Specific staining of nonpyramidal cell populations of the cerebral cortex by lectin cytochemistry on semithin sections

The pattern of lectin labeling in the cerebral cortex of the cat was studied using semithin sections. The labeling produced by some lectins (Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, wheat germ agglutinin, and succynilated-wheat germ) appeared inside every neuron as small cytoplasmic granules, probably corresponding to cisterns of endoplasmic reticulum and/or the Golgi complex. Lectins with affinity for alpha-mannosyl residues (Pisum sativum, Lens culinaris, and Concanavalin A) stained the cell surface of a subset of cortical neurons. The labeled cells were round or polygonal, medium to large neurons present in layers II-VI, exhibiting the morphological features of nonpyramidal cells. Previous lectin studies of perineuronal nets have shown that these extracellular specializations contain N-acetylgalactosamine and N-acetylglucosamine. Our results show that mannose is also a component of perineuronal nets and that lectins specific for alpha-mannose can be used as tools for the cytochemical detection of a separate class of cortical neurons, which have not yet been fully characterized. In addition, some lectins (Bandeiraea simplicifolia, Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, and succynilated-wheat germ agglutinin) specifically labeled a population of a type of microglia-related cells known as perivascular cells. The data presented here report for the first time the selective staining of perivascular cells and further support the hypothesis that they are different from typical microglial cells.

A reliable method for Golgi staining of retina and brain slices

Although the classical Golgi method is a powerful means for structural analysis of the brain, it is generally considered to be an unpredictable technique making anatomists wary of using it. Often, even when successful staining has occurred, deposits of silver chromate crystals on the surface of the tissue obscure examination. This paper describes a simple procedure for Golgi impregnation of retina and brain slices so that good, even staining is obtained and crystal formation is avoided. The most outstanding feature of the method is the consistency of results. This consistency is due to two factors: (1) the accurate determination of the optimal chromation by measuring the rise of pH in the solutions and (2) the uniform penetration of dichromate and silver nitrate to the specimen by using a freely hanging, sandwiching technique. We suggest that the method described here can be applied to other parts of the nervous system and will be a reliable way to identify and better classify new cell types.

Pilocarpine-induced changes in the saccharide composition of the tectorial membrane and interdental cells of the organ of Corti: a study with gold-labeled lectins

The glycoconjugates in the cytoplasm of inner ear interdental cells and those constituting the limbal tectorial membrane were identified by a post-embedding cytochemical method using low-temperature embedding in Lowicryl K4M and labeling with biotinylated lectins, goat anti-biotin antibody, rabbit anti-goat antibody, and gold-labeled protein A in control animals, and after the systemic injection of pilocarpine. The lectins used were ConA, PHA-E, PSA, RCA, SBA, Succ-WGA, UEA, and WGA. In control animals, a semiquantitive analysis of gold particles showed that Succ-WGA produced the strongest labeling on the tectorial membrane, followed by SBA, ConA, WGA, RCA, PHA-E, and PSA. The lowest values were obtained with UEA. The cytoplasm of the interdental cells was also labeled with all the lectins, but the number of particles/microns2 was lower than on the tectorial membrane. The concentration of gold particles on the limbal tectorial membrane in pilocarpine-treated animals was higher than in control animals for some lectins (RCA, PSA, UEA) but lower for others (WGA, SBA, PHA-E, Succ-WGA). The changes in the labeling pattern of the cytoplasm of the interdental cells paralleled those in the tectorial membrane. These results demonstrate that the saccharide composition of the limbal tectorial membrane can be modified by systemic injection of pilocarpine. This action may take place through a change in either the secretion rate or the amount of some glycoconjugates by the interdental cells.

Golgi-Colonnier method: correlation of the degree of chromium reduction and pH change with quality of staining

We examined the role of chromium reduction in the Golgi-Colonnier method, correlating the quality of neuronal impregnation with the levels of hexavalent (CrVI) and trivalent (CrIII) chromium in the tissue and in the chromation fluid (CF). The concentrations of both chromium species were assessed by measuring spectrophotometrically the CrVI before and after oxidizing the sample and by calculating the ratio of CrVI to total chromium (chromium ratio, CrR). The CrR was almost identical in the tissue and the CF, decreasing exponentially during chromation due to a progressive consumption of CrVI to form CrIII. Satisfactory cell impregnation was obtained only when the CrR was 0.45-0.7, regardless of other factors. The CrR values could be accurately predicted by the pH increase of the CF; this increase has proven to be a most reliable criterion to decide the endpoint of the chromation process. The dependence of cell staining on the [CrIII], together with the well-known ability of this species to bridge proteins, suggests that the key event for cell impregnation is the cross-linking of neuronal proteins by CrIII polymers.

Development of the tectal cells in the mouse cochlea

Tectal cells appear at birth in the outer part of the developing organ of Corti. At first they are attached to the basilar membrane, but later they ascend through the auditory epithelium. During the 1st postnatal week (coinciding with the development of the minor tectorial membrane), the newly formed tectal cells show several cytological characteristics suggesting increased metabolic and secretory activities, which include: (1) a large Golgi complex, (2) abundant amorphous material inside the cisterns of rough endoplasmic reticulum, and (3) dense granules inside the mitochondrial matrix. All these features gradually disappear, and by the 14th postnatal day the tectal cells show a dark cytoplasm and few and short microvilli. In addition, tectal cells were stained selectively by some lectins. These findings suggest that tectal cells may participate in the secretion of some components of the minor tectorial membrane, different from those produced by Deiters' cells, Hensen's cells and pillar cells.

Pilocarpine elicits the interdental cell secretory activity of the inner ear

Subcutaneous injection of pilocarpine in guinea pigs resulted in the following ultrastructural changes: 1) the apical cavities of the interdental cells were filled with a substance indistinguishable from the overlying amorphous layer of the TM; 2) a great number of spherical structures appeared over the limbal portion of the tectorial membrane. In TEM photomicrographs these structures displayed the same appearance as the amorphous layer of the TM and were usually continuous to it; 3) the number of holes that decorate the upper surface of the limbal portion of the TM was dramatically increased and it was found that they connect the endolymphatic space to the apical cavities of the interdental cells; 4) there was an increase in the number of the small extracellular vesicles found in the clear spaces of the tectorial membrane. These facts suggest that pilocarpine stimulates the secretion of the interdental cells, confirming the existence of the secretory processes previously described (Prieto et al., 1990). These findings can be related to the turnover of the TM in the adult animal and, perhaps, to the secretion of some organic compound to the endolymph. We postulate that the actions of pilocarpine on the interdental cells are most probably mediated by the activation of muscarinic acetylcholine receptors in these cells.

Morphology of the rat cochlear primary afferents during prenatal development: a Cajal's reduced silver and rapid Golgi study

In this study, we analyse the process of spatial organisation of the cochlear root related to the morphological and topographical changes in the CN during the prenatal development of Wistar rats, placing special emphasis on aspects of the latero-medial distribution of the cochlear afferents. A total of 35 embryos from 8 Wistar rats was employed, corresponding to embryonic days 14, 16, 18 and 20. Twenty of these embryos were studied by the Cajal's reduced silver stain and 15 by the rapid Golgi method (osmium dichromate method). The otocyst, the vestibulo-cochlear ganglion and vestibulo-cochlear nerve were first observed at embryonic Day 14 (E14). At E16, a sharp separation between the cochlear and vestibular roots was distinguished. The final position of the primary afferents and their main branches (anterior and posterior) in the CN was observed at E18 and E20, when the total number of cochlear turns had been formed. The cochlear afferents coming from the apical coil, the last to be incorporated into the cochlear root, project their posterior branches at the bifurcation towards more medial portions of the PVCN and their anterior branches towards the more lateral regions of the AVCN.

The effects of kainic acid on the cochlear ganglion of the rat

The effects of locally applied kainic acid on cells and fibers in the rat cochlea were examined in a quantitative and ultrastructural study. Doses of 5 nM per microliter of artificial perilymph destroyed part of the spiral ganglion type I cell population, with no ototoxic effects on cochlear hair cells or supporting cells. Type II cells also appeared unaffected. A quantitative evaluation of the cell loss with the 5 nM dosage showed that 34% of spiral ganglion neurons were lost 10 days after treatment. Doses of 20 nM per microliters and 40 nM per microliters did not result in increasing neuronal loss. This differential toxicity could reflect the presence of a sub-population of spiral ganglion cells with an increased number of KA receptors.

Reversible damage to the nerve fibres in the organ of Corti after surgical opening of the cochlea in the rat

After minimal opening of the cochlear bony wall, the efferent and the outer spiral fibres showed no changes; inner radial fibres (afferents to inner hair cells) were highly sensitive to this mild trauma, appearing swollen and empty of cytoplasmic content. Available data suggest that this may be due to alterations in the cochlear micromechanical environment, related to the surgical manipulation. The swellings were reversible, although the normal structure had not completely recovered until one month after the manipulation.

Neuronal loss in the spiral ganglion of young rats

A quantitative study of spiral ganglion neurones was performed in rats during postnatal days 4, 5, 6, 30 and 60. There are 25,194 +/- 462 ganglion cells on postnatal day 4, abruptly falling to 18,809 +/- 514 on the 6th postnatal day. This neuronal loss accounts for the 22% of the overall ganglion cell population. The number of neurones remains almost unchanged from the 6th to the 60th postnatal day. This numerical variation in the neuronal population of the spiral ganglion seems to be related to the changes that take place during cochlear synaptogenesis, at the end of the first postnatal week, on the base of the outer hair cells. These changes involve competition among efferent endings approaching the cell and some afferents connected with it at birth, that disappear as a result of such a competition.

Subsurface material in outer hair cells

Tannic acid stains a homogenous material inside the outer hair cells of the organ of Corti of the guinea pig. This material is always placed between the plasma membrane and the first layer of subsurface cisterns, but only in those areas along the lateral surface of the outer hair cell lining the spaces of Nuel. The possibility that this material is related to some particular function of outer hair cell lateral face is discussed.