Effects of vasopressin on spontaneous black-white choices in a T-maze

The effects of subcutaneous administration of vasopressin on spontaneous black-white choice were investigated to determine whether they could account for modifications of performances during learning. First, pretrial injections of 0.2 microgram of lysine-vasopressin (LVP) were given to rats fed ad lib submitted after the last injection to ten consecutive choices in the T-maze. Rats received one or five injections and were tested after either 30 minutes or 24 hours. Treatment with LVP reduced natural photophobia and modified the activity. A more striking effect was observed after one injection and with an injection-test interval of 30 min. Second, the influence of repeated injections of LVP on free choices was studied in food-motivated rats. The effect of repeated injections was marked, suggesting greater sensitivity to treatment in such rats. Third, we compared the action of posttrial administration of the peptide on the behavior of food-restricted rats submitted to appetitive learning in the T-maze, or to free choices. The treatment slightly disturbed the learning of the white arm and altered the preference for black in free choices condition. The two actions were different, showing that the effect on spontaneous behavior cannot account for the effect on learning.