Elevated plus-maze performance of Fischer-344 rats as a function of age and of exposure to 56Fe particles

Authors: RABIN, BERNARD - UMBC; CARRIHILL-KNOLL, KIRSTY - UMBC; CAREY, AMANDA - NORTHEASTERN UNIVERSITY; Shukitt-Hale, Barbara; Joseph, James; FOSTER, BRIAN - UMBC

Submitted to: Advances in Space Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2006
Publication Date: 3/15/2007
Citation: Rabin, B.M., Carrihill-Knoll, K.L., Carey, A.N., Shukitt Hale, B., Joseph, J.A., Foster, B.C. 2007. Elevated plus-maze performance of Fischer-344 rats as a function of age and of exposure to 56Fe particles. Advances in Space Research. 39:981-986.

Interpretive Summary: The aging process is characterized by a series of changes in brain chemical functioning and in physical and intellectual performance. Exposure to iron particles, a component of cosmic rays, produces accelerated aging such that these changes that are characteristic of aged organisms are observed in young animals. In addition to changes in physical and intellectual performance there are increases in measured anxiety. The present study was designed to determine the relationships between aging and exposure to iron particles on anxiety. Anxiety was measured using the elevated plus-maze. The maze is elevated off the ground and shaped like a plus sign. Two arms have walls so the rats cannot see out of the maze and two arms are open so the rats can see the ground. Rats that are more anxious will explore the open arms less and stay in the closed arms. Rats ages 2, 7, 12, and 16 months at the time of irradiation were exposed to various doses of iron particles. Concordant with previous results, the oldest rats spent less exploring the open arms of the maze. The dose needed to produce increased levels of anxiety was related to the rat’s age at the time of irradiation, such that lower does were needed to produce reduced exploration of the open arms in the rats radiated at 7 and 12 months of age than were needed in the 2-month old rats. These results suggest the possibility that exposing middle-aged astronauts to cosmic rays during exploratory missions, and the resultant effects on exploration-induced anxiety, may affect their ability to successfully complete mission requirements

Technical Abstract: The aging process is characterized by a series of changes in neurochemical functioning and in motor and cognitive performance. Exposure to 56Fe particles, a component of cosmic rays, produces accelerated aging such that these changes that are characteristic of aged organisms are observed in young animals. In addition to changes in motor and cognitive performance there are increases in anxiety measured using the elevated plus-maze. The present study was designed to determine the relationships between aging and exposure to 56Fe particles on anxiety. Fischer 344 (F344) rats 2, 7, 12, and 16 months of age at the time of irradiation were exposed to 56Fe particles (0.5-2.0 Gy). Concordant with previous results, the oldest rats spent less time exploring the open arms of the maze. Exposure to 56Fe particles also produced decreased exploration of the open arms of the plus-maze. The dose needed to produce increased levels of anxiety was a function of age at the time of irradiation, such that lower doses were needed to produce reduced exploration time in the rats radiated at 7 and 12 months of age than were needed in the 2-month old rats. These results suggest the possibility that exposing middle-aged astronauts to cosmic rays during exploratory class missions outside the magnetosphere, and the resultant effects on exploration-induced anxiety, may affect their ability to successfully complete mission requirements.