Age-series characteristics of locomotor activities in spontaneously hypertensive rats: A comparison with the Wistar–Kyoto strain

This study was to investigate the behavioral specificities of spontaneously hypertensive rats (SHR) and compare them with Wistar–Kyoto (WKY) controls using a 1-year longitudinal study of locomotor activity. Rat locomotor activity was examined every week at 4–12 weeks of age and every month at 4–12 months of age using an Automated Digiscan Activity Monitor system. Six behavioral variables were collected and analyzed: horizontal activity (HA), total distance (TD), movement time (MT), vertical activity (VA), stereotypy count (SC), and margin time (MGT). In general, a significant weekly and monthly age-dependent change (p < 0.01) in SHR was shown in the HA, TD, VA, SC and MT variables, whereas MGT showed no significant differences (p > 0.05). However, except for the first observations, SHR was significantly hyperactive relative to WKY for HA, VA, TD, MT and SC (p < 0.01) before 6 months of age. MGT in SHR were significantly lower than those of WKY (p < 0.01) before 3 months of age. Only for VA, SHR was more hyperactive than WKY (p < 0.01) and sustained for 12 months in age. From the present results, by extending the observations of locomotor activity testing from 4 weeks to 12 months of life, we were able to observe an interesting strain difference between SHR and WKY in the development pattern of spontaneous activity levels.