The distribution of monoamines and their metabolites in the brain structures of rats at later periods after exposure to 12C ions

Abstract

We investigated the levels of monoamines and their metabolites in certain brain structures of rats at 30 and 90 days after exposure to carbon ions (12C) with an energy of 500 MeV/nucleon. The linear energy transfer and radiation dose were 10.6 keV/µm and 1 Gy, respectively. The concentrations of substances were measured in five structures of the brain, including the prefrontal cortex, nucleus accumbens, hypothalamus, hippocampus, and striatum. On day 30 after the exposure, the most pronounced changes in the concentration of monoamines and their metabolites were observed in the nucleus accumbens; the smallest changes were found in the hippocampus and striatum. After 90 days, significant changes were still present in the nucleus accumbens. At the same time, these changes became less evident in other structures. A comparison of our results with the data of similar previous experiments (24 hours after exposure) showed that the most pronounced effect was observed soon after radiation exposure. The induced damage diminished at a later period. Based on the results of our study, we made the hypothesis that the change in the metabolism of monoamines may be compensated if the linear-energy transfer values were relatively low (10.6 keV/μm). At higher values of linear-energy transfer, compensatory and regenerative processes did not occur; the effect increased with time. An increased susceptibility of the nucleus accumbens was found at all the time points after the exposure, which may indicate an important role of this brain structure in the radiation-induced impairment of cognitive functions and emotional and motivational states.