Perineuronal Sulfated Proteoglycans Research Articles

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.

Perineuronal sulfated proteoglycans and cell surface glycoproteins in the visual cortex of adult and newborn cats.

Sections of the visual cortex of newborn (1-4 weeks after birth) and adult cats were stained with cationic iron colloid, aldehyde fuchsin or lectins (lectin Vicia villosa, soybean and Wisteria floribunda agglutinins). Many neurons in the adult cat visual cortex contained perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin, or cell surface glycoproteins reactive to lectins. Double staining indicated that some of the lectin-labeled neurons were not stained with cationic iron colloid, and also that some of the cationic iron colloid-stained neurons were not labeled with lectins. The perineuronal sulfated proteoglycans and cell surface glycoproteins developed 3 weeks after birth. In the newborn cats 1-2 weeks after birth, no neurons were reactive to cationic iron colloid, aldehyde fuchsin or lectins. In the newborn cats 3-4 weeks after birth, it was clearly observed that the cytoplasm of the glial cells closely associated with the neurons containing the perineuronal sulfated proteoglycans showed an intense reaction to cationic iron colloid and aldehyde fuchsin, and that the Golgi complexes of the neurons with cell surface glycoproteins were intensely labeled with lectins. These findings suggest that the perineuronal sulfated proteoglycans are derived from the associated glial cells, and that the cell surface glycoproteins are produced by the associated nerve cells.

Perineuronal sulfated proteoglycans and cell surface glycoproteins in adult and newborn mouse brains, with special reference to their postnatal developments.

Sections of the retrosplenial cortex from adult and newborn mouse brains were observed with a light microscope. The retrosplenial cortex of the adult animals contained many neurons (10% of the total), including some dark neurons, with perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin. The retrosplenial cortex of the adult animals also contained many neurons (10% of the total) with cell surface glycoproteins reactive to lectin Vicia villosa, soybean or Wisteria floribunda agglutinin. Double staining showed that the majority (75%) of the neurons labeled with lectins were stained with cationic iron colloid, and that some (25%) of them were not stained with this colloid. Double staining also showed that some (25%) of the neurons stained with cationic iron colloid were not labeled with lectins. These findings indicate that the perineuronal sulfated proteoglycans are, at least partly, independent from the cell surface glycoproteins. Observations of the sections from the newborn animals revealed that the perineuronal sulfated proteoglycans were produced by the associated satellite astrocytes 3-4 weeks after birth, and that the cell surface glycoproteins were produced by the associated nerve cells at earlier stages, or 2-3 weeks after birth. Dark neurons began to appear 3-4 weeks after birth. These dark neurons or their Golgi complexes were also reactive to lectins, suggesting the production of cell surface glycoproteins.

Perineuronal sulfated proteoglycans, cell surface glycoproteins and dark neurons in the cingulate cortex of newborn and adult rats.

Many neurons in the adult rat cingulate cortex possess perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin, or cell surface glycoproteins reactive to lectin Vicia villosa or soybean agglutinin. The perineuronal sulfated proteoglycans develop three to four weeks after birth. The cell surface glycoproteins develop at earlier stage or two to three weeks after birth. Dark or active neurons begin to appear three to four weeks after birth. These findings indicate that the brain matures after birth or during weaning period.

Perineuronal sulfated proteoglycans in the adult rat brain: histochemical and electron microscopic studies.

Neurons of cerebellar nuclei in the rat brain had a marked surface coat which was stained with cationic iron colloid or aldehyde fuchsin. Neurons with a similar surface coat were also noted in the retrosplenial cortex. The surface coat was stained doubly with cationic iron colloid and aldehyde fuchsin. Digestion with hyaluronidase eliminated the stainability of the surface coat to both agents. Combined digestion with chondroitinase ABC, heparitinase and keratanase eliminated the cationic iron colloid staining but did not interfere with the aldehyde fuchsin staining. Electron microscopy of ultrathin sections revealed that the iron particles were deposited in the perineuronal tissue spaces. These findings indicate that the surface coat consists of sulfated proteoglycans which occupy, as the extracellular matrix, the perineuronal tissue spaces. Many neurons in the retrosplenial cortex were labeled with lectin Vicia villosa agglutinin. Double staining revealed that these lectin-labeled neurons are usually reactive to cationic iron colloid. Few neurons in the cerebellar nuclei were labeled with lectin V. villosa agglutinin.

Neurons with perineuronal sulfated proteoglycans in the mouse brain and spinal cord: their distribution and reactions to lectin Vicia villosa agglutinin and Golgi's silver nitrate.

This study demonstrates that many neurons in the somatosensory cortex, cingulate cortex, retrosplenial cortex and hippocampal subiculum of the mouse brain are covered by sulfated proteoglycans which are intensely negative-charged and stained with cationic iron colloid, while being digested with hyaluronidase. Neurons with similar perineuronal proteoglycans are also recognized in the extrapyramidal system (superior colliculus, red nucleus, reticular formation, vestibular nuclei and cerebellar nuclei), in the secondary auditory system (cochlear nuclei, nucleus of trapezoid body, inferior colliculus and nucleus of lateral lemniscus), in the vestibulo-ocular reflex system (vestibular nuclei and extraocular motor nuclei), and in the pupillary reflex system. The neurons with perineuronal sulfated proteoglycans in the cerebral cortices and hippocampal subiculum are usually labeled with the lectin Vicia villosa agglutinin, though those in the cerebellar, vestibular and cochlear nuclei may not be reactive to this lectin. Double staining of the retrosplenial cortex, hippocampal subiculum and cerebellar nuclei with Golgi's silver nitrate and cationic iron colloid indicates that the perineuronal sulfated proteoglycans are identical with the Golgi's reticular coating or glial nets.

Perineuronal sulfated proteoglycans in the human brain are identical to Golgi's reticular coating.

Many neurons in the human somatosensory cortex (Area 7 of Brodmann) possess an intensely negative-charged surface coat consisting of perineuronal sulfated proteoglycans which were stained with cationic iron colloid. This surface coat was stained doubly with cationic iron colloid and Golgi's silver nitrate. The result indicates that the perineuronal sulfated proteoglycans are identical with Golgi's reticular coating, whose existence and nature have previously been controversial. The result also suggests that Golgi's silver nitrate stains the core proteins of proteoglycans.

Dark neurons in the mouse brain: an investigation into the possible significance of their variable appearance within a day and their relation to negatively charged cell coats.

This study aims to investigate the occurrence and nature of dark neurons in the central nervous system under physiological conditions. Mouse brain tissues were perfusion-fixed with paraformaldehyde or glutaraldehyde at 4 h intervals during one day (3:00, 7:00, 11:00, 15:00, 19:00, 23:00). Paraffin sections were stained with the cationic colloidal iron method, and counterstained with nuclear fast red or carbolthionin. The dark neurons were readily distinguishable as their shrunken cell bodies stained densely with nuclear fast red or thionin. Some of the dark cells were coated with perineuronal sulfated proteoglycans; this coat, which formed a smoothly extended meshwork in light cells, presented spicule-like forms in the dark cells. The occurrence of dark cells in the retrosplenial cortex varied by the time of day: the incidence of the dark neurons was low (10-15%) at 11:00, 15:00 and 23:00, while it was significantly high (50-60%) at 3:00 and 19:00. Previous authors have ascribed the occurrence of dark neurons either to artifacts due to inappropriate fixation or to pathological damage. However, the present study strongly suggests that this type of neuron occurs under physiological conditions as reversible changes, and vary over a day, showing distinct peaks. These peaks occurred coincidentally while the mice were awake. Such morphological changes may be involved in the neuronal activation and exhaustion. Our view is consistent with the hypothesis (Tewari and Bourne, 1963) that the neurons take such dark profiles at certain stages of neurosecretion.

Neurons with perineuronal sulfated proteoglycans in the human visual cortex, with special reference to their reactions to lectins.

The human visual cortex, especially its ganglionic lamina, was found to contain many neurons with perineuronal sulfated proteoglycans which were stained with cationic iron colloid and aldehyde fuchsin. It also contained many neurons with surface glycoproteins labeled with lectin Vicia villosa agglutinin (VVA) or Glycine max agglutinin (SBA). Double staining frequently showed that the neurons stained with cationic iron colloid were not labeled with lectin VVA or SBA. Hyaluronidase and chondroitinase ABC/heparitinase/keratanase digestions eliminated the perineuronal cationic iron colloid reaction, but never interfered with the cell surface lectin labeling. These findings indicate that the cell surface glycoproteins reactive to lectin VVA or SBA are neither structural elements nor adhesive molecules of the proteoglycans. Double staining further demonstrated that in some neurons with perineuronal sulfated proteoglycans, the cytoplasm was labeled with lectin Arachis hypogaea agglutinin (PNA). It was further noticed that the lectin VVA-labeled neurons were not always identical with the neurons labeled with lectin SBA or with lectin PNA.

Perineuronal sulfated proteoglycans and dark neurons in the brain and spinal cord: a histochemical and electron microscopic study of newborn and adult mice.

Neurons of intracerebellar nuclei in the mouse brain were demonstrated to possess a marked surface coat, formed 3-4 weeks after birth, which was stainable with cationic iron colloid or aldehyde fuchsin. Neurons with a similar surface coat were noted as relay or local interneurons in rather restricted areas such as the occipital cortex, retrosplenial cortex, zona incerta, hippocampal subiculum and spinal posterior horn. Dark neurons with condensed cytoplasm were also shown to be covered with the surface coat. The surface coat was stained doubly with cationic iron colloid and aldehyde fuchsin. Digestion with hyaluronidase eliminated the stainability of the surface coat to both agents. Combined digestion with chondroitinase ABC, heparitinase and keratanase eliminated the cationic iron colloid staining of the surface coat, but did not interfere with the aldehyde fuchsin staining of the surface coat. Electron microscopy of ultrathin sections revealed that the iron particles indicating sulfated proteoglycans were preferentially deposited in the perineuronal tissue spaces. Many neurons in the hippocampal subiculum possessed cell surface glycoproteins which were labeled with lectin Vicia villosa or soybean agglutinin and formed 1-2 weeks after birth. Double staining revealed that these lectin-labeled neurons were identical in part with the neurons reactive to the cationic iron colloid. Dark neurons began to appear 3-4 weeks after birth. The formation of perineuronal sulfated proteoglycans and the appearance of dark neurons, both occurring during the weaning period, may reflect the morphological and physiological completion of the brain. Dark neurons are suggested to be exhausted cells that are restored to light or normal neurons after sleep.