Irradiation of mouse brain: effects on incorporation of tyrosine--14C into catecholamines in vivo and on uptake of NE--14C by brain slices in vitro

The short-term and long-term effects of deuteron irradiation are examined with regard to the rates of incorporation of tyrosine- 14C into catecholamines in the mouse brain. Groups of mice received doses of 5 K, 10 K, 15 K, or 20 K rad covering an area of 9 x 5 mm over the parietal, visual, and cerebellar cortex and extending to a depth of 2 mm from the skull. At 12 days, 40 days, or 12.5 months after irradiation 0.25 μCi of tyrosine- 14C was injected intracerebrally, and the animals were sacrificied 20 minutes after injection. Measurement of the endogenous NE content in the mouse brain indicated a decrease in NE level 40 days and 12.5 months after irradiation at 20 K rad. However, the rate of incorporation of tyrosine- 14C into catecholamines was increased with increasing doses of irradiation and peaked at 10 K rad. Results were consistent with all three groups of mice receiving the irradiation. Furthermore, within each dose range the group injected with tyrosine- 14C 40 days after irradiation showed the highest rate of incorporation. A different group of mice was sacrificed 60 days after receiving 5 K or 15 K rad or sham irradiation, and the uptake of NE- 14C in brain slices was studied. Results indicated that slices from brains irradiated at 15 K rad showed the highest uptake of NE- 14C. (U.S.)