Active and passive avoidance learning in homozygous D.I. Brattleboro rats.

In homozygous D.I. rats and in Long-Evans controls the contemporaneous evolution of learning and retention of active and passive avoidance responses was studied by means of the light-dark box test. Passive avoidance performance of homozygous D.I. rats was almost equal to that of control subjects, while their active avoidance performance showed a significant deficit. Also, in homozygous D.I. rats the duration of the first freezing after being placed in the apparatus was consistently longer than in control Ss. The longer duration of this inhibitory behavior has been taken as an indication of a diminished ability of homozygous D.I. rats to respond to stress. The possible role of this diminished response to stress in determining the active avoidance deficit is discussed.