Genetic prenatal aqueductal stenosis with hydrocephalus in rat

Proliferative and nonproliferative lesions of the rat and mouse central and peripheral nervous systems

Harmonization of diagnostic nomenclature used in the pathology analysis of tissues from rodent toxicity studies will enhance the comparability and consistency of data sets from different laboratories worldwide. The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of four major societies of toxicologic pathology to develop a globally recognized nomenclature for proliferative and nonproliferative lesions in rodents. This article recommends standardized terms for classifying changes observed in tissues of the mouse and rat central (CNS) and peripheral (PNS) nervous systems. Sources of material include academic, government, and industrial histopathology databases from around the world. Covered lesions include frequent, spontaneous, and aging-related changes as well as principal toxicant-induced findings. Common artifacts that might be confused with genuine lesions are also illustrated. The neural nomenclature presented in this document is also available electronically on the Internet at the goRENI website (http://www.goreni.org/).

Development of an acute obstructive hydrocephalus model in rats using N-butyl cyanoacrylate

PURPOSE

Previous animal models of obstructive hydrocephalus that was frequently combined with subarachnoid inflammation are not suitable for investigating cerebrospinal fluid (CSF) flow between ventricles and cisterns in obstructive hydrocephalus. In this study, we attempted to develop a new animal model for obstructive hydrocephalus in rats sparing subarachnoid space using N-butyl cyanoacrylate (NBCA).

METHODS

Hydrocephalus was induced in adult male Sprague-Dawley rats with NBCA (n=15) or with kaolin (n=10). For the NBCA model, a silicone tube was inserted through the foramen of Magendie into the fourth ventricle, into which 20 μL of a mixture of NBCA and ethiodized oil was injected. For the kaolin model, 100 μL of 20% kaolin solution was injected into the cistern magna. The rats in the NBCA and kaolin groups were sacrificed 3 and 21 days after surgery, respectively.

RESULTS

Eleven rats in the NBCA group developed hydrocephalus (73.3%), with a 13.3% mortality rate. The kaolin group showed hydrocephalus in eight rats (80%), with a 20% mortality rate. The mean Evans' indices were 0.37 ± 0.02, 0.45 ± 0.04, and 0.53 ± 0.09 in the control, NBCA, and kaolin groups, respectively (p < 0.05). There was no remarkable arachnoid adhesion or inflammatory change of the ventricular wall in the NBCA group.

CONCLUSIONS

The NBCA model seems to be a useful animal model for acute obstructive hydrocephalus with preserved subarachnoid CSF pathway. This model can be useful for studying CSF flow between ventricles and cisterns.

Single and multiple congenic strains for hydrocephalus in the H-Tx rat

The H-Tx rat has fetal-onset hydrocephalus with a complex mode of inheritance. Previously, quantitative trait locus mapping using a backcross with Fischer F344 rats demonstrated genetic loci significantly linked to hydrocephalus on Chromosomes 10, 11, and 17. Hydrocephalus was preferentially associated with heterozygous alleles on Chrs 10 and 11 and with homozygous alleles on Chr 17. This study aimed to determine the phenotypic contribution of each locus by constructing single and multiple congenic strains. Single congenic rats were constructed using Fischer F344 as the recipient strain and a marker-assisted protocol. The homozygous strains were maintained for eight generations and the brains examined for dilated ventricles indicative for hydrocephalus. No congenic rats had severe (overt) hydrocephalus. A few pups and a significant number of adults had mild disease. The incidence was significantly higher in the C10 and C17 congenic strains than in the nonhydrocephalic F344 strain. Breeding to F344 to make F.H-Tx C10 or C11 rats heterozygous for the hydrocephalus locus failed to produce progeny with severe disease. Both bicongenic and tricongenic rats of different genotype combinations were constructed by crossing congenic rats. None had severe disease but the frequency of mild hydrocephalus in adults was similar to congenic rats and significantly higher than in the F344 strain. Rats with severe hydrocephalus were recovered in low numbers when single congenic or bicongenic rats were crossed with the parental H-Tx strain. It is concluded that the genetic and epigenetic factors contributing to severe hydrocephalus in the H-Tx strain are more complex than originally anticipated.

Widespread neuronal ectopia associated with secondary defects in cerebrocortical chondroitin sulfate proteoglycans and basal lamina in MARCKS-deficient mice

Mice deficient in MARCKS, a prominent neural substrate for protein kinase C (PKC), die before or shortly after birth. They exhibit high frequencies of exencephaly, universal agenesis of forebrain commissures, and abnormalities of cerebral cortical and retinal lamination. We show here that these mice have wide-spread and severe neuronal ectopia in the outer layers of the developing forebrain, manifested by the migration of clusters of developing neuroblasts through the basal lamina and often through the pial membrane and into the subarachnoid space. This abnormality became apparent by Embryonic Day (E) 13 or 14, shortly after the formation of the early marginal zone. MARCKS deficiency was associated with decreased staining for marginal zone chondroitin sulfate proteoglycans; this decrease was detectable earlier in development than the neuronal ectopia. Later in development, there was also marked disruption of the basal lamina at the pial-glial interface, as evidenced by gross abnormalities in laminin and reticulin staining; however, the basal lamina appeared normal at E9.5. These data indicate that MARCKS is required for the prevention of neuronal ectopia during development. Potential mechanisms responsible for the neuronal ectopia in the MARCKS-deficient mice include decreased expression or increased proteolytic destruction of basal lamina proteins and marginal zone chondroitin sulfate proteoglycans in the developing brain.

Histological changes in the midbrain around the aqueduct in congenital hydrocephalic rat LEW/Jms

Primary aqueductal stenosis is one of the main causes of congenital hydrocephalus in humans and experimental models. The congenitally hydrocephalic rat strain LEW/Jms is one such model. In this report, we describe further detailed histological features of periaqueductal structure, including the posterior commissure, subcommissural organ (SCO), and ependyma, and discuss the changes in these structures in relation to the cause of hydrocephalus. Coronal sections of the aqueduct in normal rats showed that the usual ependyma was absent in the center of the base facing the dorsal side, which was replaced by tall columnar cells. On the other hand, in hydrocephalic rats the ependyma encircled the aqueductal cavity. In midline sagittal sections, normal and hydrocephalic rats showed the SCO, although the SCO in hydrocephalic rats was shorter than in normal rats. There was also a marked difference between normal and hydrocephalic rats in the dorsoventral dimension of the rostral midbrain. In hydrocephalus, this dimension was large in comparison with normal rats. The superior collicular commissure located caudal to the posterior commissure ran along the ventral side of the midbrain in rats with hydrocephalus, and there was a cell-depleted area just dorsal to the superior collicular commissure. The same findings were observed from the 17th day of gestation until the postnatal period. Although the role of the SCO has been widely discussed from the viewpoint of secretory function, the present study indicated that this organ might be involved in the formation of the shape of the aqueduct.

Hydrocephalus in developing cats: physiological properties of visual cortex cells

We have studied electrophysiologically by single cell recording in the visual cortex, whether modification of the visual system in developing and in adult cats by hydrocephalus has an effect on processing of visual information. One of our cats (H1) had developed a complete hydrocephalus and the others partial, as proved by either complete or partial dilation of the lateral ventricles, respectively and by the thinning of the cortex. Despite this, the horizontal lamination and the vertical organization of the cortex were fully preserved. Except for the optic radiation and the corpus callosum which was remarkably modified, the optic tract, chiasm, nerve and retina were morphologically and histologically normal. The visual behavior of the hydrocephalic cats was normal. This was also reflected, by and large, in the physiological properties of the visual cortex. However, in cat H1 there were many more visually unresponsive cortical cells in comparison to its matched controls (C1) and the normal cats. A reduced responsiveness was also found in cat H2 with partial hydrocephalus but not in the other partial hydrocephalic cats. Similarly, the ocular dominance distribution of the cells was affected in cat H1 in comparison to the control cats as indicated by the changes found in the relative proportions of contralaterally and ipsilaterally driven cells in the two hemispheres. No change was, however, found in the partially hydrocephalic cats. Most of the cells in the hydrocephalic cats were orientation specific, similarly to the result of their matched controls. Direction specific cells were much smaller in proportion in cat H1 but not in the other cats, in comparison with their matched controls. In keeping with this, a large increase was found in the receptive field area of cat H1, a smaller one in cat H2 and none in the other hydrocephalic cats in comparison to the matched controls. The eccentricity distribution of the receptive fields in the hydrocephalic cats was the same as expected under normal conditions. It was concluded that in the way hydrocephalus had modified the brain of several of our cats, a quantitative effect was induced in visual cortex cells leading to some degradation of function; this change, however, did not interfere with their basic visual properties.

Critical period for induction of congenital hydrocephalus and dysplasia of subcommissural organ by prenatal X-irradiation in rats

A single whole-body X-irradiation of pregnant Wistar rats at a dose of 1.05 Gy at 10.30, 12.30 and 14.30 h respectively, of gestational day 10 resulted in significantly high incidences of hydrocephalic offspring. No hydrocephalic offspring resulted from X-irradiation of pregnant rats with 1.05 Gy at 16.30 h, whereas a dose of 1.22 Gy at 16.30 h resulted in a low but statistically significant incidence of hydrocephalus. Neither 1.05 Gy nor 1.22 Gy X-irradiation of pregnant rats at 18.30 h resulted in any hydrocephalic offspring. Dysplasia of the subcommissural organ was noticed in all the hydrocephalic brains histologically examined.

Inherited prenatal hydrocephalus in the H-Tx rat: a morphological study

The H-Tx rat has inherited hydrocephalus which is present at birth. In order to investigate the onset and early stages of hydrocephalus, the heads of fetuses from 16 to 21 days gestation and at 1 day after birth, were serially sectioned using conventional wax histology. Lateral and third ventricle volumes were measured with a graphics tablet and microcomputer. Hydrocephalus was first detected at 18-20 days gestation by enlarged lateral ventricles and it was sometimes accompanied by a large third ventricle. Most hydrocephalics had a non-patent cerebral aqueduct between the third ventricle and the posterior collicular recess and the remainder (about 25%) had an aqueduct which was patent but with a smaller lumen than in non-hydrocephalic littermates. Some fetuses prior to 18 days gestation with normal lateral ventricles also had non-patent aqueducts. Abnormal aqueducts were lined by ependymal cells which were ventrally displaced by thickening of the overlying midbrain; also the subcommissural organ was foreshortened. Infusion with fluorescent markers confirmed that the flow pathway through the aqueduct was obstructed in many hydrocephalic rats. It is concluded that the hydrocephalus may be the result of abnormal brain development in the midline region of the dorsal mesencephalon, leading to aqueduct closure.

Relationship of periventricular overgrowth to hydrocephalus in brains of fetal rats exposed to benomyl

Benomyl, a benzimidazole fungicide, was administered by gavage to pregnant Sprague-Dawley rats in a daily dose of 62.5 mg/kg of maternal body weight beginning at gestational day (GD) 7. Fetuses examined histologically at GD16 or GD20 revealed a high incidence of craniocerebral anomalies--82.6% of those examined at GD16 and 100% of those examined at GD20. Hydrocephalus occurred in 65.2% of fetuses examined at GD16 and in 58.8% at GD20 but was more severe in the GD20 fetuses. A second common anomaly, termed periventricular "overgrowth" (PVO), consisted of subependymal cell masses that in some fetuses obliterated normal subcortical structures. PVO occurred in 34.8% of fetuses examined at GD16 and 76.5% at GD20. The size of the subependymal masses and the regions involved were considerably greater in the GD20 than the GD16 fetuses. Less common anomalies in the GD20 fetuses were periventricular necrosis (41.2%), a single fetus with exencephaly and another with porencephaly. In the majority of malformed fetuses, the severity of hydrocephalus did not parallel the severity of PVO around the lateral and third ventricles. PVO involved tissues surrounding the cerebral aqueduct in 17.4% of GD16 fetuses and 38.2% of GD20 fetuses. This "overgrowth" distorted the cerebral aqueduct in a large number of fetuses with ventriculomegaly, and at GD20 moderate and severe ventriculomegaly was in every instance associated with a narrow or completely occluded cerebral aqueduct. These relationships suggest that PVO in the midbrain may play a role in the production of aqueductal stenosis and hydrocephalus in this experimental model.

Hereditary hydrocephalus in laboratory animals and humans

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