Search

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 IRENI's 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.

Glutaric acidaemia type I (GA I) is caused by the deficiency of glutaryl-CoA dehydrogenase, resulting in accumulation of glutaric acid (GA) and 3- hydroxyglutaric acid (3-OH-GA) in blood and cerebrospinal fluid (CSF). Neuropathological changes with onset in childhood consist of severe neuronal loss in the caudate and putamen. An animal model is necessary to test possible intervention strategies, and prior reports suggested that GA or 3-OH-GA could be used to create specific neuron loss in adult rats. Adult, 3-week-old and 2-week-old rats received intrastriatal injections of GA and 3-OH-GA at a range of doses. High concentrations caused necrotic lesions in striatum. Low concentrations caused white-matter axonal damage and small areas of neuron loss. Injection of lipopolysaccharide prior to administration of 3-OH-GA was not associated with enhanced neuronal loss. Our findings contradict prior claims and we conclude that the simple model of a single GA or 3-OH-GA injection into rat brain does not replicate the neuropathological findings in humans.

We examined whether following a hypoxic–ischemic insult in young animals there are long-lasting functional deficits that correlate either to histological tissue damage or to potential compensatory plasticity changes. Four-week-old rats were subjected to an episode of cerebral hypoxia–ischemia (right carotid artery occlusion + 30 min of hypoxia) or a sham operation. In hypoxic–ischemic animals there were gross neurological deficits 1, 24, and 48 h postinsult with recovery by 1 week. Behavioral deficits were observed in both the acquisition and the performance of a response duration differentiation test and a fine motor control test (staircase test) 3 months after the hypoxia–ischemia. Functional magnetic resonance imaging studies demonstrated less activation in the sensory–motor cortex of hypoxic–ischemic animals in response to left vs right forepaw stimulation 4 months postinsult. Histological assessment delineated striatal, cortical, and hippocampal damage in the hypoxic–ischemic hemisphere and a reduction in cortical thickness, bilaterally. GFAP immunoreactivity was increased in injured striatum and cortex. Neurofilament heavy chain (NF200) immunoreactivity was normally most intense in white matter and decreased in areas of ipsilateral cortical damage. Synaptophysin immunoreactivity was reduced around areas of infarction and somewhat increased in adjacent undamaged striatum and in layer IV of parietal cortex. The histological damage or chronic degenerative changes could account for much of the variance in functional outcome detected with sensitive behavioral tests so that overall the compensatory or plasticity changes evident within the juvenile brain are rather modest.

Background and Purpose —Tumor necrosis factor-α (TNF-α) expression is increased in brain after cerebral ischemia, although little is known about its abundance and role in intracerebral hemorrhage (ICH). A TNF-α–specific antisense oligodeoxynucleotide (ORF4-PE) was used to study the extent to which TNF-α 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-α 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-α mRNA and protein levels ( P P P P P P Conclusions —These results indicate a pathogenic role for TNF-α during ICH and demonstrate that reducing TNF-α expression using antisense oligodeoxynucleotides is neuroprotective.

Feline immunodeficiency virus (FIV) is a lentivirus that causes immune suppression and neurological disease in cats. Among animal viruses, individual viral strains have been shown to be neurovirulent, but the role of viral strain specificity among lentiviruses and its relationship to systemic immune suppression in the development of neurological disease remains uncertain. To determine the extent to which different FIV strains caused neurological disease, FIV V1CSF and Petaluma were compared in ex vivo assays and in vivo. Both viruses infected and replicated in macrophage and mixed glial cell cultures at similar levels, but V1CSF induced significantly greater neuronal death than Petaluma in a neurotoxicity assay. V1CSF-infected animals showed significant neurodevelopmental delay compared to the Petaluma-infected and uninfected animals. Magnetic resonance spectroscopy studies of frontal cortex revealed significantly reducedN-acetyl aspartate/creatine ratios in the V1CSF group compared to the other groups. Cyclosporin A treatment of Petaluma-infected animals caused neurodevelopmental delay and reducedN-acetyl aspartate/creatine ratios in the brain. Reduced CD4+ and CD8+ cell counts were observed in the V1CSF-infected group compared to the uninfected and Petaluma-infected groups. These findings suggest that neurodevelopmental delay and neuronal injury is FIV strain specific but that systemic immune suppression is also an important determinant of FIV-induced neurovirulence.

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 neucleotide 3'-phosphodiesterase (CNPase), and the oligodendrocyte enzyme UDP-galactose, ceramide galactosyltransferase (CGa1T). 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, CGa1T 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 micron 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 CGa1T 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.

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.

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.

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.

Haemorrhagic brain damage is frequently encountered as a complication of premature birth. Much less frequently, multifocal petechial haemorrhage is identified in asphyxiated term newborns. Our goal was to develop an experimental rat model to reproduce this pattern of brain damage.Neonatal rat pups were exposed to a 24-h period of 10% or 8% hypoxia followed by a single dose of phenylephrine. Acute and subacute changes, as well as long-term outcomes, were investigated by histology, brain magnetic resonance imaging and behavioural assessment. Immunostaining for vascular endothelial growth factor and caveolin-1 was performed in the rat brains as well as in a 17-day human case.Small foci of haemorrhage were identified in almost all regions of the rat brain subjected to hypoxia plus phenylephrine, but not hypoxia alone. Exposure to 8% hypoxia was associated with more haemorrhagic foci than 10% hypoxia. With rare exceptions, the blood deposits were too small to be detected by magnetic resonance imaging. Altered immunohistochemical detection of vascular endothelial growth factor and caveolin-1 in the child and the rat model suggests a role for blood-brain barrier compromise. There were no clear behavioural changes and no residual morphological abnormalities in the 78-day follow-up of the rats.We conclude that transient hypoxia, in a dose-dependent manner, can weaken the vasculature and predispose to brain haemorrhage in the situation of labile blood pressure. Persistent hypoxia is likely to be important in the genesis of permanent severe brain damage.

Hydrocephalus-induced damage is dependent on the rate and magnitude of ventricular dilatation, the proximity to the ventricle, and the developmental stage at which the disturbance occurs. It is mediated through a combination of mechanical, ischemic, and metabolic-toxic disturbances. Developmental processes, including myelin production, can be impaired. Periventricular axons are the primary target, however. The potential for reversal of damage by shunting diminishes as the duration and severity of hydrocephalus increases. Ancillary pharmacologic means for preventing hydrocephalus-induced brain damage are worth pursuing.

Object. It can be inferred from data published in the literature that brain compression occurs in the early stages of acute hydrocephalus and that drainage of extracellular waste products is impaired. The authors hypothesized that compression of the cortex would alter water distribution and retard the diffusion of fluid in the hydrocephalic brain.Methods. Proton diffusion, blood perfusion, and T1 and T2 relaxation times were determined in adult rat brain by using magnetic resonance imaging prior to, and 1 and 8 days after induction of hydrocephalus by kaolin injection. Five anatomical regions of interest were studied. The striatum, dorsal cortex, and lateral cortex exhibited decreased T2 and apparent diffusion coefficient (ADC) values but no change in perfusion. Examination of white matter revealed an initial decrease in ADC followed by a significant increase. The T2 relaxation times increased and perfusion decreased progressively between 1 and 8 days after induction of hydrocephalus.Conclusions. Acute experimental hydrocephalus causes compression of gray matter, perhaps associated with reduction in total water, which impairs diffusion of water in the tissue. White matter compression and hypoperfusion precede the development of edema. These findings have importance for understanding the neurochemical changes that occur in hydrocephalic brains.

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 T1-weighted magnetic resonance imaging. Non-hydrocephalic controls exhibited greater spread of the tracer and greater change in T1-weighted 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.

Inflammatory cells are postulated to mediate some of the brain damage following ischemic stroke. Intracerebral hemorrhage is associated with more inflammation than ischemic stroke. We tested the sulfated polysaccharide fucoidan, which has been reported to reduce inflammatory brain damage, in a rat model of intracerebral hemorrhage induced by injection of bacterial collagenase into the caudate nucleus. Rats were treated with seven day intravenous infusion of fucoidan (30 micrograms h-1) or vehicle. The hematoma was assessed in vivo by magnetic resonance imaging. Motor behavior, passive avoidance, and skilled forelimb function were tested repeatedly for six weeks. Fucoidan-treated rats exhibited evidence of impaired blood clotting and hemodilution, had larger hematomas, and tended to have less inflammation in the vicinity of the hematoma after three days. They showed significantly more rapid improvement of motor function in the first week following hemorrhage and better memory retention in the passive avoidance test. Acute white matter edema and eventual neuronal loss in the striatum adjacent to the hematoma did not differ between the two groups. Investigation of more specific anti-inflammatory agents and hemodiluting agents are warranted in intracerebral hemorrhage.

In the past few years, although significant efforts have been made to assess flow distribution during retrograde cerebral perfusion with microspheres, dye, or hydrogen clearance, flow distribution in real time is still undefined. We used MR perfusion imaging to monitor flow distribution in the brain during and after deep hypothermic circulatory arrest (DHCA) with antegrade or retrograde cerebral perfusion (ACP or RCP).Thirteen pigs were divided into 2 groups and exposed to 120 minutes of either RCP (n = 7) or ACP (n = 6) at 15 degrees C, followed by 60 minutes of cardiopulmonary bypass (CPB) at 37 degrees C. During DHCA, the brain was perfused antegradely through the common carotid artery or retrogradely through the superior vena cava at pressures of 60 to 70 mm Hg and 20 to 25 mm Hg in the ACP and RCP groups, respectively. Esophageal temperature was monitored continuously. MR perfusion images were acquired every 30 minutes before, during, and after DHCA. The brain was perfusion-fixed with formaldehyde solution for histopathology at the completion of each experiment. During initial normothermic CPB, MR perfusion imaging showed a nearly uniform distribution of flow in the brain. The same pattern was maintained with a significant increase in regional cerebral blood volume during ACP and reperfusion in the ACP group. RCP provided little or no detectable blood distribution to the brain, resulting in poor reperfusion of many areas of the brain on reflow with CPB at 37 degrees C. The total area suffering poor reperfusion was significantly higher in the RCP group than the ACP group. Histopathology showed no morphological changes in any area of the brain in the ACP group, whereas varying severity of neuronal damage was observed in different regions of the brain in the RCP group.ACP preserves uniform blood distribution and normal morphology of brain tissue after prolonged DHCA. RCP provides very little blood to the tissue of the brain. A 120-minute period of RCP results in abnormal flow distribution and neuronal damage during reperfusion. The damage resulting from shorter periods of RCP remains to be assessed.

Functional and behavioral disturbances associated with hydrocephalus may be due in part to altered neurotransmitter function in the brain. Hydrocephalus was induced in adult rabbits by injection of silicone oil into the cisterna magna. These and controls were killed 3 days, 1 and 4 weeks post-injection. Tissue concentrations of norepinephrine, epinephrine, serotonin, dopamine, and the metabolites 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) levels were determined in fifteen brain regions using HPLC. There were decreases in hypothalamic and medullary dopamine, transient decreases in basal ganglia serotonin, increases in thalamic noradrenaline, and increases in hypothalamic and thalamic epinephrine. Changes in the primary neurotransmitters may be attributable to damage of their axonal projection systems. Metabolite concentrations increased in the cerebrum. Reduced clearance of extracellular fluid which accompanies cerebrospinal fluid stasis may explain the accumulation of metabolites.

The motor and cognitive dysfunction associated with hydrocephalus remains a clinical problem in children. We hypothesized that young rats with hydrocephalus should exhibit similar dysfunction and that the dysfunction should be reversible by shunting. Hydrocephalus was induced in 3-week-old rats by injection of kaolin into the cisterna magna. Rats were assessed by T2-weighted images obtained with a 7-T magnetic resonance device and by repeated behavioral testing including ability to traverse a narrow beam and ability to find a hidden platform in a water pool. Some of the rats underwent a shunting procedure 1 or 4 weeks after kaolin injection. Magnetic resonance images were used to measure ventricle size. They clearly demonstrated increased signal in periventricular white matter, which corresponded to increased brain water content. A flow-void phenomenon was observed in the cerebral aqueduct. Ability to traverse the beam did not correlate with the degree of ventriculomegaly. Ability to swim to the hidden platform demonstrated a progressive impairment of learning function which may have been accentuated by motor disability. When rats were shunted after 1 week, the behavioral dysfunction was prevented. Late shunting after 4 weeks was associated with gradual recovery of the behavioral disability which was not complete after 4 weeks. We conclude that early shunting is superior to late shunting with regard to behavioral dysfunction. High-resolution MR imaging shows features in hydrocephalic rats similar to those found in hydrocephalic humans.

Brain damage due to an episode of cerebral hypoxia/ischemia remains a major problem in the human infant, providing impetus for the testing of potential neuroprotective agents in animal models. Although these animal models do not mirror the human pathology exactly (e.g., with respect to regions vulnerable to damage), they usually have the histological characteristics of gray matter hypoxic/ischemic injury in the human. An important factor in comparing models directly is the stage of development of the brain at birth, which varies widely between species. Approaches to prevent or treat cerebral hypoxic/ischemic damage in neonates have paralleled those in adults. However, most of these results should be interpreted cautiously, since neonatal rat models with little concurrent physiological monitoring are often used. As in adults, moderate hypothermia during the insult or a preconditioning stress prior to the insult has prevented hypoxic/ ischemic brain damage. Different from adults is the demonstration that pretreatment with moderate doses of glucocorticoids or hyperglycemia during the hypoxic/ ischemic insult protects the brain against infarction. Partial protection, primarily in neonatal rats, has also been produced by pretreatment with voltage-sensitive calcium channel antagonists, free radical scavengers, growth factors, gangliosides, anticonvulsants, antiinflammatory agents, and nitric oxide synthase inhibitors. Posttreatment has been effective with a few agents. The most consistent has been the protective effect observed with glutamate receptor antagonists administered before but also up to 4 h after the insult. The effects of most of these therapies on blood glucose, body temperature, and/or the systemic circulation should be measured and the protective effects confirmed in larger species prior to considering clinical applications.

Previous investigations showed that fragments of fetal rabbit brain tronsplanted into striatum of neonatal shiverer mouse give rise to cells that migrate through host tissue and differentiate into astroglia and oligodendroglia within 2 weeks. We studied the integration of transplanted astroglia at the ultrastructural level using pre-embedding labeling with a monoclonal antibody which recognizes an epitope -associated with rabbit but not mouse glial fibrillary acidic protein. The morphology of early migrating donor cells does not distinguish them from cells -arising in host germinal matrix. Once the cells complete their migration they integrate into host brain in a structurally normal manner. Transplanted astroglia form perivascular foot plates with host capillaries. They also send extensive processes into the neuropil where intimate contacts with neurons and synaptic structures are formed. Oligodendroglia send processes to nearby axons where they form normal-appearing myelin. During the rejection process, which may begin at 4 weeks, donor astroglia show evidence of reaction with increased intermediate filament content. Donor cells are attacked by leukocytes, including eosinophils, and subsequently degenerate. We conclude that crossspecies transplantation of glial cells can result in entirely normal structural integration into host brain

✓ The metabolic changes in neonatal hydrocephalus that lead to permanent brain injury are not clearly defined, nor is the extent to which these changes can be prevented by a cerebrospinal fluid shunt. To clarify these processes, cerebral glucose utilization was examined using [14C]2-deoxyglucose autoradiography in 1-month-old kittens, kaolin-induced hydrocephalic littermates, and hydrocephalic kittens in which a ventriculoperitoneal shunt had been inserted 10 days after kaolin injection. The hydrocephalic kittens showed thinning of the cerebral mantle and an anterior-to-posterior gradient of enlargement of the ventricular system, with a ventricle:brain ratio of 24% for the frontal and 35% for the occipital horns compared with control (< 0.5%) and shunted (< 5%) animals. White matter in hydrocephalic animals was edematous. Myelination was delayed in the periventricular region and in the cores of the cerebral gyri. Glucose utilization in hydrocephalic and shunted animals was unchanged from control animals in all gray-matter regions examined. However, in hydrocephalic animals, the frontal white matter exhibited a significant increase in glucose utilization (25 µmol • 100 gm−1 • min−1) in the cores of gyri compared with normal surrounding white-matter values (14.8 µmol • 100 gm−1 • min−1). Very low values (mean 4 µmol • 100 gm−1 • min−1) were found in areas corresponding to severe white-matter edema, and these areas were surrounded by a halo of increased activity (24 µmol • 100 gm−1 • min−1). In contrast, cytochrome oxidase activity in white matter was homogeneous. Shunting resulted in restoration of the cerebral mantle thickness, a return to normal levels of glucose utilization in the white matter, and an improvement in myelination. It is suggested that the areas of increased glucose utilization seen in the white matter represent anaerobic glycolysis which, if untreated, progresses to infarction. The pattern of this increased glucose utilization matches that of expected myelination and, during this period of high energy demand, white matter may be susceptible to the hypoperfusion associated with hydrocephalus.

✓ It has recently been reported that pretreatment with a single dose of dexamethasone (0.1 mg/kg) 24 hours before hypoxia in 7-day-old rat pups is protective against an hypoxic-ischemic insult (unilateral carotid artery occlusion followed by 3 hours of hypoxia in 8% O2). The authors now examine whether pretreatment 6 hours before insult is equally effective and compare other agents potentially suitable for prophylaxis in neonatal hypoxia-ischemia, including the calcium antagonists flunarizine (30 mg/kg pretreatment), nimodipine (0.5 mg/kg pretreatment), and the 21-aminosteroid U-74389F (10 mg/kg pre- and posttreatment). For each active agent, there was also a vehicle-treated control group. Comparison of the mean area of ipsilateral infarction on brain coronal sections showed that there was no statistically significant difference between the various control groups (mean area of infarction 66% ± 4%). Pretreatment with dexamethasone 6 hours prior to hypoxia offered complete protection with no infarction. A beneficial effect was seen following pretreatment with flunarizine (mean area of infarction 33.6% ± 7.8%), although this degree of damage was still significantly different from that seen with dexamethasone pretreatment. Pretreatment with nimodipine or U-74389F offered no protection (mean area of infarction 77.5% ± 4% and 59% ± 10%, respectively). Unlike findings in adult animals and clinical studies, the current studies show that dexamethasone may have a role in the treatment of neonatal hypoxia-ischemia and deserves reappraisal.

The purpose of the studies was to determine how gross physical characteristics of cerebrospinal fluid (CSF) shunts and the cellular proliferative response to shunts contribute to shunt obstruction. Ventricular catheters with round holes, slots, and flanges were implanted into the lateral ventricles of rabbits for 4 weeks. All shunt designs were subject to ingrowth of tissue from the ventricle wall or choroid plexus. There were no qualitative or quantitative differences between normal and hydrocephalic rabbits. Astroglial cells from newborn mice were cultured on shunt catheters for 2 or 4 weeks. The growth of these cells was poor, probably because the cells cannot attach well to the silicone rubber substrate. Contact between the shunt catheter and vascularized brain tissue is the most important factor in the genesis of shunt obstruction.

Hydrocephalus was induced in adult rabbits by injecting silicone oil into the cisterna magna. Mean intracranial pressure was significantly elevated for approximately 36 h post-injection, during which time maximal ventricular dilatation was attained. Stretching and compression of periventricular tissue and capillaries accompanied dilation of the lateral ventricles. Ventricular dilation promoted mitotic activity among the periventricular astroglia. Ventriculomegaly altered the metabolism of the monoamine neurotransmitters in the cortex, hippocampus, diencephalon, hypothalamus, and brain-stem. Ischemic injury to neurons of the hippocampal formation, particularly the dentate gyrus, was observed when hydrocephalus had persisted for more than 4 weeks. Cerebrospinal fluid shunting effectively reversed the neuropathologic changes only when done in the early stages of hydrocephalus. When hydrocephalus persisted for 8 weeks, rapid reversal of changes in the ependyma and periventricular capillaries was prevented largely by periventricular gliosis.

Numerous neuropathological conditions are accompanied by astroglial swelling which may contribute to secondary neuronal damage. From 4-27 days in vitro, swelling of astroglial cells was induced by hypo-osmolar solutions and high K+ solutions and the cells were examined by microscopy and flow cytometry. Regulatory volume decrease was observed beginning after approximately 30 minutes and was accompanied by increased membrane activity. Arginine vasopressin caused gradual persistent astroglial swelling. Atrial natriuretic peptide caused retraction of the astroglial cell processes but did not significantly alter the swelling induced by hypo-osmolar or elevated K+ solutions. The membrane mechanisms responsible for the control of astroglial cell volume did not appear to be specific for mature astroglia, rather they are present at all developmental stages.

Albino rabbits with experimental brain edema produced by a combined cryogenic left hemisphere lesion and metabolic 6-aminonicotinamide lesion were administered a 3-hour intravenous infusion of dimethyl sulfoxide (DMSO). Simultaneous recording of intracranial pressure (ICP), systolic arterial pressure (SAP), and central venous pressure (CVP) and electroencephalography were performed while the animals were being ventilated mechanically to produce a constant Pa CO2 value (38-42 torr). At the end of the infusion, the brain water and electrolyte contents were measured. There was a persistent and progressive reduction of ICP during the infusion, the nadir occurring at 3 hours (p less than 0.005 from zero time), with no change in SAP or CVP. There was a reduction of brain water in both hemispheres when compared to untreated controls, but this was significant for the right hemisphere only (p less than 0.005). There was a significant reduction of the brain sodium content for both hemispheres, but no significant change occurred in brain potassium content. The DMSO infusion was effective not only in reducing ICP, but also in sustaining this reduction for 3 hours.

Hydrocephalus was induced in adult rabbits by injection of silicone oil into the cisterna magna. The frontal horns of the lateral ventricles enlarged to the greatest degree and reached maximum size within 3 days. Cilia and microvilli were progressively lost from the ependymal surface primarily over the corpus callosum. Stretching and flattening of ependymal cells was most pronounced over the septal area. Mitotic activity was significantly increased among the ependymal cells and subependymal astrocytes over the caudate nucleus and corpus callosum during the 2 weeks immediately following induction of hydrocephalus. Cerebrospinal fluid shunting returned the ventricles to normal size. Following shunting, however, the periventricular tissue did not resume a normal appearance. Longer durations of hydrocephalus were associated with less recovery of the periventricular tissue following shunting.

The neuropathology of congenital hydrocephalus in SUMS/NP mice was investigated in this study. Hydrocephalus occurred with an incidence of 16.5% and was evident in the form of an enlarged head soon after birth. The condition was progressive; affected mice gradually became noticeably smaller than normals, acquired functional disturbances and died before ever breeding. Hydrocephalic mice exhibited enormous dilatation of the lateral ventricles, thinning of the cortex and compression and distortion of the diencephalon and striatum. Examination of the midbrain in these animals revealed that the proximal cerebral aqueduct was diminished in size, occluded or absent. Evidence of its anomalous development was seen as early as day 15 of foetal development. This is in substantial agreement with previous reports on this strain. Although the mechanism by which this occurs is still unknown, abnormal development of the adjoining diencephalon and/or rostral midbrain is likely to be involved.

Summary 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. Inmost 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.

Specific gravity determinations were made on fresh and desiccated samples of hydrocephalic rabbit brains. There was a density gradient in the normal cortical gray matter. Hydrocephalus was accompanied by significantly increased specific gravity of cortical gray matter at 3 days and 1 and 4 weeks. In the latter two periods, there were also significant increases in the specific gravity of white matter in the corpus callosum. These changes represent water loss throughout the whole cerebrum except at the ventricular surface. The specific gravity of solid tissue brain components changed insignificantly. We conclude that short-term brain volume changes in experimental hydrocephalus were due mainly to loss of tissue water.

The reaction of periventricular tissue to shunt tubing chronically implanted in the fourth ventricle of the rat was investigated by correlative scanning and transmission electron microscopy. Sterile silicone tubing with four 0.4 mm diameter holes was inserted into the fourth ventricle of adult Sprague-Dawley rats through an incision in the atlantooccipital membrane and the animals were killed at postoperative intervals of 5 and 8 weeks. Reactive changes that could be correlated with the extent of contact with the implant occurred in the periventricular tissue. The ependyma lining the ventricle underwent a progressive loss of cilia and microvilli, became attenuated and, in circumscribed areas, was lost entirely. A significant subependymal gliosis accompanied these changes. In regions denuded of ependyma, neurons and glia were exposed directly to the cerebrospinal fluid. Eruptions of periventricular tissue corresponding precisely to the location of holes in the implanted tubing were observed on both the vermal surface of the cerebellum and the floor of the ventricle. Evaginations from the surface of the inferior vermis and the floor of the ventricle were most prevalent at 5 and greatest at 8 weeks postimplantation, respectively. Gliosis combined with mechanical factors are believed to be responsible for development of these periventricular tissue evaginations, which may be a factor in the pathogenesis of cerebrospinal fluid shunt obstruction in treated human hydrocephalus.

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.

Following brain injury astrocytes swell acutely and proliferate thereafter. To investigate the direct relationship between swelling and proliferation, cultured astroglial cells were exposed to 60 mM K+ ion or hypo-osmolar (205 mOsm) electrolyte solution for 1 h to cause transient swelling. Proliferation was assessed by bromodeoxyuridine (BrdU) uptake 24 and 96 h later. The cells were double-labelled with antibodies to glial fibrillary acidic protein (GFAP) and BrdU. At 96 h the GFAP immunoreactive cells exposed to K+ exhibited 44.9% uptake versus 27.0% and 21.1% for control and hypo-osmolar exposed cells, respectively. We conclude that swelling of astroglia in vitro does not induce cell proliferation but transient depolarization following exposure to high K+ does.

Summary: Purpose: To determine whether the neuropathologic changes produced by vigabatrin (VGB; γ-vinyl GABA) administration in the developing rat brain are reversible. Methods: We injected rats daily with VGB (25–40 mg/kg/day, s.c.) from age 12 days for 2 weeks followed by 2 weeks of a drug-free period. Behavioral testing, magnetic resonance (MR) imaging, biochemical assays, and histologic technique were used to assess the adverse effect of VGB in developing brain and its reversibility. Results: At the end of 2 weeks' VGB administration: (a) there was a hyperactivity and a shortened latency to escape out of cool water; (b) white matter appeared hyperintense in T2 and diffusion-weighted MR images with 4–15% increases in T2; (c) microvacuolation, TUNEL-positive nuclei, and swollen axons were observed in the corpus callosum; (d) myelin staining indicated a reduction in myelination, as did the reduction in activities of myelin and oligodendrocyte-associated enzymes and the decrease in myelin basic protein on Western blots. Two weeks after stopping VGB administration: (a) MR images were normal, and microvacuolation was no longer in the white matter; (b) reduction in myelination reversed partially; (c) the T2 relaxation time remained elevated in the hypothalamus; and (d) the behavioral response remained abnormal. Conclusions: Long-term VGB administration to young rats causes brain injury, which recovers partially on its cessation. The observed cell death, disrupted myelination, and alterations in behavior indicate a need for further safety assessment in infants and children.