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K Albus

Publications and source records attributed to K Albus.

At least 37 records · Page 2Linked to original sources
PubMed1987

Divergence of single axons in afferent projections to the cat's visual cortical areas 17, 18, and 19: a parametric study.

The proportions of neurons projecting via axon collaterals to two areas in the cat's occipital cortex (diverging neurons) were determined quantitatively in subcortical and cortical afferents by making use of the retrograde axonal transport of two different tracers. The proportions of diverging neurons were determined for that part of the afferent sites in which neurons filled with tracers from both injected areas occurred (overlap zone). A number of experimental variables were tested for their role in possibly influencing the results of quantitative double-label experiments, among them the types and the combinations of retrograde tracers, the position of the injections, the survival time, and the histological procedure. The most important variable was the position of the cortical injection, which had to be restricted clearly to the cortical grey matter and to one cortical area in order to avoid false-positive double labeling. Other experimental variables affected the total number of retrogradely labeled neurons and/or the ratio between neurons labeled with the two different tracers rather than the proportions of double-labeled neurons. In particular DL proportions were largely independent of the number and density of labeled neurons. They only deviated significantly from mean values in those sections in which the number of labeled neurons amounted to less than 20% of the maximal number of labeled neurons found in one section throughout the overlap zone. Our results show that divergence is common in afferents to the cat visual cortex. The amount of divergence, however, varies considerably according to the origin of the afferent projection. The proportion of diverging neurons expressed as the percentage of the total number of neurons projecting to areas 17 and 18 was 3% in the A-laminae of the dorsal part of the lateral geniculate nucleus, about 8% in the posteromedial lateral suprasylvian area, and about 15% in the C-laminae of the dorsal part of the lateral geniculate nucleus, in the medial interlaminar nucleus, in the lateral part of the lateral posterior nucleus, and in the claustrum. The proportions of diverging neurons in the afferent projections to areas 17 and 19, and to areas 18 and 19 were about 10%. Diverging neurons were also found in the projections of the intralaminar thalamic nuclei to the visual cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1987

A neuronal subsystem in the cat's area 18 lacks retinotopy.

Single neurones were recorded extracellularly in the visual cortex of anaesthetized and paralyzed cats. In all parts of area 18, neurones with diffuse receptive fields (DRFs) were found. DRFs measured at least 50 degrees in diameter and always included the area centralis and large parts of the ipsi- and contralateral hemifeld; some DRFs even covered the entire visual field. DRF neurones gave phasic responses to diffuse light, and to light spots either presented stationary or moved rapidly across the field; they were not orientation- or direction-sensitive. In contrast to the majority of area 18 neurones, which are part of a retinotopically organized system, DRF neurones constitute a subsystem with only poor retinotopy, or no retinotopy at all. This system might be suitable for detecting sudden changes in global illumination.

Animals↗
PubMed1987

Baclofen inhibits the spontaneous and visually evoked responses of neurones in the striate cortex of the cat.

The effects of iontophoretic application of gamma-aminobutyric acid (GABA) and beta-p-chlorophenyl-GABA (baclofen) on the activity of single neurones in the striate cortex of anaesthetized and paralysed cats were compared. Both compounds inhibited the spontaneous and the visually evoked responses of 92% of the neurones tested (n = 75) and they also eliminated the enhancement of the spontaneous and the evoked responses induced by the microiontophoretic application of glutamate. Bicuculline methiodide (BMI) antagonized the GABA-induced inhibition but did not significantly alter the effectiveness of baclofen for most neurones tested. The findings suggest that GABAB receptors are ubiquitous in the striate cortex of the cat. Evidence is presented to suggest that the GABAA and GABAB receptor subtypes differ in their distribution on some striate neurons.

Action Potentials↗
PubMed1987

Morphology and axon terminal pattern of glutamate decarboxylase-immunoreactive cell types in the white matter of the cat occipital cortex during early postnatal development.

During early postnatal development glutamate decarboxylase (GAD)-immunoreactive (ir) neurons are present in the white matter of the kitten occipital cortex. Most neurons are located below layer VI in the 'upper subplate' zone, others are located deeper in the white matter. In animals at postnatal (P) days 10 and 20 we classified two cell types on the basis of their axonal pattern. One type, the axonal loop cells, displays loops of 180 degrees formed either by the main axonal stem or by a major recurrent collateral. The neurons do not form terminals in the white matter. The other type, the local axon cells, have frequently branching axons giving rise to terminal varicosities contacting other white matter neurons in a basket-like manner. The local cells form terminal plexuses which occupy the white matter of younger kittens and are concentrated in a 100-150 micron wide zone subjacent to layer VI. In P48 kittens, density and width of the plexus is reduced and axonal loop cells and the local axon cells have disappeared. Some GAD-ir white matter neurons observed at this age have large fusiform somata and straight projecting axons. The origin and fate of the early postnatal white matter neurons will be discussed.

Animals↗
PubMed1986

Localization of NPY-immunoreactivity in the cat's visual cortex.

Using a polyclonal antiserum against neuropeptide Y (NPY; J.M. Allen et al. 1983a) immunohistochemistry was carried out using the PAP method. Neurones displaying NPY-like immunoreactivity are seen mainly in cortical layers V/VI, adjacent white matter and corona radiata. Only few neurones occur in superficial layers II/III. Neurones are multipolar to bitufted with spineless dendrites; somata are either round (layers V, II/III) or spindle-like (layer VI, white matter) with diameters between 16 and 20 microns. Axons were identified by their initial smoother profiles, which are smaller in diameter than principal dendrites, by their typical branching pattern and the occurrence of terminal portions. It was found, that the degree of axonal ramification in proximal parts of axons is rather poor. Most NPY-neurones seem to project intracortically or even locally, except neurones in layers VI and the white matter. The latter neurones have ascending axonal branches terminating in layer VI and V, thus contributing to the dense NPY-plexus in these layers, whereas some layer VI neurones have axonal branches descending into the white matter. The axonal plexus in upper cortical layers is most probably fed by the ascending axons of layer V neurones, passing layer IVc in a strictly vertical direction. Fine smooth fibers of unknown origin which ascend from the white matter in a vertical direction through the grey matter also contribute to the plexus in layer II/III. In semithin sectioned material three terminal types were identified. Firstly, en passant boutons on immunonegative pyramidal neurones, secondly, perisomatically arranged, basket-like terminals, bending around unstained non-pyramidal neurones, and thirdly, about 60 microns long vertically oriented rows of boutons exclusively on apical dendrites of layer II/III pyramidal neurones. Due to the unconspicious axonal pattern and the frequently observed basket-like terminal form, we conclude that most NPY-ir neurones can be regarded as a class of unspecific local field basket cells; the origin of the vertically arranged bouton rows has been yet to determined.

Animals↗
PubMed1986

The contribution of GABA-mediated inhibitory mechanisms to visual response properties of neurons in the kitten's striate cortex.

The effect of the microiontophoretic administration of the GABA antagonist bicuculline methiodide (BMI) on the responses of striate cortical neurons to light stimulation was investigated in kittens ranging in age between 11 and 28 d. The orientation sensitivity of the majority of the 88 neurons tested for this parameter decreased (40%) or was eliminated (18%) following the administration of BMI. Changes were seen in all layers and in all neuronal types, and the proportions of neurons that changed their orientation specificity were about the same during the second, third, and fourth postnatal weeks. Twenty-eight percent of the neurons were not affected in their orientation sensitivity by BMI. These neurons were recorded at all postnatal ages; they were located preferentially in layers IV and VI; and they had unimodal, bimodal, or ON-OFF mixed receptive fields. The remaining 14% of the neurons were initially unresponsive or responded in an erratic way to visual stimulation. These neurons became responsive and even exhibited orientation-specific responses during administration of BMI. The majority (56%) of direction-specific neurons became direction-nonspecific after the administration of BMI. Seventeen percent preserved some direction specificity, whereas 27% did not show any change at all. The effects of BMI on direction sensitivity were seen at all postnatal ages and on all neuronal types throughout layers III-VI. The majority of neurons unaffected by BMI in their direction sensitivity resided in layer VI. In those cases where orientation sensitivity was reduced, direction sensitivity (if present) was usually diminished as well. However, some neurons were found in which only 1 of the 2 parameters was significantly changed by BMI. The spatial structure of the receptive field, as revealed by stationary stimulation, was changed significantly by BMI in about half the neurons tested. A straightforward correlation between the alteration of orientation and/or direction sensitivity and changes in receptive-field structure was not found. The results demonstrate that, in the immature striate cortex, receptive-field properties of many neurons are determined by inhibitory processes mediated by GABA, which may also dictate the actual visual responsiveness of the neurons. The dissociations in the effects of BMI on orientation sensitivity, direction sensitivity, and receptive-field substructure indicate that the synaptic organization responsible for the various functional parameters is unlikely to be the same.

Animals↗
PubMed1985

Cholecystokinin octapeptide-like immunoreactive material in neurons of the intralaminar nuclei of the cat's thalamus.

Cholecystokinin-like immunoreactive material (CCK-IR) was revealed in the cat's thalamus by using the peroxidase-antiperoxidase method. The most dense collection of perikarya containing CCK-IR was seen in the rostral group of the intralaminar nuclei, in rostral parts of the rhomboid nucleus and the anterodorsal nucleus. Cells with CCK-IR were also found in the caudal group of the intralaminar nuclei, in the paraventricular nucleus and the parataenial nucleus. The remaining thalamic nuclei were void of CCK-IR. By combining immunohistochemistry with retrograde transport of horseradish peroxidase, CCK-IR was shown to be present in neurons of the intralaminar nuclei projecting to the neocortex. Our findings suggest that CCK might act as a transmitter in the efferent projections of the intralaminar and midline nuclei of the cat's thalamus.

Amygdala↗
PubMed1984

Concurrent visualization of choline acetyltransferase-like immunoreactivity and retrograde transport of neocortically injected markers in basal forebrain neurons of cat and rat.

Magnocellular neurons in the basal forebrain of rats and cats were retrogradely labeled with Fast Blue or horseradish peroxidase injected into the neocortex. Using antisera against choline acetyltransferase (ChAT) a direct double-labeling technique was carried out and it was demonstrated that retrogradely transported markers and ChAT-like immunoreactivity occur within the same neurons. These findings strongly support the cholinergic nature of basal forebrain projection to the neocortex.

Animals↗
PubMed1984

On the spatial arrangement of iso-orientation bands in the cat's visual cortical areas 17 and 18: a 14C-deoxyglucose study.

The horizontal organization of iso-orientation bands in the cat's visual cortex has been investigated with the 14C-Deoxyglucose method (Sokoloff et al. 1977). Our findings suggest that in areas 17 and 18 the network formed by the bands representing one orientation comprises three basic patterns. Most frequently seen is a set of 2-4 iso-orientation bands which, straight or curved, run parallel to each other through cortical volumes usually less than 3 mm across. Beyond that distance the individual bands either end abruptly or fuse with adjacent bands. Less frequently seen are circular or triangular arrangements, or small isolated patches. Near the 17/18 border the predominant direction of the bands appears to be orthogonal to the vertical meridian, whereas in regions of areas 17 and 18 more distant from the vertical meridian the direction of the bands is more variable. In spite of irregularities in their spatial arrangement, the distance between bands and bandwidth remain constant throughout most parts of areas 17 and 18. The principles underlying the spatial arrangement of iso-orientation bands in the cat's visual cortex have yet to be identified.

Animals↗
PubMed1984

Early post-natal development of neuronal function in the kitten's visual cortex: a laminar analysis.

The normal post-natal development of visual cortical functions was studied by recording extracellularly from 612 single neurones in the striate and parastriate cortex of anaesthetized and paralysed kittens, ranging in age from 6 to 24 days. Analyses have been made of laminar differences in the developmental trends of receptive field properties such as orientation specificity and spatial organization of 'on' and 'off' zones. At the beginning of the second post-natal week the majority of neurones (76%) only respond to light 'off' (unimodal 'off' neurones). Only later does the frequency of occurrence of unimodal 'on' neurones and of bimodal or multimodal neurones (with spatially segregated 'on' and 'off' zones arranged side by side) increase so that, by the middle of the fourth week, about equal numbers of these three receptive field types are found. The proportion of 'on-off' neurones (with spatially coincident 'on' and 'off' zones) remains low (between 9% and 12%) during the early post-natal period. In layers 4 and 6 of areas 17 and 18 the frequency of occurrence of visual neurones is quite normal even in the youngest kittens, whereas the probability of recording neurones in layers 2/3 and 5 in kittens less than 14 days old is remarkably low and only gradually improves up to the middle of the fourth week. A very rudimentary order in the spatial arrangement of orientation-specific neurones and ocular dominance distribution is observed even in very young kittens. This order improves rapidly and reaches adult levels during the fourth post-natal week. In visually inexperienced kittens, on average 11% of all responsive neurones are selective for the orientation of elongated visual stimuli, and 58% are biased. The proportion of orientation-selective cells begins to increase rapidly about two days after lid opening, and proportions of orientation-selective cells similar to that in the adult are reached by the end of the fourth post-natal week. Orientation-selective neurones in kittens less than 10 days old are only found in layers 4 and 6 and the lower part of layer 3. In layers 2/3 and 5 they are first seen in larger proportions by the beginning of the third post-natal week. Our results show that, during the first post-natal month, the time course of the functional development of visual cortical neurones depends on receptive field type and on intracortical location.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Orientation bias in the response of kitten LGNd neurons to moving light bars.

The orientation sensitivity to moving light bars was determined for 113 neurons in laminae A, A1 and C of the dorsal part of the lateral geniculate nucleus (LGNd) of kittens 7-42 days old. Forty neurons (35.4%) were biased to contrast orientation (OB neurons), i.e. their response to an optimally oriented bar was 2-10 times stronger than their response to a bar oriented orthogonally to the optimal. The remaining 73 neurons were not sensitive to contrast orientation. Evidence is presented that orientation bias in the LGNd develops prior to visual experience. Orientation biased responses in the LGNd strongly depended on stimulus parameters; preferred stimuli were light bars having a length of 5 degrees or more and moving at velocities slower than 5 degrees/s. Our findings suggest that the OB neurons of the LGNd could be effective in generating the early orientation sensitivity in the visual cortex.

Animals↗
PubMed1982

The geniculocortical system in the early postnatal kitten: an electrophysiological investigation.

The transmission of neuronal impulses in the central visual system in kitten 7-42 days old has been investigated using electrophysiologic techniques. It was found that shortly after birth the axonal conduction velocities in the geniculocortical, in the corticogeniculate and in the commissural pathways of areas 17, 18, and 19 are less than 1.2 m/s, increasing up to maximal 10 m/s at the end of the first postnatal month. The monosynaptic delays across geniculocortical and commissural synapses in area 17 as measured during the third and fourth postnatal week are extremely long (between 2.8 and 6.1 ms) and do not change significantly during this time. During the first postnatal month, visual cortical neurons fatigue rapidly to visual and electrical stimulation; also, the proportion of neurons receiving polysynaptic inputs is much smaller than in the adult animal. Accordingly, neurons having complex receptive fields are rarely found in area 17 during the first postnatal month. Our experiments show that the geniculocortical and also the intracortical transmission of neuronal impulses are still immature at the end of the first postnatal month; at this time the systems for orientation and direction selectivity in the visual cortex are almost fully developed.

Animals↗
PubMed1981

The distribution of pontine projection cells in visual and association cortex of the cat: an experimental study with horseradish peroxidase.

The projections from the visual and association areas of the cat's neocortex to the pons were investigated with horseradish peroxidase as retrograde tracer. Small injections were made into the pars basalis of the pons, along its entire rostrocaudal extent. The cortical areas considered were areas 17, 18, 19, 20, 21, and the lateral suprasylvian areas (LSA); the posterior (PMSA), and the anterior middle suprasylvian association area (AMSA), the anterior lateral association area (ALA) and the anterior suprasylvian association area (ASA). A pontine projection was found for all the areas investigated; however, areas differ in the relative strength of their projection, in their intraareal distribution of projection cells, and in the location of their projection zones within the pons. A low to moderate density of projection cells is seen in the areas 17, 18, 19, 20, 21, and in PMSA. The posterior part of LSA contains only a few projection cells, whereas in more anterior parts of LSA the density of projection cells is moderate to high. A relatively dense distribution of projection cells also appears in AMSA, ALA, and ASA. In those areas which are retinotopically organized (17, 18, 19, LSA) the representation of the center of gaze contains far fewer projection cells than the representation of peripheral vision. In the association areas the distribution of projection cells appears even. The projection zones from areas 17, 18, and 19 overlap with the zones from LSA in the anterior half of the basal pons. The projection zones from areas 20 and 21 and from ALA and ASA are located in the middle third and the projection zones from PMSA and AMSA spread throughout the entire rostrocaudal extent of the basal pons. Our findings indicate that efferent impulses from the visual cortical areas and from the association areas on the middle suprasylvian gyrus are relayed to the cerebellum exclusively via the basal pontine nuclei. The findings further suggest that the visual corticopontine projections carry a map of the visual field in which the cortical magnification factor is reduced.

Animals↗
PubMed1981

Hypothalamic and basal forebrain afferents to he cat's visual cortex: a study with horseradish peroxidase.

Following injections of horseradish peroxidase into the visual cortex labeled neurons have been found in the nucleus of the diagonal band of Broca in the basal forebrain and in the lateral hypothalamus just rostral to the mammillary bodies. The projection is bilateral, with a strong prevalence of ipsilateral connections. Both the basal forebrain and the lateral hypothalamus project to each of the areas 17, 18 and 19; none of these projections, however, is retinotopically organized. This suggests that the basal forebrain and the lateral hypothalamus are sources of non-specific input to the visual cortex in the cat.

Afferent Pathways↗
PubMed1981

Spiny stellates as cells of origin of association fibres from area 17 to area 18 in the cat's neocortex.

Neurons in the cat's area 17 were stained in Golgi-like fashion following injection of horseradish peroxidase into area 18. Such staining allows classification of neurons on the basis of dendritic morphology. The types of neurons found in area 17 are: pyramidal cells in layers 2, 3 and 4ab; spiny stellate cells in the lower part of layer 3, and in layer 4ab; and a few pyramidal and spindle cells in layer 5. The axons of the spiny stellate cells are finer than those of pyramidal cells; they give off collaterals in deeper cortical layers and may bifurcate when entering the white matter. Spiny stellates in area 17 do not project to area 19; after injections are made into area 17, these neurons are found neither in area 18 nor in area 19. The spiny stellate cell with a long axon is thus categorized as a projection neuron which takes part in the pathway from area 17 to ipsilateral and contralateral area 18.

Animals↗
PubMed1980

The distribution of interhemispheric projections in area 18 of the cat: coincidence with discontinuities of the representation of the visual field in the second visual area (V2).

In normal adult cats three regions with callosal projections from the contralateral visual areas 17, 18, and 19 have been identified at the lateral border of area 18 by degeneration techniques (Sanides, 1978). The visuotopic distribution of these callosal patches has now been investigated by combining anatomical with physiological techniques. The centers of the receptive fields recorded in the callosal patches are located on or close to the vertical meridian in the contralateral hemifield reaching eccentricities of about 15 deg. Some of these fields are of extraordinary size crossing the vertical meridian and covering large areas of the ipsilateral hemifield. On the other hand, receptive fields recorded from the acallosal parts of lateral area 18 may reach eccentricities of more than 50 deg. Thus, the callosal patches of lateral area 18 are wedged in between parts of lateral area 18 which represent the periphery of the contralateral hemifield. It is concluded that the retinotopic arrangement at lateral area 18 (the second visual area) distinguishes this area fundamentally from area 17, the primary visual area.

Animals↗