Biomedical subjects

G D Mower

Publications and source records attributed to G D Mower.

34 records · Page 2Linked to original sources

PubMed1989

Evidence for an enhanced role of GABA inhibition in visual cortical ocular dominance of cats reared with abnormal monocular experience.

The effects of microiontophoretic bicuculline, a gamma-aminobutyric acid (GABA) antagonist, on the ocular dominance of visual cortical neurons were compared in normal cats and cats reared with abnormal monocular visual experience (monocular deprivation, surgical strabismus, and monocular deprivation after dark rearing). Cells that were monocular prior to drug application showed disinhibitory effects on ocular dominance far more frequently than originally binocular cells in all rearing conditions. When the total population of neurons was considered there were marked differences among rearing conditions: only 17% of cells showed change in ocular dominance in normal cats whereas over 50% showed changes in cats reared with abnormal monocular visual experience. These results indicate that GABA inhibition plays an enhanced role in cats with abnormal cortical ocular dominance. The results are interpreted in the context that the GABA system is passively biased by alterations in the pattern of excitatory input to contribute to abnormal patterns of ocular dominance.

Animals↗

PubMed1988

Quantitative comparisons of gamma-aminobutyric acid neurons and receptors in the visual cortex of normal and dark-reared cats.

Physiological studies suggest that the function of the visual cortical gamma-aminobutyric acid (GABA) system is abnormal in cats reared in total darkness. The present study asked whether visual input is necessary for the normal postnatal anatomical development of the GABA system by comparing GABA neurons and receptors in the visual cortex of normal and dark-reared cats. Immunohistochemical techniques (anti-GABA) were used to localize GABA neurons. In both rearing conditions, GABA neurons were stained rather uniformly in all cortical layers. Counts of GABA cells indicated a marked increase in density in dark-reared compared to normal cats. Counts of total cellular density in cresyl-stained sections, however, indicated a comparable increase in dark-reared cats. When corrected for total cellular density, there were no differences between dark-reared and normal cats in the density of GABA cells per layer, or the relative proportion of GABA cells across cortical layers. In vitro receptor binding of 3H-muscimol was used to compare GABAA receptors in the two rearing conditions. When corrected for total cellular density, saturation kinetics indicated no difference in the total number or affinity of receptors. Similarly, autoradiographic histology indicated no difference in the laminar distribution of receptors across cortical layers between dark-reared and normal cats. These results indicate that the postnatal development of GABA neurons and receptors occurs normally in the absence of visual input.

Aging↗

PubMed1987

Effects of monocular occlusion and diffusion on visual system development in the cat.

The effects of two forms of monocular deprivation (occlusion or diffusion) on visual system development were investigated. One group of cats monocularly deprived of all form stimulation but permitted diffuse light stimulation (diffusion, n = 4) during development showed a pattern of deficits similar to those reported for monocularly sutured cats. Most cells in the visual cortex were driven exclusively by the non-deprived eye and there were eye-specific deficits in X-cell acuity, proportion of Y-cells, and cell body size (binocular and monocular segment) in the lateral geniculate nucleus (LGN). A second group of cats monocularly deprived of all form and light stimulation (occlusion, n = 4) during development showed a less severe pattern of deficits. There was no acuity loss in LGN X-cells driven by the deprived eye, and cell body shrinkage was of smaller magnitude than in diffusion reared cats and was restricted to the binocular segment. Cortical deficits and LGN Y-cell loss were similar in the two groups. The results are consistent with the idea that monocular occlusion produces only deficits due to binocular competition while monocular diffusion reflects the combined effects of binocular competition and abnormal stimulation.

Animals↗

PubMed1986

[3H]muscimol binding of GABA receptors in the visual cortex of normal and monocularly deprived cats.

In vitro receptor binding techniques were used to compare the total number, affinity and regional distribution of GABA receptors in visual cortex, as revealed by [3H]muscimol binding, in 5 normal and 5 monocularly deprived (MD) cats. Analysis of saturation kinetics and pharmacological specificity indicated that binding was to a single site having the characteristics of the GABAA receptor. No differences were found between normal and MD cats in either number or affinity of receptors. Within visual cortex, there were laminar differences in the density of binding, but no evidence for a lateral (columnar) organization. Label was densest in the superficial layers (I-IV), lowest in layer V and intermediate in layer VI. This pattern of label varied with incubation parameters with layer IV showing the densest label when high concentrations of [3H]muscimol and short rinse times were used. There were no differences between normal and MD cats in regional distribution of receptors under any incubation condition.

Animals↗

PubMed1985

Comparative pharmacological effects on visual cortical neurons in monocularly deprived cats.

Monocularly deprived (MD) cats show a loss of responsiveness to visual stimulation of the deprived eye among visual cortical neurons. Several lines of evidence suggest that this effect involves, at least in part, a suppression of deprived eye input, possibly mediated by GABA inhibition. In order to better understand the nature of this suppression we have evaluated the effectiveness of different types of disinhibitory and excitatory agents to reverse the effects of MD. We investigated bicuculline (a GABA antagonist); picrotoxin (a GABA antagonist with a different mechanism of action from bicuculline); strychnine (a glycine antagonist); ammonium ion (a blocker of membrane chloride channels); physostigmine (a cholinesterase inhibitor); and naloxone (an opiate antagonist and also a GABA antagonist). All drugs were given intravenously. Bicuculline restored binocularity to 50% of the visual cortical neurons tested and naloxone to 36%. With both drugs, receptive fields of the normal eye tended to lose specificity. The emergent deprived eye receptive fields were usually similar to those of the normal eye after drug administration. Ammonium ion produced binocular responses in 27% of neurons tested, but receptive fields were grossly abnormal; moreover, ammonium infusion tended to depress neuronal responsiveness. All other drugs tested failed to restore binocularity. These experiments lend further credence to the hypothesis that GABA inhibition contributes to the cortical effects of MD, since only drugs with GABA antagonistic action were effective in restoring neuronal responsiveness to the deprived eye.

Acetates↗

PubMed1985

Dark rearing prolongs physiological but not anatomical plasticity of the cat visual cortex.

Recent studies (Cynader and Mitchell, '80; Mower et al., '81) have shown that total dark rearing prolongs susceptibility to the physiological effects of monocular deprivation (MD) in visual cortex beyond the normal age limits. The present study addressed whether this delayed physiological plasticity is accompanied by delayed anatomical plasticity in the geniculocortical pathway. Ocular dominance (OD) columns as defined by transsynaptic autoradiography following injection of 3H proline into one eye were studied both qualitatively and quantitatively in 17 cats. Compared to normal rearing (N-3), both binocular eyelid suture (N-2) and total dark rearing (N-3) resulted in incomplete segregation of OD columns in area 17. This apparent immaturity after binocular deprivation, however, did not reflect a delayed capacity for development and plasticity. Visual experience after dark rearing produced no marked changes. In cats who experienced MD after dark rearing, injection of either the nondeprived (N-2) or deprived eye (N-3) resulted in a nearly uniform distribution of label throughout layer IV of area 17. The same result occurred with binocular vision after dark rearing (N-1). MD from birth, however, produced expansion of columns from the nondeprived eye (N-1) and contraction of columns from the deprived eye (N-1). MD imposed after 4 months of normal vision resulted in normal OD columns (N-1). Electrophysiological studies revealed a high proportion of binocular cells within layer IV in cats who experienced monocular or binocular vision after dark rearing. Outside of layer IV there were clear environmental effects on OD of single cells in these cats. Measurements of cell sizes in the clateral geniculate nucleus showed shrinkage of cells innervated by the deprived eye when MD was initiated at birth (N-3). MD after dark rearing (N-4) produced no differences in cell sizes. It is concluded that visual input is necessary for the formation of normal OD columns, the critical period for formation and environmental modification of OD columns is limited to early life, and the physiological effects of visual experience after dark rearing reflect changes occurring beyond the geniculocortical pathway.

Animals↗

PubMed1985

Role of visual experience in activating critical period in cat visual cortex.

Cats were reared in total darkness from birth until 4-5 mo of age (DR cats, n = 7) or with very brief visual experience (1 or 2 days) during an otherwise similar period of dark rearing [DR(1) cats, n = 3; DR(2) cats, n = 7]. Single-cell recordings were made in area 17 of visual cortex at the end of this rearing period and/or after a subsequent prolonged period of monocular deprivation. Control observations were made in normal cats (n = 3), cats reared with monocular deprivation from birth (n = 4), and cats monocularly deprived after being reared normally until 4 mo of age (n = 2). After rearing cats in total darkness, the majority of visual cortical cells were binocularly driven and the overall distribution of ocular dominance was not different from that of normal cats. Orientation-selective cells were very rare in dark-reared cats. Monocular deprivation imposed after dark rearing resulted in selective development of connections from the open eye. Most cells were responsive only to the open eye and the majority of these were orientation selective. These results were similar to, though less severe than, those found in cats reared with monocular deprivation from birth. Monocular deprivation imposed after 4 mo of normal rearing did not produce selective development of connections from the open eye in terms of either ocular dominance or orientation selectivity. In DR(1) cats visual cortical physiology was degraded in comparison to dark-reared cats after the rearing period. Most cells were binocularly driven but there was a higher frequency of unresponsive cells and a reduced frequency of orientation-selective cells. Subsequent monocular deprivation resulted in a further decrease in the number of binocularly driven cells and an increase in unresponsive cells. However, it did not produce a bias in favor of the open eye in terms of either ocular dominance or orientation selectivity. In DR(2) cats there was a high incidence of unresponsive cells and a marked loss of binocularly driven cells after the rearing period. Subsequent monocular deprivation failed to produce any significant changes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1984

Microiontophoretic bicuculline restores binocular responses to visual cortical neurons in strabismic cats.

Rearing cats with surgically induced strabismus resulted in an abnormally high percentage (80%) of monocularly driven neurons in visual cortex. Microiontophoretic application of the GABA antagonist bicuculline restored binocular responses to over 50% of these monocular cells. Elevation of spontaneous rate by glutamate failed to produce binocularity. These results indicate that intracortical inhibition plays a role in the abnormal ocular dominance distribution of strabismic cats.

Animals↗

PubMed1983

Very brief visual experience eliminates plasticity in the cat visual cortex.

Rearing cats in the dark extends the critical period for development of visual cortical neurons, which indicates that the experience of visual input is necessary to begin the developmental process. A single brief pulse of visual input (6 hours) during a period of dark-rearing eliminates delayed development in the visual cortex. Light therefore seems to rapidly trigger the developmental process, and once triggered, that process runs to completion in the absence of further input.

Animals↗

PubMed1983

Animal models of strabismic amblyopia: comparative behavioral studies.

Visual acuity and visuo-motor behavior were assessed in various models of experimental amblyopia in cats (n = 15). Three models of strabismic amblyopia were studied: surgical esotropia by sectioning one lateral rectus muscle; comitant optical strabismus by rearing cats with goggles which placed a stationary wedge prism before one eye; and incomitant optical strabismus by rearing cats with goggles which placed a rotatable wedge prism before one eye. These cats were compared with normal and monocularly deprived cats. Clear amblyopic deficits were found in monocularly deprived, esotropic and rotating prism cats. The amblyopic deficits were graded among these preparations, being most severe in monocularly deprived cats and least severe in esotropic cats. The degree of behavioral amblyopia in these preparations was correlated with the extent of physiological abnormalities in visual cortex and the lateral geniculate nucleus. Fixed optical strabismus did not result in behavioral deficits and does not appear to be a good model of strabismic amblyopia. Variable optical strabismus, on the other hand, produced clear deficits in one eye, both behaviorally and physiologically, without impaired ocular motility.

Amblyopia↗

PubMed1982

Effects of early monocular deprivation on the acuity of lateral geniculate neurons in the cat.

Acuity assessments on lateral geniculate X-cells in 8 monocularly deprived cats indicated that deprived cells had significantly lower acuities than non-deprived cells. Within deprived laminae, cells having low acuity were intermixed with cells having normal acuity. Deprivation effects were clearly evident in both A and A1 laminae and in both adult and young cats. The results also pointed out several factors which should be considered in analyzing deprivation effects.

Animals↗

PubMed1982

Animal models of strabismic amblyopia: physiological studies of visual cortex and the lateral geniculate nucleus.

Receptive field properties of visual cortical and lateral geniculate cells were studied in 4 models of amblyopia in the cat: monocular deprivation (MD cats), surgical esotropia (esotropic cats), optically induced concomitant strabismus (stationary prism cats) and optically induced incomitant strabismus (rotating prism cats). Comparison observations were made in normal cats. Recordings in visual cortex indicated a reduction in responsiveness to the treated eye in MD and rotating prism cats. Esotropic and stationary prism cats showed mainly a loss of binocular cells. Recordings in the lateral geniculate nucleus indicated a reduction in the spatial resolving capacity of X-cells driven by the treated eye in MD, esotropic and rotating prism cats. The magnitude of this effect was comparable in all of these preparations. Stationary prism cats showed comparable spatial resolving capacities in X-cells driven by either eye. Y-cells were unaffected in any preparation except MD where there were reduced frequencies of Y-cells driven by the treated eye. These results indicate that: (1) interocular differences in spatial patterns without form deprivation are sufficient to produce a loss of responsiveness to one eye in visual cortex; (2) incomitant disparities are necessary to produce the physiological correlates of amblyopia in cats; and (3) deficits in spatial resolution in geniculate neurons are comparable in magnitude in various amblyopic preparations.

Amblyopia↗

PubMed1982

Behavioral recovery from binocular deprivation in the cat.

Visuo-motor behavior and visual acuity were assessed in animals who experienced monocular vision after a prolonged period of binocular deprivation. In animals who experienced initial binocular suture, there was limited recovery and no difference between the initially opened and late opened eye. In animals who experienced initial dark-rearing, the initially opened eye recovered to normal levels and the late opened eye showed severe amblyopia. These differences in behavioral recovery between dark-rearing and binocular suture are compared with physiological differences between the two rearing conditions.

Animals↗

PubMed1981

Comparison of the effects of dark rearing and binocular suture on development and plasticity of cat visual cortex.

Comparisons were made between the effects of binocular suture and dark rearing in terms of: (1) the state of visual cortical physiology after prolonged deprivation; and (2) the nature of physiological recovery seen when monocular vision was experienced after prolonged deprivation. These comparisons were based on the ocular dominance distribution and receptive field tuning characteristics of visual cortical cells. After prolonged dark rearing, most visual cortical cells were binocularly activated and had non-specific receptive field properties. Monocular vision after dark rearing produced dramatic changes: the majority of cells were responsive only to the open eye and these cells typically displayed orientation and direction selectivity. Prolonged binocular suture, on the other hand, resulted in a high incidence of unresponsive cells and cells with unmappable receptive fields, and a low proportion of binocularly responsive cells. Monocular vision experienced after binocular suture resulted in only slight physiological changes, and there was no evidence for selective development of connections from the open eye. These results indicate that dark rearing and binocular suture have different effects on the development of cat visual cortical cells. Diffuse visual stimulation through the sutured lids (binocular suture) appears to produce permanent developmental effects on cortical physiology, whereas complete deprivation (dark rearing) leaves cortex in a state which can be modified by subsequent visual experience.

Animals↗

PubMed1981

The effects of dark-rearing on the development and plasticity of the lateral geniculate nucleus.

During a prolonged period of dark-rearing, lateral geniculate X-cells developed normal spatial resolving capacities and otherwise normal receptive field properties. Y-cells were reduced in frequency. Neither of these developmental processes were altered by subsequent monocular vision. In visual cortex, on the other hand, both the development of normal receptive field properties and the susceptibility to monocular deprivation were delayed by dark-rearing.

Animals↗

PubMed1976

Perceived intensity of peripheral thermal stimuli is independent of internal body temperature.

Four adult male human subjects were tested under three conditions of internal body temperature: hypothermia, normal, and hyperthermia. Under each of these conditions, they judged the intensity (degree of warmness or coolness) and the hedonic quality (degree of pleasantness or unpleasantness) of a series of stimuli ranging from hot to cold. The results showed that whereas hedonic quality is greatly influenced by the value of internal body temperature, the perception of warmness or coolness is independent of internal temperature and dependent only on peripheral stimulation.

Adult↗