Extinction of conditioned odor potentiation of startle.

Several recent studies with rats (Sprague-Dawley strain) have documented that an odor previously paired with shock potentiates the acoustic startle response, a phenomenon referred to as conditioned odor potentiation of startle (OPS). A surprising finding in these studies was that OPS did not extinguish even though the odor was present throughout the 25-min test session. Therefore, the present study more fully examined extinction of OPS. The results of Experiment 1, which employed both within-subject and between-group comparisons, showed that extinction of OPS occurred in adult rats only after several days of testing. Experiment 2 used the between-group procedure and found similar results with 23-day-old rats, the youngest age that exhibits the OPS effect. Experiment 2 also showed that giving rats 15 odor-shock pairings at 16 days of age, an age where they acquire the odor-shock association but cannot express it via OPS, does not increase subsequent resistance to extinction following odor-shock pairings at 23 days of age. Taken together, the results of this study show that (1) although OPS is somewhat resistant to extinction, it does extinguish with repeated tests and (2) suggests that there are no age differences in the rate of extinction of OPS.