Senescence-accelerated mouse (SAM): Age-related reduced anxiety-like behavior in the SAM-P/8 strain

Abstract

Age-related behavioral changes in the passive avoidance, food neophobia, elevated plus-maze, and water-lick conflict tests were studied using substrains of senescence-accelerated mouse (SAM-P/8 and SAM-R/1) at 2 to 20 months of age. SAM-P/8 mice exhibited a significant impairment of acquisition of passive avoidance compared with SAM-R/1 mice when they were trained repeatedly, and the acquired response in SAM-P/8 mice rapidly diminished in contrast to good retention in SAM-R/1 mice. SAM-P/8 mice showed an age-related decrease in the latency to eat novel food after a 24-h food deprivation as compared with SAM-R/1 mice at 2 to 12 months of age, despite no significant difference in latency to eat familiar food between the two strains. In the elevated plus-maze test, SAM-P/8 mice had apparent increases in the number of entries into open arms and time spent on open arms in comparison to SAM-R/1 mice at 4 through 12 months of age; this difference became obvious with aging, implying age-associated reduced anxiety in the SAM-P/8 strain. In addition, SAM-P/8 mice exhibited a significant increase in punished water drinking compared to SAM-R/1 mice in the water-lick conflict test, although unpunished water intake in SAM-P/u mice did not differ from that in the SAM-R/1 control. Aged SAM-R/1 mice, 20 months old, exhibited low anxiety-like behavior in the food neophobia and elevated plusmaze tests such as was seen in SAM-P/8 mice, when compared with young (4-month-old) SAM-R/1 mice. These results indicate that the SAM-P/8 strain shows age-related reduced anxiety-like behavior compared to the SAM-R/1 strain, which may be related to learning and memory impairment in the strain. It is suggested that the SAM-P/8 strain may be a useful animal model for studying emotional disorders and related memory impairments in dementia, which can be used at an early stage of age.