Local cerebral blood flow in the newborn rabbit: an autoradiographic study of changes during development.

Cerebral ischemia in the neonate is an important cause of hypoxic-ischemic encephalopathy. Thus, it is important to have an economical and readily available animal model in which to study the local control of the cerebral circulation in the perinatal period. This study demonstrates that the newborn rabbit, a rather immature species at birth, is a suitable neonatal model in which to measure local cerebral blood flow with quantitative iodo[14C]antipyrine autoradiography. One or 2 d after birth, local cerebral blood flow in the newborn rabbit is low, but flow varies distinctly between regions [e.g. 8.9 +/- 1.5 mL.kg-1.s-1 (53 mL.100 g-1.min-1) in the nucleus tractus solitarius and 3.4 +/- 0.7 mL.kg-1.s-1 (20 mL.100 g-1.min-1) in the frontal cortex]. During early postnatal development (i.e between 1 and 8 d), local cerebral blood flow does not change greatly. However, by 17 d, 22 of 26 brain regions exhibit significant marked increases (200-350%) in local cerebral blood flow when compared with blood flow in the newborn. Between 17 and 40 d postnatally, cerebral blood flow continues to increase in 16 of 26 regions (e.g. thalamic areas). In four of the cerebral cortical areas, elevations in flow continue during the period between 40 d of age and adulthood. In contrast to the generalized increases in flow occurring postnatally, a few brain regions (i.e. within the pons and medulla) exhibit only minor changes in cerebral blood flow. The differential pattern and lower basal levels of cerebral blood flow in the neonate compared with the adult may be important determinants in regional susceptibility of the brain to ischemia.