Rabbit Visual Cortex Research Articles

Morphological organization of the neuropil in laminae II?V of rabbit visual cortex

A combined light- and electronmicroscopic study of tangential serial sections through the visual cortex of the rabbit has been performed in order to find out whether or not the vertical bundles of apical dendrites in laminae IV/V and II/III on one hand and the areas between these bundles on the other differ with respect to composition and/or spatial organization of the neuropil. Lightmicroscopically only thick profiles such as apical dendrites of pyramidal cells and myelinated axons contribute to the structural characteristics of the neuropil. The appearance of the areas between the dendrite bundles is determined by the presence or absence of radiate bundles of myelinated axons. Lamina-dependent variations were seen in the neuropil of the dendrite bundles as well as in that of the areas between them. Ultrastructurally, the dendrite bundles and the areas between them were observed to be different also with respect to the distribution of the various types of small dendritic profiles and thin axons. The neuropil within the dendrite bundles except for the shafts and thick branches of apical dendrites contains thin unmyelinated axons and numerous spines of apical dendrites contracted by axon terminals. Small irregularly shaped dendrites are few in number. The neuropil between the dendrite bundles contains a larger number of thin unmyelinated axons than that within the bundles, and, instead of spines of apical dendrites, small irregularly shaped smooth and spiny dendrites represent the prevailing postsynaptic structures. Hence, areas within dendrite bundles differ from areas between them by thickness and orientation of their profiles and by the quantitative relation of the various kinds of processes accumulating in each compartment.

Bivalent effects of electrical stimulation applied to the central nervous system upon photic evoked potentials in the visual cortex of rabbits: [formula omitted], M. Abekura, H. Takimoto and S. Masaki (Osaka Univ. Med. Sch., Dept. of Neurosurg., Fukushima-ku, Osaka 553, Japan)

Bivalent effects of electrical stimulation applied to the central nervous system upon photic evoked potentials in the visual cortex of rabbits: [formula omitted], M. Abekura, H. Takimoto and S. Masaki (Osaka Univ. Med. Sch., Dept. of Neurosurg., Fukushima-ku, Osaka 553, Japan)

Corticogeniculate neurons, corticotectal neurons, and suspected interneurons in visual cortex of awake rabbits: receptive-field properties, axonal properties, and effects of EEG arousal.

The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of antidromically identified corticotectal (CT) neurons (n = 101) and corticogeniculate (CG) neurons (n = 124) in visual area I of awake rabbits. Eye position was monitored to within 1/5 degrees. We also studied the receptive-field properties of neurons synaptically activated via electrical stimulation of the dorsal lateral geniculate nucleus (LGNd). Whereas most CT neurons had either complex (59%) or motion/uniform (15%) receptive fields, we also found CT neurons with simple (9%) and concentric (4%) receptive fields. Most complex CT cells were broadly tuned to both stimulus orientation and velocity, but only 41% of these cells were directionally selective. We could elicit no visual responses from 6% of CT cells, and these cells had significantly lower conduction velocities than visually responsive CT cells. The median spontaneous firing rates for all classes of CT neurons were 4-8 spikes/s. CG neurons had primarily simple (60%) and concentric (9%) receptive fields, and none of these cells had complex receptive fields. CG simple cells were more narrowly tuned to both stimulus orientation and velocity than were complex CT cells, and most (85%) were directionally selective. Axonal conduction velocities of CG neurons (mean = 1.2 m/s) were much lower than those of CT neurons (mean = 6.4 m/s), and CG neurons that were visually unresponsive (23%) had lower axonal conduction velocities than did visually responsive CG neurons. Some visually unresponsive CG neurons (14%) responded with saccadic eye movements. The median spontaneous firing rates for all classes of CG neurons were less than 1 spike/s. All neurons synaptically activated via LGNd stimulation at latencies of less than 2.0 ms had receptive fields that were not orientation selective (89% motion/uniform, 11% concentric), whereas most cells with orientation-selective receptive fields had considerably longer synaptic latencies. Most short-latency motion/uniform neurons responded to electrical stimulation of the LGNd (and visual area II) with a high-frequency burst (500-900 Hz) of three or more spikes. Action potentials of these neurons were of short duration, thresholds of synaptic activation were low, and spontaneous firing rates were the highest seen in rabbit visual cortex. These properties are similar to those reported for interneurons in several regions in mammalian central nervous system. Nonvisual sensory stimuli that resulted in electroencephalographic arousal (hippocampal theta activity) had a profound effect on the visual responses of many visual cortical neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of pattern deprivation on visual cortical cells in the rabbit: a reevaluation.

The response properties of 217 cells recorded from the monocular segment of primary visual cortex in rabbits reared with lid suture of the contralateral eye (monocular deprivation, MD) were studied. These data were compared with 280 cells recorded from normal rabbits. There was no change in the percentage of orientation-selective cells, nonorientation-selective cells, or unmappable/unresponsive cells in MD animals compared with normals. Among orientation selective cells the orientation-tuning range of cells in MD animals was normal, and the predominance of cells with horizontal preferred orientation was maintained. However, some abnormalities were seen in orientation-selective cells of MD animals. These included an increased frequency of SI cells; a change in the distribution of preferred orientations; a disruption of the clustered organization of the cortex; a decrease in direction selectivity; an increase in the percentage of cells preferring slow stimulus movements and having low spontaneous activity; an increase in receptive-field size in all cell classes except SI. Among nonorientation-selective cells there was an increase in the percentage of movement sensitive cells and an increase in receptive-field size in MD animals. It is concluded that the effects of MD are much less severe in rabbit than in cat. In MD rabbits, many cells develop normally. In cells that do not develop normally, many of the changes observed can be interpreted as reflecting deficits in inhibitory functions.

Laminar distribution of neurons with different types of receptive fields in the rabbit visual cortex

Investigation of receptive fields of 232 primary visual cortical neurons in rabbits by the use of shaped visual stimuli showed that 21.1% are unselective for stimulus orientation, and 34.1% have simple, 16.4% complex, and 18.5% hypercomplex receptive fields, and 9.9% have other types. Neurons with different types of receptive fields also differed in spontaneous activity, selectivity for rate of stimulus movement, and acuteness of orientational selectivity. Neurons not selective to orientation were found more frequently in layer IV than in other layers, and very rarely in layer VI. Cells with simple receptive fields were numerous in all layers but predominated in layer VI. Neurons with complex receptive fields were rare in layer IV and more numerous in layers V and VI. Neurons with hypercomplex receptive fields were found frequently in layers II + III and IV, rarely in layers V and VI. Spontaneous unit activity in layer II + III was lowest on average, and highest in layer V. Acuteness or orientational selectivity of neurons with simple and complex receptive fields in layers II + III and V significantly exceeded the analogous parameter in layers IV and VI.

Postnatal development of somatostatin- and vip-immunoreactive neurons in the rabbit's visual cortex

Postnatal development of somatostatin- and vip-immunoreactive neurons in the rabbit's visual cortex

Development of synapses on pyramidal and multipolar non-pyramidal neurons in the visual cortex of rabbits. A combined Golgi-electron microscope study

A combined Golgi-electron microscope method was used to study the ultrastructural maturation of synapses on identified pyramidal and multipolar non-pyramidal neurons in the visual cortex of young and adult rabbits. In samples of 10 (time of eye opening), 14, 20 day old and 7 month old animals, fully impregnated pyramidal neurons within the layers II–V and multipolar non-pyramidal neurons mainly located in lower layer III and layer IV were studied. We found that synapses in 10 and 14 day old animals were occasionally immature in appearance. They were characterized by either a poorly defined postsynaptic band or equal rims of pre- and postsynaptic electron-dense material and could therefore not be classified as Gray type I or II. The distinction between both types of synapses was easier at day 20 and in the adults when the postsynaptic band of the asymmetrical (type I) synapses had become remarkably thicker. In pyramidal neurons the cytoplasmic organelles increased in number during development. Although a few symmetrical synapses were present on dendritic spines of pyramidal neurons in 14 and 20 day old animals, all pyramidal neurons exhibited the same types of synapses on specific sites of their neuronal surface. They received exclusively type II synapses on their somata, type I synapses on their dendritic spines and both types of synapses on their dendritic shafts. However, in the adult animals the frequency of occurrence of type II synapses, especially on basal dendritic shafts, had increased. In some cases only type II and no type I synapses were present. A striking finding in all young and adult animals was that synapses at the borderline between somata and apical dendritic shafts as well as on dendritic spines were frequently complex or interrupted. The characteristic ultrastructural features of adult spine-free and sparsely spiny multipolar nonpyramidal neurons e.g. the many cytoplasmic organelles and type I and II synapses on somata and on dendrites were already present at day 10. After day 10 the number of organelles and synapses increased prominently and in adult animals the different types of synapses on dendrites were located at relatively short intervals of about 4 μm. In contrast with the dendritic shafts of pyramidal neurons many asymmetrical synapses were observed on dendritic shafts of the non-pyramidal neurons analysed in the adult animals. Furthermore, it appeared that the number of synapses on these non-pyramidal neurons is about twice that on pyramidal neurons in day 20 old animals and about four times in adult animals. A description of ultrastructural characteristics for differentiating pyramidal and multipolar nonpyramidal neurons is given.

Pupillo-motor areas in the rabbit visual cortex

Pupillo-motor areas in the visual cortex of the rabbit were studied. Electrical stimulation of the rabbit visual cortex induced pupillary constriction or dilation. The low threshold area (0.5–1.0 mA) for pupillary dilation was in the form of a narrow band extending rostro-caudally along the boundary between the striate cortex (VI) and the occipital cortex (VII), where the binocular area of the visual field is represented. The pupillo-constrictory cortical points were also identified in the caudal part of the splenial gyrus (lateral part) and the pupillo-dilator points in the rostral part of the gyrus (lateral part).

Postnatal development of functional influences of cortical association areas on the visual cortex in rabbits.

Postnatal development of functional influences of cortical association areas on the visual cortex in rabbits.

Critical periods in development for susceptibility to the effects of stroboscopic rearing in the rabbit visual cortex.

Previous studies have shown that rearing rabbits in a stroboscopically illuminated environment results in a decrease in orientation and direction selectivity and an increase in responsivity to stroboscopic stimuli among neurons in area 17. In the present study, the critical period for susceptibility to these effects was studied by varying the time of onset of the deprivation. Groups of Dutch belted rabbits were reared normally and then placed in a stroboscopically illuminated environment at ages 1, 2 or 3 months, and response characteristics of visual cortical neurons were compared with those obtained from normal rabbits and from rabbits reared in a stroboscopic environment from birth. Results show that the different effects of strobe rearing have different critical periods. Increased responsivity to stroboscopic stimuli was seen only in rabbits deprived from birth. The effects of strobe rearing on both direction and orientation selectivity decreased with increasing age at the time of onset of the deprivation. However, only direction selectivity was modified by deprivation beginning at 3 months of age.

Frequency specific effects of stroboscopic rearing in the visual cortex of the rabbit

Rearing animals in stroboscopic illumination deprives those animals of the experience of visual motion. In the rabbit, stroboscopic rearing produces a significant alteration in the response properties of cells in the visual cortex, demonstrating that the rabbit visual system is susceptible to environmental manipulation during early postnatal life. Response properties were determined for single units recorded in the primary visual cortex of 3 groups of rabbits. One group had been reared from birth to 2 months of age at a stroboscopic flash frequency of 8 Hz, a second group was raised at a flash frequency of 4 Hz and a third was reared normally. Compared to normal rabbits, rabbits reared at 8 Hz showed a reduction in the proportion of orientation selective cells which were also direction-selective, and there was an increase in the proportion of cells responsive to stroboscopic flashes. There was no reduction, however, in the overall proportion of orientation-selective cells. This contrasts with the finding for the rabbits raised at a flash frequency of 4 Hz. In addition, cortical cells in the rabbits raised at 8 Hz responded to frequencies of stroboscopic flashes which were significantly higher than the frequencies found for cells in the rabbits raised at 4 Hz. The effects of stroboscopic rearing on the rabbit visual cortex are dependent, therefore, on the flash frequency experienced by the rabbits during development.

The contribution of the cortical layers to the generation of the EEG: Field potential and current source density analyses in the rabbit's visual cortex

Intracortical spontaneous field potentials (EEG) were simultaneously recorded from the different layers of the rabbit's visual cortex using multielectrodes produced by thin-film technology. The signals were subjected to spectral analyses. Additionally, current source density analysis was applied to spontaneous delta waves. The results are based on 10 experiments. The spontaneous EEG of the rabbit's visual cortex consists mainly of slow delta waves. The spectral analytical studies of the delta band showed maximum power in layers I and II and in layers V and VI. Significant power minima were found in the middle layers IV and/or III. Essentially, the zones of power minima agree with the zones of minimum coherence and those zones where a phase reversal is observed. These properties of the intracortical spontaneous delta activity are best described as dipole-like. The spontaneous delta waves can be surface negative or surface positive; accordingly they show different source-sink distributions from which different generation mechanisms can be inferred. The possible mechanisms for the generation of these current source-sink distributions (dipoles) are discussed, taking into consideration the cortical anatomy. In many cases these discussions must be speculative because, for an unambiguous explanation of the observed phenomena, a much better knowledge of the cortical anatomy, the fibre connections with other cortical areas and with the deep cerebral structures is necessary.

Focal evoked potentials in the rabbit visual cortex: Current source density analysis

Focal evoked potentials arising in the rabbit visual cortex in response to photic stimulation from a point source were analyzed by determination of the current source density. The response to a point stimulus arises in a circumscribed area of cortex, corresponding retinotopically to the stimulated point of the visual field and it consists of two components. The first component is created by a local current sink at a depth of 0.6 to 1.0 mm (the level of layer IV) and has a latent period of 30 msec and a peak time of 50 msec. The second component is created by a more diffuse current sink at a depth of 0.2–0.3 to 1.3–1.5 mm (levels between layers III and VI); the time to the maximum was 90–100 msec. These local sinks are regarded as active, created by depolarizing synapses. Passive current sources are concentrated around zones of active sinks. The two components of the response may reflect two consecutive waves of activation of cortical neurons.

Efferent systems of the rabbit visual cortex: Laminar distribution of the cells of origin, axonal conduction velocities, and identification of axonal branches

Several efferent systems of visual area I in Dutch rabbits were studied with anatomical (horseradish peroxidase) and physiological (antidromic) methods. Anatomical studies provided information regarding the laminar origin of the projections to the contralateral hemisphere, visual area II, the dorsal lateral geniculate nucleus, and the superior colliculus. Physiological studies provided information regarding conduction velocities and multiple destinations of efferent axons. Both the callosal projection and the projection to V-II were shown to originate primarily in layer II-III. However, approximately 10-20% of the callosal projection and 20-40% of the projection to V-II originated in layers IV and V. In contrast, the projection to the dorsal lateral geniculate nucleus originated nearly exclusively in layer VI, while corticotectal neurons occurred primarily in layer V. A significant number of corticotectal neurons were, however, found in layer IV. Thus, the above efferent systems were found to differ in their principal laminar origin and in the diffuseness of that origin. The origins of corticocortical projections were considerably more diffuse than those of corticofugal projections. In addition to differences in laminar origin, efferent systems also differed significantly in the conduction velocities of their axons. The projection to visual area II and to the lateral geniculate nucleus consisted primarily of very slowly conducting axons, while the projection to the superior colliculus was fast conduction. The callosal projection consisted of both slow and fact conduction axons. Finally, the question of branching of V-I efferent axons was addressed. Although the laminar origin of the projections to the contralateral hemisphere and to visual area II overlapped considerably, none of these corticocortical axons could be shown to project to both locations or to a subcortical destination. In contrast, approximately one-third of corticotectal axons were shown to project a collateral into the thalamus. Although the destination of this collateral is unclear, it is medial to the lateral geniculate nucleus and may be the pulvinar.

Changes in size and shape of synaptic connections after visual training: An ultrastructural approach of synaptic plasticity

The effect of visual training 30 on the synapses in the visual cortex of rabbits was quantitatively investigated. The number, the size and the fine structural organization of synaptic grids were analyzed in 0.5 μm E-PTA sections. The size of the pre- and postsynaptic terminals, the length of the apposition zones, the number of synaptic vesicles per terminal, the dimensions of the synaptic cleft and postsynaptic density and the frequency of mitochondria and spine apparatuses were studied in conventional OsO 4 sections. As compared to control animals, the synaptic population of visually trained rabbits exhibits 3 important changes: 1. (1) the number of complex grids has significantly increased; (perforated synapses according to refs. 6 and 24), 2. (2) the size of the synaptic grids has decreased. As is deduced from careful electron microscopic observations, this decrease in size is the result of a focalization of large grids. 3. (3) a significant increase in thickness of the postsynaptic density and a decrease in synaptic cleft is observed. The changes are most pronounced in deep layers (L IV and V) and are almost absent in superficial layers (L I). On account of recent insights into the mechanism of synaptic transmission and of the intrinsic relation between the fine structural components of the synaptic junction and the process of transmitter release, the observed changes are interpreted as an expression of enhanced synaptic efficacy. It is further postulated that modification of synaptic efficacy must be considered as an important factor in the adaptation of the nervous system to changing environmental conditions and for the consolidation of memory traces.

The postnatal development of the presynaptic grid in the visual cortex of rabbits and the effect of dark-rearing

We have quantitatively investigated the postnatal development of synaptic contacts in the visual cortex of rabbits and the effects of long-term dark-rearing on this development. The synaptic contacts are visualized in full en face extension using 0.5 μm sections of E-PTA treated tissue 21. In early postnatal life the mean size and the size distribution of the synaptic grids are much the same as in adult rabbits. Only minor changes are observed. The variations in size distribution at different levels below the pial surface, characteristic for the adult animal 21, are also present in early postnatal life. Prior to eye opening many synaptic grids lack dense projections or are only partly covered. After eye opening the dense projections mature but are still different from the adult grids at postnatal days 21–27. The number of complex grids, annulate or horseshoe-shaped, gradually increases and is above adult level at days 21–27. Dark-rearing has no effect on size and size distribution of the synaptic grids and does not affect the frequency of complex grids. Careful observation reveals, however, that the dense projections do not develop normally. They remain small and fuzzy as in the visual cortex of young rabbits, and many grids are only partly covered. These observations demonstrate that the synaptic contacts are to a great extent genetically predetermined. They are also formed with a specific size which does not change during development and is not affected by dark-rearing. The gradual maturation of the dense projections and the retardation of their development during dark-rearing indicates that visual experience interferes with the development of these synaptic substructures. Because of the complementarity of dense projections and vesicle attachment sites the maturation of dense projections and the effect of dark-rearing can be interpreted as change in the efficacy of synaptic transmission.

Current source density analysis: methods and application to simultaneously recorded field potentials of the rabbit's visual cortex.

This paper deals with the application of current source density (CSD) analysis to simultaneously recorded intracortical field potentials of the rabbit's visual cortex. Recordings were made with multielectrodes with either 8 contacts at distances of 300 microns, or 16 contacts at distances of 150 microns on one carrier needle. For synchronized activities, a spatial resolution of 150 microns turned out to be sufficient to record all depth-varying details of the field potentials; for seizure potentials even a spacing of 300 microns was adequate in most cases. For practical application, an appropriate spacing of the measuring points has to be chosen for a satisfactory estimation of the first and second derivatives of the field potentials. For this reason an interpolation procedure is applied to reduce the spacing from 300 microns or 150 microns electrode contact distances, respectively, and to obtain intermediate values at 75 microns distances. With this spacing satisfactory estimations of the second derivative are obtained. Theoretically, CSD analysis has to be made three-dimensionally, but under certain conditions which are discussed, a one-dimensional analysis can be applied. An unknown quantity is sigma z, the vertical conductivity. It turned out that average values obtained from different experiments are not representative and that the vertical conductivity has to be measured in every experiment. This is caused by the great individual differences of the cortices even if the same stereotactic coordinates are chosen. Therefore, in every experiment relative conductivity measurements are performed. The influence of different conductivity values within the various layers and the influence of a conductivity gradient is discussed and demonstrated by examples.

Reactions of lateral geniculate cells to chemical and electrical excitation of the visual cortex in rabbits

In anesthetized and paralyzed rabbits unitary discharges of lateral geniculate nucleus (LGN) were studied after cortical excitation by strychnine and following electrical stimulation of the visual cortex (VC). Results showed that local application of strychnine produced a general increase of the spontaneous and evoked activity of geniculate cells. By contrast, cortical depression with KCl led to a differential decrement of one of the evoked responses (on or off). Electrical cortical stimulation paired with on or off stimuli led to a differential increment of on or off responses. The results support the notion that, in rabbits, the corticogeniculate system is center-surround organized. A diagrammatic model is proposed to account for the relationship between the VC and the LGN in rabbits.

Postnatal dendritic development in the rabbit visual cortex

Golgi preparations of rabbit visual cortex aged 1-25 days, as well as similar tissues from adults, were examined for the growth of the dendritic arbor, and in particular the development of dendritic spines. The layer 5 pyramidal neurons and layer 4 stellate neuron were chosen as representatives of larger classes of neurons in the visual cortex. It was determined that the growth of the dendritic arbor, determined by counts of total number of dendritic and total dendritic length, is quite similar for pyramidal and stellate neurons. Dendritic spine development, however, is more rapid in pyramidal neurons than in stellate. This disparity in the rate of dendritic spine development is discussed in the light of physiologic studies on the development of receptive field properties in the rabbit visual cortex.

Prostaglandin E 1-induced latent epileptogenic foci

Suprafusion of 125 microliter 6% KCl solution over the visual cortex of rabbits 2-24 h after they suffered a prostaglandin (PG) E1-induced epileptic seizure was found to cause a recurrence of seizure activity. The initial seizure was induced by the cortical suprafusion of PGE1 over the left visual cortex of PG transport inhibitor-pretreated rabbits. Control animals that were not pretreated with PG transport inhibitors (bromcresol green or probenecid), or received suprafusion of saline or PGF2 alpha rather than PGE1, did not show initial seizure activity. In these animals, and in animals that had PG-induced seizures 72 h before KCl administration, the KCl solution caused only inhibition of the visually evoked response but no seizure activity. The results are interpreted to indicate that under appropriate conditions PGE1 can create a latent epileptogenic focus which can be reactivated by KCl. It is suggested that since PGE1 is produced by the brain normally, and in increased amounts as the result of overstimulation, irritation or trauma, this potent autacoid may play a role in the spontaneous development of latent epileptogenic foci or the recurrence of epileptic seizures.