Consolidation of auditory fear memories formed by weak unconditioned stimuli requires NMDA receptor activation and de novo protein synthesis in the striatum.

Fear is one of the most potent emotional experiences and is an adaptive component of response to potentially threatening stimuli. Cumulative evidence suggests that the amygdala plays a central role in the acquisition, storage and expression of fear memory. We previously showed that the selective ablation of striatal neurons in the adult brain impairs the long-term, but not short-term, memory for auditory fear conditioning with a lower-intensity footshock. This finding raises an intriguing possibility that long-term auditory fear memory may be consolidated in the striatum. There was a significant difference in the freezing responses between two groups of mice subjected to paired and unpaired conditioning, indicating that the auditory fear conditioning with a lower-intensity footshock is an associative learning. Post-conditioning infusion of NMDA receptor inhibitors into the striatum suppressed the consolidation of auditory fear memory when mice were conditioned with a low-intensity footshock. Furthermore, intra-striatum infusion of protein synthesis blocker anisomycin immediately or 1 h after the conditioning prevented the formation of auditory fear memory. On the other hand, the infusion of anisomycin 3 h after conditioning exerted little effect on the auditory fear conditioning, consistent with the presence of a critical time window of protein synthesis for memory consolidation. These results suggest that NMDA receptors and de novo protein synthesis in the striatum are crucial for the consolidation of auditory fear memory formed with a low-intensity unconditioned stimulus.