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PubMed1982

[Noradrenaline and plasticity of the visual cortex of the kitten: a reexamination].

We have undertaken a study of the role of the noradrenergic system in the functional modifications, observed in the primary visual cortex of the Kitten, following monocular deprivation. The lids of one eye were sutured in 5 week old Kittens for a period of 1 or 2 weeks. Noradrenergic depletion was obtained by 6-OHDA injection, either intraventricular or localized in the coeruleus complex. Our results indicate that disappearance of noradrenaline in area 17 does not prevent the loss of binocularity of cortical cells, but appears to limit ocular dominance shifts at a stage equivalent to that observed in the intact Kitten after 6 days of monocular deprivation.

Animals↗
PubMed1978

Connections of striate cortex in the prosimian, Galago senegalensis.

Efferent and afferent connections of primary visual cortex, Area 17, were determined in a prosimian, Galago senegalensis, by autoradiographic methods after injections of 3H-proline or 3H-HRP. The cortical connections of Area 17 with Areas 18 and MT were homotopic and reciprocal. Projections from Area 17 terminated largely in layer IV and somewhat in layer III of both Areas 18 and MT. Most of the cells projecting to Area 17 were located in layer V of Area 18 and layer VI of MT. Subcortical projections included the reticular nucleus of the thalamus, where columns of label corresponding to injection sites were found in the caudal fourth of the nucleus. Projections to the lateral geniculate nucleus were along lines of isorepresentation and were in register with the cells projecting back to the injection site. The parvocellular layers were less densely labeled than other layers by the transport of 3H-proline, while concentrations of label were noted on the dorsal and ventral margins of the nucleus and in interlaminar regions between the internal parvocellular and magnocellular layers and between the two magnocellular layers. The pattern of terminations in the pulvinar complex suggested functional subdivisions. We have divided the inferior pulvinar into a large central nucleus, IPc, with topologically organized input from Area 17; a smaller medial nucleus, IPm, with a second pattern of input from Area 17; and a dorso-posterior nucleus, IPp, without input from striate cortex. The superior pulvinar likewise appears to have several subdivisions. One of these, a "central" nucleus of the superior pulvinar, SPc, receives topologically organized projections from Area 17. SPc is about the same size as IPc and is organized as a mirror image of IPc. Thus, both IPc and SPc represent the lower visual quadrant medially and the upper visual quadrant laterally; central vision is represented along the common border for both nuclei, while peripheral vision is represented dorsorostrally in SPc and ventrocaudally in IPc. Finally, the superficial grey of the superior colliculus receives topologically organized input from Area 17.

Animals↗
PubMed1995

Antisense oligonucleotide-induced block of individual GABAA receptor alpha subunits in cultured visual cortex slices reduces amplitude of evoked inhibitory postsynaptic currents.

Whole cell patch clamp recordings were made in layer II-IV from organotypic slices of rat primary visual cortex, explanted at postnatal day 6 and maintained in a serum-free medium. Neurons evinced current clamp characteristics typical for stellate cells. Between 7 and 21 days in culture, both glutamate- and GABA-mediated postsynaptic currents were observed. Long-term culturing in the presence of a degenerate 15-mer antisense oligonucleotide directed against the transcripts of all alpha subunits genes of the GABAA receptor resulted in a dose dependent reduction of evoked GABA synaptic currents. This reduction was maximal (80%) at 20 microM. A randomized control oligo had no effect. Evoked glutamatergic excitatory postsynaptic currents were unaffected following oligo treatment. A 15-mer antisense oligo directed against the alpha 1 subunit gave variable effects: in some cells the amplitude of evoked GABAergic inhibitory postsynaptic currents (IPSCs) was reduced by 50-75%, while in other cells recorded from the same slices, there was little or no effect. An antisense oligo, directed against the alpha 2 subunit, however, gave a consistent and robust 80% reduction of the amplitude of evoked IPSCs. A 15-mer 3-base mismatch oligo against alpha 2 had no effect. We conclude that the alpha 2 subunit functions in postsynaptic GABAA receptors located on or close to the cell bodies of stellate cells. The role of the alpha 1 subunit is less clear, but this subunit seems spatially differentiated. The in situ antisense oligo technique should provide further insight into the biophysical and pharmacological consequences of the subunit composition of ligand gated channels at functional synapses.

Animals↗
PubMed1985

Studies of the earliest generated cells of the cat's visual cortex: cogeneration of subplate and marginal zones.

The earliest generated cells of the cat's telencephalon that may play a role in the formation of the primary visual cortex are the subject of this study. Using [3H]thymidine autoradiography, we have found that these cells are generated between embryonic day 24 (E24) and E30 (gestation is 65 days) and that they are present in very low numbers in the white matter of the adult brain. These cells are rarely labeled by injections made after E30, when the cells destined for the cortical layers are generated. Examination of the labeling pattern in the fetal brain 10 days or more after administration of [3H]thymidine between E24 and E30 revealed a bistratified distribution of these early generated cells. Labeled cells were found in large numbers in two embryonic zones flanking the developing cortical plate: above in the marginal zone and below in the subplate. (Some if not all of the marginal zone cells constitute the population of Cajal-Retzius cells of the cat's telencephalon.). These experiments indicate that cells of the subplate and marginal zones are cogenerated in time during the days just preceding the genesis of the cortical plate. We also examined the distribution of the early generated cells shortly after their genesis--on E30, a time when cells of the cortical plate are just being generated at the ventricular zone. In this case, the labeling pattern at the occipital pole was not bistratified. Rather, labeled cells were situated within a single zone extending from the pial surface inward to the border of the ventricular zone. This finding indicates that the cells of the subplate and marginal zones are generated as a contiguous population that is subsequently split apart by the insertion of cells forming the cortical plate. A comparison between the number of early generated cells found in fetal and newborn brains with that found in adult brains suggests that these cells are generated initially in substantial numbers but then largely disappear during early postnatal life, since injections of [3H]thymidine between E24 and E30 yielded large numbers of labeled cells in the white matter and layer 1 at birth, but very few at 2 months postnatal. This significant loss contrasted with the results from injections made just a few days later (E33) that resulted in large numbers of labeled cells in cortical layer 6 not only at birth but also in adulthood.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Decreased dendritic spine density on prefrontal cortical pyramidal neurons in schizophrenia.

BACKGROUND: The pathophysiological characteristics of schizophrenia appear to involve altered synaptic connectivity in the dorsolateral prefrontal cortex. Given the central role that layer 3 pyramidal neurons play in corticocortical and thalamocortical connectivity, we hypothesized that the excitatory inputs to these neurons are altered in subjects with schizophrenia. METHODS: To test this hypothesis, we determined the density of dendritic spines, markers of excitatory inputs, on the basilar dendrites of Golgi-impregnated pyramidal neurons in the superficial and deep portions of layer 3 in the dorsolateral prefrontal cortex (area 46) and in layer 3 of the primary visual cortex (area 17) of 15 schizophrenic subjects, 15 normal control subjects, and 15 nonschizophrenic subjects with a psychiatric illness (referred to as psychiatric subjects). RESULTS: There was a significant effect of diagnosis on spine density only for deep layer 3 pyramidal neurons in area 46 (P = .006). In the schizophrenic subjects, spine density on these neurons was decreased by 23% and 16% compared with the normal control (P = .004) and psychiatric (P = .08) subjects, respectively. In contrast, spine density on neurons in superficial layer 3 in area 46 (P = .09) or in area 17 (P = .08) did not significantly differ across the 3 subject groups. Furthermore, spine density on deep layer 3 neurons in area 46 did not significantly (P = .81) differ between psychiatric subjects treated with antipsychotic agents and normal controls. CONCLUSION: This region- and disease-specific decrease in dendritic spine density on dorsolateral prefrontal cortex layer 3 pyramidal cells is consistent with the hypothesis that the number of cortical and/or thalamic excitatory inputs to these neurons is altered in subjects with schizophrenia.

Adolescent↗
PubMed1990

Stereotaxic preparation of circumscribed cortical areas from rat brain for biochemical studies.

A method for the rapid dissection of circumscribed areas of rat cortex is described. The technique does not depend on skull-derived landmarks but uses for stereotaxic orientation the cross-point of the interhemispheric gap with the caudal margin of the cortex. An application of this dissection method to the biochemical analysis of cholinergic markers within the hindlimb representation of the primary somatosensory cortex revealed that both the activity of the enzyme choline acetyltransferase as well as the binding of [3H] quinuclidinyl benzilate to muscarinic cholinergic receptors do not seem to be affected drastically three days after unilateral transection of the sciatic nerve. The only significant effect detected was a slight decrease in the activity of the choline acetyltransferase within the hindlimb representation of the primary somatosensory cortex contralateral to the transected sciatic nerve. In the primary visual cortex, the cholinergic markers investigated did not show significant alterations after sciatic nerve injury.

Animals↗
PubMed2006

Neocortical areas, layers, connections, and gene expression.

Cortical patterns of gene expression provide a new approach to long standing issues of lamination, and area identity and formation. In this review, we summarize recent findings where molecular biological techniques have revealed a small number of area-specific genes in the nonhuman primate cortex. One of these (occ1) is strongly expressed in primary visual cortex and is associated with thalamocortical connections. Another gene, RBP, is more strongly expressed in association areas. It is not clear whether RBP might be linked with any particular connectional system, but several possibilities are raised. We also discuss possible roles of area-specific genes in postnatal development, and conclude with a brief sketch of future directions.

Animals↗
PubMedDate not supplied

The distribution of corticotectal projection neurons correlates with the interblob compartment in macaque striate cortex.

While much attention has been given to the correlation between cytochrome-oxidase (CO) compartments and patterns of cortico-cortical projections originating from supragranular layers in the striate cortex, little is known in this regard about patterns of cortico-subcortical projections originating from infragranular cortex. We studied the tangential distribution of the striate cortex neurons projecting to the superior colliculus and used two approaches to analyze the relationship of this distribution to the arrangement of CO "blobs." First, chi-square analysis indicated that significantly fewer labeled neurons were found within the CO blob compartment than the number expected for a random distribution. Second, spatial cross-correlation analysis--which circumvents the inherent subjectivity of delineating blob boundaries--revealed an area around blob centers in which there was a decreased probability of encountering labeled cells. The size of this area compared well with that of our outlines of CO blobs. We conclude that corticotectal projection neurons in the striate cortex are distributed preferentially within the interblob compartment of the infragranular striate cortex. These results demonstrate that the spatial distribution of cortico-subcortical projection neurons within infragranular cortex can correlate with the CO architecture of the primary visual cortex.

Animals↗
PubMed2003

Flexible retinotopy: motion-dependent position coding in the visual cortex.

Although the visual cortex is organized retinotopically, it is not clear whether the cortical representation of position necessarily reflects perceived position. Using functional magnetic resonance imaging (fMRI), we show that the retinotopic representation of a stationary object in the cortex was systematically shifted when visual motion was present in the scene. Whereas the object could appear shifted in the direction of the visual motion, the representation of the object in the visual cortex was always shifted in the opposite direction. The results show that the representation of position in the primary visual cortex, as revealed by fMRI, can be dissociated from perceived location.

Attention↗
PubMed2003

Receptive fields and response properties of neurons in layer 4 of ferret visual cortex.

The ferret has become a model animal for studies exploring the development of the visual system. However, little is known about the receptive-field structure and response properties of neurons in the adult visual cortex of the ferret. We performed single-unit recordings from neurons in layer 4 of adult ferret primary visual cortex to determine the receptive-field structure and visual-response properties of individual neurons. In particular, we asked what is the spatiotemporal structure of receptive fields of layer 4 neurons and what is the orientation selectivity of layer 4 neurons? Receptive fields of layer 4 neurons were mapped using a white-noise stimulus; orientation selectivity was determined using drifting, sine-wave gratings. Our results show that most neurons (84%) within layer 4 are simple cells with elongated, spatially segregated, ON and OFF subregions. These neurons are also selective for stimulus orientation; peaks in orientation-tuning curves have, on average, a half-width at half-maximum response of 21.5 +/- 1.2 degrees (mean +/- SD). The remaining neurons in layer 4 (16%) lack orientation selectivity and have center/surround receptive fields. Although the organization of geniculate inputs to layer 4 differs substantially between ferret and cat, our results demonstrate that, like in the cat, most neurons in ferret layer 4 are orientation-selective simple cells.

Animals↗
PubMed1994

Pyramidal neurons in layer 5 of the rat visual cortex. I. Correlation among cell morphology, intrinsic electrophysiological properties, and axon targets.

Previous work has established two structure/function correlations for pyramidal neurons of layer 5 of the primary visual cortex of the rat. First, cells projecting to the superior colliculus have thick apical dendrites with a florid terminal arborization in layer 1, whereas those projecting to the visual cortex of the opposite hemisphere have thinner apical dendrites that terminate below layer 1, without a terminal tuft (e.g., Hallman et al.: J Comp Neurol 272:149, '90). Second, intracellular recording combined with dye injection has revealed two classes of cells: the first has a thick, tufted apical dendrite and fires a distinctive initial burst of two or more impulses, of virtually fixed, short interspike interval, in response to current injection; and the other, with a slender apical dendrite lacking a terminal tuft, tends to have a longer membrane time constant and higher input resistance, and does not fire characteristic bursts (e.g., Larkman and Mason: J Neurosci 10:1407, '90). The present study combined intracellular recording in isolated slices of rat visual cortex and injection of carboxyfluorescein, to reveal soma-dendritic morphology, with prior injection of rhodamine-conjugated microspheres into the superior colliculus or contralateral visual cortex to label neurons according to the target of their axons. This permitted a complete correlation of morphology, intrinsic electrophysiological properties, and identity of the projection target for individual pyramidal cells. Neurons retrogradely labeled from the opposite visual cortex were found in all layers except layer 1 while those labeled from the superior colliculus lay exclusively in layer 5. Within layer 5 interhemispheric cells were more concentrated in the lower half of the layer but extensively overlapped the distribution of corticotectal cells. Every cell studied that projected to the superior colliculus was of the bursting type and had a thick apical dendrite with a terminal tuft. Every cell in this study projecting to the opposite visual cortex was a "nonburster" and had a slender apical dendrite with fewer oblique branches that ended without a terminal tuft, usually in the upper part of layer 2/3. Interhemispheric cells also had rounder, less conical somata and generally had fewer basal dendrites than corticotectal neurons. Many cells with the physiological and morphological characteristics of interhemispheric cells were not back-labeled from the opposite visual cortex, implying that pyramidal cells of this type can have other projection targets (e.g., other cortical sites in the ipsilateral hemisphere).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

[Testing the scanning effect of a range of orientations by visual cortex neurons of the cat].

The preservation of the effect of dynamic scanning of a part of the orientation diapason during development of neuron responses in the primary visual cortex of cat was examined after equalization of their latencies and after estimation of only highly significant fragments of their reactions. It was found that this effect was preserved in 13 neurons out of 17 examined ones: it remained invariable in 7 units of this group and was modified due to a shift of the scanning beginning along the diapason of orientations, to an increase of scanning diapason or to a change of scanning direction. The stabilization of the orientational tuning occurred only in 4 cells after equalization of latencies. The obtained results confirm that the dynamic changes of orientation tuning in the majority of visual cortex neurons are connected with reorganization of the time pattern of the reaction, as suggested by the hypothesis of the spatial-temporal orientation coding in the visual system.

Animals↗
PubMedDate not supplied

Using near-infrared spectroscopy to assess neural activation during object processing in infants.

The capacity to represent the world in terms of numerically distinct objects (i.e., object individuation) is a milestone in early cognitive development and forms the foundation for more complex thought and behavior. Over the past 10 to 15 yr, infant researchers have expended a great deal of effort to identify the origins and development of this capacity. In contrast, relatively little is known about the neural mechanisms that underlie the ability to individuate objects, in large part because there are a limited number of noninvasive techniques available to measure brain functioning in human infants. Recent research suggests that near-IR spectroscopy (NIRS), an optical imaging technique that uses relative changes in total hemoglobin concentration and oxygenation as an indicator of neural activation, may be a viable procedure for assessing the relation between object processing and brain function in human infants. We examine the extent to which increased neural activation, as measured by NIRS, could be observed in two neural areas known to be involved in object processing, the primary visual cortex and the inferior temporal cortex, during an object processing task. Infants aged 6.5 months are presented with a visual event in which two featurally distinct objects emerge successively to opposite sides of an occluder and neuroimaging data are collected. As predicted, increased neural activation is observed in both the primary visual and inferior cortex during the visual event, suggesting that these neural areas support object processing in the young infant. The outcome has important implications for research in cognitive development, developmental neuroscience, and optical imaging.

Cerebrovascular Circulation↗
PubMed1996

Visuotopic organisation of striate cortex in the marmoset monkey (Callithrix jacchus).

The visuotopic organisation of the primary visual cortex (V1) was studied by extracellular recordings in adult male marmosets (Callithrix jacchus) that were anaesthetised with sufentanil/nitrous oxide and paralysed with pancuronium bromide. Extensive sampling of the occipital region in four individuals and partial coverage of V1 in five others allowed not only the establishment of the normal visuotopy but also the study of interindividual variability. As in other primates, there was a single, continuous map of the contralateral hemifield in V1, with the upper visual quadrant represented ventrally and the lower quadrant represented dorsally. The surface area of V1, which was measured in two-dimensional reconstructions of the cortical surface, varied from 192 to 217 mm2. There was a marked emphasis on the representation of the foveal and parafoveal visual fields: the representation of the central 5 degrees of the visual field occupied 36-39% of the surface area of V1, whereas the central 10 degrees occupied 57-59%. No asymmetry between the representations of the upper and lower quadrants was apparent. The visual topography of V1 was highly consistent between individuals, relative to both sulcal landmarks and stereotaxic coordinates. The entire contralateral hemifield was represented in V1; in addition, neurones with receptive fields whose borders invaded the ipsilateral hemifield were observed within V1, less than 800 microns from the V1/V2 boundary. The total invasion of the ipsilateral hemifield was less than 0.5 degree at the centre of the fovea but reached 8 degrees at the periphery of the vertical meridian. Our results demonstrate that the organisation of V1 is similar in diurnal New and Old World simians, despite major variations in size, ecological niche, and timing of postnatal development across species.

Animals↗
PubMed1991

Regional sex differences in spine density along the apical shaft of visual cortex pyramids during postnatal development.

Dendritic spines from the apical shaft of layer V pyramids were counted on Golgi-stained sections of the monocular subfield of the primary visual cortex of 10-, 20-, 40- and 60-day-old male and female rats. Dendritic segments located in layer IV and at 100-300 microns from the soma had a significantly higher spine content in 10-day-old females when compared to males. This sex difference was extended to outer dendritic segments with increasing age, and became restricted to dendritic segments of outer layers (II-III) located at 400-550 microns from the perikaryon in 40-day-old rats. Sex differences in spine content finally disappeared by day 60. These results show the existence of specific laminar and temporal sex differences in the development of dendritic spines in the apical shaft of visual cortex pyramids.

Aging↗
PubMed1999

A model for the depth-dependence of receptive field size and contrast sensitivity of cells in layer 4C of macaque striate cortex.

A model of LGN-input to layer 4C of macaque primary visual cortex has been used to test the hypothesis that feedforward convergence of P- and M-inputs onto layer 4C spiny stellate neurons is sufficient to explain the observed gradual change in receptive field size and contrast sensitivity with depth in the layer. Overlap of dendrites of postsynaptic neurons between M- and P-input zones proved sufficient to explain change in the lower two-thirds of layer 4C, while more rapid change in upper 4C was matched by proposing two different M-inputs with partial overlap in upper 4C alpha.

Animals↗
PubMed1993

Hyperpolarization-activated currents in isolated superior colliculus-projecting neurons from rat visual cortex.

1. In vivo injections of rhodamine beads into the superior colliculus of 4-9 postnatal day rat pups label a population of layer 5 cells in the primary visual cortex that can be identified in tissue sections or dissociated cell cultures. 2. Under voltage clamp, hyperpolarizations of isolated superior colliculus-projecting (SCP) neurons from rest elicit an instantaneous inward current (Iinst) with nearly linear current-voltage properties that is not blocked by extracellular application of 3 mM CsCl. 3. Voltage clamp steps to potentials more negative than -60 mV evoke a slowly activating, non-inactivating inward current that is not blocked by 1 microM TTX, 1 mM 4-aminopyridine (4-AP), 5 mM Co2+, or 25 mM TEA, but is potently blocked by extracellular application of 3 mM CsCl. This current is similar to Ih described in other systems. 4. Ih, the time-dependent inward current in SCP neurons, begins to activate near the resting membrane potential and reaches full activation at -110 mV. The voltage dependence of activation is well fitted by a Boltzmann distribution with the membrane potential at half-maximal activation (V1/2) = -81.0 mV and s (steepness of the curve parameter) = 7.2 mV. Thus, Ih may contribute to setting the resting membrane potential and resting input resistance of SCP neurons. 5. The inward rectification of the whole-cell current vs. voltage relation is accounted for by the voltage dependence of Ih activation. Current through the activated h-conductance shows slight outward rectification that is accounted for by constant field considerations. 6. The h-conductance is substantially permeable only to sodium and potassium and, under normal physiological conditions, is expected to reverse at approximately -22 mV at 20 degrees C. For [K+]o < or = 20 mM and 120 mM > or = [Na+]o > or = 70 mM, Ih obeys independence with a PNa/PK (ratio of Na+ to K+ permeability) of 0.40. 7. Extracellular potassium increases gh. If this effect is modelled as the result of potassium binding to an extracellular conductance-permitting site, potassium has an apparent dissociation constant (Kapp) of 25.7 mM and the ability to maximally increase gh in the order of 10-fold over basal levels. 8. Ih underlies the depolarizing 'sag' and 'overshoot' observed in SCP neurons following the onset and offset, respectively, of hyperpolarizing current injections. In addition, Ih appears to control the duration and the frequency of repetitive firing following the cessation of sustained hyperpolarizing current injections.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Functional specificity of callosal connections in tree shrew striate cortex.

Although callosal connections have been shown to link extensive regions of primary visual cortex, the distribution of these connections with respect to the map of visual space and the map of orientation preference remains unclear. Here we combine optical imaging of intrinsic signals with injection of fluorescent microspheres to assess the functional specificity of callosal connections in the tree shrew. By imaging both hemispheres simultaneously while presenting a series of spatially restricted stimuli, we find that a substantial region of visual space is represented bilaterally. Each hemisphere includes a representation of the ipsilateral visual field that is highly compressed relative to that of the contralateral visual field and is most extensive in the lower visual field, where approximately 30(o) of central visual space are represented bilaterally. Callosal connections extend throughout the region of bilateral representation but terminate in a spatially restricted manner that links visuotopically corresponding sites in the two hemispheres. In contrast, callosal connections appear to terminate without regard for the map of orientation preference, showing little sign of the orientation-specific modular and axial specificity that is characteristic of long-range horizontal connections. By coordinating the activity in the two hemispheres in a way that preserves nearest neighbor relationships, callosal connections may best be viewed as elements of local circuits that operate within a single bilateral representation of visual space.

Animals↗