Two experiments were conducted in which inbred C57BL/6J and DBA/2J mice were trained in an active avoidance jump-up task under distributed practice conditions at a variety of ages comprising a large part of their life-span. DBA/2J mice were found to be basically an escaping strain and exhibited little change in behavior as a function of age. C57BL/6J mice developed consistent avoidance behavior when training was initiated at 31-36 days of age. Avoidance behavior appeared to reach a peak in the 45-day-old group and progressively decreased in 145- and 560-day-old groups. Increased footshock intensity in old DBA/2J mice enhanced escape responding without increasing avoidance responding. Increased footshock intensity in old C57BL/6J mice enhanced avoidance responding.

No abstract

Animal models of human aging problems are potentially of enormous value to gerontological research. Models of behavioral problems have not often lived up to their promise. This review examines one such model system, avoidance learning in aging rodents. This model system has become increasingly popular among behavioral gerontologists, yet it has not provided the unambiguous answers to experimental questions which investigators expected. Our effort has been to determine why the system has failed, and to provide useful suggestions for future research. At the same time we have tried to provide a comprehensive review of the relevant literature and to assess the strengths and weaknesses of studies which have been conducted in the last two decades.

Mice of two ~nbred strains, C57BL/6J and DBA/2J, and the FI hybrid of a cross berween them were trained in an active avoidance jump-up cask under distributed practice conditions. Significant differences in the performance of mice of the rwo strains were observed, with relatively poor performance by DBA/ZJ mice and relatively good performance by C57BL/6 mice. The performance of Fl hybrid mice did not differ significantly from DBA/2J mice. Crosses were made to produce segregating generations of mice. Their performance supported a single-locus model of inheritance for active avoidance jump-up behavior. Under these experimental conditions the dominant allelle (Aap" was associated with poor performance while homozygosiry for the recessive allele (Aapb) was associated with superior performance.

A group of experiments were conducted to assess the interaction between environmental factors and specific genetic loci upon the performance of mice in avoidance learning situations. The performance of all mice was better in passive-avoidance than in active-avoidance situations. The performance of C57BL/6J mice was generally superior to that of DBA/2J mice. C57BL/6J mice usually avoided foot-shocks, while DBA/2J mice attempted to escape them. DBA/2J mice performed poorly in the presence of mild foot-shocks, while C57-BL/6J mice performed poorly in the presence of intense foot-shocks. Analysis of the data suggested that the loci involved probably exerted their influence by affecting the subject's response to its environment.