Neurons with intensely negatively charged extracellular matrix in the human visual cortex

Cigarette Smoke Particle-Induced Lung Injury and Iron Homeostasis

It is proposed that the mechanistic basis for non-neoplastic lung injury with cigarette smoking is a disruption of iron homeostasis in cells after exposure to cigarette smoke particle (CSP). Following the complexation and sequestration of intracellular iron by CSP, the host response (eg, inflammation, mucus production, and fibrosis) attempts to reverse a functional metal deficiency. Clinical manifestations of this response can present as respiratory bronchiolitis, desquamative interstitial pneumonitis, pulmonary Langerhans’ cell histiocytosis, asthma, pulmonary hypertension, chronic bronchitis, and pulmonary fibrosis. If the response is unsuccessful, the functional deficiency of iron progresses to irreversible cell death evident in emphysema and bronchiectasis. The subsequent clinical and pathological presentation is a continuum of lung injuries, which overlap and coexist with one another. Designating these non-neoplastic lung injuries after smoking as distinct disease processes fails to recognize shared relationships to each other and ultimately to CSP, as well as the common mechanistic pathway (ie, disruption of iron homeostasis).

Perineuronal nets and schizophrenia: the importance of neuronal coatings

Schizophrenia is a complex brain disorder associated with deficits in synaptic connectivity. The insidious onset of this illness during late adolescence and early adulthood has been reported to be dependent on several key processes of brain development including synaptic refinement, myelination and the physiological maturation of inhibitory neural networks. Interestingly, these events coincide with the appearance of perineuronal nets (PNNs), reticular structures composed of components of the extracellular matrix that coat a variety of cells in the mammalian brain. Until recently, the functions of the PNN had remained enigmatic, but are now considered to be important in development of the central nervous system, neuronal protection and synaptic plasticity, all elements which have been associated with schizophrenia. Here, we review the emerging evidence linking PNNs to schizophrenia. Future studies aimed at further elucidating the functions of PNNs will provide new insights into the pathophysiology of schizophrenia leading to the identification of novel therapeutic targets with the potential to restore normal synaptic integrity in the brain of patients afflicted by this illness.

Cyto-, myelo- and chemoarchitecture of the prefrontal cortex of the Cebus monkey

Background

According to several lines of evidence, the great expansion observed in the primate prefrontal cortex (PfC) was accompanied by the emergence of new cortical areas during phylogenetic development. As a consequence, the structural heterogeneity noted in this region of the primate frontal lobe has been associated with diverse behavioral and cognitive functions described in human and non-human primates. A substantial part of this evidence was obtained using Old World monkeys as experimental model; while the PfC of New World monkeys has been poorly studied.

In this study, the architecture of the PfC in five capuchin monkeys (Cebus apella) was analyzed based on four different architectonic tools, Nissl and myelin staining, histochemistry using the lectin Wisteria floribunda agglutinin and immunohistochemistry using SMI-32 antibody.

Results

Twenty-two architectonic areas in the Cebus PfC were distinguished: areas 8v, 8d, 9d, 12l, 45, 46v, 46d, 46vr and 46dr in the lateral PfC; areas 11l, 11m, 12o, 13l, 13m, 13i, 14r and 14c in the orbitofrontal cortex, with areas 14r and 14c occupying the ventromedial corner; areas 32r, 32c, 25 and 9m in the medial PfC, and area 10 in the frontal pole. This number is significantly higher than the four cytoarchitectonic areas previously recognized in the same species. However, the number and distribution of these areas in Cebus were to a large extent similar to those described in Old World monkeys PfC in more recent studies.

Conclusions

The present parcellation of the Cebus PfC considerably modifies the scheme initially proposed for this species but is in line with previous studies on Old World monkeys. Thus, it was observed that the remarkable anatomical similarity between the brains of genera Macaca and Cebus may extend to architectonic aspects. Since monkeys of both genera evolved independently over a long period of time facing different environmental pressures, the similarities in the architectonic maps of PfC in both genera are issues of interest. However, additional data about the connectivity and function of the Cebus PfC are necessary to evaluate the possibility of potential homologies or parallelisms.

Pericontusion axon sprouting is spatially and temporally consistent with a growth-permissive environment after traumatic brain injury

We previously reported that pericontusional extracellular chondroitin sulfate proteoglycans (CSPGs) are profoundly reduced for 3 weeks after experimental traumatic brain injury, indicating a potential growth-permissive window for plasticity. Here, we investigate the extracellular environment of sprouting neurons after controlled cortical impact injury in adult rats to determine the spatial and temporal arrangement of inhibitory and growth-promoting molecules in relation to growth-associated protein 43-positive (GAP43+) neurons. Spontaneous cortical sprouting was maximal in pericontused regions at 7 and 14 days after injury but absent by 28 days. Perineuronal nets containing CSPGs were reduced at 7 days after injury in the pericontused region (p < 0.05), which was commensurate with a reduction in extracellular CSPGs. Sprouting was restricted to the perineuronal nets and CSPG-deficient regions at 7 days, indicating that the pericontused region is temporarily and spatially permissive to new growth. At this time point,GAP43+ neurons were associated with brain regions containing cells positive for polysialic acid neural cell adhesion molecule but not with fibronectin-positive cells. Brain-derived neurotrophic factor was reduced in the immediate pericontused region at 7 days. Along with prior Western blot evidence, these data suggest that a lowered intrinsic growth stimulus, together with a later return of growth-inhibitory CSPGs, may contribute to the ultimate disappearance of sprouting neurons after traumatic brain injury.

Localization of the Human Cortical Visual Area MT Based on Computer Aided Histological Analysis

We describe human area MT histologically based on the observer independent analysis of cortical myeloarchiteture, multiple complementary staining techniques and 3-D reconstruction. The topography of an architectonic field that presented constant structural characteristics across specimens was studied in relation to the sulcal geography of the occipito-temporal region. Objective and semi-automated analysis of local microstructure revealed a distinct cortical architecture and matched topographically the localization of MT derived from functional imaging. MT was localized by the histotopographic method in relation to definite macroscopic landmarks. This study demonstrates a new set of distinguishing architectonic features of human MT that permit localization on structural grounds and suggests that the characteristic laminar structure of this area may be related to its unique pattern of connections and to its role in visual perception.

Perisynaptic barrier of proteoglycans in the mature brain and spinal cord

Cell bodies and their dendrites of motor neurons, motor-related neurons, and certain other subsets of neurons such as GABAergic interneurons in the mature brain and spinal cord possess intensely negatively charged perineuronal or perisynaptic nets of proteoglycans which are linked to the nerve cell surface glycoproteins. These perineuronal nets of proteoglycans are digested by chondroitinase ABC, hyaluronidase, or collagenase, but not by endo-alpha-N-acetylgalactosaminidase, which is reactive to the nerve cell surface glycoproteins. Aggrecan, versican, neurocan, and brevican are members of a family of chondroitin sulfate proteoglycans that bind to hyaluronan. Neurocan- or brevican-deficient mice showed a regionally heterogeneous composition of proteoglycans in perineuronal nets. Aggrecan glycoforms contribute to the molecular heterogeneity of the perineuronal nets. Proteoglycans such as phosphacan are included in matrix-associated proteoglycans. The extracellular matrix glycoprotein tenascin-R is accumulated in the perineuronal nets. The perineuronal proteoglycans are produced by associated satellite astrocytes just before weaning, while the nerve cell surface glycoproteins are produced by the associated nerve cells at earlier stages after birth. The perineuronal proteoglycans may entrap the tissue fluid and form a perineuronal gel layer which protects the synapses as a "perisynaptic barrier". Degradation of the perineuronal proteoglycans or perisynaptic barrier by treatment with chondroitinase ABC or hyaluronidase reactivates the neuronal plasticity or promotes the functional recovery of a severed nervous system. Another set of perineuronal nets occurs, which are intensely positively charged and contain guanidino compounds. It is considered that these intensely positively charged nets are intermingled with the intensely negatively charged ones of proteoglycans.

Histochemical study of perineuronal nets in the retrosplenial cortex of adult rats

The retrosplenic cortex of rats, similar to many cortical or subcortical regions, is provided with special subsets of neurons that exhibited a fenestrated or reticular coat of condensed extracellular matrix on their soma, initial dendrites and proximal axon segment. This pericellular coating, currently termed "Perineuronal Nets", was detected on the surfaces of some neurons distributing throughout the cortical layers II-V. They presented direct interconnections with each other, and appeared in close association to the astroglial processes. In addition to their collagenous ligands, the perineuronal nets (PNs) were enriched with proteoglycans (PGs, sulfated glycoconjugates) and/or glycoproteins (GPs, unsulfated glycoconjugates with terminal N-acetylgalactosamine). Accordingly, the PNs were differentially identified as belonging to three categories, depending upon their organic nature or chemical composition. First, coats exclusively formed of PGs (stained with iron colloid); second, coats formed of GPs (labeled with plant lectins binding to terminal N-acetylgalactosamine); and third, complex coats formed of PG networks intermingled with glycoprotein molecules (double stained with iron colloid and lectin). Since differential distribution of protein containing substances (GPs and/or PGs) in the extracellular matrix contributes to functional terms, we suggest that these biochemical or morphological differences in the microenvironment of some retrosplenial neurons might reflect certain functional aspects concerned with processing of navigation or episodic memory.

Perineuronal nets in the rhesus monkey and human basal forebrain including basal ganglia

Perineuronal nets of extracellular matrix have been shown to characterize the microenvironment of individual neurons and the chemoarchitecture of brain regions such as basal forebrain nuclei. Previous work has also demonstrated that neurons in the human cerebral cortex ensheathed by perineuronal nets rarely undergo cytoskeletal changes in Alzheimer's disease, suggesting a neuroprotective effect of extracellular matrix components. It is not known, however, whether or not perineuronal nets are absent in the microenvironment of the cholinergic basal forebrain neurons that are involved early in the cascade of neurodegeneration in humans. Therefore, the present study was undertaken to examine the distribution patterns of perineuronal nets in the basal forebrain of the higher primates, rhesus monkey and human. Cytochemical staining was performed with the lectin Wisteria floribunda agglutinin and a polyclonal antibody to core proteins of chondroitin sulfate proteoglycans in the perfusion-fixed tissue of rhesus monkeys. In human brains, perineuronal nets were only stained with the immunoreaction for chondroitin sulfate proteoglycans. The results showed similar characteristics in distribution patterns of perineuronal nets in the medial septum, the diagonal band of Broca, the basal nucleus of Meynert (Ch1-Ch4), the lateral septum, the caudate-putamen, and the globus pallidus in both species. Double-labelling revealed that the vast majority of cholinergic neurons, labelled either with antibodies to choline acetyltransferase or the low-affinity neurotrophin receptor p75(NTR), were not ensheathed by perineuronal nets. A small subpopulation of net-associated neurons in close proximity to or intermingled with cholinergic neurons of the Ch1-Ch4 cell groups was found to be immunoreactive for parvalbumin. In the caudate-putamen, a large number of the parvalbumin-positive neurons were surrounded by perineuronal nets, whereas in the external and internal segments of the globus pallidus the coincidence of both markers was nearly complete. The study demonstrates that perineuronal nets of extracellular matrix are associated with different types of non-cholinergic neurons in the primate basal forebrain. The absence of nets around cholinergic basal forebrain neurons may be related to their slow modulatory activity but may also contribute to their susceptibility to degeneration in Alzheimer's disease.

Bral1, a brain-specific link protein, colocalizing with the versican V2 isoform at the nodes of Ranvier in developing and adult mouse central nervous systems

Bral1, a brain-specific hyaluronan-binding protein, has been cloned recently. To gain insight into the role of Bral1, we generated a specific antibody against this protein. We have examined the detailed localization pattern of Bral1 protein and compared it with that of other members of the lectican proteoglycan family, such as brevican and versican, with which Bral1 is predicted to interact. The immunoreactivity of Bral1 antibody was predominantly observed in myelinated fiber tracts in the adult brain and could be detected at P20 in the white matter of the developing cerebellum, suggesting that expression starts when axonal myelination takes place. Furthermore, immunostaining demonstrated that Bral1 colocalized with the versican V2 isoform at the nodes of Ranvier. The present data suggest that Bral1 may play a pivotal role in the formation of the hyaluronan-associated matrix in the CNS that facilitates neuronal conduction by forming an ion diffusion barrier at the nodes.

Chondroitin sulfate proteoglycan at the basal lamina beneath high endothelial cells in human palatine tonsils: a light and electron microscopic study using the cationic colloidal iron method

The basal lamina of high endothelial venules (HEVs) in human palatine tonsils was intensely stained with cationic colloidal iron at pH 1.5 and with aldehyde fuchsin. This basal lamina exhibited a thick and double- or triple-layered structure forming small compartments, in which many lymphocytes were aligned. Digestion with hyaluronidase or collagenase eliminated both the colloidal iron and aldehyde fuchsin stainings of the basal lamina of HEVs. Treatment with chondroitinase ABC reduced colloidal iron staining, but did not interfere with the aldehyde fuchsin staining. Digestion with neuraminidase, keratanase, or heparitinase did not eliminate either the cationic colloidal or the aldehyde fuchsin staining. Digestion with neuraminidase reduced the colloidal iron staining on the luminal surface coat of the HEV. Electron microscopy of ultrathin sections revealed that cationic colloidal iron particles were deposited on the basal lamina of the HEV. The basal laminae of ordinary blood vessels were thin and single-layered, and stained only weakly with cationic colloidal iron. The present study suggests that negatively charged sites in the basal lamina of HEV derive mainly from a proteoglycan complex containing hyaluronic acid and chondroitin sulfate, which firmly binds collagen. This topochemical feature is suggested to be involved in the fascilitating migration of lymphocytes after passage through the endothelial layer.

The intensely positively charged perineuronal net in the adult rat brain, with special reference to its reactions to oxine, chondroitinase ABC, hyaluronidase and collagenase

Light microscopic observations of healthy adult rat brain sections stained with anionic iron colloid indicated that 5-10% of neurons in the hippocampal subiculum and all neurons in the medial cerebellar nucleus possessed an intensely positively charged perineuronal net. This net was demonstrated to react to oxine, and therefore suggested to consist of guanidino compounds. It was further shown that the intensely positively charged perineuronal net, in accordance with the intensely negatively charged perineuronal net of proteoglycans, was digested by chondroitinase ABC, hyaluronidase, and collagenase, but not by endo-alphaN-acetylgalactosaminidase. This finding suggested that the former positively charged net might be linked to the latter negatively charged one.

Purkinje cells in the adult cat cerebellar cortex possess a perineuronal net of proteoglycans

The Purkinje cells in the adult cat cerebellar cortex were found to possess perineuronal proteoglycans which could be stained with our fine cationic iron colloid and Fujita's highly concentrated aldehyde fuchsin, and digested by chondroitinase ABC/keratanase/ heparitinase and hyaluronidase. The Purkinje cells are surrounded by some collagenous elements which are stained with Gömöri's ammoniacal silver and digested by collagenase. The Purkinje cells also express nerve cell surface glycoproteins which are labeled with lectin Vicia villosa agglutinin and digested by a double treatment with collagenase and endo-alpha-N-acetylgalactosaminidase. Sole digestion by endo-alpha-N-acetylgalactosaminidase never erased the lectin labeling of the nerve cell surface glycoproteins. These findings suggest that the collagenous elements mediate the linkage of the perineuronal proteoglycans to the nerve cell surface glycoproteins. It is presumed that in mice and rats, the perineuronal nets of proteoglycans and nerve cell surface glycoproteins of the Purkinje cells are so thin or coarse that they can not be sufficiently visualized under the light microscope.

Intensely negative-charged pericapillary spaces in the rat pineal gland

Electron microscopy of ultrathin sections stained with cationic iron colloid revealed that the rat pineal gland is provided with wide and intensely negative-charged pericapillary spaces. Light microscopically, the negative charging of the pericapillary spaces was completely eliminated by digestion with hyaluronidase and chondroitinase ABC. This pericapillary negative charging was also erased by digestion with collagenase. The results indicate that the negative charging is derived from sulfated proteoglycans which are bound to collagen molecules. These sulfated proteoglycans in the pericapillary spaces may retain numerous water molecules to form a tissue gel, and so act as a selective sieve regulating the passage of tissue molecules.

Enhanced visualization of weak colloidal iron signals with Bodian's protein silver for demonstration of perineuronal nets of proteoglycans in the central nervous system

The present study aimed for a clear visualization of faintly deposited colloidal iron in tissue sections for light microscopy. Paraffin blocks containing paraformaldehyde-fixed brain tissue from healthy adult mice were cut into sections 10-15 microm thick. After deparaffinization, the sections were stained with fine cationic iron colloid at a pH value of 1.0-1.5, and treated with a mixture of potassium ferrocyanide and hydrochloride for Prussian blue reaction. Some sections were further treated with Bodian's protein silver after the Prussian blue reaction. This sensitized development of Prussian blue reaction with Bodian's protein silver more clearly visualized the faintly deposited cationic colloidal irons than the demonstration by Prussian blue reaction alone, and allowed an enhanced visualization of the perineuronal nets of sulfated proteoglycans in the brain. Thus, such fine perineuronal sulfated proteoglycans as those in the CA3 field of the hippocampus, which are weakly stained with cationic iron colloid and usually overlooked by a demonstration with only a Prussian blue reaction, could be clearly visualized with striking contrast by the sensitized development with Bodian's protein silver after the Prussian blue reaction. Preliminary hyaluronidase digestion erased Bodian's protein silver development of perineuronal sulfated proteoglycans. Though some axonal fibers were also additionally stained with Bodian's protein silver itself, this sensitized development is useful to enhance such weak colloidal iron signals as are hardly detectable by only Prussian blue reaction.

Intensely positively charged perineuronal nets in the adult rat brain as detected by staining with anionic iron colloid

Ferric chloride, when boiled with ammonium thiocyanate, ammonia and cacodylic acid, is converted into a fine anionic iron colloid which consists of 1.0-1.5 nm electron dense granules and gives a distinct Prussian blue reaction (OHTSUKA and MURAKAMI, 1986). Light microscopy of tissue sections stained with this fine anionic iron colloid at pH values of 6.0, 7.0 and 8.0 showed that the healthy adult rat brain contains a considerable number of neurons which possess an intensely positively charged perineuronal net. This net was most clearly demonstrable by staining with the anionic iron colloid at a pH value of 8.0, at which ionizations of almost all cationic sites of the tissue elements were obliterated. Transmission electron microscopy of ultrathin sections stained at a pH value of 8.0 showed that the anionic iron colloid was preferentially deposited in the perineuronal tissue spaces. These findings indicate that the intensely positively charged perineuronal net contains some strongly basic substances such as guanidino compounds, and occupies the perineuronal (perisynaptic) tissue space.

The spatial relationship between the perineuronal proteoglycan network and the synaptic boutons as visualized by double staining with cationic colloidal iron method and anti-calbindin-D-28K immunohistochemistry in rat cerebellar nuclei

The present study demonstrated the precise spatial relationship between meshes in the perineuronal proteoglycan network and the terminal boutons of synaptically associated axons. Sections from the rat cerebellum were stained with cationic colloidal iron (pH 1.0-1.5), and successively immunostained with anti-calbindin-D-28K monoclonal antibody. Cationic iron stained sulfated proteoglycans around the nerve cell of the medial cerebellar nucleus, whereas the anti-calbindin antibody labeled the Purkinje cells including their axons terminating on large neurons in the cerebellar nucleus. It was found that each synaptic bouton fits into a mesh of the perineuronal network. The individual meshes appeared to be divided by partitions faintly stained with the colloidal iron. Electron microscopy of cationic colloidal iron-stained ultrathin sections revealed that the synaptic boutons were separated from each other by the proteoglycan matrix and that each of them was further divided into two or more contact areas of presynaptic membrane by the same matrix. This suggests that individual synapses are protected against the effects of adjacent synaptic transmission, and that each of them may be subdivided by this manner of partitioning, like pads of a cat's paw.

Light and confocal laser-scanning microscopical evidences for complementary patterns of glial fibrillary acidic protein and Wisteria floribunda agglutinin labeled structures in human and rat brain

We investigated the pattern of glial fibrillary acidic protein (GFAP) and Wisteria floribunda agglutinin (WFA) labeled structures in the superior colliculus and in the somatosensory cortex of humans and rats of different age groups using immunohistochemical methods, light and confocal laser-scanning microscopy. We never found a double labeling of WFA and GFAP positive structures neither in the superior colliculus nor in the cortex of both man and rat. The complementary pattern of WFA and GFAP labeling was present both at the macroscopic and microscopic level. We found a clear prevalence of either WFA or GFAP expression in the arborization of the astrocytes as well as in the pattern of lamination.

The extracellular matrix in the mouse brain: its reactions to endo-alpha-N-acetylgalactosaminidase and certain other enzymes

As our previous studies have indicated, the cingulate cortex of the adult mouse brain contains many neurons with rich cell surface glycoproteins which are linked by collagenous ligands to perineuronal proteoglycans. The present study demonstrated that exclusive incubation with endo-alpha-N-acetylgalactosaminidase abolished the lectin Vicia villosa or Wisteria floribunda agglutinin (VVA or WFA) labeling of the nerve cell surface glycoproteins, while it neither interfered with the cationic iron colloid or aldehyde fuchsin stainings of the perineuronal proteoglycans nor abolished the Gömöri's ammoniacal silver impregnation of the collagenous ligands. Double incubations with endo-alpha-N-acetylgalactosaminidase and collagenase did not eliminate the lectin VVA or WFA labeling of the nerve cell surface glycoproteins, though they did eliminate the cationic iron colloid and aldehyde fuchsin stainings of the perineuronal proteoglycans as well as the Gömöri's ammoniacal silver impregnation of the collagenous ligands. Triple incubations with endo-alpha-N-acetylgalactosaminidase, collagenase, and endo-alpha-N-acetylgalactosaminidase abolished the lectin VVA or WFA labeling of the nerve cell surface glycoproteins, and also eliminated the cationic iron colloid and aldehyde fuchsin stainings of the perineuronal proteoglycans and the Gömöri's ammoniacal silver impregnation of the collagenous ligands. These findings indicate that: the nerve cell surface glycoproteins or their terminal N-acetylgalactosamines are digested by endo-alpha-N-acetylgalactosaminidase; these galactosamines associated with the collagenous ligands or perineuronal proteoglycans are not digested by endo-alpha-N-acetylgalactosaminidase; and the terminal N-acetylgalactosamines newly exposed by collagenase incubation are digested by this galactosaminidase. It was further demonstrated that hyaluronidase incubation neither digests the collagenous ligands nor revives the lectin VVA or WFA labeling of the nerve cell surface proteoglycans.

Cortical areas abundant in extracellular matrix chondroitin sulphate proteoglycans are less affected by cytoskeletal changes in Alzheimer's disease

In the human brain, the distribution of perineuronal nets occurring as lattice-like neuronal coatings of extracellular matrix proteoglycans ensheathing several types of non-pyramidal neurons and subpopulations of pyramidal cells in the cerebral cortex is largely unknown. Since proteoglycans are presumably involved in the pathogenesis of Alzheimer's disease, we analysed the distribution pattern of extracellular chondroitin sulphate proteoglycans in cortical areas, including primary motor, primary auditory and several prefrontal and temporal association areas, in normal human brains and in those showing neuropathological criteria of Alzheimer's disease. In both groups, neurons with perineuronal nets were most numerous in the primary motor cortex (approximately 10% in Brodmann's area 4) and in the primary auditory cortex as a representative of the primary sensory areas. Their number was lower in secondary and higher order association areas. Net-associated pyramidal cells occurred predominantly in layers III and V in motor areas, as well as throughout lower parts of layer III in the primary auditory cortex and neocortical association areas. In the entorhinal cortex, net-associated pyramidal cells were extremely rare. In brains showing hallmarks of Alzheimer's disease, the characteristic patterns of hyperphosphorylated tau protein, stained with the AT8 antibody, largely excluded the zones abundant in perineuronal nets and neuropil-associated chondroitin sulphate proteoglycans. As shown in double-stained sections, pyramidal and non-pyramidal neurons ensheathed by perineuronal nets were virtually unaffected by the formation of neurofibrillary tangles even in severely damaged regions. The distribution patterns of amyloid B deposits overlapped but showed no congruence with that of the extracellular chondroitin sulphate proteoglycans. It can be concluded that low susceptibility of neurons and cortical areas to neurofibrillary changes corresponds with high proportions of aggregating chondroitin sulphate proteoglycans in the neuronal microenvironment.

Perineuronal nets of proteoglycans in the adult mouse brain are digested by collagenase

As our previous study has indicated, perineuronal proteoglycans in the adult mouse brain are associated with some collagenous molecules which can be stained with Gömöri's ammoniacal silver and are resistant to hyaluronidase digestion. The present study demonstrated that these molecules are thoroughly digested with collagenase, and suggests that they represent a hyaluronic acid-binding domain of the ligand proteoglycans connecting the perineuronal proteoglycans and nerve cell surface glycoproteins.

Perineuronal nets of proteoglycans in the adult mouse brain, with special reference to their reactions to Gömöri's ammoniacal silver and Ehrlich's methylene blue

As our previous studies have indicated, many subsets of neurons in the vertebrate brain possess a sulfated proteoglycan surface coat which reacts to cationic iron colloid and aldehyde fuchsin. The present study demonstrated that this surface coat is supravitally stained with Ehrlich's methylene blue, and doubly with this blue and aldehyde fuchsin, a finding suggesting its being identical to Cajal's superficial reticulum (red superficial) and to Golgi's reticular coating (revetement reticulare). The perineuronal surface coat was further stained with Gömöri's ammoniacal silver, and doubly with this silver and cationic iron colloid. These neurons with such a proteoglycan surface coat usually expressed cell surface glycoproteins which were labeled with lectin Wisteria floribunda agglutinin. Hyaluronidase digestion did not interfere with this lectin labeling of the glycoproteins, methylene blue and Gömöri's ammoniacal silver staining of the surface coat, while it erased the cationic iron colloid and aldehyde fuchsin staining of the surface coat. These findings suggest that the perineuronal proteoglycan surface coat is associated with some additional molecules which are resistant to hyaluronidase digestion and stainable with methylene blue and Gömöri's ammoniacal silver. The possibility is suggested that these molecules might represent "ligand proteoglycans" connecting the perineuronal proteoglycans and cell surface glycoproteins.