Abstracts

Rationale: Astronauts on deep-space exploration-class missions will face a host of new challenges and risks, including exposure to galactic cosmic radiation (GCR) at levels at least 50% higher than that experienced in low Earth orbit. Previous studies of GCR exposure have shown cognitive deficits in spatial memory and other hippocampal processes suggesting specific hippocampal damage, which can be related to seizure development. One consequence of such damage is an imbalance of neuronal inhibition and excitation, triggering neuronal network hyperexcitability. This study investigates whether then neuronal damage caused by HZE radiation can lead to seizure susceptibility Methods: Male Wistar rats were exposed to 600 MeV/n 56Fe at doses of 0, 1, 3, and 5 cGy. All rats underwent seizure testing with successive doses of 10 mg/kg pentylenetetrazol (PTZ) until they experienced a stage 5 seizure according to the Racine Scale. Seizure type, frequency, and latency were compared across cohorts.  Brain samples were collected to determine degree of neuronal damage. Results: The 5 cGy group reached stage 5 seizures more quickly than sham-irradiated controls (P=0.0213). This was consistent with all other irradiated rats, which showed a non-significant trend to experience seizures more quickly than controls. Additionally, seizures occurred at a higher frequency at lower doses in the irradiated cohorts than that seen in sham-irradiated controls. Conclusions: These observations indicate an increased seizure susceptibility among rats irradiated with 600 MeV/n 56Fe, suggesting a potential loss of dendritic spines associated with impairment of functionality of GABAergic interneurons. Further research is needed to ensure proper and adequate preparation and risk assessment and neuroprotection approaches for these missions Funding: NNX14AE73G