Impairment of learning and memory and the accessory symptom in aged rats as senile dementia model (1) - Emotional behavior

It is well known that there is an increase of emotional behavior in senile dementia. There are few studies investigating age-related emotional behavior. We attempted to investigate emotional behavior of aged rats using various tests. Locomotor activity for 24 h decreased in aged rats compared with that in young rats. There was no difference in locomotor activity between light and dark periods in aged rats. There was no visual abnormality on light/dark discrimination test in aged rats. It suggests that locomotor activity during dark period may be impaired by aging. Head-dips and social interaction time in hole board and social interaction tests, respectively decreased, while start latency, defecation and urination in open field test increased in aged rats. Furthermore, ambulation and rearing in hole board, social interaction and open field tests decreased, and entries into open or closed arms in elevated plus-maze test reduced in aged rats compared with those in young rats. These findings suggest that anxiety may increase, but spontaneous activity decrease in aged rats. These results indicate that aged rats may be useful as an accessory symptom model of senile dementia.