Decrease of learning capacity in offspring with increasing paternal age in the rat.

The same 15 male Wistar rats at the ages of 2.5, 6, 10, 14, 18, and 22 months were successively randomly mated with 2.5-month-old females. In a separate experiment, 15 male Wistar rats at the age of 2.5 months and 15 at the age of 23 months were simultaneously randomly mated with 2.5-month-old females. Offspring were evaluated in regard to the mean number per litter, sex ratio, frequency of gross external malformations, growth pattern, and mortality in the first 13 weeks of life and reproductive capacity at 13 weeks of age. They were also evaluated for spontaneous activity and emotionality with an open field test and for learning capacity with an avoidance conditioning test, both carried out between 10 and 13 weeks of age. Only learning capacity of the offspring, expressed in percentage of success for male or female, decreased consistently and significantly as the father's age increased. But females did not seem to be affected in the same way as males. The genetic implications are briefly discussed.