Magnetic resonance imaging and behavioral analysis of immature rats with kaolin-induced hydrocephalus: pre- and postshunting observations

Microcirculatory Impairment and Cerebral Injury in Hydrocephalus and the Effects of Cerebrospinal Fluid Diversion

BACKGROUND AND OBJECTIVES

Hydrocephalus is characterized by progressive enlargement of cerebral ventricles, resulting in impaired microvasculature and cerebral hypoperfusion. This study aimed to demonstrate the microvascular changes in hydrocephalic rats and the effects of cerebrospinal fluid (CSF) release on cerebral blood flow (CBF).

METHODS

On postnatal day 21 (P21), male Wistar rats were intracisternally injected with either a kaolin suspension or saline. On P47, Evan's ratio (ER) was measured using MRI. On P49, the arteriolar diameter and vascular density of the pia were quantified using a capillary video microscope. The CBF was measured using laser Doppler flowmetry. The expressions of NeuN and glial fibrillary acidic protein determined by immunochemical staining were correlated with the ER. The CBF and rotarod test performance were recorded before and after CSF release. The expressions of 4-hydroxynonenal (4-HNE) and c-caspase-3 were studied on P56.

RESULTS

Ventriculomegaly was induced to varying degrees, resulting in the stretching and abnormal narrowing of pial arterioles, which regressed with increasing ER. Quantitative analysis revealed significant decreases in the arteriolar diameter and vascular density in the hydrocephalic group compared with those in the control group. In addition, the CBF in the hydrocephalic group decreased to 30%-50% of that in the control group. In hydrocephalus, the neurons appear distorted, and the expression of 4-HNE and reactive astrogliosis increase in the cortex. After CSF was released, improvements in the CBF and rotarod test performance were inversely associated with the ER. In addition, the levels of 4-HNE and c-caspase-3 were further elevated.

CONCLUSION

Rapid ventricular dilatation is associated with severe microvascular distortion, vascular regression, cortical hypoperfusion, and cellular changes that impair the recovery of CBF and motor function after CSF release. Moreover, CSF release may induce reperfusion injury. This pathophysiology should be taken into account when treating hydrocephalus.

MR Elastography demonstrates reduced white matter shear stiffness in early-onset hydrocephalus

INTRODUCTION

Hydrocephalus that develops early in life is often accompanied by developmental delays, headaches and other neurological deficits, which may be associated with changes in brain shear stiffness. However, noninvasive approaches to measuring stiffness are limited. Magnetic Resonance Elastography (MRE) of the brain is a relatively new noninvasive imaging method that provides quantitative measures of brain tissue stiffness. Herein, we aimed to use MRE to assess brain stiffness in hydrocephalus patients compared to healthy controls, and to assess its associations with ventricular size, as well as demographic, shunt-related and clinical outcome measures.

METHODS

MRE was collected at two imaging sites in 39 hydrocephalus patients and 33 healthy controls, along with demographic, shunt-related, and clinical outcome measures including headache and quality of life indices. Brain stiffness was quantified for whole brain, global white matter (WM), and lobar WM stiffness. Group differences in brain stiffness between patients and controls were compared using two-sample t-tests and multivariable linear regression to adjust for age, sex, and ventricular volume. Among patients, multivariable linear or logistic regression was used to assess which factors (age, sex, ventricular volume, age at first shunt, number of shunt revisions) were associated with brain stiffness and whether brain stiffness predicts clinical outcomes (quality of life, headache and depression).

RESULTS

Brain stiffness was significantly reduced in patients compared to controls, both unadjusted (p ≤ 0.002) and adjusted (p ≤ 0.03) for covariates. Among hydrocephalic patients, lower stiffness was associated with older age in temporal and parietal WM and whole brain (WB) (beta (SE): -7.6 (2.5), p = 0.004; -9.5 (2.2), p = 0.0002; -3.7 (1.8), p = 0.046), being female in global and frontal WM and WB (beta (SE): -75.6 (25.5), p = 0.01; -66.0 (32.4), p = 0.05; -73.2 (25.3), p = 0.01), larger ventricular volume in global, and occipital WM (beta (SE): -11.5 (3.4), p = 0.002; -18.9 (5.4), p = 0.0014). Lower brain stiffness also predicted worse quality of life and a higher likelihood of depression, controlling for all other factors.

CONCLUSIONS

Brain stiffness is reduced in hydrocephalus patients compared to healthy controls, and is associated with clinically-relevant functional outcome measures. MRE may emerge as a clinically-relevant biomarker to assess the neuropathological effects of hydrocephalus and shunting, and may be useful in evaluating the effects of therapeutic alternatives, or as a supplement, of shunting.

Fetal brain damage in congenital hydrocephalus

BACKGROUND

Congenital hydrocephalus (HCP) is a developmental brain disorder characterized by the abnormal accumulation of cerebrospinal fluid within the ventricles. It is caused by genetic and acquired factors that start during early embryogenesis with disruption of the neurogerminal areas. As might be expected, early-onset hydrocephalus alters the process of brain development leading to irreparable neurological deficit. A primary alteration of the ependyma/neural stem cells (affecting vesicle trafficking and abnormal cell junctions) leads to its loss or denudation and translocation of neural progenitor cells (NPCs) and neural stem cells (NSCs) into the cerebrospinal fluid (CSF). Under these abnormal conditions, morphological and functional processes, underlying the concept of astroglial reaction, are initiated in an attempt to recover homeostasis in the periventricular zone. This astroglial reaction includes astrocyte hypertrophy, hyperplasia, and development of a new layer with reorganized functional features that resemble the ependyma. Despite decades of research, there is a lack of information concerning the biological basis of the brain abnormalities that are associated with HCP.

DISCUSSION

The present review of current literature discusses the neuropathological changes during gestation following the onset of congenital hydrocephalus and the unanswered questions into the pathophysiology of the disease. A better understanding of those missing points might help create novel therapeutic strategies that can reverse or even prevent the ultimate neurological impairment that affects this population and improve long-term clinical outcome.

Evaluation of the effects of quercetin on brain lesions secondary to experimental hydrocephalus in rats

INTRODUCTION

Hydrocephaly is a disease that affects not only the dynamics of the cerebrospinal fluid, but also other structures of the central nervous system. Although shunt is effective in reducing ventriculomegaly, many neurological damages are not reversed with surgery. Several studies demonstrate that oxidative stress is involved in the genesis of hydrocephalus lesions.

OBJECTIVE

Evaluate the neuroprotective response of quercetin in hydrocephalus.

MATERIALS AND METHODS

Male newborns rats were used, which received the 15% kaolin injection in the cisterna magna for induction of hydrocephalus. They were divided into control group (C), untreated hydrocephalic (HN), shunted hydrocephalic (HD), hydrocephalic treated with distilled water (HA), hydrocephalic treated with distilled water and shunt (HDA), hydrocephalic treated with quercetin peritoneal (HQp), hydrocephalic treated with quercetin peritoneal and shunt (HDQp), hydrocephalic treated with quercetin by gavage (HQg), and hydrocephalus treated with quercetin by gavage and shunt (HDQg).

RESULTS

Quercetin significantly improved the immunohistochemical markers, mainly caspase and GFAP. There were no significant changes in clinical/behavioral assessment. The use of isolated quercetin does not alter the volume and ventricular size, and the realization of ventriculo-subcutaneous shunt in newborn rats with hydrocephalus presents a high morbi-mortality.

CONCLUSION

The use of quercetin shows laboratory improvement of the effects of glial lesion and corpus callosum fibers and is therefore not justified by the use of the routine substance as neuroprotective.

Hydrocephaly Analysis Supported by Computerized Tomography and Nuclear Magnetic Resonance

Hydrocephalus is widely known as "hydrocephaly" or "water in the brain," a building up of abnormal cerebrospinal fluid in the brain ventricles. Due to this abnormality, the size of the head becomes larger and increases the pressure in the skull. This pressure compresses the brain and causes damage to the brain. Identification by imaging techniques on the hydrocephalus is mandatory to treat the disease. Various methods and equipment have been used to image the hydrocephalus. Among them, computerized tomography (CT) scan and nuclear magnetic resonance (NMR) are the most considered methods and gives accurate result of imaging. Apart from imaging, cerebrospinal fluid-based biomarkers are also used to identify the condition of hydrocephalus. This review is discussed on "hydrocephalus" and its imaging captured by CT scan and NMR to support the biomarker analysis.

A Rat Model of Neurocysticercosis-Induced Hydrocephalus: Chronic Progressive Hydrocephalus with Mild Clinical Impairment

BACKGROUND

Hydrocephalus is the most common complication of extraparenchymal neurocysticercosis, combining obstructive and inflammatory mechanisms that impair cerebrospinal fluid circulation.

METHODS

We studied the long-term progression of neurocysticercosis-induced hydrocephalus in a rat model. We generated an experimental rat model of neurocysticercosis-induced hydrocephalus by cisternal inoculation of cysts or antigens of Taenia crassiceps and compared it with the classic model of kaolin-induced hydrocephalus. We used 52 animals divided into 4 groups: 1) control, 2) neurocysticercosis-induced hydrocephalus by cysts or 3) by antigens, and 4) kaolin-induced hydrocephalus. We studied behavioral, radiologic, and morphologic alterations at 1 and 6 months after inoculation by open field test, magnetic resonance imaging, and immunohistochemical localization of aquaporin-4 (AQP-4).

RESULTS

Behavioral changes were observed later in neurocysticercosis-induced than in kaolin-induced hydrocephalic rats (P = 0.023). The ventricular volume of hydrocephalus induced by experimental neurocysticercosis progressively evolved, with the magnetic resonance imaging changes being similar to those observed in humans. Periventricular inflammatory and astrocytic reactions were also observed. AQP-4 expression was higher in the sixth than in the first month after inoculation (P = 0.016) and also occurred in animals that received antigen inoculation but did not develop hydrocephalus, suggesting that AQP-4 may constitute an alternative route of cerebrospinal fluid absorption under inflammatory conditions.

CONCLUSIONS

Our neurocysticercosis-induced hydrocephalus model allows for the long-term maintenance of hydrocephalic animals, involving mild clinical performance impairments, including body weight and behavioral changes.

Cholinergic transmission is impaired in patients with idiopathic normal-pressure hydrocephalus: a TMS study

The pathophysiological mechanisms of cognitive and gait disturbances in subjects with normal-pressure hydrocephalus (NPH) are still unclear. Cholinergic and other neurotransmitter abnormalities have been reported in animal models of NPH. The objective of this study was to evaluate the short latency afferent inhibition (SAI), a transcranial magnetic stimulation protocol which gives the possibility to test an inhibitory cholinergic circuit in the human brain, in subjects with idiopathic NPH (iNPH). We applied SAI technique in twenty iNPH patients before ventricular shunt surgery. Besides SAI, also the resting motor threshold and the short intracortical inhibition to paired stimulation were assessed. A significant reduction of the SAI (p = 0.016), associated with a less pronounced decrease of the resting motor threshold and the short latency intracortical inhibition to paired stimulation, were observed in patients with iNPH at baseline evaluation. We also found significant (p < 0.001) correlations between SAI values and the gait function tests, as well as between SAI and the neuropsychological tests. These findings suggest that the impairment of cholinergic neurons markedly contributes to cognitive decline and gait impairment in subjects with iNPH.

Behavioral and Biochemical Features of the Course and Surgical Treatment of Experimental Obstructive Hydrocephalus in Young Rats

INTRODUCTION

Hydrocephalus is a multifactorial disease, affecting the dynamics of cerebrospinal fluid (CSF) and leading to severe neurological impairment in children; in spite of the recent advances in hydrocephalus research, it has many physiopathological aspects that still remain poorly understood, especially after treatment.

OBJECTIVES

To analyze the clinical, radiological, histopathological, and biochemical aspects of kaolin-induced hydrocephalus in an experimental model, both in the acute phase and after shunt treatment, by means of behavioral tests, magnetic resonance imaging (MRI) scans, histopathological studies, and level of inflammatory interleukins in the CSF.

METHODS

Seven-day-old Wistar rats were used and subdivided into three subgroups: treated hydrocephalic (n = 24), untreated hydrocephalic (n = 17), and controls (n = 5). The hydrocephalic groups underwent cisternal injection of 15% kaolin for induction of hydrocephalus at 7 days of age. The treated group was submitted to a ventricular-subcutaneous shunt (VSCS) 1 week after induction. All animals were euthanized at 21 days of age. They underwent motor function and memory testing as well as brain MRI scans. Histopathological analysis for glial fibrillary acidic protein and Ki-67 was done, and CSF was collected for measurement of IL-1β, IL-6, and TNF-α.

RESULTS

The average time to reach the water maze platform was highest in the untreated hydrocephalic group. The magnetization transfer rates were 37.21 and 33.76 before and after shunting, respectively. The mean astrocyte counts were 2.45, 1.36, and 90.5 for shunted, untreated, and control animals, respectively. The mean CSF IL-1β concentrations were 62.3 and 249.6 pg/mL, the average IL-6 levels were 104.2 and 364.7 pg/mL, and the average TNF-α values were 4.9 and 170.5 pg/mL for the treated hydrocephalic group and the untreated group, respectively.

CONCLUSIONS

Pups treated with a CSF shunt showed better performance on memory tests. VSCS did not revert demyelination caused by hydrocephalus. Likewise, reactive astrocytosis and cell proliferation over the germinal matrix were not reversed after shunting. Hydrocephalic animals had raised levels of inflammatory interleukins, which returned to normal after treatment.

Normal-pressure hydrocephalus: A critical review

Normal-pressure hydrocephalus (NPH) is a potentially reversible syndrome characterized by enlarged cerebral ventricles (ventriculomegaly), cognitive impairment, gait apraxia and urinary incontinence. A critical review of the concept, pathophysiology, diagnosis, and treatment of both idiopathic and secondary NPH was conducted. We searched Medline and PubMed databases from January 2012 to December 2018 using the keywords "normal-pressure hydrocephalus" / "idiopathic normal-pressure hydrocephalus" / "secondary normal-pressure hydrocephalus" / "NPH" / "ventriculoperitoneal shunt". The initial search produced 341 hits. After careful selection, a total of 54 articles were chosen and additional relevant studies were included during the process of writing this article. NPH is an important cause of potentially reversible dementia, frequent falls and recurrent urinary infections in the elderly. The clinical and imaging features of NPH may be incomplete or nonspecific, posing a diagnostic challenge for medical doctors and often requiring expert assessment to minimize unsuccessful surgical treatments. Recent advances resulting from the use of non-invasive MRI methods for quantifying cerebral blood flow, in particular arterial spin-labeling (ASL), and the frequent association of NPH and obstructive sleep apnea (OSA), offer new avenues to understand and treat NPH.

Acupuncture at ST36 exerts neuroprotective effects via inhibition of reactive astrogliosis in infantile rats with hydrocephalus

BACKGROUND

Acupuncture has been associated with improved cerebral circulation, analgesia, neuromodulatory function and neurogenesis. In particular, acupuncture at ST36 has been widely used in several central nervous system (CNS) disorders, including neurodegenerative diseases. However, its effects on hydrocephalus have not been studied. Our aim was to evaluate the effects of acupuncture at ST36 on behaviour, motor development and reactive astrogliosis in infantile rats with hydrocephalus.

METHODS

Hydrocephalus was induced in sixteen 7-day-old pup rats by injection of 20% kaolin into the cisterna magna. One day after hydrocephalus induction, acupuncture was applied once daily (for 30 min) for a total of 21 days in eight randomly selected animals (HAc group) while the remaining eight remained untreated (H group). An additional eight healthy animals were included as controls (C group). All animals were weighed daily and, from the fifth day after hydrocephalus induction, underwent MRI to determine the ventricular ratio (VR). Rats were also exposed to modified open-field tests every 3 days until the end of the experiment. After 21 days all the animals were euthanased and their brains removed for histology and immunohistochemistry.

RESULTS

Hydrocephalic rats showed an increase in VR when compared with control rats (P<0.01). In addition, these animals exhibited delayed weight gain, which was attenuated with acupuncture treatment. Hydrocephalic animals treated with acupuncture performed better in open field tests (P<0.05), and had a reduction in reactive astrocyte cell density in the corpus callosum and external capsule, as assessed by GFAP (glial fibrillary acidic protein) immunohistochemistry (P<0.05).

CONCLUSIONS

These findings indicate that acupuncture at ST36 has a neuroprotective potential mediated, in part, by inhibition of astrogliosis.

Memantine treatment of juvenile rats with kaolin-induced hydrocephalus

Memantine is a selective, non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist that has previously been shown to have neuroprotective qualities in some animal models of neurologic disease. We hypothesized that memantine therapy would improve behavioral, neuropathological, and/or biochemical outcomes in juvenile rats with kaolin-induced hydrocephalus. Three-week old rats received an injection of kaolin (aluminum silicate) into the cisterna magna. Magnetic resonance imaging was performed one week later to assess ventricle size and stratify rats to three treatment groups. Rats were blindly treated daily for three weeks with saline or 10 or 30 mg/kg/day memantine. Behavior measures were performed weekly. Histologic and biochemical evaluations were performed at termination. Hydrocephalic rats showed no differences in weight among treatment groups. Memantine treatment stabilized ventricular enlargement in both low and high dose groups. The high dose group exhibited increased motor activity in open field chambers compared to the vehicle-treated group. However, there were no significant differences between the three hydrocephalic treatment groups for other behavioral tasks. Ventriculomegaly was associated with periventricular white matter damage. Glial fibrillary acidic protein (GFAP) content was higher in the low dose memantine group compared to vehicle-treated group, but there were no differences in GFAP-immunoreactive astrocytes or Iba-1- immunoreactive microglia between groups. Memantine therapy stabilized ventricular expansion and improved some behavioral measures but did not reduce brain tissue changes in juvenile rats with kaolin-induced hydrocephalus.

Melatonin Attenuates Histopathological Changes in the Hippocampus of Infantile Rats with Kaolin-Induced Hydrocephalus

OBJECTIVE/AIM

Hydrocephalus is defined as an incapacitating neurological disorder characterized by ventricular enlargement in children, but the effects of melatonin on this hydrocephalus have not yet been fully elucidated. In the present experiment, we attempted to investigate the effects of exogenous melatonin administration on hydrocephalus-induced hippocampal changes in infantile rats.

METHODS

In this study, we randomly divided 45 Swiss albino rats aged 2 weeks into 3 groups: group I, the control group received a sham injection with needle insertion only; groups II and III were given kaolin injections before treatment - group II, the hydrocephalus group, was treated with an isotonic NaCl solution, and group III, the hydrocephalus plus melatonin group, was treated with 0.5 mg/100 g body weight of exogenous melatonin. Both immunohistochemical and histological analyses were performed after hydrocephalus induction and melatonin administration. Immunohistochemical staining consisted anti-glial fibrillary acidic protein staining. The TUNEL technique was used for defining quantitate apoptosis.

RESULTS

Melatonin administration significantly attenuated chronic hydrocephalus-induced histopathological changes in the hippocampal subregions of infantile rats. Compared to hydrocephalic rats treated with saline solution, melatonin significantly decreased the number of apoptotic cells and pyknotic index values of each hippocampal subregion after the kaolin-induced hydrocephalus (p < 0.001).

CONCLUSION

The present results demonstrate that the chronic hydrocephalus-induced histopathological changes in the hippocampus were partially reversible with melatonin treatment, suggesting its neuroprotective effects in infantile rats. However, these findings need to be confirmed by further experimental studies and clinical trials.

Environmental enrichment reduces brain damage in hydrocephalic immature rats

PURPOSE

We investigate the effects of environmental enrichment (EE) on morphological alterations in different brain structures of pup rats submitted to hydrocephalus condition.

METHODS

Hydrocephalus was induced in 7-day-old pup rats by injection of 20% kaolin into the cisterna magna. Ventricular dilatation and magnetization transfer to analyze myelin were assessed by magnetic resonance. Hydrocephalic and control rats exposed to EE (n = 10 per group) were housed in cages with a tunnel, ramp, and colored plastic balls that would emit sound when touched. The walls of the housing were decorated with colored adhesive tape. Moreover, tactile and auditory stimulation was performed daily throughout the experiment. Hydrocephalic and control rats not exposed to EE (n = 10 per group) were allocated singly in standard cages. All animals were weighed daily and exposed to open-field conditions every 2 days until the end of the experiment when they were sacrificed and the brains removed for histology and immunohistochemistry. Solochrome cyanine staining was performed to assess the thickness of the corpus callosum. The glial fibrillary acidic protein method was used to evaluate reactive astrocytes, and the Ki67 method to assess cellular proliferation in the subventricular zone.

RESULTS

The hydrocephalic animals exposed to EE showed better performance in Open Field tests (p < 0.05), while presenting lower weight gain. In addition, these animals showed better myelination as revealed by magnetization transfer (p < 0.05). Finally, the EE group showed a reduction in reactive astrocytes by means of glial fibrillary acidic protein immunostaining and preservation of the proliferation potential of progenitor cells.

CONCLUSION

The results suggest that EE can protect the developing brain against damaging effects caused by hydrocephalus.

Hydrocephalus compacted cortex and hippocampus and altered their output neurons in association with spatial learning and memory deficits in rats

Hydrocephalus is a common neurological disorder in children characterized by abnormal dilation of cerebral ventricles as a result of the impairment of cerebrospinal fluid flow or absorption. Clinical presentation of hydrocephalus varies with chronicity and often shows cognitive dysfunction. Here we used a kaolin-induction method in rats and studied the effects of hydrocephalus on cerebral cortex and hippocampus, the two regions highly related to cognition. Hydrocephalus impaired rats' performance in Morris water maze task. Serial three-dimensional reconstruction from sections of the whole brain freshly froze in situ with skull shows that the volumes of both structures were reduced. Morphologically, pyramidal neurons of the somatosensory cortex and hippocampus appear to be distorted. Intracellular dye injection and subsequent three-dimensional reconstruction and analyses revealed that the dendritic arbors of layer III and V cortical pyramid neurons were reduced. The total dendritic length of CA1, but not CA3, pyramidal neurons was also reduced. Dendritic spine densities on both cortical and hippocampal pyramidal neurons were decreased, consistent with our concomitant findings that the expressions of both synaptophysin and postsynaptic density protein 95 were reduced. These cortical and hippocampal changes suggest reductions of excitatory connectivity, which could underlie the learning and memory deficits in hydrocephalus.

Changes in Rat Brain Tissue Microstructure and Stiffness during the Development of Experimental Obstructive Hydrocephalus

Understanding neural injury in hydrocephalus and how the brain changes during the course of the disease in-vivo remain unclear. This study describes brain deformation, microstructural and mechanical properties changes during obstructive hydrocephalus development in a rat model using multimodal magnetic resonance (MR) imaging. Hydrocephalus was induced in eight Sprague-Dawley rats (4 weeks old) by injecting a kaolin suspension into the cisterna magna. Six sham-injected rats were used as controls. MR imaging (9.4T, Bruker) was performed 1 day before, and at 3, 7 and 16 days post injection. T2-weighted MR images were collected to quantify brain deformation. MR elastography was used to measure brain stiffness, and diffusion tensor imaging (DTI) was conducted to observe brain tissue microstructure. Results showed that the enlargement of the ventricular system was associated with a decrease in the cortical gray matter thickness and caudate-putamen cross-sectional area (P < 0.001, for both), an alteration of the corpus callosum and periventricular white matter microstructure (CC+PVWM) and rearrangement of the cortical gray matter microstructure (P < 0.001, for both), while compression without gross microstructural alteration was evident in the caudate-putamen and ventral internal capsule (P < 0.001, for both). During hydrocephalus development, increased space between the white matter tracts was observed in the CC+PVWM (P < 0.001), while a decrease in space was observed for the ventral internal capsule (P < 0.001). For the cortical gray matter, an increase in extracellular tissue water was significantly associated with a decrease in tissue stiffness (P = 0.001). To conclude, this study characterizes the temporal changes in tissue microstructure, water content and stiffness in different brain regions and their association with ventricular enlargement. In summary, whilst diffusion changes were larger and statistically significant for majority of the brain regions studied, the changes in mechanical properties were modest. Moreover, the effect of ventricular enlargement is not limited to the CC+PVWM and ventral internal capsule, the extent of microstructural changes vary between brain regions, and there is regional and temporal variation in brain tissue stiffness during hydrocephalus development.

Mechanical stress models of Alzheimer's disease pathology

INTRODUCTION

Extracellular accumulation of amyloid-β protein and intracellular accumulation of tau in brain tissues have been described in animal models of Alzheimer's disease (AD) and mechanical stress-based diseases of different mechanisms, such as traumatic brain injury (TBI), arterial hypertension (HTN), and normal pressure hydrocephalus (NPH).

METHODS

We provide a brief overview of experimental models of TBI, HTN, and NPH showing features of tau-amyloid pathology, neuroinflammation, and neuronal loss.

RESULTS

"Alzheimer-like" hallmarks found in these mechanical stress-based models were compared with AD features found in transgenic models.

DISCUSSION

The goal of this review is, therefore, to build on current concepts of onset and progression of AD lesions. We point to the importance of accumulated mechanical stress in brain as an environmental and endogenous factor that pushes protein deposition and neuronal injury over the disease threshold. We further encourage the development of preventing strategies and drug screening based on mechanical stress models.

A case of spongiform polioencephalomyelopathy in a cat with a history of behavioural problems

A 7-month-old, entire female, domestic shorthair cat was referred to our behavioural service owing to soiling in the house and a play-related problem. The owners’ complaints were that the cat had never used the litter tray, and it did not know how to play. After reviewing the behavioural history, a problem of substrate preferences acquisition was suspected with regard to the elimination problem. During the consultation, the physical examination was unremarkable, but the neurological examination revealed a moderate and hypermetric ataxic gait, and a bilateral lack of menace response. Some degree of visual impairment was suspected. The problem was located in the central nervous system (CNS); specifically, an intracranial and multifocal problem was diagnosed. After a complete work-up (complete ophthalmological examination, complete blood count and a complete biochemistry panel, feline immunodeficiency virus/feline leukaemia virus test, thorax radiographs, abdominal ultrasound, brain magnetic resonance imaging [0.2 T], cerebrospinal fluid analysis and a urinary metabolic screen test), a degenerative CNS problem was suspected. No treatment was prescribed for the neurological problem. Regarding the problem of soiling in the house, reward-based training with a clicker was used, and the cat partially improved in a few weeks. Three months later, the cat was referred to the neurology service in status epilepticus. A symptomatic treatment was prescribed, with a mild response. After 2 years of treatment and a progressive worsening, the cat was euthanased. Necropsy revealed spongiform polioencephalomyelopathy. In order to rule out prion aetiology a PrPsc inmunohistochemistry assay was performed, and the results were negative. Congenital spongiform polioencephalomyelopathy (CSP) was diagnosed. We strongly suggest that the cat’s behavioural clinical signs were caused by the CSP, causing learning impairment. To the best of our knowledge, this would be the first case in which a congenital degenerative disease affected a cat’s capability to learn, leading to behavioural signs as the main complaint of the owners, even before neurological signs are detected by the owners.

Oral antioxidant therapy for juvenile rats with kaolin-induced hydrocephalus

Background

Oxidative and nitrosylative changes have been shown to occur in conjunction with the hypoxic changes and cellular/axonal damage in hydrocephalic rodent brains. We hypothesized that antioxidant therapy would improve behavioral, neurophysiological, and/or neurobiochemical outcomes in juvenile rats following induction of hydrocephalus.

Methods

Three-week old rats received an injection of kaolin (aluminum silicate) into the cisterna magna. Magnetic resonance (MR) imaging was performed two weeks later to assess ventricle size and stratify rats to four treatment conditions. Rats were treated for two weeks daily with sham therapy of either oral canola oil or dextrose or experimental therapy of a low or high dose of an antioxidant mixture containing α-tocopherol, L-ascorbic acid, coenzyme Q10 (CoQ10), reduced glutathione, and reduced lipoic acid. Behavior was examined thrice weekly.

Results

All hydrocephalic groups lagged in weight gain in comparison to non-hydrocephalic controls, all developed significant ventriculomegaly, and all exhibited white matter destruction. Canola oil with or without the antioxidant mixture normalized antioxidant capacity in brain tissue, and the dextrose-treated rats had the greatest ventricular enlargement during the treatment period. However, there were no significant differences between the four treatment groups of hydrocephalic rats for the various behavioral tasks. Glial fibrillary acidic protein and myelin basic protein quantitation showed no differences between the treatment groups or with control rats. There was increased lipid peroxidation in the hydrocephalic rats compared to controls but no differences between treatment groups.

Conclusion

The antioxidant cocktail showed no therapeutic benefits for juvenile rats with kaolin-induced hydrocephalus although canola oil might have mild benefit.

Kaolin-induced ventriculomegaly at weaning produces long-term learning, memory, and motor deficits in rats

Ventriculomegaly occurs when there is imbalance between creation and absorption of cerebrospinal fluid (CSF); even when treated, long-term behavioral changes occur. Kaolin injection in the cisterna magna of rats produces an obstruction of CSF outflow and models one type of hydrocephalus. Previous research with this model shows that neonatal onset has mixed effects on Morris water maze (MWM) and motoric performance; we hypothesized that this might be because the severity of ventricular enlargement was not taken into consideration. In the present experiment, rats were injected with kaolin or saline on postnatal day (P)21 and analyzed in subgroups based on Evan's ratios (ERs) of the severity of ventricular enlargement at the end of testing to create 4 subgroups from least to most severe: ER0.4-0.5, ER0.51-0.6, ER0.61-0.7, and ER0.71-0.82, respectively. Locomotor activity (dry land and swimming), acoustic startle with prepulse inhibition (PPI), and MWM performance were tested starting on P28 (122cm maze) and again on P42 (244cm maze). Kaolin-treated animals weighed significantly less than controls at all times. Differences in locomotor activity were seen at P42 but not P28. On P28 there was an increase in PPI for all but the least severe kaolin-treated group, but no difference at P42 compared with controls. In the MWM at P28, all kaolin-treated groups had longer path lengths than controls, but comparable swim speeds. With the exception of the least severe group, probe trial performance was worse in the kaolin-treated animals. On P42, only the most severely affected kaolin-treated group showed deficits compared with control animals. This group showed no MWM learning and no memory for the platform position during probe trial testing. Swim speed was unaffected, indicating motor deficits were not responsible for impaired learning and memory. These findings indicate that kaolin-induced ventriculomegaly in rats interferes with cognition regardless of the final enlargement of the cerebral ventricles, but final size critically determines whether lasting locomotor, learning, and memory impairments occur.

Reduced subventricular zone proliferation and white matter damage in juvenile ferrets with kaolin-induced hydrocephalus

Hydrocephalus is a neurological condition characterized by altered cerebrospinal fluid (CSF) flow with enlargement of ventricular cavities in the brain. A reliable model of hydrocephalus in gyrencephalic mammals is necessary to test preclinical hypotheses. Our objective was to characterize the behavioral, structural, and histological changes in juvenile ferrets following induction of hydrocephalus. Fourteen-day old ferrets were given an injection of kaolin (aluminum silicate) into the cisterna magna. Two days later and repeated weekly until 56 days of age, magnetic resonance (MR) imaging was used to assess ventricle size. Behavior was examined thrice weekly. Compared to age-matched saline-injected controls, severely hydrocephalic ferrets weighed significantly less, their postures were impaired, and they were hyperactive prior to extreme debilitation. They developed significant ventriculomegaly and displayed white matter destruction. Reactive astroglia and microglia detected by glial fibrillary acidic protein (GFAP) and Iba-1 immunostaining were apparent in white matter, cortex, and hippocampus. There was a hydrocephalus-related increase in activated caspase 3 labeling of apoptotic cells (7.0 vs. 15.5%) and a reduction in Ki67 labeling of proliferating cells (23.3 vs. 5.9%) in the subventricular zone (SVZ). Reduced Olig2 immunolabeling suggests a depletion of glial precursors. GFAP content was elevated. Myelin basic protein (MBP) quantitation and myelin biochemical enzyme activity showed early maturational increases. Where white matter was not destroyed, the remaining axons developed myelin similar to the controls. In conclusion, the hydrocephalus-induced periventricular disturbances may involve developmental impairments in cell proliferation and glial precursor cell populations. The ferret should prove useful for testing hypotheses about white matter damage and protection in the immature hydrocephalic brain.

Cerebrospinal fluid volume measurements in hydrocephalic rats

Object Experimental data about the evolution of intracranial volume and pressure in cases of hydrocephalus are limited due to the lack of available monitoring techniques. In this study, the authors validate intracranial CSF volume measurements within the lateral ventricle, while simultaneously using impedance sensors and pressure transducers in hydrocephalic animals. Methods A volume sensor was fabricated and connected to a catheter that was used as a shunt to withdraw CSF. In vitro bench-top calibration experiments were created to provide data for the animal experiments and to validate the sensors. To validate the measurement technique in a physiological system, hydrocephalus was induced in weanling rats by kaolin injection into the cisterna magna. At 28 days after induction, the sensor was implanted into the lateral ventricles. After sealing the skull using dental cement, an acute CSF drainage/infusion protocol consisting of 4 sequential phases was performed with a pump. Implant location was confirmed via radiography using intraventricular iohexol contrast administration. Results Controlled CSF shunting in vivo with hydrocephalic rats resulted in precise and accurate sensor measurements (r = 0.98). Shunting resulted in a 17.3% maximum measurement error between measured volume and actual volume as assessed by a Bland-Altman plot. A secondary outcome confirmed that both ventricular volume and intracranial pressure decreased during CSF shunting and increased during infusion. Ventricular enlargement consistent with successful hydrocephalus induction was confirmed using imaging, as well as postmortem. These results indicate that volume monitoring is feasible for clinical cases of hydrocephalus. Conclusions This work marks a departure from traditional shunting systems currently used to treat hydrocephalus. The overall clinical application is to provide alternative monitoring and treatment options for patients. Future work includes development and testing of a chronic (long-term) volume monitoring system.

The relationship between ventricular dilatation, neuropathological and neurobehavioural changes in hydrocephalic rats

Background

The motor and cognitive deficits observed in hydrocephalus are thought to be due to axonal damage within the periventricular white matter. This study was carried out to investigate the relationship between ventricular size, cellular changes in brain, and neurobehavioural deficits in rats with experimental hydrocephalus.

Methods

Hydrocephalus was induced in three-week old rats by intracisternal injection of kaolin. Behavioural and motor function were tested four weeks after hydrocephalus induction and correlated to ventricular enlargement which was classified into mild, moderate or severe. Gross brain morphology, routine histology and immunohistochemistry for oligodendrocytes (CNPase), microglia (Iba-1) and astrocytes (GFAP) were performed to assess the cellular changes.

Results

Decreases in open field activity and forelimb grip strength in hydrocephalus correlated with the degree of ventriculomegaly. Learning in Morris water maze was significantly impaired in hydrocephalic rats. Gradual stretching of the ependymal layer, thinning of the corpus callosum, extracellular oedema and reduced cortical thickness were observed as the degree of ventriculomegaly increased. A gradual loss of oligodendrocytes in the corpus callosum and cerebral cortex was most marked in the severely-hydrocephalic brains, whereas the widespread astrogliosis especially in the subependymal layer was most marked in the brains with mild hydrocephalus. Retraction of microglial processes and increase in Iba-1 immunoreactivity in the white matter was associated ventriculomegaly.

Conclusions

In hydrocephalic rats, oligodendrocyte loss, microglia activation, astrogliosis in cortical areas and thinning of the corpus callosum were associated with ventriculomegaly. The degree of ventriculomegaly correlated with motor and cognitive deficits.

Cerebral white matter oxidation and nitrosylation in young rodents with kaolin-induced hydrocephalus

Hydrocephalus is associated with reduced blood flow in periventricular white matter. To investigate hypoxic and oxidative damage in the brains of rats with hydrocephalus, kaolin was injected into the cisterna magna of newborn 7- and 21-day-old Sprague-Dawley rats, and ventricle size was assessed by magnetic resonance imaging at 7, 21, and 42 days of age. In-situ evidence of hypoxia in periventricular capillaries and glial cells was shown by pimonidazole hydrochloride binding. Biochemical assay of thiobarbituric acid reaction and immunohistochemical detection of malondialdehyde and 4-hydroxy-2-nonenal indicated the presence of lipid peroxidation in white matter. Biochemical assay of nitrite indicated increased nitric oxide production. Nitrotyrosine immunohistochemistry showed nitrosylated proteins in white matter reactive microglia and astrocytes. Activities of the antioxidant enzymes catalase and glutathione peroxidase were not increased, and altered hypoxia-inducible factor 1α was not detected by quantitative reverse transcription-polymerase chain reaction. Cerebral vascular endothelial growth factor expression determined by quantitative reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay was not changed, but vascular endothelial growth factor immunoreactivity was increased in reactive astrocytes of hydrocephalic white matter. To determine if nitric oxide synthase is involved in the pathogenesis, we induced hydrocephalus in 7-day-old wild-type and neuronal nitric oxide synthase-deficient mice. At 7 days, the wild-type and mutant mice exhibited equally severe ventriculomegaly and no behavioral differences, although increased glial fibrillary acidic protein was less in the mutant mice. We conclude that hypoxia, via peroxidation and nitrosylation, contributes to brain changes in young rodents with hydrocephalus and that compensatory mechanisms are negligible.

Correlating magnetic resonance findings with neuropathology and clinical signs in dogs and cats

The histologic characteristics that are the basis for diagnosis of central nervous system conditions cannot be visualized directly using magnetic resonance (MR) methods, but clinical diagnosis may be based on the frequency and pattern of MR imaging signs, which represent predominantly the gross morphologic features of lesions. Additional quantitative MR measures of myelination, cell swelling, gliosis, and neuronal loss may also be used for more specific characterization of lesions. These measures include magnetization transfer ratio, apparent diffusion coefficient, and the concentrations or ratios of metabolites identified by spectroscopy. Confidence that an MR abnormality is responsible for the clinical signs depends primarily on the degree of correspondence between the site of the lesion and the neuroanatomical localization.

Neonatal rat model of intraventricular haemorrhage and post-haemorrhagic ventricular dilatation with long-term survival into adulthood

AIMS

post-haemorrhagic ventricular dilatation (PHVD) is a significant problem in neonatal care, with sequelae extending beyond childhood. Its management is important in determining outcome. Although rodent hydrocephalus models have been developed, PHVD, as a specific entity with a distinct pathophysiology, has not been studied in a small animal model surviving to adulthood. Our objective is to evaluate survival, to adulthood, in our immature (7-day-old, P7) neonatal rat model, and to analyse early motor reflexes and fine motor and cognitive function, and neuropathology, at 8-12 weeks.

METHODS

sixty-six rats underwent sequential bilateral stereotactic intraventricular haemorrhage (IVH); 36 more acted as controls. Staircase and radial maze evaluations were carried out at 7-11 weeks; animals were sacrificed at 12 weeks. Post mortem ventricular size and corpus callosum thickness were determined.

RESULTS

seventy-six per cent of IVH animals developed PHVD; median (interquartile range) composite ventricular area was 3.46 mm(2) (2.32-5.24). Sixteen (24%) animals demonstrated severe ventricular dilatation (area > 5 mm(2) ). IVH animals failed to improve on the negative geotaxis test at 2 weeks. The staircase test did not identify any significant difference. On the radial maze, animals with severe PHVD made more reference errors. Histopathology confirmed PHVD, ependymal disruption and periventricular white matter injury. Median anterior corpus callosum thickness was significantly lower in IVH animals (0.35 mm) than in those not undergoing IVH (0.43 mm).

CONCLUSION

our P7 neonatal rat IVH model is suitable for long-term survival and replicates many of the morphological and some of the behavioural features seen in human PHVD.

Dopaminergic neuronal injury in the adult rat brain following neonatal exposure to lipopolysaccharide and the silent neurotoxicity

Our previous studies have shown that neonatal exposure to lipopolysaccharide (LPS) resulted in motor dysfunction and dopaminergic neuronal injury in the juvenile rat brain. To further examine whether neonatal LPS exposure has persisting effects in adult rats, motor behaviors were examined from postnatal day 7 (P7) to P70 and brain injury was determined in P70 rats following an intracerebral injection of LPS (1 mg/kg) in P5 Sprague-Dawley male rats. Although neonatal LPS exposure resulted in hyperactivity in locomotion and stereotyped tasks, and other disturbances of motor behaviors, the impaired motor functions were spontaneously recovered by P70. On the other hand, neonatal LPS-induced injury to the dopaminergic system such as the loss of dendrites and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra persisted in P70 rats. Neonatal LPS exposure also resulted in sustained inflammatory responses in the P70 rat brain, as indicated by an increased number of activated microglia and elevation of interleukin-1β and interleukin-6 content in the rat brain. In addition, when challenged with methamphetamine (METH, 0.5 mg/kg) subcutaneously, rats with neonatal LPS exposure had significantly increased responses in METH-induced locomotion and stereotypy behaviors as compared to those without LPS exposure. These results indicate that although neonatal LPS-induced neurobehavioral impairment is spontaneously recoverable, the LPS exposure-induced persistent injury to the dopaminergic system and the chronic inflammation may represent the existence of silent neurotoxicity. Our data further suggest that the compromised dendritic mitochondrial function might contribute, at least partially, to the silent neurotoxicity.

Neuropathology and structural changes in hydrocephalus

In the context of spina bifida, hydrocephalus is usually caused by crowding of the posterior fossa with obstruction to cerebrospinal fluid flow from the forth ventricle, and less often by malformation of the cerebral aqueduct. Enlargement of the cerebral ventricles causes gradual destruction of periventricular white matter axons. Motor, sensory, visual, and memory systems may be disturbed through involvement of the long projection axons, periventricular structures including the corpus callosum, and the fimbria-fornix pathway. Secondary changes occur in neuronal cell bodies and synapses, but there is minimal death of neurons. The clinical syndrome of hydrocephalic brain dysfunction is thus due to subcortical disconnection. Some of the brain dysfunction is reversible by shunting, probably through restoration of cerebral blood flow and normalization of the extracellular environment. However, destroyed axons cannot be restored.

The dynamics of brain and cerebrospinal fluid growth in normal versus hydrocephalic mice

OBJECT

Hydrocephalus has traditionally been quantified by linear measures of ventricular size, with adjunct use of cortical mantle thickness. However, clinical outcome depends on cognitive function, which is more directly related to brain volume than these previous measures. The authors sought to quantify the dynamics of brain and ventricular volume growth in normal compared with hydrocephalic mice.

METHODS

Hydrocephalus was induced in 14-day-old C57BL/6 mice by percutaneous injection of kaolin into the cisterna magna. Nine hydrocephalic and 6 normal mice were serially imaged from age 2-12 weeks with a 14.1-T MR imaging unit. Total brain and ventricle volumes were calculated, and linear discriminant analysis was applied.

RESULTS

Two very different patterns of response were seen in hydrocephalic mice compared with mice with normative growth. In one pattern (3 mice) brain growth was normal despite accumulation of CSF, and in the second pattern (6 mice) abnormal brain enlargement was accompanied by increased CSF volume along with parenchymal edema. In this latter pattern, spontaneous ventricular rupture led to normalization of brain volume, implying edema from transmantle pressure gradients. These 2 patterns of hydrocephalus were significantly discriminable using linear discriminant analysis (p < 0.01). In contrast, clinically relevant measurements of head circumference or frontal and occipital horn ratios were unable to discriminate between these patterns.

CONCLUSIONS

This study is, to the authors' knowledge, the first serial quantification of the growth of brain and ventricle volumes in normal versus hydrocephalic development. The authors' findings demonstrate the feasibility of constructing normative curves of brain and fluid growth as complements to normative head circumference curves. By measuring brain volumes, distinct patterns of brain growth and enlargement can be observed, which are more likely linked to cognitive development and clinical outcome than fluid volumes alone.

Dynamic brain phantom for intracranial volume measurements

Knowledge of intracranial ventricular volume is important for the treatment of hydrocephalus, a disease in which cerebrospinal fluid (CSF) accumulates in the brain. Current monitoring options involve MRI or pressure monitors (InSite, Medtronic). However, there are no existing methods for continuous cerebral ventricle volume measurements. In order to test a novel impedance sensor for direct ventricular volume measurements, we present a model that emulates the expansion of the lateral ventricles seen in hydrocephalus. To quantify the ventricular volume, sensor prototypes were fabricated and tested with this experimental model. Fluid was injected and withdrawn cyclically in a controlled manner and volume measurements were tracked over 8 h. Pressure measurements were also comparable to conditions seen clinically. The results from the bench-top model served to calibrate the sensor for preliminary animal experiments. A hydrocephalic rat model was used to validate a scaled-down, microfabricated prototype sensor. CSF was removed from the enlarged ventricles and a dynamic volume decrease was properly recorded. This method of testing new designs on brain phantoms prior to animal experimentation accelerates medical device design by determining sensor specifications and optimization in a rational process.

Low levels of amyloid-beta and its transporters in neonatal rats with and without hydrocephalus

Background

Previous studies in aging animals have shown that amyloid-beta protein (Aβ) accumulates and its transporters, low-density lipoprotein receptor-related protein-1 (LRP-1) and the receptor for advanced glycation end products (RAGE) are impaired during hydrocephalus. Furthermore, correlations between astrocytes and Aβ have been found in human cases of normal pressure hydrocephalus (NPH) and Alzheimer's disease (AD). Because hydrocephalus occurs frequently in children, we evaluated the expression of Aβ and its transporters and reactive astrocytosis in animals with neonatal hydrocephalus.

Methods

Hydrocephalus was induced in neonatal rats by intracisternal kaolin injections on post-natal day one, and severe ventriculomegaly developed over a three week period. MRI was performed on post-kaolin days 10 and 21 to document ventriculomegaly. Animals were sacrificed on post-kaolin day 21. For an age-related comparison, tissue was used from previous studies when hydrocephalus was induced in a group of adult animals at either 6 months or 12 months of age. Tissue was processed for immunohistochemistry to visualize LRP-1, RAGE, Aβ, and glial fibrillary acidic protein (GFAP) and with quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) to quantify expression of LRP-1, RAGE, and GFAP.

Results

When 21-day post-kaolin neonatal hydrocephalic animals were compared to adult (6–12 month old) hydrocephalic animals, immunohistochemistry demonstrated levels of Aβ, RAGE, and LRP-1 that were substantially lower in the younger animals; in contrast, GFAP levels were elevated in both young and old hydrocephalic animals. When the neonatal hydrocephalic animals were compared to age-matched controls, qRT-PCR demonstrated no significant changes in Aβ, LRP-1 and RAGE. However, immunohistochemistry showed very small increases or decreases in individual proteins. Furthermore, qRT-PCR indicated statistically significant increases in GFAP.

Conclusion

Neonatal rats with and without hydrocephalus had low expression of Aβ and its transporters when compared to adult rats with hydrocephalus. No statistical differences were observed in Aβ and its transporters between the control and hydrocephalic neonatal animals.

Normal pressure hydrocephalus: Diagnostic and predictive evaluationon

In typical cases, normal pressure hydrocephalus (NPH) manifests itself with the triad of gait disturbance, which begins first, followed by mental deterioration and urinary incontinence associated with ventriculomegaly (on CT or MRI) and normal cerebrospinal fluid (CSF) pressure. These cases present minor diagnostic difficulties and are the most likely to improve after shunting. Problems arise when NPH shows atypical or incomplete clinical manifestations (25–50% of cases) or is mimicked by other diseases. In this scenario, other complementary tests have to be used, preferentially those that can best predict surgical outcome. Radionuclide cisternography, intracranial pressure monitoring (ICP) and lumbar infusion tests can show CSF dynamics malfunction, but none are able to confirm whether the patient will benefit from surgery. The CSF tap test (CSF-TT) is the only procedure that can temporarily simulate the effect of definitive shunt. Since the one tap CSF-TT has low sensitivity, it cannot be used to exclude patients from surgery. In such cases, we have to resort to a repeated CSF-TT (RTT) or continuous lumbar external drainage (LED). The most reliable prediction would be achieved if RTT or LED proved positive, in addition to the occurrence of B-waves during more than 50% of ICP recording time. This review was based on a PubMed literature search from 1966 to date. It focuses on clinical presentation, neuroimaging, complementary prognostic tests, and differential diagnosis of NPH, particularly on the problem of selecting appropriate candidates for shunt.

Brain metabolism in adult chronic hydrocephalus

Normal pressure hydrocephalus (NPH) is the most frequent form of chronic hydrocephalus in adults. NPH remains underdiagnosed although between 5% and 10% of all demented patients may suffer from this disorder. As dementia is an increasing demographic problem, treatable forms such as in NPH have become a central issue in neurology. Despite the traditional perception of hydrocephalus being a disorder of disturbed CSF dynamics, in NPH metabolic impairment seems at least as important. So far, the only valid animal model of NPH is chronic adult kaolin hydrocephalus. In this model, opening of alternative CSF outflow pathways leads to normal or near-normal intracranial pressure and CSF outflow resistance. Yet, various metabolic disturbances cause ongoing ventricular enlargement and characteristic symptoms including cognitive decline and gait ataxia. Delayed hippocampal neuronal death, accumulation of beta-amyloid and disturbed cholinergic neurotransmission may contribute to memory dysfunction. Compromised periventricular blood flow, decreased dopamine levels in the substantia nigra and damaged striatal GABAergic interneurons may reflect basal ganglia symptoms. At least in human hydrocephalus cerebrovascular co-morbidity of the white matter plays an important role as well. It seems that in hydrocephalus from a certain 'point of no return' metabolic impairment becomes decoupled from CSF dynamics and, at least partly, self-sustained. This is probably the reason why despite restored CSF circulation by shunting many patients with chronic hydrocephalus still suffer from severe neurological deficits. The present paper offers a comprehensive review of the experimental and clinical data suggesting metabolic disturbances in chronic hydrocephalus.

Calcium antagonism in neonatal rats with kaolin-induced hydrocephalus

Juvenile rats with kaolin-induced hydrocephalus have reduced brain injury if treated with nimodipine or magnesium sulfate. Experiments were conducted to determine if the neuroprotective effects could be replicated in neonatal rats with experimental hydrocephalus at an age comparable to prematurely born humans. In a blinded and randomized manner, drugs were administered for 14 days beginning 7 days after induction of hydrocephalus. Nimodipine was given twice daily by subcutaneous injections. Daily doses greater than 38 mg/kg of body weight were fatal. Daily doses of 3.8 to 30 mg/kg were not associated with behavioral, structural, or biochemical improvements. Magnesium chloride was administered via daily subcutaneous minipump infusion (0.87 or 1.74 mM/kg) along with twice daily injections of 0.74 or 1.48 mM/kg. Magnesium sulfate was administered by twice daily subcutaneous doses of 1.54 or 7.72 mM/kg. Sedation occurred, but there was no statistically significant protection in regard to behavior, brain structure, or brain composition in any of the magnesium experiments. Developmental alterations in calcium channels of the neonatal rat brain could account for differences from prior experiments in young hydrocephalic rats.

Protein and synthetic polymer injection for induction of obstructive hydrocephalus in rats

Background

The objective of this study was to develop a simple and inexpensive animal model of induced obstructive hydrocephalus with minimal tissue inflammation, as an alternative to kaolin injection.

Materials

Two-hundred and two male Sprague-Dawley rats aged 3 weeks received intracisternal injections of kaolin (25% suspension), Matrigel, type 1 collagen from rat tail, fibrin glue (Tisseel), n-butyl-cyanoacrylate (NBCA), or ethylene vinyl alcohol copolymer (Onyx-18 and Onyx-34). Magnetic resonance imaging was used to assess ventricle size. Animals were euthanized at 2, 5, 10 and 14 days post-injection for histological analysis.

Results

Kaolin was associated with 10% mortality and successful induction of hydrocephalus in 97% of survivors (ventricle area proportion 0.168 ± 0.018). Rapidly hardening agents (fibrin glue, NBCA, vinyl polymer) had high mortality rates and low success rates in survivors. Only Matrigel had relatively low mortality (17%) and moderate success rate (20%). An inflammatory response with macrophages and some lymphocytes was associated with kaolin. There was negligible inflammation associated with Matrigel. A severe inflammatory response with giant cell formation was associated with ethylene vinyl alcohol copolymer.

Conclusion

Kaolin predictably produces moderate to severe hydrocephalus with a mild chronic inflammatory reaction and fibrosis of the leptomeninges. Other synthetic polymers and biopolymers tested are unreliable and cause different types of inflammation.

Minocycline attenuates hypoxia-ischemia-induced neurological dysfunction and brain injury in the juvenile rat

To investigate whether minocycline provides long-lasting protection against neonatal hypoxia-ischemia-induced brain injury and neurobehavioral deficits, minocycline was administered intraperitoneally in postnatal day 4 Sprague-Dawley rats subjected to bilateral carotid artery occlusion followed by exposure to hypoxia (8% oxygen for 15 min). Brain injury and myelination were examined on postnatal day 21 (P21) and tests for neurobehavioral toxicity were performed from P3 to P21. Hypoxic-ischemic insults resulted in severe white matter injury, enlarged ventricles, deficits in the hippocampus, reduction in numbers of mature oligodendrocytes and tyrosine hydroxylase-positive neurons, damage to axons and dendrites, and impaired myelination, as indicated by the decrease in myelin basic protein immunostaining in the P21 rat brain. Hypoxic-ischemic insult also significantly affected physical development (body weight gain and eye opening) and neurobehavioral performance, including sensorimotor and locomotor function, anxiety and cognitive ability in the P21 rat. Treatments with minocycline significantly attenuated the hypoxia-ischemia-induced brain injury and improved neurobehavioral performance. The protection of minocycline was associated with its ability to reduce microglial activation. The present results show that minocycline has long-lasting protective effects in the neonatal rat brain in terms of both hypoxia-ischemia-induced brain injury and the associated neurological dysfunction.

Aquaporin 4 changes in rat brain with severe hydrocephalus

Hydrocephalus is characterized by impaired cerebrospinal fluid (CSF) flow with enlargement of the ventricular cavities of the brain and progressive damage to surrounding tissue. Bulk water movement is altered in these brains. We hypothesized that increased expression of aquaporins, which are water-permeable channel proteins, would occur in these brains to facilitate water shifts. We used quantitative (real-time) RT-PCR, Western blotting and immunohistochemistry to evaluate the brain expression of aquaporins (AQP) 1, 4, and 9 mRNA and protein in Sprague-Dawley rats rendered hydrocephalic by injection of kaolin into cistern magna. AQP4 mRNA was significantly up-regulated in parietal cerebrum and hippocampus 4 weeks and 9 months after induction of hydrocephalus (P < 0.05). Although Western blot analysis showed no significant change, there was more intense perivascular AQP4 immunoreactivity in cerebrum of hydrocephalic brains at 3-4 weeks after induction. We did not detect mRNA or protein changes in AQP1 (located in choroid plexus) or AQP9 (located in select neuron populations). Kir4.1, a potassium channel protein linked to water flux, exhibited enhanced immunoreactivity in the cerebral cortex of hydrocephalic rats; the perineuronal distribution was entirely different from that of AQP4. These results suggest that brain AQP4 up-regulation might be a compensatory response to maintain water homeostasis in hydrocephalus.

Brain damage in neonatal rats following kaolin induction of hydrocephalus

Neonatal and congenital hydrocephalus are common problems in humans. Hydrocephalus was induced in 1-day-old rats by injection of kaolin into the cisterna magna. At 7 and 21 days, magnetic resonance (MR) imaging was used to assess ventricle size, then brains were subjected to histopathological and biochemical analyses. Hydrocephalic pups did not exhibit delays in righting or negative geotaxis reflexes during the first week. At 7 days, there was variable ventricular enlargement with periventricular white matter edema, axon damage, reactive astrogliosis, and accumulation of macrophages in severe but not mild hydrocephalus. Cellular proliferation in the subependymal zone was significantly reduced. The cortical subplate neuron layer was disrupted. In rats allowed to survive to 21 days, weight was significantly lower in severely hydrocephalic rats. They also exhibited impaired memory in the Morris water maze test. Despite abnormal posture, there was minimal quantitative impairment of walking ability on a rotating cylinder. At 21 days, histological studies showed reduced corpus callosum thickness, fewer mature oligodendrocytes, damaged axons, and astroglial/microglial reaction. Reduced myelin basic protein, increased glial fibrillary acidic protein, and stable synaptophysin content were demonstrated by immunochemical methods. In conclusion, impairment in cognition and motor skills corresponds to ventricular enlargement and white matter destruction. Quantitative measures of weight, memory, ventricle size, and myelin, and glial proteins in this neonatal model of hydrocephalus will be useful tools for assessment of experimental therapeutic interventions.

Minocycline reduces lipopolysaccharide-induced neurological dysfunction and brain injury in the neonatal rat

Preferential brain white matter injury and hypomyelination induced by intracerebral administration of the endotoxin lipopolysaccharide (LPS) in the neonatal rat brain has been characterized as associated with the activation of microglia. To examine whether inhibition of microglial activation might provide protection against LPS-induced brain injury and behavioral deficits, minocycline (45 mg/kg) was administered intraperitoneally 12 hr before and immediately after an LPS (1 mg/kg) intracerebral injection in postnatal day 5 (P5) Sprague-Dawley rats and then every 24 hr for 3 days. Brain injury and myelination were examined on postnatal day 21 and the tests for neurobehavioral toxicity were carried out from P3 to P21. LPS administration resulted in severe white matter injury, enlarged ventricles, deficits in the hippocampus, loss of oligodendrocytes and tyrosine hydroxylase neurons, damage to axons and dendrites, and impaired myelination as indicated by the decrease in myelin basic protein immunostaining in the P21 rat brain. LPS administration also significantly affected physical development (body weight) and neurobehavioral performance, such as righting reflex, wire hanging maneuver, cliff avoidance, locomotor activity, gait analysis, and responses in the elevated plus-maze and passive avoidance task. Treatment with minocycline significantly attenuated the LPS-induced brain injury and improved neurobehavioral performance. The protective effect of minocycline was associated with its ability to attenuate LPS-induced microglial activation. These results suggest that inhibition of microglial activation by minocycline may have long-term protective effects in the neonatal brain on infection-induced brain injury and associated neurologic dysfunction in the rat.

Cellular damage and prevention in childhood hydrocephalus

The literature concerning brain damage due to hydrocephalus, especially in children and animal models, is reviewed. The following conclusions are reached: 1. Hydrocephalus has a deleterious effect on brain that is dependent on magnitude and duration of ventriculomegaly and modified by the age of onset. 2. Animal models have many histopathological similarities to humans and can be used to understand the pathogenesis of brain damage. 3. Periventricular axons and myelin are the primary targets of injury. The pathogenesis has similarities to traumatic and ischemic white matter injury. Secondary changes in neurons reflect compensation to the stress or ultimately the disconnection. 4. Altered efflux of extracellular fluid could result in accumulation of waste products that might interfere with neuron function. Further research is needed in this as well as the blood-brain barrier in hydrocephalus. 5. Some, but not all, of the changes are preventable by shunting CSF. However, axon loss cannot be reversed, therefore shunting in a given case must be considered carefully. 6. Experimental work has so far failed to show any benefit in reducing CSF production. Pharmacologic protection of the brain, at least as a temporary measure, holds some promise but more pre-clinical research is required.

Acute hydrocephalus upregulates monoamine oxidase mRNA in neonatal rat brain

Metabolic derangement of the dopamine system in hydrocephalic brain has been observed, but the change of monoamine oxidase (MAO), the major enzyme to metabolize dopamine, is not known. The metabolic changes of dopamine and MAO mRNA in the striatum were examined in acute hydrocephalic rats whose ventricular size and intracranial pressure were controlled to a similar degree. The tissue levels of dopamine and its metabolites as well as MAO-A and MAO-B mRNA elevated significantly in hydrocephalus. Cerebrospinal fluid (CSF) diversion reversed these changes and induced an initial decline, followed by an elevation of these substances in extracellular fluid. In summary, the metabolism of dopamine system in the striatum was up-regulated in acute hydrocephalus and CSF diversion reversed this metabolic derangement.

CSF removal in infantile posthemorrhagic hydrocephalus results in significant improvement in cerebral hemodynamics

Rational intervention in infants with posthemorrhagic hydrocephalus (PHH) would be facilitated greatly by bedside measure of impaired cerebral perfusion, as there is substantial evidence that impaired perfusion and oxidative metabolism contribute to irreversible brain injury in hydrocephalus. Near-infrared spectroscopy (NIRS) measures changes in the cerebral concentration of oxygenated and deoxygenated hemoglobin and oxidized cytochrome oxidase at the bedside of infants continuously and noninvasively. The total hemoglobin and the hemoglobin difference signal are derived from the sum and difference, respectively, of oxygenated and deoxygenated hemoglobin. Changes in total hemoglobin reflect changes in cerebral blood volume; our previous work has shown that changes in hemoglobin difference signal reflect changes in cerebral blood flow. We hypothesized that cerebrospinal fluid (CSF) removal in infants with PHH would result in significant increases in cerebral perfusion, cerebral blood volume, and oxidative metabolism, as measured by NIRS. Continuous NIRS recordings were performed during CSF removal on 16 infants with PHH. There was a statistically significant increase in oxygenated hemoglobin (p < 0.001), total hemoglobin (p = 0.001), and hemoglobin difference signal (p = 0.006), but not oxidized cytochrome oxidase, accompanying CSF removal. There was no significant correlation between either the volume of CSF removed (in milliliters per kilogram body weight) or the opening pressure and the change in any of the measured or calculated NIRS signals. These findings demonstrate the pronounced effect of CSF removal on cerebral perfusion in infants with PHH. NIRS may be a useful technique to detect impending cerebral ischemia in such infants and thereby provide a means to guide the rational management of PHH.

Association of learning and memory impairments with changes in the septohippocampal cholinergic system in rats with kaolin-induced hydrocephalus

OBJECTIVE

The septohippocampal cholinergic (SHC) system plays an important role in the maintenance of normal memory and learning. However, the fact that memory and learning impairments under hydrocephalic conditions are directly related to the SHC system is less well known. We investigated the relationships between pathological changes in SHC neurons and impairments in memory and learning among hydrocephalic rats.

METHODS

Rats with kaolin-induced hydrocephalus were prepared with injections of kaolin suspension into the cisterna magna. Learning and memory performance was assessed with the passive avoidance and Morris water maze tests. Ventricular sizes were measured for the lateral and third ventricles. Acetylcholinesterase and choline acetyltransferase immunostaining was performed to investigate degenerative changes in cholinergic neurons in the medial septum and hippocampus.

RESULTS

Hydrocephalic rats demonstrated significant learning and memory impairments in the passive avoidance and Morris water maze tests. Decreased hesitation times in the passive avoidance test and markedly increased acquisition times and decreased retention times in the Morris water maze test indicated learning and memory dysfunction among the hydrocephalic rats. The numbers of cholinergic neurons in the medial septum and hippocampus were decreased in the hydrocephalic rats. The decreases in choline acetyltransferase and acetylcholinesterase immunoreactivity were significantly correlated with enlargement of the ventricles.

CONCLUSION

Impairment of spatial memory and learning may be attributable to degeneration of SHC neurons. These results suggest that learning and memory impairments in rats with kaolin-induced hydrocephalus are associated with the dysfunction of the SHC system induced by ventricular dilation.

Magnesium sulfate therapy is of mild benefit to young rats with kaolin-induced hydrocephalus

Hydrocephalus causes damage to periventricular white matter at least in part through chronic ischemia. Magnesium sulfate (MgSO4) has been shown to be protective in various models of neurologic injury. We hypothesized that this agent would ameliorate the effects of experimental childhood-onset hydrocephalus. Hydrocephalus was induced in 3- and 4-wk-old rats by injection of kaolin into the cisterna magna. Tests of cognitive and motor function were performed on a weekly basis. In a blinded and randomized manner, MgSO4 was administered in two separate experiments (s.c. injection 0.85, 4.1, or 8.2 mM/kg/d), supplemented by osmotic minipump infusion (0.03 mM/d) to prevent low trough levels for 2 wk, beginning 2 wk after induction of hydrocephalus. The brains were then subjected to histopathological and biochemical analyses. With the 4.1 mM/kg/d dose, serum Mg++ levels were elevated transiently from 1.3 to approximately 7 mM/L. We observed statistically significant improvement in gait performance and reduced astroglial reaction. There was also a trend to improved memory performance, but no evidence of increased myelin or synaptic protein content. The 8.2 mM/kg/d dose was associated with sedation and there was no evidence of improvement in any parameter. We conclude that MgSO4 might be mildly protective in experimental hydrocephalus.

Chronic hydrocephalus in rats and humans: white matter loss and behavior changes

Chronic hydrocephalus that begins in childhood and progresses only very gradually is sometimes called "arrested" hydrocephalus. Data suggest that this state eventually can become symptomatic and may be treatable by shunting. However, the pathological substrate of the disorder is not entirely understood. We studied chronic hydrocephalus in rats, 9 months after induction by kaolin injection into the cisterna magna, and in humans. In both circumstances, destruction of periventricular white matter structures was worst in those with the largest ventricles. Structures damaged include the corpus callosum, corticospinal tract, and fimbria/fornix projections from the hippocampus. Myelin turnover was increased. These changes were associated with deficits of motor and cognitive function. The cerebral cortex was largely spared. There appears to be a threshold of ventricle size beyond which functional changes manifest, but this undoubtedly is modified by factors such as age of onset and rate of enlargement. These data support the need for persistent follow-up of patients with chronic, apparently stable hydrocephalus. A slight increase in size of already enlarged ventricles might cause significant axonal damage.

Sodium channel-blocking agents are not of benefit to rats with kaolin-induced hydrocephalus

OBJECTIVE

Hydrocephalus causes damage to periventricular white matter at least in part through chronic ischemia. The sodium channel-blocking agents mexiletine and riluzole have been shown to be of some protective value in various models of neurological injury. We hypothesized that these agents would ameliorate the effects of experimental childhood-onset hydrocephalus.

METHODS

Hydrocephalus was induced in 4-week-old rats by injection of kaolin into the cisterna magna. Tests of cognitive and motor function were performed on a weekly basis. In a blinded and randomized manner, mexiletine (0.7, 7, or 42 mg/kg/d) or riluzole (1.4 or 13.6 mg/kg/d) was administered by osmotic minipump for 2 weeks, beginning 2 weeks after induction of hydrocephalus. The brains were then subjected to histopathological and biochemical analyses.

RESULTS

Compared with untreated hydrocephalic rats, neither mexiletine nor riluzole was associated with a protective effect on behavioral, structural, or biochemical abnormalities.

CONCLUSION

Protection of hydrocephalic brains through pharmacological sodium channel blockade is probably an approach not worth pursuing.

Impairment of spatial memory in kaolin-induced hydrocephalic rats is associated with changes in the hippocampal cholinergic and noradrenergic contents

We investigated the relationship between the degree of spatial memory impairment in an 8-arm radial maze and the changes in the contents of acetylcholine (ACh) and noradrenaline (NA) in the dorsal and ventral hippocampus and the frontal cortex, along with histological changes in kaolin-induced hydrocephalic rats. Kaolin-induced hydrocephalic rats were divided into three groups (non-impaired, impaired and severely impaired) according to the degree of impairment in a radial maze. Thirty percent of the hydrocephalic rats could not solve a radial maze (severely impaired group), while the remaining hydrocephalic rats could (non-impaired rats in the standard task). Forty percent of the non-impaired rats in the standard task failed to solve the delayed-response task (impaired group), whereas the remaining rats were able to solve it (non-impaired group). A positive correlation was observed between the impairment of spatial memory and ventricular dilatation. The ACh content in the dorsal and ventral hippocampus, and the NA content in the ventral hippocampus were decreased in the severely impaired group. Moreover, the NA content in the ventral hippocampus was decreased in the impaired group. These results suggest that the impairment of spatial memory in kaolin-induced hydrocephalic rats is associated with dysfunction of the hippocampal cholinergic and noradrenergic systems.