THE UPTAKE OF ?-[3H]AMINOBUTYRIC ACID BY SLICES FROM VARIOUS REGIONS OF RAT BRAIN AND THE EFFECT OF LITHIUM

— Slices from various regions of rat brain, incubated at 25°C, rapidly accumulate [3H]GABA from the surrounding medium until after 60min tissue:medium ratios as high as 300 may be achieved. Kinetic analysis has demonstrated two distinct uptake systems for GABA in all the brain regions examined. One system has a relatively high substrate affinity (Km= 1.2 ± 10-5 M) while the other has a lower affinity (Km= 4 ± 10-4 M). Studies at low GABA concentration (5 ± 10-8 M), as well as estimates of maximum velocities, have shown that the distribution of the high affinity uptake system is heterogeneous. Cortex, hypothala mus, midbrain and hippocampus have relatively high uptake rates while the striatum, cerebellum and pons and medulla have a lower uptake rate. Maximum velocities for the low affinity uptake system show much less regional variation. Lithium, either added to the incubation medium or fed to rats, had no effect on the uptake of GABA by cortical slices.