Stressor-provoked response patterns in a swim task: modification by diazepam.

When placed in a water-filled arena in which one area is illuminated mice tend to remain in the illuminated region. Moreover, in a forced-swim task mice initially exhibit vigorous responding followed by a rapid decay of active swimming, and the adoption of a characteristic floating posture. Immediately following exposure to inescapable shock the response invigoration was appreciably enhanced, as was the tendency to remain in the illuminated region of the arena. Administration of low doses of diazepam (0.5 and 1.0 mg/kg) prior to testing effectively eliminated the response invigoration, as well as the response of approaching the illuminated region of the arena. It is proposed that the behavioral variations evident soon after uncontrollable shock are related to a transient increase of anxiety or vigilance. Moreover, it is suggested that several time-dependent behavioral variations associated with inescapable shock may be related to alterations of anxiety.