Exposure to low level chronic radiation leads to adaptation to a subsequent acute X-ray dose and communication of modified acute X-ray induced bystander signals in medaka (Japanese rice fish, Oryzias latipes)

PURPOSE: To determine the effect of acute high dose X-rays on the direct and bystander response of chronically exposed medaka in vivo using the fish communication model. METHODS: Medaka were obtained from the Low Dose Rate Irradiation Facility (LoDIF) located at the Savannah River Ecology Laboratory (SREL), University of Georgia, Aiken, South Carolina, USA where they had been exposed over 264 days to cumulative total doses of 0, 0.03, 0.66 and 5.88 Gy. They were exposed to the acute dose at McMaster University and then allowed to swim with unexposed medaka. All groups were sacrificed and fins were cultured as explants and assayed using an established technique and reporter assay. RESULTS: Directly irradiated medaka with no chronic exposure showed a classic in vivo bystander response. Chronic pre-exposure resulted in a chronic dose-dependent increase in reporter cell survival in directly exposed fish. A 'pro-survival' response was also seen in the bystander fish. The proteins bcl-2 (b cell lymphoma 2) and c-Myc (myelocytomatosis oncogene cellular) in tissue explants were good predictors of pro-life or pro-death signals. CONCLUSIONS: Environmentally relevant chronic exposure to medaka in vivo results in adaptive responses in fish subsequently irradiated with high acute doses and in communication of protective signals to fish swimming with exposed fish. The data have implications for interpretation of radiation effects in biota.