Improvement of Cortical Morphology in Infantile Hydrocephalic Animals after Ventriculoperitoneal Shunt Placement

Neuronal damage in hydrocephalus and its restoration by shunt insertion in experimental hydrocephalus: a study involving the neurofilament-immunostaining method

OBJECT

The morphological and functional impairments of neurons and their connections caused by hydrocephalus, and their restoration by ventricular shunt placement were investigated in experimental hydrocephalus by the immunostaining of neurofilaments, which constitute the major component of the neuronal cytoskeleton.

METHODS

Progressive hydrocephalus was induced in 15 young mongrel dogs 1 to 2 months of age, 3 to 4 weeks after cisternal injection of kaolin. The dogs were divided into three groups of five animals each, a "preshunt," "post-shunt," and "nonshunt" group, depending on whether the hydrocephalic animals underwent a procedure to insert a ventriculoperitoneal shunt. Neurofilament, glial fibrillary acid protein (GFAP), and synaptophysin immunostaining were performed using samples of brain tissue from each hydrocephalic group and a fourth "control" group (five animals). In the cortex, morphological deformation and heterogeneous neurofilament immunoreactivity of the apical dendrites became pronounced in accordance with the progression of hydrocephalus (from the preshunt to the nonshunt group), and these changes remained after shunt insertion (postshunt group). In the periventricular white matter, swollen and fragmented axons increased in number along with hydrocephalic progression and were incompletely repaired by ventricular shunt placement. The GFAP-positive astrocytes observed around repaired axons in the postshunt group were seen more prominently than in the untreated hydrocephalic groups. In the internal capsule, fairly good recovery from axonal damage caused by the hydrocephalic condition was achieved by insertion of a ventricular shunt, compared with that seen in the periventricular white matter.

CONCLUSIONS

Cytoskeletal damage of neurons in hydrocephalus and its incomplete restoration by shunt placement were most significant in the periventricular white matter. This finding may account for the impaired cognitive function seen in children who have shunts and an apparently reconstituted cerebral mantle; therefore, neuronal protection in the early hydrocephalic state should be considered.

Decreased c-fos expression in experimental neonatal hydrocephalus: evidence for reduced neuronal activation

Although neonatal hydrocephalus often results in residual neurological impairments, little is known about the cellular mechanisms responsible for these deficits. The immediate early gene, fos (c-fos), functions as a “third messenger” to regulate protein synthesis and is a good marker for neuronal activation. To identify functional changes in neurons at the cellular level, the authors quantified fos RNA expression and localized fos protein in the H-Tx rat model of congenital hydrocephalus. Tissue samples from sensorimotor and auditory regions were obtained from hydrocephalic rats and age-matched, normal litter mates at 1, 6, 12, and 21 days of age (four-six animals in each group) and processed for immunohistochemical analysis of fos and Northern blot analysis of RNA. At 12 days of age, hydrocephalic animals exhibited significant decreases in the ratio of fos immunoreactive cells to Nissl-stained neurons from both cortical regions, but no statistical differences were noted in fos expression. At 21 days of age, both the ratio of fos immunoreactive cells to Nissl-stained neurons and fos expression decreased significantly. The number of fos-positive neurons decreased in all cortical layers but was most prominent in layers V through VI. This decrease did not appear to be caused by neuronal death because examination of Nissl-stained sections revealed many viable neurons within the areas where fos immunoreactivity was absent. These results suggest that progressive neonatal hydrocephalus reduces the capacity for neuronal activation in the cerebral cortex, primarily in those neurons that provide corticofugal projections, and that this impairment may begin during relatively early stages of ventriculomegaly.