A threshold dose of heavy ion radiation that decreases the oxidative enzyme activity of spinal motoneurons in rats.

The effect of heavy ion radiation exposure of the spinal cord on the properties of the motoneurons innervating the slow soleus and fast plantaris muscles was investigated. A 15-, 20-, 40-, 50-, or 70-Gy dose of carbon ions (5 Gy/min) was applied to the 2nd to the 6th lumbar segments of the spinal cord in rats. After a 1-month recovery period, the number and cell body size of the irradiated motoneurons innervating the soleus and plantaris muscles did not differ from that of the non-irradiated controls, irrespective of the dose received. However, the oxidative enzyme activity of these motoneurons was decreased by heavy ion radiation at doses of 40, 50, and 70 Gy compared to that of the non-irradiated controls. This decrease in oxidative enzyme activity levels in the motoneurons returned to that of the non-irradiated controls after a 6-month recovery period. We conclude that heavy ion radiation at doses of 40-70 Gy reversibly decreases the oxidative enzyme activity of motoneurons in the spinal cord of rats.