Immunocytochemical localization of carbonic anhydrase in the spinal cords of normal and mutant (shiverer) adult mice with comparisons among fixation methods

Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned

Although astrogliosis and microglia activation are characteristic features of multiple sclerosis (MS) and other central nervous system (CNS) lesions the exact functions of these events are not fully understood. Animal models help to understand the complex interplay between the different cell types of the CNS and uncover general mechanisms of damage and repair of myelin sheaths. The so called cuprizone model is a toxic model of demyelination in the CNS white and gray matter, which lacks an autoimmune component. Cuprizone induces apoptosis of mature oligodendrocytes that leads to a robust demyelination and profound activation of both astrocytes and microglia with regional heterogeneity between different white and gray matter regions. Although not suitable to study autoimmune mediated demyelination, this model is extremely helpful to elucidate basic cellular and molecular mechanisms during de- and particularly remyelination independently of interactions with peripheral immune cells. Phagocytosis and removal of damaged myelin seems to be one of the major roles of microglia in this model and it is well known that removal of myelin debris is a prerequisite of successful remyelination. Furthermore, microglia provide several signals that support remyelination. The role of astrocytes during de- and remyelination is not well defined. Both supportive and destructive functions have been suggested. Using the cuprizone model we could demonstrate that there is an important crosstalk between astrocytes and microglia. In this review we focus on the role of glial reactions and interaction in the cuprizone model. Advantages and limitations of as well as its potential therapeutic relevance for the human disease MS are critically discussed in comparison to other animal models.

Differential induction of apoptosis in demyelinating and nondemyelinating infection by mouse hepatitis virus

The role of apoptosis in mouse hepatitis virus (MHV) infection is still controversial. To better assess the role of apoptosis in MHV infection, we used three different biologic phenotypes of MHV to examine their differential effect on the induction of apoptosis. MHV-A59 produces acute hepatitis, meningoencephalitis, and chronic demyelination. MHV-2 causes only acute hepatitis and meningitis, whereas Penn98-1 produces acute hepatitis and meningoencephalitis without demyelination. We detected TdT-mediated dUTP nick-end labeling (TUNEL) staining in the livers and meninges of MHV-A59-, MHV-2-, and Penn98-1-infected mice. TUNEL staining in brain parenchyma was only detected in MHV-A59- and Penn98-1-infected mice. We detected apoptosis by electronmicroscopy in olfactory neurons during acute infection with MHV-A59. The kinetics and distribution of TUNEL staining correlated with the pathologic damage and colocalized with viral antigen in some cells. At 1 month, TUNEL staining was found exclusively in areas of demyelination in the spinal cord of MHV-A59-infected mice; however, it was not found in nondemyelinated mice infected with MHV-2 or Penn98-1, or in mock-infected mice. TUNEL-positive cells were identified as macrophage/microglial cells, some astrocytes, and some oligodendrocytes, by colabeling with cell-specific markers. The presence of TUNEL staining in oligodendrocytes suggests that apoptosis may play an important role in MHV-induced demyelination.

Transplantation of glial cell progenitors from brains of normal rats and mice into brains of neonatal carbonic anhydrase II-deficient mutant mice

Carbonic anhydrase II (CAII) is expressed in oligodendrocytes, astrocytes and myelin in brains of rats and normal mice, but not in the brains of CAII-deficient mutant mice. We have transplanted mixed glial-cell suspensions from normal mouse brains, and oligodendrocyte-enriched precursor cells cultured from normal rat brains, respectively, into the brains of neonatal CAII-deficient mutant mice. Some CAII-positive astrocytes and oligodendrocytes developed in the brains of the host CAII-deficient mice at 8, 14 and 18 days posttransplant (DPT). In transplants of either mixed glial cells or oligodendrocyte precursors, CAII-positive oligodendrocytes were less plentiful than CAII-positive astrocytes and appeared to be less healthy. CAII-positive astrocytes developed by 8 DPT, and there were some oligodendrocytes in cerebral cortex at 14 DPT and in brainstem by 18 DPT. The data suggested that if glial-cell progenitors were to be injected into demyelinated lesions, any oligodendrocytes descended from the donor would be accompanied by astrocytes also descended from donor cells.

Glial-cell cultures from brains of carbonic anhydrase II-deficient mutant mice: delay in oligodendrocyte maturation

Carbonic anhydrase II (CAII) is a multifunctional enzyme found in oligodendrocytes and astrocytes in normal mouse brains. We have begun to compare the glial cells in primary cultures from neonatal genetically CAII-deficient (Car) mice to those from normal (con) mice in order to detect developmental defects, if any, in Car glial cells. In con cultures intensely CAII-positive cells costained with antibodies against the oligodendrocytic markers, O4 and myelin basic protein (MBP), respectively. Most (82%) of the CAII-positive cells were O4-positive, but only approximately 60% were MBP-positive. Some clumps of GFAP-positive cells were CAII-positive. At each respective number of days in vitro (DIV) total numbers of O4-positive cells were similar in Car and con cultures, and total numbers of galactocerebroside-positive cells also were similar in Car and con cultures. However, compared to cells in con cultures at 7 DIV, a lower percent of Car cells in the oligodendrocyte lineage expressed MBP, and morphological differentiation also was subnormal in that the Car cells showed fewer processes and membrane sheets. Car and con cultures expressed similar numbers of MBP-positive cells by 10 DIV. The results suggest a temporary delay in the maturation of Car oligodendrocytes.

A reappraisal of ganglioside GD3 expression in the CNS

GD3 ganglioside is a major glycolipid component of the developing central nervous system but diminishes considerably as the CNS matures. Despite consistent biochemical data, the cellular localization of GD3 expression has been controversial. In this commentary we will review the cellular expression of GD3 during CNS development and in neuropathological circumstances as determined by studies with the two most commonly used anti GD3 monoclonal antibodies, R24 and LB1. GD3 is not restricted to any one cell lineage, being expressed in development to varying degrees by immature neuroectodermal cells, oligodendrocyte progenitors, ameboid microglia, and subpopulations of developing neurons and astrocytes. In the adult CNS, GD3 is expressed in low amounts by some neuronal subpopulations, on reactive and resting microglia, and by reactive astrocytes. In the appropriate contexts of development or neuropathology, anti-GD3 antibodies are useful for cell type identification and for cell isolation, but caution should be exercised because of the lack of cellular specificity.

Embedding, sectioning, immunocytochemical and stereological methods that optimise research on the lesioned adult rat spinal cord

Numerous methods have been developed to embed, section and immunocytochemically label nervous tissue and the method chosen depends upon numerous factors. However, many of these methods have technical drawbacks that make them difficult to use in studies using injured/lesioned tissue. We present here, methods for embedding, sectioning and immunocytochemically labelling lesioned adult spinal cord tissue at the light microscope level. We have developed a novel, gelatine-embedding technique for vibratome sectioning which overcomes many of the difficulties encountered with lesioned tissue. Individualised immunocytochemical protocols have also been developed for the antibodies GFAP (to label astrocytes), MBP (to label myelin) and CNP-ase (to label oligodendrocytes). Sequential pre-treatment with proteinase-K, methanol and sodium borohydride achieved optimal GFAP localisation. MBP and CNP-ase were optimally localised after sequential pre-treatment with proteinase-K (at different concentrations) and sodium borohydride. Methanol pre-treatment resulted in a loss of immunoreactivity for these latter two antibodies. Each protocol achieved full immunocytochemical penetration throughout 40 microns vibratome sections. These techniques enable the new unbiased stereological tools (that is, the Cavalieri and optical disector principles) to be utilised.

On the cellular localization and distribution of carbonic anhydrase II immunoreactivity in the rat brain

Evidence is provided that carbonic anhydrase-II is localized in the central nervous system to wide spread systems of oligodendrocytes and restricted astroglia populations, involving both fiber bundles and neuropil. It is suggested that CO2 formed in activated axons may, via carbonic anhydrase-II, give rise to protons controlling the excitability of surrounding neuropil. Thus, CO2 may represent an important, highly diffusible, signal in brain, involved in the tonic control of neuronal activity.

Effects of carbonic anhydrase II (CAII) deficiency on CNS structure and function in the myelin-deficient CAII-deficient double mutant mouse

In the choroid plexus carbonic anhydrase II (CAII) supports the transport of bicarbonate ions, sodium ions, and water from blood to the CSF, and in the myelin sheath CAII supports compaction of myelin by stimulating cotransport of ions and water out from between the myelin membranes. In view of the latter, it is surprising that mutant mice deficient in CAII (Car-2n) have compact myelin. Since myelin basic protein also takes part in myelin compaction, we bred double CAII-deficient, myelin-deficient (Mld) mutant mice, in which the adults would have some compact myelin sheaths and a partial deficiency in myelin basic protein, with a view to examining oligodendrocytes and myelin sheaths in the double mutant. Like the parent Mld strain, the double mutants displayed tremors and seizures; however, the onset of seizures was delayed significantly in the double mutants, and the lifespan increased by several months. Like the brains of Car-2n mutants, those of double mutants (MldCar-2n) were deficient in mRNA and protein for CAII and showed upregulation of a different isozyme, CAIV. In the double mutants, oligodendrocytes were reduced in number, and the myelin sheaths and oligodendrocytes were swollen. The partial protection against seizures, which CAII deficiency conferred, suggests that acidosis in the central nervous system (CNS) of the Car-2n and MldCar-2n mice, due to absence of CAII from the choroid plexus, may downregulate the activity of NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural and molecular heterogeneity of astrocytes and oligodendrocytes in the gerbil lateral superior olive

The goal of this study was to determine the distribution and diversity of astrocytes and oligodendrocytes within the lateral superior olive of the gerbil. We used morphometric analyses and several immunocytochemical markers to assess differences in glial cell composition between the lateral (low-frequency projection) and the medial (high-frequency projection) limb of the lateral superior olive. Cell counts from Toluidine-stained semithin sections revealed a similar density of total astrocytes in both the lateral and the medial limbs. However, based on cytologic features, there was a prevalence of fibrous-like astrocytes in the lateral limb and protoplasmic-like astrocytes in the medial limb. In a similar manner, glial fibrillary acidic protein staining of astrocytes was intense in the lateral limb, but was largely restricted to the nucleus borders in the medial limb of the lateral superior olive. While glial fibrillary acidic protein was largely restricted to astrocytic processes, glutamine synthetase and S100 protein staining occurred, for the most part, in glial cell bodies. The density of glutamine synthetase positive cell bodies was homogeneous between the two limbs, while the density of S100-positive somata was significantly greater in the lateral limb. Cell counts obtained from semithin sections demonstrated a greater density of oligodendrocytes in the lateral limb than in the medial limb of the lateral superior olive. In a similar manner, there was a 40% greater density of carbonic anhydrase-positive somata in the lateral limb compared to the medial limb. Transferrin immunostaining was restricted to oligodendrocytes, but the density of labeled somata was identical in the lateral and medial limbs. 2',3'-Cyclic nucleotide 3'-phosphodiesterase and myelin-associated glycoprotein were also localized to the somata of oligodendrocytes, labeling both perisomatic and interfascicular cells. At the ultrastructural level, specialized contacts were found between pairs or clusters of oligodendrocytes. These results suggest that more than one type of astrocyte and oligodendrocyte is present within the gerbil lateral superior olive. Furthermore, glial cells were unevenly distributed, such that a greater density of oligodendrocytes and fibrous-like astrocytes were found in the low-frequency projection region. This heterogeneity is well correlated with known differences in the neuronal morphology within the lateral superior olive.

pH transients evoked by excitatory synaptic transmission are increased by inhibition of extracellular carbonic anhydrase

Excitatory synaptic transmission has been associated with a rapid alkalinization of the brain extracellular space. These pH shifts are markedly increased by acetazolamide, an inhibitor of carbonic anhydrase. Although this effect can be readily explained by inhibition of extracellular carbonic anhydrase, this enzyme has been considered strictly intracellular in the central nervous system. To determine whether these alkaline shifts are regulated by extracellular carbonic anhydrase, we studied the effects of a membrane impermeant, dextran-bound inhibitor of this enzyme. Extracellular alkaline transients, measured with pH-sensitive microelectrodes, were generated in the CA1 region of rat hippocampal slices by repetitive electrical stimulation of Schaeffer collateral fibers or by local ejection of glutamate. More direct alkalinizations were elicited by focal ejection of NaOH in the vicinity of a pH microelectrode. These pH transients were reversibly enhanced by addition of the dextran-bound inhibitor. We conclude that there is significant carbonic anhydrase activity in the extracellular space of the brain. We postulate that this enzyme functions in the regulation and modulation of extracellular pH transients associated with neuronal activity.

Carbonic anhydrase IV on brain capillary endothelial cells: a marker associated with the blood-brain barrier

Carbonic anhydrase (CA) activity plays an important role in controlling cerebrospinal fluid production and also influences neuroexcitation and susceptibility to seizures. Until recently, CA II was the only CA demonstrated in brain. Its distribution is limited to the epithelial cells of the choroid plexus and to the myelin-forming cells, the oligodendrocytes. In this report, we present immunoblots, using an antibody raised to CA IV from rat lung, that show that CA IV is also present in rat and mouse brain. Results of immunohistochemistry and immunoelectron microscopy on sections from rat and mouse brain are presented that show the distribution of CA IV to be quite distinct from that of CA II. CA IV is expressed on and is limited to the luminal surface of endothelial cells of cerebral capillaries. These results establish CA IV as a cytochemical marker associated with the blood-brain barrier and suggest an important role for CA IV in CO2 and HCO3- homeostasis in brain.

Comparison of immunocytochemical staining of astrocytes, oligodendrocytes, and myelinated fibers in the brains of carbonic anhydrase II-deficient mice and normal littermates

Immunostaining for carbonic anhydrase (CA) was performed in paraffin sections from the brains of CA II-deficient mutant mice and their normal littermates. Double immunofluorescence staining showed CA in myelinated tracts and oligodendrocytes in the cerebellum of the normal but not the CA II-deficient mice, and also in astrocytes in the cerebral cortex of the normal mice but not the mutants. The data show that the CA in normal oligodendrocytes, astrocytes, and myelin is the II isoenzyme, because these structures in the mutants would be positively stained if the staining normally were due to a contaminant in the antiserum or an antibody against a different isoenzyme. The findings in normal gray matter also suggest that many neuronal cell bodies are surrounded by a network of fine, CA-positive astrocytic processes.

Double-labeling in situ hybridization analysis of mRNAs for carbonic anhydrase II and myelin basic protein: expression in developing cultured glial cells

We applied in situ hybridization to analyze the location and the developmental changes in the distribution of the transcripts for carbonic anhydrase II (CAII) and myelin basic protein (MBP) in mouse primary cultured glial cells. Both mRNAs were localized to the oligodendrocyte using double-labeling in situ hybridization. No evidence for CAII transcripts in astrocytes was obtained, indicating that CAII is expressed only by oligodendrocytes in normal rodent glia. As early as 48 h after plating, CAII and MBP mRNAs are present in a few, small round cells. Message is present 2-4 days before levels of these proteins can be detected in similar primary glial cultures. The intensity of labeling for MBP and CAII mRNA positive cells increases significantly during the second week but then decreases after the end of the third week. Only the oligodendrocyte perikaryon and a few processes are positive during the first week. In contrast, at 14 days, a large number of cell processes in addition to the cell bodies are heavily stained for both mRNAs. Both mRNAs could be detected far away from the cell body, up to 250 microns in some cell processes. Some segments on a cell process accumulate higher levels of mRNA than other areas. These areas may correspond to the accumulation of free ribosomes and to starting points for the membrane sheets elaborated by cultured oligodendrocytes. The developmental profile for timing and distribution of these two messages mimics closely their in situ pattern.

Glutamine synthetase in oligodendrocytes and astrocytes: new biochemical and immunocytochemical evidence

The results of recent immunocytochemical experiments suggest that glutamine synthetase (GS) in the rat CNS may not be confined to astrocytes. In the present study, GS activity was assayed in oligodendrocytes isolated from bovine brain and in oligodendrocytes, astrocytes, and neurons isolated from rat forebrain, and the results were compared with new immunochemical data. Among the cells isolated from rat brain, astrocytes had the highest specific activities of GS, followed by oligodendrocytes. Oligodendrocytes isolated from white matter of bovine brain had GS specific activities almost fivefold higher than those in white matter homogenates. Immunocytochemical staining also showed the presence of GS in both oligodendrocytes and astrocytes in bovine forebrain, in three white-matter regions of rat brain, and in Vibratome sections as well as paraffin sections.

Individual C6 glioma cells migrate in adult rat brain after neural homografting

Cultured C6 glioma cells were prelabeled with the plant lectin Phaseolus vulgaris leuco-agglutinin (PHAL) and grafted as a cell suspension (10(6) cells in 5.0 microliters) into freshly made cortical implantation pockets in adult host rats. Animals were killed 1-21 days post-implantation (DPI). The brains were removed, dehydrated, embedded in paraffin and sectioned at 8 microns. Paraffin sections were processed for light level immunofluorescent double labeling for PHAL, a marker for graft derived cells, and glial fibrillary acidic protein (GFAP), a specific marker for C6 glioma cells and astrocytes. Cells positive for both PHAL and GFAP were graft-derived C6 cells. By 7 DPI a large mass developed which extended above the surface of the brain and invaded (displacement of host tissue by a cell mass) the host parenchyma. This mass increased in size over the next 14 days. The invading tumor mass contained double labeled cells at all time periods examined. In addition to the invasion process, grafted C6 cells spread through the host parenchyma by migration (movement of single cells). Individual graft-derived C6 (GFAP/PHAL positive) cells migrated into host cortex surrounding the implantation pocket, corpus callosum ventral to the implantation pocket, ipsilateral internal capsule and bilaterally in the habenula.

Glial contribution to seizure: carbonic anhydrase activity in epileptic mammalian brain

The activity of carbonic anhydrase (CA), a glial enzyme, was measured in the epileptic cortex of audiogenic DBA/2 mice and of cats with a freeze lesion. In mice, the activity increased with age from birth to 24 days, but were always higher in audiogenic mice than in normal C57/BL mice, reflecting species differences. The difference between the two strains increased sharply from 25 to 40 days of age, after the period of maximal audiogenic susceptibility. Acetazolamide, a CA-specific inhibitor, greatly decreased the seizure severity score of DBA/2 mice after a single intraperitoneal (i.p.) administration (150 mg/kg). After 24 days of age, when CA activities were high, the effect of acetazolamide was less important, suggesting that the increased cortical CA activity might reflect a protective mechanism. In cats with a freeze lesion, no significant changes in CA activities were observed in the actively discharging primary and secondary foci as compared with the nonepileptogenic perifocal cortex and the control cortex of sham-operated animals. The results indicate that the cortex of genetically susceptible audiogenic mice has an increased CA activity. The hypothesis of an adaptive glial mechanism, relating to the age-dependent decrease of seizure susceptibility in DBA/2 mice, is postulated.

Glutamine synthetase in the central nervous system is not confined to astrocytes

Glutamine synthetase (GS) immunoreactivity is frequently used as an astroglial 'marker'. However, when sections of adult rat spinal cords were immunostained with antibodies against sheep glutamine synthetase, intense immunofluorescence was observed in cells resembling oligodendrocytes. In white matter in the rat brain GS immunostaining was also found in ovoid oligodendrocyte-like cells, whereas in gray matter in the same tissue sections GS immunostaining was found in astrocytes. Like the antibodies against sheep GS, antibodies against rat GS also immunostained putative oligodendrocytes, and colocalization with 2',3'-cyclic nucleotide-3'-phosphohydrolase in spinal cord supported the designation of the GS-positive cells as oligodendrocytes.

Carbonic anhydrase activity in the peripheral nervous system of rat: the enzyme as a marker for muscle afferents

The distribution of carbonic anhydrase (CA) activity was determined histochemically using Hansson's cobalt phosphate method in cross-sections of peripheral nerves from rats. As the studied nerves contain either efferent, proprioceptive or exteroceptive myelinated fibres, our survey particularly focused on the question whether CA-reactive nerve fibres are functionally related. Intense CA activity was detected in all large diameter (8-12 microns) muscle afferents. The amount of similarly reactive cutaneous afferents was negligibly low (3.6%). Efferent fibres displayed only weak CA activity, which was confined to the small myelinated fibres (3-6 microns). Moderate staining could be assessed in medium-sized (4-11 microns) proprioceptive fibres. The same reactivity occurred in a sizeable percentage (11.4%) of exteroceptive afferents. Their diameters ranged from 4 to 11 microns. These results indicated, that high enzyme activity is found predominantly in large-calibre proprioceptive afferents, which according to Hunt's classification were identified as group IA and IB fibres. Further confirmation for our observations was obtained by demonstrating high levels of enzyme activity in primary nerve endings of muscle spindles (IA fibres) and in axon terminals of Golgi tendon organs (IB fibres) constantly. Finally possible functions for neuronal CA are discussed with respect to its high activity in a functionally related subpopulation of nerve fibres.

Oligodendrocytes express a normal phenotype in carbonic anhydrase II-deficient mice

The nervous system of a mouse mutant characterized by a carbonic anhydrase II (CA II) deficiency was examined with light and electron microscopy and with immunocytochemistry using different glial cell markers. No major morphologic abnormalities at either the cellular or subcellular level are detectable in the brains of CAII-deficient mice, even though CAII is the main isozyme of CA in the brain. The oligodendrocytes, which characteristically express high levels of CA II, do not exhibit signs of degeneration or abnormalities even in 1-year-old CA II-deficient mice. Similarly, neurons and astrocytes have a normal structure and distribution. Oligodendrocytes show a normal staining pattern and distribution for galactocerebroside (GC), 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), and myelin basic protein (MBP). Astrocytes have a normal morphology and distribution when stained for GFAP and S100 protein. The lack of major degeneration in the brain due to a CA II deficiency suggests these mice utilize other enzymatic or physiological pathways to compensate for the enzyme absence.

Maintenance of host medullary nucleus gracilis neurons after C3 homografting of fetal spinal cord into host fasciculus gracilis

The fasciculus gracilis (FG) of the third cervical spinal cord segment (C3) of adult rats was aspirated and fresh whole pieces of rat 14-day gestation cervical spinal cord, prelabeled with Phaseolus vulgaris leucoagglutinin, immediately placed in the pocket of one-half the operates. One to three months later there were no transplant derived rostro-caudal nerve fibers in the C1 or C2 segment of the aspiration-only or aspiration-graft FG. However, the neurons of the nucleus gracilis of the host medulla of the aspiration-only group were significantly atrophied whereas the neurons of the aspiration-graft group were not statistically different from normal. There were normal numbers of neurons in all groups. Using immunohistochemical double labeling for prelabeled astrocytes with PHAL and GFAP, graft-derived astrocytes were found in the nucleus gracilis of the host medulla. These data indicate that the trophic action of spinal graft-derived astrocytes maintained neurons in the medulla of the host nucleus gracilis.

Defective myelination in the optic nerve of the Browman-Wyse (BW) mutant rat

The Browman-Wyse (BW) rat displays a spectrum of ocular abnormalities which include myelination by Schwann cells of retinal ganglion cell (RGC) axons within the retina. Immunohistochemical and ultrastructural studies of the optic nerves of adult BW rats (30-60 days of age) with myelinated intraretinal axons were performed. Although individual nerves displayed considerable morphological variability, all were characterized by an initial dysmyelinated proximal segment which was separated from a normally myelinated distal segment by a transitional junctional zone. The proximal segment contained axons which were predominantly unmyelinated: where myelination occurred, almost all sheaths were Po-positive, proteolipid protein-negative, and the myelinating cell was a Schwann cell. In the distal segment the distribution of myelinated axons appeared to be normal, sheaths were PLP+, and the myelinating cell was an oligodendrocyte. Within the proximal segment, axons that were myelinated by Schwann cells were isolated by a basal lamina and expanded extracellular spaces from the bulk of other RGC axons within the optic nerve. Few carbonic anhydrase (CAII)+ or GalC+ oligodendrocytes were seen in proximal segments that contained Schwann cells: anti-CAII antibody stained atypical cells within the proximal segments which did not resemble CAII+ oligodendrocytes in the distal segment, and which were probably GalC-. Astrocytes appeared normal throughout the length of the nerve, and there was no morphological specialization at the junctional zone similar to that at the lamina cribrosa. The possible source(s) of the intraneural Schwann cells, and the pathogenetic mechanisms underlying the aberrant myelination of RGC axons within the BW optic nerve are discussed.

Graft derived reafferentation of host spinal cord is not necessary for amelioration of lesion-induced deficits: possible role of migrating grafted astrocytes

The present study explores the ability of fetal spinal cord homografts into lesioned host C3 fasiculus gracilis to influence the expected deterioration of hindlimb performance following this lesion. Rats were trained to traverse a narrow platform for a water reward. Animals were ranked for hindlimb performance utilizing slips, recovery and manner of traversing the platform. After training the animals, numbers were recorded, laminectomy performed at C3 and subject fasiculus gracilis (FG) bilaterally aspirated. Half the subjects were randomly selected for implantation of two, one mm segments of 14 day gestation cervical spinal cord. Recorded lesion-only and lesion-transplanted animals were tested 21, 30, 45, 60 and 90 days later. C3 fetal transplants significantly decreased the severity of hindlimb deficit at 21 and 90 days postlesion (p less than 0.05). The C1-FG of both groups contained no nerve fibers. However, the host nucleus gracilis of lesion-transplant animals contained normal sizes and numbers of neurons whereas the lesion-only group did not. This neuronal maintenance may have been due to factor(s) secreted by transplant derived astrocytes which migrated at 0.72-0.76 mm/day and reside in the host nucleus gracilis.

Acetyl-CoA carboxylase in rat brain. II. Immunocytochemical localization

Acetyl-CoA carboxylase (ACC) catalyzes the first and, possibly, the rate-limiting step in fatty acid biosynthesis. Because oligodendrocytes must synthesize large amounts of lipid during myelination, the hypothesis was proposed that ACC might be localized in cells of that type. In sections from the brains of 12-day-old rats, ACC immunostaining was observed in glial cells in white matter and gray matter. These cells resembled carbonic anhydrase-positive oligodendrocytes at mature and immature stages of their development. Cells resembling typical oligodendrocytes were also ACC-positive in white matter from the forebrains and brainstems of 15-17 day-old-rats. In both the gray matter and the white matter of 21-day-old rats there were intensely ACC-positive cells that strongly resembled oligodendrocytes. Oligodendrocytes in the brains of adult rats also were ACC-positive. While recognizing that some ACC must be present at lower levels in other types of cells and at all ages, it was concluded that the present findings are consistent with its primary locus as the oligodendrocytes, particularly during myelination. Further, enrichment of ACC and carbonic anhydrase in the same type of cell suggested that carbonic anhydrase might serve in providing a substrate, bicarbonate, to be utilized by ACC.

The astrocyte as a locus of carbonic anhydrase in the brains of normal and dysmyelinating mutant mice

There is some controversy in the literature whether carbonic anhydrase occurs in astrocytes, as well as in oligodendrocytes and myelin, in the mammalian brain. In the present study this issue was addressed by double immunostaining for carbonic anhydrase and two astrocytic "markers" in the brains of normal mice and two dysmyelinating mutants, jimpy and shiverer. In the brains of young mice, carbonic anhydrase and glutamine synthetase were colocalized in astrocytes in the cortical gray matter. In gray matter of the adult mouse brain, it was possible to immunostain both carbonic anhydrase and glial fibrillary acidic protein (GFAP) in the same cells. However, in contrast to the findings in gray matter, in and near subcortical white matter carbonic anhydrase could be detected only in oligodendrocytes and myelinated fibers. In the brains of jimpy mice, virtually all the carbonic-anhydrase-positive cells were also GFAP positive, even in regions normally occupied by white matter. In the brains of young and adult shiverer mice, carbonic anhydrase was localized in astrocytes in the gray matter, but in and near the tracts normally occupied by white matter carbonic anhydrase could be detected only in oligodendrocytes and their abundant processes. The findings confirmed the oligodendrocyte-myelin unit to be the primary locus of carbonic anhydrase in the normal mouse brain and showed the astrocytes in gray matter normally to be a secondary locus of carbonic anhydrase. The immunostaining in the jimpy mouse brain suggested further that reactive astrocytes, in particular, might be rich in carbonic anhydrase.

Monoclonal antibody 14E identifies the oligodendrocyte cell body in normal adult human and rat white matter

A monoclonal antibody, 14E, which detects immunocytochemically the perikarya of interfascicular oligodendrocytes in sections of normal adult human and rat white matter, was obtained using isolated normal human oligodendrocytes as the immunogen. 14E is an IgM antibody that reacts with a polypeptide of approximate molecular weight 23,000 on immunoblots of the particulate fraction of normal white matter. In sections of active multiple sclerosis plaques and recent infarcts, 14E immunostained the cell bodies and processes of only a small number of hypertrophic glial cells which could be oligodendrocytes undergoing pathological changes or a subpopulation of reactive astrocytes.

Localization of glial cell antigens in the brains of young normal mice and the dysmyelinating mutant mice, jimpy and shiverer

Tissue sections from the brains of normal, jimpy, and shiverer mice were immunostained by the peroxidase antiperoxidase method for carbonic anhydrase (CA) and the putative astrocytic "markers" glutamine synthetase (GS) and glial fibrillary acidic protein (GFAP). The cells in normal gray matter that immunostained with anti-CA and anti-GS were similar to one another in size and process elaboration. In the normal gray matter there were relatively few GFAP-positive astrocytes. When present, these cells resembled the CA- and GS-positive cells; however, the GFAP appeared to be concentrated in the astroglial processes, as distinguished from the cell bodies. Glial cell processes, immunostained for CA or GS, surrounded blood vessels and unstained neurons in the normal gray matter. The glial cells in shiverer gray matter were similar to those in the normal gray matter. When stained for GS or GFAP, the glial cells in the jimpy gray matter appeared to be somewhat hypertrophied, and when the glial cells in this mutant were stained for CA, the nuclei appeared to be swollen. It was concluded that some of the CA-positive cells in the gray matter of the normal and of each mutant mouse brain could be astrocytes. The patterns of immunostaining in the white matter emphasized the different complements of glial cells in the mutants. In the normal and shiverer mouse corpus callosum, CA, in particular, was detected only in the oligodendrocytes, their processes, and myelin. However, the data concerning the jimpy mouse suggested that the few CA-positive cells in the corpus callosum of that mutant could be astrocytes.

Differential effects of distal and proximal nerve lesions on carbonic anhydrase activity in rat primary sensory neurons, ventral and dorsal root axons

The effect of proximal and distal peripheral nerve injuries on the histochemistry of carbonic anhydrase (CA) in rat dorsal root ganglion (DRG) neurons, and myelinated (MyF) dorsal and ventral root fibers was studied. Sciatic neurectomy induced no change. Contrariwise, 7 days after lumbar spinal nerve section the numbers of CA-stained ventral root MyF and DRG cells at the L4 and L5 levels decreased to 73.2% and 51.9% of their original values respectively, although the numbers returned to normal by the 90th postoperative day. Dorsal root MyF followed a similar trend, albeit with some delay. Major morphological changes comprised atrophy of dorsal root sensory neurons and axons, particularly in long term experiments, as well as nuclear eccentricity in DRG neurons. These results suggest that, depending on the site of lesion, the rat peripheral nervous system (PNS) either maintains or quickly restores its capacity to synthesize CA. They stand in contrast to the long-lasting metabolic dysfunctions reported to occur when primary neurons are disconnected from the periphery. It is uncertain whether this difference is due to the critical role of CA in neuronal metabolism.

Biotin enrichment in oligodendrocytes in the rat brain

Cytochemical localization of endogenous biotin in the rat brain was detected by two different staining methods, avidin-biotin-HRP and goat-anti-biotin with HRP-rabbit-anti-goat. In both staining methods, oligodendrocytes were labeled to a far greater degree than other brain cells. This finding may be important for identification of the role of carbonic anhydrase, which is elevated in the oligodendrocyte, and it may help to explain how the oligodendrocyte generates large quantities of lipids for myelin production.

Carbonic anhydrase and horseradish peroxidase: double labelling of rat dorsal root ganglion neurons innervating motor and sensory peripheral nerves

Dorsal root ganglion neurons supplying peroneus longus, soleus and gastrocnemius medius muscles and the sural nerve of the rat were labelled with horseradish peroxidase and analysed for their carbonic anhydrase content. Staining of the sections was done either on the same or on alternate slides. Both methods led to the same results, despite a slight fading of the carbonic anhydrase reaction in double-stained sections. The data indicated that the muscles under study were supplied by approximately the same number of horseradish peroxidase-labelled cells, irrespective of their differences in size. 74.9% of these labelled neurons had diameters exceeding 30 microns and 52.4% of them also stained for carbonic anhydrase. The double-labelled cells represented 66.9% of the population of large neurons (greater than 30 microns) and comprised most of those measuring over 47.5 microns. Richness in carbonic anhydrase of the large muscle afferent neurons may be linked to their innervation of the stretch receptors, as components of an active apparatus which includes the gamma motor axons which also stain positively for carbonic anhydrase. In contrast, the ganglion cells supplying the sural nerve were almost totally devoid of carbonic anhydrase, as only 6.4% showed double labelling. This contingent possibly represents the muscle afferents of the small motoneural population which supplies, through this nerve, part of the foot musculature of the rat.

Characterization and localization of glutathione-S-transferases in rat brain and binding of hormones, neurotransmitters, and drugs

Rat brain glutathione-S-transferases are rich in Yb type subunits with major RNA transcripts coding for a relatively uncommon Yb3 form. The Yb-containing isoenzymes of brain cytosol bind glucocorticoids and are covalently labeled with dexamethasone 21-methanesulfonate. Certain neurotransmitters, hormones, and drugs, such as serotonin, dopamine, glucocorticoids, thyroxine, apomorphine, and benzodiazepine derivatives, are effective inhibitors of brain glutathione transferase activity. Immunocytochemical studies show that Yb forms are localized in ependymal cells, subventricular zone cells, astrocytes, tanycytes, and astrocyte foot processes on blood vessels, but Yb was not detected in oligodendrocytes or neurons. Based on their localization and binding properties, brain glutathione-S-transferases have the potential to function in intracellular binding of a variety of compounds and thereby govern their uptake and release in brain, transport to neurons, as well as in their detoxification.

Migration of cultured fetal spinal cord astrocytes into adult host cervical cord and medulla following transplantation into thoracic spinal cord

Cell suspensions from 14-day-gestation rat spinal cord, which had previously been soaked for 1 hr in a 2 micrograms/ml solution of Phaseolus vulgaris leucoagglutinin (PHAL), were cultured on collagen gels containing laminin for 2 weeks. Pieces of the gel and attached cells were then transplanted into the dorsal column of adult host thoracic spinal cord. At 1, 2, and 3 months postimplantation (MPI), animals were sacrificed, and the spinal cords were removed, embedded in paraffin, and sectioned at 8 micron for immunohistochemistry at the light microscopic level. Sections were double labeled for PHAL and utilized as a marker for transplant-derived cells and glial fibrillary acidic protein (GFAP), a specific marker for astrocytes. Transplant-derived astrocytes (PHAL-GFAP positive cells) migrated from the transplantation site in both rostral and caudal directions and were observed within the host dorsal column ipsilateral to the transplantation site. At 2 months, lateral migration into the contralateral dorsal column and ipsilateral dorsal horn was observed. At 3 MPI transplant-derived astrocytes were observed in host medulla (nucleus gracilis). Transplant-derived astrocytes were also observed on the glial limitans as far as nucleus gracilis. A migration rate of 0.72 mm/day was calculated, assuming a 14-day delay in the initiation of migration. The ramifications of such extensive migration are discussed with regard to return of function and amelioration of lesion-induced deficits.

Carbonic anhydrase immunostaining in astrocytes in the rat cerebral cortex

Carbonic anhydrase is known to occur in the choroid plexus, oligodendrocytes, and myelin, and to be virtually absent from neurons, in the mammalian CNS; however, there is significant controversy whether it is also present in astrocytes. When brain sections from adult rats were stained for simultaneous immunofluorescence of carbonic anhydrase and the astrocyte marker glutamine synthetase, both antigens were detected in the same glial cells in the cortical gray matter, whereas the oligodendrocytes and myelinated fibers in and adjacent to the white matter showed immunofluorescence only for carbonic anhydrase. Some glial cells in the gray matter also showed double immunofluorescence for carbonic anhydrase and glial fibrillary acidic protein. These results indicate that there is carbonic anhydrase in some astrocytes in the mammalian CNS.

Identification of Theiler's virus infected cells in the central nervous system of the mouse during demyelinating disease

Theiler's virus is a picornavirus responsible for a persistent, demyelinating infection of mouse central nervous system. We examined the nature of infected cells during the course of this disease using a simultaneous immunoperoxidase-in situ hybridization assay. Cell types were identified with antigenic markers and infected cells were recognized by the presence of viral RNA. We found that, depending on the animal, approximately 10% of infected cells were migroglia-macrophages, 5 to 10% were astrocytes and 25 to 40% were oligodendrocytes. Approximately half of the infected cells could not be identified.

Immunocytochemical localization of 5'-nucleotidase in myelinated peripheral nerves from the rat

In sciatic and trigeminal nerves from the rat, 5'-nucleotidase immunostaining was observed on the surfaces of the myelinated fibers and in the membranes encircling the outermost loops of the myelin sheaths, the paranodal loops, and perhaps the inner loops, but neither in the compact myelin nor in the axoplasm. These results, which were consistent with previous biochemical data regarding sciatic nerve, suggest that the function of 5'-nucleotidase in myelinated fibers in the peripheral nervous system may be to promote diffusion of adenosine between the glial and neuronal compartments.

Decrease in oligodendrocyte carbonic anhydrase activity preceding myelin degeneration in cuprizone induced demyelination

Both immunohistochemical and biochemical evidence is presented to show for the first time that carbonic anhydrase II (CA II) activity falls in the brain of mice in cuprizone (bis(cyclohexanone)oxalyldihydrazone) induced demyelination well before demyelination develops. This fall began during the first week, whereas the first signs of myelin degeneration induced by cuprizone did not appear until 3 weeks and demyelination in the superior cerebellar peduncle in the mouse took 6-8 weeks to develop. The findings suggest that oligodendrocyte CA II activity is essential either for the survival of oligodendrocytes or for the maintenance of central myelin.

Carbonic anhydrase activity develops postnatally in the rat optic nerve

We examined the appearance of carbonic anhydrase (CA) activity in rat optic nerves (RONs) 5-77 postnatal days of age and correlated the appearance of enzyme activity with structural and physiological alterations. CA activity was nearly absent before 10 days of age and appeared in this CNS white matter tract with a developmental time-course similar to that of oligodendrogliogenesis and myelinogenesis. When oligodendrocytes and myelin were depleted in the RON by treatment with a mitotic inhibitor, CA activity was markedly reduced. These observations support the hypothesis that CA is contained primarily in oligodendrocytes and myelin. Neural activity in the RON caused changes in extracellular pH (pHo) and the character of these pHo responses was very age dependent; older nerves exhibited much larger acid shifts than neonatal nerves. The development of CA activity may be a factor contributing to this physiological alteration.

Transplant-derived astrocytes migrate into host lumbar and cervical spinal cord after implantation of E14 fetal cerebral cortex into adult thoracic spinal cord

Fourteen-day gestation fetal cerebral cortex homografts were transplanted into the thoracic (T6) spinal cord between the left dorsal column and dorsal horn of adult host rats. The transplants were soaked in 2.0 micrograms/ml of the lectin Phaseolus vulgaris leucoagglutinin (PHAL) prior to implantation. Transplanted host spinal cords were utilized at 7, 14, and 24 d and at 1 and 2 months postimplantation. Paraffin-sectioned spinal cords were double labeled for PHAL and glial fibrillary acidic protein (GFAP) by using FITC- and RITC-conjugated secondary antisera, respectively. Montages of FITC- and RITC-positive cells were analyzed for cells containing both fluorescences. Double-labeled cells (PHAL-GFAP) were transplant-derived astrocytes. Transplant-derived astrocytes were observed to initiate migration in the white matter columns of the host at approximately 14 d after transplantation. Double-labeled astrocytes were observed in cervical and lumbar spinal cord of the host (ca. 3.5 cm away from the center of the transplant) at 2 months postoperative. These astrocytes migrated at approximately 0.76 mm a day (after a 14-d delay). At 2 months, transplant-derived astrocytes composed as much as 50% of the astrocytes in the white matter of the host 2.0 mm from the transplant. The migrated astrocytes were hypertrophied and appeared reactive. Astrocytes in spinal gray matter only migrate about 1.0 mm from the graft-host interface. Transplant-derived astrocytes can migrate the entire length of the spinal cord white matter.

Brain extracellular space: developmental studies in rat optic nerve

Analysis of neural activity-dependent fluctuations in K+, H+, and ECS dimensions in the developing RON has revealed major changes during the first two to three postnatal weeks. The emergence of the adult ceiling level for evoked extracellular K+ (10 to 12 mM) and significant ECS shrinkage are roughly correlated in time with the proliferation and maturation of glial cells in this structure. This observation and others have led to the hypothesis that ECS shrinkage depends upon electrolyte and water transport into glial cells with subsequent swelling. Development of the adult K+ ceiling level may also depend upon glial cells, but it is likely that other factors contribute to this homeostatic mechanism. Marked alterations in activity-dependent pHo shifts were seen with development and may be related to changes in the activity of carbonic anhydrase in this structure. The technological means are at hand to pursue these questions vigorously in an effort to provide further insight into the mechanisms of ionic and fluid homeostasis of brain ECS, and the developing RON appears to be a useful model system in this regard.

Biochemical and immunocytochemical evidence for a deficiency of normal interfascicular oligodendroglia in the CNS of the dysmyelinating mutant (md) rat

Carbonic anhydrase was assayed and carbonic anhydrase and 5'-nucleotidase were localized in the CNS of myelin-deficient mutant rats and normal littermates. The carbonic anhydrase specific activities were reduced by 61% and 29% in the mutants' forebrains and cerebella, respectively, and the total carbonic anhydrase activity in the spinal cords was reduced by 35%. Immunostained cells were found in gray matter from both normal and mutant rats, but, in the mutants, there was a marked deficiency of interfascicular oligodendrocytes in the regions that are normally occupied by white matter. It is suggested that a developmental study could indicate the step(s) at which normal differentiation of interfascicular oligodendroglia is blocked in this mutant.

5'-nucleotidase localization in the brains and spinal cords of adult normal and dysmyelinating mutant (shiverer) mice

Immunocytochemical staining with the antibody against mouse liver 5'-nucleotidase revealed 5'-nucleotidase antigenicity in myelinated fibers in the brains and in myelinated fibers and some interfascicular oligodendroglia in the spinal cords of normal adult mice. Although the 5'-nucleotidase specific activity in adult shiverer mouse CNS tissue homogenates had been shown to be normal, immunocytochemical staining with anti-mouse-5'-nucleotidase could be demonstrated in CNS tissue sections from only 2 out of 10 of the mutant animals. In tissue from these animals the staining, which was relatively faint, was localized specifically to cell-bodies, usually arranged in rows, and to material oriented parallel to nerve fibers. This pattern of immunostaining with anti-5'-nucleotidase resembled the immunostaining with anti-carbonic anhydrase but not with anti-glial-fibrillary-acidic-protein. This suggested that the rows of cells were oligodendrocytes, not astrocytes, and that the material parallel to nerve fibers might consist of oligodendrocyte processes wrapped loosely around axons. The antibody against rat 5'-nucleotidase, as distinguished from mouse, immunostained only the blood vessels in the shiverer mouse CNS, a finding similar to a previous observation in the normal mouse CNS. From these findings it was inferred that the primary loci of 5'-nucleotidase in the shiverer mouse CNS were interfascicular oligodendrocytes, their processes, and blood vessels, and in the normal mouse CNS, the myelin in some tracts, the blood vessels, and some interfascicular oligodendrocytes.

Antibody against mouse liver 5'-nucleotidase immunostains white matter in the adult mouse central nervous system

An antiserum against rat liver 5'-nucleotidase has been shown to immunostain myelinated fibers and oligodendrocytes in the rat CNS, consistent with evidence for 5'-nucleotidase activity in rat brain myelin and oligodendrocytes (Cammer, Sacchi and Kahn, Devel. Brain Res., 1985, 20: 89-96). However, in the mouse CNS, in which myelin also has 5'-nucleotidase activity, that antiserum stained only blood vessels. To obtain an antibody against the mouse enzyme, 5'-nucleotidase was partly purified from mouse liver membranes by detergent extraction, heat treatment, affinity chromatography, acidification, and ammonium sulfate fractionation. The preparation, which was enriched about 110-fold in 5'-nucleotidase specific activity, compared to the starting extract, was electrophoresed on a preparative slab gel containing Triton X-100, a strip was stained histochemically for 5'-nucleotidase, and the material corresponding to the stained band was used to immunize a rabbit. The immune IgG fraction, but not the preimmune IgG, reacted with mouse brain homogenates. The immune serum gave consistently greater inhibition of 5'-nucleotidase activity in mouse liver homogenates, mouse brain myelin and mouse brain homogenates, but not rat brain or liver homogenates, compared to the preimmune serum. The immune serum, but not the preimmune serum, immunostained white matter in the normal adult mouse brain and spinal cord. The findings suggest that the mouse may have one isozyme of 5'-nucleotidase similar to that in rat with respect to subunit sizes but differing in primary structure at one or more antigenic sites and support previous observations of 5'-nucleotidase activity in myelin from mouse brains and spinal cords.

Immunocytochemical demonstration of both carbonic anhydrase isoenzyme II and glial fibrillary acidic protein in some immature rat glial cells in primary culture

In glial cell cultures from newborn rat hemispheres we have demonstrated by immunocytochemistry the presence of carbonic anhydrase (CAII) and glial fibrillary acidic protein (GFAP) in the same cell. These double-stained cells are detected between day 5 and day 13 after seeding. These cells could be morphologically identified as oligodendroblasts. At 5 days in culture about 10% of the cells containing CAII also contained GFAP. At 11 days only 2% preserved this property. After 13 days in culture GFAP was only localized in typical astrocytes and CAII in oligodendroglial-like cells. The presumption that the immature glial cells, which contained specific markers of astrocytes and oligodendrocytes, became in our culture conditions essentially oligodendroglial cells is discussed.

Immunocytochemical localization of 5'-nucleotidase in oligodendroglia and myelinated fibers in the central nervous system of adult and young rats

Rat central nervous system (CNS) tissue sections were immunostained by the peroxidase-anti-peroxidase (PAP) method using a rabbit serum directed against rat liver 5'-nucleotidase. In paraffin sections from the brains of 60-day-old rats 5'-nucleotidase immunoreactivity occurred in the same white-matter regions as myelin-basic protein immunoreactivity and histological staining of myelin. The immunostaining of cerebral white matter for 5'-nucleotidase was more intense and wide-spread at the age of 120 days than at 60 days, and the choroid plexus and blood vessels were stained consistently. In the paraffin sections from the brains of younger (20-day-old) rats the staining of 5'-nucleotidase in the white matter was faint and patchy. In paraffin sections from spinal cord, 5'-nucleotidase immunoreactivity was observed throughout the lateral white-matter columns and, frequently, in the cell bodies of interfascicular oligodendroglia. Interfascicular oligodendroglia also showed 5'-nucleotidase immunoreactivity in vibratome sections from the CNS tissue of young and adult rats. The findings were consistent with histochemical and biochemical evidence for 5'-nucleotidase in rat brain myelin and oligodendroglia, with substantial increases in activity in the myelin as rats develop from the ages of 20 to 120 days. 5'-Nucleotidase immunoreactivity was not observed in any astrocytes or in oligodendrocytes in the gray matter; however, the enzyme may occur in those glial cells at levels lower than were detectable using the present method.

Oligodendroglial structures and distribution shown by carbonic anhydrase immunostaining in the spinal cords of developing normal and shiverer mice

The spinal cords of young and adult normal and dysmyelinating mutant (shiverer) mice were immunostained with anticarbonic anhydrase to investigate the distribution of oligodendroglial populations into the gray- and white-matter regions in the developing normal and mutant animals; the morphology of oligodendrocytes and their processes at the light microscopic level in gray matter and white matter; and the apparent gliosis in the gray matter, as well as the white matter, of the mutants. Immunocytochemistry and enzyme assays revealed consistent increases in carbonic anhydrase antigenicity and specific activity in controls and mutants between the ages of approximately 15 days and approximately 60 days. As shown previously in adult animals, oligodendroglia in larger than normal proportions were situated at the periphery of the "white-matter" columns, as compared to gray matter, in the shiverers, with, however, significant numbers of oligodendroglia were heterogeneous with respect to shapes, configuration of processes, and intensity of carbonic anhydrase immunostaining. In the shiverer "white matter" the oligodendrocytes were smaller than normal, and their shapes and arrangement were relatively irregular. In the normal gray matter short oligodendroglial processes appeared to be associated with neuronal perikarya, and those processes were more pronounced at approximately 90 days than at approximately 20 days of age. Background staining in normal gray matter suggested that oligodendroglial processes were, in addition, tightly wound around many axons. In shiverer gray matter the oligodendrocytes were smaller, and their processes appeared to be wrapped more loosely around smaller numbers of conspicuous axons and to be associated less frequently with neuronal perikarya. This finding suggests that the deficiency in the myelin basic protein in the mutant may affect interactions between oligodendrocytes and neurons in the gray matter as well as in the white matter. The astrocytic "marker," glial fibrillary acidic protein, was detected in gray and white matter of shiverers as young as 16 days, and the differences from carbonic anhydrase localization supported the conclusion that the processes enwrapping axons in the shiverer mouse CNS are derived from oligodendrocytes, not astrocytes.