GLIAL AND NEURONAL ALTERATIONS IN THE CORPUS STRIATUM OF RATS WITH CCl4-INDUCED LIVER DISEASE

The density and size of astrocyte-, oligodendrocyte- and neurone nuclei in corpus striatum were determined in rats with CCl₄-induced liver encephalopathy by means of an electronic image analyzer. After 8 weeks of CCl₄-administration, the astrocyte number had nearly doubled, and astrocytes with increased nuclear size appeared. After 20 weeks, a reduction (appr. 25 per cent) was found in the number of nerve cells and oligodendrocytes. The total number of glial cells, however, was unchanged during the experiment; this demonstrates the need of performing differential counts when evaluating gliosis. Probably, a part of the increase in the number of astrocytes was due to a transformation from precursor cells, usually classified as oligodendrocytes. The increased number and size of astrocyte nuclei are probably connected with an enhanced astrocyte metabolic capacity due to alterations in the ammonia and amino acid metabolism.     

GLIAL CELL REACTIONS IN RATS WITH HYPERAMMONIEMIA INDUCED BY UREASE OR PORTO-CAVAL ANASTOMOSIS

The density and size of astrocyte, oligodendrocyte and neurone nuclei were determined in the corpus striatum of rats with urease-induced hyperammoniemia (plasma NH₄+-concentration about 800 μmol/l). No changes in the number of neurone nuclei were found. After 4 days the density of astrocyte nuclei increased from 13 to 23 per cent of the glial nuclei. However, the number of oligodendrocyte nuclei decreased correspondingly and the total glial nuclear number remained constant. The number of astrocyte nuclei was normalized 1 week after the 4-day period of hyperammoniemia. Moreover, intracerebral injections of colchicine at different times of the experimental period revealed no mitoses, indicating that no astrocyte divisions took place in pure hyperammoniemia. The astrocyte nuclei were of normal size in the urease animals in contrast to the animals with porto-caval anastomosis (PCA) which showed enlarged astrocyte nuclei. Thus, hyperammoniemia caused a reversible transformation of glial nuclei, but no real proliferation. A comparison of the glial reactions 4 days after a brain lesion showed the same frequency of astrocyte mitoses in control and urease animals but a higher incidence of mitoses in the PCA animals. The number of Alzheimer type I astrocytes was the same in control and PCA animals, whereas no such cells were found in the urease animals, indicating that this form of hyperammoniemia did not lead to arrest of astrocyte metaphases with subsequent formation of Alzheimer type I cells.     

Size and density of oligodendroglial nuclei in rats with CCl4-induced liver disease.

The nuclear size and density of oligodendrocytes in corpus callosum were investigated in rats with CCl4-induced hepatic encephalopathy. An increase in density (15 per cent) of oligodendroglial nuclei was found after 8 weeks of CCl4-administration. Measurements using an electronic image analysing system demonstrated a simultaneous decrease (13 per cent) in the nuclear size. It was concluded that these changes were due to an increase in the number of oligodendrocytes with small, dark nuclei. The corpus callosum did not show significant signs of axonal or myelin degeneration. In the cortical and subcortical grey matter degenerated neurones were observed; the oligodendroglial proliferation could, possibly, be a reaction to neuronal degeneration.     

The fate of human glial cells following transplantation in normal rodents and rodent models of neurodegenerative disease

Investigations on xenografting in the brain have previously focused on the anatomical and functional integration of the transplanted neurons. More recently, astrocytes are being implicated as having complex functions following transplantation, and are being investigated to determine their role(s) in transplantation. The present study was undertaken to investigate the migration of human astrocytes following transplantation of thalamic, striatal, and mesencephalic tissue into the rodent striatum. Human donor fetuses (9–16 weeks in gestation) obtained through elective and spontaneous abortions were utilized in this study. Following transplantation, donor astrocytes were labeled with an antiserum directed against human glial fibrillary acidic protein. Our results demonstrate that astrocytic elements from all three tissue types are capable of incorporating into the host brain, and have a tendency to follow white matter tracts (such as the corpus callosum, internal capsule, and fiber bundles in the striatum). Human astrocytes originating from the striatum and thalamus exhibited extensive migration, while migration was more limited in animals with ventral mesencephalon transplants. Ventral mesencephalon transplanted animals demonstrated positive astrocytes within the transplant, with processes (very few cell bodies) extending into white matter of adjacent host striatum. Astrocytes demonstrating immature morphology were observed with all transplant types, but were most prevalent in the striatal transplanted animals. The extent of astrocyte migration and the morphologies observed in this study reflect regional differences of the developing human brain. These results confirm and extend previous investigations on glial cell migration following transplantation in the brain.     

Localization of mu class glutathione-S-transferase in the forebrains of neonatal and young rats: implications for astrocyte development.

The Yb (Mu class) isoform of glutathione-S-transferase has recently been localized in ependymal cells, subependymal cells, and astrocytes in the forebrains of rats 3 weeks to adult in age. It was not known, however, at what age Mu might first be observed during postnatal development and whether the first cells in which it was found would be immature astrocytes or some less differentiated glial precursor cell, if the latter were present in vivo. Tissue sections from the forebrains of neonatal to 16 day old rats were immunostained with antibodies against Mu. In neonates Mu was observed in vimentin-positive cells and their processes adjacent to the lateral ventricles, and in the corpus striatum. The colocalization with vimentin suggested that these were subependymal cells and radial glia. In the corpus striatum the radial glia, while still vimentin-positive, rapidly lost Mu from their radial cell processes, whereas the cell-bodies remained Mu-positive. During the first postnatal week the Mu-positive, glial-fibrillary-acidic-protein (GFAP)-positive cell bodies of immature astrocytes appeared in the corpus striatum. The earliest Mu-positive cells in the immature white matter of the corpus callosum were vimentin-positive and had striking longitudinal processes that also were vimentin- and Mu-positive. Like the processes of radial glia, the longitudinal processes lost their Mu-immunoreactivity, only later and more gradually. Mu-positive, GFAP-positive cells appeared later in the corpus callosum than in the corpus striatum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolonged seizures recruit caudal subventricular zone glial progenitors into the injured hippocampus

Neurogenesis persists in the adult rat rostral forebrain subventricular zone (SVZ) and is stimulated by status epilepticus (SE). More caudal SVZ (cSVZ) neural progenitors migrate to the hippocampus after ischemic injury and contribute to CA1 pyramidal cell regeneration. Because SE also damages the hippocampus, we examined the effects of SE on cSVZ precursors. SE was induced in adult rats with pilocarpine, and cell proliferation in cSVZ and hippocampus was examined by bromodeoxyuridine (BrdU) and retroviral reporter labeling. Neural precursors were assayed by immunostaining for specfic markers between 1 and 35 days after SE. BrdU-positive cells labeled prior to SE markedly increased in numbers within 1-2 weeks in the cSVZ and infracallosal region, but not in the corpus callosum. Doublecortin-, polysialic acid neural cell adhesion molecule-, and TUC-4 (TOAD/Ulip/CRMP family-4)-immunostained cells with migrating morphology increased with a similar time course after SE and extended from the cSVZ to CA1 and CA3 regions. Retroviral reporters injected into the cSVZ of controls showed labeled cells with oligodendroglial morphology located in the cSVZ and corpus callosum; when injected 2 days prior to SE, many more reporter-labeled cells appeared several weeks later and were located in the cSVZ, corpus callosum, and hippocampus. Labeled cells showed glial morphologies and expressed astrocyte or oligodendrocyte markers. Neither BrdU- nor retroviral reporter-labeled cells coexpressed neuronal markers in controls or pilocarpine-treated rats. These results indicate that SE increases cSVZ gliogenesis and attracts newly generated glia to regions of hippocampal damage. Further study of seizure-induced gliogenesis may provide insight into mechanisms of adult neural progenitor regulation and epileptogenesis.     

Astrocyte decrease in the subgenual cingulate and callosal genu in schizophrenia

Decreases in glial cell density and in GFAP mRNA in the anterior cingulate cortex have been reported in schizophrenia, bipolar disorder and major depressive disorder. Our study examines astrocyte and oligodendrocyte density in the white and grey matter of the subgenual cingulate cortex, and at the midline of the genu of the corpus callosum, in schizophrenia, bipolar disorder, depression and normal control cases. Serial coronal sections were stained with H and E for anatomical guidance, cresyl haematoxylin for oligodendrocyte identification and GFAP immunohistochemistry for astrocyte identification. Oligodendrocyte and astrocyte density was measured using systematic anatomical distinctions and randomised counting methods. A significant decrease in astrocyte density was observed in schizophrenia compared with normal controls in the cingulate grey matter, cingulate white matter and the midline of the corpus callosum (p = 0.025). Bipolar disorder and depression cases showed no significant changes in astrocyte density. Oligodendrocytes did not show any changes between diagnostic groups. In subgenual cingulate cortex, the ratio of oligodendrocytes to astrocytes was decreased between the controls and the three disease groups, suggesting a specific glial cell type specific change in schizophrenia.     

Morphological evidence for direct interaction between gonadotrophin-releasing hormone neurones and astroglial cells in the human hypothalamus

In rodents, there is compelling evidence indicating that dynamic cell-to-cell communications involving cross talk between astroglial cells (such as astrocytes and specialised ependymoglial cells known as tanycytes) and neurones are important in regulating the secretion of gonadotrophin-releasing hormone (GnRH), the neurohormone that controls both sexual maturation and adult reproductive function. However, whether such astroglial cell-GnRH neurone interactions occur in the human brain is not known. In the present study, we used immunofluorescence to examine the anatomical relationship between GnRH neurones and glial cells within the hypothalamus of five women. Double-staining experiments demonstrated the ensheathment of GnRH neurone perikarya by glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte processes in the periventricular zone of the tuberal region of the hypothalamus. GFAP immunoreactivity did not overlap that of GnRH at the GnRH neurone's projection site (i.e. the median eminence of the hypothalamus). Rather, human GnRH neuroendocrine fibres were found to be closely associated with vimentin or nestin-immunopositive radial glial processes likely belonging to tanycytes. In line with these light microscopy data, ultrastructural examination of GnRH-immunoreactive neurones showed numerous glial cells in direct apposition to pre-embedding-labelled GnRH cell bodies and/or dendrites in the infundibular nucleus, whereas postembedding immunogold-labelled GnRH nerve terminals were often seen to be enwrapped by glial cell processes in the median eminence. GnRH nerve button were sometimes visualised in close proximity to fenestrated pituitary portal blood capillaries and/or evaginations of the basal lamina that delineate the pericapillary space. In summary, these data demonstrate that GnRH neurones morphologically interact with astrocytes and tanycytes in the human brain and provide evidence that glial cells may contribute physiologically to the process by which the neuroendocrine brain controls the function of GnRH neurones in humans.     

Connexin 43 deletion in astrocytes promotes CNS remyelination by modulating local inflammation

As the most abundant gap junction protein in the central nervous system (CNS), astrocytic connexin 43 (Cx43) maintains astrocyte network homeostasis, affects oligodendroglial development and participates in CNS pathologies as well as injury progression. However, its role in remyelination is not yet fully understood. To address this issue, we used astrocyte-specific Cx43 conditional knockout (Cx43 cKO) mice generated through the use of a hGFAP-cre promoter, in combination with mice carrying a floxed Cx43 allele that were subjected to lysolecithin so as to induce demyelination. We found no significant difference in the demyelination of the corpus callosum between Cx43 cKO mice and their non-cre littermate controls, while the remyelination process in Cx43 cKO mice was accelerated. Moreover, an increased number of mature oligodendrocytes and an unaltered number of oligodendroglial lineage cells were found in Cx43 cKO mouse lesions. This indicates that oligodendrocyte precursor cell (OPC) differentiation was facilitated by astroglial Cx43 depletion as remyelination progressed. Underlying the latter, there was a down-regulated glial activation and modulated local inflammation as well as a reduction of myelin debris in Cx43 cKO mice. Importantly, 2 weeks of orally administrating boldine, a natural alkaloid that blocks Cx hemichannel activity in astrocytes without affecting gap junctional communication, obviously modulated local inflammation and promoted remyelination. Together, the data suggest that the astrocytic Cx43 hemichannel is negatively involved in the remyelination process by favoring local inflammation. Consequently, inhibiting Cx43 hemichannel functionality may be a potential therapeutic approach for demyelinating diseases in the CNS.     

Nerve cell loss in the thalamic centromedian-parafascicular complex in patients with Huntington’s disease

The centromedian-parafascicular complex represents a nodal point in the neuronal loop comprising striatum – globulus pallidus – thalamus – striatum. Striatal neurone degeneration is a hallmark in Huntington's disease and we were interested in estimating total neurone and glial number in this thalamic nuclear complex. Serial 500-μm-thick gallocyanin-stained frontal sections of the left hemisphere from six cases of Huntington's disease patients (three females, three males) and six age- and sex-matched controls were investigated applying Cavalieri's principle and the optical disector. Mean neurone number in the controls was 646,952 ± 129,668 cells versus 291,763 ± 60,122 in Huntington's disease patients (Mann-Whitney U-test, P < 0.001). Total glial cell number (astrocytes, oligodendrocytes, microglia, and unclassifiable glial profiles) was higher in controls with 9,544,191 ± 3,028,944 versus 6,961,989 ± 2,241,543 in Huntington's disease patients (Mann-Whitney U-test, P < 0.021). Considerable increase of fibrous astroglia within the centromedian-parafascicular complex could be observed after Gallyas' impregnation. Most probably this cell type enhanced the numerical ratio between glial number and neurone number (glial index: Huntington's disease patients = 24.4 ± 8.1; controls = 15.0 ± 5.2; Mann-Whitney U-test, P < 0.013). The neurone number in the centromedian-parafascicular complex correlated negatively, although statistically not significantly, with the striatal neurone number. This lack of correlation between an 80% neuronal loss in the striatum and a 55% neurone loss in the centromedian-parafascicular complex points to viable neuronal circuits connecting the centromedian-parafascicular complex with cortical and subcortical regions that are less affected in Huntington's disease. Received: 13 April 1995 / Revised: 26 June 1995 / Revised, accepted: 30 August 1995     

Effects of diabetes mellitus on astrocyte GFAP and glutamate transporters in the CNS

Diabetes mellitus increases the risk of central nervous system (CNS) disorders such as stroke, seizures, dementia, and cognitive impairment. The cellular mechanisms responsible for the increased risk of these disorders are incompletely understood. Astrocytes are proving critical for normal CNS function, and alterations in their activity could contribute to diabetes-related disturbances in the brain. We examined the effects of streptozotocin (STZ)-induced diabetes in rats on the level of the astrocyte intermediate filament protein, glial fibrillary acidic protein (GFAP), number of astrocytes, and levels of the astrocyte glutamate transporters, glutamate transporter-1 (GLT-1) and glutamate/aspartate transporter (GLAST), in the cerebral cortex, hippocampus, and cerebellum by Western blotting (WB) and immunohistochemistry (IH). Studies were carried out at 4 and 8 weeks of diabetes duration. Diabetes resulted in a significant decrease in GFAP protein levels (WB) in the hippocampus and cerebellum at 4 weeks and in the cerebral cortex, hippocampus and cerebellum by 8 weeks. Attenuated GFAP immunoreactivity (IH) was evident in the hippocampus, cerebellum and white matter regions such as the corpus callosum and external capsule at both 4 and 8 weeks of diabetes. Astrocyte cell counts of adjacent sections immunoreactive for S-100B were not different between control and diabetic animals. No significant differences were noted in astrocyte glutamate transporter levels in the cerebral cortex, hippocampus, or cerebellum at either time period (WB, IH). With the expanding list of astrocyte functions in the CNS, the role of astrocytes in diabetes-induced CNS disorders clearly warrants further investigation.     

A qualitative and quantitative study of the glial cells in normal and athymic mice

A qualitative and quantitative light and electron microscopic analysis of the glial cells in the supraventricular part of the corpus callosum of the neonatal and adult homozygous athymic nude (nu/nu) and normal BALB/c (+/+) mice was carried out to determine the possible contribution of nude gene mutation to glial cell development. Quantitative cell counts using toluidine blue stained serial callosal sections of 0.5 μm thickness showed that the overall glial cell population was significantly reduced in both neonatal and adult athymic mice. The number of glioblasts, astrocytes and microglia of 5-day-old athymic mouse was reduced by 10%, 27%, and 39%, respectively, when compared to the 5-day-old normal mouse. The frequency of necrotic cells in the neonatal athymic mouse increased by 70% when compared with the normal mouse. In the 13-week-old adult athymic mouse, the number of oligodendrocytes, astrocytes, and microglia decreased by 19%, 31%, and 33%, respectively, when compared to normal mouse. There was no significant difference in the area covered by the corpus callosum in 5-day-old and adult nude mice versus the normal ones of corresponding ages. Except for microglia and astrocytes, the ultrastructural features of the other glial cell types in both strains were comparable. Most of the microglial cells of the neonatal normal mouse were round and were selectively marked by Mac-1 monoclonal antibody at their plasma membrane. The immunoreactivity appeared to be more intense in the normal than the athymic mouse, suggesting a down regulation of CR3 receptors and reduced phagocytic activity of this cell type in the athymic mouse. It is proposed that the increased number of necrotic cells in the neonatal athymic mouse may be attributed to the delay in the removal of dead cells normally phagocytosed by microglia. The microglia in both strains of mouse showed comparable lectin staining intensity at the plasma membrane, indicating that their glycoprotein binding receptors to lectin remained unchanged. Some astrocytes in the adult athymic mice showed hypertrophy. The reduced number of glial cells may be the direct result of genetic mutation or consequential to the lack of certain trophic factors arising from the genetic mutation. Thus, the reduction of microglial cells in both neonatal and adult athymic mice may be due to the lack of thymic hormones which, together with lymphokines have been shown to affect the maturation of bone marrow derived cells including monocytes, the putative precursor cells of microglia. The reduction in the number of glioblasts and astrocytes may be attributed to the diminution of T lymphocytes or consequential to the reduction of microglia which are known to secrete interleukin-1 that would influence gliogenesis and produce specific growth factors for promoting astrocyte proliferation. Last, as interaction exists between astrocytes and oligodendrocytes, the products of astrocytes may affect the development of oligodendrocytes and vice vasa. The present findings point to a relation between glial cell development and immune network system. © 1995 Wiley-Liss, Inc.     

Is reactive gliosis a property of a distinct subpopulation of astrocytes?

We have shown previously that the A2B5 monoclonal antibody distinguishes two types of glial fibrillary acidic protein-containing astrocytes in semithin frozen sections of adult rat optic nerve: A2B5- (type-1) astrocytes are found mainly at the periphery of the nerve, where they form the glial limiting membrane, while A2B5+ (type-2) astrocytes are found mainly in the interior of the nerve and constitute more than 65% of the astrocytes in the adult optic nerve. In the present study we show that although most astrocytes in semithin frozen sections of adult rat corpus callosum and optic nerve are A2B5+, the great majority of reactive astrocytes in similar sections of corpus callosum examined 20 weeks after a stab lesion, and in optic nerve examined 20 weeks after adult transection, are A2B5-. Although both A2B5+ and A2B5- astrocytes are stimulated to synthesize DNA in the first week after transection, adult optic nerves examined 20 weeks after transection contain only half as many astrocytes as do normal optic nerves: While A2B5+ astrocytes are reduced almost 10-fold, A2B5- astrocytes are increased by about 25%. We consider the simplest interpretation of these findings to be that type-1 astrocytes are largely responsible for forming glial scars in adult white matter following either a stab lesion or Wallerian degeneration and that in transected optic nerves, most type-2 astrocytes eventually die, possibly because they depend on axons for their long-term survival.     

Establishment of a culture system for the study of oligodendroglial development: complementary effects of boiled serum and astrocyte extract.

Mixed glial primary cultures derived from neonatal rat brain were used to isolate the progenitor glial cell with the capacity to differentiate into oligodendroglia or type 2 astrocytes depending on the culture medium. Subcultures composed primarily of this progenitor were utilized, first, to study the regulation of oligodendroglial differentiation by two factors added to chemically defined medium (CDM), i.e. boiled fetal calf serum (FCS) and cellular extract of type 1 astrocytes, and, second, to devise culture conditions that would cause the progenitor cells to differentiate virtually exclusively along oligodendroglial lines (judged by immunologically identified expression of galactocerebroside; GC) and with high specific and total activity of the oligodendroglial enzymes, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) and glycerol-3-phosphate dehydrogenase (GPDH). Addition of untreated FCS to CDM of the progenitors resulted in 6 days in richly cellular, mixed glial cultures composed of slightly more GFAP-positive astrocytes than oligodendroglia. Addition of boiled FCS to CDM of the progenitors resulted in 6 days in cultures composed almost exclusively (95%) of GC-positive cells and with high specific activity of CNP. This effect of boiled serum, compared to untreated serum, was related to virtual elimination of astrocytes, in the presence of continued differentiation to GC-positive oligodendroglia. Addition of type 1 astrocyte extract as well as boiled FCS to CDM was necessary to generate high specific activity of GPDH. Additionally, the total number of oligodendroglia increased 2-fold when astrocyte extract as well as boiled FCS was added to the CDM.(ABSTRACT TRUNCATED AT 250 WORDS)     

Radioautographic evidence for slow astrocyte turnover and modest oligodendrocyte production in the corpus callosum of adult mice infused with 3H-thymidine

To find out whether glial cells proliferate in the corpus callosum of adult mice, two series of experiments were carried out. The first one made use of 9-month-old "aged" male mice. Some of them were given 3H-thymidine as a 2-hour pulse to examine which cells became labeled and, therefore, had the ability to divide. Others were sacrificed after a continuous infusion of 3H-thymidine for 30 days to examine whether the label would then appear in different cells. In other aged animals, the 30-day infusion was followed by 60 or 180 days without 3H-thymidine to determine whether cells retained or lost their label with time. A second series of experiments was carried out in 4-month old "young adult" male mice to seek confirmation of the main conclusions. Following the 3H-thymidine pulse given to aged mice, only immature glial cells were labeled. After a 30-day infusion, 12.1% astrocytes and 1.1% oligodendrocytes were labeled, so that the net daily addition rate of astrocytes averaged 0.4% and of oligodendrocytes, 0.04%. In young adult mice, the rate after a 7-day infusion averaged 0.9% for astrocytes and 0.08% for oligodendrocytes. However, when the 30-day infusion into aged mice was followed by 60 and 180 days without 3H-thymidine, the labeled astrocytes decreased to 5.3% and 0%, respectively, whereas the number of labeled oligodendrocytes did not change significantly. The interpretation of the results is that the immature cells present in the corpus callosum of mice continue dividing throughout life and their progeny give rise to astrocytes and oligodendrocytes. In the case of astrocytes, the production of new cells occurs in parallel with a loss, so that the astrocyte population turns over. In the case of oligodendrocytes, there is a small production of new, apparently stable cells.     

Corpus striatum in infants under the age of one year: A quantitative morphological study

A quantitative morphological study of the corpus striatum was carried out on the brains of 13 infants under the age of 8 months. The brain of a fetus born after 7 months of pregnancy was also examined. The findings are compared with the results of a previously published similar examination of the corpus striatum in the adult. Most of the children died suddenly and unexpectedly at ages between birth and 8 months. The examination of the brains did not reveal any signs indicating a cerebral cause of death. The volume of the striatum and pallidum was found to be positively correlated to the weight of the brain. The number of nerve cells and glial cells and the distribution was recorded. The number of neurones in the corpus striatum of the fetus, the child and the adult are virtually the same. The density of the neurones, however, is very different in the infant from that of the adult, since the volume of the striatum increases considerably with age. The number of glial cells is significantly smaller in the infant striatum than in the adult. The distribution of the glial cells in the adult striatum is bimodal, with a satellite relationship between the nerve and glial cells, whereas the distribution of the infant glial cells is unimodal, without any satellite phenomenon.     

Correlation of glial proliferation with age in the mouse brain

Radioautographs of brain sections were prepared after injection of ³H-thymidine into mice aged 23, 100, 200 or 400 days. The presence of a small number of labeled cells in all animals indicates that neuroglia do proliferate even at an advanced age. Proliferation is most active in the corpus callosum and least so in the corpus striatum. Comparison of the counts of labeled and unlabeled nuclei suggests that glial cells are produced in numbers exceeding growth requirements and, accordingly, that they turn over, although slowly.     

Dicer Deletion in Astrocytes Inhibits Oligodendroglial Differentiation and Myelination

Increasing evidence has shown that astrocytes are implicated in regulating oligodendrocyte myelination, but the underlying mechanisms remain largely unknown. To understand whether microRNAs in astrocytes function in regulating oligodendroglial differentiation and myelination in the developing and adult CNS, we generated inducible astrocyte-specific Dicer conditional knockout mice (hGFAP-CreERT; Dicer fl/fl). By using a reporter mouse line (mT/mG), we confirmed that hGFAP-CreERT drives an efficient and astrocyte-specific recombination in the developing CNS, upon tamoxifen treatment from postnatal day 3 (P3) to P7. The Dicer deletion in astrocytes resulted in inhibited oligodendroglial differentiation and myelination in the developing CNS of Dicer cKO mice at P10 and P14, and did not alter the densities of neurons or axons, indicating that Dicer in astrocytes is required for oligodendrocyte myelination. Consequently, the Dicer deletion in astrocytes at P3 resulted in impaired spatial memory and motor coordination at the age of 9 weeks. To understand whether Dicer in astrocytes is also required for remyelination, we induced Dicer deletion in 3-month-old mice and then injected lysolecithin into the corpus callosum to induce demyelination. The Dicer deletion in astrocytes blocked remyelination in the corpus callosum 14 days after induced demyelination. Together, our results indicate that Dicer in astrocytes is required for oligodendroglia myelination in both the developing and adult CNS.     

The trophic factors S-100beta and basic fibroblast growth factor are increased in the forebrain reactive astrocytes of adult callosotomized rat.

S-100 is a calcium-binding protein that is predominantly found in astrocytes of the central nervous system. In the present study, we investigated the temporal and spatial changes of S-100beta immunoreactivity after a stereotaxic mechanical lesion of the adult rat corpus callosum performed with an adjustable wire knife. Rats were killed 7, 14 and 28 days after surgery. S-100beta immunoreactivity was found within the cytoplasm and processes of quiescent putative astrocytes that were observed throughout the gray and white matters of the forebrain of sham-operated rats. Following callosotomy, the S-100beta immunoreactive profiles showed increased size and thick processes, as well as increased amount of S-100beta immunoreactivity. Unbiased stereologic analysis revealed a sustained and widespread increase of the Areal Fraction of S-100beta immunoreactive profiles in the medial and lateral regions of the white matter of callosotomized rats at the studied time-intervals. In the cerebral cortex of callosotomized rats, the estimated total number of S-100beta immunoreactive profiles was also increased 7 and 14 days after the lesion. Since the cellular and temporal changes in S-100beta immunoreactivity were closely similar to those described for basic fibroblast growth factor (bFGF) following brain lesions, we co-localized the S-100beta and bFGF immunoreactivities after callosotomy. bFGF immunoreactivity was found in the nuclei of S-100beta immunoreactive glial profiles throughout the forebrain regions of the sham-operated rats. bFGF immunoreactivity was increased in the nuclei of reactive S-100beta immunoreactive putative astrocytes in the forebrain white matter and in the cerebral cortex of callosotomized rats. These results indicate that after transection of the corpus callosum of adult rats, the reactive astrocytes may exert paracrine trophic actions through S-100beta and bFGF. Interactions between S-100beta and bFGF may be relevant to the events related to neuronal maintenance and repair following brain injury.