Maze-Learning Ability in Rat Populations after a Number of Generations of Gonadal Irradiation

Abstract

Maze-learning ability has been studied since August, 1956, in offspring from irradiated and unirradiated rat populations. ln three separate experiments, doses of 600 r, 800 r, and 1000 r of 2-Mev x rays were administered to the gonads of all males in each generation, immediately prior to mating, in populations consisting of 30, 30, and 60 mating couples, respectively. These and the corresponding control populations were studied over periods of 6, 4, and 2 generations, respectively. Maze-learning tests on unirradiated offspring from the irradiated and control populations in each generation, the tests extending over 6 weeks for any one animal, have been carried out on a total of 464 animals. No significant effect of irradiation on learning ability was observed in the 600- r experiment. However, in the two other experiments mistakes were made more often by offspring from irradiated populations, amounting to a 20% and a 36% increase in the actual numbers of errors in the 800-r and 1000-r experiments, the combined data for all generations being used in each case. The interpretation is complicated by a reduction in litter size in the irradiated, but not in the control, populations, and by the remote possibility of genetic drift inmore » both the control and the irradiated groups. There is some evidence that the observed reductions in average learning ability are not due wholly to differences in the numbers of animals showing extremely poor maze performance.« less