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PubMed1984

Somatosensory cortical map changes following digit amputation in adult monkeys.

The cortical representations of the hand in area 3b in adult owl monkeys were defined with use of microelectrode mapping techniques 2-8 months after surgical amputation of digit 3, or of both digits 2 and 3. Digital nerves were tied to prevent their regeneration within the amputation stump. Successive maps were derived in several monkeys to determine the nature of changes in map organization in the same individuals over time. In all monkeys studied, the representations of adjacent digits and palmar surfaces expanded topographically to occupy most or all of the cortical territories formerly representing the amputated digit(s). With the expansion of the representations of these surrounding skin surfaces (1) there were severalfold increases in their magnification and (2) roughly corresponding decreases in receptive field areas. Thus, with increases in magnification, surrounding skin surfaces were represented in correspondingly finer grain, implying that the rule relating receptive field overlap to separation in distance across the cortex (see Sur et al., '80) was dynamically maintained as receptive fields progressively decreased in size. These studies also revealed that: the discontinuities between the representations of the digits underwent significant translocations (usually by hundreds of microns) after amputation, and sharp new discontinuous boundaries formed where usually separated, expanded digital representations (e.g., of digits 1 and 4) approached each other in the reorganizing map, implying that these map discontinuities are normally dynamically maintained. Changes in receptive field sizes with expansion of representations of surrounding skin surfaces into the deprived cortical zone had a spatial distribution and time course similar to changes in sensory acuity on the stumps of human amputees. This suggests that experience-dependent map changes result in changes in sensory capabilities. The major topographic changes were limited to a cortical zone 500-700 micron on either side of the initial boundaries of the representation of the amputated digits. More distant regions did not appear to reorganize (i.e., were not occupied by inputs from surrounding skin surfaces) even many months after amputation. The representations of some skin surfaces moved in entirety to locations within the former territories of representation of amputated digits in every monkey studied. In man, no mislocation errors or perceptual distortions result from stimulation of surfaces surrounding a digital amputation.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1998

Experience-dependent changes in function and anatomy of adult barrel cortex.

Manipulations of sensory input to vibrissal mechanoreceptors can modify columnar functioning of the barrel cortex in adult animals. In mice, partial vibrissectomy sparing one row of vibrissae in young adults results 7 days later in an increase in the functional cortical column activated by the spared whiskers and visualized with 2-deoxyglucose autoradiography. The increase in the extent of the labelled area is visible in all cortical layers, but particularly in layer V, where the metabolic labelling is more intense in the representation of the spared vibrissae. Two months after vibrissectomy the enlargement of the labelled area is accentuated. Deprivation of a row of vibrissae results in a decrease in the areal extent of its cortical representation. Investigations of cortico-cortical connections carried out in living slices of the barrel cortex of mice 2 months after vibrissectomy sparing one row of whiskers, revealed elongation and increased branching of axons originating in the spared cortical column. The dendritic spine density was increased on the basal dendrites of layer V pyramidal neurons of the spared column and decreased on layer III apical dendrites of the deprived column. Thus, prolonged changes in functional activation of adult barrel cortex are accompanied by rearrangement of cortico-cortical circuitry.

Adaptation, Physiological↗
PubMed1990

Ocular dominance plasticity and developmental changes of 5'-nucleotidase distributions in the kitten visual cortex.

The distribution of the adenosine-producing ecto-enzyme 5'-nucleotidase was investigated histochemically in the visual cortex of normally reared and monocularly deprived kittens and cats. In normally reared kittens aged between 11 to 44 days, 5'-nucleotidase activity formed a band of intense neuropil staining throughout cortical layer IV of areas 17 and 18. The other layers were almost devoid of reaction product. Between the 4th and 6th week, this band had a patchy appearance in area 17, the center-to-center spacing of 5'-nucleotidase patches being approximately 1 mm. Monocular enucleation accentuated these patches of enhanced 5'-nucleotidase activity or made them reappear at developmental stages at which they had normally faded. Simultaneous visualization of ocular dominance columns by transneuronal transport of intraocularly injected 3H-proline showed that the patches of enhanced 5'-nucleotidase activity coincided with the territories of afferents from the intact eye. With increasing age and normal visual development, the patches disappeared and 5'-nucleotidase activity spread to the supra- and infragranular layers. The adult pattern was characterized by dense staining of all cortical laminae in both areas 17 and 18 and was established at about 8 weeks of age. At approximately 7 weeks of age, when the patches in layer IV had disappeared in the course of normal development, monocular enucleation caused a reappearance of the discontinuous pattern of 5'-nucleotidase activity in layer IV. These results reveal a close relation between the distribution of 5'-nucleotidase and the time course of the developmental phase during which the visual cortex is susceptible to experience-dependent alterations. As suggested by the correlation between sites of enzyme activity and eye dominance columns, the expression of 5'-nucleotidase patches in layer IV appears to be associated with the remodelling of ocular dominance territories that occurs both in normal development and after manipulation of afferent retinal input. Thus, 5'-nucleotidase is likely to serve a function in activity-dependent modifications of cortical circuitry. Moreover, 5'-nucleotidase activity is the only endogenous marker known to date that exhibits a columnar pattern in cat visual cortex.

5'-Nucleotidase↗
PubMed1996

Transient expression of NADPH diaphorase activity in the mouse whisker to barrel field pathway.

Development of the topographic map of the somatosensory cortex of rodents appears to depend on fine-tuned patterns of neuronal activity. Nitric oxide (NO) has been described as a potent messenger in the modulation of neural activity associated with synaptic plasticity. To evaluate the role of NO in the murine somatosensory pathway, we investigated NO synthase activity by NADPH diaphorase histochemistry at crucial developmental stages. At birth, NADPH diaphorase activity was detected in the cortical plate of the developing somatosensory cortex. At day 3, diffuse NADPH diaphorase activity increased within the emerging layer 4 in the future barrel field hollows. This staining was most intense at day 6 in the barrel field hollows and became undetectable by the end of the second postnatal week. The appearance of the diffuse NADPH diaphorase staining pattern was also observed in a similar time course and topography in the ascending relays of the somatosensory cortex, specifically in the barreloids within the ventrobasal nucleus of the thalamus and the barrelettes of the trigeminal nucleus of the brainstem. Lesioning the C row of whiskers at day 1 (i.e. during the critical period of barrel formation) led to fused C barrels of diffuse NADPH diaphorase activity in the barrel fields. In addition, highly NADPH diaphorase activity-positive individual cells present in the deeper layers of the somatosensory cortex at days 0 and 3 became visible in the upper layers at day 6 and remained until day 15. In layer 4, these cells were predominantly localized in the septa at day 6 and 9. No positive individual cells were detected in barrelettes or barreloids at any age. We conclude that NADPH diaphorase activity is present during experience-dependent consolidation of synaptic contacts in the somatosensory pathway.

Aging↗
PubMed1998

Experience-dependent depression of vibrissae responses in adolescent rat barrel cortex.

A short period of vibrissae deprivation in an adolescent (approximately 1 month old) rat can lead to depression of the cortical response to stimulation of the regrown vibrissae. In a barrel column representing the deprived vibrissa, depression is greater for neurons located close to the barrel column representing the spared vibrissa. One possible explanation is that the spared vibrissa produces heterosynaptic depression of the principal vibrissa response (Glazewski & Fox, 1996). To test this idea further, we compared the effect of depriving all vibrissae (no heterosynaptic influence at all) with depriving a single vibrissa (maximal heterosynaptic influence expected). In addition we tested the origin of the depression by recording from subcortical structures. After 7 days' deprivation and 6-8 days' regrowth, we tested the responses of barrel cortex cells, thalamic VPm neurons and trigeminal ganglion cells to stimulation of the regrown vibrissae. We found that depression was greater in cortex if a single vibrissa had been deprived than if all vibrissae had been deprived. (Average principal vibrissae responses in single vibrissae deprived animals were 36% of those in all vibrissae deprived animals for layer II/III and 41% for layer IV.) This implicates the spared vibrissae in actively down-regulating responses to the deprived vibrissae. However, some depression could also be produced in animals deprived of all vibrissae (layers II/III were 39% and layer IV 74% of control levels). These results indicate that simple withdrawal of activation has a depressive effect on responses but that depression is far greater if some active inputs remain. Neither form of deprivation had an effect on responses to principal vibrissa stimulation in the thalamus or trigeminal ganglion however, suggesting that depression originates in the cortex. Within the cortex, intracortical connections seem most affected as the greatest depression was found in layers II/III and in layer IV among cells responding at intermediate latencies (9-14 ms).

Animals↗
PubMed1997

Critical period-dependent reduction of the permissiveness of cat visual cortex tissue for neuronal adhesion and neurite growth.

During postnatal development, the visual cortex undergoes an experience-dependent refinement of its circuitry. This process includes synapse formation, as well as synapse elimination. Both mechanisms appear to be restricted to a limited 'critical period' which lasts for approximately 2 months in cats. We tested whether the termination of the critical period for cortical malleability is paralleled by changes in the growth permissiveness of the tissue. These changes may inhibit progressive reorganization of functional circuitries mediated by axon growth. Embryonic cortical neurons were cultured on unfixed cryostat sections of the visual cortex obtained from cats aged 2-50 weeks. After 2-3 days in vitro the distribution of viable cells and the percentage of neurite-bearing cells were determined and analysed with respect to the developmental age and subdivisions of the underlying tissue substrate. It was shown that cell adhesion and neurite formation are correlated with the developmental age of the substrate tissue and the time period of myelination. While embryonic neurons adhered and survived on grey and white matter tissue from 2- and 4-week-old kittens, there was a significant reduction in cell adhesion on the myelinated white matter regions of the tissue sections of older animals. Quantitative analyses showed that neurite formation by cultured neurons also became successively impaired on grey and white matter areas of tissue substrates, corresponding to the time course of the critical period for cortical malleability. On grey matter tissue this effect was most pronounced between the second and sixth postnatal weeks. The effects were not antagonized by coating the substrate sections with the growth-promoting molecule laminin. It is therefore proposed that neurite growth-inhibiting factors, most probably associated with central nervous system myelin, are gradually expressed postnatally and may contribute to the termination of the critical period in the visual cortex of cats.

Animals↗
PubMed1992

Agonists of cholinergic and noradrenergic receptors facilitate synergistically the induction of long-term potentiation in slices of rat visual cortex.

Acetylcholine (ACh) and noradrenaline (NA) have been shown to facilitate experience-dependent modifications of synaptic connectivity during postnatal development of the kitten visual cortex. To further investigate the mechanisms of this facilitation we studied the effects of these neuromodulators in an in vitro model of use-dependent synaptic plasticity. We have chosen long-term potentiation (LTP) in rat visual cortex slices because it shares several features with the in vivo model. In both cases induction of synaptic modifications requires that postsynaptic activation reaches a critical threshold and in both cases changes are induced more easily in young animals and when N-methyl-D-aspartate (NMDA) receptor-gated conductances are activated. Intracellular recordings were obtained from regular spiking cells in supragranular layers of rat visual cortex and LTP was induced by tetanic stimulation of the underlying white matter. Both cholinergic and noradrenergic agonists raised the probability that tetanic stimuli induced LTP and as in vivo they acted synergistically. These effects were mediated by agonists of muscarinic and beta-receptors, respectively. The agonists of both receptor systems enhanced the depolarizing response to the tetanus and increased NMDA receptor-gated conductances during this response. We suggest that this mode of action also accounts for the facilitatory effects which ACh and NA have on use-dependent synaptic plasticity in the developing visual cortex.

Acetylcholine↗
PubMed1997

Emergent properties of neural systems: how focal molecular neurobiological alterations can affect behavior.

Whereas the basic wiring diagram of the mammalian central nervous system (CNS) is genetically preprogramed, its fine tuning throughout different phases of infancy, childhood, and adulthood are highly experience dependent. The potential neurobiological mechanisms and behavioral effects of such experience-dependent neuroplasticity as a function of stage of development are outlined. A basic thesis of this paper is that mechanisms involved in neuronal learning and memory, such as long-term potentiation (LTP) and long-term depression (LTD), are used and reused not only in the sculpting of the CNS in the initial establishment of connections, but also again in the molding of personality and behavior based on experience. It is postulated that for higher order processes such as emotional memory, such neuroplasticity is occurring at increasingly larger numbers of synapses and cell assemblies with increasing mechanistic complexity and self-organization. Just as overexcitation or deprivation can profoundly affect the development of the visual system, it is postulated that similar phenomena exist in the neural substrates of emotional and cognitive development. In addition, a secondary and potentially more widespread series of ramifications are likely to occur in the higher order and integrative systems, such as secondary and tertiary cortical association areas and prefrontal cortex that become the ultimate integrators of emotion and experience, leading to subsequent actions and plans for the future. This process is by definition, plastic, and such remodeling is likely to take place not only at the level of the single synapse, but also at higher levels of network integration of which we currently have only the barest glimpse. Nonetheless, beginning to discuss the neurobiology of such self-organizing plastic systems may begin to change our conceptual approaches to psychopathology and open new avenues of therapeutics for the major psychiatric illnesses that are critically dependent on such higher order learning and memory mechanisms.

Adult↗
PubMed1996

A synaptic basis for memory storage in the cerebral cortex.

A cardinal feature of neurons in the cerebral cortex is stimulus selectivity, and experience-dependent shifts in selectivity are a common correlate of memory formation. We have used a theoretical "learning rule," devised to account for experience-dependent shifts in neuronal selectivity, to guide experiments on the elementary mechanisms of synaptic plasticity in hippocampus and neocortex. These experiments reveal that many synapses in hippocampus and neocortex are bidirectionally modifiable, that the modifications persist long enough to contribute to long-term memory storage, and that key variables governing the sign of synaptic plasticity are the amount of NMDA receptor activation and the recent history of cortical activity.

Animals↗
PubMed1998

The acquisition of skilled motor performance: fast and slow experience-driven changes in primary motor cortex.

Behavioral and neurophysiological studies suggest that skill learning can be mediated by discrete, experience-driven changes within specific neural representations subserving the performance of the trained task. We have shown that a few minutes of daily practice on a sequential finger opposition task induced large, incremental performance gains over a few weeks of training. These gains did not generalize to the contralateral hand nor to a matched sequence of identical component movements, suggesting that a lateralized representation of the learned sequence of movements evolved through practice. This interpretation was supported by functional MRI data showing that a more extensive representation of the trained sequence emerged in primary motor cortex after 3 weeks of training. The imaging data, however, also indicated important changes occurring in primary motor cortex during the initial scanning sessions, which we proposed may reflect the setting up of a task-specific motor processing routine. Here we provide behavioral and functional MRI data on experience-dependent changes induced by a limited amount of repetitions within the first imaging session. We show that this limited training experience can be sufficient to trigger performance gains that require time to become evident. We propose that skilled motor performance is acquired in several stages: "fast" learning, an initial, within-session improvement phase, followed by a period of consolidation of several hours duration, and then "slow" learning, consisting of delayed, incremental gains in performance emerging after continued practice. This time course may reflect basic mechanisms of neuronal plasticity in the adult brain that subserve the acquisition and retention of many different skills.

Adult↗
PubMed1995

The effects of early postnatal modification of body shape on the somatosensory-visual organization in mouse superior colliculus.

Different regions of the body of an animal have their own shape and location within visual space. Accordingly, in the superior colliculus there are somatosensory-visual bimodal neurons receiving tactile and visual input from the same region of space. In newborn mice, we changed the position of some body parts within visual space in order to see what happened to the alignment of the somatosensory and visual receptive fields of superior colliculus bimodal neurons. To do this, we modified the shape of the head by displacing the superior vibrissae and the ears, normally in the superior portion of visual space, into the inferior visual space. Analogously, we bent the inferior vibrissae into the superior visual space. At the sixth postnatal week we recorded from somatosensory-visual bimodal neurons of the deep layers of the superior colliculus and found that the tactile and visual receptive fields were aligned. Neurons receiving tactile input from the downward-displaced superior vibrissae and ears showed visual receptive fields in the inferior portion of visual space, whereas neurons receiving input from the upward-displaced inferior vibrissae showed visual receptive fields in the superior visual space. These results show that an experience-dependent interaction between visual and somatosensory inputs occurs during development, and that early exposure to abnormal visual-somatosensory experience modifies the organization of multisensory neurons in the superior colliculus.

Animals↗
PubMed1996

Brain-derived neurotrophic factor reversed experience-dependent synaptic modifications in kitten visual cortex.

During a critical period of early postnatal development the functional architecture of the visual cortex is shaped by experience-dependent circuit selection following a Hebbian mechanism. One consequence is that monocular deprivation (MD) leads to competitive repression of the input from the deprived eye. Recently it has been proposed that this process might involve activity-dependent competition for neurotrophic substances because the synthesis of brain-derived neurotrophic factor (BDNF) is regulated by visual input. Here we investigate the effects of intracortical infusion of BDNF and nerve growth factor (NGF) on MD effects in the visual cortex. Neuronal responses were monitored with optical and single unit recording techniques in the visual cortex of kittens that had been infused intracortically either with BDNF, NGF or cytochrome C while subjected to MD for 1 week during the peak of the critical period. NGF or cytochrome C had no effect on the consequences of MD. After BDNF treatment, by contrast, ocular dominance (OD) shifted towards the deprived eye in a zone extending 2.5-3.5 mm from the infusion cannula, and neurons lost their orientation selectivity. At intermediate distances both eyes activated the cortex equally well and responses were again tuned for orientation; at still larger distances OD was shifted towards the normal eye. Thus, BDNF antagonizes the functional effects of MD and at high concentrations causes paradoxical disconnection of non-deprived afferents and a loss of orientation selectivity.

Animals↗
PubMed1996

Newly learned auditory responses mediated by NMDA receptors in the owl inferior colliculus.

Alignment of auditory and visual receptive fields in the optic tectum of the barn owl (Tyto alba) is maintained through experience-dependent modification of auditory responses in the external nucleus of the inferior colliculus (ICX), which provides auditory input to the tectum. Newly learned tectal auditory responses, induced by altered visual experience, were found to be pharmacologically distinct from normal responses expressed at the same tectal sites. N-methyl-D-aspartate (NMDA) receptor antagonists administered systemically or applied locally in the ICX reduced learned responses more than normal responses. This differential blockade was not observed with non-NMDA or broad-spectrum antagonists. Thus, NMDA receptors preferentially mediate the expression of novel neuronal responses induced by experience during development.

2-Amino-5-phosphonovalerate↗
PubMed1991

Synaptic plasticity in visual cortex: comparison of theory with experiment.

1. The aim of this work was to assess whether a form of synaptic modification based on the theory of Bienenstock, Cooper, and Munro (BCM) can, with a fixed set of parameters, reproduce both the kinetics and equilibrium states of experience-dependent modifications cortex. 2. According to the BCM theory, the connection strength of excitatory geniculocortical synapses varies as the product of a measure of input activity (d) and a function (phi) of the summed postsynaptic response. For all postsynaptic responses greater than spontaneous but less than a critical value called the "modification threshold" (theta), phi has a negative value. For all postsynaptic responses greater than theta, phi has a positive value. A novel feature of the BCM theory is that the value of theta is not fixed, but rather "slides" as a nonlinear function of the average postsynaptic response. 3. This theory permits precise specification of theoretical equivalents of experimental situations, allowing detailed, quantitative comparisons of theory with experiment. Such comparisons were carried out here in a series of computer simulations. 4. Simulations are performed by presenting input to a model cortical neuron, calculating the summed postsynaptic response, and then changing the synaptic weights according to the BCM theory. This process is repeated until the synaptic weights reach an equilibrium state. 5. Two types of geniculocortical input are simulated: "pattern" and "noise." Pattern input is assumed to correspond to the type of input that arises when a visual contour of a particular orientation is presented to the retina. This type of input is said to be "correlated" when the two sets of geniculocortical fibers relaying information from the two eyes convey the same patterns at the same time. Noise input is assumed to correspond to the type of input that arises in the absence of visual contours and, by definition, is uncorrelated. 6. By varying the types of input available to the two sets of geniculocortical synapses, we simulate the following types of visual experience: 1) normal binocular contour vision, 2) monocular deprivation, 3) reverse suture, 4) strabismus, 5) binocular deprivation, and 6) normal contour vision after a period of monocular deprivation. 7. The constraints placed on the set of parameters by each type of simulated visual environment, and the effects that such constraints have on the evolution of the synaptic weights, are investigated in detail.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

The formation of cooperative cell assemblies in the visual cortex.

During a critical period of postnatal development of the mammalian visual cortex, synaptic connections are susceptible to use-dependent modifications. Synaptic connections strengthen if pre- and postsynaptic elements are active simultaneously and postsynaptic depolarization is sufficient to allow for the activation of N-methyl-D-aspartate (NMDA)-receptor-gated conductances. By contrast, synaptic gain decreases if postsynaptic activation exceeds a critical threshold and presynaptic afferents are not capable of activating NMDA-receptor-dependent conductances. These processes lead to selective stabilization of connections between neuronal elements which often exhibit correlated activity and thus modify connectivity according to functional criteria. It is suggested that such experience-dependent selection of circuits serves different purposes at different levels of visual processing. At the input stage to the striate cortex it contributes to optimize the match between the representations of the two eyes. At a later stage of processing it participates in the development of selective connections between cortical columns and thereby serves to establish neuronal representations for frequently occurring constellations of features. Use-dependent changes of synaptic gain can also be induced in the mature visual cortex. These modifications follow the same rules as those occurring during early development and appear to depend on similar molecular mechanisms. However, in the adult the changes of synaptic gain do not seem to be followed by major rearrangements of connectivity. This suggests developmental alterations in mechanisms responsible for growth, removal and stabilization of synaptic connections. Actually, many of the cellular mechanisms thought to be involved in use-dependent synaptic plasticity change during development but it is still unclear which of them are responsible for the definitive stabilization of functionally confirmed pathways.

Aging↗
PubMed1994

The flexible fly: experience-dependent development of complex behaviors in Drosophila melanogaster.

We demonstrate that Drosophila melanogaster provides a rich model system for studying behavioral development. Two additions to the many well-known advantages of this species are exploited here. First, as in mammals and higher vertebrates, early experience affects behavioral development of Drosophila. Second, the affected behaviors are complex and yet readily studied in the laboratory. Thus, Drosophila can be used to study the developmental mechanisms by which organisms can optimize their behavioral repertoires to enhance their chances for survival. Evidence that early experience affects female responsiveness to courting males is reviewed; in each case, experience modifies responses to behavioral targets. Our results demonstrate that developmental plasticity allows adjustment of intrinsically determined responses to visual targets so that they can take into account the actual characteristics of the developing animal's environment. Furthermore, plasticity makes it possible to introduce 'cultural' and 'social' elements into courtship and mate choice in insects. This previously unrecognized role for developmental plasticity in insects has broad theoretical and practical implications.

Animals↗
PubMed1990

Molecular and morphological changes in the cat lateral geniculate nucleus and visual cortex induced by visual deprivation are revealed by monoclonal antibodies Cat-304 and Cat-301.

Monoclonal antibody Cat-301 recognizes a surface-associated proteoglycan on subsets of neurons in the mammalian CNS (Hockfield and McKay, 1983). The expression of Cat-301 immunoreactivity on Y cells in the cat LGN is sharply reduced by early visual deprivation (Sur et al., 1988). We employed an immunosuppression strategy (Hockfield, 1987) to further study alterations in the expression of experience-dependent molecules. Newborn BALB/c mice were injected with LGN from dark-reared cats to induce a suppression of the immune response to antigens expressed in visually deprived animals. These mice were then immunized with LGN from normal cats to elicit an immune response to antigens with an expression dependent on normal early visual experience. This strategy permitted the generation of monoclonal antibody Cat-304, which recognizes a surface-associated antigen on neuronal cell bodies and proximal dendrites, and which appears histologically identical to Cat-301. Further analyses show that Cat-304 and Cat-301 recognize different epitopes on the same 680-kDa chondroitin sulfate proteoglycan. We examined the effects of early visual deprivation on Cat-304 immunoreactivity in the LGN and visual cortex of cats. In LGN from normal cats, Cat-304 labels neurons in layers A, A1, and C, in interlaminar zones, and in the medial interlaminar nucleus. In LGN from dark-reared cats, the number of antibody-positive neurons is markedly reduced, and the cross-sectional area of the remaining positive neurons is smaller than normal. In cortical area 17 of normally reared cats, Cat 304-positive neurons are densely distributed in 2 bands, in layers IV and V/VI. Labeled neurons are also present in layers II and III. In area 17 of dark-reared cats, the number of antibody-positive neurons is reduced. The reduction in the number of labeled neurons is most pronounced in layers II/III and V/VI. Antibody-positive neurons are smaller in all cortical layers of dark-reared cats. The changes in the expression of Cat-301 immunoreactivity in dark-reared visual cortex and LGN are identical to those of Cat-304. The laminar differences in the effect of dark rearing on Cat-301 and Cat-304 expression in the visual cortex provides support for the suggestion that layer IV of cortical area 17 may be less susceptible to prolongation of plasticity by dark rearing than layers II/III and V/VI. Further, the biochemical and histological studies reported provide evidence that early visual experience regulates protein expression in the cat LGN and visual cortex.

Animals↗
PubMed1997

Experience-dependent modifications in MAP2 phosphorylation in rat olfactory bulb.

Microtubule-associated protein 2 (MAP2) is a neuron-specific cytoskeletal protein, enriched in dendrites and cell bodies, that helps determine dendritic shape. MAP2 regulates microtubule stability in a phosphorylation-dependent manner. The present study used immunocytochemistry with phosphoepitope-specific and phosphorylation state-independent antibodies to examine experience-dependent changes in MAP2 expression during postnatal development of the olfactory bulb. Our results demonstrate that immunoreactivity reflecting total MAP2 expression reaches a maximal level by postnatal day 20 (P20). The degree of staining for phosphoindependent forms of MAP2 is relatively unaffected by blocking odorant passage to one half the nasal epithelium via unilateral naris closure, a manipulation that attenuates physiological activity in the bulb. However, olfactory restriction from P1 dramatically reduces immunoreactivity for antibody AP18, which recognizes MAP2 only when phosphorylated on Ser136. Quantification of staining in the granule cell layer indicates that the greatest difference (64%) between control and experimental bulbs occurs after occlusion from P1 to P30 compared with animals deprived from P1 to P10 or P1 to P20. The shift in MAP2 phosphorylation occurs even when deprivation is delayed until P30, after the sensitive period for experience-dependent changes in bulb volume. Thus, the degree of the phosphorylation shift depends on the duration but not the time of onset of naris closure. Because staining for phosphorylation-independent forms of MAP2 is unchanged by naris closure, the total amount of the protein per unit area is probably not significantly altered. However, the large reductions of AP18-immunoreactivity in the bulb after olfactory restriction suggest that there is an activity-dependent stimulation of MAP2 phosphorylation.

Animals↗