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  • By Author: Drake, James M. x
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Marcia C. da Silva, James M. Drake, Claude Lemaire, Albert Cross and Ursula I. Tuor

✓ The authors studied the effects of hydrocephalus on the high-energy phosphate metabolism of the brain and the impact of ventriculoperitoneal (VP) shunting on these changes in an experimental model of hydrocephalus. High-energy phosphate metabolism was analyzed using in vivo magnetic resonance (MR) imaging and 31P MR spectroscopy. Hydrocephalus was produced in 34 1-week-old kittens by cisternal injection of 0.05 ml of a 25% kaolin solution. Sixteen litter mates were used as controls. A VP shunt with a distal slit valve was implanted in 17 of the 34 hydrocephalic animals 10 days after induction of hydrocephalus. Both MR imaging and 31P MR spectroscopy were obtained 1 and 3 weeks after either kaolin or distilled water injection. Untreated hydrocephalic animals had marked dilatation of the lateral ventricles and periventricular edema. Magnetic resonance spectroscopy showed a significant decrease in the energy index ratio of phosphocreatine (PCR): inorganic phosphate (PI) and an increase in the PI:adenosine triphosphate (ATP) ratio. There was a direct correlation between the decrease in the energy index and ventricular size. Compared with preoperative scans, shunted animals showed no periventricular edema, and the ventricles decreased in size. Also, PCR:PI and PI:ATP ratios were within the levels of controls. This study suggests that neonatal hydrocephalus results in a mild hypoxic/ischemic insult that is treatable by VP shunting.

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Paul D. Chumas, James M. Drake, Marc R. Del Bigio, Marcia Da Silva and Ursula I. Tuor

✓ The metabolic changes in neonatal hydrocephalus that lead to permanent brain injury are not clearly defined, nor is the extent to which these changes can be prevented by a cerebrospinal fluid shunt. To clarify these processes, cerebral glucose utilization was examined using [14C]2-deoxyglucose autoradiography in 1-month-old kittens, kaolin-induced hydrocephalic littermates, and hydrocephalic kittens in which a ventriculoperitoneal shunt had been inserted 10 days after kaolin injection. The hydrocephalic kittens showed thinning of the cerebral mantle and an anterior-to-posterior gradient of enlargement of the ventricular system, with a ventricle:brain ratio of 24% for the frontal and 35% for the occipital horns compared with control (< 0.5%) and shunted (< 5%) animals. White matter in hydrocephalic animals was edematous. Myelination was delayed in the periventricular region and in the cores of the cerebral gyri.

Glucose utilization in hydrocephalic and shunted animals was unchanged from control animals in all gray-matter regions examined. However, in hydrocephalic animals, the frontal white matter exhibited a significant increase in glucose utilization (25 µmol • 100 gm−1 • min−1) in the cores of gyri compared with normal surrounding white-matter values (14.8 µmol • 100 gm−1 • min−1). Very low values (mean 4 µmol • 100 gm−1 • min−1) were found in areas corresponding to severe white-matter edema, and these areas were surrounded by a halo of increased activity (24 µmol • 100 gm−1 • min−1). In contrast, cytochrome oxidase activity in white matter was homogeneous. Shunting resulted in restoration of the cerebral mantle thickness, a return to normal levels of glucose utilization in the white matter, and an improvement in myelination.

It is suggested that the areas of increased glucose utilization seen in the white matter represent anaerobic glycolysis which, if untreated, progresses to infarction. The pattern of this increased glucose utilization matches that of expected myelination and, during this period of high energy demand, white matter may be susceptible to the hypoperfusion associated with hydrocephalus.

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Paul D. Chumas, Marc R. Del Bigio, James M. Drake and Ursula I. Tuor

✓ It has recently been reported that pretreatment with a single dose of dexamethasone (0.1 mg/kg) 24 hours before hypoxia in 7-day-old rat pups is protective against an hypoxic-ischemic insult (unilateral carotid artery occlusion followed by 3 hours of hypoxia in 8% O2). The authors now examine whether pretreatment 6 hours before insult is equally effective and compare other agents potentially suitable for prophylaxis in neonatal hypoxia-ischemia, including the calcium antagonists flunarizine (30 mg/kg pretreatment), nimodipine (0.5 mg/kg pretreatment), and the 21-aminosteroid U-74389F (10 mg/kg pre- and posttreatment). For each active agent, there was also a vehicle-treated control group.

Comparison of the mean area of ipsilateral infarction on brain coronal sections showed that there was no statistically significant difference between the various control groups (mean area of infarction 66% ± 4%). Pretreatment with dexamethasone 6 hours prior to hypoxia offered complete protection with no infarction. A beneficial effect was seen following pretreatment with flunarizine (mean area of infarction 33.6% ± 7.8%), although this degree of damage was still significantly different from that seen with dexamethasone pretreatment. Pretreatment with nimodipine or U-74389F offered no protection (mean area of infarction 77.5% ± 4% and 59% ± 10%, respectively). Unlike findings in adult animals and clinical studies, the current studies show that dexamethasone may have a role in the treatment of neonatal hypoxia-ischemia and deserves reappraisal.