Post-training vasopressin injections may facilitate or delay shuttle-box avoidance extinction

Abstract

After training to avoid footshock in a two-way shuttle box rats were injected with lysine vasopressin (LVP) and returned to the shuttle box 24 hr later for 10 extinction trials. Experiment 1 shows that when injected 30 min after training subsequent extinction responding varied as an inverted “U”-shaped function of the LVP dose within the range tested (0.036 to 2.97 μg/rat). Responding was increased with 0.11 μg/rat whereas 2.97 μg/rat reduced responding. Experiment 2 shows that these two doses also have opposite effects when injected 30 min after training at a higher shock level (0.45 mA/2 sec). Experiment 3 examined time-dependent effects for these oppositely acting doses and shows that whereas 0.11 μg/rat increased extinction responding when injected 0 or 60 min after training, 2.97 μg/rat was ineffective when injected immediately and increased responding when injected 60 min after training. The data are discussed in relation to the hypothesis that vasopressin facilitates memory consolidation and with respect to anomalous time × dose interactions with various post-training drug treatments.