Presented at the Neonatal Society 2003 Spring Meeting.
Derrick M, Ji X, Fisher K, Bregman J, Jilling T, Tan S (introduced by Marianne Thoresen)
Department of Pediatrics, Evanston Northwestern Healthcare, 2650 Ridge Ave, Evanston, IL, 60201 USA
Background: Periventricular leukomalacia (PVL) is a leading cause of brain injury in premature infants. Since hypoxia-ischemia (H-I) plays a major role in PVL, we developed a uterine ischemia model in preterm fetal rabbits. Injury to vulnerable oligodendrocyte precursors has been proposed to explain the white matter injury in PVL. We have previously shown that pre-oligodendrocytes constitute the predominant oligodendrocyte population at E22 in rabbits.
Objective: The objective was to investigate the effect of hypoxia-ischemia to the fetus at a preterm gestation during a vulnerable time period of oligodendrocyte development.
Methods: New Zealand white rabbits were subjected to uterine ischemia for 37-40 min at E21-22 or no ischemia. Uterine ischemia was achieved with a 4F Fogarty catheter inserted 10cm into the left femoral artery and inflating the balloon with 0.2ml of sterile saline using spinal anesthesia. At the end of the ischemia the catheter was removed and the artery reconstructed. The rabbits were allowed to deliver spontaneously at E31-32. A panel of neurobehavioral tests was conducted on the newborn rabbits at 32 days gestation (4 pups/litter). The examination was videotaped and scored by two blinded observers. The hypoxic animals were compared to non-ischemic controls by nonparametric analysis. In a subset of animals after the neurobehavioral testing the brains were removed digested with trypsin to produce a single cell suspension. The suspension was analyzed on a flow cytometer to assess total cell number and cell death with propidium iodide.
Results: The H-I group had a phenotype consistent with cerebral palsy. The limbs were held in a flexed position. Muscle tone was increased particularly in the upper extremities. The most severely effected were not able to purposefully move forward or turn from supine to prone position. Comparing H-I with control animals, the quality of movement of head, front and hind legs were impaired in the H-I group. The time of locomotion, the number of line crosses per minute, and overall level of activity, were all impaired in the H-I group. The righting reflex and coordinated sucking and swallowing patterns were also impaired. Compared to controls, H-I resulted in impairment of the olfactory response to peppermint and alcohol and the tactile response to the face. The H-I group had a poorly controlled suck and swallow. The total cells by flow cytometer increased significantly, in the hypoxia group, by 38%. There was no difference in cell death.
Conclusions: Antenatal hypoxia-ischemia, when the oligodendrocyte is most vulnerable, results in motor, sensory and reflex deficits in the newborn rabbit. These are consistent with cerebral palsy.
Acknowledgements: Supported by: NIH HD01138 & March of Dimes 294