Kitten Visual Cortex Research Articles

The effects of glutamate iontophoresis on single cell responses and inter-neuronal interactions in the kitten visual cortex.

We studied the effect of glutamate (Glu) micro-iontophoresis on visual responses (PSTHs) and cross-correlograms of neurones recorded simultaneously in the cortex of 4-6 weeks old kittens. PSTHs and cross-correlograms were tested before, during and after Glu injections and compared with adult cats data from previous experiment. Before the injection cross-correlogram shapes and numbers did not differ in young and adult cats, whereas PSTHs differed dramatically. Glu iontophoresis typically elevated background PSTHs levels rather than peak responses in young kittens. In adult animals the opposite effect predominated. After the termination of iontophoresis visual responses were enhanced in 21% of kitten neurones. In adult cats this effect was not observed. In kittens, a clear increase of cross-correlogram strength was recorded in one neuronal pair (3.6%) after the injection terminated. In adult cats similar effect was also found in 3% of pairs.

Involvement of Serotonin in Developmental Plasticity of Kitten Visual Cortex

During a critical period of postnatal development, neuronal connections in the kitten visual cortex are susceptible to experience-dependent modifications. These modifications are facilitated by the neuromodulators noradrenaline and acetylcholine. To address the question of whether serotonin (5-hydroxytryptamine; 5-HT), the other major neuromodulator in the cerebral cortex, also plays a role in developmental plasticity, we investigated whether interference with serotoninergic transmission in the kitten visual cortex affects ocular dominance (OD) plasticity. The serotonin neurotoxin 5,7-dihydroxytryptamine or the serotonin receptor blockers ketanserin and methysergide were infused into the visual cortex of kittens undergoing monocular deprivation. We found that both methods of disrupting serotoninergic transmission reduced OD plasticity. However, to be effective, the receptor blockers ketanserin and methysergide had to be applied in combination, suggesting that coactivation of serotonin receptor subtypes of both the 5-HT1 and 5-HT2 families have a permissive function in OD plasticity. Since activation of 5-HT2 receptors stimulates phosphoinositide hydrolysis, our data suggest that second messengers from the phospholipid pathway may play an important role in developmental plasticity of visual cortex.

Experience-dependent maturation of the spatial and temporal characteristics of the cell receptive fields in the kitten visual cortex

The development of contrast sensitivity to spatial and temporal frequencies was studied in the visual cortex of 6-week-old kittens reared from birth in three conditions: normal, dark-reared (DR) and dark-reared after 6 h of visual experience. Receptive fields of cells recorded in area 17 were quantitatively analysed using drifting sine-wave gratings. Compared to the low values obtained in the DR kittens, we observed after 6 h of visual experience: (1) an adult-like detection of higher spatial frequencies, (2) an increase of contrast sensitivity at low temporal frequencies; (3) a shift of the cell optimum towards 3 Hz, all values close to the normal ones. Unlike the spatial frequency selectivity, contrast sensitivity and detection of higher temporal frequencies continue to develop with age and visual experience.

Development and regulation of alpha adrenoceptors in kitten visual cortex

Alpha-1 and alpha-2 adrenergic receptors were localized in developing cat visual cortex by using [ 3H]prazosin and [ 3H]rauwolscine, respectively as selective ligands. The effects of neuronal input on the development of the two receptor subtypes were also studied in animals with lesions at various sites within the central visual pathways. Binding densities for both ligands increased during the first few postnatal weeks and declined thereafter. For both receptor subtypes, the highest concentration of binding sites was found in the subplate zone of the cortex in neonatal animals. Both ligands showed their highest concentrations in cortical layer IV beginning at postnatal day 30 and in the superficial cortical layers in adulthood. However, the developmental redistribution of alpha-1 receptors began at earlier ages than that of the alpha-2 sites. The alpha-1 sites were still concentrated in the subplate zone up to 60 days postnatal, while the alpha-2 sites in this region disappeared much earlier. Receptor binding densities were also examined in animals with quinolinic acid lesions within cortex, lesions of the lateral geniculate nucleus and lesions of the optic tract. The results indicate that both alpha-adrenoceptor subtypes were mainly located on cortical cells, and that the absence of neuronal activity during development resulted in a reduction of the binding density for both subtypes in the visual cortex. An additional major reduction in alpha-2 but not alpha-1 binding sites was observed following the lateral geniculate nucleus lesion, suggesting that the development of alpha-2 receptors is also dependent on input from the lateral geniculate nucleus. Removal of the lateral geniculate nucleus early in life resulted in a significant increase in alpha-1 receptors in the subplate region, indicating that receptor densities in this zone may be negatively regulated by the lateral geniculate nucleus afferents. These results show that adrenergic receptors reorganize during postnatal cortical development with a strong temporary concentration in the subplate zone. The reorganization process is heavily influenced by cortical inputs.

Regulation of basal release of GABA by noradrenaline in the kitten visual cortex.

To determine the modulatory effect of noradrenaline (NA) on basal release of gamma-aminobutyric acid (GABA), we measured the extracellular GABA with a brain microdialysis technique in the kitten visual cortex. Local infusion of NA through a cannula, which was implanted 2 mm away from the dialysis probe, gave rise to a marked increase in GABA release. This NA-induced GABA release was suppressed by tetrodotoxin, a sodium channel blocker, which was perfused at the probe site. The effect of NA was antagonized by pretreatment with metoprolol, a beta 1-selective antagonist. These results suggest that the cortical noradrenergic system may be involved in the regulation of basal GABA release that is possibly due to the activity of inhibitory neurones in the kitten visual cortex.

Postnatal development and laminar distribution of noradrenergic fibers in cat visual cortex

Previous studies have indicated that adrenergic receptors show significant changes either in laminar distribution or in number during the critical period of kitten visual cortex development. In order to further investigate the postnatal development of this neurotransmitter system, especially in relation to the critical period, we used a polyclonal antibody against dopamine-β-hydroxylase to localize noradrenaline-containing afferents in visual cortex of kittens of various ages from birth to adulthood. In young kittens, less than 2 weeks of age, noradrenergic fibers were sparse, short and randomly oriented, and were concentrated in layer I and in deep cortical layers V and VI. By postnatal day 40, the fibers were present throughout all cortical layers and exhibited higher densities in layers I, II, III, V and VI, with a band of lower staining in layer IV. While tangential fibers predominated in layers I, V and VI, relatively straight radial fibers traversed layers II and III. After postnatal day 40 we did not find major changes in the laminar distribution of adrenergic fibers. This developmental laminar distribution pattern of adrenergic fibers resembles that of the β-adrenergic receptors that we and others have studied in kitten visual cortex, but differs from that of α-adrenergic receptors.

The correlation between cortical neuron maturation and neurofilament phosphorylation: a developmental study of phosphorylated 200 kDa neurofilament protein in cat visual cortex

Neurofilament proteins are major constituents of the neuronal cytoskeleton. When phosphorylated, neurofilament proteins are thought to be involved in slowing down the slower component of axonal transport, thereby increasing neurofilament stability and conferring resistance to proteolysis. In order to investigate the correlation between phosphorylated neurofilament and plasticity of the cat visual cortex, we applied a monoclonal antibody, which recognizes only the phosphorylated form of neurofilament protein, to kitten visual cortex. This antibody appeared to recognizes only axons. There was a progressive increase of phosphorylated neurofilament-immunoreactive axons in the cortical layers and white matter during development. In the visual cortex of young kittens, phosphorylated neurofilament immunoreactive processes were mostly long, fine, and continuous axons. However, in kittens older than 2 months of age, phosphorylated neurofilament immunoreactivity was characterized by short, punctae-like staining. The immunoreactive axons were most dense in deep cortical layers V and VI initially, followed at later ages by layers IVa and IVb, and finally in layer IVc and in the superficial layers of adult animals. This developmental laminar pattern of distribution was not affected by early input restriction and coincides with electrophysiological evidence of early neuronal maturation. In addition, the phosphorylated neurofilament immunoreactivity can also be found in the dendrites and perikaya of degenerating neurons. These results suggest that phosphorylated neurofilament can be used as an index of functional maturity in the kitten visual cortex and also as a marker for neurodegeneration.

Plasticity of excitatory synaptic transmission in kitten visual cortex depends on voltage-dependent Ca 2+ channels but not on NMDA receptors

Long-term potentiation (LTP) of excitatory synaptic transmission occurs in in vitro slices of cat and rat visual cortex. Earlier studies suggested that activation of N- methyl- d-aspartate (NMDA)-selective glutamate receptors is essential for the induction of LTP. However, our studies on kitten visual cortex demonstrate that LTP induction requires the activation of low-threshold Ca 2+ channels in postsynaptic cells but not of NMDA receptors.

Formation of receptive fields in realistic visual environments according to the Bienenstock, Cooper, and Munro (BCM) theory.

The Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity has successfully reproduced the development of orientation selectivity and ocular dominance in kitten visual cortex in normal, as well as deprived, visual environments. To better compare the consequences of this theory with experiment, previous abstractions of the visual environment are replaced in this work by real visual images with retinal processing. The visual environment is represented by 24 gray-scale natural images that are shifted across retinal fields. In this environment, the BCM neuron develops receptive fields similar to the fields of simple cells found in kitten striate cortex. These fields display adjacent excitatory and inhibitory bands when tested with spot stimuli, orientation selectivity when tested with bar stimuli, and spatial-frequency selectivity when tested with sinusoidal gratings. In addition, their development in various deprived visual environments agrees with experimental results.

Evidence that molecules influencing axonal growth and termination in the developing geniculocortical pathway are conserved between divergent mammalian species

The general architecture of the visual system is similar for all species of mammal. To determine if the development of connections in the visual system might be under the influence of conserved molecules, we co-cultured explants of the murine lateral geniculate nucleus with slices from either murine or feline occipital cortex. Neurite outgrowth from embryonic murine geniculate explants was significantly enhanced by slices of newborn mouse occipital cortex or kitten visual cortex or by medium previously conditioned by these slices. Slices of similar volume but from sites other than occipital cortex had less or no effect on the murine geniculate explants. Fibers from murine geniculate explants grew freely on cortical slices from the kitten. They terminated mainly in layer 4 and also in layer 6, in both murine and feline visual and frontal cortical slices, irrespective of whether they entered through the white matter or pial side. Only the deep layers of the kitten's cortex sent projections to co-cultured murine geniculate explants. We suggest that the diffusible factors released by the cortex that stimulate the growth of axons from the lateral geniculate nucleus and the molecules that mark specific cortical laminae as targets for ingrowing afferents, are conserved in divergent species. We also found that murine geniculate axons grew freely on feline cerebellar slices. It is known from previous co-culture experiments that rodent geniculate axons are inhibited on rodent cerebellum and we suggest that the inhibitory factors involved are not conserved.

Masked long-term potentiation in kitten visual cortex in vitro.

In slices from the visual cortex of kittens maintained in vitro, long-term potentiation of synaptic transmission following high frequency stimuli (10 Hz, 2 min) delivered at low to medium stimulus intensities (80 to 200 microA), is accompanied by changes of certain electrophysiological measures recorded intracellularly, such as long-lasting depolarization of membrane potential and decreased threshold to elicitation of an action potential. These parameters have never before been shown to be altered following high frequency stimulation in other systems widely used in studying synaptic plasticity, such as in hippocampal neurons. Another important difference between results from these two systems is that the amplitude of the excitatory post-synaptic potential is enhanced after high frequency stimulation in hippocampal neurons, whereas in striate cortex from young kittens, we observed a decrease. We demonstrate here that this decrease can be reversed to show enhancement from the original amplitude, upon clamp of membrane potential back to the voltage observed prior to stimulation. Thus, what appears to be "long-term depression" of synaptic transmission, as recorded extracellularly and represented by diminished flow of synaptic current, can be reversed by stepping membrane voltage back to the pre-high frequency stimulation level, to produce responses that then become consistent with long-term potentiation.

Dynamic synaptic modification threshold: computational model of experience-dependent plasticity in adult rat barrel cortex.

Previous electrophysiological experiments have documented the response of neurons in the adult rat somatic sensory ("barrel") cortex to whisker movement after normal experience and after periods of experience with all but two whiskers trimmed close to the face (whisker "pairing"). To better understand how the barrel cortex adapts to changes in the flow of sensory activity, we have developed a computational model of a single representative barrel cell based on the Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity. The hallmark of the BCM theory is the dynamic synaptic modification threshold, theta M, which dictates whether a neuron's activity at any given instant will lead to strengthening or weakening of the synapses impinging on it. The threshold theta M is proportional to the neuron's activity averaged over some recent past. Whisker pairing was simulated by setting input activities of the cell to the noise level, except for two inputs that represented untrimmed whiskers. Initially low levels of cell activity, resulting from whisker trimming, led to low values for theta M. As certain synaptic weights potentiated, due to the activity of the paired inputs, the values of theta M increased and after some time their mean reached an asymptotic value. This saturation of theta M led to the depression of some inputs that were originally potentiated. The changes in cell response generated by the model replicated those observed in in vivo experiments. Previously, the BCM theory has explained salient features of developmental experience-dependent plasticity in kitten visual cortex. Our results suggest that the idea of a dynamic synaptic modification threshold, theta M, is general enough to explain plasticity in different species, in different sensory systems, and at different stages of brain maturity.

Involvement of muscarinic acetylcholine receptors in regulation of kitten visual cortex plasticity

Receptor autoradiographic methods specific for M 3 and M 1 muscarinic acetylcholine receptors were used to investigate the development and input-dependent laminar redistribution of these receptor populations during the critical period for kitten visual cortex plasticity. Analysis of the binding curves of [ 3 H]4- diphenylacetyl-N- methyl-piperidine (4-DAMP) and [ 3H]pirenzepine (PZ) indicated that these two ligands bound heterogeneously to muscarinic acetylcholine receptors with different affinities. While [ 3H]4-DAMP showed a high affinity for M 3 receptors and much lower affinities for M 1 and M 2 receptors, [ 3H]PZ displayed higher affinity for M 1 receptors. By carefully choosing concentrations of labelled and unlabeled ligands, the patterns of laminar distribution for both receptor subtypes within visual cortex were obtained. Both receptors were most concentrated in cortical layer IV immediately after birth and during the most sensitive period of visual cortex plasticity. The binding density for both receptor subtypes thinned out progressively in this layer to concentrate in more superficial layers as plasticity waned with age. Moreover, interruption of visual or spontaneous input to visual cortex induced either by lesion or by tetrodotoxin infusion into lateral geniculate nucleus prevented the developmental redistribution of these receptors from layer IV to superficial layers, that is, the pattern of laminar distribution remained that of the age at which the lesion or tetrodotoxin infusion into the lateral geniculate nucleus was performed. The results indicate that the developmental expression of M 3 and M 1 muscarinic acetylcholine receptors in kitten visual cortex depends on cortical inputs. The parallel time course of these receptors' expression and laminar redistribution and their relation to the critical period of the developing visual cortex suggest that these muscarinic receptor classes may be involved in regulation of visual cortex plasticity.

Identification of cDNA clones expressed selectively during the critical period for visual cortex development by subtractive hybridization

We have used the method of subtractive hybridization to isolate cDNA clones of mRNAs expressed in abundance in the visual cortex of 30-day-old kittens but absent or in lower abundance in the adult cat visual cortex. Of 12,000 colonies screened, 200 clones which hybridized to the subtracted probe were isolated and characterized. Northern blots confirmed the specificity of the vast majority of the isolated clones. 120 of the 200 clones were sequenced and the EMBL and GenBank (release 76) databases were searched for known identities using FASTA and BLAST programs. Twenty-seven of these sequenced clones were identifiable. The identities showed that these sequences code for proteins involved in a variety of cellular processes. These include cell-cell interaction (TAPA-1, contactin, tachykinin receptor, phospholipase A2), cellular remodeling (C1q beta isoform, heat shock protein), neurofilament assembly (alpha tubulin and alpha internexin), neurotransmitter release (VAMP-2, amphiphysin, car☐ypeptidase E, scg 10 and proton channel), energy metabolism (mitochondrial hinge protein, ADP/ATP transporter, cytochrome oxidase subunits), RNA processing (helix destabilizing protein, ribonucleoprotein) and protein synthesis (eIF-4A initiation factor, ribosomal protein S27). The results show that gene expression in the kitten visual cortex differs rather little from that of the adult visual cortex since over 98% of the sequences appear common. The relatively rare kitten-specific sequences are likely to form the basis for the critical period plasticity in this system.

Development and regulation of β adrenergic receptors in kitten visual cortex: An immunocytochemical and autoradiographic study

The developmental pattern and laminar distribution of β 1 and β 2 adrenergic receptor subtypes were studied in cat visual cortex with autoradiography using [ 125I]iodocyanopindolol as a ligand and also with immunocytochemistry using a monoclonal antibody directed against β adrenergic receptors. In the primary visual cortex of adult cats, the laminar distributions of both β 1 and β 2 adrenergic receptors revealed by autoradiography were very similar, with concentrations in layers I, II, III and VI. In young kittens (postnatal days 1 and 10), fewer β adrenergic receptors were present, and they were concentrated in the deep cortical layers (V–VI) and subcortical white matter. Between postnatal days 15 and 40, β adrenergic receptors increased in density more quickly in the superficial layers than they did in the deep and middle cortical layers. By postnatal day 40, the adult pattern was achieved, with two bands of intense binding in the superficial and deep cortical layers and a lower density in layer IV. Immunocytochemical techniques applied to adult cat cortex showed that β adrenergic receptor-like immunoreactivity was found in different populations of neurons and glial cells. The immunoreactive neural cells were most dense in layers II, III and VI. About 50% of these immunoreactive neural cells were glial cells, primarily astrocytes. Immunoreactive pyramidal cells were mostly located in layers III and V. In layer IV, many stellate cells were stained. Immunoreactive astrocytes in the subplate and white matter progressively increased in number during development until adulthood. The pattern of laminar distribution and the developmental process was not affected by interrupting noradrenergic innervation from locus ceruleous either before or after the critical period. However, when visual input was interrupted by lesions of the lateral geniculate nucleus in young kittens (postnatal day 10), the density of both β adrenergic receptor subtypes decreased significantly in the deep cortical layers. Lateral geniculate nucleus lesions in adult cats resulted in a pronounced decrease in β adrenergic receptor density in layer IV.

Transient association of the HNK-1 epitope with 5'-nucleotidase during development of the cat visual cortex.

During early postnatal development of the kitten visual cortex the ectoenzyme 5'-nucleotidase undergoes a characteristic redistribution. Until about postnatal week 6 it is essentially confined to synaptic contacts in input layer IV and its expression is related to the use-dependent segregation of thalamic afferents into ocular dominance columns. Subsequently, 5'-nucleotidase becomes distributed uniformly throughout all layers and is then associated selectively with glial cells. Here we describe an age-dependent alteration in the expression of a carbohydrate epitope of 5'-nucleotidase which correlates with the developmental change of the enzyme's localization. We have isolated 5'-nucleotidase from the occipital cortex of kittens of varying age and from adult cats and investigated by immunoblotting the association of the HNK-1 carbohydrate epitope with the protein. 5'-Nucleotidase carries the HNK-1 epitope in kittens of 3-9 weeks but the epitope is absent from 12-week-old kittens or adult cats. Thus, the appearance of the HNK-1 epitope correlates with the transient localization of the enzyme at synapses. The HNK-1 carrying 5'-nucleotidase may be involved in synaptogenesis and use-dependent modifications of synaptic connections.

An interdigitated columnar mosaic of cytochrome oxidase, zinc, and neurotransmitter-related molecules in cat and monkey visual cortex.

There is considerable physiological evidence for the compartmentalization of mammalian visual cortex into functional columnar modules, representing features of visual information processing such as eye and orientation specificity. However, anatomical markers of visual cortical compartmentalization have been described only for primate visual cortex. In this report, we describe an interdigitated mosaic of four neuroactive molecules which demarcate two distinct columnar systems in the kitten visual cortex. Serotonin 1C receptors and synaptic zinc were found to demarcate columns within layer IV of kitten visual cortex, which were interdigitated with a second, patchy system characterized by increased levels of cytochrome oxidase and acetylcholinesterase. In primate visual cortex, as well as in the kitten, synaptic zinc was periodically distributed in a manner precisely complementary to cytochrome oxidase. These findings provide an anatomical framework on which unifying hypotheses of the functional organization of columnar systems in mammalian visual cortex can be built.

Effects of intracortical infusion of anticholinergic drugs on neuronal plasticity in kitten striate cortex.

During a critical period of postnatal development the mammalian visual cortex is highly susceptible to experience-dependent alterations of neuronal response properties. These modifications are facilitated by the neuromodulators noradrenaline and acetylcholine. To identify the cholinergic mechanisms responsible for this facilitation, muscarinic and nicotinic antagonists were infused into the visual cortex of kittens while the animals were subject to monocular deprivation. Subsequently the ocular dominance of cortical cells was assessed by single-unit recording. Ocular dominance changes were suppressed by scopolamine and pirenzepine but not by gallamine, hexamethonium and mecamylamine. This blocking effect was concentration-dependent, and control experiments revealed that it was not due to suppression of neuronal responses to light. It is concluded from these results that acetylcholine facilitates neuronal plasticity in the visual cortex through mechanisms activated by muscarinic M1 receptors.

Effects of nerve growth factor on neuronal plasticity of the kitten visual cortex.

1. The effect of intraventricular administration of nerve growth factor (NGF) by means of a cannula-minipump system was studied in kittens monocularly deprived during the critical period. The ocular dominance of area 17 neurones of NGF-treated and control kittens was determined by conventional extracellular recordings. The soma size of cells in A and A1 laminae of the lateral geniculate nucleus (LGN) was also evaluated in Cresyl Violet preparations. 2. Binocularly responsive neurons were found to be significantly more numerous in NGF-treated than in control kittens. The shrinkage of cells from the deprived LGN laminae normally observed in control kittens was prevented by NGF administration. 3. Following an initial period of monocular deprivation (MD) kittens subsequently treated with NGF showed a substantial recovery of functional binocular connections. 4. These findings indicate that the administration of NGF during the period of deprivation reduces the amblyopic effects of MD, while its administration to kittens with both eyes open following the initial deprivation promotes recovery of the deprived eye. 5. Neurotrophic factors may contribute to the regulation of experience-dependent modifications of synaptic connectivity in the visual cortex.

Gliotoxin-induced suppression of ocular dominance plasticity in kitten visual cortex

We studied the role of astrocytes in the regulation of ocular dominance plasticity. A small quantity of 10 μM fluorocitrate (0.2 nmol in 20 μl) was pressure-injected into the visual cortex of 7-9-week-old kittens (subcortical depth: 0–5 mm, 20 μl/10 min). Immediately after injection, 1 eye contralateral to the injected cortex was closed for 3 days. Single-unit recordings revealed that the proportion of binocular cells was significantly higher in a region close (∼ 1 mm) to the fluorocitrate injection site than that in a remote region (> 4 mm) within the same hemisphere and that in the opposite hemisphere. The results suggest that reduction of glial functions by fluorocitrate retarded the usual process of shift in ocular dominance of visual cells following monocular deprivation.