Retarded growth of the suprachiasmatic nucleus and pineal body in dw and lit dwarf mice

The suprachiasmatic nucleus (SCN) and the pineal body in 3 types of inherited hormone-deficient mice, the dw, lit and hyt mice were examined by morphological, morphometric and biochemical techniques. In the dw and lit mice the SCN was underdeveloped. In the ventral part of the SCN, where most of the retinal fibers appeared to terminate, both cell number and cell size were decreased, although the size of the SCN was unaltered. In addition, the pineal bodies of both mice were morphologically underdeveloped and showed low levels of N-acetyltransferase activity. In contrast, the hyt SCN was comparable to the normal controls in every respect. The hyt pineal was well developed and showed levels of enzyme activity comparable to the controls. However, in all the deficient mice, the optic nerve appeared to be normal in morphological and biochemical studies. These results suggest that the underdevelopment of the pineal body, the reduced levels of spontaneous locomotion and the indistinct diurnal periodicity of the dw and lit mice might be related to the retarded neuronal growth of the SCN, and that growth hormone likely is indispensable for the development of the SCN.     

Bergmann glia require continuous association with purkinje cells for normal phenotype expression

Bergmann glia (Bg) respond to the early postnatal Purkinje cell (Pc) death in Lurcher (Lc) mutant mouse cerebellum by down-regulating expression of the enzyme glycerol-3-phosphate dehydrogenase (GPDH). To determine whether glial GPDH expression requires the continued presence of Pcs in adults, we used single intracerebellar injections of kainic acid to kill Pcs in wild-type mice from 7 weeks to 11 months old. Bg at all ages tested responded to Pc loss by down-regulating GPDH expression. To learn whether a high level of GPDH could be reinduced following down-regulation in Lc Bg, we grafted wild-type fetal Pcs into Lc cerebella. The influence of grafted Pcs on GPDH expression is host-age and implant-position dependent. Only Pcs implanted into hosts less than 6 weeks old were later found to be associated with GPDH-positive Bg. Grafted Pcs that migrated into the anterior folia of young hosts were more likely to be associated with GPDH-positive Bg than Pcs migrating to other positions. EM analysis showed that Bg ensheathment of grafted Pcs is thinner and more discontinuous, but qualitatively similar to normal. The results suggest that the interaction between host Bg and grafted Pcs can sustain elevated GPDH expression in Bg that have not yet down-regulated, but is not adequate to reinduce expression in those cells that have. © 1993 Wiley-Liss, Inc.     

Abnormal growth of the corticospinal axons into the lumbar spinal cord of the hyt/hyt mouse with congenital hypothyroidism

Thyroid hormone deficiency may cause severe neurological disorders resulting from developmental deficits of the central nervous system. The mutant hyt/hyt mouse, characterized by fetal-onset, life-long hypothyroidism resulting from a point mutation of the thyroid-stimulating hormone receptor of the thyroid gland, displays a variety of abnormalities in motor behavior that are likely associated with dysfunctions of specific brain regions and a defective corticospinal tract (CST). To test the hypothesis that fetal and neonatal hypothyroidism cause abnormal CST development, the growth of the CST was investigated in hypothyroid hyt/hyt mice and their euthyroid progenitors, the BALB/cByJ mice. Anterograde labeling with biotinylated dextran amine demonstrated a decrease in the number of CST axons in the hyt/hyt mouse at the first lumbar level at postnatal day (P) 10. After retrograde tracing with fast blue (FB), fewer FB-labeled neurons were found in the motor cortex, the red nucleus, and the lateral vestibular nucleus of the hyt/hyt mouse. At the fourth lumbar level, the hyt/hyt mouse also showed smaller CST cross-sectional areas and significantly lower numbers of unmyelinated axons, myelinated axons, and growth cones within the CST during postnatal development. At P10, the hyt/hyt mouse demonstrated significantly lower immunoreactivity of embryonic neural cell adhesion molecule in the CST at the seventh cervical level, whereas the expression of growth-associated protein 43 remained unchanged. Our study demonstrated an abnormal development of the CST in the hyt/hyt mouse, manifested by reduced axon quantity and retarded growth pattern at the lumbar spinal cord.     

Expression of the metabotropic glutamate receptor mGluR1α and the ionotropic glutamate receptor GluR1 in the brain during the postnatal development of normal mouse and in the cerebellum from mutant mice

Expression of the metabotropic glutamate receptor type 1α (mGluR1α) and the non-N-methyl-D-aspartate (NMDA) ionotropic glutamate receptor type 1 (GluR1) in mouse brain was investigated using the antibodies raised against the synthetic peptides corresponding to their C-terminal amino acid sequences. Both receptor proteins are glycosylated predominantly in an asparagine-linked manner, and are abundant in post-synaptic membranes. We showed that mGluR1α and GluR1 expression within the first 3 postnatal weeks undergoes dramatic changes in time and space, i.e., in the hippocampus and cerebellum. These spatio-temporal expression patterns appear to be correlated with the postnatal ontogenesis and establishment of the glutamatergic neurotransmission system in the hippocampus and cerebellum, cell migration, dendritic and axonal growth, spine formation, and synaptogenesis. In the adult cerebellum, mGluR1α is intensely expressed in Purkinje neurons and GluR1 in Bergmann glial cells. Both receptors are expressed to a fair degree in weaver mutant cerebellum despite granule cell degeneration. However, the intrinsic expression levels of both mGluR1α and GluR1 are markedly reduced in the cerebellum of the Purkinje cell-deficient and underdeveloped mutant mice, Purkinje-cell-degeneration, Lurcher, and staggerer, suggesting that GluR1 expression in Bergmann glia cells may be correlated with the sustained interaction with adjacent Purkinje neurons. © 1993 Wiley-Liss, Inc.     

DNER as key molecule for cerebellar maturation

Notch signaling plays an important role in the process of cell-fate assignation during nervous system development. DNER is a neuron-specific transmembrane protein carrying extracellular EGF-like repeats and is expressed in somatodendritic regions. In vitro studies demonstrated that DNER mediates Notch signaling by cell-cell interaction. In the cerebellum, DNER is abundantly expressed in Purkinje cells and moderately in granule cells. DNER-knockout mice showed motor discoordination. The mutant cerebellum showed morphological impairments of Bergmann glia and multiple innervation between climbing fibers and Purkinje cells. Moreover, glutamate clearance at the synapses between parallel fibers and Purkinje cells was significantly weakened, and the expression of GLAST, a glutamate transporter in Bergmann glia, was reduced in the mutant cerebellum. Therefore, DNER contributes to the morphological and functional maturation of Bergmann glia via the Notch signaling pathway, and is essential for precise cerebellar development.     

The toppler mouse: a novel mutant exhibiting loss of Purkinje cells

We describe the genetic and neurological features of toppler, a spontaneous autosomal mutation that appeared in a colony of FVB/N mice and that manifests as severe ataxia appearing at around 12 days of age, worsening with age. The lifespan of affected mice is 8-12 months, with occasional mice living longer. Both homozygous males and females are fertile, and females are able to nurture litters. Histological examination of brain revealed no striking abnormalities other than the loss of cerebellar Purkinje cells. The toppler mutation was mapped to mouse chromosome 8, and to assess whether it was novel or a recurrence of a previously described chromosome 8 mouse mutant, toppler mice were crossed with the nervous and tottering mouse mutants. These studies demonstrate that toppler is a unique mouse mutation. Purkinje cell abnormalities in toppler mice were obvious around postnatal day (P) 14, i.e., toppler Purkinje cells already exhibited abnormal morphology. Staining for calbindin, a calcium binding protein enriched in Purkinje cells, showed altered dendritic morphology. Between P14 and P30, dramatic Purkinje cell loss occurred, although there were differences in the degree of Purkinje cell loss in each lobule. At P30, the surviving Purkinje cells expressed zebrin II. From P30 through 6 months, many of the remaining Purkinje cells gradually degenerated. Purkinje cell loss was analyzed by terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL), and Purkinje cells were TUNEL-positive most abundantly at P21. In addition, Bergmann glia were TUNEL positive at P21, and they expressed activated caspase-3 at earlier time points. Interestingly, despite the apparent death of some Bergmann glia, there was up-regulation of glial fibrillary acidic protein, expressed in astrocytes as well as Bergmann glia. Given the changes in both Purkinje cells and glia in toppler cerebellum, this may be a very useful model in which to investigate the developmental interaction of Purkinje cells and Bergmann glia.     

Influence of thyroid hormones on rat cerebellar cell aggregation and survival in culture

In order to study the effect of thyroid hormones on rat cerebellar granule cells, cerebellar perikarya isolated from 5-7-day-old rats were cultured in the presence of normal fetal calf serum, fetal calf serum treated with Dowex-2 ion exchange resin to remove thyroid hormones, or ion exchange-treated serum resupplemented with physiological concentrations of T4 and T3. Granule cells grown under hypothyroid conditions showed abnormal cellular aggregation, neurite fasciculation and cell survival. Cell aggregation, which may be an in vitro correlate of cerebellar granule cell migration to the internal granule layer, was reduced by over 50% under hypothyroid conditions. The rate of protein synthesis in hypothyroid cultures was stimulated by as much as 3-fold compared to thyroid hormone-containing cultures consistent with a proposal that the normal developmental pattern of diminishing protein synthesis specific activity is delayed or prevented under hypothyroid conditions. In addition ultrastructural studies revealed abnormalities in the density of cold-stable microtubules in thyroid hormone-deficient cultures. These results demonstrate that thyroid hormones can influence granule neuron behavior in the absence of Purkinje cells. Furthermore, the observed defects bear numerous similarities to documented abnormalities within the hypothyroid cerebellum, suggesting that this in vitro culture system may serve as a useful model for studying the mechanism of action of thyroid hormones on the cells of the cerebellum.     

5'-Nucleotidase of cerebellar molecular layer: reduction in Purkinje cell-deficient mutant mice

The molecular layer of the cerebellar cortex contains high levels of the enzyme 5'-nucleotidase (EC 3.1.3.5), localized predominantly to Bergmann glia. In the present study, histochemical methods have been employed to examine the distribution of cerebellar 5'-nucleotidase in mice of two separate mutant strains in which Purkinje cells are eliminated selectively. In homozygous 'Purkinje cell degeneration' (pcd) and 'nervous' (nr) mice, molecular layer 5'-nucleotidase is greatly reduced and residual enzyme activity in colocalized with surviving Purkinje cells. These results suggest strongly that the expression of 5'-nucleotidase activity by Bergmann glia is under the inductive influence of their associated Purkinje cells.     

Creatine Kinase Isoenzymes in Chicken Cerebellum: Specific Localization of Brain-type Creatine Kinase in Bergmann Glial Cells and Muscle-type Creatine Kinase in Purkinje Neurons

Creatine kinase isoenzymes were localized in the chicken cerebellum by the use of isoenzyme-specific anti-chicken creatine kinase antibodies. Brain-type creatine kinase was found in high amounts in the molecular layer, particularly in Bergmann glial cells but also in other cells of the cerebellar cortex, e.g. in astrocytes and in the glomerular structures, as well as in cells of the deeper nuclei. A mitochondrial creatine kinase isoform was primarily localized to the glomerular structures in the granule cell layer and was also identified in Purkinje neurons. Surprisingly, a small amount of the muscle-type creatine kinase isoform was identified in cerebellar extracts by immunoprecipitation, immunoblotting and native enzyme electrophoresis, and was shown to be localized exclusively in Purkinje neurons. Cell type-specific expression of brain- and muscle-type creatine kinase in Bergmann glial cells and Purkinje neurons, respectively, may serve to adapt cellular ATP regeneration to the different energy requirements in these specialized cell types. The presence of brain-type creatine kinase in Bergmann glial cells and astrocytes is discussed within the context of the energy requirements for ion homeostasis (K⁺ resorption), as well as for metabolite and neurotransmitter trafficking. In addition, the presence of muscle-type creatine kinase in Purkinje neurons, which also express other muscle-specific proteins, is discussed with respect to the unique calcium metabolism of these neurons and their role in cerebellar motor learning.     

Cocaine induces the expression of homer 1b/c, homer 3a/b, and hsp 27 proteins in rat cerebellum

The long homer proteins 1b/c, 2a/b, and 3a/b play an important role in postsynaptic neurons by clustering glutamate receptors and by coupling the receptors with various intracellular effectors. Using immunohistochemistry and Western-blot analysis, this study shows that the expression of the long homer isoforms 1b/c and 3a/b was induced in rat cerebellum in response to cocaine administration. Acute treatment produced a very robust induction of both constitutive isoforms, whereas repeated treatment for 10 days induced a large expression of homer 1b/c and a more modest increase in the expression of the 3a/b isoform. The heat shock protein hsp 27 was also considerably induced in the cerebellum of cocaine-treated rats, suggesting that it participates in assisting the correct folding of proteins, and by counteracting oxidative stress mechanisms triggered by the psychostimulant. In addition of being expressed in Purkinje neurons, homer 3a/b and hsp 27, but not homer 1b/c, were localized within Bergmann glial cells and in their extensions, which surround Purkinje cells, as assessed by coimmunoreactivity with glial fibrillary acidic protein. Cocaine was also found to induce both proteins in the Bergmann glial cells. Since we found that homer 3a/b colocalized with the mGluR1 receptor in Purkinje cells, the data suggest that the long homer isoforms are involved in the cocaine-induced neuroplasticity that takes place in the cerebellum, by reshaping postsynaptic densities in Purkinje cell dendrites.     

Glial S100B Positive Vacuoles In Purkinje Cells: Earliest Morphological Abnormality In SCA1 Transgenic Mice

Spinocerebellar ataxia-1 (SCA1) is caused by the expansion of a polyglutamine repeat within the disease protein, ataxin-1. The overexpression of mutant ataxin-1 in SCA1 transgenic mice results in the formation of cytoplasmic vacuoles in Purkinje neurons (PKN) of the cerebellum. PKN are closely associated with neighboring Bergmann glia. To elucidate the role of Bergmann glia in SCA1 pathogenesis, cerebellar tissue from 7 days to 6 wks old SCA1 transgenic and wildtype mice were used. We observed that Bergmann glial S100B protein is localized to the cytoplasmic vacuoles in SCA1 PKN. These S100B positive cytoplasmic vacuoles began appearing much before the onset of behavioral abnormalities, and were negative for other glial and PKN marker proteins. Electron micrographs revealed that vacuoles have a double membrane. In the vacuoles, S100B colocalized with receptors of advanced glycation end-products (RAGE), and S100B co-immunoprecipated with cerebellar RAGE. In SCA1 PKN cultures, exogenous S100B protein interacted with the PKN membranes and was internalized. These data suggest that glial S100B though extrinsic to PKN is sequestered into cytoplasmic vacuoles in SCA1 mice at early postnatal ages. Further, S100B may be binding to RAGE on Purkinje cell membranes before these membranes are internalized.     

Comparative anatomy of the cerebellar cortex in mice lacking vimentin, GFAP, and both vimentin and GFAP

In the cerebellum of adult mammals, glial fibrillary acidic protein (GFAP) and vimentin (VIM) are coexpressed in Golgi epithelial cells (GEC), also known as Bergmann glia. In this study we used three transgenic knockout mice (GFAP, VIM and double GFAP and VIM) to analyze the involvement of these proteins in the building of glial filaments and in neuron-glia interactions. The cerebella of VIM, GFAP, and GFAP/VIM mutant mice were processed by the rapid Golgi method and also for electron microscopy. In VIM mutant mice, Bergmann fibers are hypertrophic with thickened appendages. In the electron microscope they appear as large glial profiles devoid of glial filaments, with embedded dendritic thorns and parallel fiber boutons. In addition, signs of degeneration are observed in Purkinje cells. In GFAP mutant mice, GEC exhibit fine, delicate processes, as those seen in wild-type animals, however, a large accumulation of lamellae and granular appendages was observed along their surfaces, which came into contact with each other. The electron microscope exhibited fine and scarce astroglial profiles containing some glial filaments, a stunted glia limitans, and the presence of large extracellular spaces. In double mutant mice, the two phenotypes are expressed but appear attenuated, with a total absence of glial filaments and the general appearance of immaturity for GEC. In conclusion, it appears that the absence of each of the proteins yields a specific phenotype and that the defects are not necessarily additive.     

Tissue plasminogen activator mRNA expression in granule neurons coincides with their migration in the developing cerebellum

Tissue plasminogen activator activity in the developing cerebellum, as quantified by zymography of cerebellar homogenates from embryonic day (E) 17 to adult mice, shows a peak of activity at postnatal day (P) 7, followed by a steady 75% decrease into adulthood. Northern blot analysis reveals a similar pattern for tissue plasminogen activator mRNA levels, which are low at E17 but increase dramatically, reaching their highest levels of specific mRNA/μg RNA in P1–P7 mice and declining about threefold in the adult mouse. In situ hybridization of whole mouse brain sections with a tissue plasminogen activator antisense cRNA probe shows pronounced reactivity in the cerebellum. Although some binding is associated with the cerebellar meninges, the external granule layer is devoid of tissue plasminogen activator mRNA at all ages. However, highly labeled elongated cells, which also bind antibody to neuronal nuclear antigen and are adjacent to Bergmann glial fibers (i.e., migrating granule neurons), are readily visible throughout the molecular and Purkinje layers at P7 and P14. In the adult mouse cerebellum, tissue plasminogen activator mRNA labeling is restricted to cells in the Purkinje/internal granule layers. Thus, tissue plasminogen activator gene expression is induced as granule neurons leave the external granule layer and begin their inward migration. © 1995 Wiley-Liss, Inc.     

Hypothyroidism reduces the rate of slow component A (SCa) axonal transport and the amount of transported tubulin in the hyt/hyt mouse optic nerve.

Thyroid hormone deficiency in the developing brain leads to disorders of neuronal process growth. This is evidenced by reduced axonal and dendritic size and complexity (Garza et al.: Developmental Brain Research 43:287-297, 1988; Ruiz-Marcos: Iodine and the Brain. New York: Plenum Press, pp 91-102, 1989). These findings may be related to alterations in the neuronal cytoskeleton in hypothyroidism, such as reduced or abnormal microtubular number and density (Faivre et al.: Developmental Brain Research 8: 21-30, 1983), and altered assembly, stabilization, and composition of microtubule protein in the hypothyroid brain. Neurofilaments also contribute to axonal caliber and process stability. Similar to microtubules, certain properties of neurofilaments are altered in developing hypothyroid axons (Marc and Rabie: International Journal of Developmental Neuroscience 3: 353-358, 1985; Faivre et al.: Developmental Brain Research 8:21-30, 1983) that may affect axonal caliber and process stability. Normal process growth is predicted on formation of appropriate numbers of microtubules and on the normal synthesis and axonal transport of cytoskeletal components [tubulin, microtubule associated proteins (MAPs), and neurofilament proteins]. Hypothyroidism might alter the neuronal cytoskeleton and neuronal growth either by affecting the developmental programs for expression of specific isoforms of cytoskeletal proteins or by changing the delivery of cytoskeletal proteins via slow axonal transport, particularly slow component a (SCa). Previous studies had demonstrated changes in the amount of specific microtubule protein isoforms and mRNAs (Stein et al.: Iodine and the Brain. New York: Plenum Press, pp 59-78, 1989a). To further elucidate the molecular basis for process growth abnormalities in the hypothyroid brain, we investigated slow axonal transport in the mouse to determine the effects of thyroid hormone deficiency on the rate and composition of SCa. Comparisons of SCa in the optic nerve of hyt/hyt hypothyroid mouse and euthyroid hyt/+ littermates and euthyroid progenitor strain, BALB/cBY +/+ mice, indicated that the velocity of SCa was significantly reduced in hyt/hyt optic nerve relative to hyt/+ and +/+. The axonal transport rate for tubulin, which is carried in SCa, was 0.118 mm/day in the hyt/hyt optic nerves. This rate was significantly different for the tubulin rates for the hyt/+ optic nerves (0.127 mm/day) and for the +/+ optic nerves (0.138 mm/day). Neurofilament proteins, as measured by the 140,000 daltons component, NFM, also appeared to be reduced in velocity in the hyt/hyt versus the hyt/+ and +/+ optic nerves.(ABSTRACT TRUNCATED AT 400 WORDS)     

Loss of adenomatous polyposis coli in Bergmann glia disrupts their unique architecture and leads to cell nonautonomous neurodegeneration of cerebellar Purkinje neurons

The tumor suppressor adenomatous polyposis coli (APC) is a multifunctional protein that inhibits the Wnt/beta-catenin signaling pathway and regulates the microtubule and actin cytoskeletons. Using conditional knockout (CKO) mice in which the APC gene is inactivated in glial fibrillary acidic protein (GFAP)-expressing cells, we show a selective and critical role for APC in maintaining the morphology and function of cerebellar Bergmann glia, which are specialized astroglia that extend polarized radial processes from the Purkinje cell layer to the pial surface. APC-CKO mice developed Bergmann glia normally until the accumulation of beta-catenin started around postnatal day 10 (P10). Their radial fibers then became shortened with a marked reduction of branching collaterals and their cell bodies translocated into the molecular layer followed by loss of their pial contact and transformation into stellate-shaped cells by P21. Purkinje neurons were normal in appearance and number at P21, but there was significant loss of Purkinje neurons and cerebellar atrophy by middle age. Outside the cerebellum, neither beta-catenin accumulation nor morphological changes were identified in GFAP-expressing astroglia, indicating region-specific effects of APC deletion and an essential role for APC in maintaining the unique morphology of Bergmann glia as compared with other astroglia. These results demonstrate that loss of APC selectively disrupts the Bergmann glial scaffold in late postnatal development and leads to cerebellar degeneration with loss of Purkinje neurons in adults, providing another potential mechanism for region-specific non-cell autonomous neurodegeneration.     

Glial pathology in development of cerebellar dysplasia in the hereditary cerebellar vermis defect (CVD) rat

The cerebellar vermis defect (CVD) rat is a new neurological mutant characterized by a cerebellar vermis defect and dysplasia in the cerebellum, especially at the cerebellopontine junctions. In this study, the cytokinetics of glia in terms of the development of cerebellar dysplasia in the CVD rat was investigated using glial fibrillary acidic protein (GFAP) and vimentin immunohistochemistry. In the cerebellar hemispheres, dislocation of the Bergmann glia was observed from postnatal day 5 (P5) in lesions with abnormally aggregated external granule cells (EGCs). Rearranging Bergmann glia were often seen around the EGCs penetrating into the white matter. In the cerebellopontine junctional areas, Bergmann glia were induced after penetration of the Purkinje cells, identified with calbindin immunohistochemistry, and EGCs into the pons from P10. Bergmann fibers were frequently arranged perivascularly. In the clusters of Purkinje cells without EGC settlement in the pons, a small number of Bergmann fibers were observed and their alignment was completely disturbed. These findings suggest that morphological changes in the Bergmann glia depend on their contact with Purkinje cells, but that the orientation of their processes may be influenced by EGC settlement. These glial fibers in the CVD rat may play an important role in the aberrant migration of EGCs, resulting in the development of cerebellar dysplasia. Received: 13 April 1999 / Revised, accepted: 20 July 1999     

Consequences of combined maternal, fetal and persistent postnatal hypothyroidism on the development of auditory function in Tshrhyt mutant mice

Tshrhyt/hyt mutant mice express a point mutation in the gene encoding the thyrotropin receptor, and affected animals are congenitally hypothyroid and profoundly deaf as a consequence when the condition is untreated. In this investigation, a previously unrecognized developmental stage was identified in the hypothyroid, mutant progeny of hypothyroid dams by tracking developmental changes in the auditory brainstem response (ABR). ABR thresholds develop rapidly in normal, euthyroid animals, decreasing as much as 80 dB between P12 (postnatal day 12) and P15, with mature sensitivity being gradually acquired by P18. In contrast, Tshrhyt/hyt mutant mice remained profoundly deaf on P24 and although thresholds improved by approximately 30 dB by P60, residual frequency-dependent deficits of 20-70 dB were observed in animals exhibiting end-stage disease. The rate of threshold improvement in mutant mice was approximately ten times slower than in normal mice. While ABR wave latencies and interpeak intervals decreased early in postnatal life, values decreased over a delayed and protracted time period, reaching adult values well after those of controls attained maturity. As with normal mice, slopes of wave I latency-intensity curves were significantly steeper in immature animals than those observed in adults and decreased during development, but failed to achieve normal adult values and remained significantly steeper than those for controls. Findings reported here suggest that passive aspects of electromechanical transduction achieve maturity in Tshrhyt/hyt progeny of Tshrhyt/hyt mice and that development, limited as it may be, occurs most prominently in the basal half of the cochlea.     

Autoradiographic analysis of sulfate metabolism in the cerebellum of the mouse

The metabolism of [³⁵S]sulfate in the cerebellum of young adult mice was studied by autoradiography. Labeled sulfate was concentrated in the cytoplasma near the nucleus of capillary endothelial cells, Bergmann glia, oligodendroglia, and Purkinje cells. A few neurons in the granular layer took up small amounts of radiosulfate. Utilization of inorganic sulfate by other cerebellar cells, with the possible exception of astrocytes, was negligible. This measns that production of sulfate materials in the cerebellum is not specifically a glial or neuronal function, but is a characteristic of certain glial cells and certain neurons, as well as the cells which line the capillary bed.

The sulfated compounds did not remain where they were produced. Instead, they were redistributed throughout all the layers of the cerebellum. Oligodendroglia deposited sulfated material in myelin, presumably in the form of sulfated lipids (sulfatides). In Purkinje cells the radioactive material (probably sulfated mucopolysaccharide) spread into the dendrites which ramify in the molecular layer. This indicates that the process of cytoplasmic flow occurs in dendrites as well as axons. Part of the labeling of the molecular layer could be accounted for by assuming a comparable process of cytoplasmic flow in the Bergmann glia.     

Modulation of AMPA receptor subunits GluR1 and GluR2/3 in the rat cerebellum in an experimental hepatic encephalopathy model

The immunohistochemical expression and distribution of the AMPA-selective receptor subunits GluR1 and GluR2/3 were investigated in the rat cerebellum following portocaval anastomosis (PCA) at 1 and 6 months. With respect to controls, GluR1 and GluR2/3 immunoreactivities increased over 1 to 6 months following PCA, although immunolabelling patterns for both antibodies were different at the two analysed times. GluR1 immunoreactivity was expressed by Bergmann glial cells, which showed immunoreactive glial processes crossing the molecular layer at 6 months following PCA. The GluR2/3 subunit was expressed by Purkinje neurons and moderately expressed by neurons of the granule cell layer. Immunoreactivity for GluR2/3 was detectable in cell bodies and dendrites of Purkinje cells in young control cerebella, whereas GluR2/3 immunoreactivity was scarce 1 month post PCA. However, despite a lack of immunoreactivity in the Purkinje somata and main processes of adult control rats, GluR2/3 immunoreactivity was strongly enhanced in Purkinje neurons following long-term PCA. These findings suggest that the localization of the GluR2/3 subunit in Purkinje cells undergoes an alteration and/or reorganization as a consequence of long-term PCA. The combination of enhanced GluR immunoreactivity in long-term PCA, both in Bergmann glial cells and in Purkinje neurons, suggests some degree of neuro-glial interaction, possibly through glutamate receptors, in this type of encephalopathy.