and populations is presented. The factors influencing myopia occurrence are characterized. Special attention is focused on the results of studies indicating environmental and genetic reasons of myopia. Most recent investigations concerning the influence of light on myopia occurrence as well as concerning a genetic locus for high myopia are described.

Adolescent↗

PubMed1999

Injection of MK-801 affects ocular dominance shifts more than visual activity.

Kittens were given intramuscular injections of the N-methyl--aspartate (NMDA) antagonist MK-801 twice daily (morning and midday) during the peak of the period of susceptibility for ocular dominance changes. They were then exposed to light with one eye closed for 4 h after each injection. The ocular dominance of these kittens was shifted significantly less than that of kittens injected with saline and exposed to light over the same period at the same age. After recording a sample of cells for an ocular dominance histogram, the kittens were injected with the same dose of MK-801 that was used during rearing to observe its effect on the activity of single cells in the visual cortex. In the majority of cells (7/13) there was no significant change in activity. Positive evidence for a reduction in activity was seen in only a minority (3/13) of cells. In a separate series of experiments, dose-response curves were measured for cells in the visual cortex in response to iontophoresis of NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and the effect of an injection of MK-801 on these curves was measured. MK-801, at doses similar to those used in the ocular dominance experiments, had a significant effect on the dose-response curves for NMDA, but little effect on the dose-response curves for AMPA, or the visual responses of the cells. We conclude that ocular dominance shifts can be reduced significantly by a treatment that has little effect on the level of activity of cells in the visual cortex but does specifically affect the responses of the cells to NMDA as opposed to the responses to AMPA.

Algorithms↗

PubMed1999

[David H. Hubel, Torsten N. Wiesel, Nigel W. Daw: the creators of modern visual neurophysiology].

Curriculum vitae as well as scientifical out-put of the Nobel Price winners--David Hunter Hubel and Torsten Nils Wiesel, and the Friedenwald Memorial Award laureate--Nigel Warwick Daw are described. D.H. Hubel was born in 1926 in Windsor, Canada. In 1951 he received a medical degree from McGill University. From 1955-1958 he worked at Walter Reed Army Institute of Research, from 1958-1959 at Johns Hopkins University, and since 1959 at Harvard University. T.N. Wiesel was born in 1924 in Uppsala, Sweden. In 1954 he received a medical degree from Karolinska Institute. From 1955-1959 he worked at Johns Hopkins University, from 1959-1982 at Harvard University, and since 1983 at the Rockefeller University, New York. N.W. Daw was born in 1933 in London, England. In 1961 he received a bachelor's degree in mathematics from Trinity College. In 1967 he became a doctor of philosophy in biophysics at Johns Hopkins University. From 1967-1969 he worked at Harvard University, from 1969-1992 at Washington University, and since 1992 at Yale University.

Canada↗

PubMed1999

[The possibilities of using the newest experimental results in the progressive myopia treatment].

Most recent experimental results concerning the pathomechanism of myopia are discussed. Anatomical, physiological, and biochemical changes taking place in the eye with experimental myopia are described. Special attention is focused on the following substances inhibiting the progress of experimental myopia: apomorphine, reserpine, 6-hydroxydopamine, atropine, pirenzepine, chlorpyrifos, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, kainic acid, naloxane, formoguanamine, gentamicin, sodium iodate, central and peripheral antagonist of vasoactive intestinal polypeptide, basic fibroblast growth factor. The possibilities of the above-mentioned pharmacological agents in the progressive myopia treatment are indicated.

Animals↗

PubMed1999

[The study of the NMDA receptor function in the visual cortex. Summary of habilitation thesis].

PURPOSE: Finding the agents influencing the function of NMDA receptors in the visual cortex. MATERIAL AND METHODS: The experiments were performed on cats aged from three weeks to several years. Recordings were made from single neurons of the visual cortex after iontophoresis of N-methyl-D-aspartate acid, D-2-amino-5-phosphonovaleric acid, D-serine, 7-chlorokynurenic acid. RESULTS: It was found that: 1. Light is one of the factors which has an influence on the development of NMDA receptors in the visual cortex. Rearing cats in the dark is delaying the changes in the function of NMDA receptors, reducing the number of directional sensitive neurons, lowering the firing rate during the visual response. 2. Monocular deprivation is first creating the reduction of the NMDA receptors' contribution to the visual response and later the functional degradation of the synapse. 3. In the Brodmann's 17th area most glycine sites at the NMDA receptors are not saturated by endogenous glycine.

Animals↗

PubMed1999

[The role of the NMDA receptors in the creating of amblyopia].

The present state of knowledge concerning the etiopathogenesis of amblyopia is discussed. The morphological and functional changes taking place in the neuronal system of the Brodmann's 17th area during the amblyopia creation are described. The factors affecting the primary and secondary visual cortex are characterized. Special attention was focused on the N-methyl-D-aspartate (NMDA) receptors. Their structure and function is described. The role of the NMDA receptors in the formation of the visual cortex plasticity is discussed. The necessity of amblyopia treatment before the critical period is over has been pointed out. The possibilities of using the newest experimental results in amblyopia treatment are indicated.

Amblyopia↗

PubMed1999

[Contemporary views on the etiology, pathogenesis as well as treatment of school-age and progressive myopia].

The contemporary views on the etiology, pathogenesis as well as treatment of school-age and progressive myopia are discussed. The history of myopia investigations is described. The results of papers indicating environmental and genetic reasons of myopia are presented. The anatomical, physiological, and biochemical changes taking place during the school-age and progressive myopia progress are characterized. The attitude towards some conservative and surgical methods of school-age and progressive myopia is expressed. The possibilities of using the newest experimental results in progressive myopia treatment are indicated.

Adolescent↗

PubMed1998

[Contemporary knowledge on the subject of visual cortex structure and function].

The present state of knowledge concerning the structure and the function of the visual cortex was discussed. Special attention was focused on the: (1) retino-geniculo-cortical pathway (2) representation and topography of the visual cortex (3) anatomy, physiology, and functional architecture of the primary visual cortex (4) organization and function of the parvocellular, magnocellular, and koniocellular pathway (5) functional specialization and connections between the visual areas (6) neurotransmitters' presence and function in the Brodmann's 17th area.

Humans↗

PubMed1996

The contribution of NMDA receptors to the visual response in animals that have been partially monocularly deprived.

Kittens were monocularly deprived to give a partial shift in the ocular dominance histograms from their visual cortices. Responses were measured for the normal and deprived eyes at a variety of contrasts, and curves fitted to give measurements of background activity and peak visual response. The N-methyl-D-aspartate (NMDA) antagonist D-2-amino-5-phosphonovalerate (APV) was then applied, and the effect on the contrast-response curves was measured, and compared in the two eyes. In normal animals, the effect of APV on the contrast-response curve was similar in the two eyes. In monocularly deprived animals, on average, peak visual response was affected similarly in the two eyes, although there was wide variability from cell to cell. When the effect of APV on background activity was measured, there was difference between the normal and deprived eyes. APV reduced background activity in the normal eye more than it reduced background activity in the deprived eye. In other words, the NMDA contribution to background activity in the deprived eye was reduced compared to the NMDA contribution to background activity in the normal eye. This could represent a reduction of NMDA receptors in the pathway from the deprived eye, like the reduction of acetylcholine receptors associated with the losing input at the neuromuscular junction before the nerve is eliminated.

2-Amino-5-phosphonovalerate↗

PubMed1996

Inhibition of nitric oxide synthase does not alter ocular dominance shifts in kitten visual cortex.

1. Since nitric oxide has been proposed as a feedback factor in plasticity in the hippocampus, we tested whether it might also be a feedback factor in sensory-dependent plasticity in the cat visual cortex. 2. The effects of monocular deprivation were compared between eight hemispheres with infusion of a nitric oxide synthase inhibitor, and eight control hemispheres with either infusion of the inactive isomer, or no infusion. Although nitric oxide synthase activity was reduced significantly, the ocular dominance histograms were not substantially different in the two groups of animals. We conclude that the feedback factor for sensory-dependent plasticity in the visual cortex is likely to be some factor other than nitric oxide.

Animals↗

PubMed1996

Glycine at the NMDA receptor in cat visual cortex: saturation and changes with age.

1. Saturation of the glycine site at the N-methyl-D-aspartate (NMDA) receptor in cat visual cortex was tested by iontophoresing D-serine, and the contribution of this site to the visual response was tested by iontophoresing 7-chlorokynurenic acid (7-Cl-KYNA). Animals were tested at ages 3 wk, 6 wk, 5 mo, and adult. 2. In at least 40% of cells (24/57), D-serine increased the response significantly, showing that the glycine site was not saturated. However, the increase was rarely > 100%. 3. The amount by which D-serine increased the response did not vary significantly with age. 4. In five cases there was positive evidence for saturation of the glycine site. D-Serine did not increase the response significantly; however, when D-serine was applied on top of 7-Cl-KYNA, it did increase the response compared with that seen with 7-Cl-KYNA alone. These cases were all in 3-wk-old animals. In other cases (28/57), D-serine did not increase the response significantly, but we could not be absolutely certain that the D-serine had reached the site of action. 5. The effect of 7-Cl-KYNA was largest in 3-wk animals, in agreement with previous findings that the effect of D-2-amino-5-phosphonovalerate (APV) is largest at this age. 6. These results may provide a small part of the explanation for the finding that the NMDA receptor-mediated component of the visual response decreases between 3 and 6 wk of age, while the number of NMDA receptors is increasing. However, the magnitude of the results make it likely that other factors are more important.

Aging↗

PubMed1994

Effect of longer periods of dark rearing on NMDA receptors in cat visual cortex.

1. Cats were reared in the dark to 3, 5, and 11 mo. We studied the N-methyl-D-aspartate (NMDA) receptor contribution to the visual response in the cortex, defined as the percentage reduction in visual response after application of 2-amino-5-phosphonovaleric acid (APV). We also studied the firing rate in response to the optimal visual stimulus and the spontaneous activity. We made comparisons of all these properties between light-reared and dark-reared animals. 2. The NMDA receptor contribution to the visual response in layers IV, V, and VI of dark-reared animals was substantially above that in light-reared animals at all ages tested. 3. The specificity of receptive field properties in dark-reared animals showed some degeneration between 6 wk and 3 mo of age. At > or = 3 mo, almost no cells were specific for orientation and direction of movement. 4. Firing rate was lower in dark-reared animals at all ages, suggesting a decrease in excitatory drive to the visual cortex. 5. Spontaneous activity was equal in dark- and light-reared animals, suggesting that the overall level of activity (including visual responses as well as spontaneous activity) in light-reared animals is higher than in dark-reared animals. This should tend to upregulate glutamate receptors in general in dark-reared animals.

2-Amino-5-phosphonovalerate↗

PubMed1992

Critical period for monocular deprivation in the cat visual cortex.

1. Cats were monocularly deprived for 3 mo starting at 8-9 mo, 12 mo, 15 mo, and several years of age. Single cells were recorded in both visual cortexes of each cat, and the ocular dominance and layer determined for each cell. Ocular dominance histograms were then constructed for layers II/III, IV, and V/VI for each group of animals. 2. There was a statistically significant shift in the ocular dominance for cells in layers II/III and V/VI for the animals deprived between 8-9 and 11-12 mo of age. There was a small but not statistically significant shift for cells in layer IV from the animals deprived between 8-9 and 11-12 mo of age, and for cells in layers V/VI from the animals deprived between 15 and 18 mo of age. There was no noticeable shift in ocular dominance for any other layers in any other group of animals. 3. We conclude that the critical period for monocular deprivation is finally over at approximately 1 yr of age for extragranular layers (layers II, III, V, and VI) in visual cortex of the cat.

Aging↗

PubMed1992

The effect of visual experience on development of NMDA receptor synaptic transmission in kitten visual cortex.

We have studied the effect of dark rearing on the development of excitatory amino acid transmission in 6-week-old kittens. In normal kittens, the NMDA component of the visual response decreases between 3 and 6 weeks of age for cells located in layers IV, V, and VI (Fox et al., 1991). Dark rearing to 6 weeks of age prevents this decrease. Subsequent exposure to light allows the decrease to proceed. Ten days in the light after 6 weeks in the dark was sufficient to decrease the NMDA component of the visual response to the same levels seen in light-reared animals of the same age. Comparison of the effect of the non-NMDA antagonist 6-cyano-7-dinitroquinoxaline-2,3-dione with the NMDA antagonist aminophosphonovalerate showed that the changes were due to the relative contributions of NMDA and non-NMDA receptors to the visual response rather than the overall contribution of glutamate receptors. We also studied the receptive field properties of the cells in the various groups of kittens. Cells given 4 d in the light after 6 weeks in the dark showed increased direction selectivity but little change in response firing rate. After 10 d in the light, visual responses did show some recovery toward adult values, but neither average firing rates nor the proportion of direction-selective cells reached the levels found in normal 6-week-old animals, contrary to the suggestion that a short period in the light can reverse the effect of dark rearing completely. These results show that the decrease in the NMDA component of the visual response seen during normal development of the cortex is caused by visual experience. Changes in NMDA receptors and developmental events such as geniculocortical afferent segregation and acquisition of orientation tuning covary as a function of visual experience rather than age, strongly suggesting that NMDA receptors are involved in experience-dependent developmental processes.

2-Amino-5-phosphonovalerate↗

PubMed1991

Dark-rearing delays the loss of NMDA-receptor function in kitten visual cortex.

Some features of the visual cortex develop postnatally in mammals. For example, geniculocortical axons that initially overlap throughout cortical layer IV segregate postnatally into two sets of interleaved eye-specific bands. NMDA (N-methyl-D-aspartate) receptors are necessary for eye-specific axon-segregation in the frog tectum, and as NMDA receptors play a greater part in synaptic transmission in early life and decrease in function during the period of axon segregation, they may be involved in the segregation of geniculocortical axons: they are well placed to do so as they transduce retinally derived signals essential for segregation. Rearing animals in the dark in early life delays segregation and prolongs the critical period for plasticity. We now report that dark-rearing of kittens also delays the loss of NMDA receptor function in the visual cortex, supporting the view that they play an important part in neuronal development and plasticity.

2-Amino-5-phosphonovalerate↗

PubMed1990

[Experimental studies of the role of the adrenergic system in the development of bioelectric response of the retina and visual cortex. IV. Visual evoked potentials in rabbits after administration of alpha and beta receptor agonists and blockaders].

The influence of noradrenaline, dihydroergotamine, isoprenaline and propranolol on the VEP in rabbit was examined. The records of VEP showed a lowering of the amplitude of the A and B waves after compounds stimulating and restraining the adrenergic alpha and beta receptors. The C wave increased after dihydroergotoxine, isoprenaline and propranolol; it was lowered after noradrenaline. On the basis of the obtained results the author discusses the role of the adrenergic system in formation of the bioelectric response of the visual cortex.

Animals↗

PubMed1990

Influence of alpha and beta-adrenergic stimulators and blockers on the electroretinogram and visually evoked potentials of the rabbit.

The effect of alpha and beta-adrenergic stimulators and blockers on the electroretinogram and visually evoked potentials of the rabbit was studied. It has been observed that subcutaneous administration of noradrenaline, dihydroergotoxine, isoprenaline, propranolol and adrenaline influence the amplitudes of ERG and VEP waves. On the basis of the established results, the role of the adrenergic system in forming the bioelectric response of the retina and visual cortex is discussed.

Animals↗