Sensitive Assessment of Hippocampal Learning Using Temporally Dissociated Passive Avoidance Task.

The temporally dissociated passive avoidance (TDPA) paradigm is a variant of passive avoidance testing, and allows for more sensitive investigation of mild impairments in avoidance learning. Passive avoidance learning measures the latency to enter a "dark" context in which an aversive stimulus (foot shock) has been previously experienced using a light-dark box paradigm. Briefly, the animal is placed into the light side of the box and the time spent to cross into the dark side is measured. After entry into the dark chamber, the animal receives a mild (0.4-1.6 mA) footshock and is removed from the box. After a period of time, typically 24 h (note that this is entirely dependent on whether various levels of memory retention, e.g., short or long, are being measured), the animal is placed back into the box and cross-over latency is measured. Passive avoidance is learned after one trial and results in a robust increase in crossover latency. This behavior requires the association between a normally neutral environment and an aversive stimulus, and is dependent on hippocampal function (Stubley-Weatherly et al., 1996; Impey et al., 1998). TDPA extends this learning across multiple once-daily trials, producing a more graded and malleable latency score, and thus allows a more sensitive evaluation of changes in hippocampal function The task remains dependent on an intact hippocampus (Zhang et al., 2008), and subtle changes in hippocampal gene expression can result in robust alterations in TDPA latency scores (Eagle et al., 2015). We describe here a common method used to assess TDPA learning in mice.