Basolateral amygdala activity is required for enhancement of memory consolidation produced by histone deacetylase inhibition in the hippocampus

Histone acetylation, a type of chromatin modification that allows increased gene transcription and can be pharmacologically promoted by histone deacetylase (HDAC) inhibitors (HDACis), has been consistently associated with promoting memory formation in the hippocampus. The basolateral nucleus of the amygdala (BLA) is a brain area crucially involved in enabling hormones and drugs to influence memory formation. Here, we show that BLA activity is required for memory enhancement by intrahippocampal administration of an HDACi. Two different HDACis, sodium butyrate (NaB) and trichostatin A (TSA), differentially enhanced the retention of memory for inhibitory avoidance (IA) when administered to the dorsal hippocampus after training. TSA showed a biphasic pattern of response during consolidation, in which infusions given immediately or 3h after training produced memory enhancement, whereas no effect was observed when it was infused 1.5 or 6h posttraining. Muscimol (MUS)-induced unilateral functional inactivation of the BLA prevented the enhancement of memory retention produced by posttraining infusion of TSA into the ipsilateral hippocampus. TSA did not affect IA extinction or reconsolidation. These results indicate that HDACis can increase IA memory retention when given into the hippocampus, and, most importantly, BLA activity is necessary for enabling HDACi-induced influences on memory formation.