Acidic amino acid accumulation by rat choroid plexus during development

Acidic amino acid accumulation by the choroid plexuses of the lateral ventricles was investigated using 1, 2, 3 week and adult (7-10 weeks old) rats. The accumulation from both blood and CSF sides of the choroid plexuses were investigated. The uptake from blood side was studied using the bilateral in situ brain perfusion, and time-dependent uptake profiles (2, 10, 20, and 30 min) of 14C-labelled aspartate, glutamate, and NMDA were measured. [3H]Mannitol was also included in perfusion fluid as a baseline for [14C]amino acid uptake into choroidal tissue. Uptake of [14C]aspartate and [14C]glutamate declined with age, while [14C]NMDA showed no significant uptake at any age. Twenty min [3H]mannitol uptake in the 1-week-old rat was significantly greater than the adult (P < 0.05). The K(m) for [14C]aspartate and [14C]glutamate obtained from multiple time uptake profiles also showed reduction with development but it was greater than that for mannitol. [14C]Aspartate declined from 69.8 +/- 21.1 microliters.min-1.g-1 in the neonate to 40.6 +/- 4.0 microliters.min-1.g-1 in the adult (P < 0.05), while glutamate showed a sharper decline from 78.9 +/- 24.2 microliters.min-1.g-1 to 17.7 +/- 5.4 microliters.min-1.g-1 (P < 0.01). Accumulation of 14C-labelled aspartate and glutamate by the choroid plexus from CSF side was also measured using ventriculo-cisternal perfusion. The accumulation in the adult was found to be 2-3 times greater than that in the neonatal rat (P < 0.05) for both amino acids. The uptake from either side was found to be saturable, stereospecific, not inhibited by neutral amino acid analogues, and shared by both aspartate and glutamate.