Proliferating cell populations in experimentally-induced hydrocephalus in developing rats

Early deterioration of cerebrospinal fluid dynamics in a neonatal piglet model of intraventricular hemorrhage and posthemorrhagic ventricular dilation

OBJECT

The optimal management of neonatal intraventricular hemorrhage (IVH) and posthemorrhagic ventricular dilation is challenging. The importance of early treatment has been demonstrated in a recent randomized study, involving early ventricular irrigation and drainage, which showed significant cognitive improvement at 2 years. The objective of this study was to define the changes in CSF absorption capacity over time in a neonatal piglet model of IVH.

METHODS

Ten piglets (postnatal age 9-22 hours) underwent intraventricular injection of homologous blood. A ventricular access device was inserted 7-10 days later. Ventricular dilation was measured by ultrasonography. Serial constant flow infusion studies were performed through the access device from Week 2 to Week 8.

RESULTS

Seven piglets survived long term, 43-60 days, and developed ventricular dilation; this reached a maximum by Week 6. There was no significant difference in baseline intracranial pressure throughout this period. The resistance to CSF outflow, R(out), increased from 63.5 mm Hg/ml/min in Week 2 to 118 mm Hg/ml/min in Week 4. Although R(out) decreased after Week 5, the ventriculomegaly persisted.

CONCLUSIONS

In this neonatal piglet model, reduction in CSF absorptive capacity occurs early after IVH and accompanies progressive and irreversible ventriculomegaly. This suggests that early treatment of premature neonates with IVH is desirable.

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.

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.

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.

Biomarkers in chronic adult hydrocephalus

Awareness of the importance of chronic adult hydrocephalus has been raised again with the recent emergence of epidemiological studies. It is estimated that between 5 and 10% of patients suffering from dementia might, in fact, have chronic hydrocephalus. Although, surgical diversion of the cerebrospinal fluid (CSF) represents the only known procedure able to treat the symptoms of this condition, the selection of surgical patients has always been problematic. In the last 40 years, we have become wiser in using appropriate diagnostic tests for the selection of these patients; however, the area of biological markers has so far been overlooked in this condition, in contrast to that for other neurodegenerative disorders and dementias. Biomarkers are biological substances that may be used to indicate either the onset or the presence, and the progression of a clinical condition, being closely linked to its pathophysiology. In such a setting they might assist in the more appropriate selection of patients for shunt surgery. In this article, we have reviewed research carried out in the last 25 years regarding the identification of serum and CSF biomarkers for chronic hydrocephalus, discussed the potential for each one, and finally discussed the limitations for use, as well as future directions and possibilities in this field. It is concluded that tumour-necrosis factor, tau protein, lactate, sulfatide and neurofilament triple protein are the most promising CSF markers for chronic hydrocephalus. At present however, none of these meet the criteria required to justify a change clinical practice. In the future, collaborative multi-centre projects will be needed to obtain more substantial data that overcome the problems that arise from small individual and uncoordinated studies.

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.