Effects of Exposure to Fe Particles or Protons on Fixed-ratio Operant Responding in Rats

Protons / Fe / Fixed-ratio / Conditioning On long-duration trips outside of the magnetosphere, astronauts will be exposed to protons and to heavy particles which can affect their performance of required tasks. It is essential to determine the range of behaviors that might be affected by exposure to these types of radiation in order to understand the nature of behavioral deficits and to develop effective countermeasures. The present experiment examined the ability of rats to make an operant response following exposure to protons (250 MeV, 4 Gy) or Fe particles (1 GeV/n, 1 or 2 Gy). Following irradiation, rats were trained to press a lever in order to obtain food reinforcement. They were then placed on an ascending fixed-ratio schedule from FR-1 (each lever press rewarded with a food pellet) through FR-35 (35 lever presses required for 1 food pellet). Rats exposed to 4 Gy of protons or 1 Gy of Fe particles responded similarly to controls, increasing their rate of responding as the ratio increased. However, rats exposed to 2 Gy of Fe particles failed to increase their rate of responding at ratios greater than FR-20, indicating that rats exposed to 2 Gy of Fe particles cannot respond appropriately to increasing work requirements.