Post training lysine-vasopressin injections increase conditioned suppression in rats

Male rats were trained to lever press for food reward on a variable interval schedule of reinforcement. When stable response rates had been achieved they were trained to avoid footshock (UCS) in a two way shuttle box using a compound conditioning stimulus (CS) of tone and light. Having reached the learning criterion of ten consecutive avoidance responses they were returned to their home cage and injected with saline or lysine vasopressin (LVP 1 microgram/rat/SC) after 30 min. Twenty four hours later, the suppressive effect of the avoidance CS on the appetitive baseline was tested. Rats which had been injected with LVP after avoidance training showed significantly more suppression of the operant response than saline controls. The results are discussed in terms of the behavioural substrate underlying the long term effects of vasopressin on behaviour.