Adenalin, sodium amobarbital, and the "Kamin effect"

108 rats were given training in an approach-avoidance spatial conflict situation. Following completion of training, Ss were tested for retention of the avoidance response after intervals of 15 min., 3 hrs., or 24 hrs. Injections of saline, adrenalin, and sodium amobarbital were administered to independent groups at each retention interval. Avoidance responding was a non-nonotonic function of retention interval and was significantly affected by drug conditions. Saline groups showed a marked decrease in avoidance at 3 hrs. which subsequently recovered at 24 hrs. Sodium amobarbital was effective in reducing the overall level of fearful responding while Ss receiving adrenalin showed an increase in fear relative to the saline groups; no significant avoidance deficit at 3 hrs. was observed for the adrenalin and sodium amobarbital groups. The results were discussed in relation to the Karnin effect and it was concluded that the present evidence demonstrates conclusively that fear initially decreases over time as originally suggested by Karnin (1957).