Changes in acidic amino acid efflux from rat brain with maturation

ABSTRACT

Our previous studies have shown a greater uptake of acidic amino acids from the blood into the brain of neonatal when compared to that of adult rats. The aim of this study is to investigate whether a developmental change exists in the brain to blood efflux of this group of amino acids. The whole brain was perfused in situ with Ringer's solution containing 14C-aspartate or 14C-glutamate for 10 min. The perfusion was then continued with 14C-free perfusate for a further 20 min and samples of jugular venous outflow were taken at 30-second intervals. The amount of radioactivity [in ln dpm] in each sample was then plotted against the sampling time, and the half-time [t1/2] for 14C-efflux was calculated. Paper chromatography of the outflow samples revealed that more than 91% of the 14C-labelled acidic amino acid present in the effluent samples for up to 30 min of perfusion was chemically intact. The t1/2 for aspartate efflux in neonatal rats was 16.16 +/- 0.76 min which was significantly slower [p < 0.05] than that for the adults, 10.06 +/- 0.46 min [means +/- SEM, n = 3 and 4]. The t1/2 for glutamate efflux was also small in the adult brain where it was 50% the value seen in the neonates. The above results indicate that the systems involved in the efflux of acidic amino acids out of the brain favour retention and increased levels of this group of amino acids in the developing brain