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PubMed1991

Postnatal development of the pontine projections from the visual cortex of the mouse.

We studied the postnatal development of the corticopontine tract in mice by the injection of the axon tracer DiI into the visual cortex. In the postnatal day (P) 0.5 mouse, labeled pyramidal tract fibers pass through the internal capsule and cerebral peduncle, grow over the basilar pontine gray, and enter into the medullary pyramid (in this study, P0 refers to the first 24 hours after birth). Small collateral branches arise from these pyramidal tract fibers on P0.5-1.0, and elongate quickly into the basilar pontine gray around P2-4. These collateral branches give off many secondary branches on P4 and form the bright terminal zone in the rostral portion of the lateral basilar pontine gray on P9. In the P16 mouse, this terminal zone is more restricted, suggesting, on the basis of the anterograde DiI labeling technique, that the visual corticopontine projection matures by P16. DiI-labeled pyramidal tract fibers distal to the branching point of the pontine collaterals are found during the postnatal two weeks, but disappear by the later stages. We conclude that the visual corticopontine tract develops as collateral branches of the transient pyramidal tract fibers arising from the visual cortex of the mouse, as just described in the rat (O'Leary and Terashima, Neuron 1:901-910, 1988).

Animals↗
PubMed1987

A current source density analysis of field potentials evoked in slices of visual cortex.

The method of one-dimensional current source density (CSD) analysis was applied to field potentials recorded from 350 microns 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 microns. 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 micron 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.

Age Factors↗
PubMed1978

Aspinous and sparsely-spinous stellate neurons in the visual cortex of rats contain glutamic acid decarboxylase.

Glutamic acid decarboxylase (GAD), the enzyme that synthesizes the neurotransmitter gamma-amino-butyric acid (GABA), has been localized in the rat visual cortex by immunocytochemical methods with both light and electron microscopy. In both colchicine-injected and non-injected preparations of the visual cortex, GAD-positive reaction product was observed in somata, proximal dendrites and axon terminals of non-pyramidal neurons. The GAD-positive terminals were observed to form symmetric synaptic junctions most commonly with dendritic shafts and somata of pyramidal and stellate neurons and less frequently with initial axon segments of pyramidal neurons and dendritic spines. In colchicine-injected preparations, GAD-positive somata were located in all cortical layers including the immediately subjacent white matter. In contrast, sections from non-injected rats displayed GAD-positive somata within a superficial and a deep cortical band. The GAD-positive somata observed in both types of preparations received both symmetric and asymmetric synaptic junctions, lacked apical dendrites, and had radially oriented dendrites of small diameter. These characteristics of GAD-positive neurons indicate that they are aspinous and sparsely-spinous stellate neurons. The localization of GAD within these neurons in combination with physiological and pharmacological data indicate that these local circuit neurons mediate GABA-ergic inhibition in the neocortex.

Animals↗
PubMed2001

Critical flicker frequency responses in visual cortex.

Critical flicker frequency (CFF) threshold is defined as the frequency at which a flickering light is indistinguishable from a steady, non-flickering light. CFF is useful for assessing the temporal characteristics of the visual system. While CFF responses are believed to reflect activity in the central visual system, little is known about how these temporal frequencies are processed in the visual cortex. The current paper estimated the CFF threshold for cells in the rat visual cortex by recording single unit responses to flickering stimuli. Results showed that: (1) there was a broad range of temporal tuning, (2) CFF threshold was lower in simple cells than in complex and hypercomplex cells, and (3) there was no significant difference in CFF threshold between areas 17 and 18.

Action Potentials↗
PubMed1961

Correspondences in the behavior of the electroretinogram and of the potentials evoked at the visual cortex.

Electrical potentials from the eye (ERG) and from the contralateral visual cortex were recorded in response to flashes of white and of colored light of various intensities and durations. The evoked potentials were found to parallel the behavior of the ERG in several significant respects. Selective changes in the ERG brought about by increasing the light intensity and by light adaptation led to parallel selective changes in the cortical responses. The dual waves (b(1), b(2)) of the ERG were found to have counterparts in two cortical waves (c(1), c(2)) which, in respect to changes in light intensity and to light adaptation, behaved analogously to the two retinal components. The responses evoked at high intensity showed only the diphasic c(1)-potential. As stimulus intensity was lowered the c(1)-wave decreased in magnitude and a delayed c(2)-component appeared. The c(2)-potential increased in amplitude as light intensity of the flash was further reduced. Eventually the c(2)-wave, too, decreased as stimulus reduction continued. There was no wave length specificity in regard to either the duplex b-waves or duplex cortical waves. Both appeared at all wave lengths from 454 mmicro to 630 mmicro. The two cortical waves evoked by brief flashes of colored light showed all the behavior to changes in stimulus intensity and to light adaptation that occurred with white light.

Adaptation, Ocular↗
PubMedDate not supplied

Estimates of the net excitatory currents evoked by visual stimulation of identified neurons in cat visual cortex.

The action potential discharge response of single neurons to both visual stimulation and injections of current were obtained during intracellular recordings in cat visual cortex in order to estimate the net excitatory current arriving at the soma during visual stimulation. Of 45 neurons recorded intracellularly, 19 pyramidal neurons and one basket cell were labelled with horseradish peroxidase. The discharge of all neurons adapted to constant current. For 40 neurons, a single exponential provided a good fit to the adapting discharge (r2 = 0.73 +/- 0.03) for all current intensities. Superficial layer neurons were significantly faster adapting [P < 0.001, mean (+/- SEM) time constant of adaptation = 11.5 +/- 1.3 ms; n = 20] than deep layer neurons (mean time constant of adaptation = 51.4 +/- 6.4 ms; n = 10). The percentage adaptation of the spike frequency, %(peak - adapted rate)/peak, was determined from the fitted exponential. Superficial layer neurons adapted significantly more strongly (P < 0.01, mean = 67 +/- 3%) than deep layer neurons (mean = 51 +/- 5%). The mean firing frequency in response to a current step of 320 ms duration had a linear relationship to the amplitude of the injected current (slope 66 spikes/s/nA; origin zero, mean r2 = 0.94; n = 33). This relationship provided a means of estimating the net peak excitatory current generated by visual stimuli. The estimated mean peak somatic current during the passage of a bar across the receptive field was 1.1 nA and the average current for the duration of the visually evoked discharge was 0.64 nA (n = 17). The transfer response of real and model neurons was obtained by differentiating the discharge response to a step input current and was then used to predict the output of the neuron following an arbitrary input. When these transfer responses were convolved with known input signals in model neurons, the predicted output was close to the simulated response of the model neuron to the same input waveforms. The transfer response was calculated for eight real neurons. Estimates of the net excitatory current arriving at the soma during visual stimulation was obtained by deconvolution. The mean peak somatic current for these neurons was 0.62 nA.

Action Potentials↗
PubMed1988

State dependent activity in monkey visual cortex. II. Retinal and extraretinal factors in V4.

Responses were recorded from isolated neurons in the visual cortex of rhesus monkeys while they performed an orientation match to sample task. In each trial the animal was first cued with randomly selected orientation, and then presented with a sequence of gratings whose orientations were randomly selected. The animal was required to release a switch when it saw a grating that matched the cued orientation. For some recordings the animal was given a tactile cue by having it feel the orientation of a grooved plate that it could not see. In other experiments the cue orientation was presented visually on the screen in front of the animal and then removed before the sequence of gratings was presented. Using this task it was possible to determine if a neuron's response to a particular orientation was affected by whether or not it was the orientation for which the animal was looking. Over half the neurons examined in V4 (110/192) responded differently to the visual stimuli when the animal was cued to look for different orientations. For some neurons responses to all stimuli were strong when the animal was cued to look for a particular orientation, but weak when the same stimuli were presented in trials where the animal had been cued to look for another orientation. This type of sensitivity was found in neurons recorded while the animal was given a tactile cue, and also in other neurons tested when a visual cue was used, suggesting that the activity was not of direct sensory origin. In support of this, neurons in V4 were not strongly affected when the animal felt the grooved plate while not performing the orientation matching task. The prevalence of behavioral effects that was found using the orientation matching task suggests that extraretinal signals represent a prominent component of the activity in V4 of the behaving monkey.

Animals↗
PubMed1981

Maturation of rat visual cortex. I. A quantitative study of Golgi-impregnated pyramidal neurons.

The early postnatal maturation of pyramidal neurons in layers II/III and V of the rat visual cortex has been examined in an attempt to elucidate some determinants of their mature morphology. Three indices have been quantified using Golgi-impregnated pyramidal cells; densities of spines along apical dendrites, numbers of primary based dendrites and volumes of cell bodies. The mean density of spines on the apical dendrites of all pyramidal neurones increases in a stepwise fashion. The first significant increase occurs between days 6 and 9 and the second, between days 12 and 15; these increases may correlate with the arrival of geniculate afferents and with the opening of the eyes, respectively. In younger animals, the distribution of spines along the apical shafts is relatively even, whereas in older animals, spine density increases significantly over the proximal 125 micrometers portion and is relatively constant over the remaining distal portion. By day 21, layer V pyramidal cells have acquired more primary basal dendrites and larger somatic volumes than layer II/III cells. Furthermore, as the cells mature the rate of change in these characteristics are significantly different for neurons in layer II/III and in layer V. For both cell populations, the mean number of primary basal dendrites increases to a maximum before falling to a steady level, but for neurons in layer V, the maximum is higher and attained three days earlier than for layer II/III cells. Moreover, the increase in volume of cell bodies of layer V neurons begins three days before that of layer II/III cells. This three day phase difference in maturation may reflect the cell birth dates, since autoradiographic evidence indicates that layer V pyramidal neurons reach the cortical plate about three days prior to those which occupy layer II/III in the adult visual cortex.

Aging↗
PubMed1993

Single-fibre EPSPs in layer 5 of rat visual cortex in vitro.

Simultaneous intracellular recordings were made from pairs of synaptically connected layer 5 pyramidal neurones less than 150 microns apart, in slices of rat visual cortex. Action potentials were evoked in one cell of a pair by depolarizing current pulses, while spike-triggered averaging was employed to reveal connections in the other cell and vice versa. Only 4 excitatory postsynaptic potentials (EPSPs) (0.7-1.2 mV) were recorded out of 270 cell pairs tested, equivalent to a connection probability of less than 0.02. Therefore, single-fibre EPSPs between pyramidal cells in layer 5 are less frequent, but individually larger in amplitude, than those found previously between pyramidal cells in layer 2/3 of rat visual cortex.

Animals↗
PubMed1981

Recovery of orientation selectivity in kitten primary visual cortex is slowed down by bilateral section of ophthalmic trigeminal afferents.

The recovery of orientation selectivity in the primary visual cortex has been studied in 6-week-old dark-reared (DR) kittens after visual exposure of various durations following bilateral section of either the ophthalmic (V1) or the maxillary (V2) branches of the Vth nerve. After 6 h of vision, visual cortical neurones become orientation selective in V2-operated kittens as well as in intact animals, while they remain non-specific in V1-operated kittens. However, in this latter case, if the duration of visual exposure is extended to 4 weeks, a slow and incomplete recovery of orientation selectivity takes place.

Animals↗
PubMed2000

Light-induced zif268 expression is dependent on noradrenergic input in rat visual cortex.

In the present paper we investigated the role of the noradrenergic projection from the locus coeruleus on the expression of the immediate early gene zif268 in the visual cortex of rats exposed to ambient light stimulation. Local administrations of 6-hydroxydopamine (6-OHDA), a specific toxin directed against the catecholaminergic system, were performed in the locus coeruleus prior to visual stimulation. Animals were stimulated for 2 h by ambient light, after a 2-week dark adaptation period. Sham-operated controls displayed a massive increase in the number of zif268 positive cells after light stimulation. To the contrary, lesioned animals demonstrated a dramatic reduction in the number of zif268 positive nuclei across all cortical layers. A few scattered immunopositive nuclei were identified in cortical layer IV, however, this region also underwent a significant reduction in the number of zif268 immunopositive nuclei. Our results indicate that the noradrenergic system plays an important role in the expression of zif268 in the visual cortex of rats exposed to ambient light after dark isolation.

Adrenergic Agents↗
PubMed2001

Patterns of GABA(B)R1a,b receptor gene expression in monkey and human visual cortex.

In situ hybridization histochemistry and immunocytochemistry were used to examine GABA(B)R1a,b receptor mRNA and protein expression in areas 17 and 18 of the visual cortex of normal macaque monkeys and of monkeys that had been deprived of vision in one eye. In addition, the normal patterns of GABA(B)R1a,b protein expression were immunocytochemically studied in the human visual cortex. Overall levels of GABA(B)R1a,b transcript were higher in area 17 than in area 18. In area 17 GABA(B)R1a,b mRNA levels were highest in layers IVC and VI, moderate in layers II-IVA and low in layers I, IVB and V. In area 18 GABA(B)R1a,b transcript expression was high in layers II and III, moderate in layers IV and VI and low in layers I and V. Immunocytochemistry revealed nearly identical patterns of GABA(B)R1a,b protein expression in areas 17 and 18 in monkey and human. Both pyramidal and non-pyramidal neurons were GABA(B)R1a,b immunoreactive. The majority of intensely immunoreactive neurons in layers II, III, V and VI were pyramidal cells. Numerous non-pyramidal cells were intensely immunoreactive in layer IV of area 17 but layer IV cells were only lightly immunoreactive in area 18. Following 10 day periods of monocular deprivation, induced by intravitreal injections of tetrodotoxin, levels of GABA(B)R1a,b mRNA and protein were decreased in the deprived eye dominance columns of layers IVC and VI.

Adult↗
PubMed1994

Cholecystokinin neurons in the developing visual cortex of normal and dark reared rats. Comparison with other peptidergic populations.

The laminar distribution and the density of cholecystokinin-like (CCK) neurons in the developing visual cortical areas (17, 18 and 18 a) were studied in Wistar rats that were reared under normal lighting conditions or in complete darkness. Immunocytochemistry on paraffin sections at postnatal days (P) 7, 14, 21, 30 and 60 showed that the density of CCK neurons in all visual areas of both groups of animals progressively increases from P7 to P21 but declines thereafter, to reach 50-75% of peak densities at P30. From P30 to P60 the density of CCK neurons in the visual cortex remains relatively unchanged in non-deprived animals, but increases slightly again in areas 17 and 18 a of dark reared rats. Fluctuations in the density of CCK neurons reflect changes in the number of immunoreactive neurons mainly present in layers IV-VI. It is concluded that the development of the CCK neurons in the rat visual cortex is minimally affected by light deprivation.

Aging↗
PubMed2004

Developmental regulation of spine and filopodial motility in primary visual cortex: reduced effects of activity and sensory deprivation.

Dendritic protrusions are highly motile during postnatal development. Although spine morphological plasticity could be associated with synaptic plasticity, the function of rapid spine/filopodial motility is still unknown. To investigate the role of spine motility in the development of the visual cortex and its relation with critical periods, we used two-photon imaging of neurons from layers receiving visual input in developing mouse primary visual cortex and compared motility between control and visually deprived animals. Spine and filopodia motility was prominent during early synaptogenesis (P11-P13) but greatly decreased after P15. This "switch" was coincident with a 2.5-fold increase in protrusion density and spine formation. Spine motility was not regulated during the critical period for monocular deprivation (P19-P34). Moreover, delaying the critical period by dark rearing did not delay the normal developmental decrease of spine motility, but caused a modest further reduction in motility at P28-P35. Dark rearing and enucleation also mildly reduced spine motility before eye opening and dark rearing reduced the proportion of filopodia. We conclude that (1) rapid spine motility is not related to critical period plasticity, but is likely to play a role in early synaptogenesis, and (2) neuronal activity stimulates spine motility during synaptogenesis and promotes the appearance of dendritic filopodia.

Animals↗
PubMed1977

The distribution of degenerating axons after small lesions in the intact and isolated visual cortex of the cat.

The extent of the spread of axonal degeneration was investigated in the visual cortex of the cat after making small lesions restricted to the grey matter. Two series of experiments were undertaken. In the first, normal adult cats were used, and in the second, the cortex of the postlateral gyrus was isolated from its extrinsic afferents by surgical undercutting 3 months before making the lesions. The results were similar in the two series in most respects. 1. Horizontal fibres extended in considerable numbers for some 500 micrometer from the lesion, mainly in layers I, III/IV and V, a few reaching 2/3 mm. These fibres were better seen in the intact than in the isolated cortex. Their spread was usually asymmetrical, being greater posteromedially than anterolaterally. 2. Oblique axons ran downwards from the middle layers into layers V and VI, or upwards into layers I and II. 3. Axons arising from layers II to VI descended vertically into the white matter. Degeneration patterns after lesions in areas 17 and 18 were compared.

Afferent Pathways↗
PubMed1990

Release of glutamate and aspartate from the visual cortex of the cat following activation of afferent pathways.

To test the possibility that glutamate (Glu) and aspartate (Asp) are transmitters at geniculo-cortical synapses in the visual cortex of the cat, we studied the release of amino acids from the striate cortex consequent upon visual and electrical stimulation of the dorsal lateral geniculate nucleus (LGN) and of the optic tract, using push-pull cannulae. We perfused a discrete region that included layer IV of the cortex with an artificial cerebrospinal fluid (aCSF) and analysed the amino acid content of these perfusates by high-performance liquid chromatography (HPLC). Significant increases only of Glu and Asp were obtained among all 17 amino acids measured, except for gamma-aminobutyric acid (GABA), during electrical stimulation of the afferent pathways. Visual stimulation by stroboscopic diffuse flashes of light increased the level of Glu released, but did not change that of Asp significantly. The level of GABA released did not change during diffuse flash stimulation, suggesting that the increase in Glu was not derived from cortical neurons. The increases in release of Glu/Asp were not seen when the perfusion medium was replaced with a Ca2(+)-free, high-Mg2(+)-containing solution. The basal (resting) release of Glu/Asp in the absence of stimulation also was decreased during perfusion with Ca2(+)-free/high-Mg2+ solutions. Intraocular injections of a sodium channel blocker, tetrodotoxin (TTX), resulted in a remarkable decrease in the basal release of Glu. These results suggest that Glu is released as in excitatory synaptic transmitter at least from terminals of geniculo-cortical afferents and Asp from axons of a certain type of visual cortical neuron.

Animals↗
PubMed1991

Nonlinearity of spatial summation in simple cells of areas 17 and 18 of cat visual cortex.

1. Nonlinearity of spatial summation in areas 17 and 18 of cat visual cortex was compared with the type of spatial nonlinearity that differentiates X and Y cells in the lateral geniculate nucleus (LGN) and retina. The comparisons were made to examine to what extent the information from X and Y cells may remain separated in higher visual centers. 2. Responses of simple cells in areas 17 and 18 were recorded while stationary, optimally oriented sinewave gratings were sinusoidally modulated within the receptive field of the cell. Both the spatial frequency and spatial phase of the stimulus were varied. 3. Y cells in the retina and LGN are defined by the presence of a specific form of spatial nonlinearity. When tested with contrast-modulated sinewave gratings of spatial frequencies about three-fold greater than the optimal, their responses are dominated by a frequency-doubled component. The amplitude of the frequency-doubled component is not dependent on the spatial phase of the stimulus. 4. Many simple cells in the cortex showed a form of spatial nonlinearity similar to the defining nonlinearity found in retinal and geniculate Y cells. A frequency-doubled response dominated at spatial frequencies more than threefold greater than the optimal spatial frequency. When this response was present, it was phase independent. 5. More than 50% of the simple cells in area 18 showed the Y-like spatial nonlinearity. Fewer than 10% of the simple cells in area 17 showed the Y-like spatial nonlinearity. 6. The virtual absence of Y-like nonlinearity in area 17 and its relative abundance in area 18 suggest that the functional separation between the parallel X and Y pathways remains distinct within areas 17 and 18 of cat visual cortex.

Animals↗
PubMed2002

Disinhibition outside receptive fields in the visual cortex.

By definition, the region outside the classical receptive field (CRF) of a neuron in the visual cortex does not directly activate the cell. However, the response of a neuron can be influenced by stimulation of the surrounding area. In previous work, we showed that this influence is mainly suppressive and that it is generally limited to a local region outside the CRF. In the experiments reported here, we investigate the mechanisms of the suppressive effect. Our approach is to find the position of a grating patch that is most effective in suppressing the response of a cell. We then use a masking stimulus at different contrasts over the grating patch in an attempt to disinhibit the response. We find that suppressive effects may be partially or completely reversed by use of the masking stimulus. This disinhibition suggests that effects from outside the CRF may be local. Although they do not necessarily underlie the perceptual analysis of a figure-ground visual scene, they may provide a substrate for this process.

Animals↗