The broad goal of the proposed project is to understand how long-term memories are stored in the brain through the activity of protein kinase Mzeta (PKM?). Using rats, this project will determine the specific subset of hippocampal-dependent associations that require PKM? activity for maintenance to better understand PKM? requirements in the brain.
Three specific aims will be addressed.
The first aim i s to determine whether PKM? activity is differentially required in the hippocampus and amygdala to maintain aversive, contextually-based memories. To achieve this aim, trace fear conditioning (TFC) will be used to create an aversive context-based memory that requires both the hippocampus and amygdala for acquisition (1,2). In TFC, a neutral conditioned stimulus (CS) is paired with an aversive unconditioned stimulus (US) with an empty trace period separating the two stimuli.
The second aim, which addresses whether appetitive spatial memory requires hippocampal PKM? activity, will be achieved using the spatially-based 8-arm radial arm maze task. In the radial arm maze task, rats must use spatial cues to determine which 4 of the 8 available arms contain hidden sucrose pellets. This task requires the hippocampus for acquisition and relies on external spatial cues in the training room, rather than contextual cues present within the apparatus (3).
The final aim i s to determine whether different requirements exist for hippocampal PKM? activity in the maintenance of spatial and contextual appetitive memory associations. To achieve this goal, the place conditioning task will be used to create a hippocampal- dependent appetitive context memory that can be directly compared with the spatial radial arm maze memory used in aim 2. In place conditioning, sucrose pellets are repeatedly available in one context while no reward is provided in a second context, leading the animal to prefer the sucrose-paired context in a subsequent test (40). In order to test the requirement for hippocampal PKM? activity in each of these forms of memory, a specific, potent inhibitor of PKM? activity called ?-pseudosubstrate inhibitory peptide (ZIP) will be locally microinjected into the dorsal hippocampus or amygdala during the storage phase of each memory (5). Animals will be prepared with bilateral cannulae aimed at the appropriate structure to allow for restricted, local injection of the drug. This set of experiments will elucidate whether PKM? is required to maintain a broad set of hippocampal- dependent memories or whether it only maintains an exclusive subset of memories that require the hippocampus for acquisition. This research has important implications for both improving memory storage and disrupting maladaptive memory storage in human patients.
This project will expand the current literature on the physiological underpinnings of long-term memory storage. Enhanced understanding of the biological mechanisms underlying memory maintenance is necessary not only to increase our basic knowledge of this process, but also to potentially translate research findings to both normal and disordered memory in humans.
