CNS myelinogenesis in vitro: time course and pattern of rat oligodendrocyte development

Involvement of Degenerating 21.5 kDa Isoform of Myelin Basic Protein in the Pathogenesis of the Relapse in Murine Relapsing-Remitting Experimental Autoimmune Encephalomyelitis and MS Autopsied Brain

Multiple sclerosis (MS) is the chronic inflammatory demyelinating disease of the CNS. Relapsing-remitting MS (RRMS) is the most common type of MS. However, the mechanisms of relapse and remission in MS have not been fully understood. While SJL mice immunized with proteolipid protein (PLP) develop relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE), we have recently observed that some of these mice were resistant to the active induction of relapsing EAE after initial clinical and histological symptoms of EAE with a severity similar to the relapsing EAE mice. To clarify the mechanism of relapsing, we examined myelin morphology during PLP_139-151-induced RR-EAE in the SJL mice. While RR-EAE mice showed an increased EAE severity (relapse) with CNS inflammation, demyelination with abnormal myelin morphology in the spinal cord, the resistant mice exhibited a milder EAE phenotype with diminished relapse. Compared with the RR-EAE mice, the resistant mice showed less CNS inflammation, demyelination, and abnormalities of the myelin structure. In addition, scanning electron microscopic (SEM) analysis with the osmium-maceration method displayed ultrastructural abnormalities of the myelin structure in the white matter of the RR-EAE spinal cord, but not in that of the resistant mice. While the intensity of myelin staining was reduced in the relapsing EAE spinal cord, immunohistochemistry and immunoblot analysis revealed that the 21.5 kDa isoform of degenerating myelin basic protein (MBP) was specifically induced in the relapsing EAE spinal cord. Taken together, the neuroinflammation-induced degenerating 21 kDa isoform of MBP sheds light on the development of abnormal myelin on the relapse of MS pathogenesis.

Myelination of the developing lateral olfactory tract and anterior commissure

Both the lateral olfactory tract (LOT) and anterior limb of the anterior commissure (AC) carry olfactory information. The LOT forms the projection from the olfactory bulb to the ipsilateral olfactory cortices, while the AC carries odor information across the midline to the contralateral olfactory cortex and bulb. The LOT and AC differ on a number of dimensions, including early development and functional onset. The present work, examining their myelination in mice, reveals additional important differences. For example, the LOT initiates myelination 3-4 days earlier than the AC, evidenced by both an earlier increase in myelin basic protein staining seen with immunohistochemistry and an earlier appearance of myelinated fibers using electron microscopy. While both exhibit a period of rapid myelination, it occurs 4-5 days earlier in the LOT than the AC. The tracts also respond differently to early sensory restriction. Unilateral naris occlusion from the day after birth to postnatal day 30 had no consistent effects on the AC but resulted in significantly thinner myelin sheaths relative to axon caliber in the LOT. Finally, the two tracts differ structurally (the LOT contains larger, more densely packed axons with significantly thicker myelin sheaths resulting in a conduction velocity that is more than twice as fast as the AC). The findings indicate that these two large, accessible tracts provide an important means for studying brain maturation due to basic differences in both the timing of their maturation and general organization.

Effect of type-2 astrocytes on the viability of dorsal root ganglion neurons and length of neuronal processes

The role of type-2 astrocytes in the repair of central nervous system injury remains poorly understood. In this study, using a relatively simple culture condition in vitro, type-2 astrocytes, differentiated from oligodendrocyte precursor cells by induction with bone morphogenetic protein-4, were co-cultured with dorsal root ganglion neurons. We examined the effects of type-2 astrocytes differentiated from oligodendrocyte precursor cells on the survival and growth of dorsal root ganglion neurons. Results demonstrated that the number of dorsal root ganglion neurons was higher following co-culture of oligodendrocyte precursor cells and type-2 astrocytes than when cultured alone, but lower than that of neurons co-cultured with type-1 astrocytes. The length of the longest process and the length of all processes of a single neuron were shortest in neurons cultured alone, followed by neurons co-cultured with type-2 astrocytes, then neurons co-cultured with oligodendrocyte precursor cells, and longest in neurons co-cultured with type-1 astrocytes. These results indicate that co-culture with type-2 astrocytes can increase neuronal survival rate and process length. However, compared with type-1 astrocytes and oligodendrocyte precursor cells, the promotion effects of type-2 astrocytes on the growth of dorsal root ganglion neurons were weaker.

Myelin management by the 18.5-kDa and 21.5-kDa classic myelin basic protein isoforms

The classic myelin basic protein (MBP) splice isoforms range in nominal molecular mass from 14 to 21.5 kDa, and arise from the gene in the oligodendrocyte lineage (Golli) in maturing oligodendrocytes. The 18.5-kDa isoform that predominates in adult myelin adheres the cytosolic surfaces of oligodendrocyte membranes together, and forms a two-dimensional molecular sieve restricting protein diffusion into compact myelin. However, this protein has additional roles including cytoskeletal assembly and membrane extension, binding to SH3-domains, participation in Fyn-mediated signaling pathways, sequestration of phosphoinositides, and maintenance of calcium homeostasis. Of the diverse post-translational modifications of this isoform, phosphorylation is the most dynamic, and modulates 18.5-kDa MBP's protein-membrane and protein-protein interactions, indicative of a rich repertoire of functions. In developing and mature myelin, phosphorylation can result in microdomain or even nuclear targeting of the protein, supporting the conclusion that 18.5-kDa MBP has significant roles beyond membrane adhesion. The full-length, early-developmental 21.5-kDa splice isoform is predominantly karyophilic due to a non-traditional P-Y nuclear localization signal, with effects such as promotion of oligodendrocyte proliferation. We discuss in vitro and recent in vivo evidence for multifunctionality of these classic basic proteins of myelin, and argue for a systematic evaluation of the temporal and spatial distributions of these protein isoforms, and their modified variants, during oligodendrocyte differentiation.

Expression and function of ferroportin 1 in O-2A progenitor cells

Iron plays a crucial role in the survival, differentiation, and myelin formation of oligodendrocyte lineages. However, the regulation mechanism of iron homeostasis in oligodendrocytes remains unclear. Recently, much research has focused on Ferroportin 1 (FPN1), an iron exporter protein. First, about 95% pure primary rat O-2A progenitor cells were obtained by shaking methods in our laboratory. The expression of FPN1 mRNA and protein in O-2A progenitor cells were determined by reverse transcription-PCR and western blot. In addition, the localization of FPN1 at the cell membrane, in the cytoplasm and in processes was assayed by double-labeling immunofluorescence. A time-dependent increase of iron efflux from O-2A progenitor cells was confirmed by the calcein-indicated iron efflux assay. However, the same cells treated with FPN1 antibody showed no obvious change in iron release. For further confirmation, overexpression of FPN1 in O-2A progenitor cells was transduced with lentivirus. The release of iron in O-2A progenitor cells was dramatically increased by the overexpressed FPN1 when compared with that of the control group. Both ferritin (Ft) and transferrin receptor (TfR) are routinely used as indicators of labile iron pool. Cells pretreated with FPN1 antibody upregulated Ft and downregulated TfR protein level, while the opposite results occurred in the FPN1 overexpressing cells. Determination of Ft and TfR indirectly indicated that FPN1 might contribute to iron release from O-2A progenitor cells. We suggested that expression of FPN1 in O-2A progenitor cells might play a critical role in iron efflux from these cells.

Identification of a novel oligodendrocyte cell adhesion protein using gene expression profiling

Oligodendrocytes undergo extensive changes as they differentiate from progenitors into myelinating cells. To better understand the molecular mechanisms underlying this transformation, we performed a comparative analysis using gene expression profiling of A2B5+ oligodendrocyte progenitors and O4+ oligodendrocytes. Cells were sort-purified ex vivo from postnatal rat brain using flow cytometry. Using Affymetrix microarrays, 1707 transcripts were identified with a more than twofold increase in expression in O4+ oligodendrocytes. Many genes required for oligodendrocyte differentiation were upregulated in O4+ oligodendrocytes, including numerous genes encoding myelin proteins. Transcriptional changes included genes required for cell adhesion, actin cytoskeleton regulation, and fatty acid and cholesterol biosynthesis. At the O4+ stage, there was an increase in expression of a novel proline-rich transmembrane protein (Prmp). Localized to the plasma membrane, Prmp displays adhesive properties that may be important for linking the extracellular matrix to the actin cytoskeleton. Together, our results highlight the usefulness of this discovery-driven experimental strategy to identify genes relevant to oligodendrocyte differentiation and myelination.

Increased myelinating capacity of embryonic stem cell derived oligodendrocyte precursors after treatment by interleukin-6/soluble interleukin-6 receptor fusion protein

Neurosphere cells (NSc) derived from embryonic stem cells have characteristics of neural stem cells and can differentiate into oligodendrocyte precursors. Culture of NSc with IL6RIL6 chimera (soluble interleukin-6 receptor fused to interleukin-6) enhances their differentiation into oligodendrocytes with longer and more numerous branches and with peripheral accumulation of myelin basic protein (MBP) in myelin membranes indicating maturation. Gene expression profiling reveals that one of the proteins strongly induced by IL6RIL6 is a regulator of microtubule dynamics, stathmin-like 2 (SCG10/Stmn2), and gene silencing shows that Stmn2 plays an important role in the development of the mature oligodendrocyte morphology. IL6RIL6 acts as an effective stimulator of the myelinating function of ES cell-derived oligodendrocyte precursors, as observed upon transplantation of the IL6RIL6- pretreated cells into brain slices of MBP-deficient shiverer mice.

Biochemical and morphologic evidence of the interaction of oligodendrocyte membrane rafts with actin filaments

Cytoskeletal structures under the cell membrane carry out pivotal roles in the maintenance and remodeling of the cell structures. Reforming of the cytoskeletal networks after partial extraction of membrane components could be a good clue to identify molecular components pertaining the interaction of cytoskeleton with membrane. A detergent extract from 3-week-old rat brain membrane fraction was found to make an actin-based gel upon incubation at 25 degrees C. Some protein components of the gelation products were recovered in a Triton-insoluble low-density microdomain fraction (raft) after depolymerization of actin filaments. Some of these proteins were identified as 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG) through electrospray time-of-flight (ESI-TOF) analysis and Western blotting. Because these proteins are well-known marker proteins of oligodendrocytes, localization of these proteins and cholesterol, a raft-localized lipid, with actin filaments was studied using cultured oligodendrocytes. Clear colocalization of these proteins and cholesterol with actin filaments was observed after Triton treatment at 4 degrees C before fixation. These results indicate that raft microdomains participate in the formation of cell shape through interaction with microfilaments in oligodendrocytes.

Hoxb4 in oligodendrogenesis

1. Although recent advances have provided insight into the transcriptional control of oligodendrocyte (OG) development, little information exists on the role of clustered Hox genes in this process. The aim of this study was to examine the expression profile of Hoxb4 in the oligodendroglial lineage. 2. Immunocytochemical analysis of primary mixed glial cultures demonstrated that Hoxb4 was expressed throughout OG development, being coexpressed with oligodendroglial markers, A2B5, O4 (97%). GalC (91%), and MBP (93%). 3. Immunohistochemical analysis of transverse spinal cord sections demonstrated diffuse expression of Hoxb4 throughout the spinal cord at E12.5 (C16/T19), after which expression was confined primarily to the presumptive gray matter. 4. At E14.25 (C19+/T21), Olig2+ cells had begun to migrate out from the ventral ventricular zone into the presumptive gray matter. These results suggest that Olig2+ cells could coexpress Hoxb4 since it is expressed throughout this region. 5. The expression of Hoxb4 by cells of the OG lineage indicates that it could play a role in OG maturation.

Rho kinase regulates schwann cell myelination and formation of associated axonal domains

The myelin sheath forms by the spiral wrapping of a glial membrane around an axon. The mechanisms involved are poorly understood but are likely to involve coordinated changes in the glial cell cytoskeleton. Because of its key role as a regulator of the cytoskeleton, we investigated the role of Rho kinase (ROCK), a major downstream effector of Rho, in Schwann cell morphology, differentiation, and myelination. Pharmacologic inhibition of ROCK activity results in loss of microvilli and stress fibers in Schwann cell cultures and strikingly aberrant myelination in Schwann cell-neuron cocultures; there was no effect on Schwann cell proliferation or differentiation. Treated Schwann cells branch aberrantly and form multiple, small, independent myelin segments along the length of axons, each with associated nodes and paranodes. This organization partially resembles myelin formed by oligodendrocytes rather than the single long myelin sheath characteristic of Schwann cells. ROCK regulates myosin light chain phosphorylation, which is robustly, but transiently, activated at the onset of myelination. These results support a key role of Rho through its effector ROCK in coordinating the movement of the glial membrane around the axon at the onset of myelination via regulation of myosin phosphorylation and actomyosin assembly. They also indicate that the molecular machinery that promotes the wrapping of the glial membrane sheath around the axon is distributed along the entire length of the internode.

Primary culture of cortical neurons, type-1 astrocytes, and microglial cells from cynomolgus monkey (Macaca fascicularis) fetuses

We established selective primary cultures of neurons, astrocytes, and microglial cells from cryopreserved fetal cerebral cortex of cynomolgus monkeys (Macaca fascicularis). At 14 days in serum-containing medium, the cell cultures of the fetal cerebral cortex consisted primarily of neurons, astrocytes, and floating microglial cells. At 21 days, we observed a small number of myelin basic protein (MBP)-positive oligodendrocytes. The addition of cytosine arabinoside (a selective DNA synthesis inhibitor) at 2 days in culture eliminated proliferative glial cells, allowing adequate numbers of neurons to survive selectively. A chemically defined serum-free medium successfully supported neuronal survival at a level equivalent to that supported by the serum-containing medium. Brain-derived neurotrophic factor (BDNF) significantly affected the survival of primate neurons. Glutamate induced a significant degree of neuronal cell death against primate neurons and MK-801, a selective N-methyl-D-aspartate receptor (NMDAR) antagonist, blocked cell death, which suggests that primate cortical neurons have NMDAR and the glutamate-induced cell toxicity is mediated by NMDAR. In the serum-free medium, type-1 astrocytes responded to dibutyryl cyclic AMP and showed a process-bearing morphology. The growth of type-1 astrocytes in the serum-free medium was stimulated by epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and hydrocortisone, which are known growth factors in rat type-1 astrocytes. Cultured microglial cells expressed CD68, a monocyte marker. Macrophage-colony stimulating factor (M-CSF) stimulated microglial cell growth in the serum-free medium. These selective primary culture systems of primate cerebral cortical cells will be useful in issues involving species specificity in neuroscience.

Early stages of oligodendrocyte development in the embryonic murine spinal cord proceed normally in the absence ofHoxa2

Recent discoveries have enhanced our knowledge of the transcriptional control of oligodendrocyte (OG) development. In particular, the transcription factors (TFs) Olig2, Pax6, and Nkx2.2 have been shown to be important in the specification and/or maturation of the OG lineage. Although numerous other TFs are expressed by OGs, little is known regarding their role(s) in oligodendrogenesis. One such TF is the homeobox gene Hoxa2, which was recently shown to be expressed by O4(+) pro-oligodendrocytes. The objectives of this study were to examine the expression of Hoxa2 during the early stages of OG development, as well as to determine whether Hoxa2 is required for specification and/or early maturation of OGs. Immunocytochemical analysis of primary mixed glial cultures demonstrated that Hoxa2 was expressed throughout oligodendrogenesis, diminishing only with the acquisition of a myelinating phenotype. Serial transverse spinal cord sections from embryonic days 12.5, 14.25, 16, and 18 Hoxa2(+/+), Hoxa2(+/-), and Hoxa2(-/-) mice were subjected to single and double immunohistochemical analysis in order to examine Hoxa2, Olig2, Nkx2.2, and Pax6 expression profiles. Results obtained from Hoxa2(+/+) and Hoxa2(+/-) mice suggested that Hoxa2 was expressed by migratory oligodendroglial cells. In addition, comparison of spinal cord sections obtained from Hoxa2(+/+), Hoxa2(+/-), and Hoxa2(-/-) mice suggested that specification and early maturation of OGs proceeded normally in the absence of Hoxa2, since there were no obvious alterations in the expression patterns of Olig2, Nkx2.2, and/or Pax6. Hence, although Hoxa2 is expressed throughout OG development, it does not appear to be critical for early stages of oligodendrogenesis in the murine spinal cord.

Increase of oligodendrocyte progenitor cells after spinal cord injury

The reaction of oligodendrocyte progenitor cells (OPCs) after spinal cord injury (SCI) is poorly understood. In this study, we examined oligodendroglial reactions after contusion SCI in adult rats by immunohistochemistry. OPCs were identified by staining with monoclonal antibodies (mAbs) A2B5 and O4. Each of the A2B5-, O4-positive OPCs and galactocerebroside-positive oligodendrocytes dramatically increased in the lesion of the dorsal posterior funiculus. Bromodeoxyuridine (BrdU) incorporation studies showed that most O4-positive cells in the lesion were labeled with BrdU, suggesting that these OPCs were proliferative. In contrast, the expression of myelin basic protein was decreased in the lesion compared with controls that received laminectomy only. From the injured cord, OPCs were isolated by immunopanning with mAb A2B5. We observed an increased number of OPCs from the injured spinal cords compared with those isolated from controls and unoperated animals. After several days in culture, the OPCs from the lesion expressed galactocerebroside. These results suggest that OPCs are induced and can differentiate following SCI in the adult rat.

NBQX attenuates excitotoxic injury in developing white matter

The excitatory neurotransmitter glutamate is released from axons and glia under hypoxic/ischemic conditions. In vitro, oligodendrocytes (OLs) express non-NMDA glutamate receptors (GluRs) and are susceptible to GluR-mediated excitotoxicity. We evaluated the role of GluR-mediated OL excitotoxicity in hypoxic/ischemic white matter injury in the developing brain. Hypoxic/ischemic white matter injury is thought to mediate periventricular leukomalacia, an age-dependent white matter lesion seen in preterm infants and a common antecedent to cerebral palsy. Hypoxia/ischemia in rat pups at postnatal day 7 (P7) produced selective white matter lesions and OL death. Furthermore, OLs in pericallosal white matter express non-NMDA GluRs at P7. Unilateral carotid ligation in combination with hypoxia (6% O(2) for 1 hr) resulted in selective, subcortical white matter injury with a marked ipsilateral decrease in immature and myelin basic protein-expressing OLs that was also significantly attenuated by 6-nitro-7-sulfamoylbenzo(f)quinoxaline-2,3-dione (NBQX). Intracerebral AMPA demonstrated greater susceptibility to OL injury at P7 than in younger or older pups, and this was attenuated by systemic pretreatment with the AMPA antagonist NBQX. These results indicate a parallel, maturation-dependent susceptibility of immature OLs to AMPA and hypoxia/ischemia. The protective efficacy of NBQX suggests a role for glutamate receptor-mediated excitotoxic OL injury in immature white matter in vivo.

The oligodendroglia cytoskeleton in health and disease

Oligodendrocytes have a high rate of synthetic activity and produce vast amounts of myelin. The membrane production requires specific sorting and transport processes and structural support. In culture, oligodendrocytes extend flat membranous sheets containing an extensive cytoskeletal network of microtubules (MTs) and microfilaments (MFs). The microtubules participate in the elaboration and stabilization of the myelin-containing cellular processes and have an impact not only on the complex oligodendroglia architecture but also influence their functions. They participate in intracellular sorting processes and the translocation of myelin basic protein (MBP) mRNAs to the forming myelin sheath. The two major groups of neuronal microtubule-associated proteins (MAPs), MAP2 and tau are expressed in oligodendrocytes and might be involved in the regulation of MT stability and organization. Myelin-specific proteins, such as MBP and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), interact with the cytoskeleton. Glial changes occur in a variety of neurodegenerative diseases, and glial fibrillary tangles and glial cytoplasmic inclusions (GCls), containing abnormal microtubular structures which stain positively for stress proteins and microtubule-associated proteins, are found in oligodendrocytes of the affected brains. The role of MTs and their associated proteins in oligodendrocytes during normal development and pathological situations is specifically emphasized in this review.

Monoclonal antibody 14F7, which recognizes a stage-specific immature oligodendrocyte surface molecule, inhibits oligodendrocyte differentiation mediated in co-culture with astrocytes

Cells at an intermediate stage of oligodendrocyte lineage are not only well characterized by biochemical studies but also are likely to relate to the outcome of physiological events. To elucidate the molecular events leading to the development of oligodendrocyte lineage cells, we have raised monoclonal antibodies against stage-specific immature oligodendrocytes, which have previously been isolated by a novel oligodendrocyte-lineage cell culture technique (Sakurai et al.: J Neurosci Res 52:17-26, 1998). We have isolated a mouse monoclonal antibody termed 14F7 which predominantly labels stage-specific immature oligodendrocytes and have found that the expression of 14F7 immunoreactivity in the developing neonatal rat forebrain is closely associated with cells expressing the oligodendrocyte progenitor marker A2B5 and to immature oligodendrocyte expressing O4 antigen. 14F7+ cells were distributed in the ventricular and subventricular zone and the nearby forming corpus callosum as non-myelinating cells. In contrast to cell culture observations, 14F7+ cells were seen only in oligodendrocyte lineage cells. For instance, dissociated cell culture studies indicated that 14F7 labels a cell surface molecule, and its cellular distribution is coincident with all of O4+ cells and A2B5+ cells, and even A2B5- cells. By contrast, 14F7-positive cells did not label astrocytes and, furthermore, did not label myelin basic protein (MBP)-positive oligodendrocytes. 14F7 recognized a 48-kDa protein on sodium dodecyl sulfate polyacrylamide gel electrophoresis. 14F7 immunoreactivity was detectable in rat brain as early as embryonic day 18. Furthermore, in these cells, the total time for differentiation was extended, and on maturation, these cells subsequently expressed an array of myelin-specific proteins, which normally occurs by direct contact with type-1 astrocytes. However, in the presence of 14F7, stage-specific oligodendrocytes co-cultured with astrocytes completely failed to express MBP. These data suggest that the 14F7 antigen is a novel cell surface molecule that is expressed in the intermediate stage of oligodendrocyte-lineage cells, and it is expected that it regulates the differentiation of oligodendrocyte throughout development.

Glucocorticoids and progestins signal the initiation and enhance the rate of myelin formation

Dexamethasone and progesterone have been found to accelerate the time of initiation and enhance the rate of myelin synthesis in Schwann cell/neuronal cocultures. The expression of mRNA for cytochrome P450scc (converts cholesterol to pregnenolone), 3beta-hydroxysteroid dehydrogenase (converts pregnenolone to progesterone), and the progesterone receptor were detected and markedly induced during peak myelin formation in the cocultures. The mRNA for the glucocorticoid receptor was detected, but was found to be constituitively expressed. In addition, the specific activity of 3beta-hydroxysteroid dehydrogenase was measured and found to increase by 10-fold. The mRNA for cytochrome P450scc and 3beta-hydroxysteroid dehydrogenase also were found to be induced during the differentiation of O-2A precursor cells to oligodendrocytes. Fibroblast growth factor and platelet-derived growth factor were found to have proliferative effects on Schwann cells, but they had no effect on the initiation or the rate of myelin formation. These results demonstrate that myelin-forming cells have inducible enzymes responsible for steroid biosynthesis and suggest a critical role for endogenous steroid hormones in signaling the initiation and enhancing the rate of myelin formation.

Morphometric analysis of the postnatal mouse optic nerve following prenatal exposure to alcohol

Pregnant female mice were divided on day 12 post coitum into a control and an experimental group. The experimental group was given a single intraperitoneal dose of 0.015 ml/g body weight of 25% solution of alcohol in distilled water while the control group was exposed to a similar weight related dose of normal saline. The optic nerves were isolated from the offspring of both control and experimental groups at wk 2, 3 and 5 (i.e. during the juvenile period of postnatal development) and analysed by light and electron microscopy. Although in both groups the optic nerve grew in size rapidly during the period studied, the rate of growth in the experimental groups lagged behind that of the controls. The difference was initially significant but tailed off, so that by wk 5 it was no longer significant. The time of initial onset and progression of myelinogenesis in the optic nerve of alcohol exposed mice also lagged behind that of controls. In both groups the size distribution of the myelinated nerve fibres in the optic nerve was unimodal with a positive skewing for all ages. The spectrum of size distribution of the nerve fibres was, however, broader in controls than in the corresponding experimental groups. With increasing age the proportion of small and medium size fibres was greater in the experimental group than in the controls, while for the large diameter fibres the reverse was observed. It is suggested that this study may shed light on the teratogenic effect of 'binge' drinking during pregnancy and that it is the critical period when exposure occurs that is more important than the duration of administration.

Digital fluorescence imaging of elementary steps of neurosteroid synthesis in rat brain glial cells

With fluorescence microscopic imaging, we have examined Ca2+ signaling, LDL uptake and distribution of cytochrome P450 scc on individual rat brain glial cells in order to investigate the molecular mechanisms of neurosteroid synthesis. Astrocytes and oligodendrocytes were cultured from newborn rat brain. Ca2+ signaling was observed in Calcium Green-1 loaded astrocytes upon neurotransmitter stimulations using video-enhanced microscopy. Upon stimulation of serotonin and glutamate, we observed typically three types of Ca2+ signaling which were Ca2+ oscillations, a transient increase in Ca2+ concentration and Ca2+ oscillations superimposed on a transient Ca2+ increase. On the other hand, histamine and ATP induced only a transient increase in Ca2+ without oscillatory response. Uptake of octadecyl rhodamine (R18) labeled LDL by astrocytes and oligodendrocytes was observed in the time scale of 30 min with confocal laser scanning microscopy. Some localization of LDL in the cytoplasm was observed for astrocytes. For oligodendrocytes, incorporated LDL was distributed over the entire cytoplasmic region of both cell body and multiple branched cell processes. The presence of a significant amount of cytochrome P450 scc was demonstrated with immunofluorescence staining in both astrocytes and oligodendrocytes. The density of P450 scc in both glial cells was suggested to be around 1% of that in bovine adrenocortical fasciculata cells. The results lead to an improved quantitative picture of neurosteroid synthesis in glial cells.