Bidirectional regulation of Munc13-3 protein expression by age and dark rearing during the critical period in mouse visual cortex

Rearing in darkness slows the time course of the visual cortical critical period, such that at 5 weeks of age normal cats are more plastic than dark-reared cats, while at 20 weeks dark-reared cats are more plastic [Mower GD (1991) The effect of dark rearing on the time course of the critical period in cat visual cortex. Dev Brain Res 58:151-158]. Thus, genes that are important for visual cortical plasticity should show differences in expression between normal and dark-reared visual cortex that are of opposite direction in young versus older animals. Previously, we showed by differential display polymerase chain reaction and northern blotting that mRNA for Munc13-3, a mammalian homologue of the C. elegans uncoordinated (unc) gene, shows such bidirectional regulation in cat visual cortex [Yang CB, Zheng YT, Li GY, Mower GD (2002) Identification of Munc13-3 as a candidate gene for critical period neuroplasticity in visual cortex. J Neurosci 22:8614-8618]. Here, the analysis is extended to Munc13-3 protein in mouse visual cortex, which will provide the basis for gene manipulation analysis. In mice, Munc13-3 protein was elevated 2.3-fold in dark-reared compared with normal visual cortex at 3.5 weeks and 2.0-fold in normal compared with dark-reared visual cortex at 9.5 weeks. Analysis of variance of protein levels showed a significant interaction, indicating that the effect of dark rearing depended on age. This bidirectional regulation was restricted to visual cortex and did not occur in frontal cortex. Bidirectional regulation was also specific to Munc13-3 and was not found for other Munc13 family members. Munc13 proteins serve a central priming function in synaptic vesicle exocytosis at glutamatergic and GABAergic synapses and this work contributes to the growing evidence indicating a role of Munc13 genes in synaptic plasticity.     

Differential effect of dark rearing on long-term potentiation induced by layer IV and white matter stimulation in rat visual cortex

In the earlier work, we showed that primed-burst stimulation (PBs) is an effective protocol to induce long-term potentiation (LTP) in layer II/III of adult rat visual cortex in vitro. In the present study, we investigated effects of dark rearing on potentiation of layer II/III responses to stimulation of layer IV or the underlying white matter in the visual cortex in vitro. Long-term potentiation was induced by PBs applied to white matter or layer IV of the cortex in light and dark reared rats. Regardless of the stimulation site, layer II/III field potentials consisted of two components. In general, the latency of responses in dark reared rats was shorter than that in light reared ones. Whereas PBs of layer IV produced LTP of two components in both the groups, that of white matter induced an appreciable potentiation of the second component in both groups and the first component only in dark reared rats. These results indicate that PBs of either white matter or layer IV can gain access to the modifiable synapses that are related to the second component of layer II/III responses in light and dark reared visual cortex, but accessibility of the modifiable synapses that are related to first component depends on the tetanization site. The dark rearing enhances accessibility of the modifiable synapses that are related to the first component following PBs of the white matter. It is suggested that the immaturity of inhibitory circuits and/or better function of excitatory ones in the visual cortex of dark reared rats may contribute to the enhanced accessibility of the first component.     

Age-dependent decline in supragranular long-term synaptic plasticity by increased inhibition during the critical period in the rat primary visual cortex

Supragranular long-term potentiation (LTP) and depression (LTD) are continuously induced in the pathway from layer 4 during the critical period in the rodent primary visual cortex, which limits the use of supragranular long-term synaptic plasticity as a synaptic model for the mechanism of ocular dominance (OD) plasticity. The results of the present study demonstrate that the pulse duration of extracellular stimulation to evoke a field potential (FP) is critical to induction of LTP and LTD in this pathway. LTP and LTD were induced in the pathway from layer 4 to layer 2/3 in slices from 3-wk-old rats when FPs were evoked by 0.1- and 0.2-ms pulses. LTP and LTD were induced in slices from 5-wk-old rats when evoked by stimulation with a 0.2-ms pulse but not by stimulation with a 0.1-ms pulse. Both the inhibitory component of FP and the inhibitory/excitatory postsynaptic potential amplitude ratio evoked by stimulation with a 0.1-ms pulse were greater than the values elicited by a 0.2-ms pulse. Stimulation with a 0.1-ms pulse at various intensities that showed the similar inhibitory FP component with the 0.2-ms pulse induced both LTD and LTP in 5-wk-old rats. Thus extracellular stimulation with shorter-duration pulses at higher intensity resulted in greater inhibition than that observed with longer-duration pulses at low intensity. This increased inhibition might be involved in the age-dependent decline of synaptic plasticity during the critical period. These results provide an alternative synaptic model for the mechanism of OD plasticity.     

Role of visual experience in activating critical period in cat visual cortex

Cats were reared in total darkness from birth until 4-5 mo of age (DR cats, n = 7) or with very brief visual experience (1 or 2 days) during an otherwise similar period of dark rearing [DR(1) cats, n = 3; DR(2) cats, n = 7]. Single-cell recordings were made in area 17 of visual cortex at the end of this rearing period and/or after a subsequent prolonged period of monocular deprivation. Control observations were made in normal cats (n = 3), cats reared with monocular deprivation from birth (n = 4), and cats monocularly deprived after being reared normally until 4 mo of age (n = 2). After rearing cats in total darkness, the majority of visual cortical cells were binocularly driven and the overall distribution of ocular dominance was not different from that of normal cats. Orientation-selective cells were very rare in dark-reared cats. Monocular deprivation imposed after dark rearing resulted in selective development of connections from the open eye. Most cells were responsive only to the open eye and the majority of these were orientation selective. These results were similar to, though less severe than, those found in cats reared with monocular deprivation from birth. Monocular deprivation imposed after 4 mo of normal rearing did not produce selective development of connections from the open eye in terms of either ocular dominance or orientation selectivity. In DR(1) cats visual cortical physiology was degraded in comparison to dark-reared cats after the rearing period. Most cells were binocularly driven but there was a higher frequency of unresponsive cells and a reduced frequency of orientation-selective cells. Subsequent monocular deprivation resulted in a further decrease in the number of binocularly driven cells and an increase in unresponsive cells. However, it did not produce a bias in favor of the open eye in terms of either ocular dominance or orientation selectivity. In DR(2) cats there was a high incidence of unresponsive cells and a marked loss of binocularly driven cells after the rearing period. Subsequent monocular deprivation failed to produce any significant changes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Traveling waves of activity in primary visual cortex during binocular rivalry

When the two eyes view large, dissimilar patterns that induce binocular rivalry, alternating waves of visibility are experienced as one pattern sweeps the other out of conscious awareness. Here we combine psychophysics with functional magnetic resonance imaging to show tight linkage between dynamics of perceptual waves during rivalry and neural events in human primary visual cortex (V1).     

The binocular organization of simple cells in the cat's visual cortex

We have studied the manner by which inputs from the two eyes are combined in simple cells of the cat's visual cortex. The stimuli for this study are drifting sinusoidal gratings, shown dichoptically at optimal spatial frequency and orientation. The relative spatial phase (disparity) between the gratings for left and right eyes is varied over 360 degrees. Most simple cells show phase-specific binocular interaction such that response amplitudes and phases vary depending on the relative spatial phase. At one phase, response is greater than either of the monocular responses and often greater than the sum of the two. At the phase 180 degrees away from the optimal, the cell's responses are strongly inhibited and often completely suppressed. Phase-specific binocular interaction disappears when the gratings presented to one eye are made orthogonal to the optimal orientation. The degree of binocular interaction does not depend critically on the ocular dominance of the cells. Simple cells that are nearly equally dominated by each eye always exhibit strong phase-specific interaction. The majority of cells that are strongly dominated by one eye, and even those that appear monocular, show phase-dependent changes in responses. We examined the extent of binocular interaction for cells with preferred orientations near vertical compared with those tuned to other optimal orientations. If these cells are conveying information about depth, one might expect a greater degree of binocular phase-specificity for units preferring nearly vertical orientations, which would then be processing horizontal disparities. We find no evidence for this. Predictions of simple-cell responses are derived from a linear model of binocular convergence in which light-evoked neural signals from each eye are summed linearly to determine cell responses. Data from cells generally follow the prediction of the model for both response amplitude and phase. Deviations from predictions of the linear model are found for a minority of cells. This deviation may be accounted for by a threshold mechanism that comes into play after the linear binocular summation. A small proportion of simple cells that appear monocular by alternate tests of each eye show a purely inhibitory influence from the silent eye. This inhibition is not generally dependent on the relative phase of the gratings. We conclude that most binocular interaction in striate simple cells may be accounted for by linear summation of neural signals from each eye.(ABSTRACT TRUNCATED AT 400 WORDS)     

The binocular organization of complex cells in the cat's visual cortex

We have studied the manner by which inputs from the two eyes are combined in complex cells of the cat's visual cortex. The stimuli are drifting sinusoidal gratings presented dichoptically at optimal spatial frequency and orientation. The relative phase between the gratings for left and right eyes is varied over 360 degrees. Approximately 40% of complex cells show phase-specific binocular interaction where response amplitudes vary depending on the relative phase of the gratings shown to the two eyes. This interaction is similar to that observed for most simple cells. We devised a test to examine whether the phase-specific interaction in complex cells results from linear convergence of neural signals at subunits of the receptive fields. The data from this test are consistent with a linear combination model. The phase-specific binocular interaction data from complex cells imply that the optimal relative phase of the receptive field subunits is closely matched. Another type of complex cell, approximately 40% of the total, could be driven through either eye, but exhibited non-phase-specific responses to dichoptically presented gratings. This type of interaction is found only in complex cells. Binocularly non-phase-specific complex cells may have subunits whose optimal relative phases are random or monocular. The division of complex cells into these two major groups (binocularly phase specific and non-phase specific) is independent of whether they are standard or special complex-cell types. A small proportion (8%) of complex cells that appear monocular by alternate tests of each eye show a purely inhibitory influence from the silent eye. This inhibition is not generally dependent on the relative phase of the gratings. Unlike simple cells, complex cells are not a homogeneous group. However, nearly half of complex cells show phase-specific binocular interaction that is probably the result of linear convergence. Combined with the results from simple cells, the majority of binocular interaction in the striate cortex may be accounted for by linear summation of neural signals from each eye. This provides a simplified view of the nature of binocular interaction in the visual cortex.     

Effects of dark rearing on the development of visual callosal connections

Summary It is now well established that during normal postnatal development there is a partial elimination of the callosal projections of cortical areas 17 and 18 in the cat and that visual experience early in life can modulate this process. In the present experiments, we quantitatively studied the influence of light, per se, by rearing cats in total darkness. Dark rearing exaggerates the normally occurring partial elimination of immature callosal projections: it causes a significant reduction in the total number of neurons in both the supra-and infragranular layers that send an axon through the corpus callosum and slightly narrows the distribution of these neurons across areas 17 and 18. These data demonstrate that visual stimulation is not necessary either to initiate the partial elimination of immature callosal projections or to stabilize a large fraction of the callosal projections present at birth. However, normal visual stimulation is necessary for the stabilization of the normal complement of callosal projections.     

Mechanisms of binocular interaction in the visual cortex of rodents

New hypotheses are advanced relating to the functional role and mechanisms of interaction of afferentation from the two eyes in the visual cortex of animals with poorly developed binocular vision. The proposed approach sheds light on a number of questions, particularly those concerning the relatively large level of disparity of the receptor fields in cortical neurons, the role of non-overlapping fibers in the visual tract, and others. Hypothesis relating to the evolutionary relationships between these mechanisms and the mechanisms of stereopsis are discussed. A. B. Kogan Science Research Institute of Neurocybernetics, Rostov State University, Rostov-on-Don. Translated from Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 81, No. 5, pp. 31–39, May, 1995.     

Developmental changes in NMDA receptor-mediated visual activity in the rat superior colliculus, and the effect of dark rearing

N-methyl-D-aspartate (NMDA) receptor-mediated activity is considered important for experience-dependent plasticity in the developing visual system. We investigated the influence of age and experience on the role of NMDA receptors in the visual transmission in the superficial grey layer of the superior colliculus (SGS) of the superior colliculus, where, in the adult, NMDA receptors mediate a substantial part of the visual response. In normally reared (postnatal day 14, P14, to adult) rats, visual responses were challenged with NMDA receptor-selective iontophoretic applications of the antagonist D-2-amino-5-phosphonovalerate (AP5). After eye opening (at P14), there was a significant increase in the number of neurones whose visual responses were reduced during AP5 ejection, which peaked at P22 (85%; n = 21), and then declined to adult levels (66%; n = 47) at P25. The mean reduction of the response (from control levels) by AP5 was similar at all ages (approximately 40%). Dark rearing had striking effects on the role of NMDA receptors in visual transmission, especially when comparisons were made between age-matched subjects greater than P25. In these subjects, AP5 ejection reduced the visual responses of all neurones studied. In addition, AP5 ejection caused a significantly larger reduction of visual responses in dark-reared rats (mean reduction 62 ± 4; n = 29) compared with age-matched controls (mean reduction 44 ± 8; n = 23). The D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) reduced the visual responses of every neurone studied and there were no age- or experience-dependent effects. We conclude that NMDA receptors, but not AMPA receptors, assume greater importance for visual transmission in the SGS of dark-reared rats. Received: 2 May 1997 / Accepted: 19 November 1997     

猫初级视区急性毁损对高级视区刺激诱导的c-fos蛋白表达的影响

目的:研究初级视区急性毁损对猫的高级视区刺激诱导的c-fos蛋白表达的影响,探索初级视区毁损后的残留视觉(称盲视)可能机制。方法:本研究采用免疫组织化学检测了初级视区(包括17和18区)急性毁损对猫的高级视区(包括19、20和21区)中立早基因c-fos蛋白基础表达量和刺激诱导的c-fos蛋白表达量的影响,以正常猫为对照。结果:急性毁损初级视区后,高级视区内c-fos免疫阳性神经元密度及c-fos免疫阳性反应的光吸收值(OA)在初级视区毁损猫和正常对照猫之间无显著差异;然而,双侧初级视区毁损猫的高级视区中刺激诱导的c-fos免疫阳性神经元密度比正常猫下降了92%以上,c-fos蛋白免疫阳性反应的OA值下降了78.9%以上。结论:初级视区急性毁损后高级视区的绝大多数神经元失去了对视觉刺激的反应性,因此,初级视区毁损后出现的盲视现象可能主要与皮层下中枢至高级视区的神经通路重组有关。     

大鼠视皮层组织型纤溶酶原激活剂、神经元周围网络与小清蛋白的发育性共表达关系及其与视皮层可塑性关键期的相关性

目的:探讨出生后的Long Evans大鼠视皮层组织型纤溶酶原激活剂(tPA)与小清蛋白(PV)、神经元周围网络(PNs)三者发育性共表达的关系及其与视皮层发育可塑性的相关性.方法:应用免疫荧光组织化学对生后3(关键期起始)、4(高峰)、5(后期)、7(终止)、9(成年)周龄的Long Evans大鼠视皮层分别进行tPA、NeuN、DAPI和tPA、PV、PNs三重标记以检测它们的表达随发育的时空关系.结果:tPA+ PNs阳性细胞密度在4周龄显著增加达高峰,随后在9周龄显著减少,tPA+PV和PV+PNs阳性细胞密度在3周龄已达峰值并维持至4周龄,在5周龄显著减少至最低水平,随后显著增加至成年高水平;tPA+PV/tPA和PV+PNs/PNs比值在3周龄已达最大值,在5周龄显著降至最低,随后显著上升至成年水平;tPA+ PV+ PNs阳性细胞密度在可塑性关键期的高峰期即4周龄出现峰值.结论:PNs对PV的包绕随发育的变化可能是PNs参与关键期终止的结构基础;存在tPA+ PV+ PNs阳性细胞,此类神经元在可塑性高峰期富集提示它们可能与关键期可塑性的增强有关.     

Distribution of glial fibrillary acidic protein and vimentin immunoreactivity during rat visual cortex development

Summary The postnatal maturation of astrocytes in the rat visual cortex was analysed by immunostaining the astroglial proteins vimentin and glial fibrillary acidic protein with poly- and monoclonal antibodies. Vimentin immunoreactivity was present in the visual cortex up to the third postnatal week, whereas immunolabelling first disappeared in the cortical layers and then in the white matter. In the early postnatal period, vimentin antibodies labelled radial glial fibres. After the first postnatal week staining of radial glial fibres gradually disappeared and vimentin immunoreactivity was localized in a few protoplasmic astrocytes in the grey matter and fibrous astrocytes in the white matter. The development of glial fibrillary acidic protein-positive astrocytes was not fully complete until postnatal day 50. Glial fibrillary acidic protein-positive radial glial fibres were present after birth and disappeared towards the end of the third postnatal week. Staining of astrocytes in the white matter and in cortical layers I and VI reached an adult density at postnatal days 8 and 20, respectively. A progressively later development of glial fibrillary acidic protein-positive astrocytes was observed in cortical layers II–V which was completed between postnatal days 47 and 50. In the adult rat visual cortex glial fibrillary acidic protein-positive astrocytes were especially dense in layers I and VI, moderate in layers II/III and V and nearly absent in layer IV and lower layer III. The time course of the loss of vimentin and the gradual appearance of glial fibrillary acidic protein immunoreactivity in the visual cortex is considered as an index of astrocytic maturation and the spatiotemporal sequence of this maturation pattern is discussed in terms of reciprocal neuron-astrocyte interactions during brain development.     

Proto-oncogene c-fos is transiently induced in the rat cerebral cortex after forebrain ischemia

The amounts of mRNAs for proto-oncogene c-fos and structural protein beta-actin were measured in the rat cerebral cortex after transient forebrain ischemia. A transient and specific induction of c-fos mRNA was noticed in the cerebral cortex 30-90 min after ischemia followed by decline to control value. In contrast, the level of mRNA for beta-actin was not altered throughout the recirculation period examined. These results suggest specific role of c-fos gene after brain damage.     

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.     

Environmental enrichment prevents effects of dark-rearing in the rat visual cortex

Environmental enrichment potentiates neural plasticity, enhancing acquisition and consolidation of memory traces. In the sensory cortices, after cortical circuit maturation and sensory function acquisition are completed, neural plasticity declines and the critical period 'closes'. In the visual cortex, this process can be prevented by dark-rearing, and here we show that environmental enrichment can promote physiological maturation and consolidation of visual cortical connections in dark-reared rats, leading to critical period closure.     

Receptive-field properties of neurons in binocular and monocular segments of striate cortex in cats raised with binocular lid suture

1. We studied the receptive fields of 171 striate cortical neurons from 17 cats raised with binocular lid suture. Of these, 102 fields were within 10 degrees of the area centralis and the remaining 69 were at least 38 degrees from the vertical meridian. 2. Based on their different response properties, cells were divided into three broad groups: the mappable cells (49%) had clearly defined receptive fields, the unmappable cells (31%) were activated by visual stimuli but had diffuse fields which could not be hand plotted, and the visually inexcitable cells (20%) could not be activated by visual stimuli. Very few (less than or equal to 12% of the total sample) normal simple or complex cells could be found. 3. Orientation selectivity was assessed in these cells. Only 12% displayed orientation selectivity within normal bounds, and these were all mappable cells. None of the unmappable cells had discernible orientation selectivity. 4. Ocular dominance was assessed for 62 of the centrally located receptive fields. Among mappable cells, there was an abnormally low proportion of binocular fields, while no such abnormality was seen for unmappable cells. 5. For 47 of the neurons, average response histograms were compiled for moving stimuli of various parameters in an effort to evoke the maximum discharge or peak response. This peak response was normal for mappable cells but reduced for unmappable cells. 6. We devised a technique for studying potential inhibitory receptive-field zones in these neurons, validated the method in normal striate cortex, and used it to test 20 mappable cells in the lid-sutured cats. None showed the pattern of strong inhibitory side bands seen in normal simple cells, although six showed weak or abnormal inhibitory zones. Interestingly, six of the seven visually inexcitable cells tested by this method had purely inhibitory receptive fields. 7. The effects of binocular suture were essentially identical for the binocular and monocular segments since the cell types and their response properties did not differ between these two areas of cortex. Furthermore, the cortical monocular segments of these cats seemed qualitatively different from the deprived cortical monocular segment after monocular suture. This extends an analogous difference for these cats reported for the monocular segments of the lateral geniculate nucleus. We thus conclude that monocularly and binocularly sutured cats develop by qualitatively different mechanisms. For the former, competition between central synapses related to each eye is a prominent feature of geniculocortical development, whereas, for the latter, such specific forms of geniculocortical development may not obtain.