Behavioral reactivity in spontaneously hypertensive rats.

Spontaneously hypertensive rats of the Okamoto strain (SHR) were compared with inbred normotensive rats of the Wistar-Kyoto strain (WKY) and with normally bred Wistar rats (NT) in tests on the audiogenic immobility reaction (freezing), open-field behavior in a dark and an enlightened arena respectively, auditory startle response and male sexual behavior. Compared to the WKYs the SHRs showed increased locomotion and rearing in the open-field situations, reduced startle response and shortened immobility reaction. The SHRs differed in the same way from the NT rats with the exception for motor activity in the dark arena, where no differences were observed. The WKY rats showed less motor activity than the NT animals. Both SH and WKY rats showed shorter latency time for ejaculation than the NT rats. The characteristics of the behavior patterns displayed by the SH rats were interpreted as indicating a reduced propensity for fear reactions in this strain of rats compared to the WKY and NT strains used in the present study.