UNCOUPLING OF LCBF AND LCGU IN 2 DIFFERENT MODELS OF HYDROCEPHALUS - A REVIEW

We have used two different experimental models to examine the relation ship between local cerebral blood flow and metabolism in hydrocephalus . In our first experiments local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were measured by quantitative auto radiographic methods in adult rats rendered hydrocephalic, though asym ptomatic, by the injection of kaolin intracisternally at 3 weeks of ag e and in control animals. There were no significant differences in LCG U or LCBF in any of the 29 areas of grey matter examined, including la yer IV of the cerebral cortex. Scanning across the cerebral cortex rev ealed an appreciable fall in LCGU and LCBF towards the inside and the outside of the mantle in control animals. Hydrocephalus had no signifi cant effect on this ''transmantle'' pattern of reduction in cortical m etabolism towards the periphery, but in contrast, significantly enhanc ed the reduction in cortical blood flow in 7 out of the 10 cortical re gions examined. Hence, in this model of asymptomatic hydrocephalus the re is relative uncoupling of LCBF and LCGU in the inner and outer laye rs of the cerebral mantle. In a study performed in congenitally hydroc ephalic H-Tx rats at 10, 20 and 28 days we found that uptake of deoxyg lucose was impaired in hydrocephalic rats compared with their non-hydr ocephalic siblings. Small changes were seen at 10 and 21 days, but sta tistically significant changes were seen only at 28 days. A small redu ction in LCBF was observed in all regions at 10 days, with statistical ly significant differences between control and hydrocephalic rats in a uditory and parietal cortex. By 21 days, reductions of between 25% and 70% in local cerebral blood flow were observed in all regions, with s tatistically significant differences in visual, auditory and parietal cortex. At 30 days, a statistically significant difference was found b etween controls and hydrocephalic rats in pens, caudate nucleus and vi sual, auditory, parietal and sensorimotor cortex. This second study in dicates that decreases in local cerebral blood flow precede decreases in cerebral metabolism and occur before the appearance of obvious symp toms. Our experiments suggest that in hydrocephalus a decrease in tiss ue perfusion precedes any impairment of cerebral glucose metabolism an d may occur before the appearance of any gross symptoms.