Abstract
1. The concentration of epinephrine, norepinephrine and dopamine, and the activity of norepinephrine N-methyltransferase, the epinephrine-forming enzyme, were determined in hypothalamus and brain stem in several species. 2. Epinephrine concentration in hypothalamus, a nerve terminal region, varied in the order frog > turtle > chicken > cat > dog > pigeon > rat > ferret > hamster > mouse, with concentrations being undetectable in rabbits, horses and guinea pigs. 3. Epinephrine concentration was lower than norepinephrine concentration in all species except the frog. 4. NMT activity was detected in all species except guinea pigs. 5. Epinephrine concentration was lower in brain stem, a cell body region, than in hypothalamus in all species. Only in the frog brain stem was there more epinephrine than norepinephrine. 6. No epinephrine or NMT activity was detected in either brain region in guinea-pigs.
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