The effect of low-pressure blast-wave exposure on middle-aged rats

The objective of this study was to explore how age at the time of blast-exposure affects behavioral and cognitive responses. Non-anesthetized male middle-aged rats were exposed to visual, auditory, olfactory, and tactile effects of a low-pressure explosive blast-wave produced by exploding a thin copper wire. Validated cognitive and behavioral paradigms were used to assess both the PTSD-phenotype and mTBI-phenotype. Naïve middle-aged rats displayed very heterogeneous individual responses. Whereas some middle-aged rats performed as well as young rats, others showed pronounced cognitive deficits and several were unable to find the platform at all. The variance made it difficult to determine "normal" criteria for learning patterns. The middle-aged rats displayed significantly worse behavioral outcomes following blast exposure than young rats. This finding was especially evident in depression-related behavior, and there was a significant decline in spatial reference learning ability, which
was not observed in younger rats. These results indicate that middle-aged rats respond differently to blast exposure than young rats and that age is an important factor to consider in pre-clinical efficacy studies. This study emphasizes the complexity of working with older subjects, both in terms of determining "baseline norms" and in terms of the pattern of responses to the experimental paradigm. These characteristics are also found in studies involving older human subjects, certainly in terms of age-related baseline characteristics.