M. R. Del Bigio

Ependyma: Normal and pathological. A review of the literature ☆

A review of the available literature reveals that proliferation of ependyma occurs during embryological and early postnatal periods of development. Turnover, however, declines significantly during postnatal life and only low levels of residual activity persist into adulthood under normal conditions. In some regions of the ventricle, however, morphological and histochemical differentiation of ependyma is not attained for some considerable time postnatally. Recent immunocytochemical studies using GFAP indicate that only tanycytes may acquire antigenicity during development and that they may share a common phylogeny and/or function with astrocytes. Under pathological conditions, the bulk of available evidence suggests that inherent differences may exist in the proliferative capacity of ependyma in different regions of the neuraxis. Although the response of ependyma to various pathological conditions is equivocal, proliferation has been often observed in response to spinal cord injury. Indeed, ependyma is believed to play a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In hydrocephalus there appears to be a remarkable similarity in cytopathological changes regardless of the mode of induction. The sequence, severity and extensiveness of damage appear to correlate with the degree of ventricular dilatation. The most commonly observed changes are (1) stretching and flattening of ependyma, most pronounced over white matter, (2) characteristic ependymal cell surface changes associated with ventricular distension, (3) increased extracellular space and periventricular edema and (4) demyelination and subependymal gliosis. Although ependymal cell proliferation has been reported as part of the overall tissue response to chronic hydrocephalus and to the pathology of ventricular shunt occlusion, the evidence is not entirely convincing and there is clearly a need for further research on the subject.

Antisense Oligodeoxynucleotide Inhibition of Tumor Necrosis Factor-α Expression Is Neuroprotective After Intracerebral Hemorrhage

Background and Purpose— Tumor necrosis factor-&agr; (TNF-&agr;) expression is increased in brain after cerebral ischemia, although little is known about its abundance and role in intracerebral hemorrhage (ICH). A TNF-&agr;–specific antisense oligodeoxynucleotide (ORF4-PE) was used to study the extent to which TNF-&agr; expression influenced neurobehavioral outcomes and brain damage in a collagenase-induced ICH model in rat. Methods— Male Sprague-Dawley rats were anesthetized, and ICH was induced by intrastriatal administration of heparin and collagenase. Immediately before or 3 hours after ICH induction, ORF4-PE was administered directly into the site of ICH. TNF-&agr; mRNA and protein levels were measured by reverse transcriptase–polymerase chain reaction and immunoblot analyses. Cell death was measured by terminal deoxynucleotidyl transferase–mediated uridine 5′triphosphate-biotin nick end labeling (TUNEL). Neurobehavioral deficits were measured for 4 weeks after ICH. Results— ICH induction (n=6) elevated TNF-&agr; mRNA and protein levels (P <0.01) at 24 hours after the onset of injury compared with sham controls (n=6). Immunohistochemical labeling indicated that ICH was accompanied by elevated expression of TNF-&agr; in neutrophils, macrophages, and microglia. Administration of ORF4-PE (2.0 nmol) directly into striatal parenchyma, 15 minutes before (n=4) or 3 hours after (n=6) ICH, decreased levels of TNF-&agr; mRNA (P <0.001) and protein (P <0.01) in the brain tissue surrounding the hematoma compared with animals treated with saline alone (n=6). Mean±SEM striatal cell death (cells per high-powered field) was also reduced in animals receiving ORF4-PE (34.1±5.0) compared with the saline-treated ICH group (80.3±7.50) (P <0.001). ORF4-PE treatment improved neurobehavioral deficits observed at 24 hours (P <0.001) after induction of ICH (n=6) compared with the untreated ICH group (n=6). This improvement was maintained at 28 days after hemorrhage induction (P <0.001). Conclusions— These results indicate a pathogenic role for TNF-&agr; during ICH and demonstrate that reducing TNF-&agr; expression using antisense oligodeoxynucleotides is neuroprotective.

Myelination Delay in the Cerebral White Matter of Immature Rats with Kaolin-induced Hydrocephalus Is Reversible

We hypothesized that hydrocephalus in young animals could cause a delay in myelination. Hydrocephalus was induced in 3-week-old rats by injecting kaolin into the cisterna magna. Ventricular size was assessed by magnetic resonance imaging. After 1 to 4 weeks, rats were either sacrificed, or treated by diversionary shunting of cerebrospinal fluid and then sacrificed 3 to 4 weeks later. Samples of corpus callosum/supraventricular white matter, fimbria, medulla, and spinal cord were assayed for myelin-related enzyme activities including p-nitrophenylphosphorylcholine phosphocholine phosphodiesterase (PNPCP), glycerophosphocholine phosphocholine phosphodiesterase (GPCP), and 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNPase), and the oligodendrocyte enzyme UDP-galactose, ceramide galactosyltransferase (CGalT). Myelin basic protein (MBP) and proteolipid protein (PLP) were assayed in cerebrum by immunoblots and Northern blot. The corpus callosum was processed for electron microscopy and myelin thickness to axon diameter ratios were quantified. One week after induction of hydrocephalus, CGalT and GPCP activity were reduced in the corpus callosum, there was less MBP and PLP in the cerebrum, and myelin sheaths around axons greater than 0.4 wμm in diameter were abnormally thin. With persistent hydrocephalus, the corpus callosum became thinned, axons were lost, and myelin-related enzyme activities and proteins were decreased. Treatment of hydrocephalus at 1 week largely prevented the damage while shunting at 4 weeks failed to restore the injured white matter. Early reduction in CGalT activity in the medulla and spinal cord suggest that oligodendrocyte production of myelin was reduced, even before irreversible damage occurred in the corticospinal tracts. We conclude that hydrocephalus in the immature rat brain delays myelination, but compensatory myelination is possible if treatment is instituted prior to the development of axonal injury. Possible mechanisms of oligodendrocyte impairment are discussed.

Diffusion- andT2-Weighted Increases in Magnetic Resonance Images of Immature Brain during Hypoxia–Ischemia: Transient Reversal Posthypoxia

Hypoxic-ischemic changes in brain are detected earlier with diffusion-weighted (DW) than with T2-weighted magnetic resonance (MR) imaging techniques in adults, whereas the response in immature brain is not known. We investigated MR imaging changes prior to, during, and/or after 2 h of hypoxia-ischemia (right carotid artery occlusion + 2 h of hypoxia) in 7-day-old rats anesthetized with isoflurane. In general, within the first 45 min of hypoxia-ischemia there were no changes in the DW or T2-weighted images. By the second hour of hypoxia-ischemia there were marked areas of increased intensity in both the T2 and the DW images, with cortex and striatum being affected prior to thalamus and hippocampus. The area of DW exceeded that of T2 hyperintensities. In the first hour after hypoxia-ischemia there was a transient recovery of hyperintensities on both T2 and DW images. Between 24 and 72 h the hyperintense area on DW images decreased, whereas that on T2-weighted images increased. The distribution of pathological damage assessed histologically correlated with the areas of hyperintensity on the MR images. In contrast to adult brain, early hypoxic-ischemic injury in immature brain is detected as an increase in intensity in both diffusion- and T2-weighted images, indicating a unique alteration in brain water dynamics in this neonatal model of hypoxia-ischemia. These imaging changes and alterations in brain water can rapidly but transiently reverse upon the start of normoxia and reperfusion, suggestive of secondary energy failure or delayed neuronal death.

Prevention of hypoxic-ischemic damage with dexamethasone is dependent on age and not influenced by fasting

Pretreatment with the synthetic glucocorticoid dexamethasone prevents hypoxic-ischemic brain damage in 7-day-old neonatal rats. We presently characterize the response further by examining the effect of varying the age, the glucocorticoid, and the time of injection and by examining whether fasting can influence the response. Rats (n = 193) were randomized to one of 16 different treatment groups and subjected to hypoxia-ischemia (right carotid artery occlusion +8% O2 which was 3 h in duration for 7-day, 1 h for 2-week, and 30 min for 1-month-old animals). The brains were subsequently perfusion fixed and the area of infarction was measured from hematoxylin- and eosin-stained sections. Time dependence studies demonstrated that treatment with 0.1 mg/kg intraperitoneal dexamethasone 4 h prior to hypoxia reduced infarct size compared to vehicle-treated animals whereas pretreatment at either 48 h or 4 days was ineffective. Dexamethasone pretreatment (4 h) also provided neuroprotection against 4 h of hypoxia-ischemia. Fasted animals which received dexamethasone had reduced blood glucose levels yet markedly less damage than controls. Another glucocorticoid, methylprednisolone (0.7 mg/kg), also reduced infarction. In 2-week-old animals the area of infarction was reduced by pretreatment with dexamethasone, whereas in 1-month-old animals dexamethasone was ineffective. The results suggest that a glucocorticoid-mediated response intervenes in events leading to neuronal death in young animals but not older animals once myelination and synaptogenesis are complete.

Biochemical label-free tissue imaging with subcellular-resolution synchrotron FTIR with focal plane array detector.

The critical questions into the cause of neural degeneration, in Alzheimer disease and other neurodegenerative disorders, are closely related to the question of why certain neurons survive. Answers require detailed understanding of biochemical changes in single cells. Fourier transform infrared microspectroscopy is an excellent tool for biomolecular imaging in situ, but resolution is limited. The mid-infrared beamline IRENI (InfraRed ENvironmental Imaging) at the Synchrotron Radiation Center, University of Wisconsin-Madison, enables label-free subcellular imaging and biochemical analysis of neurons with an increase of two orders of magnitude in pixel spacing over current systems. With IRENIs capabilities, it is now possible to study changes in individual neurons in situ, and to characterize their surroundings, using only the biochemical signatures of naturally-occurring components in unstained, unfixed tissue. We present examples of analyses of brain from two transgenic mouse models of Alzheimer disease (TgCRND8 and 3xTg) that exhibit different features of pathogenesis. Data processing on spectral features for nuclei reveals individual hippocampal neurons, and neurons located in the proximity of amyloid plaque in TgCRND8 mouse. Elevated lipids are detected surrounding and, for the first time, within the dense core of amyloid plaques, offering support for inflammatory and aggregation roles. Analysis of saturated and unsaturated fatty acid ester content in retina allows characterization of neuronal layers. IRENI images also reveal spatially-resolved data with unprecedented clarity and distinct spectral variation, from sub-regions including photoreceptors, neuronal cell bodies and synapses in sections of mouse retina. Biochemical composition of retinal layers can be used to study changes related to disease processes and dietary modification.

Effect of Long‐Term Vigabatrin Administration on the Immature Rat Brain

Summary: Purpose: To determine whether the neuropathologic changes produced by vigabatrin (VGB; γ‐vinyl GABA) administration in the developing rat brain are reversible.

Protection against hypoxic–ischemic damage with corticosterone and dexamethasone: inhibition of effect by a glucocorticoid antagonist, RU38486

We investigated whether the neuroprotection provided by dexamethasone against neonatal hypoxic-ischemic damage can be inhibited by a glucocorticoid antagonist and whether corticosterone, the endogenous glucocorticoid in the rat, also provides protection. Rats (6 days old) were treated with either vehicle (0.1 ml/10 g), corticosterone (3.5-80 mg/kg, s.c.) or dexamethasone alone or in combination with RU38486 (20-80 mg/kg, s.c.) 15 min prior to dexamethasone (0.1 mg/kg, i.p.). At 7 days of age, cerebral hypoxia-ischemia was produced by right carotid artery ligation under anesthesia and subsequent exposure to 2 h of hypoxia. Damage was quantified from brains perfusion-fixed and processed 2 days later. The reduction in somatic growth, thymus weight and the relatively elevated blood glucose levels at the end of hypoxia-ischemia were inhibited by RU38486. The protective effect of dexamethasone was also prevented by RU38486 (P < 0.001). Similar to pre-treatment with dexamethasone, administration of corticosterone (40-80 mg/kg) markedly reduced the extent of infarction compared to vehicle-treated controls (P < 0.0001). Thus, the endogenous glucocorticoid in the rat also provides protection against hypoxic-ischemic damage. RU38486 inhibits the beneficial effects of dexamethasone demonstrating that the neuroprotection observed with dexamethasone is a glucocorticoid receptor-mediated effect.

Hereditary hydrocephalus in laboratory animals and humans

Cerebral ventricle dilatation secondary to disturbed flow of CSF has been observed as an inheritable trait in a variety of laboratory animals as well as in humans. In few groups, however, has the neuropathology been adequately elucidated. In most cases, defective development of the cerebral aqueduct or of the subarachnoid space has been observed. Further study is needed to understand the developmental mechanisms that fail and give rise to hydrocephalus in such models.

Magnetic resonance imaging study of extracellular fluid tracer movement in brains of immature rats with hydrocephalus.

Abstract Hydrocephalus is associated with brain compression and accumulation of neurotransmitter waste products in the brain and cerebrospinal fluid. We postulated that the extracellular compartment is compressed and specifically hypothesized that extracellular fluid tracer movement through brain would differ between control and hydrocephalic rats. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) was injected into the cerebral cortex of 4-week-old rats, 7-11 days after induction of hydrocephalus by kaolin injection into the cisterna magna. The movement of this soluble paramagnetic compound was followed over successive timed intervals from 20 min to 180 min with T^weighted magnetic resonance imaging. Nonhydrocephalic controls exhibited greater spread of the tracer and greater change in Trweighted signal intensity in the ipsilateral cortex than hydrocephalic animals. Hydrocephalic animals exhibited preferential accumulation of tracer in edematous white matter. Gd-DTPA penetrated the lateral ventricles within 30 min in both control and hydrocephalic rats. The results suggest that there is a relative impairment of extracellular fluid movement through the cerebral cortex of young hydrocephalic rats. [Neurol Res 2000; 22: 111-116]