Carbonic anhydrase in distinct precursors of astrocytes and oligodendrocytes in the forebrains of neonatal and young rats

Huntington disease oligodendrocyte maturation deficits revealed by single-nucleus RNAseq are rescued by thiamine-biotin supplementation

The complexity of affected brain regions and cell types is a challenge for Huntington's disease (HD) treatment. Here we use single nucleus RNA sequencing to investigate molecular pathology in the cortex and striatum from R6/2 mice and human HD post-mortem tissue. We identify cell type-specific and -agnostic signatures suggesting oligodendrocytes (OLs) and oligodendrocyte precursors (OPCs) are arrested in intermediate maturation states. OL-lineage regulators OLIG1 and OLIG2 are negatively correlated with CAG length in human OPCs, and ATACseq analysis of HD mouse NeuN-negative cells shows decreased accessibility regulated by OL maturation genes. The data implicates glucose and lipid metabolism in abnormal cell maturation and identify PRKCE and Thiamine Pyrophosphokinase 1 (TPK1) as central genes. Thiamine/biotin treatment of R6/1 HD mice to compensate for TPK1 dysregulation restores OL maturation and rescues neuronal pathology. Our insights into HD OL pathology spans multiple brain regions and link OL maturation deficits to abnormal thiamine metabolism.

Carbonic Anhydrases in Metazoan Model Organisms: Molecules, Mechanisms, and Physiology

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, β, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and β-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs but also contribute to a plethora of previously undescribed functions.

The Expression of Carbonic Anhydrases II, IX and XII in Brain Tumors

Carbonic anhydrases (CAs) are zinc-containing metalloenzymes that participate in the regulation of pH homeostasis in addition to many other important physiological functions. Importantly, CAs have been associated with neoplastic processes and cancer. Brain tumors represent a heterogeneous group of diseases with a frequently dismal prognosis, and new treatment options are urgently needed. In this review article, we summarize the previously published literature about CAs in brain tumors, especially on CA II and hypoxia-inducible CA IX and CA XII. We review here their role in tumorigenesis and potential value in predicting prognosis of brain tumors, including astrocytomas, oligodendrogliomas, ependymomas, medulloblastomas, meningiomas, and craniopharyngiomas. We also introduce both already completed and ongoing studies focusing on CA inhibition as a potential anti-cancer strategy.

Cuprizone-induced demyelination in the rat cerebral cortex and thyroid hormone effects on cortical remyelination

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the Central Nervous System which is characterized by multifocal demyelinated lesions dispersed throughout the brain. Although white matter lesions have been the most extensively studied, cortical demyelinaton lesions are also detected in MS brains. Cuprizone (CPZ)-induced demyelination in rodents has been widely used as a model for MS. Most of these studies focus on oligodendrocyte-rich structures, such as the corpus callosum (CC) and the cerebellar peduncles. However, it has been recently described that CPZ administration in mice also produces cortical demyelination, resembling some of the lesions found in MS patients. In this work we used CPZ-demyelinating model in Wistar rats to study demyelination in cortical forebrain areas. At the ultrastructural level, demyelination in the cortex was observed before detectable myelin loss in the subcortical white matter. During the course of CPZ intoxication Myelin Basic Protein immunodetection was decreased in cortical layers I-III due to a reduction in the number of cortical oligodendrocytes (OL). Oligodendroglial loss in CPZ-intoxicated rats correlated with an increase in the number of Glial Fibrillary Acidic Protein positive astrocytes and a shift in the location of Carbonic Anhydrase II from OL to astrocytes. After removal of CPZ from the diet, we evaluate intranasal Thyroid hormone (TH) effects on the progression of cortical lesions. As previously reported in the CC, TH treatment also accelerates remyelination rate in the cortex compared to rats undergoing spontaneous remyelination. Our results suggest that manipulation of TH levels could be considered as a strategy to promote remyelination process in the cortex and to prevent neuronal irreversible damage in patients suffering from MS.

Carbonic anhydrase II in the developing and adult human brain

Carbonic anhydrase II (CA II) is one of 14 isozymes of carbonic anhydrases, zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide to bicarbonate. Mutations in CA II in humans lead to osteopetrosis with renal tubular acidosis and cerebral calcifications, a disorder often associated with mental retardation. Recently, new avenues in CA II research have opened as a result of discoveries that the enzyme increases bicarbonate and proton fluxes and may play an important role in brain tissue. In the human brain, CA II was localized to oligodendrocytes, myelin, and choroid plexus epithelium. Because this conclusion was based on a few fragmentary reports, we analyzed in more detail the expression of the enzyme in human telencephalon. By immunoblotting, we found a gradual increase in CA II levels from 17 weeks' gestation to childhood and adolescence. By immunohistochemistry, CA II was found to be present not only in oligodendrocytes and choroid plexus epithelium (declining with aging in both these locations), but also in a subset of neurons mostly with GABAergic phenotype, in a few astrocytes, and transiently during brain development in the endothelial cells of microvessels. The enzyme also occurred in oligodendrocyte processes in contact with myelinating axons, myelin sheaths, and axolemma, but was either absent or appeared in minute amounts in compact myelin. These findings suggest the possible involvement of CA II in a wide spectrum of biologic processes in the developing and adult human brain and may contribute to better understanding of the pathogenesis of cerebral calcifications and mental retardation caused by CA II deficiency.

Expression of discoidin domain receptor 1 during mouse brain development follows the progress of myelination

Discoidin domain receptor 1 is a tyrosine kinase receptor expressed in a variety of tissues including the brain. This study describes mRNA and protein expression of discoidin domain receptor 1 in mouse brain during development and provides new insights into its role during gliogenesis and neurogenesis. We performed in situ hybridization for discoidin domain receptor 1 in mouse brains at embryonic day 18, postnatal days 5, 9, 15, 21 and adulthood and observed a diffuse pattern in the proliferative areas during embryogenesis. From postnatal day 5 onwards, a defined cellular expression pattern of discoidin domain receptor 1 was observed, mainly located in white matter tracts and following a spatio-temporal pattern that overlapped the progress of myelination. Next, we performed double-labeling reactions (in situ hybridization followed by immunohistochemistry) that confirmed that discoidin domain receptor 1 was expressed by mature oligodendrocytes. We observed that cells positive for discoidin domain receptor 1 also expressed carnosine and anti-adenomatous polyposis coli, two mature oligodendrocyte markers. Based on the localization of discoidin domain receptor 1 specifically in the white matter fiber tracts during postnatal development, we suggest that discoidin domain receptor 1 participates in the development and maintenance of the myelin sheath.

Decreased brain levels of 2',3'-cyclic nucleotide-3'-phosphodiesterase in Down syndrome and Alzheimer's disease

In Down syndrome (DS) as well as in Alzheimer's disease (AD) oligodendroglial and myelin alterations have been reported. 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) and carbonic anhydrase II (CA II) are widely accepted as markers for oligodendroglia and myelin. However, only data on CNPase activity have been available in AD and DS brains so far. In our study we determined the protein levels of CNPase and CA II in DS, AD and in control post mortem brain samples in order to assess oligodendroglia and myelin alterations in both diseases. We used two dimensional electrophoresis to separate brain proteins that were subsequently identified by matrix assisted laser desorption and ionization mass-spectroscopy (MALDI-MS). Seven brain areas were investigated (frontal, temporal, occipital and parietal cortex, cerebellum, thalamus and caudate nucleus). In comparison to control brains we detected significantly decreased CNPase protein levels in frontal and temporal cortex of DS patients. The level of CA II protein in DS was unchanged in comparison to controls. In AD brains levels of CNPase were decreased in frontal cortex only. The level of CA II in all brain areas in AD group was comparable to controls. Changes of CNPase protein levels in DS and AD are in agreement with the previous finding of decreased CNPase activity in DS and AD brain. They probably reflect decreased oligodendroglial density and/or reduced myelination. These can be secondary to disturbances in axon/oligodendroglial communication due to neuronal loss present in both diseases. Alternatively, reduced CNPase levels in DS brains may be caused by impairment of glucose metabolism and/or alterations of thyroid functions.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

A proteolipid protein-specific pre-mRNA (Ppm-1) contains intron 3 and is up-regulated during myelination in the CNS

Alternative splicing of the precursor for messenger RNA (pre-mRNA) is a common process utilised by higher eukaryotes to modulate gene expression. A single primary transcript may generate several proteins with distinct functions, expressed in tissue-specific, developmental patterns. This article describes an oligodendrocyte-specific pre-mRNA product of proteolipid protein gene (P/p) transcription, which is the precursor for P/p but not Dm20 mRNA in the CNS. This P/p-specific pre-mRNA (Ppm-1) includes the intact intron 3 of the P/p gene. It is first expressed during active myelination, and it localises to the nucleus of oligodendrocytes, in both normal and jimpy (jp) murine CNS. In addition to mouse, Ppm-1 is found also in rat and dog, but not toad or trout. Our work suggests that alternative splicing of the P/p gene primary transcript follows a branching pattern, resulting in the presence of at least one P/p isoform-specific pre-mRNA molecule, Ppm-1. Therefore, Dm20 mRNA may be the product of a divergent set of pre-mRNA splicing events.

Cerebrocortical microdysgenesis is enhanced in c57BL/6J mice exposed in utero to acetazolamide

A small percentage of C57BL/6 mice spontaneously develop focal collections of neurons in the molecular layer of the cerebral neocortex. Usually only one "ectopia" is present in each affected brain. Studies in other mouse strains have shown that these ectopias occur before birth, probably because of a breach in the superficial glial membrane during neuronal migration. The ectopias are heritable and are caused by multiple genes. C57BL/6J mice exposed prenatally to acetazolamide, a carbonic anhydrase-specific inhibitor and teratogen, develop an increased frequency of limb malformations, especially in the right forelimb. In the present study, we hypothesized that the prevalence and severity of ectopias would be increased in acetazolamide-exposed mice because carbonic anhydrase plays a key role in brain development. Further, we wanted to determine whether there was a correlation between the side of limb deformity and the hemisphere containing an ectopia. Thus, we injected C57BL/6J time-mated mice intraperitoneally on embryonic day 9 with either sodium acetazolamide (750 mg/kg) or water. Histological analysis of the brains from 105 acetazolamide-exposed offspring and 89 control offspring revealed no difference in the overall prevalence of cerebrocortical ectopias between the acetazolamide and control groups: 34% of the acetazolamide-exposed and 28% of the control mice had ectopias. There was, however, a striking difference in the shape and size of ectopias: 67% of the ectopias were large in the acetazolamide-exposed group in comparison to 32% in controls. The acetazolamide-exposed offspring also were more likely to have multiple ectopias. Thus, there may be a genetic predisposition for developing ectopias in some mouse strains, but epigenetic factors such as prenatal exposure to acetazolamide can influence their severity.

Treatment of posthemorrhagic hydrocephalus in the preterm infant with a ventricular access device

Intraventricular hemorrhage (IVH) and subsequent posthemorrhagic hydrocephalus (PHH) commonly complicate the course of extremely preterm infants. Many methods for treating the hydrocephalus have been used, none of which are ideal. We present the largest series of infants with PHH treated with one modality, the ventricular access device (VAD). One hundred and forty-nine preterm infants with PHH were treated by placement of a VAD and serial taps to control intracranial pressure and ventricular size. Variables recorded include gender, race, gestational age, weight at birth, IVH grade, incidence of VAD infection, malfunction or local wound problems and indwelling time to either shunt placement or VAD removal. Of the 149 preterm infants, 91 were males and 58 females. The average birth weight was 994 g and the average gestational age at birth was 26.3 weeks. Three infants were IVH grade 1, 8 were grade 2, 62 were grade 3 and 76 were grade 4. VAD occlusion occurred in 15 infants (10%). Nine infants required contralateral VAD placement for a trapped ventricle. VAD infection occurred in 12 infants (8%), 5 of whom were treated successfully with a combination of systemic and intra-VAD antibiotics without removal of the VAD. The total rate of revision was thus 20% (15 for occlusion, 9 for trapped ventricle, 7 for infection). Wound problems were minimal and consisted of 4 cerebrospinal fluid leaks and 14 subgaleal fluid collections. For the 133 survivors, the rate of shunt placement was 88%. The VAD, while not ideal, is an excellent treatment at this time for PHH. It can be utilized for several months with acceptable rates of infection, blockage and wound complications. The VAD tap is simple to perform, not disruptive to minimal stimulation protocols, and can be done by physician extenders. In addition, medications can be administered via the access device, thus allowing treatment of some infections without VAD removal as well as instillation of thrombolytic agents such as urokinase.

Posthemorrhagic hydrocephalus and brain injury in the preterm infant: dilemmas in diagnosis and management

Advances in neonatal critical care have reduced the incidence of intraventricular hemorrhage (IVH) in the newborn. Paradoxically, however, the prevalence of the complications of IVH including posthemorrhagic hydrocephalus (PHHC) has increased. By virtue of its association with long-term neurodevelopmental disability, posthemorrhagic hydrocephalus is an ominous diagnosis in the premature infant. Animal models have demonstrated that ventricular distention may cause direct cerebral parenchymal injury. Evidence for secondary parenchymal injury in the premature infant with PHHC is by necessity indirect. The precise impact of secondary parenchymal injury on the overall neurological outcome of premature infants with PHHC remains unclear in large part because of the vulnerability of the immature brain to other forms of injury (e.g., periventricular leukomalacia) that may be difficult to distinguish from injury due to distention. Furthermore, parenchymal injury due to PVL may cause ventricular enlargement that does not benefit from CSF diversion. Because these primary and secondary mechanisms of injury may operate concurrently, the precise or dominant cause of ventricular enlargement is often difficult to establish with certainty in the neonatal period. These diagnostic dilemmas have in turn impeded the development and evaluation of therapies specifically aimed at reversing ventricular distention and preventing secondary parenchymal injury. This article focuses on the current dilemmas in diagnosis and management of this potentially reversible form of injury as well as on potential future strategies for its prevention.

Characterization of a putative novel type of oligodendrocyte in cultures from rat spinal cord

Oligodendrocytes originate in different neural tube domains, within boundaries of expression of a series of patterning genes which condition the diverse morphogenetic programme of each area. Although neuronal and astrocyte heterogeneity are widely accepted, and despite accumulating evidence for oligodendrocyte heterogeneity in vivo, oligodendrocytes in vitro are currently considered as a homogeneous cell population. The present investigation demonstrates that oligodendrocyte diversity can be detected in vitro and characterizes a novel morphological class of O4-positive oligodendrocyte which is consistently identifiable in rat central nervous system cultures. These cells have a very characteristic epithelioid, unbranched and often lobulated morphology which enables their identification within 2 h of plating. Immunostaining shows that this morphological type is sometimes positive for GD3, A2B5 and vimentin, and most of the time positive for Ranscht antibody, O1 and Rip but negative for glial fibrillary acidic protein, OX-42, neuron-specific enolase, nestin and erbB2. The apparent levels and/or distributions of (i) microtubules, (ii) surface glycolipids recognized by O4, O1 and Ranscht antibody, and (iii) the less specific marker carbonic anhydrase II, typically differ from those of nearby classical, branched oligodendrocytes. Cells with this epithelioid morphology also express myelin basic protein and O10 (a proteolipid protein epitope), both of which are markers for mature oligodendrocytes. Conversely, O4+/O1- cells with this membranous appearance were also seen. Although these atypical oligodendrocytes were most abundant in spinal cord cultures (representing >10% of the O4+ population), they were not exclusive to this region and occurred at a low frequency in neonatal optic nerve cultures.

Carbonic anhydrase II in microglia in forebrains of neonatal rats

In the brains of adult rodents carbonic anhydrase II (CA) immunoreactivity has been observed in the choroid plexus and in oligodendrocytes, astrocytes, and myelin. Localization and functions of CA in the neonatal brain, however, have been controversial. One issue is whether the CAII-immunopositive round and ameboid cells in the corpus callosum and cingulum in the rat CNS during the first postnatal week are oligodendrocytes or microglia. Colocalization of CAII with the microglial antigen, ED1, and the microglia-specific isolectin, BSI-B4, suggested that most (approx. 60%) of the CAII-positive round and ameboid cells in rat brain during the first postnatal week were, indeed, macrophages and microglia. During that initial week, some CAII-positive protoplasmic astrocytes (approx. 40%) were observed as well. At the end of the first postnatal week smooth-surfaced CAII-positive cells began to appear in the corpus callosum. Those cells also bound MAbO4, a marker for the oligodendrocyte cell line. We conclude that during the first postnatal week most of the CAII-positive cells are macrophages and microglia, and that some are protoplasmic astrocytes. During the second postnatal week CAII-positive cells in the oligodendrocyte lineage become apparent, and by the end of that week there are few CAII-positive microglia. Confocal microscopy suggests that in brains of three-day-old rats the ameboid microglia are associated with nerve fibers, where they may perform phagocytosis of axons, directional guidance of axons, or disinhibition of axonal growth.

Glial cells in transected optic nerves of immature rats. II. An immunohistochemical study

The glia response to Wallerian degeneration was studied in optic nerves 21 days after unilateral enucleation (PED21) of immature rats, 21 days old (P21), using immunohistochemical labelling. Nerves from normal P21 and P42 nerves were also studied for comparison. At PED21, there was a virtual loss of axons apart from a few solitary fibres of unknown origin. The nerve comprised a homogeneous glial scar tissue formed by dense astrocyte processes, oriented parallel to the long axis of the nerve along the tracks of degenerated axons. Astrocytes were almost perfectly co-labelled by antibodies to glial fibrillary acid protein and vimentin in both normal and transected nerves. However, there was a small population of VIM+GFAP- cells in normal P21 and P42 nerves, and we discuss the possibility that they correspond to O-2A progenitor cells described in vitro. Significantly, double immunofluorescence labelling in transected nerves revealed a distinct population of hypertrophic astrocytes which were GFAP+VIM-. These cells represented a novel morphological and antigenic subtype of reactive astrocyte. It was also noted that the number of oligodendrocytes in transected nerves did not appear to be less than in normal nerves, on the basis of double immunofluorescence staining for carbonic anhydrase II, myelin oligodendrocyte glycoprotein, myelin basic protein, glial fibrillary acid protein and ED-1 (for macrophages), although it was not excluded that a small proportion may have been microglia. A further prominent feature of transected nerves was that they contained a substantial amount of myelin debris, notwithstanding that OX-42 and ED1 immunostaining showed that there were abundant microglia and macrophages, sufficient for the rapid and almost complete removal of axonal debris. In conclusion, glial cells in the immature P21 rat optic nerve reacted to Wallerian degeneration in a way equivalent to the adult CNS, i.e. astrocytes underwent pronounced reactive changes and formed a dense glial scar, oligodendrocytes persisted and were not dependent on axons for their continued survival, and there was ineffective phagocytosis of myelin possibly due to incomplete activation of microglia/macrophages.

Increased susceptibility of brain slices from carbonic anhydrase II-deficient mice to low [Mg2+]O-induced seizures

Brain pH is thought to be an influential factor in determining susceptibility to seizures. We compared the susceptibility of brain slices from carbonic anhydrase II (CA II)-deficient mice to epileptiform activity induced by low extracellular [Mg2+], with slices from normal littermates, both bathed in artificial cerebrospinal fluid at pH 7.3. In both entorhinal cortex and hippocampal field CA1, epileptiform activity started earlier in CA II-deficient slices. Raising extracellular [CO2] (20%; extracellular pH, 6.7) reversibly blocked the epileptiform activity in normal, but not in CA II-deficient, slices. The data, combined with previous in vivo findings showing an increased resistance of mutants to seizures, suggest the presence of in vivo anticonvulsant acidosis with long-term compensatory changes that lead to in vitro 'proconvulsant' behavior in CA II-deficient slices clamped at pH 7.3.

Retinoic acid treated P19 embryonal carcinoma cells differentiate into oligodendrocytes capable of myelination

Retinoic acid treatment of P19 embryonal carcinoma cells induces their differentiation into cultures containing neurons and astrocytes. We present two lines of experimentation indicating that oligodendrocytes also develop from retinoic acid-treated P19 cells. We isolated an immortal cell line from retinoic acid-treated P19 cell cultures whose proliferation is dependent upon epidermal growth factor. Upon removal of the growth factor these cells differentiate into both astrocytes and oligodendrocytes as determined by immunostaining with antibodies to the astrocyte marker glial fibrillar acidic protein and the oligodendrocyte markers, myelin associated glycoprotein and 2', 3'-cyclic nucleotide 3'-phosphodiesterase. This cell line appears to be a bi-potential glial precursor. We also found that oligodendrocytes developed directly from P19 cells when retinoic acid-treated cells were transplanted into the brains of neonatal rat pups. Cells that developed into oligodendrocytes migrated into fiber bundles up to several millimeters from the site of the graft. These P19-derived oligodendrocytes appeared to myelinate axons from host neurons. Thus, retinoic acid-treated P19 cells differentiate into neurons, astrocytes and oligodendrocytes, the three cell types that normally develop from embryonic neuroectoderm, indicating that these cell cultures differentiate in a fashion closely resembling that of embryonic neuroectoderm.

Biochemical subtypes of oligodendrocyte in the anterior medullary velum of the rat as revealed by the monoclonal antibody Rip

Oligodendrocytes were studied in the anterior medullary velum (AMV) of the rat using the monoclonal antibody Rip, an oligodendrocyte marker of unknown function. Confocal microscopic imaging of double immunofluorescent labelling with antibodies to Rip and carbonic anhydrase II (CAII) revealed two biochemically and morphologically distinct populations of oligodendrocyte which were either Rip+CAII+ or Rip+CAII-. Double immunofluorescent labelling with Rip and myelin basic protein (MBP) or glial fibrillary acidic protein (GFAP) provided direct evidence that Rip-labelled cells were phenotypically oligodendrocytes and confirmed that Rip did not recognise astrocytes. Oligodendrocytes which were Rip+CAII+ supported numerous myelin sheaths for small diameter axons, whilst Rip+CAII- oligodendrocytes supported fewer myelin sheaths for large diameter axons. Morphologically, Rip+CAII+ oligodendrocytes corresponded to types I or II of classical nomenclature, whilst Rip+CAII- oligodendrocytes corresponded to types III and IV. The results demonstrated a biochemical difference between oligodendrocytes which myelinated small and large diameter fibres.

Proliferative capacity of oligodendrocytes in the demyelinating twitcher spinal cord

The proliferative capacity of oligodendrocytes was investigated in the spinal white matter of the twitcher mouse, a murine model of a genetic demyelinating disease globoid cell leukodystrophy (GLD), in which degeneration of oligodendrocytes due to metabolic perturbation has been well documented. In normal mice at 30 and 45 days of age, proliferating cells labeled with 5-bromo-2'-deoxyuridine (BrdU) were scarce, and the majority of BrdU-labeled cells did not immunostain with antibodies for oligodendrocytes, astrocytes, or microglia/macrophages. Only a few cells with markers for oligodendrocytes, carbonic anhydrase (CA), or the Pi form of glutathione-S-transferase (Pi), were labeled with BrdU. In the twitcher spinal cord, total numbers of BrdU-labeled cells were almost 6 times that of the normal littermate mice at 30 days of age, and 28 times at 45 days of age. However, this increase was largely due to an increase of cells labeled with F4/80, a marker for the microglia/macrophages. CA or Pi positive cells only constituted less than 10% of all labeled cells. With progression of demyelination from 30-45 days, total numbers of CA positive or Pi positive oligodendrocytes decreased, but percentages of cells double-labeled with BrdU and CA or Pi remained fairly constant. The results indicated that oligodendrocytes proliferated, to some extent, in the twitcher despite the genetic metabolic defect, and their decrease in number with progression of disease was not due to declined proliferation but rather cellular degeneration as the result of an intrinsic metabolic perturbation.

Strongly GD3+ cells in the developing and adult rat cerebellum belong to the microglial lineage rather than to the oligodendrocyte lineage

A recent study has shown that ramified microglia in the adult rat optic nerve express the ganglioside GD3 [Wolswijk Glia 10:244-249, 1994], thereby raising the possibility that some GD3+ in the developing rat central nervous system (CNS) belong to the microglial lineage rather than to the oligodendrocyte lineage, as previously thought. To examine this possibility, sections of postnatal and adult cerebellum were double-labelled with markers for rat microglia [the B4 isolectin derived from Griffonia simplicifolia (GSI-B4), the ED1 monoclonal antibody (mAb), and the OX-42 mAb] and anti-GD3 mAbs (the mAbs R24 and LB1). These immunolabellings showed that ramified microglia as well as amoeboid microglia are strongly GD3+ in vivo. Moreover, most, if not all, cells that express high levels of GD3 in sections of developing cerebellum appear to belong to the microglial lineage. These observations contradict previous suggestions that the strongly GD3+ cells in the putative white matter regions of the developing brain are oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells; the cells that give rise to oligodendrocytes in the CNS. The present study did, however, confirm that some O-2A progenitor cells in sections of postnatal cerebellum are weakly GD3+ in vivo. Amoeboid microglia are present in areas of the developing cerebellum where newly generated oligodendrocytes are found, suggesting that these cells play a role in the phagocytosis of the large numbers of oligodendrocytes that die as part of CNS development.

Expression of the raf protooncogene in glial cells of the adult rat cerebral cortex, brain stem and spinal cord

The raf protooncogenes encode cytoplasmic serine/threonine-specific protein kinases which can be activated from different growth factor receptors by phosphorylation. Our previous immunohistochemical studies proved that raf kinases are present in neurons of the mammalian central nervous system. The present study describes the immunohistochemical localization of raf kinases in glia-like cells of the rat cerebral cortex, spinal cord and brain stem. Small glia-like cells measuring 8-12 microns were observed in the neocortex, the entorhinal and prepiriform allocortical areas and the subcortical white matter. In the hippocampus, the immunoreactive cells were most numerous in the fimbria, the alveus and the molecular layer of the dentate fascia. Ultrastructural studies following preembedding immunohistochemistry revealed that in the cerebral cortex only astrocytes contained raf-protein-like immunoreactivity. Our immunofluorescence studies showed, that the white matter of the spinal cord, the pyramids of the medulla and the basis of the pons contained small glia-like cells, too. No electron microscopic investigations were performed, but the location (white matter tracts) and size (6-12 microns) of these cells suggested their glial nature. On the basis of data from other cell systems we expect that raf kinases participate in growth factor- and cytokine-regulated glial functions of the mammalian central nervous system.

Atypical localization of the oligodendrocytic isoform (PI) of glutathione-S-transferase in astrocytes during cuprizone intoxication

Immunocytochemical staining for the Pi and Mu isoforms of glutathione-S-transferase was used to investigate changes in the glial cells in the mouse forebrain. During early development in mouse forebrains the localizations of carbonic anhydrase, Pi and Mu were similar to the respective cellular localizations that had been observed in neonatal rat brain. That is, Pi was found in oligodendrocyte precursors, Mu in astrocytes, and carbonic anhydrase in both oligodendrocyte precursors and astrocytes. In forebrains of 6-week-old mice the neurotoxicant, cuprizone, induced oligodendrocyte degeneration, gliosis, and partial demyelination. Degeneration, gliosis, and partial demyelination. Degeneration of oligodendrocytes, and astrocytosis, began during the initial week of cuprizone feeding, and by the end of the eighth week some demyelination was observed. After mice were fed cuprizone for 4 to 7 weeks, Pi appeared in some of the reactive astrocytes, and Pi-positive astrocytes were present for at least 7 additional weeks. Normally, Pi appeared only in oligodendrocytes. Very few Pi-positive oligodendrocytes remained after the second week. During the eighth week healthy-looking carbonic anhydrase-positive oligodendrocytes reappeared and began to accumulate, and a few small patches of Pi-positive oligodendrocytes were also observed. In summary, some novel findings about glial cells were the observation of an enzyme (Pi) that is lost earlier from oligodendrocytes than is carbonic anhydrase, the apparently unique shift in Pi expression from oligodendrocytes to astrocytes and the greater temporal dissociation between loss of oligodendrocytes and demyelination in the older mice.

Developmental changes in seizure susceptibility in carbonic anhydrase II-deficient mice and normal littermates

Mice deficient in carbonic anhydrase II (CA II) were tested along with their normal littermates for susceptibility to seizures induced by flurothyl and loud sound at ages 10-180 days. In the flurothyl seizure model, CA II-deficient mice displayed increased resistance to clonic seizures from 32 to 90 days of age, whereas tonic-clonic seizures were suppressed at all ages. The mortality of CA II-deficient mice was significantly decreased at ages 19-40 days. The incidence of sound-induced seizures was very low and no difference between CA II-deficient and normal mice was found. The anticonvulsant effect of CA II deficiency appears to be dependent on seizure model and seizure type and to have age-specific characteristics.