Incorporation of thymidine-H3 by cells in normal and injured mouse spinal cord

Neurogenesis and gliogenesis in the spinal cord of turtles

A 5-bromo-3'-deoxyuridine (BrdU) pulse administered to juvenile turtles resulted in cell labeling throughout the gray matter (GM) and white matter (WM) of the spinal cord. One and twenty-four hours postinjection, larger densities of BrdU-labeled nuclei (LN) occurred within the GM, with a density peak localized in the central region (CR). Seven days later, density differences between GM and WM disappeared, accompanying a more uniform distribution of LN in the GM (absence of the central peak). Multiple injection experiments also showed similar evolution in the distribution of LN. Morphometric studies revealed that the size of LN had undergone time-related increments: Larger nuclei appeared at protracted fixation time points. Double-labeling experiments indicated that BrdU-labeled cells expressed neuroactive substances, such as gamma-aminobutyric acid (GABA), neuron-specific nuclear protein (NeuN), and the cytoplasmic early postmitotic neuronal marker (TUC-4). Other BrdU-labeled cells expressed the glial-specific protein (GFAP). GABA-BrdU, TUC-4-BrdU, and GFAP-BrdU double-labeled cells were recognized 6 days after the first BrdU injection. NeuN-BrdU double-labeled cells were found at 50 days postinjection. Three-dimensional transmission electron microscopy revealed the presence of synapses and typical kinocilia in putative immature nerve cells. Kinocilia were also found in putative immature glial cells. In consideration of the scattered distribution pattern of BrdU-labeled cells, in animals fixed 1 hour postinjection, the existence of a single proliferating center was discarded. The CR, including the ependymal epithelium, showed the highest density of LN.

Differentiation of proliferated NG2-positive glial progenitor cells in a remyelinating lesion

Cells that express the NG2 proteoglycan (NG2+ cells) constitute a large cell population in the adult mammalian central nervous system (CNS). They give rise to mature oligodendrocytes in culture and are thus considered to be oligodendrocyte progenitor cells (OPCs). They proliferate in response to a variety of insults to the CNS, but their ability to differentiate into oligodendrocytes in vivo has not been established. We used bromodeoxyuridine (BrdU) to trace the fate of NG2+ cells that proliferated in response to a chemically induced demyelinating lesion in the adult rat spinal cord. Cells that were proliferating 24 hr after lesioning were labeled by a single injection of BrdU, and their antigenic phenotype was examined at various times up to 28 days post-lesioning (28 dpl). Initially, at 2 dpl, NG2+/BrdU+ cells were found almost exclusively at the periphery of the lesion. At 7 dpl, the number of NG2+/BrdU+ cells increased in the lesion center and decreased from the surrounding areas. The number of NG2+/BrdU+ cells inside the lesion further decreased with time, concomitant with progression of remyelination and appearance of BrdU+ mature oligodendrocytes. Double labeling with (3)H-thymidine and BrdU combined with NG2 immunohistochemistry showed that some NG2+ cells in the lesion had undergone at least two rounds of cell division. These observations strongly suggest that NG2+/BrdU+ cells that appeared in response to the demyelinating insult gave rise to mature remyelinating oligodendrocytes, providing an in vivo evidence for the differentiation of NG2+ cells into oligodendrocytes.

In vivo infusions of exogenous growth factors into the fourth ventricle of the adult mouse brain increase the proliferation of neural progenitors around the fourth ventricle and the central canal of the spinal cord

Stem cells isolated from the fourth ventricle and spinal cord form neurospheres in vitro in response to basic fibroblast growth factor (FGF2)+heparin (H) or epidermal growth factor (EGF)+FGF2 together. To determine whether these growth factor conditions are sufficient to induce stem cells within the fourth ventricle and spinal cord to proliferate and expand their progeny in vivo, we infused EGF and FGF2, alone or together, with or without H, into the fourth ventricle for 6 days via osmotic minipumps. Animals were injected with bromodeoxyuridine (BrdU) on days 4, 5 and 6 of infusion in order to label cells proliferating in response to the growth factors. Infusions of EGF+FGF2+H into the fourth ventricle resulted in the largest proliferative effect, a 10.8-fold increase in the number of BrdU+ cells around the fourth ventricle, and a 33.5-fold increase in the number of BrdU+ cells around the central canal of the spinal cord, as compared to vehicle infused controls. The majority of the cells were nestin+ after 6 days of infusion. Seven weeks post-infusion, 22 and 30% of the number of BrdU+ cells induced to proliferate after 6 days of EGF+FGF2+H infusions were still detected around the fourth ventricle and central canal of the spinal cord, respectively. Analysis of the fates of the remaining cells showed that a small percentage of BrdU+ cells around the fourth ventricle and in the white matter of the spinal cord differentiated into astrocytes and oligodendrocytes. BrdU+ neurons were not found in the brainstem or in the grey matter of the cervical spinal cord 7 weeks post-infusion. These results show that endogenous stem cells and progenitors around the fourth ventricle and central canal of the spinal cord proliferate in response to exogenously applied growth factors, but unlike in the lateral ventricle where they generate some new neurons, they only produce new astrocytes and oligodendrocytes at 7 weeks post-infusion.

Proliferation of parenchymal neural progenitors in response to injury in the adult rat spinal cord

It has long been believed that the fully developed mammalian central nervous system (CNS) lacks significant regenerative capacity. Recent advances have revealed, however, that many regions of the adult CNS contain neural progenitors that have the ability to generate new neurons and glia. Although the periventricular area has been identified as a rich source of these progenitors, their precise location in each region and details of their properties in vivo still remain poorly understood. Here we provide evidence that in the adult rat spinal cord, a significant number of neural progenitors are present, not only in the periventricular area, but also in other regions of the parenchyma. These progenitors could proliferate in vitro as neurosphere-like cell aggregates in the presence of growth factors and also gave rise to neurons and glia under appropriate conditions. We further demonstrate that these parenchymal neural progenitors were capable of proliferating in vivo in response to injury. Immunohistochemical studies suggested that proliferative progenitors emerged throughout the gray and white matter in the lesioned spinal cord. Consistently, an increased number of neurosphere-forming cells could be isolated from injured tissues, and they were able to differentiate into neurons in vitro. The widespread occurrence of neural progenitors in the parenchyma expands the possibility of repairing damaged tissue by activating the latent regenerative potential of the adult spinal cord.

EGF-responsive neural stem cells are a transient population in the developing mouse spinal cord

The adult mouse forebrain, which exhibits substantial ongoing cell genesis, contains self-renewing multipotent neural stem cells that respond to epidermal growth factor (EGF), but the adult spinal cord, which exhibits limited cell genesis, does not. Spinal cord development is a process characterized by defined periods of cell histogenesis. Thus, in the present study we asked whether EGF-responsive neural stem cells are present within the spinal cord during development. At embryonic day (E) 11, subsequent to the onset of neurogenesis, only fibroblast growth factor (FGF) receptors and FGF-2 (requiring heparan sulphate)-responsive stem cells are present in the spinal cord. Between E12 and 14, at the peak of spinal cord neurogenesis and the onset of gliogenesis, EGF receptors appear along with clonally derived highly expandable EGF-responsive neural stem cells. Following the cessation of cell histogenesis, the adult spinal cord is largely devoid of both EGF receptors and EGF-responsive stem cells. On the other hand, the FGF receptor1c subtype and multipotent FGF-2-responsive neural stem cells are present in early development and in the adult. The order of appearance of spinal cord neural stem cells and in vitro lineage analysis suggests that a more primitive FGF-2-responsive stem cell produces the EGF-responsive stem cell. These findings suggest that EGF-responsive neural stem cells appear transiently in the spinal cord, during the peak period of cell histogenesis, but are no longer present in the relatively quiescent adult structure.

Proliferation of NG2-positive cells and altered oligodendrocyte numbers in the contused rat spinal cord

Given the numerous reparative roles glia may play after spinal cord injury (SCI), glial proliferation and cell number were examined in a model of traumatic SCI. Emphasis was placed on analysis of oligodendrocytes and NG2-positive (NG2+) cells, an endogenous cell population that may be involved in oligodendrocyte replacement. Overall, proliferation (assessed by bromodeoxyuridine incorporation) was markedly elevated during the first 2 weeks after injury and declined thereafter; a large portion of these dividing cells likely consisted of microglia-macrophages. Although the total number of NG2+ cells in the epicenter was reduced by half, we noted protracted proliferation in surviving NG2+ cells, with values sevenfold greater than in uninjured controls. Elevated proliferation of NG2+ cells persisted throughout the first 4 weeks after injury. However, the absolute number of NG2+ cells was not increased over controls, suggesting that the daughter cells either did not survive or they differentiated into other cell types. As expected, oligodendrocyte numbers were drastically altered after SCI. By 7 d after injury, the number of oligodendrocytes at the impact site was reduced by 93%. Despite ongoing tissue loss, the number of oligodendrocytes in spared tissue rose threefold at 14 d after injury. Although the function of NG2+ cells within the spinal cord is not completely understood, several studies suggest that they may differentiate into oligodendrocytes. Thus, proliferating NG2+ cells may contribute to the increased oligodendrocyte number observed at 2 weeks after injury. Future studies are required, however, to definitively determine the role NG2+ cells play in oligodendrocyte genesis, remyelination, and other post-injury events.

Adult spinal cord stem cells generate neurons after transplantation in the adult dentate gyrus

The adult rat spinal cord contains cells that can proliferate and differentiate into astrocytes and oligodendroglia in situ. Using clonal and subclonal analyses we demonstrate that, in contrast to progenitors isolated from the adult mouse spinal cord with a combination of growth factors, progenitors isolated from the adult rat spinal cord using basic fibroblast growth factor alone display stem cell properties as defined by their multipotentiality and self-renewal. Clonal cultures derived from single founder cells generate neurons, astrocytes, and oligodendrocytes, confirming the multipotent nature of the parent cell. Subcloning analysis showed that after serial passaging, recloning, and expansion, these cells retained multipotentiality, indicating that they are self-renewing. Transplantation of an in vitro-expanded clonal population of cells into the adult rat spinal cord resulted in their differentiation into glial cells only. However, after heterotopic transplantation into the hippocampus, transplanted cells that integrated in the granular cell layer differentiated into cells characteristic of this region, whereas engraftment into other hippocampal regions resulted in the differentiation of cells with astroglial and oligodendroglial phenotypes. The data indicate that clonally expanded, multipotent adult progenitor cells from a non-neurogenic region are not lineage-restricted to their developmental origin but can generate region-specific neurons in vivo when exposed to the appropriate environmental cues.

Proliferation and differentiation of progenitor cells throughout the intact adult rat spinal cord

The existence of multipotent progenitor populations in the adult forebrain has been widely studied. To extend this knowledge to the adult spinal cord we have examined the proliferation, distribution, and phenotypic fate of dividing cells in the adult rat spinal cord. Bromodeoxyuridine (BrdU) was used to label dividing cells in 13- to 14-week-old, intact Fischer rats. Single daily injections of BrdU were administered over a 12 d period. Animals were killed either 1 d or 4 weeks after the last injection of BrdU. We observed frequent cell division throughout the adult rodent spinal cord, particularly in white matter tracts (5-7% of all nuclei). The majority of BrdU-labeled cells colocalized with markers of immature glial cells. At 4 weeks, 10% of dividing cells expressed mature astrocyte and oligodendroglial markers. These data predict that 0.75% of all astrocytes and 0.82% of all oligodendrocytes are derived from a dividing population over a 4 week period. To determine the migratory nature of dividing cells, a single BrdU injection was given to animals that were killed 1 hr after the injection. In these tissues, the distribution and incidence of BrdU labeling matched those of the 4 week post injection (pi) groups, suggesting that proliferating cells divide in situ rather than migrate from the ependymal zone. These data suggest a higher level of cellular plasticity for the intact spinal cord than has previously been observed and that glial progenitors exist in the outer circumference of the spinal cord that can give rise to both astrocytes and oligodendrocytes.

FGF-2 is sufficient to isolate progenitors found in the adult mammalian spinal cord

The adult rat brain contains progenitor cells that can be induced to proliferate in vitro in response to FGF-2. In the present study we explored whether similar progenitor cells can be cultured from different levels (cervical, thoracic, lumbar, and sacral) of adult rat spinal cord and whether they give rise to neurons and glia as well as spinal cord-specific neurons (e.g., motoneurons). Cervical, thoracic, lumbar, and sacral areas of adult rat spinal cord (>3 months old) were microdissected and neural progenitors were isolated and cultured in serum-free medium containing FGF-2 (20 ng/ml) through multiple passages. Although all areas generated rapidly proliferating cells, the cultures were heterogeneous in nature and cell morphology varied within a given area as well as between areas. A percentage of cells from all areas of the spinal cord differentiate into cells displaying antigenic properties of neuronal, astroglial, and oligodendroglial lineages; however, the majority of cells from all regions expressed the immature proliferating progenitor marker vimentin. In established multipassage cultures, a few large, neuron-like cells expressed immunoreactivity for p75NGFr and did not express GFAP. These cells may be motoneurons. These results demonstrate that FGF-2 is mitogenic for progenitor cells from adult rat spinal cord that have the potential to give rise to glia and neurons including motoneurons.

Soman-induced seizures rapidly activate astrocytes and microglia in discrete brain regions

Neurons in the piriform cortex and the pontine nucleus locus coeruleus express elevated levels of the immediate early gene protein product, Fos, within 30-45 minutes of a seizurogenic dose of the anticholinesterase, soman (Zimmer et al., [1997] J. Comp. Neurol. 378:468-481). By 24 hours following soman injection, there is marked neuropathology in the piriform cortex. These findings suggest selective, regional vulnerability in response to the seizurogenic actions of soman. In the present study, we determined that soman-induced seizures also cause selective, rapid activation of astrocytes and microglia in the piriform cortex and other brain regions. Animals were killed at different intervals between 1 hour and 24 hours after a convulsive dose of soman. Brain sections were processed for immunocytochemical detection of astrocytes with antibodies against glial fibrillary acidic protein, and microglia and macrophages with antibodies against the complement receptor 3 protein, OX-42. The results demonstrate that following soman administration: (1) there is a rapid increase in glial fibrillary acidic protein staining in astrocytes of the piriform cortex (1 hour); (ii) reactive astrocytes are specifically restricted to layer II and the superficial boundaries of layer III of the piriform cortex. These are the same layers in which neurons express Fos within 30-45 minutes following soman administration; (3) between 1 and 4 hours, resting (ramified) microglia in the piriform cortex and the hippocampus alter their morphology to resemble active microglia. From 4-8 hours, active microglia undergo morphological changes characteristic of reactive microglia that resemble macrophages. Taken together, these observations indicate that astrocytes and microglia in brain regions susceptible to soman become rapidly "reactive" in response to seizures. The highly specific anatomical codistribution of reactive glia and Fos-expressing neurons suggests that intensely active neurons provide local signals that trigger reactive changes in neighboring glia.

Cellular inflammatory response after spinal cord injury in Sprague-Dawley and Lewis rats

The distribution of microglia, macrophages, T-lymphocytes, and astrocytes was characterized throughout a spinal contusion lesion in Sprague-Dawley and Lewis rats by using immunohistochemistry. The morphology, spatial localization, and activation state of these inflammatory cells were described both qualitatively and quantitatively at 12 hours, 3, 7, 14, and 28 days after injury. By use of OX42 and ED1 antibodies, peak microglial activation was observed within the lesion epicenter of both rat strains between three and seven days post-injury preceding the bulk of monocyte influx and macrophage activation (seven days). Rostral and caudal to the injury site, microglial activation plateaued between two and four weeks post-injury in the dorsal and lateral funiculi as indicated by morphological transformation and the de-novo expression of major histocompatibility class II (MHC II) molecules. Similar to the timing of microglial reactions, T-lymphocytes maximally infiltrated the lesion epicenter between three and seven days post-injury. Reactive astrocytes, while present in the acute lesion, were more prominent at later survival times (7-28 days). These cells were interspersed with activated microglia but appeared to surround and enclose tissue sites occupied by reactive microglia and phagocytic macrophages. Thus, trauma-induced central nervous system (CNS) inflammation, regardless of strain, occurs rapidly at the site of injury and involves the activation of resident and recruited immune cells. In regions rostral or caudal to the epicenter, prolonged activation of inflammatory cells occurs preferentially in white matter and primarily consists of activated microglia and astrocytes. Differences were observed in the magnitude and duration of macrophage activation between Sprague-Dawley (SD) and Lewis (LEW) rats throughout the lesion. Increased expression of complement type 3 receptors (OX42) and macrophage-activation antigens (ED1) persisted for longer times in LEW rats while expression of MHC class II molecules was attenuated in LEW compared to SD rats at all times examined. Variations in the onset and duration of T-lymphocyte infiltration also were observed between strains with twice as many T-cells present in the lesion epicenter of Lewis rats by 3 days post-injury. These strain-specific findings potentially represent differences in corticosteroid regulation of immunity and may help predict a range of functional neurologic consequences affected by neuroimmune interactions.

Multipotent CNS stem cells are present in the adult mammalian spinal cord and ventricular neuroaxis

Neural stem cells in the lateral ventricles of the adult mouse CNS participate in repopulation of forebrain structures in vivo and are amenable to in vitro expansion by epidermal growth factor (EGF). There have been no reports of stem cells in more caudal brain regions or in the spinal cord of adult mammals. In this study we found that although ineffective alone, EGF and basic fibroblast growth factor (bFGF) cooperated to induce the proliferation, self-renewal, and expansion of neural stem cells isolated from the adult mouse thoracic spinal cord. The proliferating stem cells, in both primary culture and secondary expanded clones, formed spheres of undifferentiated cells that were induced to differentiate into neurons, astrocytes, and oligodendrocytes. Neural stem cells, whose proliferation was dependent on EGF+bFGF, were also isolated from the lumbar/sacral segment of the spinal cord as well as the third and fourth ventricles (but not adjacent brain parenchyma). Although all of the stem cells examined were similarly multipotent and expandable, quantitative analyses demonstrated that the lateral ventricles (EGF-dependent) and lumbar/sacral spinal cord (EGF+bFGF-dependent) yielded the greatest number of these cells. Thus, the spinal cord and the entire ventricular neuroaxis of the adult mammalian CNS contain multipotent stem cells, present at variable frequency and with unique in vitro activation requirements.

Beneficial effects of x-irradiation on recovery of lesioned mammalian central nervous tissue

We examined the potential of x-irradiation, at clinical dose levels, to manipulate the cellular constituents and thereby change the consequences of transection injury to adult mammalian central nervous tissue (rat olfactory bulb). Irradiation resulted in reduction or elimination of reactive astrocytes at the site of incision provided that it was delivered within a defined time window postinjury. Under conditions optimal for the elimination of gliosis (15-18 days postinjury), irradiation of severed olfactory bulbs averted some of the degenerative consequences of lesion. We observed that irradiation was accompanied by prevention of tissue degeneration around the site of lesion, structural healing with maintenance of the typical cell lamination, and rescue of some axotomized mitral cells (principal bulb neurons). Thus radiation resulted in partial preservation of normal tissue morphology. It is postulated that intrusive cell populations are generated in response to injury and reactive astrocytes are one such group. Our results suggest that selective elimination of these cells by irradiation enabled some of the regenerative processes that are necessary for full recovery to maintain their courses. The cellular targets of these cells, their modes of intervention in recovery, and the potential role of irradiation as a therapeutic modality for injured central nervous system are discussed.

Brain macrophages: questions of origin and interrelationship

Brain tissue appears to contain several distinct types of macrophages. An effort is made here to present a description of the complete cohort of macrophages and sources of phagocytic activity in this tissue. Initially, the criteria and methods used for the identification of tissue macrophages in general are considered. These include some morphological and ultrastructural features, assessment of phagocytic activity, and histochemistry for intracellular and surface components. Each of these methods or criteria has certain advantages but also associated problems and limitations; all have been applied in various instances to brain tissue. In a final analysis, the most reliable means of identification of tissue macrophages involves a combination of all of these approaches. The identification and characterization of macrophages have been rendered extremely confusing in the brain because of so many different sources of these cells, both intrinsic and blood-derived. The classes of macrophages or phagocytic cells in brain tissue are microglia, supraependymal cells, epiplexus cells, meningeal macrophages, pericytes, and direct blood-derived macrophages. The morphology, location, and functional properties of each of these classes is described. In an overall view, brain tissue is very well protected by intrinsic macrophages, and the locations and distribution of these cells are consistent with other tissues. Finally, in a consideration of origin and interrelationship, the idea is presented that the most likely source for all or most brain macrophages is monocytic blood cells. The latter cells appear to migrate into the tissue from several sites during embryogenesis and may continue to enter, at least from blood vessels, in the adult state.

Imaging of primary and remote ischaemic and excitotoxic brain lesions. An autoradiographic study of peripheral type benzodiazepine binding sites in the rat and cat

Seven days after unilateral middle cerebral artery occlusion in rats, peripheral type benzodiazepine binding sites (PTBBS), using [3H]PK 11195 as a specific radioligand, were greatly increased in the cortical and striatal regions surrounding the focus of infarction with smaller increases in the ventrolateral and posterior thalamic complexes and in the substantia nigra, all ipsilateral to the occlusion. Similarly, PTBBS increases were observed in the caudate nucleus and entorhinal cortex of cats likewise subjected to prior unilateral occlusion of the middle cerebral artery. Intrastriatal administration of N-methyl-D-aspartate (250 nmol) in the rat resulted in a dramatic ipsilateral increase in PTBBS levels in the striatum and in the deeper laminae of the ipsilateral frontoparietal cortex. Intrastriatal kainic acid administration (12 nmol) also elicited PTBBS increases ipsilaterally in rat striatum and cortex; a bilateral elevation of PTBBS levels was observed in the hippocampus. With all these interventions there existed a good spatial correlation between the PTBBS increase and neuronal loss as assessed either histologically or by the autoradiographic detection of the putative neuronal marker [3H]SCH 23390 (a D1 dopamine receptor ligand). Moreover, a glial proliferation of non-neuronal cells (macrophage and glial cells) was observed in brain regions noted to have increased PTBBS levels. PTBBS autoradiography thus constitutes a suitable technique for the localization of damaged areas in several experimental models of brain injury. PTBBS label not only the primary lesions but also functionally related areas and could further our understanding of phenomena such as partial neuronal loss and diaschisis. The study of PTBBS could be envisaged for the detection, localization and quantification of all neuropathological situations which engender a glial reaction or macrophage invasion and is potentially applicable to both experimental and human subjects, in which both autoradiographic and tomographic approaches could be undertaken.

Glucocorticoid hormones inhibit DNA synthesis in glial cells cultured in chemically defined medium

Primary cultures of glial cells from 2-day-old rat cerebellum were used to examine the growth control properties of steroid hormones. Immunocytochemical staining with antiglial fibrillary acidic protein (anti-GFAP) demonstrated that the cultures were highly enriched for astrocytes (90%). In an effort to avoid the potential influence of serum-borne steroids, cultures were switched from serum-supplemented to serum-free, chemically defined medium prior to experimentation. Assays for DNA synthesis used [3H]thymidine incorporation with either liquid scintillation counting of TCA-insoluble material or light microscopic autoradiography. Glial cells grown in serum-free, chemically defined medium (F12 basal medium supplemented with putrescine, selenium, insulin, transferrin, and BSA) replicated their DNA to a limited extent even in the absence of serum mitogens. When the glial cells were shifted to defined medium supplemented with various steroid hormones (corticosterone, dexamethasone, hydrocortisone, 17 beta-estradiol, progesterone, or testosterone) at a concentration of 10(-7) M, it was found that the glucocorticoids, corticosterone and dexamethasone inhibited synthesis of DNA by 49.6 and 56.9%, respectively. Hydrocortisone, another glucocorticoid, caused only a small reduction in DNA synthesis. The growth-controlling activity of the glucocorticoids was dose-dependent with concentrations of 10(-7) -10(-6) M showing maximal effect on DNA synthesis. These results suggest that physiological concentrations of glucocorticoid hormones may exert negative control over DNA synthesis of glial cells in the developing or injured central nervous system.

Quantitative electron microscopic observations on the non-neuronal cells and lipid droplets in the posterior funiculus of the cat after dorsal rhizotomy

Adult cats were subjected to unilateral dorsal L6, L7, and S1 rhizotomies. After survival times of 1-1,552 days the different glial cell types, the perivascular cells, and the lipid droplet content of each cell type were studied quantitatively at the ultrastructural level in sections from the posterior funiculus at the L1 level. The number of astrocytes did not appear to change during the degeneration process. From 105 days postoperatively (p.o.), a marked reduction in the oligodendroglial cell population was observed. The number of microglial cells increased from 5 days p.o. onward. A large increase was observed particularly between 20 and 160 days p.o. The occurrence of pericytes was unchanged during the degeneration but the number of non-pericytic perivascular cells/blood vessel was increased from 10 days p.o. onward. The number of lipid droplets in the microglial cells increased early during the degeneration period. Subsequently an increase in lipid droplet number was observed in the astrocytes and somewhat later also in the non-pericytic perivascular cells. These findings have been interpreted to reflect a redistribution of lipid droplet material from the degenerating white matter to cells in the perivascular space during the observed time period.

Acidic protein in macrophages

An antiserum to unstimulated rat peritoneal macrophages was produced in rabbits. The antibodies were directed against an acidic protein with a molecular weight of 35,000 and with an isoelectric point at 4.6. The macrophage acidic protein (MAP) was purified by gel filtration of rat lung soluble proteins, followed by preparative isoelectric focusing. The preparation of MAP was pure as assayed by agar gel electrophoresis and showed one precipitation peak in crossed immunoelectrophoresis against the crude antiserum directed against peritoneal macrophages. The purified MAP was used for immunization of rabbits, and the antiserum obtained was monospecific, assayed by crossed immunoelectrophoresis and Grabar-Williams immunoelectrophoresis. The titre was 4 times higher in the anti-MAP antiserum (1:80) than in the crude antimacrophage antiserum (1:20), tested against MAP by counter-current immunoelectrophoresis. The antigen (MAP) was demonstrated by direct and indirect immunofluorescence microscopy in rat blood monocytes, in spleen and lung monocytic cells, in clusters of cells in the thymus, and in adventitial macrophages around larger blood vessels in liver, kidney, lung and brain. Scattered meningeal macrophages showed fluorescence in the normal, brain. In stab-wounded areas of rat brain MAP was localized to perivascular and perineuronal macrophages with a morphology similar to that of microglial cells. The localization of the fluorescence was the same both for the antiserum against MAP and for the antiserum raised against crude peritoneal macrophages.

Hematogenous cells in the central nervous system of developing human embryos and fetuses

Examination of large blocks of Epon-embedded, 1.0-micrometer sections of human embryos and fetuses reveal the presence of hematogenous cells in various stages of differentiation in neural tissue. In every embryo and fetus of 10 weeks ovulation age and younger, hematogenous cells are found randomly scattered in the cerebrum, cerebellum, and spinal cord. Many of these cells appear to undergo spontaneous degeneration in neural tissue and become rarer in older fetuses. Also identified in the neuropil of normal embryos and fetuses are cells with the typical morphological appearance of macrophage containing numerous inclusions of various kinds, both inside and outside the blood vessels. In addition, scattered in the subpial, perivascular, and perineuronal regions of the neural parenchyma are small cells with fusiform nuclei and a small amount of cytoplasm as well as cells with a moderate amount of elongated cytoplasm containing various inclusions and oblong nuclei. All of these cells have clumped heterochromatin along the nuclear membrane which differs from other neuroectodermal cells of the developing human CNS. Although there is no direct evidence to indicate transformation of macrophages to "microglia" or vice versa, the presence of cells having similar nuclear morphology and chromatin pattern while appearing to be transitional forms of macrophage, varying from undifferentiated to fully developed, suggest a common lineage of these latter types. It is concluded that migration of hematogenous cells into neural tissue is a ubiquitous developmental phenomenon in young human embryos and fetuses.

Non-specific esterase activity in reactive cells in injured nervous tissue labeled with 3H-thymidine or 125iododeoxyuridine injected before injury

Tritiated thymidine (3H-TdR) injected before a stab wound of the spinal cord or transection of the hypoglossal nerve has resulted in many labeled reactive cells in the CNS after injury, most of which have the ultrastructural features of microglia. To test for the possible origin of these labeled cells from monocytes, we examined them for the presence of sodium fluoride- (NaF) sensitive non-specific esterase (NSE), an enzyme characteristic of monocytes. Some of the labeled cells in stab wounds had NaF-sensitive NSE, but no such cells were found in the nucleus of the injured hypoglossal nerve. To test for the possibility that the NSE-negative labeled cells had been labeled by reutilization of 3H-TdR, we used 125I-5-iodo-2'-deoxyuridine (125I-UdR), a thymidine analogue with a much lower rate of reutilization, to label blood mononuclear cells prior to either a spinal cord stab wound or hypoglossal axotomy. The number of labeled cells was decreased in the spinal cord wound, but more than half were NSE-negative. No labeled blood mononuclear cells were found in the hypoglossal nucleus, although there was no decrease in the hyperplasia of unlabeled non-neuronal cells. When 125I-UdR was injected on the fourth day after hypoglossal axotomy, or when both 3H-TdR and 125I-UdR were injected simultaneously before hypoglossal axotomy, many labeled cells were found in the hypoglossal nucleus, indicating that 125I-UdR can be used by the reactive cells and that it did not inhibit their proliferation. Therefore, the microglial cells that proliferate in response to peripheral nerve injury are not recently derived from any type of circulating large blood mononuclear cell. The most likely explanation for the presence of the 3H-TdR-labeled cells in the nucleus of the injured hypoglossal nerve is that they were proliferating intrinsic cells labeled by reutilization of 3H-TdR.

Relation of age and cerebral ventricle size to central canal in man. Morphological analysis

The central canal of the spinal cord in man with and without hydrocephalus was studied histologically. The lumen was patent in most patients in the first two decades of life. Cells lining the canal in the prenatal and newborn state and in the first decade of life were predominantly pseudostratified ciliated epithelium. In the second decade, the epithelium became simple columnar or cuboidal. The central canal closed in most cases after the age of 20 years, secondary to proliferation of ependymal cells and astrocytes. Mechanisms whereby the number of glial cells increase are considered. The canal was closed in all adults with normal ventricular size, and in 94% of persons with various degrees of hydrocephalus. In the remaining 6% of cases with hydrocephalus, the lining of the canal resembled that seen in the first two decades, and could have acted as a pathway of cerebrospinal fluid (CSF) absorption. Three cases of severe hydrocephalus in the first two decades of life were encountered; the central canal was patent in one, and occluded in two. Based on these data, the canal was not a significant pathway of CSF absorption in most instances of hydrocephalus and in persons with dilated ventricles who were older than 20 years of age.

Demonstration of cross reaction between anti-macrophage antibodies and mononuclear mesodermal cells

An anti-macrophage antiserum to rat peritoneal macrophages was prepared in rabbits. The antibodies produced showed cross reaction with perivascular adventitial macrophages, with macrophages in thymus and spleen, and with brain microglial cells.

Fine structure of reactive cells in injured nervous tissue labeled with 3H-thymidine injected before injury

To examine the fine structure of blood mononuclear cells in injured nervous tissue, mice were given repeated injections of 3H-thymidine with the last injection at least 16 hours before injury. Under ether anesthesia the animals either were given a stab wound to the spinal cord or had their left hypoglossal nerve transected. The animals were killed at 2, 4, 8, or 16 days after injury. Tissue sections containing the spinal cord wound or both hypoglossal nuclei were prepared for electron microscopic radioautography, and all labeled cells were photographed. About half the labeled cells in the injured spinal cords and almost all the labeled cells in the nuclei of the injured hypoglossal nerves had nuclei with dark staining peripheral heterochromatin, dark cytoplasm with long cisternae of granular endoplasmic reticulum, and other ultrastructural features characteristic of the cells usually identified as microglia. The remaining labeled cells in the injured spinal cords were macrophages, fibroblasts, cells with pale nuclei, some of which contained cytoplasmic filaments, and vascular cells. Since uninjured nervous tissue has extremely few labeled cells and since 3H-thymidine should be available for only a short time following injection, most of the labeled cells in this experiment should be derived from blood mononuclear cells. However, the possibility is discussed that some or all of the labeled cells may be intrinsic cells proliferating in response to the injury and labeled through reutilization of labeled DNA precursor material.

Chemotherapy of malignant gliomas: comparison of the effect of polychemo- and CCNU-therapy

Postoperative survival times of patients suffering from glioblastoma (astrozytoma III-IV) were compared in unselected groups receiving different forms of therapy: standard surgical therapy (16 cases, mean survival time 6.27 +/- 3.75 months), postoperative polychemotherapy (16 patients, survival time 8.96 +/- 4.97 months) or postoperative CCNU-monotherapy (24 cases, survival time 6.98 +/- 4.46 months). The mean survival time in the group receiving polychemotherapy was prolonged significantly when compared to the group with standard treatment. Survival time of the patient group treated with CCNU was not significantly increased. The results indicate that postoperative combination chemotherapy is more effective than CCNU monotherapy.

Vascular and neuroglial changes in experimental herpes simplex encephalitis: ultrastructural study

Generalized vascular changes and diffused proliferation of reactive microglia were observed in an experimental model of HSV encephalitis of mice. The wide spread of these changes contrasted with the localized character of virus replication and the confined areas of damaged nervous tissue. The vascular and microglial changes were precocious in animals inoculated with concentrated virus suspension (10(5.5)LD50) while they appeared late in mice inoculated with diluted virus suspension (100 LD50). After inoculation with U.V. inactivated virus no changes were seen. The results obtained in this study suggest that the vascular and microglial modifications are not related to a direct cytopathic effect of the virus but dependent on the amount of virus present in the central nervous system and linked to the virus DNA.

Macrophages in brain tumours induced transplacentally by N-ethyl-N-nitrosourea in rats: an electron-microscope study

The fine structure of macrophages has been studied in experimental brain tumours induced transplacentally in BD-IX rats by a single intravenous injection of 30 mg of N-ethyl-N-nitrosourea per kg of body weight on the 15th day of gestation. The tumours, depending on their localisation and size, caused various lesions in the brain, namely axonal degeneration, loss of myelin, oedema, haemorrhage and cell necrosis. The tumours and the resulting alterations elicited a strong reaction by macrophages: activation of microglial cells in situ and infiltration of the brain by leucocytes, chiefly by monocytes. Since both microglial cells and monocytes underwent morphological changes, it was difficult, or impossible, to establish the origin of these reacting cells. In a few cases, however, microglial cells and monocytes could be distinguished; this indicated that microglial cells were still being activated and leucocytes were still entering the brain. Various stages of activity of macrophages have been described: the number of lysosomes and cytoplasmic inclusions were thought to indicate activation, phagocytosis and repletion. Activation is characterised by an increase of lysosomes and frequent cell divisions. Phagocytic activity is accompanied by the appearance of inclusions which varied in different lesions: protein-like material in oedema, remnants of erythrocytes in haemorrhages and myelin-lamellae with lipid droplets in demyelination. These various inclusions were frequently present in the same cell, since the different lesions not uncommonly occurred at the same time. In the stage of repletion macrophages contained mainly lipid droplets and unidentifiable debris in their abundant cytoplasm and thus corresponded to the compound granular corpuscles.

Histone-acetylating enzyme of brain

1. Acetylation of histones by an enzyme system derived from rat brain and liver (histone acetylase) was studied by using [1-(14)C]acetyl-CoA as the acetyl group donor. 2. The activity of this enzyme was largely confined to the nucleus. 3. Histone-acetylating activity of cerebral nuclei purified by centrifugation through 1.9m-sucrose was not altered by the presence of the cytoplasmic fraction. 4. Cerebral nuclei from adult rats exhibited greater histone-acetylating activity than did the corresponding preparation from newborn animals. 5. Nuclear acetylating activity was higher in brain than in liver of adult rats but not in newborn animals. 6. The partially purified enzyme from cerebral nuclei, prepared by ammonium sulphate fractionation of an acetone-dried powder, specifically catalysed histone acetylation. 7. Polylysine, protamine, serum albumin and gamma-globulin were not enzymically acetylated by this preparation. 8. Soluble acetylating preparations from both brain and liver nuclei were more active towards arginine-rich F3 and slightly lysine-rich F2a and F2b histone fractions than towards the lysine-rich F1 fraction. 9. Enzymic acetylation of chromatin-bound proteins was much less extensive than that of free histones. 10. The high histone acetylase activity in mature brain may reflect the importance of this process in the genetic control of cerebral function.