ACTH produces long-lasting recovery following partial extinction of an active avoidance response

Recent data suggest that ACTH administration produces recovery of an extinguished passive avoidance response at an unusually long injection-to-test interval. The present experiment sought to explore further the durability of recovery by examining the effect of ACTH following extinction of one-way active avoidance. Adult rats were injected with 16 IU ACTH, an equivalent volume of the ACTH vehicle gel, or saline 48 h after a previously learned active avoidance response was partially extinguished. Different groups from each treatment condition were tested 15 min, 24 h, or 7 days after injection. ACTH improved avoidance performance at all injection-to-test intervals relative to saline and vehicle gel injected controls. These data indicate that unlike reversal of other types of performance decrements, in which the effect of ACTH appears to be transient, administration of the hormone following an extinction treatment can produce enduring improvement of avoidance performance.