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  • 1
    Electronic Resource
    Electronic Resource
    Functional amblyopia in kittens with unilateral exotropia (1980)
    Springer
    Experimental brain research 40 (1980), S. 305-310 
    Details
    ISSN: 1432-1106
    Keywords: Squint amblyopia ; Visual cortex ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In two dark reared, 40 day old kittens unilateral divergent squint was induced be resecting the insertion of the medial rectus muscle. Behavioural testing revealed that the kittens used only the normal eye for fixation. Contrast sensitivity functions of the two eyes and visual acuity were determined behaviourally in a jumping stand whereby the kittens had to discriminate sine-wave gratings or variable spatial frequency and contrast from a flux equated homogeneous field. At photopic luminance levels the deviated eye showed a significant deficit in both kittens. This impairment was apparent over the whole range of spatial frequencies (0.18–0.99 c/deg) except for the lowest spatial frequency in one kitten. The interocular difference of visual acuity disappeared at scotopic luminance levels. In subsequent electrophysiological experiments contrast sensitivity functions were determined from cortical evoked potentials that were elicited by phase reversing square wave gratings. Comparison between behavioural and electrophysiological results revealed a very good correspondence between the two sets of data. It is concluded that exotropia without alternating fixation leads to functional amblyopia of the deviated eye.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237795
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  • 2
    Electronic Resource
    Electronic Resource
    Functional amblyopia in kittens with unilateral exotropia (1980)
    Springer
    Experimental brain research 40 (1980), S. 294-304 
    Details
    ISSN: 1432-1106
    Keywords: Squint amblyopia ; Visual cortex ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In two cats in which surgically induced, unilateral divergent strabismus had led to behaviourally determined amblyopia, a variety of electrophysiological parameters were determined in search of neuronal correlates of squint amblyopia. Tests that assess global neuronal excitability along the pathways from the two eyes to the visual cortex (areas 17 and 18) failed to reflect the functional inferiority of the squinting eye: retinographic responses and cortical evoked potentials elicited by Ganzfeld-stimulation and by stimulation of the optic nerves were identical for the two eyes. The ocular dominance distribution of neurons in area 17 showed the expected disruption of binocularity but failed to provide clear evidence for a functional inferiority of the squinting eye. At other levels of analysis, however, a clear difference between the two eyes was apparent: 1. Responses to optimally aligned light stimuli tended to be more sluggish and the under-representation of neurons with vertically oriented receptive fields was more pronounced in neurons driven from the deviated eye than in cells dominated by the normal one. 2. Interocular inhibition as assessed from electrically evoked potentials was found to be asymmetric; responses evoked from the amblyopic eye were suppressed more readily and over longer periods by conditioning shocks applied to the normal nerve than vice versa. 3. Numerous abnormalities reflecting the functional inferiority of the squinting eye became apparent in cortical potentials evoked by phase reversal of gratings of variable spatial frequency and contrast. A laminar analysis of these field potentials suggests impaired transmission along the intracortical pathways which relay activity to supragranular layers as a major cause for abnormal responses from the squinting eye. It is concluded that squint amblyopia is associated with a variety of neuronal changes at various levels of the visual system, the present data providing evidence for alterations at the cortical level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237794
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  • 3
    Electronic Resource
    Electronic Resource
    Central core control of developmental plasticity in the kitten visual cortex: I. Diencephalic lesions (1982)
    Springer
    Experimental brain research 47 (1982), S. 209-222 
    Details
    ISSN: 1432-1106
    Keywords: Developmental plasticity ; Visual cortex ; Attention ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In five, dark-reared, 4-week-old kittens the posterior two thirds of the corpus callosum were split, and a lesion comprising the intralaminar nuclei was made of the left medial thalamic complex. In addition, the right eye was closed by suture. Postoperatively, the kittens showed abnormal orienting responses, neglecting visual stimuli presented in the hemifield contralateral to the side of the lesion. Sudden changes in light, sound, or somatosensory stimulation elicited orienting responses that all tended toward the side of the lesion. These massive symptoms faded within a few weeks but the kittens continued to neglect visual stimuli in the hemifield contralateral to the lesion when a second stimulus was presented simultaneously in the other hemifield. Electrophysiologic analysis of the visual cortex, performed after the end of the critical period, revealed marked interhemispheric differences. In the visual cortex of the normal hemisphere most neurons were monocular and responded exclusively to stimulation of the open eye, but otherwise had normal receptive field properties. In the visual cortex of the hemisphere containing the thalamic lesion, the majority of the neurons remained binocular. In addition, the selectivity for stimulus orientation and the vigor of responses to optimally aligned stimuli were subnormal on this side. Thus, the same retinal signals, which in the control hemisphere suppressed the pathways from the deprived eye and supported the development of normal receptive fields, failed to do either in the hemisphere containing the thalamic lesion. Apparently, experience-dependent changes in the visual cortex require both retinal stimulation and the functioning of diencephalic structures which modulate cortical excitability and control selective attention.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239380
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  • 4
    Electronic Resource
    Electronic Resource
    Central core control of developmental plasticity in the kitten visual cortex: II. Electrical activation of mesencephalic and diencephalic projections (1982)
    Springer
    Experimental brain research 47 (1982), S. 223-233 
    Details
    ISSN: 1432-1106
    Keywords: Visual cortex ; Development ; Plasticity ; Central core ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Fifteen dark-reared, 4- to 5-week-old kittens were stimulated monocularly with patterned light while they were anesthetized and paralyzed. Six of these kittens were exposed to the light stimuli only, in four kittens the light stimuli were paired with electric stimulation of the mesencephalic reticular formation and in five kittens with electric activation of the medial thalamic nuclei. Throughout the conditioning period, the ocular dominance of neurons in the visual cortex was determined from evoked potentials that were elicited either with electric stimulation of the optic nerves or with phase reversing gratings of variable spatial frequencies. In two kittens, ocular dominance changes were assessed after the end of the conditioning period by analyzing single unit receptive fields. Monocular stimulation with patterned light induced a marked shift of ocular dominance toward the stimulated eye, when the light stimulus was paired with electric activation of either the mesencephalic reticular formation or of the medial thalamus. Moreover, a substantial fraction of cells acquired mature receptive fields. No such changes occurred with light or electric stimulation alone. It is concluded that central core projections which modulate cortical excitability gate experience-dependent modifications of connections in the kitten visual cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239381
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  • 5
    Electronic Resource
    Electronic Resource
    Developmental changes of the distribution of binding sites for organic Ca2+-channel blockers in cat visual cortex (1988)
    Springer
    Experimental brain research 70 (1988), S. 266-275 
    Details
    ISSN: 1432-1106
    Keywords: Calcium ; Plasticity ; Visual cortex ; Organic Ca2+-channel blockers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary There are indications that during a critical period of visual cortex development Ca2+-fluxes from extra- to intracellular compartments serve as a trigger signal for experience-dependent changes of neuronal response properties. In this study we investigate the possibility of a relation between the time course of the critical period and age-dependent changes in the density and topographical distribution of Ca2+-channels. As a marker for the latter we used Ca2+-channel blockers of the 1,4-Dihydropyridine (1,4-DHP) class since these are supposed to bind to voltage-dependent Ca2+-channels. We used the tritiated 1,4-DHP derivative 3H-PN 200 110 for autoradiographic determination of 1,4-DHP binding sites in the visual cortex of adult cats and kittens ranging in age from two to ten weeks. The binding of 3H-PN 200 110 to slide-mounted tissue sections was saturable and of high affinity. The overall density of specific 3H-PN 200 110 binding sites decreased during development and their laminar distribution underwent marked changes: in young kittens specific binding was accentuated in lower layer IV, whereas in adult cats the supragranular layers were most intensely labeled. Dark rearing did not affect these developmental changes of 3H-PN 200 110 binding sites. The time course of the reduction of 1,4-DHP binding sites correlates well with that of the age-dependent decrease of the susceptibility to experience-dependent modifications. We consider this result as compatible with the hypothesis that use-dependent modifications of the response properties of cortical neurons involve changes in the Ca2+-fluxes from extra- to intracellular compartments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248352
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of short periods of monocular deprivation on excitatory transmission in the striate cortex of kittens: a current source density analysis (1991)
    Springer
    Experimental brain research 85 (1991), S. 519-527 
    Details
    ISSN: 1432-1106
    Keywords: Monocular deprivation ; Visual cortex ; Current source density ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The goal of this study was to assess changes in synaptic activity in the visual cortex of kittens following brief periods of monocular deprivation. Field potentials evoked by electrical stimulation of both optic nerves were registered in vertical penetrations through areas 17 and 18 of 4–5 week-old kittens which had been monocularly deprived for 2–7 days. In order to assess the laminar distribution of synaptic currents these field potentials were subjected to a current source density analysis. Current source density profiles elicited from the deprived eye differed from those induced from the normal eye in several respects: 1) The amplitudes of the responses showed considerable variation at different recording sites across the tangential dimension of cortex. 2) On the average, sinks and sources were markedly reduced, and this reduction was relatively more pronounced in nongranular than in granular layers. 3) However, in 30% of the tracks the layer IV sink showed no attenuation. It was reduced in 48% of the tracks and completely suppressed in 22% of the tracks. These results indicate that a substantial fraction of the deprived thalamocortical synapses remained functional, but that many of these synaptic events remained subthreshold. The significance of these findings is discussed in the context of recovery processes following reverse suture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231735
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  • 7
    Electronic Resource
    Electronic Resource
    A current source density analysis of field potentials evoked in slices of visual cortex (1987)
    Springer
    Experimental brain research 69 (1987), S. 213-219 
    Details
    ISSN: 1432-1106
    Keywords: Cortex slices ; Field potentials ; Current source density analysis ; Visual cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The method of one-dimensional current source density (CSD) analysis was applied to field potentials recorded from 350 μm thick slices of the primary visual cortex of rats and cats. Field potentials were elicited by stimulation of the white matter and recorded along trajectories perpendicular to the cortical layers at spatial intervals of 25 to 50 μm. The resulting CSD distributions resembled closely those recorded from the cat visual cortex “in vivo”. The responses with the shortest latency were distinct sinks in layers IV and VI probably reflecting monosynaptic EPSP's from specific thalamic afferents. From layer IV activity was relayed along three major routes: 1. to the supragranular layers via strong local connections to layer III and from there via both short and long range connections to layer II, 2. to targets within layer IV, and 3. to layer V. The source distributions suggest that the projections to layers III and II terminate on the proximal and distal segments, respectively, of apical dendrites of layer III pyramidal cells while the projection to layer V contacts the apical dendrites of layer VI pyramidal cells. These results indicate that all the excitatory pathways that are detectable with the CSD technique in the “in vivo” preparation remain intact in 350 μm thick cortical slices. However, in the slice paired pulse stimulation did not lead to a depression of the response to the second stimulus while this is the case “in vivo”. This might be due to reduced inhibition in the slice which has been reported by several authors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00247044
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  • 8
    Electronic Resource
    Electronic Resource
    Experience-dependent modifications of kitten striate cortex are not prevented by thalamic lesions that include the intralaminar nuclei (1988)
    Springer
    Experimental brain research 70 (1988), S. 627-631 
    Details
    ISSN: 1432-1106
    Keywords: Visual cortex ; Development ; Plasticity ; Intralaminar nuclei ; Kitten
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary It has been shown previously that surgical lesions of the antero-medial thalamus interfere with ocular dominance modifications that normally result from monocular deprivation in young kittens (Singer 1982). The aim of the present study was to determine whether this effect was due specifically to the destruction of the visual cortical projections of the anterior intralaminar nuclei. We report here that large excitotoxin lesions of the anterior dorsal thalamus have no effect on the cortical response to monocular deprivation. These data indicate that the intralaminar projection is not essential for ocular dominance plasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00247611
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  • 9
    Electronic Resource
    Electronic Resource
    Topographic relations between ocular dominance and orientation columns in the cat striate cortex (1988)
    Springer
    Experimental brain research 71 (1988), S. 33-46 
    Details
    ISSN: 1432-1106
    Keywords: Columns ; Visual cortex ; Orientation ; Ocular dominance ; Maps ; Cat ; Development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the visual cortex of four adult cats ocular dominance and orientation columns were visualized with (3H)proline and (14C)deoxyglucose autoradiography. The two columnar systems were reconstructed from serial horizontal sections or from flat-mount preparations and graphically superimposed. They share a number of characteristic features: In both systems the columns have a tendency to form regularly spaced parallel bands whose main trajectory is perpendicular to the border between areas 17 and 18. These bands frequently bifurcate or terminate in blind endings. The resulting irregularities are much more pronounced in the ocular dominance than in the orientation system. The periodicity of the columnar patterns was assessed along trajectories perpendicular to the main orientation of the bands and differed in the two columnar systems. The spacing of the ocular dominance stripes was significantly narrower than the spacing of orientation bands. The mean periodicity of a particular columnar system was virtually identical in the two hemispheres of the same animal but it differed substantially in different animals. However, the spacing of orientation columns covaried with that of the ocular dominance columns, the ratios of the mean spacings of the two columnar systems being similar in the four cats. The superposition of the two columnar systems revealed no obvious topographic relation between any of the organizational details such as the location of bifurcations, blind endings and intersections. We suggest the following conclusions: 1. The developmental processes generating the two columnar systems seem to obey the same algorithms but they act independently of each other. 2. The space constants of the two systems are rigorously specified and appear to depend on a common variable. 3. The main orientation of the bands in both columnar systems is related to a) the representation of the vertical meridian, b) the anisotropy of the cortical magnification factor, and c) the tangential spread of intracortical connections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00247520
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrastructure of PkC(II/III)-immunopositive structures in rat primary visual cortex (1990)
    Springer
    Experimental brain research 82 (1990), S. 575-584 
    Details
    ISSN: 1432-1106
    Keywords: Ca2+- and phospholipid-dependent protein kinase ; Visual cortex ; EM-immunocytochemistry ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the primary visual cortex of adult rats the cellular and subcellular distribution of protein kinase C isozymes II and III (PkCII/III) was examined by immunohistochemical methods with a monoclonal antibody against PkCII/III. Strong PkC(II/III)-immunoreactivity was found in neurons and astrocytes. Immunopositive neurons exhibited morphological features characteristic for both pyramidal and non-pyramidal cells. They were distributed in layers II through VI but were concentrated in layers II/III. At the electron microscopic level immunoprecipitate was found predominantly in distinct regions of the somata, except the nuclei, and only a few labeled dendrites and axons were seen. Two different patterns of cytoplasmic immunoreactivity could be distinguished. In most neurons, PkC(II/III)-staining was confined to cytoplasmic spots associated with the Golgi complex, while a few neurons exhibited additional labeling in the vicinity of the cell membrane. Moreover, PkC(II/III)-immunoreactivity was present in numerous astroglial processes and in the perikaryal cytoplasm of a subpopulation of astrocytes. Present data provide morphological indications for specifie functions of PkC isozymes II and III in neurons as well as in astrocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228798
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