Abstract

The accumulation of H³-norepinephrine into slices from seven different areas of rat brain has been studied. There were marked regional differences in amine accumulation. The striatum showed the greatest accumulation, the cerebellum and medulla oblongatapons had lowest values and the hypothalamus, hippocampus, midbrain and cerebral cortex were intermediate. Amine accumulation was linear in all areas for 45 min. C¹⁴-urea was taken up to a similar extent by all regions and equilibrated between slice and medium with 5 min of incubation. There were regional differences in the susceptibility of H³-norepinephrine accumulation to inhibition by desmethylimipramine or reserpine. The striatum and cerebellum were least and most sensitive, respectively, to the effects of these drugs. Desmethylimipramine inhibited amine accumulation with both 5- and 45-min incubations, whereas reserpine was effective only with a 45-min incubation. When brain slices were incubated with concentrations of H³-norepinephrine varying from 0.05 to 0.80 µM, regional differences in saturation of amine accumulation were detected. The cerebellum was the only area in which amine accumulation was not saturable. In the other regions, graphic analysis permitted estimation of K_m values. The midbrain and striatum showed the highest K_m values, 2.0 x 10^-6 M and 1.0 x 10^-6 M, respectively; K_m values in the other areas were between 4.0 x 10^-7 M and 5.0 x 10^-7 M. These findings suggest regional differences in neuronal affinity for norepinephrine.