A developmental analysis of differences in the uptake of [123I]isopropyliodoamphetamine versus 99mTc-pertechnetate by the choroid plexus and brain.

The uptake of intravascular [123I]isopropyliodoamphetamine (IMP) and 99mTc-pertechnetate into choroid plexus (CP) and brain (frontal cortex) was studied by an indicator fractionation method applied to immature, ketamine-anesthetized Sprague-Dawley rats (1.5, 2, and 3 wk). Assessment of the rate and extent of uptake of these indicators provides functional information (eg blood flow; transport) about various regions of the developing CNS. IMP uptake by lateral ventricle CP was 1.15 ml/g/min in 1.5-wk-old infant rats and gradually increased to 3.9 mg/g/min by adulthood (7-8 wk) (P < 0.05); over the same postnatal period, 99mTc uptake went from 2.82 to 3.18 ml/g/min. IMP uptake by cortex was 0.39 and 0.99 ml/g/min in infants and adults, respectively (P < 0.05); however, 99mTc uptake by cortex was only 0.07 +/- 0.01 ml/g/min at all ages, reflecting early development of blood-brain barrier (BBB) to pertechnetate. Overall, our findings indicated a progressive increase with age in the rate of uptake of IMP by CP and brain; and that 99mTc penetration into CP was relatively constant and substantially greater than into cortex at all developmental stages. Thus the nature of uptake of IMP, relative to 99mTc, was markedly different at the blood-cerebrospinal fluid barrier (i.e., CP) vs. the blood-brain barrier.