Cell proliferation in injured spinal cord. An electron microscopic study

Neuroprotective potential of Spirulina platensis on lesioned spinal cord corticospinal tract under experimental conditions in rat models

Spinal cord injury (SCI) results from penetrating or compressive traumatic injury to the spine in humans or by the surgical compression of the spinal cord in experimental animals. In this study, the neuroprotective potential of Spirulina platensis was investigated on ultrastructural and functional recovery of the spinal cord following surgical-induced injury. Twenty-four Sprague-Dawley rats were divided into three groups; sham group, control (trauma) group, and experimental (S. platensis) group (180 mg/kg) of eight rats each. For each group, the rats were then subdivided into two groups to allow measurement at two different timepoints (day 14 and 28) for the microscopic analysis. Rats in the control and experimental S. platensis groups were subjected to partial crush injury at the level of T12 with Inox number 2 modified forceps by compressing on the spinal cord for 30 s. Pairwise comparisons of ultrastructural grading mean scores difference between the control and experimental S. platensis groups reveals that there were significant differences on the axonal ultrastructure, myelin sheath and BBB Score on Day 28; these correlate with the functional locomotor recovery at this timepoint. The results suggest that supplementation with S. platensis induces functional recovery and effective preservation of the spinal cord ultrastructure after SCI. These findings will open new potential avenue for further research into the mechanism of S. platensis-mediated spinal cord repair.

Neurogenesis in the lamprey central nervous system following spinal cord transection

After spinal cord transection, lampreys recover functionally and axons regenerate. It is not known whether this is accompanied by neurogenesis. Previous studies suggested a baseline level of nonneuronal cell proliferation in the spinal cord and rhombencephalon (where most supraspinal projecting neurons are located). To determine whether cell proliferation increases after injury and whether this includes neurogenesis, larval lampreys were spinally transected and injected with 5-bromo-2&prime-deoxyuridine (BrdU) at 0-3 weeks posttransection. Labeled cells were counted in the lesion site, within 0.5 mm rostral and caudal to the lesion, and in the rhombencephalon. One group of animals was processed in the winter and a second group was processed in the summer. The number of labeled cells was greater in winter than in summer. The lesion site had the most BrdU labeling at all times, correlating with an increase in the number of cells. In the adjacent spinal cord, the percentage of BrdU labeling was higher in the ependymal than in nonependymal regions. This was also true in the rhombencephalon but only in summer. In winter, BrdU labeling was seen primarily in the subventricular and peripheral zones. Some BrdU-labeled cells were also double labeled by antibodies to glial-specific (antikeratin) as well as neuron-specific (anti-Hu) antigens, indicating that both gliogenesis and neurogenesis occurred after spinal cord transection. However, the new neurons were restricted to the ependymal zone, were never labeled by antineurofilament antibodies, and never migrated away from the ependyma even at 5 weeks after BrdU injection. They would appear to be cerebrospinal fluid-contacting neurons.

The effect of the platelet derived wound healing formula and the nerve growth factor on the experimentally injured spinal cord

The main purpose of this study is to investigate the effect of platelet derived wound healing formula (PDWHF) and nerve growth factor (NGF) in the treatment of experimental spinal cord injury. PDWHF is a conglomerate of growth factors which include platelet derived growth factor (PDGF), platelet derived angiogenesis factor (PDAF), transforming growth factor-beta (TGF beta) and platelet factor IV (PF4). Complete spinal cord transection was performed at T12 in rats and the treatment of the spinal cord injury was achieved by filling the dead space with type 1 collagen gel impregnated with PDWHF, or with 2.5S-NGF. Controls were treated with only type 1 collagen gel. Animals were sacrificed at 1, 2 or 3 months. Histopathologically, tissue autolysis and cavity formation by phagocytosis expanded 1-3 mm into the cord stumps and the volume of cavitation was less in the two treated groups. In the NGF group, a greater number of surviving nerve cells were observed in this region. Most of the control animals formed only thin, short axonal bundles, however, increased axonal regrowth was noted in animals treated with trophic factors, especially in the NGF group. The NGF group formed thick axonal bundles and abundant neuroma. Increased angiogenesis was observed in the collagen gel matrix and the injured spinal cord parenchyma, in the PDWHF group. Recent studies have shown that mammalian adult CNS possesses the ability for structural and/or functional plasticity following injury under appropriate circumstances. In this in vivo study, exogenous NGF appeared to induce axomal outgrowth and nerve cell survival. PDWHF produced notable angiogenesis which seemed to improve the extracellular microenvironment. This may be important for the delivery of exogenous trophic factors, nutrients and for the changes of extracellular matrices to support nerve cells and axons.

Oxysterol (7 beta-hydroxycholesteryl-3-oleate) promotes serotonergic reinnervation in the lesioned rat spinal cord by reducing glial reaction

In the present study, following previous experience with electrolytic lesion of the rat brain, and subsequent reduction of reactive gliosis with 7 beta-hydroxycholesterol derivatives (Bochelen et al.: Neuroscience 51:827-834, 1992), we have performed a hemisection of the spinal cord in adult rats and investigated the influence of 7 beta-hydroxycholesteryl-3-oleate (oxysterol) on the intensity of the astrocytic reaction and the axonal regeneration. We have shown here that local administration of liposomes containing this oxysterol reduced the intensity of the astroglial reaction on the sectioned side, as seen with immunocytochemical detection of glial fibrillary acidic protein (GFAP) and by in situ hybridization with a specific RNA probe. Moreover, radioautographic evaluation of astrocyte proliferation with tritiated thymidine evidenced a reduction of the astrocyte labelling index. In addition, double immunocytochemical detection of GFAP and polysialylated neural cell adhesion molecule (E-NCAM) revealed a decrease of the expression of this molecule in reactive astrocytes of the treated animals. Finally, immunocytochemical detection of serotonin (5HT) was determined in the raphespinal projections, which constitute a major descending system. In treated animals, serotonergic axons originating from the intact side reinnervated the dorsal horn of the sectioned side, below the hemisection. These results demonstrate that 7 beta-hydroxycholesteryl-3-oleate can reduce the astrocytic reaction following spinal cord injury, promoting the serotonergic reinnervation of a denervated territory.

NADPH-diaphorase histochemistry identifies isolated endothelial cells at sites of traumatic injury in the adult rat brain

In addition to labelling endothelium, some ependymal cells (including tanycytes), and a subpopulation of neurons, nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry of stab lesion sites in the neocortex revealed a large population of cells concentrated within several hundred micrometers of the lesion site. To determine the identity of these cells, NADPH-diaphorase reactivity was compared to binding with either the I-B4 isolectin from Bandeiraea simplicifolia (which has previously been shown to identify endothelial cells and activated mononuclear phagocytes), or a monoclonal antibody (OX-42) that recognizes activated mononuclear phagocytes. Many I-B4 lectin-labelled cells were also NADPH-diaphorase reactive, and other I-B4 lectin-labelled cells were also OX-42 immunoreactive, but co-existence of OX-42 immunoreactivity and NADPH-diaphorase reactivity was not observed. Only a small minority of NADPH-diaphorase-reactive cells did not exhibit I-B4 lectin binding. In contrast to the simple somatic morphology of the majority of NADPH-diaphorase-reactive cells, the I-B4 lectin-negative cells had a ramified appearance, and while readily observed at two days postlesion, they were only rarely seen at three days postlesion. Primary cultures of bovine aortic endothelial cells also exhibited NADPH-diaphorase reactivity which occupied most of the cytoplasm in a filamentous web pattern. Endothelial cells possess a constitutive form of nitric oxide synthase which, as demonstrated in NADPH-diaphorase-reactive neurons, may be the basis of their NADPH-diaphorase reactivity. These findings indicate that NADPH-diaphorase-reactive cells observed at lesion sites are probably angiogenic endothelial cells not associated with extant blood vessels. Thus, NADPH-diaphorase histochemistry offers an effective method of visualizing neovascularization in the brain and other tissues.

Morphological study of the effects of intranasal zinc sulfate irrigation on the mouse olfactory epithelium and olfactory bulb

The effects of intranasal zinc sulfate (ZnSO4) irrigation on the morphology of the olfactory epithelium and olfactory bulb were studied in mice with short survival times (as early as 1 day) and with long survival times (up to 593 days) after the irrigation procedure. As in several previous studies, the olfactory epithelium was completely destroyed within a few days after the ZnSO4 treatment. Within 2-4 days, the septum and turbinates were covered by a new, cuboidal epithelium, the cells of which differed significantly from any cells normally seen in the olfactory epithelium. Slowly, over several months, small areas of the olfactory epithelium regenerated in many of the animals. The ultrastructural changes occurring in the olfactory bulb from 1 to 25 days (the reactive stage) were characterized by degenerating olfactory axons and axon terminals, hypertrophy of astroglial cell processes, and proliferation of or extravasation by phagocytic cells. By 25 days after intranasal ZnSO4 irrigation, the number of reactive glial processes and phagocytic cells returned to normal. In some mice with survival times of 150 days or longer, there was reinnervation of small areas of the olfactory bulb by regenerated olfactory axons. These new olfactory axons innervated only superficial glomeruli or the outer portions of deeper glomeruli, but they formed synaptic contacts with mitral/tufted cells and periglomerular cells that did not differ from control animals. These findings were supported by tract-tracing experiments with 3H-amino acids and by behavioral analysis. In summary, the ultrastructural changes observed in the olfactory bulb in this study were not significantly different from those observed after surgical lesions of the olfactory epithelium or nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

The response of the cerebral hemisphere of the rat to injury. I. The mature rat

The response to injury of the cerebrum of the mature rat was studied chronologically in stereotactically placed knife wounds by using both light and electron microscopical, and immunohistochemical, techniques. Immediately after injury haematogenous cells fill the lesion and ischaemic necrosis occurs along the margins and a zone of cell swelling occupies the surrounding area. This phase is transformed by the appearance of large numbers of macrophages and fibroblasts, and some reactive astrocytes in the zone of cell swelling at 4 days. Blood vessels grow into the lesion at this time. Collagen deposition begins in the subpial region of the wound and, with time, scarring progresses into the deeper parts of the wound. By 8 days, the lesion contains a matrix of collagen fibrils, capillaries, fibroblasts, macrophages and astrocytes. The wound margins are better defined as astrocytes become aligned and secrete the basement membrane of the glia limitans, initially in the subpial regions of the scar. By 16 days, a glia limitans is complete along the margins of the entire lesion and the scar tissue between is reduced in area and contain fibroblasts, scattered macrophages, collagen fibrils and a few extra- parenchymatous astrocytes. Subsequently the scar condenses to a thin layer and becomes less vascularized; few cells remain. The persistence of astrocytes within mesenchymatous scar tissue excluded from the cerebral neuropile is a new finding. No further changes are seen in the scar after 30 days. The progressive development and maturation of scar tissue from the pial surface of the wound into the deeper regions of the cerebrum suggests that the major source of fibroblasts is from the meninges. The appearance of macrophages before fibroblasts in the wound may indicate that macrophages secrete a substance that is a trophic stimulus for fibroblasts. The organization of a glia limitans by astrocytes also proceeds inwards from the pial surface. Within the neuropile, degeneration of damaged neural elements is the prominent feature in the first 8 days after injury. Macrophages and reactive astrocytes also appear among the debris and are numerous by 4 days at the junctions of viable and necrotic neuropile. Signs of a regenerative response of neural processes is first seen at 4 days as growth cones appear in the viable neuropile at the edges of the necrotic zone. Growth cones are most numerous at 8 days. Evidence for new synapse formation is seen over the surface of dendritic swellings from 16 days onwards. Synapses of varying maturity are present, the most mature are adjacent to the dendritic shaft. This observation may suggest-that these swellings are true growth cones, in which case, this new synaptogenesis is similar to that over dendritic growth cones during development. It is not possible to judge the relative importance of either collateral sprouting or true regeneration in the reorganization of connections after injury, but neurite growth and the associated synaptogenesis described here could contribute to the recovery process. If the swellings on dendritic processes are true growth cones, then this is evidence for the regeneration of dendritic processes.

Remote astrocytic response as demonstrated by glial fibrillary acidic protein immunohistochemistry in the visual cortex of dorsal lateral geniculate nucleus lesioned rats

The reaction of astroglia was investigated after unilateral destruction of the dorsal lateral geniculate nucleus in the primary visual cortex of adult albino rats. The destruction of the dorsal lateral geniculate nucleus was performed by stereotaxic injections of ibotenic acid, and the location was verified in Nissl stained sections in each animal. Electron microscopic observations demonstrated the presence of degenerating axon terminals surrounded by hypertrophic astroglial processes mainly in layers III and IV of the ipsilateral primary visual cortex. The ipsilateral (impaired) and contralateral (control) sides of the primary visual cortex showed light microscopically a clearly differing appearance and distribution of glial fibrillary acidic protein (GFAP) immunoreactivity 7 to 11 days after the unilateral injection of ibotenic acid into the dorsal lateral geniculate nucleus. Whereas the control side of the primary visual cortex showed GFAP staining only in the subpial zone of layer I and close to the white matter, all layers of the impaired cortex showed an intense GFAP immunoreactivity. The increase in immunoreactivity was confined to the primary visual cortex. The extent of and increase in immunoreactivity was corroborated by image analysis. These findings were interpreted as a localized hypertrophy of astroglia caused by the anterograde degeneration of geniculocortical terminals. This hypertrophy is accompanied by an increase in GFAP, which may represent the stabilization of the cytoskeleton of newly formed glial processes involved in the rearrangement of the impaired neuropil.

Reactions of S-100-positive glia after injury of mouse cerebral cortex

Reactions of glial cells after stab wounding of mouse cerebral cortex were studied by [3H]thymidine autoradiography combined with immunohistochemistry for S-100 protein. S-100-positive cells in the stabbed cortex had the light and electron microscopic characteristics of astrocytes, and they showed remarkable hypertrophic changes 4 to 5 days after stabbing. There were many cells labeled with [3H]thymidine in the stabbed cortex from 24 h to 8 days after stabbing, and the number of labeled cells was maximum at 48 h. A few of the labeled cells were S-100-positive, and the labeled S-100-positive cells were seen 24 h to 6 days after stabbing, mostly after 72-96 h. By successive injections of [3H]thymidine for 6 days after stabbing, about 90% of labeled cells were S-100-negative, and about 90% of S-100-positive cells were unlabeled with [3H]thymidine. The increase in number of S-100-positive cells by day 6 after stabbing was not statistically significant (P greater than 0.05). These results suggest that reactive proliferation of astrocytes is a minor phenomenon in gliosis of injured cerebral cortex, in contrast with their remarkable reactive hypertrophy.

Effects of intraneural injection of Ricinus communis agglutinin-60 into rat vagus nerve

The dorsal motor nucleus (DMN) of the rat was studied at various survival periods following an intraneural injection of Ricinus communis agglutinin-60 (RCA-60) into the vagus nerve at the mid-cervical region. No obvious structural changes were noted in the DMN 2 and 4 days after the injection of RCA-60. At 5 and 6 days after the RCA-60 injection, the larger neurons (measuring 19 X 12 microns) in the DMN underwent chromatolytic degeneration whereas the smaller ones (measuring 10 X 6 microns), characterized by their infolded nuclei, remained unaffected. The majority of the degenerating DMN neurons became pale and crenated in outline. Other structural changes included swollen mitochondria with disrupted cristae and profiles of rough endoplasmic reticulum denuded of ribosome particles. A few of the degenerating neurons became extremely condensed and darkened. Axon terminals which showed synaptic contacts with these cells remained normal. Both pale and darkened degenerating dendrites, derived from the degenerating neurons, were present in the neuropil. In addition to these, degenerating axon terminals with clumping or swelling of synaptic vesicles were also present. They were presynaptic to dendrites of various sizes. Massive infiltration of mononuclear cells occurred in the DMN. These cells reached the DMN by diapedesis and were actively engaged in the phagocytosis of degenerating neuronal elements. While most of the invading cells transformed into active neuronal macrophages, some of them eventually died in the neuropil of the DMN. Light microscopic study by Fink-Heimer's method for degenerating fibres and terminals revealed their distribution to the DMN, nucleus of the tractus solitarius, nucleus commissuralis, dorsolateral and lateral part of the hypoglossal nucleus and the area postrema. It was concluded from this study that RCA-60, when injected into the cervical vagus was retrogradely transported to the cell body of the DMN neurons of the larger category. The selective destruction of the DMN neurons by RCA-60 elicited a massive infiltration of mononuclear cells which gave rise to the neural macrophages. The RCA-60 injected also killed the vagal sensory neurons as demonstrated by the numerous degenerating fibres and axon terminals in the DMN which would represent their central processes.

Cell proliferation after ischemic infarction in gerbil brain

In order to study cell proliferation after ischemic infarction, a model of bilateral common carotid artery occlusion in the gerbil was developed. A comparison of survival rates after 15, 30, 45 and 60 min of occlusion revealed that 45 min was the maximum duration of ischemia after which most (72%) of the gerbils were alive at 1 week. The administration of pentobarbital (single dose, 30 mg/kg) postoperatively to badly seizing animals increased survival to 100%. Large, well-demarcated infarcts were present in posterior thalamus or midbrain in 62% of gerbils subjected to 45 min bilateral occlusion. In 60% of these animals the infarcts were unilateral; in 40% they were bilateral. To quantitate cell proliferation in the infarcts from 12 h to 25 days after ischemia, gerbils were injected with [3H]thymidine 4 h prior to sacrifice, and autoradiographs were prepared from sectioned brains. Proliferation took place from 2 to 7 days after occlusion, with a maximum of 24% labeled cells at 6 days.

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.

Connective tissue scarring in experimental spinal cord lesions: significance of dural continuity and role of epidural tissues

Neoformation of connective tissue occurring at the level of spinal cord injury is considered a factor in the failure of regeneration in the mammalian spinal cord. The purpose of the present research was to experimentally investigate the origin and characteristics of connective proliferation following spinal cord lesion produced by compression in the rat. The role of the dural sheath and that of the tissues surrounding the spinal cord were studied. In one group of animals (1), the dura mater was left intact; in a second group (2) a transverse incision of the dura was performed at the level of the spinal cord compressive lesion. In group (1) a few collagenous fibres were seen within the lesion but no connective septum was observed. In group (2) a transversely orientated septum of fibrous scar tissue was constantly found within the lesioned cord. Our experimental study shows that: 1. dural continuity prevents the formation of connective tissue scarring and limits fibrous reactions in the epidural space; 2. opening of the dural sheath is followed by a vigorous fibroblastic reaction in the epidural tissue which extends into the spinal cord to form a connective septum.

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.

A fine structural study of the cells that proliferate in the partially denervated dentate gyrus of the rat

Tritiated thymidine autoradiography has established that after interrupting the commissural afferents to the dentate gyrus a number of non-neuronal cells proliferate in the molecular layer. In the present study the fine structure of the proliferating cells was analyzed by reembedding the 2-microns thick plastic sections of the dentate gyrus which had been previously coated with a nuclear emulsion and processed for light microscopic autoradiography. The location of the labeled cells was plotted with a camera lucida and a few ultrathin sections were taken from the re-embedded sections. In these the labeled cells were re-identified and photographed in an electron microscope. Most of the identified proliferating cells exhibited the following morphological features: The nuclei were irregularly oval, sometimes with deep indentations and contained dense clumps of chromatin; their diameters ranged between 4.5 and 6.5 microns. The cytoplasm was generally disposed to one side of the nucleus and often extended into a few broad processes. The Golgi apparatus was well developed. Many rosettes of free ribosomes were scattered throughout the cytoplasm, and the rough endoplasmic reticulum usually consisted of a few short cisternae. Small multilamellated bodies were common, but dense inclusion bodies were infrequent. The observations reported in this paper suggest: 1. that the nonneuronal cells which proliferate in a neuropil undergoing a mild denervation are morphologically closely related to microglia; 2. that in young adult animals these cells do not seem to have been previously involved in intense phagocytic activity; and 3. that the proliferating cells are present in the neuropil at the time of the denervation.

Deposition of scar tissue in the central nervous system

Standard parasagittal lesions were placed stereotactically in the cerebral hemispheres of neonatal and adult rats in order to compare scarring in the immature and mature animal. Lesions were examined by light and electron-microscopy and immunofluorescence to study the astrocyte reaction, collagen deposition, and the formation of the basement membrane of the glia limitans. Normal mature scarring characterized by the deposition of collagen, astrocyte end-feet alignment over a glia limitans, and the permanent presence of mesodermal cells (fibroblasts and macrophages) in the core of the lesion, does not occur in wounds before 8-10 days post-partum (dpp). Instead there is no deposition of collagen, and only a transitory astrocyte response occurs with the formation of an interrupted glia limitans. These latter features disappear with time so that the wound is ultimately obliterated by the growth of axons and dendrites through the lesion. Mature scarring is attained over 8-12 dpp when increasing amounts of collagen are deposited and a continuous permanent glia limitans is formed. The acquisition of the mature response to injury from 8-12 dpp may be correlated with the presence of increasing titres of a fibroblast growth factor (FGF), derived from autolytic digestion of injured brain tissue. We have investigated FGF activity using a 3 T 3 fibroblast tissue culture assay to detect mitogenic activity in brain extracts from rats lesioned at different ages and from leukodystrophic mice which have no myelin. Our results show that high titres of FGF are present in the developing brain long before myelination commences, and that normal levels of FGF are found in the brains of leukodystrophic mice which have no myelin. Scarring in brain lesions in these mutants is quite normal.

Trauma-induced glial proliferation: possible involvement of the immune system

Rat neurologlial cells proliferate following trauma to the frontal cortex. Since previous reports have indicated that activated T-lymphocytes secrete a factor which can induce the proliferation of glial cells in vitro, we investigated the effects of immunosuppression on the trauma-induced proliferation of glial cells in the rat. Animals were treated with either methotrexate (2.5 and 10 mg/kg/day), hydrocortisone (100 mg/kg/day), or saline for five days prior to lesioning of the cortex. Immunocompetence was estimated by measuring sheep red blood cell hemagglutination titers at the time of killing. On the last day of drug treatment, rats were mechanically lesioned on the frontal cortex, and the incorporation of intraventricularly injected 3H-thymidine (3H-TdR) into cortical DNA, a measure of glial cell proliferation, was determined two days after lesioning. Intraperitoneal treatment with methotrexate before the lesioning depressed 3H-TdR incorporation into brain DNA, and reduced hemagglutination titers and thymus and spleen weight. However, intramuscular hydrocortisone pretreatment, which had immunosuppressive actions similar to methotrexate, had a much smaller effect on 3H-TdR incorporation into brain DNA following trauma. Methotrexate given acutely after lesioning did not depress thymidine utilization in the lesioned rat cortex, apparently because of poor penetration of the folate analog into the brain. Thus, we conclude that inhibition of glial cell proliferation resulting from methotrexate pretreatment had been produced indirectly, probably by its severe immunosuppressive effects.

Glial DNA synthesis and cell proliferation in the lesioned frontal cortex of the rat

Proliferation of rat neurological cells was quantified following a lesion of the frontal cortex, with the rate of incorporation of intraventricularly administered [3H]thymidine ([3H]TdR) into cortical DNA serving as an index of glial proliferation. Incorporation of [3H]uridine into the corresponding RNA fractions did not serve this purpose. The intraventricular route of administration of thymidine greatly reduced the amount of [3H]TdR needed to label DNA relative to systemic injection. The rate of incorporation of [3H]TdR into DNA was linear for 75 min post-injection. Significantly more [3H]TdR was incorporated into DNA of the lesioned frontal cortex than that of the contralateral control cortex, during the first 4 days post-trauma. The majority of the acid-insoluble radioactivity (from [3H]TdR) was localized in the nuclear subcellular fraction of the cortex. Experiments indicated that the enhanced incorporation of [3H]TdR was not the result of altered metabolism or pool sizes of TdR in the lesioned cortex. Histological analysis indicated that there was a significant increase in the number of glial cells in the lesioned cortex by day 4 post-lesion, which corresponded to the increase in DNA synthetic activity. It was concluded that mechanical trauma to the frontal cortex of the rat results in an increase in the number of glial cells at and near the lesion which is accompanied by an increase in incorporation of [3H]TdR into cortical DNA. This method of measuring posttraumatic DNA synthesis has several advantages over autoradiography.

Astrocyte cultures from adult rat brain. Derivation, characterization and neurotrophic properties of pure astroglial cells from corpus callosum

It has not as yet been routinely possible to derive primary cultures of glial cells from adult rat brain tissue even when adopting strategies that have proven successful with perinatal tissue. We now report that in response to a surgical lesion and a period of postoperative 'priming' in vivo, proliferating cultures of astroglial cells can be derived from the normally quiescent glia of the corpus callosum region of the adult rat brain. In such cultures the predominance of astroglia and the virtual absence of oligodendroglia and neurons has been established by the use of a variety of cell-type specific antisera. Fibroblasts, the only other cell type identified, when not numerous could be successfully eliminated by treatment of the cultures with anti-Thy-1 antibodies and guinea pig complement. Pure astroglial cells from adult brain have been sub-cultured and maintained for up to 4 months in vitro, providing suitable quantities of cells for studies on the trophic interaction between glia and neurons. In long-term culture the adult astrocytes maintain a flattened undifferentiated morphology but readily assume a stellate shape with long branching processes upon the addition of a crude homogenate from bovine pituitary.

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.

Degeneration of hippocampal CA3 pyramidal cells induced by intraventricular kainic acid

Degeneration of hippocampal CA3 pyramidal cells was investigated by light and electron microscopy after intraventricular injection of the potent convulsant, kainic acid. Electron microscopy revealed evidence of pyramidal cell degeneration within one hour. The earliest degenerative changes were confined to the cell body and proximal dendritic shafts. These included an increased incidence of lysosomal structures, deformation of the perikaryal and nuclear outlines, some increase in background electron density, and dilation of the cisternae of the endoplasmic reticulum accompanied by detachment of polyribosomes. Within the next few hours the pyramidal cells atrophied and became electron dense. Then these cells became electron lucent once more as ribosomes disappeared and their membranes and organelles broke up and disintegrated. Light microscopic changes correlated with these ultrastructural observations. The dendritic spines and the initial portion of the dendritic shaft became electron dense within four hours and degenerated rapidly, whereas the intermediate segment of the dendrites swelled moderately and became more electron lucent. No degenerative changes were evident in pyramidal cell axons and boutons until one day after kainic acid treatment. Less than one hour after kainic acid administration, astrocytes in the CA3 area swelled, initially in the vicinity of the cell body and mossy fiber layers. It is suggested that the paroxysmal discharges initiated in CA3 pyramidal cells by kainic acid served as the stimulus for this response. Phagocytosis commenced between one and three days after kainic acid administration, but remained incomplete at survival times of 6-8 weeks. Astrocytes, microglia, and probably oligodendroglia phagocytized the degenerating material. These results point to the pyramidal cell body and possibly also the dendritic spines as primary targets of kainic acid neurotoxicity. In conjunction with other data, they support the view that lesions made by intraventricular kainic acid can serve as models of epileptic brain damage.

A comparison of two factors affecting the proliferation of non-neuronal (glial) cells in vitro

Earlier studies have shown that the proliferation of sympathetic non-neuronal cells in vitro can be stimulated either by direct contact with growing neurons or by addition of sonicated neurons of the same type to the culture medium. Several lines of evidence presented herein suggest that intact neurons and neuronal sonicate probably stimulate [3H]thymidine incorporation by distinctly different mechanisms. First, mitogenic factors are present in sonicates of cell types (fibroblasts and non-neuronal cells) which do not stimulate non-neuronal cell proliferation when added as intact cells. Second, neuronal sonicate and intact neurons differ in the types of cells which are responsive to their mitogenic influence. Third, intact neurons do not appear to stimulate non-neuronal cell proliferation by the same mechanism as that of neuronal sonicate. Further similarities between stimulation of non-neuronal cell proliferation in vitro and reactive gliosis in vivo are discussed.

Endocytic activity of subependymal microglial cells in the toad brain: a cytochemical study of peroxidase uptake

A population of microglial cells that rapidly incorporate extracellular material introduced into the ventricular system has been identified just beneath the ependyma of all four cerebral ventricles in the toad (Bufo marinus). In untreated tissue these cells appear to be scattered, possess few processes and have an elongate shape with their long axes lying parallel to the ventricular surface. Their most distinctive ultrastructural features are nuclei containing clumps of chromatin, cytoplasmic dense bodies and single strands of granular endoplasmic reticulum. When horseradish peroxidase (HRP) is perfused through the ventricular system and the tissue processed using the DAB cytochemical method, the cells change shape and incorporate HRP into cytoplasmic structures. Even after very short perfusion periods (2-5 minutes) cells become rounded, the surface is ruffled and pseudopodia develop that contain characteristic flocculent material. Reaction product for HRP is contained in plain and coated vesicles, tubules, vacuoles and long structures composed of two closely apposed membranes. At these early times, relatively few multivesicular bodies and dense bodies contain reaction product, but when the cells are viewed at longer time periods after the ventricular perfusion of HRP an increasing proportion of the multivesicular bodies and dense bodies contain reaction product. By 320 minutes reaction product is found almost exclusively in these two organelles. In addition, many pseudopodia containing dense bodies with peroxidase activity are found in the neurophile; some, but not all, can be traced from the subependymal microglial cells. The cell bodies have resumed their flattened shape. When compared to the subependymal microglial cells, other brain cells--oligodendrocytes, astrocytes, ependymal cells and neurons--contain relatively little reaction product at short time intervals; only by 320 minutes are moderate amounts of HRP present. Because of the position of the microglial cells and their ingestive capacity, it is suggested that they function to protect the brain from foreign substances entering from the CSF.

Electron microscopic studies of serially sectioned cat spinal alpha-motoneurons. I. Effects of microelectrode impalement and intracellular staining with the fluorescent dye "Procion Yellow"

Cat spinal alpha-motoneurons were studied in the light and electron microscope after intracellular recording and staining with the fluorescent dye Procion Yellow. Generally, the ultrastructural preservation of the stained neurons improved when the amount of dye delivered was decreased, and when the duration of the microelectrode impalement of the neuron as well as the time between the intracellular staining and the tissue fixation was kept as short as possible. Utilizing the optimal experimental procedure finally arrived at, about one-third of the stained neurons could be used for further quantitative morphometric analysis. With respect to synaptology and gross architecture these cells appeared to differ from control motoneurons mainly with regard to a focal disarrangement of the cell body periphery, probably a result of the microelectrode injury, and a certain degree of damage to some large boutons.

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.

Stimulation of non-neuronal cell proliferation in vitro by mitogenic factors present in highly purified sympathetic neurons

Sympathetic neurons have been demonstrated to contain one or more mitogens which are active on highly purified non-neuronal cells cultured in medium containing an optimal concentration of fetal calf serum. Neurons and homologous non-neuronal cells were separated by a method recently developed in this laboratory. The highly purified neurons were either sonicated or homogenized prior to addition to nonneuronal cultures. The presence of neuronal sonicate (1) greatly stimulated [3H]thymidine incorporation into acid-precipitable macromolecules without altering the soluble [3H]thymidine pool, (2) increased both the fraction of non-neuronal cells which took up [3H]thymidine and the density of labeling as observed by autoradiography, and (3) increased the number of cells present in treated cultures after 40 h. The enhancement of [3H]thymidine incorporation was dose-dependent and did not involve cyclic AMP. Addition of neuronal sonicate also caused marked non-neuronal cell elongation which resulted in the elaboration of very long cell processes. The active factor(s) in the neuronal sonicate were partially heat-labile. Norepinephrine was ruled out as a possible mitogenic factor.

Initial response of silver-impregnated "resting microglia" to stab wounding in rabbit hippocampus

Adult rabbits received stab wound in the cerebrum and were sacrificed at intervals of 20, 30, and 39 h thereafter. Each animal was injected intracerebrally with 3H-thymidine 2h before fixation. Altered brain tissues of the stratum radiatum of hippocampus were taken for examination. Response of "resting microglia" to stab wounding was investigated by electron microscopic autoradiography and by autoradiography applied on silver-impregnated materials. Following results were obtained: (1) Resting microglia undergo marked swelling shortly after the brain damage. We designate these cells as "swollen microglia". (2) Swollen microglia form the only cell population that proliferate actively in the initial stage of glial response to the brain injury, and (3) astroglia do not proliferate during the same experimental periods, in the rabbit hippocampus.

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.

Radioautographic investigation of gliogenesis in the corpus callosum of young rats. II. Origin of microglial cells

Microglial cells are absent from the corpus callosum of newborn rats. In the hope of finding out when and how microglial cells appear with age, 3H-thymidine was given intraperitoneally as single or three shortly spaced injections to 5-day-old rats weighing about 15 g; and these animals were sacrificed at various time intervals from 2 hours to 35 days later. Pieces of corpus callosum were taken near the superior lateral angle of the lateral ventricles; and semithin sections were radioautographed and stained with toluidine blue. The corpus callosum of 5-day-old rats is composed of loosely arranged unmyelinated fibers and scattered cells. Among these cells, microglia are rare; there are a few astrocytes, many immature glial cells, rare pericytes, and 6--7% of phagocytic "ameboid cells" consisting of a few monocytes and many macrophages. In the animals sacrificed two hours after 3H-thymidine administration, label is present only in immature cells and "ameboid cells." As time elapses and the fibers of corpus callosum become myelinated, oligodendrocytes and, later, microglial cells appear. At the age of 12 days, microglial cells are present in substantial number; and by 19 days, the number doubles to reach a plateau. Many of the new microglial cells are labeled, e.g., 78.1% in 12-day-old animals (7 days after 3H-thymidine administration). The labeled microglial cells must have come from the transformation of cells that acquired label early, that is, from the immature cells or the "ameboid cells." The height of the peaks of labeling--59.8% at nine days for immature cells and 77.8% at 12 days for "ameboid cells"--points to the latter as precursors of the highly labeled microglial cells. Furthermore, the "ameboid cells" disappear as microglial cells appear and there are transitional elements between these two cell types. Cell counts suggest that about a third of the "ameboid cells" transform into microglial cells, while the others degenerate and die. Thus, the microglial cells which appear in the corpus callosum during the first three weeks of life result from transformation of the "ameboid cells"--a group of macrophages showing various stages of transition from monocytes. As for the occasional microglial cell appearing after the third week or in the adult, they presumably come directly from monocytes. In either case, monocytes would be the initial precursors.

The fine structure of pulse labeled (3-H-thymidine cells) in degenerating rat optic nerve

The ultrastructure of pulse labeled (3-H-thymidine) cells in rat optic nerve undergoing Wallerian degeneration is described. The study was limited to the first ten days after enucleation since cell proliferation during this interval is greater than in normal optic nerve (Skoff and Vaughn, '71). Approximately one-third of the pulse labeled cells are astrocytes. The majority of the proliferating astrocytes are in a reactive state, having changed their normal fibrous appearance to one showing a paucity of filaments. Thirty percent of the pulsed cells can be classified as microglia. Only immature oligodendrocytes proliferate, and they account for less than 10% of the pulse labeled cells. About 30% of the labeled population are undifferentiated glial precursor cells. Electron microscopic autoradiographic data obtained from normal optic nerve and presented in this paper indicates that glial precursor cells which have divided shortly before enucleation continue to proliferate after it. The evidence suggest that recently formed glial precursor cells transform into phagocytes following enucleation. Less than 3% of the pulse labeled cells examined in this study are ultrastructurally similar to mononuclear leukocytes. The results of the present study together with previous studies of degenerating optic nerve indicate that most phagocytes in Wallerian degeneration are derived from proliferation of intrinsic glia rather than from an invasion of exogenous cells.

The relationship between microglia and brain macrophages. Experimental investigations

A series of experiments are reported which indicate that the microglia are endogenous cells which may constitute the only source of phagocytes in certain mild degenerative conditions, such as Wallerian degeneration and retrograde nerve cell disintegration. In more extensive lesions with increased vascular permeability a substantial number of the phagocytes are derived from the blood monocytes.