Inhibition of protein synthesis or mTOR in the basolateral amygdala blocks retrieval-induced memory strengthening.

Fear memory retrieval can lead to either reconsolidation (accompanied or not by strengthening of the memory trace) or extinction. Here, we show that non-reinforced retrieval of inhibitory avoidance (IA) conditioning can induce memory strengthening assessed in a subsequent retention test trial. Infusion of the protein synthesis inhibitor cycloheximide or the mTOR inhibitor rapamycin into the rat basolateral complex of the amygdala (BLA) after a reactivation (retrieval) session impaired retrieval-induced strengthening. Intra-BLA infusion of the mRNA synthesis inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) after retrieval had no effect. These findings provide the first evidence suggesting that non-reinforced IA retrieval can lead to memory strengthening through a mechanism dependent on protein synthesis and mTOR activity in the BLA.

Administration of the phosphodiesterase type 4 inhibitor rolipram into the amygdala at a specific time interval after learning increases recognition memory persistence.

Here we show that administration of the phosphodiesterase type 4 (PDE4) inhibitor rolipram into the basolateral complex of the amygdala (BLA) at a specific time interval after training enhances memory consolidation and induces memory persistence for novel object recognition (NOR) in rats. Intra-BLA infusion of rolipram immediately, 1.5 h, or 6 h after training had no effect on retention tested at 1, 7, and 14 d later. However, rolipram infused 3 h post-training promoted memory persistence for up to at least 14 d. The findings suggest that PDE4 inhibition in the BLA can enhance long-term memory formation when induced specifically 3 h after learning.

Inhibition of mTOR by rapamycin in the amygdala or hippocampus impairs formation and reconsolidation of inhibitory avoidance memory.

Mammalian target of rapamycin (mTOR), a central regulator of protein synthesis in neurons, has been implicated in synaptic plasticity and memory. Here we show that mTOR inhibition by rapamycin in the basolateral amygdala (BLA) or dorsal hippocampus (DH) impairs both formation and reconsolidation of memory for inhibitory avoidance (IA) in rats. Male Wistar rats received bilateral infusions of vehicle or rapamycin into the BLA or DH before or after IA training or retrieval. Memory retention was tested at different time points after drug infusion. Rapamycin impaired long-term IA retention when given before or immediately after training or retrieval into the BLA. When infused into the DH, rapamycin produced memory impairment when given before training or immediately after retrieval. The impairing effects of post-retrieval rapamycin required memory retrieval and were not reversed by a reminder shock. The results provide the first evidence that mTOR in the BLA and DH might play a role in IA memory reconsolidation.

Impairment of object recognition memory by rapamycin inhibition of mTOR in the amygdala or hippocampus around the time of learning or reactivation.

The role of the basolateral complex of the amygdala (BLA) in recognition memory remains poorly understood. The mammalian target of rapamycin (mTOR) in the BLA and other brain areas has been implicated in synaptic plasticity and memory. We have recently shown that mTOR signaling in both the BLA and the dorsal hippocampus (DH) is required for formation and reconsolidation of inhibitory avoidance, a fear-motivated memory task. Here we examined the effects of infusions of the mTOR inhibitor rapamycin into the BLA before or after either training or reactivation on retention of novel object recognition (NOR) memory in rats, and compared the effects with those obtained using intra-DH infusions. Male Wistar rats received bilateral infusions of vehicle or rapamycin into the BLA or DH before or after NOR training or reactivation. Rapamycin impaired NOR retention tested 24h after training when given either before or immediately after training into the BLA or DH. Rapamycin also impaired retention measured 24h after reactivation when infused before reactivation into the BLA or DH, or immediately after reactivation into the BLA, but not when given 6h after reactivation into either the BLA or DH. The results suggest that mTOR signaling in the BLA and DH is involved in NOR memory formation and stabilization.