Effects of age on open-field behavior of male rats

As age advances, the performance of animal behavior declines gradually. The purpose of this study was to investigate the onset of age-related changes in open-field behavior of rats from a wide age spectrum. Male Long-Evans rats, ranging from 2 to 22 months, were placed in an open-field apparatus during the dark phase for a cumulative period of 28 min. Data were collected for the following parameters of open-field behavior: horizontal activity (HA), total distance (TD), stereotypy count (SC), vertical activity (VA), movement time (MT) and margin time (MGT). The highest value of HA, TD, SC and MT was found in rats at the age of 3 months. After 3 months, the values for these parameters gradually declined, subsequently reaching statistical significance by 6 months (HA, TD and SC) or 8.5 months (MT) of age. Maximum activity of VA occurred at 8.5 months of age and thereafter gradually declined with increasing age, however, no significantly statistical difference was reached as compared to the highest value. In contrast, the values for MGT gradually declined after 2 months of age, thereby reaching statistical significance by 11 months of age. These results indicate that the onset of age-related decline in open-field behavioral parameters can differ and the age-related changes in open-field behavior depends on observational parameters.