Fig. 4. Effects of age, repeated measurements, and genotype. ( A ) Comparison of locomotor activity in the open field between young and aged control mice of both genotypes. Age was a significant factor only in knockout (KO) mice, where aged mice moved a significantly shorter distance than young mice did ( P < 0.01). Among wild-type (WT) mice, no effect of age was observed. Genotype was a significant factor only in young mice, where KO mice moved a significantly longer distance than WT mice did ( P < 0.01). In aged mice, no such effect of genotype was observed. ( B ) Effects of age on locomotor activity in the plus maze, expressed as number of transitions between the walled arms of the apparatus. Aged KO mice made fewer transitions than young KO mice did ( P < 0.01), whereas no such age difference was observed in WT mice. ( C ) Comparison of locomotor activity in the open field between the first and second test session, i.e. , effect of habituation, in young control mice of both genotypes. Locomotor activity is significantly higher in young KO mice than in young WT mice on both the first and second test occasion ( P < 0.01 for both). The reduction in activity from the first to the second session is significant for all groups ( P < 0.01 for all groups). ( D ) Comparison of locomotor activity in the open field between the first and second test session, i.e. , effect of habituation, in aged control mice of both genotypes. In aged mice, there is no longer any difference between KO and WT in activity on the first and second sessions. However, within each genotype, the difference from the first to the second session is significant ( P < 0.001 for both). Statistical significance for planned comparisons between groups is indicated above the corresponding horizontal lines .ko =β2knockout control group (young n = 18, aged n = 11); wt = wild-type control group (young n = 20, aged n = 7). ** P < 0.01. *** P < 0.001. - P > 0.05.
