The CPFE procedure took place in three phases: preexposure, training and testing with the preexposure-to-training interval varying across groups but with the training and testing sessions always occurring 24 h apart. On the preexposure day (PND 24 or PND 31), pups were preexposed using PYZD-4409 multiple preexposure procedure  and  to either the training context (Pre Group) or the alternate context (Alt-Pre Group). The Pre Group pups were taken from their home cages, weighed, placed into opaque transport boxes and wheeled to a waiting area outside of the conditioning room while the chambers were cleaned using a 5% ammonium hydroxide solution. The Alt-Pre Group pups experienced the same procedure but were taken to the alternate context on the preexposure day for a total time approximately equal to carrying capacity of the Pre Group. Pups were taken from their opaque transport boxes and placed inside the chambers for 5 min then removed and placed back in the chamber 5 times for 1 min at approximately 1 minute intervals.