In utero release from a single transient hypoxic episode: a positive reinforcer?

In this experiment, fetal rats, Rattus norvegicus, were subjected to a single transient hypoxic episode before an injection of orange essence or isotonic saline through the uterine and amniotic membranes into the amniotic fluid within 5 s of the release from hypoxia. Other animals experienced either orange essence or isotonic saline alone following no hypoxic episode. At 120 days after birth, adult rats were given a two-choice preference test between orange and water. Only those animals who experienced the orange following release from hypoxia showed a preference for the orange. These results suggest that the acquired preference is not a result of simple exposure but is suggestive of a role for reoxygenation as a positive reinforcer.