Adenomatous polyposis coli heterozygous knockout mice display hypoactivity and age-dependent working memory deficits

Abstract

A tumor suppressor gene, Adenomatous polyposis coli (Apc), is expressed in the nervous system from embryonic to adulthood stages, and transmits the Wnt signaling pathway in which schizophrenia susceptibility genes, including T-cell factor 4 (TCF4) and calcineurin (CN), are involved. However, the functions of Apc in the nervous system are largely unknown. In this study, as the first evaluation of Apc function in the nervous system, we have investigated the behavioral significance of the Apc gene, applying a battery of behavioral tests to Apc heterozygous knockout (Apc(+/-)) mice. Apc(+/-) mice showed no significant impairment in neurological reflexes or sensory and motor abilities. In various tests, including light/dark transition, open-field, social interaction, eight-arm radial maze, and fear conditioning tests, Apc(+/-) mice exhibited hypoactivity. In the eight-arm radial maze, Apc(+/-) mice 6-7 weeks of age displayed almost normal performance, whereas those 11-12 weeks of age showed a severe performance deficit in working memory, suggesting that Apc is involved in working memory performance in an age-dependent manner. The possibility that anemia, which Apc(+/-) mice develop by 17 weeks of age, impairs working memory performance, however, cannot be excluded. Our results suggest that Apc plays a role in the regulation of locomotor activity and presumably working memory performance.

Keywords: Apc; behavioral test battery; hypoactivity; locomotor activity; working memory performance.

Figure 1

Decreased locomotor activity of Apc^+/−mice 7–9 weeks of age. (A) Distance traveled of Apc^+/− mice (Mutants) was significantly decreased compared to wild-type mice (Controls) in light and dark. (B) No significant difference in time spent in light between genotypes was detected. (C) The number of transitions between the light and dark sides of Apc^+/− mice was significantly decreased. (D) No significant difference in latency to light between genotypes was observed. Apc^+/− mice, n = 18; wild-type mice, n = 22.

Figure 2

Decreased locomotor activity of Apc^+/− mice 8–9 weeks of age in an open-field test. (A) Total distance was significantly decreased in Apc^+/− mice compared to wild-type mice in the first 30 min and in the entire 60 min. (B) Vertical activity of Apc^+/− mice was significantly decreased. Apc^+/− mice showed a slight, but not significant, decrease in time spent in the center area (C), and stereotypic counts (D). Apc^+/− mice, n = 18; wild-type mice, n = 22.

Figure 3

Decreased locomotor activity of Apc^+/− mice 8–9 weeks of age in a social interaction test. Total duration of contacts (A), number of contacts (B), total duration of active contacts (C), mean duration of per contact (D), and distance traveled (E) were analyzed. Statistical difference between genotypes was not found in total duration of contacts, number of contacts, total duration of active contacts, or mean duration of per contacts. Distance traveled of Apc^+/− mice was significantly decreased compared to wild-type mice. Apc^+/− mice, n = 9 pairs; wild-type mice, n = 11 pairs.

Figure 4

Normal performance in behavioral despair of Apc^+/− mice 9–10 weeks of age in the Porsolt forced swim test. (A) Apc^+/− mice showed a significant decrease in immobility time compared to wild-type mice at day 1, whereas there was no significant difference between genotypes at day 2. (B) No significant differences between genotypes in distance traveled were observed. Apc^+/− mice, n = 18; wild-type mice, n = 22.

Figure 5

Suppressed startle response and normal prepulse inhibition in Apc^+/− mice 8–10 weeks of age. (A) Acoustic startle response for the 110 and 120 dB startle stimulus was significantly suppressed in Apc^+/− mice. (B) Apc^+/− mice showed normal prepulse inhibition for the 74 and 78 dB prepulse sound levels. Apc^+/− mice, n = 13; wild-type mice, n = 21.

Figure 6

Age-dependent impairment in working memory performance of Apc^+/− mice in the eight-arm radial maze test. Adult Apc^+/− mice 11–12 weeks of age showed impaired working memory performance (A–B). (A) Adult Apc^+/− mice showed a significant decrease in the number of different arm choices in the first eight entries compared to controls during both trials without a delay (blocks 1–19) and trials with a delay (blocks 20–22). (B) Apc^+/− mice exhibited a decrease in the number of revisiting errors during the earlier trials (blocks 1–7), and an increase in the later trials (blocks 8–19) and the trials with a delay (blocks 20–22). There was no significant difference in the number of revisiting errors between genotypes during the whole session. Apc^+/− mice, n = 13; wild-type mice, n = 21. Young Apc^+/− mice 6–7 weeks of age showed almost intact working memory performance in spatial memory tasks (C–D). (C) There was no significant difference between genotypes during the whole session in the number of different arm choices the first eight entries. (D) Apc^+/− mice exhibited a slight but significant increase in the number of revisiting errors during the earlier trials (blocks 5–10) and the later trials (blocks 13–16). There was no significant difference in the number of revisiting errors between genotypes during the whole session. Apc^+/− mice, n = 14; wild-type mice, n = 11.

Figure 7

Increased levels of freezing and decreased locomotor activity of Apc^+/− mice during conditioning, context, and cued testing with altered context testing 11–12 weeks of age. (A) Apc^+/− mice showed increased freezing during the conditioning phase, context testing, and cued testing with altered context before the auditory cue (before tone), while freezing after the auditory cue (after tone) was normal.(B) Apc^+/− mice showed a decrease in distance traveled immediately after footshocks 2 and 3 in the training phase. Apc^+/− mice, n = 23; wild-type mice, n = 21.