Cerebellar cortex of rat and other animals. A structural and ultrastructural study

Impacts of Egyptian propolis extract on rat cerebellum intoxicated by aluminum silicate: histopathological studies

Human is exposed to traces of aluminum silicate (AlS), i.e., cosmetics, pesticides. Accumulation of aluminum compounds including AlS is associated with neuropathological diseases, e.g., Alzheimer's disease. The aim of the current study is to investigate the neuroprotective effects of propolis extracts in AlS-induced cerebellum intoxication in rats. Forty adult rats were randomly divided into four groups (n = 10). The first group served as a control; the second group treated with 200 ml propolis/kg bwt. every other day by stomach gavage tube, third group was intraperitoneally injected with AIS (20 mg/kg) twice a week for 8 weeks, and the fourth group received propolis extract and AIS. At the end of 8 weeks, the cerebellum was harvested for further ultrastructure, histological, and histochemical investigations. Using electron microscopy, the ultrastructure of the cerebellar cortex of AlS intoxicated rats showed Purkinje cells with an irregular euchromatic nucleus and extremely increased invagination of the nuclear envelope. In addition, the cytoplasm revealed numerous damaged mitochondria (> 20%) as well as swollen lysosomes (> 40%) compared to controls. These AlS-related ultrastructure changes were to some extent normalized to < 10% and < 30% in case of mitochondria and lysosomes, respectively, if rats were co-treated with propolis extract. Further, histopathological examination showed that AlS-exposed rats revealed abnormal Purkinje cells with irregular size and shrank shape, evidence of pre-necrotic stage in the form of nuclear pyknosis, and condensed and frequent darkly stained cells in cerebellar layers. However, propolis extract co-administration reversed from 35 to 25% (p < 0.05) these alterations. The carbohydrate and protein contents were reduced in case of AlS treatment and surprisingly propolis co-treatment was able to rescue these neurotoxic effects. Propolis extract might have neuroprotective effects against AIS-induced toxicity. Further studies are required to identify the mechanism of the pharmacological action and optimal settings for medical testing of propolis extract.

Comparative neuronal morphology of the cerebellar cortex in afrotherians, carnivores, cetartiodactyls, and primates

Although the basic morphological characteristics of neurons in the cerebellar cortex have been documented in several species, virtually nothing is known about the quantitative morphological characteristics of these neurons across different taxa. To that end, the present study investigated cerebellar neuronal morphology among eight different, large-brained mammalian species comprising a broad phylogenetic range: afrotherians (African elephant, Florida manatee), carnivores (Siberian tiger, clouded leopard), cetartiodactyls (humpback whale, giraffe) and primates (human, common chimpanzee). Specifically, several neuron types (e.g., stellate, basket, Lugaro, Golgi, and granule neurons; N = 317) of the cerebellar cortex were stained with a modified rapid Golgi technique and quantified on a computer-assisted microscopy system. There was a 64-fold variation in brain mass across species in our sample (from clouded leopard to the elephant) and a 103-fold variation in cerebellar volume. Most dendritic measures tended to increase with cerebellar volume. The cerebellar cortex in these species exhibited the trilaminate pattern common to all mammals. Morphologically, neuron types in the cerebellar cortex were generally consistent with those described in primates (Fox et al., 1967) and rodents (Palay and Chan-Palay, 1974), although there was substantial quantitative variation across species. In particular, Lugaro neurons in the elephant appeared to be disproportionately larger than those in other species. To explore potential quantitative differences in dendritic measures across species, MARSplines analyses were used to evaluate whether species could be differentiated from each other based on dendritic characteristics alone. Results of these analyses indicated that there were significant differences among all species in dendritic measures.

Calcium-binding proteins in the cerebellar cortex of the bottlenose dolphin and harbour porpoise

Studying the distribution of Ca2+-binding proteins allows one to discover specific neuron chemotypes involved in the regulation of the activity of various neural elements. While extensive data exist on Ca2+-binding proteins in the nervous system, in particular, in the cerebellar cortex of terrestrial mammals, the localization of these proteins in the cerebellar cortex of marine mammals has not been studied. We studied the localization of calretinin, calbindin, and parvalbumin immunoreactivity in the cerebellar cortex of the bottlenose dolphin Tursiops truncates and harbour porpoise Phocoena phocoena. In both species, most Purkinje cells were calbindin-immunoreactive, while calretinin and parvalbumin were expressed in a small portion of Purkinje cells. In addition, calretinin-immunoreactive unipolar brush and granule cells and calbindin- and parvalbumin-immunoreactive basket, stellate, and Golgi cells were observed. Calretinin-immunoreactive corticopetal (mossy and climbing) fibers were found. Based on the length of the primary dendrite, short-, middle-, and long-dendrite unipolar brush cells could be distinguished. The validity of this classification was supported using cluster analysis suggesting the presence of several natural types of these cells. The distribution of Ca2+-binding proteins in the cerebellar cortex of the cetaceans studied was generally similar to that reported for terrestrial mammals, suggesting that this trait is evolutionarily conservative in mammals.

Expression mapping of tetracycline-responsive prion protein promoter: digital atlasing for generating cell-specific disease models

We present a digital atlas system that allows mapping of molecular expression patterns at cellular resolution through large series of histological sections. Using this system, we have mapped the distribution of a distinct marker, encoded by the LacZ reporter gene driven by the tetracycline-responsive prion protein promoter in double transgenic mice. The purpose is to evaluate the suitability of this promoter mouse line for targeting genes of interest to specific brain regions, essential for construction of inducible transgenic disease models. Following processing to visualize the promoter expression, sections were counterstained to simultaneously display cytoarchitectonics. High-resolution mosaic images covering entire coronal sections were collected through the mouse brain at intervals of 200 microm. A web-based application provides access to a customized virtual microscopy tool for viewing and navigation within and across the section images. For each section image, the nearest section in a standard atlas is defined, and annotations of key structures and regions inserted. Putative categorization of labeled cells was performed with use of distribution patterns, followed by cell size and shape, as parameters that were compared to legacy data. Among the ensuing results were expression of this promoter in putative glial cells in the cerebellum (and not in Purkinje cells), in putative glial cells in the substantia nigra, in pallidal glial cells or interneurons, and in distinct cell layers and regions of the hippocampus. The study serves as a precursor for a database resource allowing evaluation of the suitability of different promoter mouse lines for generating disease models.

Morphological characteristics of Lugaro cells in the cerebellar cortex

Two types of Lugaro cells were identified in the cat cerebellar cortex using sections impregnated with silver nitrate by the Golgi-Kopsch method; these cells were fusiform and triangular and their bodies were located at different levels in the granular layer. Their processes were directed horizontally, vertically, or obliquely to the axis of the leaf; axons never left the cerebellar cortex. These cells should therefore be regarded as interneurons. The processes of Lugaro cells were very extended, with the result that these cells formed numerous axosomatic and axodendritic contacts with all cerebellar cortical neurons and fibers. The structural and topographical characteristics of Lugaro cells and the features of their contacts with other cells in the cerebellar cortex, taken together with data on their neurotransmitter contents, show that they function as inhibitory interneurons.

Loss of GABAergic neuronal phenotype in primary cerebellar cultures following blockade of glutamate reuptake

Prolonged inhibition of glutamate reuptake by L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a specific glutamate transporter blocker, reduced the number of GABA positive neurons in a primary cerebellar culture by 54%. The disappearance of immunostaining for GABA was gradual and was partially prevented by the N-methyl-D-aspartate (NMDA) receptor blocker, MK-801, and the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist, NBQX. Combined blockade of NMDA and AMPA receptors restored the original proportion of GABAergic neurons observed in control cultures. Following the PDC exposure, expression of other GABAergic markers, such as glutamic acid decarboxylase (GAD) and vesicular GABA transporter (VGAT) was also dramatically decreased in an AMPA receptor-dependent manner. Loss of GABA or GAD immunostaining is commonly regarded as a sign of degeneration of GABAergic neurons. However, none of the GABAergic neurons were positive for propidium iodide uptake or showed abnormal nuclear morphology. Based on the above data we conclude that prolonged activation of ionotropic glutamate receptors by endogenously released glutamate was not toxic to cerebellar GABAergic neurons, but lead to the loss of their characteristic neurotransmitter phenotype.

Extending the cerebellar Lugaro cell class

We describe here, in Golgi-impregnated rat cerebellar cortex, a new group of large granular layer neurons. These cells have a globular soma located at variable depths in the granular layer, and three to four long radiating dendrites coursing through the three layers of the cortex. The axon projects more or less directly into the molecular layer, where it expands in a local plexus of oblique and tortuous thick collaterals ascending through the major part of the layer. Interestingly, the axons of several of these cells give off a collateral that courses for a long distance in the transverse direction, just above the Purkinje cell somata, parallel to the parallel fibers. While the granular layer location and the polymorphous somato-dendritic pattern of these cells is reminiscent of that of Golgi cells, their axonal pattern is clearly of the same type as that of another large granular layer interneuron, the Lugaro cell. Moreover, double anti-calretinin and anti-calbindin immunolabellings show that Lugaro cells as well as some globular somata dispersed in the granular layer are both calretinin-positive and in close apposition with numerous calbindin-positive varicosities of Purkinje cell axon recurrent collaterals. These latter are known from previous ultrastructural studies to be pre-synaptic to Lugaro cells. The common granular layer location and calretinin labelling, the striking similarity in axonal projection pattern, and the important common recurrent afferentation by Purkinje cell axons strongly argue in favor of the classification of these globular interneurons as a subgroup of a widened Lugaro cell type.

Three-dimensional morphology of cerebellar climbing fibers. A study by means of confocal laser scanning microscopy and scanning electron microscopy

The intracortical pathway of cerebellar climbing fibers have been traced by means of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) to study the degree of lateral collateralization of these fibers in the granular Purkinje cell and molecular layers. Samples of teleost fish were processed for conventional and freeze-fracture SEM. Samples of hamster cerebellum were examined by means of CLSM using FM4-64 as an intracellular stain. High resolution in lens SEM of primate cerebellar cortex was carried out using chromium coating. At scanning electron and confocal laser microscopy levels, the climbing fibers appeared at the white matter and granular layer as fine fibers with a typical arborescence or crossing-over branching pattern, whereas the mossy fibers exhibited a characteristic dichotomous bifurcation. At the granular layer, the parent climbing fibers and their tendrils collaterals appeared to be surrounding granule and Golgi cells. At the interface between granule and Purkinje cell layers, the climbing fibers were observed giving off three types of collateral processes: those remaining in the granular layer, others approaching the Purkinje cell bodies, and a third type ascending directly to the molecular layer. At this layer, retrograde collaterals were seen descending to the granular layer. By field emission high-resolution SEM of primate cerebellar cortex, the climbing fiber terminal collaterals were appreciated ending by means of round synaptic knobs upon the spines of secondary and tertiary Purkinje cell dendrites.

Extraordinary synapses of the unipolar brush cell: an electron microscopic study in the rat cerebellum

A neglected type of neuron, termed the unipolar brush cell, was recently characterized in the granular layer of the mammalian cerebellar cortex with several procedures, including light and electron microscopic immunocytochemistry utilizing antibodies to calretinin and neurofilament proteins. Although certain features of the unipolar brush cells were highlighted in these studies, the internal fine structure was partially obfuscated by immunoreaction product. In this study, rat cerebella were prepared for electron microscopy after perfusion fixation and Araldite embedding, and folia of the vestibulo-cerebellum, where unipolar brush cells are known to be enriched, were studied by light microscopy in semithin (0.5-1 micron) sections and by electron microscopy in ultrathin sections. Unipolar brush cells were easily identified in semithin sections immunostained with antibodies to GABA and/or glycine, and counterstained with toluidine blue. The unipolar brush cells have a pale cytoplasm and are GABA and glycine negative, while Golgi cells are darker and appear positive for GABA and, for the most part, also for glycine. Sets of identification criteria to differentiate unipolar brush cells from granule and Golgi cells in standard electron micrographs are presented. The unipolar brush cells possess many distinctive features that make them easily distinguishable from other cerebellar neurons and form unusually conspicuous and elaborate synapses with mossy rosettes. The unipolar brush cell has a deeply indented nucleus containing little condensed chromatin. The Golgi apparatus is large and the cytoplasm is rich in neurofilaments, microtubules, mitochondria, and large dense core vesicles, but contains few cisterns of granular endoplasmic reticulum. In addition, unipolar brush cells contain an unusual inclusion, which invariably lacks a limiting membrane and is made up of peculiar ringlet subunits. The cell body usually emits a thin axon and is provided with a single, large dendritic trunk that terminates with a paintbrush-like bunch of branchlets. Numerous nonsynaptic appendages emanate from the cell body, the dendritic stem, and the branchlets. The appendages contain rare organelles and lack neurofilaments. The branchlets contain numerous mitochondria, neurofilaments, large dense core vesicles, and clusters of clear, small, and round synaptic vesicles. They form extensive asymmetric synaptic junctions with one or two mossy fibers, which indicates minimal convergence of excitatory inputs. Under the postsynaptic densities, the branchlet cytoplasm displays a microfilamentous web. Besides their contact with mossy rosettes, the branchlets form symmetric and asymmetric synaptic junctions with presumed Golgi cell boutons that contain pleomorphic synaptic vesicles, indicating that the unipolar brush cells receive an inhibitory modulation. Some of these junctions are unusually extensive.(ABSTRACT TRUNCATED AT 400 WORDS)

The candelabrum cell: a new interneuron in the cerebellar cortex

A new cell type is described in silver-impregnated sections of the rat cerebellar cortex, uniformly distributed through all the cerebellar folia. The soma is rather small, roughly pyriform, vertically oriented, and squeezed, in a sandwich-like manner, between the Purkinje cell somata. One or two thick dendrites arise from the upper pole of the cell body and course through the entire molecular layer, dividing into a few, slightly oblique, branches that can reach the pia mater. These dendrites are covered with irregularly distributed spines. Some more slender dendrites emerge from the lower part of the cell body, or from the proximal trunk of a molecular dendrite, and spread tortuously for a short distance in the upper granular layer. A thick initial segment emerges directly from the soma or from the proximal portion of a dendrite, the axon winding then horizontally through or just above the Purkinje cell layer. During this horizontal course it gives off vertically oriented beaded branches ascending through the major part of the molecular layer. These branches, rather closely spaced, occupy different parasagittal planes, separated by about 10 to 30 microns. This axonal arborisation can thus be compared with a candelabrum. The peculiar three-dimensional spread of the axonal collaterals suggests a functional relationship between these branches and the dendritic trunks of neighbouring Purkinje cells. A comparative analysis of the morphological differences between this candelabrum interneuron and the other corticocerebellar interneurons found in the vicinity of the ganglionic layer confirms the specificity of this new cell class.

Molecular identification of the Lugaro cell in the cat cerebellar cortex

The cerebellar cortex contains five major classes of neurons that can be differentiated from one another on the basis of their location, size, shape, and, in some cases, molecular characteristics. The cerebellar cortex also contains other, less numerous neuronal types, including the Lugaro cell, which has been described on only a few occasions. The Lugaro cell is a relative rare cell type and is characterized by a fusiform cell body with thick, horizontally oriented dendrites. It is located in or slightly below the Purkinje cell layer. Because the Lugaro cell shares some morphological characteristics with the other large granular layer neurons, it often has been classified as a Golgi cell. In the present study we have taken advantage of differences in the molecular properties of neurons and have used monoclonal antibodies to identify and classify the Lugaro cell. Three large neuronal types in the cerebellar cortex were examined with cell-type-specific antibodies: Cat-301 and Cat-304 for Lugaro cells; Rat-303 for Golgi cells; and anti-calbindin for Purkinje cells. Double label immunocytochemistry on sections of the cat cerebellum was performed with subclass- or species-specific secondary antibodies. Each of the three antibodies was selective for one of the three large neuron classes. Cat-301 and Cat-304 recognized Lugaro cells but not Golgi or Purkinje cells. Our results demonstrate that the Lugaro cells are molecularly, as well as morphologically, distinct from Purkinje and Golgi cells and thus constitute a distinct cell type in the cerebellar cortex.

Purkinje cell axon collateral distributions reflect the chemical compartmentation of the rat cerebellar cortex

Monoclonal antibody mabQ113 has been used to study the distribution of Purkinje cell axon collaterals in the rat cerebellar cortex. MabQ113 recognizes a polypeptide antigen, zebrin I, that is confined to a subset of Purkinje cells. Antigenic Purkinje cells are arranged in parasagittal compartments running throughout the cortex. No other cerebellar cells are immunoreactive. Immunoreactive axon collaterals are confined principally to the infraganglionic plexus with only a few extending into the molecular layer. Three probable target cells for the axon collaterals have been identified: Golgi cells, Lugaro cells, and other Purkinje cells. About 90% of immunoreactive axon collaterals in the anterior lobe are located beneath the mabQ113+ Purkinje cell compartment in which they originate but some do invade the neighboring mabQ113- territory. In the anterior lobe vermis, the distribution of invading mabQ113+ collaterals is not symmetrical, such that the probability of an invading collateral from the P2+ compartment is greater at the medial boundary into P1- than at the lateral into P2-. The distribution of immunoreactive collaterals is consistent with their playing a role in synchronizing the firing of Purkinje cells within the same compartment.

The olivocerebellar projection in the rat: an autoradiographic study

The extent of the olivocerebellar projection was examined in the rat using autoradiographic techniques. In animals in which injections of [3H]leucine encompassed the whole olive unilaterally (4 cases), the vast majority of olive cells was densely labelled and climbing fibres were heavily labelled throughout the contralateral hemicerebellum, except for some small gaps which were not consistently located between cases. The multiple injections required to cover the oliver inevitably labelled cells in the reticular formation surrounding the olive, and it is possible that these neurones might also provide climbing fibres to the cerebellum. To control for this possibility, the inferior olive was pharmacologically destroyed (4 cases) prior to [3H]leucine injections similar in size and placement to those given to normal animals. Examination of the cerebellar cortex of these pretreated animals revealed no molecular layer labelling despite identification of labelled reticular neurones. It was thus demonstrated that all regions of the cerebellar cortex receive afferents from the inferior olive which terminate as climbing fibres. The distribution of these terminations over the entire cortex permits the conclusion that the inferior olive is the major source of climbing fibres in the rat. The same conclusions are reached using [3H]methionine as the tracer (4 cases).

Golgi studies on Purkinje cell development in the frog during spontaneous metamorphosis. III. Axonal development

The development and organization of Purkinje cell axons and their collaterals was studied in the bullfrog using the Golgi-Kopsch method. In the tadpole, axonal collaterals are few and usually unbranched. In the adult, however, intracortical axonal collaterals of Purkinje cells are more numerous, and they form a meager supraganglionic plexus and a more extensive infraganglionic plexus. In contrast to the pattern seen in higher vertebrates, these plexuses have a tendency to be distributed along the length of the cerebellar plate in both tadpoles and froglets. In addition, collateral branches that form intracortical plexuses apparently increase throughout the course of cerebellar development in this species.

The pattern of distribution of the local axonal collaterals of Purkinje cells in the intermediate cortex of the anterior lobe and paramedian lobule of the cat cerebellum

Purkinje cells in the intermediate cortex of the anterior lobe and paramedian lobule of the cat cerebellum were intracellularly injected with horseradish peroxidase. Light microscopic analysis of the distribution patterns of the local collaterals arising from the axons of Purkinje cells in these two cortical areas was carried out. These data suggest that the distribution of the axon collaterals is different in these two areas of the cerebellar cortex. Collaterals arising from the axons of Purkinje cells in the anterior lobe form a highly branched, densely beaded plexus which is restricted to the immediate area of the cell of origin. The axonal ramification is located primarily along the Purkinje cell layer, although a few branches extend into the deep to middle molecular layer. In contrast, collaterals derived from Purkinje cells in the paramedian lobule branch infrequently, and give rise to only a few beaded chains. They extend for great distances, up to 1 mm from the cell of origin. In some cases, collateral branches of paramedian lobule Purkinje cells course into the subcortical white matter to the opposite side of their folium of origin or extend to adjacent folia. These data suggest that the distribution pattern of recurrent collaterals within the cerebellar cortex may not be uniform. In addition, differences in distribution may be correlated with differences in the afferent and efferent organization of the two areas in the cerebellar cortex.

The parasagittal zonation within the olivocerebellar projection. I. Climbing fiber distribution in the vermis of cat cerebellum

After lesions of inferior olive, survival times of 5 to 12 days and Nauta staining, degeneration is present in white matter and central cerebellar nuclei and Deiters' nucleus. Shorter survival times from 40 to 60 hours and Fink-Heimer impregnantion reveal degenerating climbing fiber terminals in the molecular layer. With 3H-leucine autoradiography and survival times of three to seven days the entire trajectory of the climbing fibers can be traced. Olivocerebellar fibers cross in the brain stem and terminate contralaterally in cortex and central nuclei. Occasional labeling of mossy fiber terminals is explained by involvement of reticular nuclei. Small parts of the inferior olive connect with narrow longitudinal zones in the cortex through compartments in the white matter. The corresponding distribution of olivocerebellar fibers and Purkinje cell axons over these compartments suggests that the organization of the olivocerebellar and corticonuclear projection is essentially similar. Collaterals always terminate in the central cerebellar nucleus which receives a corticonuclear projection from the zone in which the parent fibers terminate. Caudal medial accessory olive projects to medial vermal zone A and to fastigial nucleus, subnucleus beta projecting to lobule VII and caudal fastigial nucleus. Caudal dorsal accessory olive projects to lateral vermal zone B in lobules I-VI, Deiters' nucleus and dorsomedial subnucleus of interposed nucleus. The caudal principal olive (dorsal cap, ventrolateral outgrowth receiving visual and vestibular input) projects to flocculo-nodular lobe.