Recurrent hemoptysis following a systemic-to-pulmonary anastomosis in a child with a complex congenital cardiomyopathy

A 14-year-old boy with a history of congenital cardiopathy is presented. At age 4, a left systemic-to-pulmonary fistula was performed, using a tubular prosthesis to anastomose the left subclavian artery to the left pulmonary artery. Following this procedure, he developed recurrent episodes of hemoptysis, cough, and left upper lobe consolidation. Treatment resulted in clinical but no radiologic resolution. At age 6, a new right systemic-to-pulmonary anastomosis was needed, as the left one was no longer functioning. After placement of the second shunt, the hemoptysis disappeared. At age 14, flexible bronchoscopy revealed a foreign body granuloma at the left secondary carina. Rigid bronchoscopy and laser photoresection showed it to be the left vascular prosthesis, placed 10 years before. Surgery failed to remove it.

Reactive gliosis of immature Bergmann glia and microglial cell activation in response to cell death of granule cell precursors induced by methylazoxymethanol treatment in developing rat cerebellum

The morphology, organization and expression of proliferating cell nuclear antigen (PCNA) and the cytoskeletal proteins vimentin and GFAP in immature Bergmann glial cells were studied after a developmental injury induced by a single dose of the cytotoxic agent methylazoxymethanol (MAM) administered on postnatal day 5. This drug, which produces cell death of cerebellar granule cell precursors, did not induce apoptosis in Bergmann glial cells, which are in a proliferative stage. After MAM treatment, PCNA staining showed a severe depletion of PCNA-positive granule cell precursors, whereas PCNA-positive Bergmann glial nuclei in the Purkinje cell layer were preserved. Moreover, the quantitative analysis revealed an increase in the density of both Purkinje cells and PCNA-positive Bergmann glial cells per mm of Purkinje cell layer in MAM-treated rats relative to age-matched controls, but the numerical ratio between these two cell populations remains invariable after MAM treatment. Vimentin and GFAP immunocytochemistry revealed a reinforcement of the Bergmann glial palisade with overexpression of both proteins and thicker immunoreactive glial processes in MAM-treated rats. At the ultrastructural level, Bergmann glial processes closely associated with dying cells in different stages of apoptosis were observed. Frequently, these processes enclosed dying cells in extracellular compartments. Furthermore, phagosomes containing apoptotic bodies were found in Bergmann fibers of MAM-treated rats. These data indicate that the cell death of granule cell precursors triggers a reactive response in immature Bergmann glia. We suggest that this response reflects the plasticity of Bergmann glia to control the neuronal microenvironment in the maturing molecular layer, protecting healthy cells against the potentially harmful contents of dying cells. In situ labeling of cell death with the TUNEL method revealed that the cell death of granule cell precursors is of the apoptotic type. The participation of ameboid microglial cells in the phagocytosis of apoptotic cells was shown with tomato lectin histochemistry and ultrastructural analysis. Moreover, the presence of mitosis in this microglial population demonstrates its proliferative activity in regions of extensive cell death.

Acute osmotic/stress stimuli induce a transient decrease of transcriptional activity in the neurosecretory neurons of supraoptic nuclei

Administration of hypertonic NaCl solutions by intraperitoneal injection evokes a transient expression of immediate-early genes in the hypothalamic magnocellular neurons of supraoptic nuclei (SON), which is followed by an upregulation of arginine vasopressin synthesis and a general increase in cellular metabolic activity. Here we have analysed the changes that occur in the nucleus of SON neurons during the period of transient Fos expression after injection of hypertonic saline. Within the first 30 minutes after injection, the nuclei become significantly smaller, contain more condensed chromatin and incorporate less 3H-uridine than the controls. By 12 hours these effects are reverting and at 24 hours the nuclei are already more active than the controls. Additionally, we observe an initial decrease in the number of coiled bodies per nucleus within the first 2 hours, followed by a 3-fold increase at 24 hours after injection. As coiled bodies are transcription-dependent subnuclear 'organelles', these results further support the view that injection of hypertonic saline causes a transient inhibition of nuclear activity. Our data show that SON neurons respond to acute osmotic/stress stimuli first with inhibition and then with activation of gene expression. Importantly, inhibition of transcriptional activity occurs simultaneously with maximal accumulation of Fos protein in the nucleus, raising the possibility that activation of c-fos expression may cause repression of target genes.

Tumor necrosis factor-alpha enhances antitumor effects of radiation against glioma xenografts

Long-term control of high-grade brain tumors is rarely achieved with current therapeutic regimens. The aim of this study was to determine if low doses of tumor necrosis factor-alpha (TNF-alpha) could augment the effects of radiation in a glioma xenograft model and to evaluate hematological and other parameters that might indicate treatment-related toxicity. Nude mice were injected subcutaneously with C6 rat glioma cells and randomized into groups. Two different time-dose protocols were employed using intravenous human recombinant TNF-alpha and radiation beginning within 24 h after tumor cell implantation. The administration of radiation as a single agent slowed tumor progression, whereas TNF-alpha alone had no effect. However, TNF-alpha, especially when given twice per week before radiation for a total of four doses each, significantly increased the efficacy of the radiation. Low leukocyte counts were associated with combination treatment, whereas transforming growth factor-beta 1 levels were depressed in all treated groups. TNF-alpha did not modulate radiation-induced inhibition of C6 cell proliferation in vitro. The data show that TNF-alpha at relatively nontoxic doses can significantly enhance the antitumor effects of radiation against a rapidly growing glioma. This effect was more than additive, because TNF-alpha alone did not slow tumor progression.

Apoptosis induced by methylazoxymethanol in developing rat cerebellum: organization of the cell nucleus and its relationship to DNA and rRNA degradation

We present a cytological and biochemical study of the cell death of granule cell precursors in developing rat cerebellum following treatment with the cytotoxic agent methylazoxymethanol (MAM) during the first postnatal week. The density of apoptotic figures per square millimeter progressively increases after 6, 12, 24 and 44 h of treatment, whereas cells immunoreactive for proliferating cell nuclear antigen tend to disappear in the external granular layer (EGL). DNA migration on gel electrophoresis reveals a typical ladder pattern of internucleosomal cleavage following MAM treatment, whereas gel electrophoresis of rRNA shows a conspicuous degradation of both 28S and 18S rRNAs. Ultrastructural analysis has revealed the alterations of structures containing chromatin and ribonucleoprotein (RNP) in dying cells of the EGL. The typical granular beaded configuration of the condensed chromatin changes to a denser, more homogeneous texture suggesting nucleosomal disruption. The reorganization of RNP nuclear domains is reflected by the appearance of dispersed nucleoplasmic RNP particles and the formation of a coiled-body-like structure. However, typical nuclear domains involved in the splicing of RNAs, namely interchromatin granule clusters and typical "coiled bodies", are not found in apoptotic cells. Intranuclear bundles of filaments have also been detected. In the cytoplasm, the presence of dispersed single ribosomes is an initial sign of apoptosis. The massive dispersion and disruption of ribosomes detected after 24 h and 44 h of MAM treatment is reflected by the degradation of both 28S and 18s rRNAs. These results show that MAM treatment provides a useful experimental model for the study of apoptosis in the developing central nervous system. The organization of the cell nucleus in cells undergoing apoptosis clearly reflects a disruption of the nuclear compartments involved in transcription and the processing and transport of RNA and is related to the patterns of DNA and rRNA degradation.

Schwann cell nuclear remodelling and formation of nuclear and coiled bodies in Guillain-Barré syndrome

We have examined the reorganization of the cell nucleus in myelin-related Schwann cells (SCs) in a case of acute Guillain-Barré syndrome (GBS). Spinal root samples of the GBS case and human controls were processed for light and electron microscopy. The cytochemical EDTA method for ribonucleoproteins (RNPs) and a specific silver staining technique for nucleolar organizer regions were used on ultrathin sections. In SCs of the GBS case, we observed a significant increase in nuclear size (64.99 +/- 10.47 microns 2 in the GBS vs 35.07 +/- 8.74 microns 2 in the controls, mean +/- SD) accompanying partial decondensation of heterochromatin domains and elaboration of an extensive network of RNP-containing perichromatin fibrils. In addition, the formation of two types of nuclear structures, coiled bodies and nuclear bodies of Bouteille, was induced in SCs of the case of acute GBS. Free coiled bodies were observed in the nucleoplasm and were characteristically stained with both RNP and silver procedures. Typical "simple" and "complex" nuclear bodies were regularly found, sometimes in association with coiled bodies. On the basis of cell nucleus physiology, all of these changes are considered cytological indicators of enhanced transcription and cellular hyperactivity, and they seem to reflect a reactive response of SCs triggered by the constellation of cellular and humoral signals associated with acute GBS.

Age-induced hypertrophy of astrocytes in rat supraoptic nucleus: a cytological, morphometric, and immunocytochemical study

BACKGROUND

In the adult rat, neuron-astroglia interactions in the supraoptic nucleus (SON) are characterized by the structural and functional plasticity of astrocytes in response to several physiological and experimental conditions. This study has analyzed the plasticity of the supraoptic nucleus astrocytes in response to the age-induced changes in neuronal activity.

METHODS

The study was performed in 5-, 12-, 18- and 24-month-old rats. The cytology and organization of astrocytes in the SON were examined using glial fibrillary acidic and vimentin immunocytochemistry and ultrastructural and morphometric analysis.

RESULTS

No significant age-related variations in the total number of neurons and astrocytes in the SON were detected, although a few degenerating neurons were found in old rats. An age-dependent increase in GFAP immunoreactivity was observed at the ventral glial lamina, perivascularly and between neuronal perikarya. Vimentin overexpression was also detected in ventral lamina astrocytes with advancing age. At the cell nucleus level, we observed an age-associated increase in nuclear size and in the number of coiled bodies, nuclear bodies, and "cleared" nucleoplasmic areas, as well as changes in the nucleolar organization. At the cytoplasmic level, characteristic ultrastructural features in astrocytes of old rats were the hypertrophy of intermediate filament bundles and the formation of an extensive network of Golgi stacks interlinked by tubulovesicular elements. Glial filaments were often associated with the nuclear envelope and polyribosomes.

CONCLUSIONS

The increased GFAP and vimentin immunoreactivity and the morphometric and cytological changes in rat SON astrocytes may reflect a sustained upregulation of cellular activity with age, resulting in hypertrophy of glial perikarya and cell processes. Several factors that are known to influence the expression of the astrocytic phenotype, such as signals produced by degenerating neurons and activated microglia, as well as variations in neuronal activity are considered possible causes of the age-associated changes in SON astrocytes.

Effects of cycloheximide on the structural organization of the nucleolus and the coiled body in normal and stimulated supraoptic neurons of the rat

This study was designed to determine the effects of cycloheximide, a protein synthesis inhibitor that interferes with rRNA synthesis and processing, on the nucleoli and coiled bodies of supraoptic nucleus neurons from normally-hydrated and osmotically-stimulated rats. The number of nucleoli and the nucleolar size were estimated on smear preparations of previously silver-impregnated supraoptic nucleus. No significant differences were registered in the mean number of nucleoli per cell in cycloheximide-treated rats. The number of nucleoli per neuron remained constant, at about 1.3, in all animal groups, suggesting that the nucleoli number is strictly regulated in differentiated neurons. By contrast, a significant reduction in the average nucleolar volume of supraoptic nucleus neurons was detected in cycloheximide-treated groups of rats in comparison with their equivalent non-treated groups. By electron microscopy, most nucleoli and coiled bodies of supraoptic nucleus neurons exhibited cycloheximide-induced alterations in their fine structure and configuration. Nucleolar changes included the occurrence of a few large fibrillar centres, the formation of microspherules and small intranucleolar vacuoles or dilated interstices, and the partial segregation of nucleolar components coupled with the transformation of reticulated nucleoli--a nucleolar configuration characteristic of supraoptic nucleus neurons of non-cycloheximide-treated rats--into compact ones. The redistribution of nucleolar components might reflect the interference with rDNA transcription, and also supports the hypothesis that the normal assembly of these components into the nucleolus depends upon ongoing nucleolar transcription. Concerning coiled bodies, most of them revealed ultrastructural alterations, particularly segregation of the amorphous matrix, compactation of coiled threads and formation of coiled body-derived dense bodies of fibrillar nature. Moreover, cycloheximide also induced the formation of smaller dense bodies--here referred to as dense microbodies--which presumably represent a distinct nuclear entity different from coiled bodies. Ultrastructural silver staining of nuclear bodies showed a selective silver reaction on the dense fibrillar component of normal and altered coiled bodies, as well as on the dense microbodies. The possible relationship between the nucleolus and both coiled bodies and dense microbodies is discussed.

Apolipoprotein E expression in the cerebellum of normal and hypercholesterolemic rabbits

We have studied the expression of apolipoprotein E (ApoE) mRNA in the cerebella of control and experimental rabbits fed with a cholesterol-rich diet for 8 weeks. Cholesterol-treated rabbits show a dramatic increase in serum cholesterol levels; however, no significant variations in the expression level of cerebellar ApoE mRNA were found in comparison to control rabbits. In addition, no differences were observed between control and hypercholesterolemic rabbits in the in situ hybridization pattern of ApoE mRNA on cerebellar cortex sections. ApoE mRNA was localized in astroglial processes associated with Purkinje cell bodies and dendrites, granule cell clusters, blood vessels and nerve fibers of the white matter. No expression of ApoE mRNA was observed in Purkinje and granule cell neurons. Polarized light examination of cryostat cerebellar sections revealed the absence of cholesterol-rich microglia/macrophage cells induced by the hypercholesterolemia. In this way, neither reactive microglial cells nor perivascular phagocytes were found by ultrastructural analysis in hypercholesterolemic conditions. The pattern of glial fibrillary acidic protein of the astroglial cells of the cerebellar cortex as well as their nuclear size were unchanged following cholesterol treatment, indicating the absence of astroglial activation induced by hypercholesterolemia. Our results suggest that cerebellar ApoE does not contribute to the general cholesterol homeostasis outside of the brain and supports the view that this cerebellar ApoE is involved in paracrine and autocrine functions particularly related with synapse turnover and membrane remodelling of astroglial cells.

Nuclear Fos domains in transcriptionally activated supraoptic nucleus neurons

This study has analysed by light and electron microscopy immunolocalization the nuclear pattern of distribution of Fos-related proteins in supraotic neurons. Two experimental models of transcriptional activation have been used: sustained, global transcriptional activation, at relatively near physiological conditions, by six days of chronic intermittent salt loading; and superinduction of c-fos gene by this salt loading regime plus cycloheximide treatment for 4 h. In the first condition, the ultrastructural analysis showed a distribution of Fos-like immunoreactivity on the reticular network of dispersed chromatin that extends between the nucleolar surface and the nuclear envelope, whereas the Fos-negative adjacent interchromatin spaces appeared rich in interchromatin granules by using a cytochemical staining for ribonucleoproteins. The nucleolus associated heterochromatin, fibrillar centers of the nucleolus and coiled bodies were free of immunoreactivity. This immunoelectron pattern seems to indicate that active genes containing activator protein-1 and cyclic AMP response element recognition sites are extensively distributed in euchromatin regions and suggests that the Fos-positive nuclear domains correspond to the actively transcribing chromatin regions, at least in supraoptic neurons. It also suggests that these Fos-positive transcription domains are complementary to adjacent ribonucleoprotein-rich interchromatin spaces which are involved in the processing and splicing of pre-messenger RNA. Moreover, the absence of immunoreactivity on the fibrillar centers, the sites of pre-ribosomal RNA synthesis, suggests that the Fos protein complexes are not involved in regulating the expression of ribosomal RNA genes. Following superinduction of c-fos gene by osmotic stimulation plus cycloheximide treatment, a conspicuous Fos-like immunoreactivity was detected in dispersed chromatin regions, whereas the heterochromatin masses, nucleoli and coiled bodies showed no immunoreaction. Moreover, this treatment induced the formation of nuclear "dense bodies" of a fibrillar nature which were free of immunolabelling. Since Fos proteins are known to be short-lived, the expression of these nuclear constituents, under conditions of protein synthesis inhibition induced by the cycloheximide, suggests the stabilization of chromatin-bound Fos complexes or, alternatively, a preferential synthesis of Fos proteins.

Influences of age and hearing loss on the precedence effect in sound localization

Cranford, Boose, & Moore (1990a) reported that many elderly persons exhibit problems in perceiving the apparent location of fused auditory images in a sound localization task involving the Precedence Effect (PE). In the earlier study, differences in peripheral hearing sensitivity between young and elderly subjects were not controlled. In the present study, four groups of young and elderly subjects, matched with respect to age and the presence or absence of sensorineural hearing loss, were examined to determine the effects of these two factors on performance with the PE task. Although significantly poorer performances on the PE task were found to be associated with both increased age and hearing loss, additional tentative evidence was obtained that the presence of hearing loss may have a relatively greater detrimental effect on the performance of at least some elderly subjects than it does on younger persons.

Reactive astroglia-neuron relationships in the human cerebellar cortex: a quantitative, morphological and immunocytochemical study in Creutzfeldt-Jakob disease

In order to investigate the role of neuron-glia interactions in the response of astroglial to a non-invasive cerebellar cortex injury, we have used two cases of the ataxic form of Creutzfeldt-Jakob disease (CJD) with distinct neuronal loss and diffuse astrogliosis. The quantitative study showed no changes in cell density of either Purkinje or Bergmann glial cells in CJ-1, whereas in the more affected CJ-2 a loss of Purkinje cells and an increase of Bergmann glial cells was found. The granular layer in both CJD cases showed a similar loss of granule cells (about 60%) in parallel with the significant increase in GFAP+ reactive astrocytes. GFAP immunostaining revealed greater reactivity of Bergmann glia in CJ-2 than in CJ-1, as indicated by the thicker glial processes and the higher optical density. Granular layer reactive astrocytes were regularly spaced. In both CJD cases there was strict preservation of the spatial arrangement of all astroglial subtypes--Fañanas cells, Bergmann glia and granular layer astrocytes. Reactive Fañanas and Bergmann glial cells and microglia/macrophages expressed vimentin, while only a few vimentin+ reactive astrocytes were detected in the granular layer. Karyometric analysis showed that the increase in nuclear volume in reactive astroglia was directly related with the level of glial hypertrophy. The number of nucleoli per nuclear section was constant in astroglial cells of human controls and CJD, suggesting an absence of polyploidy in reactive astroglia. Ultrastructural analysis revealed junctional complexes formed by the association of macula adherens and gap junctions. In the molecular layer numerous vacant dendritic spines were ensheathed by lamellar processes of reactive Bergmann glia. Our results suggest that quantitative (neuron/astroglia ratio) and qualitative changes in the interaction of neurons with their region-specific astroglial partners play a central role in the astroglial response pattern to the pathogenic agent of CJD.

Protein-synthesis inhibition induces perichromatin granule accumulation and intranuclear rodlet formation in osmotically stimulated supraoptic neurons

The distribution of perichromatin granules (PGs), a storage form of pre-mRNAs, was studied in supraoptic neurons of control and osmotically stimulated rats, and also after treatment with cycloheximide, a protein-synthesis inhibitor. In non-cycloheximide-treated rats, neuronal activation by dehydration significantly decreased the number of PGs. Conversely, PGs were drastically increased in the supraoptic neurons of dehydrated rats treated with cycloheximide for 4 h. This suggests that cycloheximide does not interfere with the transcriptional activation induced by dehydration, but it affects the processing of newly synthesized pre-mRNAs. Moreover, protein-synthesis inhibition was associated with the formation of intranuclear bundles of tubular filaments.

Fos-like expression and nuclear size in osmotically stimulated supraoptic nucleus neurons

This study has analysed by immunocytochemistry the pattern of expression of Fos-related proteins, as well as variations in nuclear size, after the osmotically induced activation of supraoptic nucleus neurons of the rat. In control rats most supraoptic nucleus neurons were Fos-like negative. After acute and chronic dehydration by salt-loading, the number of Fos-like positive neurons increased dramatically. The level of Fos-like immunoreactivity was higher in chronically stimulated rats, and also the neurons of the ventral region of the supraoptic nucleus were more intensely stained than those of the dorsal region. The karyometric analysis was made on electron micrographs. The mean nuclear profile area showed a significant increase in dehydrated rats with respect to the controls (73 +/- 16 microns 2 in those dehydrated for six days vs 54 +/- 13 in controls, mean +/- S.D.). However, no significant differences in this parameter were found when one-day and six-day dehydrated groups were compared. The invagination factor of the nuclear membrane, a nuclear shape indicator, decreased significantly in dehydrated rats, indicating a tendency towards spherical nuclei. It is noteworthy that the nuclear profile perimeter was constant, about 32 microns, in control and osmotically simulated rats. The higher nuclear accumulation of Fos-related antigens after six days of dehydration suggests that in chronically stimulated supraoptic nucleus neurons there is a sustained induction of cell-specific genes. Moreover, the transcription rate of the target genes containing the consensus DNA sequence TGAC/GTCA or c-AMP responsive elements recognition sites may depend upon the nuclear concentration of Fos-related antigens in supraoptic nucleus neurons. Our results also suggest that the initial Fos-related antigen expression and nuclear size increase are triggered concomitantly in supraoptic nucleus neurons after a short period of osmotic stimulation. On the other hand, we propose that nuclear envelope invaginations represent a reservoir of nuclear membrane which allows dynamic changes in nuclear size and shape depending on the metabolic status of the supraoptic nucleus neurons.

Osmotic stimulation induces changes in the expression of beta-adrenergic receptors and nuclear volume of astrocytes in supraoptic nucleus of the rat

The influence of osmotic stimulation on the density of beta-adrenoceptor binding sites in the rat supraoptic nucleus (SON) was studied by quantitative autoradiography using 125I-cyanopindolol (ICYP). Increased density of beta-adrenoceptor binding sites was observed in osmotically stimulated rats and also after the suppression of neuronal activation by rehydration of animals. This was mainly due to a significant increase in the concentration of beta 2 binding sites. The overexpression of beta-adrenoceptors occurred concomitantly with nuclear expansion in SON astrocytes. Moreover, the higher concentration of beta-adrenoceptors observed in the ventral portion of the SON largely coincided with the area that showed intense GFAP-immunostaining. These results provide indirect evidence of an astrocytic location of beta-adrenoceptors and also of beta-adrenergic mediation in the structural and functional changes of SON astrocytes.

Organization of nucleoli and nuclear bodies in osmotically stimulated supraoptic neurons of the rat

This study has analyzed variations in the number of nucleoli and nuclear bodies, as well as in their ultrastructural and cytochemical organization, after the osmotically induced activation of supraoptic nucleus (SON) neurons of the rat. The number of nucleoli and nuclear bodies and also the nucleolar size were determined on smear preparations of previously block-impregnated SON. The mean number of nucleoli per cell was 1.35 +/- 0.6 (mean +/- SDM) in control rats. No significant variations in this value were registered either in dehydrated or rehydrated rats. The mean nucleolar volume and the total nucleolar volume per cell showed a significant increase in dehydrated rats with respect to the controls, whereas these two parameters tended to return to control values in rats rehydrated after dehydration. The mean number of nuclear bodies per cell increased significantly from 0.56 +/- 0.50 (mean +/- SDM) in control rats to 1.54 +/- 1.1 after 6 days of dehydration. By electron microscopy, SON neurons displayed a reticulated nucleolar configuration. After the osmotically induced neuronal activation, there was an increase in the proportion of the total nucleolar area occupied by the granular component, and also a reduction in the mean fibrillar-center area. The most characteristic nucleolar features in rehydrated rats were the tendency for the granular component to be segregated and the occurrence of intranucleolar vacuoles. Ultrastructural cytochemistry with a specific silver method revealed a selective silver reaction on the coiled threads of the nuclear bodies--identified as "coiled bodies"--and on the nucleolar fibrillar components in all animal groups studied. Since nucleoli play a major role in ribosome biogenesis, a relationship between these nucleolar changes and the level of cellular activity of SON neurons is proposed. Furthermore, the response of nuclear "coiled bodies" to neuronal activation suggests their participation in the processing and transport of rRNA precursors.

Cytology and organization of reactive astroglia in human cerebellar cortex with severe loss of granule cells: a study on the ataxic form of Creutzfeldt-Jakob disease

In order to investigate the cellular basis of human astrogliosis, we have selected the cerebellar cortex because it provides a relatively simple and geometrical organization of both neuronal and glial populations. A pathological system with severe and progressive loss of granule cells was studied: the ataxic form of Creutzfeldt-Jakob disease, where the tissue geometry is minimally disturbed. The quantitative study revealed a drastic reduction in the numerical density of granule cells in the Creutzfeldt-Jakob disease cerebellum, and a significant increase in the numerical density of astrocytes. Karyometric analysis showed that the nuclear area was significantly greater in reactive astroglial cells than in normal astroglia. Glial fibrillary acidic protein immunocytochemistry revealed astroglial hypertrophy, but the geometry and spatial domains of astroglial subtypes were strictly preserved. Vimentin expression was detected in Bergmann glia and in certain astrocytes of the granular layer. Ultrastructural analysis showed that reactive astroglia had large nuclei, with expanded interchromatinic regions which contained clusters of interchromatin granules and nuclear bodies, and prominent reticulate nucleoli. In the cytoplasm, hypertrophied bundles of intermediate filaments were observed, some of them associated with the nuclear envelope. Numerous adhering and gap junctions were also found among reactive astroglial cells. Perivascular glial processes showed a terminal web of intermediate filaments and a conspicuous plasmalemmal undercoat. Interendothelial tight junctions were preserved. Our results suggest that the severe loss of granule cells induces a highly ordered astroglial response which tends to preserve the geometry of the astroglial scaffold, the domains of each astroglial subtype, the neuronal microenvironmental conditions and the efficiency of the blood brain barrier, in order to promote neuron survival.

Distribution of nuclear pores and chromatin organization in neurons and glial cells of the rat cerebellar cortex

Nuclear pores were assessed on freeze-fracture replicas from different neuronal and glial cell types of the rat cerebellar cortex. Nuclear diameter and perimeter were measured on semithin sections, and nuclear surface area and volume were calculated from these data. The proportion of inner nuclear membrane in apposition to condensed chromatin was measured on thin sections. The values of nuclear pore numerical density (number/micron2) were as follows (mean +/- S.D.): Purkinje cells, 22 +/- 3; Golgi cells 17 +/- 3; granule cells, 6 +/- 4; stellate and basket cells, 6 +/- 1; protoplasmic astrocytes, 11 +/- 1; Bergmann glia, 10 +/- 1; oligodendrocytes, 6 +/- 1. The total number of nuclear pores per nucleus varied from 18,451 +/- 2,336 (Purkinje cells) to 621 +/- 394 (granule cells) among neurons, and from 1,782 +/- 162 (protoplasmic astrocytes) to 402 +/- 67 (oligodendrocytes) among glial cells. The number of nuclear pores per unit nuclear volume (number/micron3), a parameter related to nucleocytoplasmic transport capacity, varied from 15 +/- 2 in Purkinje cells to 6 +/- 4 in granule cells. The proportion of nuclear membrane free of condensed chromatin was significantly (P less than 0.01) correlated to pore numerical density and total number of pores per nucleus. Some nuclear pores were associated in clusters of two or more pores. The amount of pore clustering was measured by counting the proportion of pores associated in clusters. This proportion varied among the different cell types from 82% in Purkinje cells to 44% in stellate and basket cells. The amount of pore clustering showed a positive linear correlation to pore numerical density and pore number per nucleus. However, the proportion of pores in clusters was not significantly correlated with the amount of condensed chromatin applied against the inner nuclear membrane.