PKMζ Maintains 1-Day- and 6-Day-Old Long-Term Object Location but Not Object Identity Memory in Dorsal Hippocampus

Continuous activity of the atypical protein kinase C isoform M zeta (PKM zeta) is necessary for maintaining long-term memory acquired in aversively or appetitively motivated associative learning tasks, such as active avoidance, aversive taste conditioning, auditory and contextual fear conditioning, radial arm maze, and watermaze. Whether unreinforced, nonassociative memory will also require PKM zeta for long-term maintenance is not known. Using recognition memory for object location and object identity, we found that inactivating PKM zeta in dorsal hippocampus abolishes 1-day and 6-day-old long-term recognition memory for object location, while recognition memory for object identity was not affected by this treatment. Memory for object location persisted for no more than 35 days after training. These results suggest that the dorsal hippocampus mediates long-term memory for where, but not what things have been encountered, and that PKM zeta maintains this type of spatial knowledge as long as the memory exists. (C) 2009 Wiley-Liss, Inc.