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Thomson AM. Circuits and Synapses: Hypothesis, Observation, Controversy and Serendipity - An Opinion Piece. Front Neural Circuits 2021; 15:732315. [PMID: 34602985 PMCID: PMC8482872 DOI: 10.3389/fncir.2021.732315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Accepted: 08/11/2021] [Indexed: 11/29/2022] Open
Abstract
More than a century of dedicated research has resulted in what we now know, and what we think we know, about synapses and neural circuits. This piece asks to what extent some of the major advances - both theoretical and practical - have resulted from carefully considered theory, or experimental design: endeavors that aim to address a question, or to refute an existing hypothesis. It also, however, addresses the important part that serendipity and chance have played. There are cases where hypothesis driven research has resulted in important progress. There are also examples where a hypothesis, a model, or even an experimental approach - particularly one that seems to provide welcome simplification - has become so popular that it becomes dogma and stifles advance in other directions. The nervous system rejoices in complexity, which should neither be ignored, nor run from. The emergence of testable "rules" that can simplify our understanding of neuronal circuits has required the collection of large amounts of data that were difficult to obtain. And although those collecting these data have been criticized for not advancing hypotheses while they were "collecting butterflies," the beauty of the butterflies always enticed us toward further exploration.
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Affiliation(s)
- Alex M. Thomson
- Department of Pharmacology, UCL School of Pharmacy, London, United Kingdom
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Rockland KS. Cytochrome oxidase "blobs": a call for more anatomy. Brain Struct Funct 2021; 226:2793-2806. [PMID: 34382115 DOI: 10.1007/s00429-021-02360-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 07/31/2021] [Indexed: 11/29/2022]
Abstract
An ordered relation of structure and function has been a cornerstone in thinking about brain organization. Like the brain itself, however, this is not straightforward and is confounded both by functional intricacy and structural plasticity (many routes to a given outcome). As a striking case of putative structure-function correlation, this mini-review focuses on the relatively well-characterized pattern of cytochrome oxidase (CO) blobs (aka "patches" or "puffs") in the supragranular layers of macaque monkey visual cortex. The pattern is without doubt visually compelling, and the semi-dichotomous array of CO+ blobs and CO- interblobs is consistent with multiple studies reporting compartment-specific preferential connectivity and distinctive physiological response properties. Nevertheless, as briefly reviewed here, the finer anatomical organization of this system is surprisingly under-investigated, and the relation to functional aspects, therefore, unclear. Microcircuitry, cell type, and three-dimensional spatiotemporal level investigations of the CO+ CO- pattern are needed and may open new views to structure-function organization of visual cortex, and to phylogenetic and ontogenetic comparisons across nonhuman primates (NHP), and between NHP and humans.
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Affiliation(s)
- Kathleen S Rockland
- Department of Anatomy and Neurobiology, Boston University School of Medicine, 72 East Concord St., Boston, MA, 02118, USA.
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Marcar VL, Wolf M. An investigation into the relationship between stimulus property, neural response and its manifestation in the visual evoked potential involving retinal resolution. Eur J Neurosci 2021; 53:2612-2628. [PMID: 33448503 DOI: 10.1111/ejn.15112] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 12/23/2020] [Accepted: 12/29/2020] [Indexed: 11/28/2022]
Abstract
The visual evoked potential (VEP) has been shown to reflect the size of the neural population activated by a processing mechanism selective to the temporal - and spatial luminance contrast property of a stimulus. We set out to better understand how the factors determining the neural response associated with these mechanisms. To do so we recorded the VEP from 14 healthy volunteers viewing two series of pattern reversing stimuli with identical temporal-and spatial luminance contrast properties. In one series the size of the elements increased towards the edge of the image, in the other it decreased. In the former element size was congruent with receptive field size across eccentricity, in the later it was incongruent. P100 amplitude to the incongruent series exceeded that obtained to the congruent series. Using electric dipoles due the excitatory neural response we accounted for this using dipole cancellation of electric dipoles of opposite polarity originating in supra- and infragranular layers of V1. The phasic neural response in granular lamina of V1 exhibited magnocellular characteristics, the neural response outside of the granular lamina exhibited parvocellular characteristics and was modulated by re-entrant projections. Using electric current density, we identified areas of the dorsal followed by areas of the ventral stream as the source of the re-entrant signal modulating infragranular activity. Our work demonstrates that the VEP does not signal reflect the overall level of a neural response but is the result of an interaction between electric dipoles originating from neural responses in different lamina of V1.
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Affiliation(s)
- Valentine L Marcar
- Biomedical Optics Research Laboratory, University Hospital Zürich, Zürich, Switzerland
| | - Martin Wolf
- Biomedical Optics Research Laboratory, University Hospital Zürich, Zürich, Switzerland
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D'Souza RD, Bista P, Meier AM, Ji W, Burkhalter A. Spatial Clustering of Inhibition in Mouse Primary Visual Cortex. Neuron 2019; 104:588-600.e5. [PMID: 31623918 DOI: 10.1016/j.neuron.2019.09.020] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Revised: 08/08/2019] [Accepted: 09/12/2019] [Indexed: 12/12/2022]
Abstract
Whether mouse visual cortex contains orderly feature maps is debated. The overlapping pattern of geniculocortical inputs with M2 muscarinic acetylcholine receptor-rich patches in layer 1 (L1) suggests a non-random architecture. Here, we found that L1 inputs from the lateral posterior thalamus (LP) avoid patches and target interpatches. Channelrhodopsin-2-assisted mapping of excitatory postsynaptic currents (EPSCs) in L2/3 shows that the relative excitation of parvalbumin-expressing interneurons (PVs) and pyramidal neurons (PNs) by dLGN, LP, and cortical feedback is distinct and depends on whether the neurons reside in clusters aligned with patches or interpatches. Paired recordings from PVs and PNs show that unitary inhibitory postsynaptic currents (uIPSCs) are larger in interpatches than in patches. The spatial clustering of inhibition is matched by dense clustering of PV terminals in interpatches. The results show that the excitation/inhibition balance across V1 is organized into patch and interpatch subnetworks, which receive distinct long-range inputs and are specialized for the processing of distinct spatiotemporal features.
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Affiliation(s)
- Rinaldo D D'Souza
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Pawan Bista
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Andrew M Meier
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Weiqing Ji
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Andreas Burkhalter
- Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA.
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Connectional Modularity of Top-Down and Bottom-Up Multimodal Inputs to the Lateral Cortex of the Mouse Inferior Colliculus. J Neurosci 2017; 36:11037-11050. [PMID: 27798184 DOI: 10.1523/jneurosci.4134-15.2016] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 09/04/2016] [Indexed: 12/14/2022] Open
Abstract
The lateral cortex of the inferior colliculus receives information from both auditory and somatosensory structures and is thought to play a role in multisensory integration. Previous studies in the rat have shown that this nucleus contains a series of distinct anatomical modules that stain for GAD-67 as well as other neurochemical markers. In the present study, we sought to better characterize these modules in the mouse inferior colliculus and determine whether the connectivity of other neural structures with the lateral cortex is spatially related to the distribution of these neurochemical modules. Staining for GAD-67 and other markers revealed a single modular network throughout the rostrocaudal extent of the mouse lateral cortex. Somatosensory inputs from the somatosensory cortex and dorsal column nuclei were found to terminate almost exclusively within these modular zones. However, projections from the auditory cortex and central nucleus of the inferior colliculus formed patches that interdigitate with the GAD-67-positive modules. These results suggest that the lateral cortex of the mouse inferior colliculus exhibits connectional as well as neurochemical modularity and may contain multiple segregated processing streams. This finding is discussed in the context of other brain structures in which neuroanatomical and connectional modularity have functional consequences. SIGNIFICANCE STATEMENT Many brain regions contain subnuclear microarchitectures, such as the matrix-striosome organization of the basal ganglia or the patch-interpatch organization of the visual cortex, that shed light on circuit complexities. In the present study, we demonstrate the presence of one such micro-organization in the rodent inferior colliculus. While this structure is typically viewed as an auditory integration center, its lateral cortex appears to be involved in multisensory operations and receives input from somatosensory brain regions. We show here that the lateral cortex can be further subdivided into multiple processing streams: modular regions, which are targeted by somatosensory inputs, and extramodular zones that receive auditory information.
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Co-localization of glutamic acid decarboxylase and vesicular GABA transporter in cytochrome oxidase patches of macaque striate cortex. Vis Neurosci 2016; 32:E026. [PMID: 26579566 DOI: 10.1017/s0952523815000218] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The patches in primary visual cortex constitute hot spots of metabolic activity, manifested by enhanced levels of cytochrome oxidase (CO) activity. They are also labeled preferentially by immunostaining for glutamic acid decarboxylase (GAD), γ-aminobutyric acid (GABA), and parvalbumin. However, calbindin shows stronger immunoreactivity outside patches. In light of this discrepancy, the distribution of the vesicular GABA transporter (VGAT) was examined in striate cortex of two normal macaques. VGAT immunoreactivity was strongest in layers 4B, 4Cα, and 5. In tangential sections, the distribution of CO, GAD, and VGAT was compared in layer 2/3. There was a close match between all three labels. This finding indicates that GABA synthesis is enriched in patches, and that inhibitory synapses are more active in patches than interpatches.
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Vascularization of cytochrome oxidase-rich blobs in the primary visual cortex of squirrel and macaque monkeys. J Neurosci 2011; 31:1246-53. [PMID: 21273409 DOI: 10.1523/jneurosci.2765-10.2011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The close correlation between energy supply by blood vessels and energy consumption by cellular processes in the brain is the basis of blood flow-related functional imaging techniques. Regional differences in vascular density can be detected using high-resolution functional magnetic resonance imaging. Therefore, inhomogeneities in vascularization might help to identify anatomically distinct areas noninvasively in vivo. It was reported previously that cytochrome oxidase-rich blobs in the striate cortex of squirrel monkeys are characterized by a notably higher vascular density (42% higher than interblob regions). However, blobs have so far never been identified in vivo on the basis of their vascular density. Here, we analyzed blobs of the primary visual cortex of squirrel monkeys and macaques with respect to the relationship between vascularization and cytochrome oxidase activity. By double staining with cytochrome oxidase enzyme histochemistry to define the blobs and collagen type IV immunohistochemistry to quantify the blood vessels, a close correlation between oxidative metabolism and vascularization was confirmed and quantified in detail. The vascular length density in cytochrome oxidase blobs was on average 4.5% higher than in the interblob regions, a difference almost one order of magnitude smaller than previously reported. Thus, the vascular density that is closely associated with local average metabolic activity is a structural equivalent of cerebral metabolism and blood flow. However, the quantitative differences in vascularization between blob and interblob regions are small and below the detectability threshold of the noninvasive hemodynamic imaging methods of today.
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Judaš M, Sedmak G, Pletikos M, Jovanov-Milošević N. Populations of subplate and interstitial neurons in fetal and adult human telencephalon. J Anat 2011; 217:381-99. [PMID: 20979586 DOI: 10.1111/j.1469-7580.2010.01284.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In the adult human telencephalon, subcortical (gyral) white matter contains a special population of interstitial neurons considered to be surviving descendants of fetal subplate neurons [Kostovic & Rakic (1980) Cytology and the time of origin of interstitial neurons in the white matter in infant and adult human and monkey telencephalon. J Neurocytol9, 219]. We designate this population of cells as superficial (gyral) interstitial neurons and describe their morphology and distribution in the postnatal and adult human cerebrum. Human fetal subplate neurons cannot be regarded as interstitial, because the subplate zone is an essential part of the fetal cortex, the major site of synaptogenesis and the 'waiting' compartment for growing cortical afferents, and contains both projection neurons and interneurons with distinct input-output connectivity. However, although the subplate zone is a transient fetal structure, many subplate neurons survive postnatally as superficial (gyral) interstitial neurons. The fetal white matter is represented by the intermediate zone and well-defined deep periventricular tracts of growing axons, such as the corpus callosum, anterior commissure, internal and external capsule, and the fountainhead of the corona radiata. These tracts gradually occupy the territory of transient fetal subventricular and ventricular zones.The human fetal white matter also contains distinct populations of deep fetal interstitial neurons, which, by virtue of their location, morphology, molecular phenotypes and advanced level of dendritic maturation, remain distinct from subplate neurons and neurons in adjacent structures (e.g. basal ganglia, basal forebrain). We describe the morphological, histochemical (nicotinamide-adenine dinucleotide phosphate-diaphorase) and immunocytochemical (neuron-specific nuclear protein, microtubule-associated protein-2, calbindin, calretinin, neuropeptide Y) features of both deep fetal interstitial neurons and deep (periventricular) interstitial neurons in the postnatal and adult deep cerebral white matter (i.e. corpus callosum, anterior commissure, internal and external capsule and the corona radiata/centrum semiovale). Although these deep interstitial neurons are poorly developed or absent in the brains of rodents, they represent a prominent feature of the significantly enlarged white matter of human and non-human primate brains.
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Affiliation(s)
- Miloš Judaš
- University of Zagreb School of Medicine, Croatian Institute for Brain Research, Salata 12, Zagreb, Croatia.
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Abstract
The visual system is one of the most energetically demanding systems in the brain. The currency of energy is ATP, which is generated most efficiently from oxidative metabolism in the mitochondria. ATP supports multiple neuronal functions. Foremost is repolarization of the membrane potential after depolarization. Neuronal activity, ATP generation, blood flow, oxygen consumption, glucose utilization, and mitochondrial oxidative metabolism are all interrelated. In the retina, phototransduction, neurotransmitter utilization, and protein/organelle transport are energy-dependent, yet repolarization-after-depolarization consumes the bulk of the energy. Repolarization in photoreceptor inner segments maintains the dark current. Repolarization by all neurons along the visual pathway following depolarizing excitatory glutamatergic neurotransmission preserves cellular integrity and permits reactivation. The higher metabolic activity in the magno- versus the parvo-cellular pathway, the ON- versus the OFF-pathway in some (and the reverse in other) species, and in specialized functional representations in the visual cortex all reflect a greater emphasis on the processing of specific visual attributes. Neuronal activity and energy metabolism are tightly coupled processes at the cellular and even at the molecular levels. Deficiencies in energy metabolism, such as in diabetes, mitochondrial DNA mutation, mitochondrial protein malfunction, and oxidative stress can lead to retinopathy, visual deficits, neuronal degeneration, and eventual blindness.
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Affiliation(s)
- Margaret T T Wong-Riley
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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Basu K, Gravel C, Tomioka R, Kaneko T, Tamamaki N, Sík A. Novel strategy to selectively label excitatory and inhibitory neurons in the cerebral cortex of mice. J Neurosci Methods 2008; 170:212-9. [PMID: 18321591 DOI: 10.1016/j.jneumeth.2008.01.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Revised: 01/10/2008] [Accepted: 01/14/2008] [Indexed: 01/28/2023]
Abstract
Revealing the connections of neuronal systems is critical for understanding how they function. The vast majority of neurons in all cortical areas consist of excitatory cells whose activity is controlled by inhibitory cells. Distribution and projection patterns of inhibitory and excitatory cells are key information to understand the organization of the nervous system. To investigate axonal projections, we developed a method to uniquely distinguish excitatory axons from inhibitory ones in the cortex using transgenic mice expressing Cre recombinase in the Ca2+/calmodulin-dependent protein kinase IIalpha-containing neurons. These animals were injected by an adenoviral vector engineered so that it directs red fluorescent protein expression in non-Cre-expressing cells, and green fluorescent protein in Cre-positive neurons. We demonstrated in vitro and in vivo that GFP-expressing neurons are GABA-immunonegative (excitatory), while the RFP-expressing cells are either GABAergic neurons or glial cells. One week after the viral vector injection RFP and GFP signals overlapped in a subset of cells but after 1 month, the two signals showed total segregation. Six months post-inoculation, GFP-labelling was clearly visible in axons but RFP remained only in somata and proximal dendrites. This technique can thus be used to differentiate excitatory axonal projections from inhibitory ones, and represent a unique tool in neuronal circuit analysis.
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Affiliation(s)
- Kaustuv Basu
- Department of Psychiatry, Faculty of Medicine, Centre de Recherché Université Laval Robert-Giffard, 2601, chemin de la Canardiere, Quebec, G1J 2G3 Canada
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Economides JR, Horton JC. Labeling of cytochrome oxidase patches in intact flatmounts of striate cortex. J Neurosci Methods 2005; 149:1-6. [PMID: 16026853 DOI: 10.1016/j.jneumeth.2005.05.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2004] [Revised: 03/21/2005] [Accepted: 03/22/2005] [Indexed: 11/16/2022]
Abstract
Primate striate cortex contains a prominent system of columns referred to as cytochrome oxidase (CO) patches. Studies directed at the morphology and interconnections of cells in patches would be facilitated by a method that revealed the location of patches in the intact cortex. In three adult rhesus monkeys we prepared flatmounts of striate cortex [Horton JC, Hocking DR. Intrinsic variability of ocular dominance column periodicity in normal macaque monkeys. J Neurosci 1996;16:7228-39; Sincich LC, Adams DL, Horton JC. Complete flatmounting of the macaque cerebral cortex. Vis Neurosci 2003;20:663-86]. The flattened specimens were then reacted for CO activity prior to sectioning. Transillumination of the intact cortical sheet revealed an extensive pattern of dark ovals. It was confirmed that this pattern corresponded to the CO patches by subsequently cutting tangential sections and comparing them with images from the intact block. In vitro labeling of CO patches in the intact striate cortex may prove useful for directing injections of anatomical tracers such as Lucifer Yellow or DiI into identified patch and interpatch compartments.
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Affiliation(s)
- John R Economides
- Beckman Vision Center, University of California, 10 Koret Way, San Francisco, CA 94143-0730, USA
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Abstract
Primary and secondary visual cortex (V1 and V2) form the foundation of the cortical visual system. V1 transforms information received from the lateral geniculate nucleus (LGN) and distributes it to separate domains in V2 for transmission to higher visual areas. During the past 20 years, schemes for the functional organization of V1 and V2 have been based on a tripartite framework developed by Livingstone & Hubel (1988) . Since then, new anatomical data have accumulated concerning V1's input, its internal circuitry, and its output to V2. These new data, along with physiological and imaging studies, now make it likely that the visual attributes of color, form, and motion are not neatly segregated by V1 into different stripe compartments in V2. Instead, there are just two main streams, originating from cytochrome oxidase patches and interpatches, that project to V2. Each stream is composed of a mixture of magno, parvo, and konio geniculate signals. Further studies are required to elucidate how the patches and interpatches differ in the output they convey to extrastriate cortex.
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Affiliation(s)
- Lawrence C Sincich
- Beckman Vision Center, University of California-San Francisco, San Francisco, CA 94143, USA.
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Horton JC, Adams DL. The cortical column: a structure without a function. Philos Trans R Soc Lond B Biol Sci 2005; 360:837-62. [PMID: 15937015 PMCID: PMC1569491 DOI: 10.1098/rstb.2005.1623] [Citation(s) in RCA: 310] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
This year, the field of neuroscience celebrates the 50th anniversary of Mountcastle's discovery of the cortical column. In this review, we summarize half a century of research and come to the disappointing realization that the column may have no function. Originally, it was described as a discrete structure, spanning the layers of the somatosensory cortex, which contains cells responsive to only a single modality, such as deep joint receptors or cutaneous receptors. Subsequently, examples of columns have been uncovered in numerous cortical areas, expanding the original concept to embrace a variety of different structures and principles. A "column" now refers to cells in any vertical cluster that share the same tuning for any given receptive field attribute. In striate cortex, for example, cells with the same eye preference are grouped into ocular dominance columns. Unaccountably, ocular dominance columns are present in some species, but not others. In principle, it should be possible to determine their function by searching for species differences in visual performance that correlate with their presence or absence. Unfortunately, this approach has been to no avail; no visual faculty has emerged that appears to require ocular dominance columns. Moreover, recent evidence has shown that the expression of ocular dominance columns can be highly variable among members of the same species, or even in different portions of the visual cortex in the same individual. These observations deal a fatal blow to the idea that ocular dominance columns serve a purpose. More broadly, the term "column" also denotes the periodic termination of anatomical projections within or between cortical areas. In many instances, periodic projections have a consistent relationship with some architectural feature, such as the cytochrome oxidase patches in V1 or the stripes in V2. These tissue compartments appear to divide cells with different receptive field properties into distinct processing streams. However, it is unclear what advantage, if any, is conveyed by this form of columnar segregation. Although the column is an attractive concept, it has failed as a unifying principle for understanding cortical function. Unravelling the organization of the cerebral cortex will require a painstaking description of the circuits, projections and response properties peculiar to cells in each of its various areas.
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Li L, Rema V, Ebner FF. Chronic suppression of activity in barrel field cortex downregulates sensory responses in contralateral barrel field cortex. J Neurophysiol 2005; 94:3342-56. [PMID: 16014795 DOI: 10.1152/jn.00357.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Numerous lines of evidence indicate that neural information is exchanged between the cerebral hemispheres via the corpus callosum. Unilateral ablation lesions of barrel field cortex (BFC) in adult rats induce strong suppression of background and evoked activity in the contralateral barrel cortex and significantly delay the onset of experience-dependent plasticity. The present experiments were designed to clarify the basis for these interhemispheric effects. One possibility is that degenerative events, triggered by the lesion, degrade contralateral cortical function. Another hypothesis, alone or in combination with degeneration, is that the absence of interhemispheric activity after the lesion suppresses contralateral responsiveness. The latter hypothesis was tested by placing an Alzet minipump subcutaneously and connecting it via a delivery tube to a cannula implanted over BFC. The minipump released muscimol, a GABA(A) receptor agonist at a rate of 1 mul/h, onto one barrel field cortex for 7 days. Then with the pump still in place, single cells were recorded in the contralateral BFC under urethan anesthesia. The data show a approximately 50% reduction in principal whisker responses (D2) compared with controls, with similar reductions in responses to the D1 and D3 surround whiskers. Despite these reductions, spontaneous firing is unaffected. Fast spiking units are more sensitive to muscimol application than regular spiking units in both the response magnitude and the center/surround ratio. Effects of muscimol are also layer specific. Layer II/III and layer IV neurons decrease their responses significantly, unlike layer V neurons that fail to show significant deficits. The results indicate that reduced activity in one hemisphere alters cortical excitability in the other hemisphere in a complex manner. Surprisingly, a prominent response decrement occurs in the short-latency (3-10 ms) component of principal whisker responses, suggesting that suppression may spread to neurons dominated by thalamocortical inputs after interhemispheric connections are inactivated. Bilateral neurological impairments have been described after unilateral stroke lesions in the clinical literature.
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Affiliation(s)
- Lu Li
- Dept of Psychology, Vanderbilt University, Nashville, TN 37203, USA
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Hwang IK, Kim DW, Yoo KY, Kim DS, Kim KS, Kang JH, Choi SY, Kim YS, Kang TC, Won MH. Age-related changes of γ-aminobutyric acid transaminase immunoreactivity in the hippocampus and dentate gyrus of the Mongolian gerbil. Brain Res 2004; 1017:77-84. [PMID: 15261102 DOI: 10.1016/j.brainres.2004.05.022] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/10/2004] [Indexed: 11/16/2022]
Abstract
We investigated the age-related changes of gamma-aminobutyric acid transaminase (GABA-T, a GABA degradation enzyme) in the hippocampus and dentate gyrus of the gerbil at postnatal month 1 (PM 1), PM 3, PM 6, PM 12, and PM 24. Age-related changes of GABA-T immunoreactivity were distinct in the hippocampal CA1 region and in the dentate gyrus. GABA-T immunoreactivity was weak at PM 1, but at PM 3, it had increased significantly, and then increased further. Between PM 6 and PM 12, strong GABA-T immunoreactivity was found in nonpyramidal cells (GABAergic) in the stratum pyramidale of the CA1 region, and at PM 6, strong GABA-T immunoreactivity was found in neurons of the dentate gyrus subgranular zone. At PM 24, CA1 pyramidal cells showed strong GABA-T immunoreactivity. Western blot analysis showed a pattern of GABA-T expression similar to that shown by immunohistochemistry at various ages. In conclusion, our results suggest that the age-related changes of GABA-T provide important information about the aged brain with GABA dysfunction.
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Affiliation(s)
- In Koo Hwang
- Department of Anatomy, College of Medicine, Hallym University, Chunchon 200-702, South Korea
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Xiao Y, Felleman DJ. Projections from primary visual cortex to cytochrome oxidase thin stripes and interstripes of macaque visual area 2. Proc Natl Acad Sci U S A 2004; 101:7147-51. [PMID: 15118090 PMCID: PMC406480 DOI: 10.1073/pnas.0402052101] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been controversial whether the cytochrome oxidase (CO)-dense blobs in primate primary visual cortex (V1) and CO-dense thin stripes in visual area 2 (V2) are parts of a cortical color-processing stream that is segregated from other functional streams. One of the key pieces of evidence for the segregated color stream is the previous report of specific connections between blobs and thin stripes, which is parallel to the connections between interblobs and interstripes. To study the degree of the segregation between the proposed different streams, in the current study, anatomical tracers were injected into different V2 compartments with the functional guidance of optical imaging. The spatial relationship between each labeled cell and the CO blobs in V1 were analyzed quantitatively. After tracer injections in the color-preferring modules in CO thin stripes, equal amounts of labeled cells were found in the blobs and interblobs. However, the density of the labeled cells was more than twice as high in the blobs as that in the interblobs, and most of the clusters of labeled cells partially overlapped with the blobs. Tracer injections in the interstripes labeled cells predominantly in the interblobs. Our results suggest that both the blobs and interblobs project to the thin stripes and call into question the proposition that different CO compartments in V1 and V2 are connected in parallel to form highly segregated functional streams.
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Affiliation(s)
- Youping Xiao
- Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, TX 77030, USA
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Duffy KR, Livingstone MS. Distribution of non-phosphorylated neurofilament in squirrel monkey V1 is complementary to the pattern of cytochrome-oxidase blobs. Cereb Cortex 2003; 13:722-7. [PMID: 12816887 PMCID: PMC2646847 DOI: 10.1093/cercor/13.7.722] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The geniculo-recipient zones of the primate primary visual cortex (V1) stain more strongly for cytochrome oxidase (CO) than other regions. Labeling V1 with an antibody (SMI-32) against neurofilament protein produces a laminar pattern that is largely complementary to that of CO: the layers that receive the strongest geniculate input react weakly for SMI-32. We evaluated whether the complementary laminar relationship extends throughout the superficial layers where there are regularly spaced blobs of dark CO staining that are known to receive geniculate input. In all hemispheres, neurofilament labeling in the superficial layers was indeed complementary to the CO pattern. The density of SMI-32 labeled neurons was quantified and found to be greater within the CO interblobs than in the blobs. These results demonstrate that blobs and interblobs can be distinguished by examining the pattern of neurofilament expression in V1. That neurofilament expression is highest within interblobs raises the possibility that the distribution of cell types may be non-uniform across blobs and interblobs.
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Affiliation(s)
- Kevin R Duffy
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA.
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18
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Rodriguez MA, Caruncho HJ, Costa E, Pesold C, Liu WS, Guidotti A. In Patas monkey, glutamic acid decarboxylase-67 and reelin mRNA coexpression varies in a manner dependent on layers and cortical areas. J Comp Neurol 2002; 451:279-88. [PMID: 12210139 DOI: 10.1002/cne.10341] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
In nonhuman and human primates, reelin immunoreactivity is expressed consistently in gamma-aminobutyric acid (GABA)-ergic interneurons of the three upper cortical layers (Impagnatiello et al. [1998] Proc. Natl. Acad. Sci. U S A 95:15718-15723; Rodriguez et al. [2000] Proc. Natl. Acad. Sci. U S A 97:3550-3555). To understand in detail the pattern of reelin synthesis in GABAergic interneurons of primate neocortex, a quantitative analysis of reelin and of glutamic acid decarboxylase-67 (GAD(67)) mRNA-positive neurons as well as a quantitative analysis of total neuronal density measured by neuron-specific nuclear protein (NeuN) immunoreactivity was carried out in Patas monkey neocortex (Brodmann's areas 2, 3, 4, 6, 9, 17, 18, and 24). Reelin mRNA is expressed in every cortical area and layer studied, but layer II of each cortical area consistently revealed the largest neuronal population expressing reelin mRNA compared with other layers. The percentages of GAD(67)-positive neurons in each layer of the eight cortical areas were 83-98% in layer I, 55-64% in layer II, 37-49% in layer III, 71-89% in layer IV, 54-68% in layer V, and 71-85% in layer VI. The percentages of GABAergic neurons expressing reelin were 86-100% in layer I, 76-84% in layer II, 52-96% in layer III, 23-33% in layer IV, 33-57% in layer V, and 34-54% in layer VI. These findings suggest that there may be two classes of GABAergic neurons that can be differentiated by their ability to express reelin mRNA and reelin protein. This differentiation may have a functional significance, considering that reelin is secreted into the extracellular matrix, where it plays a putative role in the maturation of newly formed dendritic spines and binds selectively to dendritic shafts and to spine postsynaptic densities and presumably to integrin receptors, including alpha(3) subunits (Rodriguez et al. [2000]).
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Affiliation(s)
- Miguel A Rodriguez
- Psychiatric Institute, Department of Psychiatry, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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Abstract
After the collective work of many investigators, beginning with the early studies of Cajal, the following main [figure: see text] conclusions may be drawn regarding the morphology, biochemical characteristics and synaptic connections of interneurons: 1. Interneurons show a great variety of morphological, biochemical and physiological types. They constitute approximately 15-30% of the total population of neurons. 2. Because of the heterogeneity of interneurons and the lack of consensus as to which characteristics are essential for an individual neuron to be considered a member of a given cell type, there is no definitive classification of interneurons. Nevertheless, certain interneurons can be readily recognized by their unique morphological characteristics, or they can be more generally divided into subgroups on the basis of their biochemical characteristics, patterns of axonal arborization, or synaptic connections with pyramidal cells. 3. All interneurons have a more or less dense axonal arborization distributed near the cell body, mainly within the area occupied by their dendritic field. However, some interneurons may display, in addition, prominent long, horizontal or vertical axonal collaterals. [figure: see text] 4. Most interneurons form symmetrical synapses with both pyramidal cells and other interneurons, with the exception of chandelier cells, which only form synapses with the axon initial segment of pyramidal cells. Furthermore, interneurons are not only connected by chemical synapses (unidirectional connections), but they may also form electrical synapses through gap junctions (bidirectional) in a specific manner. 5. With the exception of chandelier cells, other types of interneurons include among their synaptic targets more than one type of postsynaptic element. But the degree of preference for these postsynaptic elements varies markedly between different types of interneurons. 6. The number of synapses made by a single axon originating from a given interneuron on another neuron is on the order of ten or less. Since, in general, cortical neurons receive many more interneuronal (symmetrical) synapses (on the order of a few hundred or thousand), a considerable convergence of various types of interneurons to pyramidal cells and interneurons appears to occur. 7. Most interneurons are GABAergic and also express a number of different neurotransmitters (or their synthesizing enzymes), neuropeptides and calcium-binding proteins. Thus, interneurons are, biochemically, widely heterogeneous. 8. Some of the morphologically identifiable neurons can be characterized by their particular biochemical characteristics, and some biochemically definable subgroups of interneurons display a particular morphology. However, different morphological types of GABAergic neurons may share one or several neurotransmitters, neuroactive substances and/or other molecular markers. Therefore, a great variety of subgroups of morphologically and biochemically identifiable neurons exist. 9. Some interneurons appear to be common to all species and, therefore, may be considered as basic elements of cortical circuits, whereas others may represent evolutionary specializations which are characteristic of particular mammalian subgroups and, thus, cannot be taken as essential, or general, features of cortical organization. 10. Given the complexity of cortical circuits and the areal and species differences, it is impossible to draw a "sufficiently" complete basic diagram of cortical microcircuitry that is valid for all cortical areas and species.
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Affiliation(s)
- Javier DeFelipe
- Instituto Cajal (CSIC), Avenida del Doctor Arce 37, 28002 Madrid, Spain.
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Abstract
New approaches to the study of ocular dominance development, a model system for the development of neural architecture, indicate that eye-specific columns in primary visual cortex emerge substantially before the onset of the critical period, during which neural connections can be altered by visual experience. The timing, speed and specificity of column emergence implicate molecular patterning mechanisms, along with patterns of neural activity, in the generation of this columnar architecture.
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Affiliation(s)
- Justin C Crowley
- Howard Hughes Medical Institute and Department of Neurobiology, Box 3209, Duke University Medical Center, Durham, North Carolina 27710, USA
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He Y, Hof PR, Janssen WG, Vissavajjhala P, Morrison JH. AMPA GluR2 subunit is differentially distributed on GABAergic neurons and pyramidal cells in the macaque monkey visual cortex. Brain Res 2001; 921:60-7. [PMID: 11720711 DOI: 10.1016/s0006-8993(01)03083-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The cellular and synaptic distribution of the AMPA receptor subunit GluR2 was analyzed in the monkey primary visual cortex (area V1), by immunocytochemistry and postembedding immunogold methods. GluR2 immunoreactivity was widely distributed in all of the layers of area V1. A quantitative double labeling analysis in layers II and III revealed that the vast majority of GABAergic interneurons in this area also contained GluR2. Postembedding immunogold analysis revealed that GluR2 immunoreactivity was present at asymmetric synapses on both GABAergic interneurons and pyramidal cells. A quantitative study indicated that the number of GluR2 immunogold particles at asymmetric synapses on pyramidal cells was significantly higher than that on GABAergic interneurons. These results from the primate neocortex are in agreement with and extend our previous studies on the rat hippocampus and amygdala. In view of the dominant role of the GluR2 subunit in regulating calcium flux through AMPA receptors, the differential synaptic distribution of GluR2 on different neuronal types might provide a mechanism for cell-specific response properties to glutamate as well as clues to selective neuronal vulnerability and cell death mediated by calcium-dependent excitotoxic mechanisms.
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Affiliation(s)
- Y He
- Kastor Neurobiology of Aging Laboratories and Fishberg Research Center for Neurobiology, Mount Sinai School of Medicine, New York, NY 10029, USA
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22
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Silver MA, Stryker MP. Distributions of synaptic vesicle proteins and GAD65 in deprived and nondeprived ocular dominance columns in layer IV of kitten primary visual cortex are unaffected by monocular deprivation. J Comp Neurol 2000; 422:652-64. [PMID: 10861531 PMCID: PMC2412910 DOI: 10.1002/1096-9861(20000710)422:4<652::aid-cne11>3.0.co;2-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Two days of monocular deprivation (MD) of kittens during a critical period of development is known to produce a loss of visual responses in the primary visual cortex to stimulation of the nondeprived eye, and 7 days of deprivation results in retraction of axon branches and loss of presynaptic sites from deprived-eye geniculocortical arbors. The rapid loss of responsiveness to deprived-eye visual stimulation could be due to a decrease in intracortical excitatory input to deprived-eye ocular dominance columns (ODCs) relative to nondeprived-eye columns. Alternatively, deprived-eye visual responses could be suppressed by an increase in intracortical inhibition in deprived columns relative to nondeprived columns. We tested these hypotheses in critical period kittens by labeling ODCs in layer IV of primary visual cortex with injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) into lamina A of the lateral geniculate nucleus (LGN). After either 2 or 7 days of MD, densities of intracortical excitatory presynaptic sites within deprived relative to nondeprived ODCs were estimated by measuring synaptic vesicle protein (SVP) immunoreactivity (IR). Because most of the synapses within layer IV of primary visual cortex are excitatory inputs from other cortical neurons, levels of SVP-IR provide an estimate of the amount of intracortical excitatory input. We also measured levels of immunoreactivity of the inhibitory presynaptic terminal marker glutamic acid decarboxylase (GAD)65 in deprived relative to nondeprived ODCs. Monocular deprivation (either 2 or 7 days) had no effect on the distributions of either SVP- or GAD65-IR in deprived and nondeprived columns. Therefore, the rapid loss of deprived-eye visual responsiveness following MD is due neither to a decrease in intracortical excitatory presynaptic sites nor to an increase in intracortical inhibitory presynaptic sites in layer IV of deprived-eye ODCs relative to nondeprived columns.
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Affiliation(s)
- M A Silver
- W.M. Keck Center for Integrative Neuroscience and Neuroscience Graduate Program, Department of Physiology, University of California, San Francisco, California 94143-0444, USA
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23
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Vargas C, Sousa A, Bittencourt F, Santos C, Pereira A, Bernardes R, Rocha-Miranda C, Volchan E. Cytochrome oxidase and NADPH-diaphorase on the afferent relay branch of the optokinetic reflex in the opossum. J Comp Neurol 1998. [DOI: 10.1002/(sici)1096-9861(19980824)398:2<206::aid-cne4>3.0.co;2-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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24
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Hendry SH, Calkins DJ. Neuronal chemistry and functional organization in the primate visual system. Trends Neurosci 1998; 21:344-9. [PMID: 9720602 DOI: 10.1016/s0166-2236(98)01245-4] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Beginning with the first step of visual processing and proceeding outward from that point, the neurons involved in different aspects of vision are distinct. Stated simply, neurons doing different things look different. They often display distinct morphological features and they usually express different molecules. In addition, neurons that perform a common function usually aggregate together to form recognizable layers or compartments that can be studied in isolation because they are neurochemically distinct. Here is found, then, a junction of two major domains in neuroscience research, as discovery of molecular diversity among neurons is exploited to study organization and function of the primate visual system.
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Affiliation(s)
- S H Hendry
- Dept of Neuroscience, Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, MD 21218, USA
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25
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Monocular core zones and binocular border strips in primate striate cortex revealed by the contrasting effects of enucleation, eyelid suture, and retinal laser lesions on cytochrome oxidase activity. J Neurosci 1998. [PMID: 9651225 DOI: 10.1523/jneurosci.18-14-05433.1998] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In primate striate cortex, geniculocortical afferents in layer IVc terminate in parallel stripes called ocular dominance columns. We propose that this segregation of ocular inputs generates a related but distinct columnar system of monocular core zones alternating with binocular border strips. Evidence for this functional parcellation was obtained by comparing the effects of enucleation, eyelid suture, and retinal laser lesions on cytochrome oxidase (CO) activity in eight macaques. Enucleation produced a high-contrast pattern of dark and light columns in layer IVc, corresponding precisely to the ocular dominance columns, whereas eyelid suture produced a low-contrast pattern of thin dark columns alternating with wide pale columns. [3H]Proline eye injection showed that the thin dark columns corresponded to the core zones of the open eye's ocular dominance columns. The wide pale columns resulted from loss of CO activity in the sutured eye's core zones and within both eyes' border strips. Loss of CO activity within both eyes' border strips suggested that these regions are binocular. To confirm our findings, we compared different CO patterns in the same cortex by making retinal laser lesions in four animals. They produced a CO pattern tantamount to "focal" enucleation, although contrast was low when laser damage was confined to the outer retina. CO levels in cortical scotomas remained severely depressed for months after retinal lesions, even when the other eye was enucleated. This observation provided little anatomical support for the notion of topographic plasticity after visual deafferentation. In a single human subject with macular degeneration, CO revealed a low-contrast pattern of ocular dominance columns, resembling the pattern in monkeys with laser-induced photoreceptor damage.
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Morrison BM, Janssen WG, Gordon JW, Morrison JH. Light and electron microscopic distribution of the AMPA receptor subunit, GluR2, in the spinal cord of control and G86R mutant superoxide dismutase transgenic mice. J Comp Neurol 1998. [DOI: 10.1002/(sici)1096-9861(19980615)395:4<523::aid-cne8>3.0.co;2-3] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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27
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Abstract
The progressive frontalization of both eyes in mammals causes overlap of the left and right visual fields, having as a consequence a region of binocular field with single vision and stereopsis. The horizontal separation of the eyes makes the retinal images of the objects lying in this binocular field have slight horizontal and vertical differences, termed disparities. Horizontal disparities are the main cue for stereopsis. In the past decades numerous physiological studies made on monkeys, which have in many aspects a similar visual system to humans, showed that a population of visual cells are capable of encoding the amplitude and sign of horizontal disparity. Such disparity detectors were found in cortical visual areas V1, V2, V3, V3A, VP, MT (V5) and MST of monkeys and in the superior colliculus of the cat and opossum. According to their disparity tuning function, these cells were first grouped into tuned excitatory, tuned inhibitory, near and far sub-groups. Subsequent studies added two more categories, tuned near and tuned far cells. Asymmetries between left and right receptive field position, on and off regions, and intra-receptive field wiring are believed to be the neural mechanisms of disparity detection. Because horizontal disparity alone is insufficient to compute reliable stereopsis, additional information about fixation distance and angle of gaze is required. Thus, while there is unequivocal evidence of cells capable of detecting horizontal disparities, it is not known how horizontal disparity is calibrated. Sensitivity to vertical disparity and information about the vergence angle or eye position may be the source of this additional information.
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Affiliation(s)
- F Gonzalez
- Department of Physiology, School of Medicine, University of Santiago and Complejo Hospitalario Universitario de Santiago, Santiago de Compostela, Spain.
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28
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Ding Y, Casagrande VA. Synaptic and neurochemical characterization of parallel pathways to the cytochrome oxidase blobs of primate visual cortex. J Comp Neurol 1998; 391:429-43. [PMID: 9486823 DOI: 10.1002/(sici)1096-9861(19980222)391:4<429::aid-cne2>3.0.co;2-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The primary visual cortex (V1) of primates is unique in that it is both the recipient of visual signals, arriving via parallel pathways (magnocellular [M], parvocellular [P], and koniocellular [K]) from the thalamus, and the source of several output streams to higher order visual areas. Within this scheme, output compartments of V1, such as the cytochrome oxidase (CO) rich blobs in cortical layer III, synthesize new output pathways appropriate for the next steps in visual analysis. Our chief aim in this study was to examine and compare the synaptic arrangements and neurochemistry of elements involving direct lateral geniculate nucleus (LGN) input from the K pathway with those involving indirect LGN input from the M and P pathways arriving from cortical layer IV. Geniculocortical K axons were labeled via iontophoretic injections of wheat germ agglutinin-horseradish peroxidase into the LGN and intracortical layer IV axons (indirect P and M pathways to the CO-blobs) were labeled by iontophoretic injections of Phaseolus vulgaris leucoagglutinin into layer IV. The neurochemical content of both pre- and postsynaptic profiles was identified by postembedding immunocytochemistry for gamma-amino butyric acid (GABA) and glutamate. Sizes of pre- and postsynaptic elements were quantified by using an image analysis system, BioQuant IV. Our chief finding is that K LGN axons and layer IV axons (indirect input from M and P pathways) exhibit different synaptic relationships to CO blob cells. Specifically, our results show that within the CO blobs: 1) all K cell axons contain glutamate, and the vast majority of layer IV axons contain glutamate with only 5% containing GABA; 2) K axons terminate mainly on dendritic spines of glutamatergic cells, while layer IV axons terminate mainly on dendritic shafts of glutamatergic cells; 3) K axons have larger boutons and contact larger postsynaptic dendrites, which suggests that they synapse closer to the cell body within the CO blobs than do layer IV axons. Taken together, these results suggest that each input pathway to the CO blobs uses a different strategy to contribute to the processing of visual information within these compartments.
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Affiliation(s)
- Y Ding
- Department of Cell Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
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29
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Morrison J, Hof P, Huntley G. Neurochemical organization of the primate visual cortex. HANDBOOK OF CHEMICAL NEUROANATOMY 1998. [DOI: 10.1016/s0924-8196(98)80004-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Abstract
In the primary visual cortex, neurons with similar response properties are arranged in columns. As more and more columnar systems are discovered it becomes increasingly important to establish the rules that govern the geometric relationships between different columns. As a first step to examine this issue we investigated the spatial relationships between the orientation, ocular dominance, and spatial frequency domains in cat area 17. Using optical imaging of intrinsic signals we obtained high resolution maps for each of these stimulus features from the same cortical regions. We found clear relationships between orientation and ocular dominance columns: many iso-orientation lines intersected the borders between ocular dominance borders at right angles, and orientation singularities were concentrated in the center regions of the ocular dominance columns. Similar, albeit weaker geometric relationships were observed between the orientation and spatial frequency domains. The ocular dominance and spatial frequency maps were also found to be spatially related: there was a tendency for the low spatial frequency domains to avoid the border regions of the ocular dominance columns. This specific arrangement of the different columnar systems might ensure that all possible combinations of stimulus features are represented at least once in any given region of the visual cortex, thus avoiding the occurrence of functional blind spots for a particular stimulus attribute in the visual field.
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31
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Yan XX, Cariaga WA, Ribak CE. Immunoreactivity for GABA plasma membrane transporter, GAT-1, in the developing rat cerebral cortex: transient presence in the somata of neocortical and hippocampal neurons. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1997; 99:1-19. [PMID: 9088561 DOI: 10.1016/s0165-3806(96)00192-7] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The immunoreactivity for a gamma-aminobutyric acid (GABA) membrane transporter, GAT-1, was examined in the neocortex and hippocampal formation of developing rats from the day of birth (postnatal day 0, P0) to the adult stage. The immunolabeling was mainly localized to the neuropil, but was also in a select population of cell bodies during a limited time period. Layers I and VIb of neocortex exhibited relatively high reactivity at birth, but diminished their staining with development. In contrast, GAT-1 immunoreactivity in the neuropil in the cortical plate and its derivatives was light at birth, but increased rapidly during the first 2-3 postnatal weeks in an inside-out order. An adult pattern with immunoreactive puncta more densely distributed in layers II to IV than the deeper layers was completed by P30-45. The neuropil reactivity in the hippocampal formation at P0 was greater than that in the neocortex, densely localized in a supragranular band, and less densely in the hilus of the dentate gyrus and the strata radiatum and oriens of the hippocampus. This pattern was basically maintained at later stages except that the immunoreactivity in the supragranular band diminished, whereas that in the subgranular zone was enhanced. A population of cell bodies morphologically characteristic of cortical and hippocampal interneurons was substantially immunolabeled for GAT-1 by P5 and remained until P30. At the electron microscopic level, GAT-1 immunoreactivity was localized mainly to axon terminals and astrocytes between P5 and P45, but was also found in neuronal somata and their dendrites between P5 and P30. Our data show a differential postnatal development of GAT-1 immunoreactivity in the rat cerebral cortex, including a transient presence of immunoreactivity in the somata of a subpopulation of cerebral interneurons and a developmental downregulation of GAT-1 expression in the earliest generated cortical elements (layers 1 and VIb). The findings in the present study suggest that GAT-1 expression in the neocortex and hippocampus may relate to the functional maturation of the GABAergic system.
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Affiliation(s)
- X X Yan
- Department of Anatomy and Neurobiology, University of California at Irvine 92697, USA.
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Kim CB, Pier LP, Spear PD. Effects of aging on numbers and sizes of neurons in histochemically defined subregions of monkey striate cortex. Anat Rec (Hoboken) 1997; 247:119-28. [PMID: 8986309 DOI: 10.1002/(sici)1097-0185(199701)247:1<119::aid-ar14>3.0.co;2-s] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND In addition to its horizontal layers, primate striate cortex has a vertical modular organization. Among the vertical modules are histochemically defined areas of high and low cytochrome oxidase labeling in the supragranular layers, referred to, respectively, as blobs and interblobs. Cytochrome c oxidase (CO) blobs and interblobs differ in their inputs from the magnocellular and parvocellular visual pathways, their physiological properties, and many aspects of their neurochemistry. The present study investigated whether aging differentially affects neuron numbers or sizes in the supragranular blobs or interblobs. METHODS The right hemisphere from three young adult (5.2-12.4 years) and four old (24.0-26.7 years) rhesus monkeys was used. Tangential sections through the central visual-field representation were stained for CO and counterstained with cresyl violet. Montages were constructed through cortical layers 2 and 3, and neuron counts and size measurements were made in blob and interblob regions using stereological procedures that yield unbiased estimates. Blob density also was calculated. RESULTS CO blob density was 3.76/mm2 in young adults and 3.95/mm2 in old animals, a difference that was not statistically significant. Neuron soma sizes also did not differ significantly between young adult and old animals or between blob and interblob regions. In addition, neuron density was not significantly different between young adult and old animals. However, independent of age, neuron density was significantly higher in the center of interblobs (394,058 cells/mm3) than in the center of blobs (333,638/mm3). CONCLUSIONS Our results and those of previous studies (Vincent et al. 1989. Anat. Rec. 223:329-341; Peters and Sethares. 1993. Anat. Rec. 236:721-729) suggest that aging has little or no effect on the densities or sizes of the different functional or morphological types of neurons that exist in the different cortical layers or in the different vertical modules marked by CO blobs and interblobs. These findings are consistent with the results of our previous anatomical and physiological studies of the rhesus monkey retina and lateral geniculate nucleus. These results suggest that the retinogenic-ulostriate pathways are relatively unaffected by aging in the rhesus monkey.
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Affiliation(s)
- C B Kim
- Department of Psychology, University of Wisconsin-Madison, USA
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33
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Abstract
The squirrel monkey is the only primate reported to lack ocular dominance columns. Nothing anomalous about the visual capacity of squirrel monkeys has been found to explain their missing columns, leading to the suggestion that ocular dominance columns might be "an epiphenomenon, not serving any purpose" (Livingstone et al., 1995). Puzzled by the apparent lack of ocular dominance columns in squirrel monkeys, we made eye injections with transneuronal tracers in four normal squirrel monkeys. An irregular mosaic of columns, averaging 225 microns in width, was found throughout striate cortex. They were double-labeled by placing wheat germ agglutinin-horseradish peroxidase into the left eye and [3H]proline into the right eye. The tracers labeled opposite sets of interdigitating columns, proving they represent ocular dominance columns. The columns were much clearer in layer IVc alpha (magno-receiving) than IVc beta (parvo-receiving). In the lateral geniculate body, the parvo laminae showed extensive mixing of ocular inputs, suggesting that increased label spillover contributes to the blurred columns in layer IVc beta. The cytochrome oxidase (CO) patches were organized into distinct rows, but they bore no consistent relationship to the ocular dominance columns. These experiments indicate that ocular dominance columns are less well segregated in squirrel monkeys than macaques, but they are present. This fact is pertinent to a recent study reporting that ocular dominance columns are absent in normal squirrel monkeys, but induced to form by strabismus (Livingstone, 1996).
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34
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Abstract
This paper explores the possibility that the formation of color blobs in primate striate cortex can be partly explained through the process of activity-based self-organization. We present a simulation of a highly simplified model of visual processing along the parvocellular pathway, that combines precortical color processing, excitatory and inhibitory cortical interactions, and Hebbian learning. The model self-organizes in response to natural color images and develops islands of unoriented, color-selective cells within a sea of contrast-sensitive, orientation-selective cells. By way of understanding this topography, a principal component analysis of the color inputs presented to the network reveals that the optimal linear coding of these inputs keeps color information and contrast information separate.
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Affiliation(s)
- H G Barrow
- School of Cognitive and Computing Sciences, University of Sussex, Falmer, Brighton, UK
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35
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Mrzljak L, Levey AI, Rakic P. Selective expression of m2 muscarinic receptor in the parvocellular channel of the primate visual cortex. Proc Natl Acad Sci U S A 1996; 93:7337-40. [PMID: 8692994 PMCID: PMC38985 DOI: 10.1073/pnas.93.14.7337] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Visual information in primates is relayed from the dorsal lateral geniculate nucleus to the cerebral cortex by three parallel neuronal channels designated the parvocellular, magnocellular, and interlaminar pathways. Here we report that m2 muscarinic acetylcholine receptor in the macaque monkey visual cortex is selectively associated with synaptic circuits subserving the function of only one of these channels. The m2 receptor protein is enriched both in layer IV axons originating from parvocellular layers of the dorsal lateral geniculate nucleus and in cytochrome oxidase poor interblob compartments in layers II and III, which are linked with the parvocellular pathway. In these compartments, m2 receptors appear to be heteroreceptors, i.e., they are associated predominantly with asymmetric, noncholinergic synapses, suggesting a selective role in the modulation of excitatory neurotransmission through the parvocellular visual channel.
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Affiliation(s)
- L Mrzljak
- Section of Neurobiology, Yale University School of Medicine, New Haven, CT 06511, USA
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Nie F, Wong-Riley MT. Differential glutamatergic innervation in cytochrome oxidase-rich and -poor regions of the macaque striate cortex: quantitative EM analysis of neurons and neuropil. J Comp Neurol 1996; 369:571-90. [PMID: 8761929 DOI: 10.1002/(sici)1096-9861(19960610)369:4<571::aid-cne7>3.0.co;2-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase (CO)-rich puffs and CO-poor interpuffs in its supragranular layers. However, the neurochemical basis for their differences in metabolic activity and physiological properties is not well understood. The goals of the present study were to determine whether CO levels in postsynaptic neuronal compartments were correlated with the proportion of excitatory glutamate-immunoreactive (Glu-IR) synapses they received and if Glu-IR terminals and synapses in puffs differed from those in interpuffs. By combining CO histochemistry and postembedding Glu immunocytochemistry on the same ultrathin sections, the simultaneous distribution of the two markers in individual neuronal profiles was quantitatively analyzed. As a comparison, adjacent sections were identically processed for the double labeling of CO and GABA, an inhibitory neurotransmitter. In both puffs and interpuffs, most axon terminals forming asymmetric synapses (84%)--but not symmetric ones, which were GABA-IR--were intensely immunoreactive for Glu. GABA-IR neurons received mainly Glu-IR synapses on their cell bodies, and they had three times as many mitochondria darkly reactive for CO than Glu-rich neurons, which received only GABA-IR axosomatic synapses. In puffs, GABA-IR neurons received a significantly higher ratio of Glu-IR to GABA-IR axosomatic synapses and contained about twice as many darkly CO-reactive mitochondria than those in interpuffs. There were significantly more Glu-IR synapses and a higher ratio of Glu- to GABA-IR synapses in the neuropil of puffs than of interpuffs. Moreover, Glu-IR axon terminals in puffs contained approximately three times more darkly CO-reactive mitochondria than those in interpuffs, suggesting that the former may be synaptically more active. Thus, the present results are consistent with our hypothesis that the levels of oxidative metabolism in postsynaptic neurons and neuropil are positively correlated with the proportion of excitatory synapses they receive. Our findings also suggest that excitatory synaptic activity may be more prominent in puffs than in interpuffs, and that the neurochemical and synaptic differences may constitute one of the bases for physiological and functional diversities between the two regions.
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Affiliation(s)
- F Nie
- Department of Cellular Biology and Anatomy, Medical College of Wisconsin, Milwaukee, 53226, USA
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37
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Abstract
During a critical period in early life, physiological studies reveal that either prolonged or brief periods of monocular occlusion induce similar plastic changes in the primary visual cortex (area 17) of the cat, leading to a nearly complete loss of visual responses from the deprived eye (Hubel and Wiesel [1970], J. Physiol. (London) 160: 106-154). However, the recovery of function is markedly different in the two conditions, being complete and thorough only after a brief period of monocular occlusion (Movshon [1976] J. Physiol. (London) 261: 125-174). In search for anatomical correlates that distinguish between these two experimental conditions, we compared the geniculocortical connectivity in normal kittens with that following brief (4 days and 6-7 days) or prolonged (> 5 weeks) periods of occlusion of vision in one eye. Transneuronal labeling of the geniculocortical pathway revealed changes in both cases, and single afferent arbors reconstructed in serial sections were similarly shrunken after short or long periods of deprivation. However, a significant expansion of the geniculocortical afferents serving the nondeprived eye was evident mainly after prolonged deprivation. These findings provide further evidence for rapid, activity-dependent remodeling of afferents during development.
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Affiliation(s)
- A Antonini
- W.M. Keck Foundation Center for Integrative Neuroscience, Department of Physiology, University of California San Francisco 94143-0444, USA
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38
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Yoshioka T, Dow BM. Color, orientation and cytochrome oxidase reactivity in areas V1, V2 and V4 of macaque monkey visual cortex. Behav Brain Res 1996; 76:71-88. [PMID: 8734044 DOI: 10.1016/0166-4328(95)00184-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Color and orientation processing in the macaque monkey first segregates into cytochrome oxidase (CO)-rich blobs and -poor interblobs of area V1, from where the two streams flow through areas V2 and V4. This parallel representation is believed to enhance processing speed by compartmentalizing tasks of similar kinds, though our knowledge of the mechanisms is still elementary. We have examined the interaction and separation of color and orientation processing in neurons (n = 569) of the macaque visual cortex (V1, V2, V4) on the basis of microelectrode recordings. In all three areas, neurons selective for midspectral (MS) colors (e.g., yellow, green) were also found to be more orientation selective than those preferring endspectral (ES) colors (e.g., blue, red). The majority of achromatic (AC) cells responsive to bright stimuli were also orientation selective. When locations of cells and penetration columns were correlated with cytochrome oxidase (CO) landmarks in V1 and V2, V1 interblob and V2 interstripe cells were found to be predominantly midspectral and oriented, while V1 blob and V2 thin stripe cells were found to be predominantly endspectral and non-oriented. Cells preferring dark colors were found to cluster in thick stripes in V2, and in columns in V4. Separate clustering of midspectral (MS) and endspectral (ES) systems in V4 was also noted. With the results shown in a companion paper (Behav. Brain Res., 76 (1996) 51-70), the present data indicate that the visual system appears to optimize color and spatial acuity by separating chromatic information into non-oriented endspectral and oriented midspectral components.
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Affiliation(s)
- T Yoshioka
- Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, MD 21218, USA.
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39
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Clément Y. Structural and pharmacological aspects of the GABAA receptor: involvement in behavioral pathogenesis. JOURNAL OF PHYSIOLOGY, PARIS 1996; 90:1-13. [PMID: 8803850 DOI: 10.1016/0928-4257(96)87164-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The gamma-aminobutyric acidA (GABAA) receptor is a complex hetero-oligomeric protein. It is composed of several subunits which assemble to form a functional chloride channel. The precise molecular organization of the receptor is as yet unknown. In the first part, we review recent literature dealing with the molecular and pharmacological aspects of the GABAA receptor, the second part will review some of the pathologies probably associated with gene defects and/or quantitative differential expression of transcripts encoding GABAA receptor subunits.
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Affiliation(s)
- Y Clément
- URA-CNRS 1957, Groupe Hospitalier Pitié-Salpêtrière, Paris, France
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40
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Yoshioka T, Hendry SH. Compartmental organization of layer IVA in human primary visual cortex. J Comp Neurol 1995; 359:213-20. [PMID: 7499525 DOI: 10.1002/cne.903590203] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Immunostaining for three neuronal proteins, nonphosphorylated neurofilament protein (with antibody SMI-32), calbindin, and parvalbumin, was used to examine the organization of layer IV in human primary visual cortex (area 17 or V1) specifically to determine whether, similar to the case in macaque V1, layer IVA is present and is divided into neurochemically distinct compartments. All three proteins are expressed by neurons that are unevenly distributed in layer IV of human V1; immunostaining for each protein includes a thin band corresponding to layer IVA of classic cytoarchitectonic studies. In this band, nonphosphorylated neurofilament protein immunoreactivity is present in relatively broad clusters of pyramidal cell somata and dendrites that appear as upwardly protruding parts of intense immunostaining in layer IVB, whereas immunoreactivity for calbindin and parvalbumin exists in somata of nonpyramidal neurons and in thin, dense clusters of punctate profiles. In tangential sections through layer IVA, the three proteins are seen in distinct compartments. Calbindin- and parvalbumin-immunostained neurons make up a thinly walled honeycomb or lattice, whereas neurons immunostained for nonphosphorylated neurofilament protein occupy the central lacunae. Direct comparison shows that neurons immunostained for calbindin occupy regions in layer IVA complementary to those immunostained for nonphosphorylated neurofilament protein. These data demonstrate a basic similarity in the organization of layer IV in macaques and humans. Layer IVA specifically is organized into complementary and neurochemically distinct compartments, including what appears to be a geniculocortically innervated and parvicellular-driven lattice and the interstitial lacunae formed by the periodic, upward protrusion of magnocellular-dominated layer IVB neurons.
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Affiliation(s)
- T Yoshioka
- Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, Maryland 21218, USA
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41
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Deyoe EA, Trusk TC, Wong-Riley MT. Activity correlates of cytochrome oxidase-defined compartments in granular and supragranular layers of primary visual cortex of the macaque monkey. Vis Neurosci 1995; 12:629-39. [PMID: 8527365 DOI: 10.1017/s0952523800008920] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
To determine if changes in metabolic capacity revealed by cytochrome oxidase (CO) histochemistry are related to sustained changes in energy-utilizing neuronal activity, we assayed CO levels and recorded multiunit firing rates along nearly tangential penetrations of V1 in seven adult macaque monkeys before and after single, monocular injections of TTX. Within as little as 14 h, TTX blockade began to reduce CO staining in zones of layer 4C that received dominant input from the injected eye. Since simple monocular occlusion has only minor effects on cortical CO levels (Trusk et al., 1990), the changes in activity that were specifically associated with CO depletion were isolated by comparing spike rates during monocular TTX blockade and during monocular occlusion. Five second samples of multiunit spike rate were obtained after 2-min adaptation to each of four adapting fields: black, gray, white, and textured. Results were similar for these four conditions. In layer 4C, ocular dominance zones with input from the TTX eye had ongoing spike rates that were 48% of the rates in zones with input from a normal but occluded eye. In six animals, it was possible to record activity at a single site before, during, and after the onset of TTX blockade. Background activity at these interpuff sites decreased as much as 3-fold in less than 1 h but stabilized within 3-4 h to an average of 53% of pre-TTX rates. These data support the interpretation that energy utilization linked to sustained spike rates partially regulates CO levels under normal conditions, at least in layer 4. Furthermore, changes in neuronal activity induced by retinal TTX preceded the detectable reduction in CO activity in V1 suggesting that the adjustment of CO levels was in response to the altered activity.
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Affiliation(s)
- E A Deyoe
- Department of Cellular Biology and Anatomy, Medical Collegy of Wisconsin, Milwaukee 53226, USA
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42
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Edwards DP, Purpura KP, Kaplan E. Contrast sensitivity and spatial frequency response of primate cortical neurons in and around the cytochrome oxidase blobs. Vision Res 1995; 35:1501-23. [PMID: 7667910 DOI: 10.1016/0042-6989(94)00253-i] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The striate cortex of macaque monkeys contains an array of patches which stain heavily for the enzyme cytochrome oxidase (CO blobs). Cells inside and outside these blobs are often described as belonging to two distinct populations or streams. In order to better understand the function of the CO blobs, we measured the contrast sensitivity and spatial frequency response of single neurons in and around the CO blobs. Density profiles of each blob were assessed using a new quantitative method, and correlations of local CO density with the physiology were noted. We found that the CO density dropped off gradually with distance from blob centers: in a typical blob the CO density dropped from 75% to 25% over 100 microns. Recordings were confined to cortical layers 2/3. Most neurons in these layers have poor contrast sensitivity, similar to that of the parvocellular neurons in the lateral geniculate nucleus. However, in a small proportion of layers 2/3 neurons we found higher contrast sensitivity, similar to that of the magnocellular neurons. These neurons were found to cluster near blob centers. This finding is consistent with (indirect) parvocellular input spread uniformly throughout layers 2/3, and (indirect) magnocellular input focused on CO blobs. We also measured spatial tuning curves for both single units and multiple unit activity. In agreement with other workers we found that the optimal spatial frequencies of cells near blob centers were low (median 2.8 c/deg), while the optimal frequencies of cells in the interblob regions were spread over a wide range of spatial frequencies. The high cut-off spatial frequency of multi-unit activity increased with distance from blob centers. We found no correlation between spatial bandwidth and distance from blob centers. All measured physiological properties varied gradually with distance from CO blob centers. This suggests that the view of blob cells subserving visual functions which are entirely distinct from non-blob cells may have to be reevaluated.
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Affiliation(s)
- D P Edwards
- Laboratory of Biophysics, Rockefeller University, New York, NY 10021, USA
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43
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Nie F, Wong-Riley MT. Double labeling of GABA and cytochrome oxidase in the macaque visual cortex: quantitative EM analysis. J Comp Neurol 1995; 356:115-31. [PMID: 7629306 DOI: 10.1002/cne.903560108] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In the primate striate cortex, cytochrome oxidase (CO)-rich puffs differ from CO-poor interpuffs in their metabolic levels and physiological properties. The neurochemical basis for their metabolic and physiological differences is not well understood. The goal of the present study was to examine the relationship between the distribution of gamma aminobutyric acid (GABA)/non-GABA synapses and CO levels in postsynaptic neuronal profiles and to determine whether or not a difference existed between puffs and interpuffs. By combining CO histochemistry and postembedding GABA immunocytochemistry on the same ultrathin sections, the simultaneous distribution of the two markers in individual neuronal profiles was quantitatively analyzed. In both puffs and interpuffs, GABA-immunoreactive (GABA-IR) neurons were the only cell type that received both non-GABA-IR (presumed excitatory) and GABA-IR (presumed inhibitory) axosomatic synapses, and they had three times as many mitochondria darkly reactive for CO than non-GABA-IR neurons, which received only GABA-IR axosomatic synapses. GABA-IR neurons and terminals in puffs had a larger mean size, about twice as many darkly reactive mitochondria, and a higher ratio of non-GABA-IR to GABA-IR axosomatic synapses than those in interpuffs (2.3:1 vs. 1.6:1; P < 0.01). There were significantly more synapses of both non-GABA-IR and GABA-IR types in the neuropil of puffs than of interpuffs; however, the ratio of non-GABA-IR to GABA-IR synapses was significantly higher in puffs (2.86:1) than in interpuffs (2.08:1; P < 0.01). Our results are consistent with the hypothesis that the level of oxidative metabolism in postsynaptic neurons and neuronal processes is tightly governed by the strength and proportion of excitatory over inhibitory synapses. Thus, the present results suggest that (1) GABA-IR neurons in the macaque striate cortex have a higher level of oxidative metabolism than non-GABA ones because their somata receive direct excitatory synapses and their terminals are more tonically active; (2) the higher proportion of presumed excitatory synapses in puffs imposes a greater energy demand there than in interpuffs; and (3) excitatory synaptic activity may be more prominent in puffs than in interpuffs because puffs receive a greater proportion of excitatory synapses from multiple sources including the lateral geniculate nucleus, which is not known to project to the interpuffs.
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Affiliation(s)
- F Nie
- Department of Cellular Biology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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44
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Götz M, Williams BP, Bolz J, Price J. The specification of neuronal fate: a common precursor for neurotransmitter subtypes in the rat cerebral cortex in vitro. Eur J Neurosci 1995; 7:889-98. [PMID: 7613625 DOI: 10.1111/j.1460-9568.1995.tb01076.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Neurotransmitter choice is a crucial step in neural development. In the cerebral cortex, pyramidal neurons use the excitatory neurotransmitter glutamate, whereas non-pyramidal cells use the inhibitory neurotransmitter GABA. We are interested in how these two neuronal types are generated. We labelled precursor cells from embryonic rat cerebral cortex with a retroviral vector in dissociated cell cultures, and examined the neurotransmitter phenotype of their progeny immunohistochemically after 2 weeks in vitro. We discovered, first, that precursor cells in culture generate glutamatergic and GABAergic neurons in proportions similar to those in vivo. Second, we found that neuronal precursor cells gave rise to both GABAergic and glutamatergic neurons. These results suggest that neuronal precursor cells in the cerebral cortex have the potential to generate both neuronal subtypes. Moreover, these data are consistent with a stochastic model of neurotransmitter specification.
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Affiliation(s)
- M Götz
- National Institute for Medical Research, London, UK
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45
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Abstract
The mammalian neocortex is composed of functional areas that are specified to process particular aspects of information. How is this specification achieved during development? Since cells migrate to their final positions in the developing nervous system, a central issue is the relation between cellular migration and positional information. This review combines evidence for early positional specification in the developing cortex with evidence for cellular dispersion during migration. A model is suggested whereby stable cues provide positional information and minorities of 'displaced' cells are respecified accordingly. Comparison with other parts of the CNS reveals that cellular dispersal is ubiquitous and has to be included in any mechanism relaying positional specification. Ontogenetic and phylogenetic considerations suggest that radial glial cells might provide the positional information in the developing nervous system.
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Affiliation(s)
- M Götz
- SmithKline Beecham, Harlow, Essex, England, UK
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46
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47
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Wong-Riley MT, Trusk TC, Kaboord W, Huang Z. Effect of retinal impulse blockage on cytochrome oxidase-poor interpuffs in the macaque striate cortex: quantitative EM analysis of neurons. JOURNAL OF NEUROCYTOLOGY 1994; 23:533-53. [PMID: 7815086 DOI: 10.1007/bf01262055] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase-rich puffs in its supragranular layers. Neurons in puffs have been classified as type A, B, and C in ascending order of cytochrome oxidase content, with type C cells being the most vulnerable to retinal impulse blockade. The present study aimed at analysing cytochrome oxidase-poor interpuffs with reference to their metabolic cell types and the effect of intraretinal tetrodotoxin treatment. The same three metabolic types were found in interpuffs, except that type B and C neurons were smaller and less cytochrome oxidase-reactive in interpuffs than in puffs. Type A neurons had small perikarya, low levels of cytochrome oxidase, and received exclusively symmetric axosomatic synapses. The largest neurons were pyramidal, type B cells with moderate cytochrome oxidase activity and were also contacted exclusively by symmetric axosomatic synapses. Type C cells medium-sized with a rich supply of large, darkly reactive mitochondria and possessed all the characteristics of GABAergic neurons. They were the only cell type that received both symmetric and asymmetric axosomatic synapses. Two weeks of monocular tetrodotoxin blockade in adult monkeys caused all three major cell types in deprived interpuffs to suffer a significant downward shift in the size and cytochrome oxidase reactivity of their mitochondria, but the effects were more severe in type B and C neurons. In nondeprived interpuffs, all three cell types gained both in size and absolute number of mitochondria, and type A cells also had an elevated level of cytochrome oxidase, indicating that they might be functioning at a competitive advantage over cells in deprived columns. However, type B and C neurons showed a net loss of darkly reactive mitochondria, indicating that these cells became less active. Thus, mature interpuff neurons remained vulnerable to retinal impulse blockade and the metabolic capacity of these cells remains tightly regulated by neuronal activity.
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Affiliation(s)
- M T Wong-Riley
- Department of Cellular Biology and Anatomy, Medical College of Wisconsin, Milwaukee, 53226
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48
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Yamada K, Goto S, Oyama T, Inoue N, Nagahiro S, Ushio Y. Elevated immunoreactivity for glutamic acid decarboxylase in the rat cerebral cortex following transient middle cerebral artery occlusion. Acta Neuropathol 1994; 88:55-9. [PMID: 7941972 DOI: 10.1007/bf00294359] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We investigated the expression of glutamic acid decarboxylase (molecular weight 67,000; GAD67) immunohistochemically in the rat cerebral cortex following transient middle cerebral artery occlusion (MCAO) capable of producing slowly progressive neuronal damage. An increase in GAD67 immunoreactivity was observed in the cerebral cortex ipsilateral to the ischemic insult, most prominent in lamina IV, 3 to 14 days after MCAO. At this stage, light microscopy showed GAD67-positive puncta to be larger and more strongly immunoreactive in the ipsilateral cortex than those in the contralateral side. The elevated expression of GAD67 in the insulted cortex may reflect part of the adaptive functional changes in GABA transmission with slowly progressive cortical ischemic damage.
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Affiliation(s)
- K Yamada
- Department of Neurosurgery, Kumamoto University Medical School, Japan
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49
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Prieto JJ, Peterson BA, Winer JA. Laminar distribution and neuronal targets of GABAergic axon terminals in cat primary auditory cortex (AI). J Comp Neurol 1994; 344:383-402. [PMID: 8063959 DOI: 10.1002/cne.903440305] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The form, density, and neuronal targets of presumptive axon terminals (puncta) that were immunoreactive for gamma-aminobutyric acid (GABA) or its synthesizing enzyme, glutamic acid decarboxylase (GAD), were studied in cat primary auditory cortex (AI) in the light microscope. High-resolution, plastic-embedded material and frozen sections were used. The chief results were: 1) There was a three-tiered numerical distribution of puncta, with the highest density in layer Ia, an intermediate number in layers Ib-IVb, and the lowest concentration in layers V and VI, respectively. 2) Each layer had a particular arrangement: layer I puncta were fine and granular (less than 1 micron in diameter), endings in layers II-IV were coarser and more globular (larger than 1 micron), and layer V and VI puncta were mixed in size and predominantly small. 3) The form and density of puncta in every layer were distinctive. 4) Immunonegative neurons received, in general, many more axosomatic puncta than immunopositive cells, with the exception of the large multipolar (presumptive basket) cells, which invariably had many puncta in layers II-VI. 5) The number of puncta on the perikarya of GABAergic neurons was sometimes related to the number of puncta in the layer, and in other instances it was independent of the layer. Thus, while layer V had a proportion of GABAergic neurons similar to layer IV, it had only a fraction of the number of puncta; perhaps the intrinsic projections of supragranular GABAergic cells are directed toward layer IV, as those of infragranular GABAergic neurons may be. Since puncta are believed to be the light microscopic correlate of synaptic terminals, they can suggest how inhibitory circuits are organized. Even within an area, the laminar puncta patterns may reflect different inhibitory arrangements. Thus, in layer I the fine, granular endings could contact preferentially the distal dendrites of pyramidal cells in deeper layers. The remoteness of such terminals from the spike initiation zone contrasts with the many puncta on all pyramidal cell perikarya and the large globular endings on basket cell somata. Basket cells might receive feed-forward disinhibition, pyramidal cells feed-forward inhibition, and GABAergic non-basket cells would be the target of only sparse inhibitory axosomatic input. Such arrangements imply that the actions of GABA on AI neurons are neither singular nor simple and that the architectonic locus, laminar position, and morphological identity of a particular neuron must be integrated for a more refined view of its role in cortical circuitry.
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Affiliation(s)
- J J Prieto
- Department of Molecular and Cell Biology, University of California, Berkeley 94720-2097
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50
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Hendrickson AE, Tillakaratne NJ, Mehra RD, Esclapez M, Erickson A, Vician L, Tobin AJ. Differential localization of two glutamic acid decarboxylases (GAD65 and GAD67) in adult monkey visual cortex. J Comp Neurol 1994; 343:566-81. [PMID: 8034788 DOI: 10.1002/cne.903430407] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Adult monkey primary visual cortex contains a diverse population of stellate neurons that utilize the neurotransmitter gamma aminobutyric acid (GABA). Two glutamic acid decarboxylase (GAD) enzymes that synthesize GABA, GAD65 and GAD67, were localized within these stellate neurons by in situ hybridization of 35S or digoxigenin (DIG) labeled riboprobes. Double labels were done by using 35S GAD67 riboprobe and GABA immunocytochemistry on the same section to verify that the neuronal population identified by immunocytochemistry was the same one studied in the in situ hybridization experiments. We find that GAD65 mRNA and GAD67 mRNA are widely distributed in the cortex, with four bands of heavily labeled neurons in upper layer 2, lower 3, 4C, and 6. GAD67 labeled neurons were more obvious in layer 4C beta, while GAD65 containing neurons were common in layer 1 and white matter. Northern blots and in situ hybridization on sections with both 35S and DIG riboprobes indicate that cortical neurons typically contain more GAD67 mRNA. Cell counts show that 18% of all cortical neurons contain GAD67 mRNA and 13% contain GAD65 mRNA, suggesting that a small population of GABA neurons might lack GAD65. Cell bodies that contain high amounts of GAD65 mRNA are prominent in layers deep 3, 4B, 4C alpha, and 6 and often are the largest cells in their respective layers. Double labels demonstrate that 96% of all GABA+ neurons contain GAD67 mRNA. Neurons heavily labeled for GABA tend to have smaller cell bodies and contain less GAD67 mRNA, while lightly labeled GABA neurons are larger and contain more GAD67 mRNA. These data indicate that most GABA neurons in monkey striate cortex contain both GAD enzymes. Although the differences in GABA content, cell size, laminar distribution, and GAD mRNA concentration suggest different requirements for GAD67 and GAD65 in cortical circuits, our experiments do not reveal what different roles these two enzymes subserve within GABAergic stellate neurons.
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Affiliation(s)
- A E Hendrickson
- Department of Biological Structure, University of Washington, Seattle 98195
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