Rat Frontal Cortex Involved In Long When You Entered The Inhibitory Avoidance Memory Read Out

Part I: The anterior cingulate cortex is involved in retrieval of long-term memory for step-through inhibitory avoidance in ratsIt is known that the anterior cingulate cortex (ACC) is involved in the formation of contextual fear memory. Recent studies showed that the ACC is important for retrieval of spatial memory and contextual fear memory. In order to further examine the role of ACC in fear memory, we investigated the effects of lesion to or inactivation of ACC on the retrieval or expression of step-through inhibitory avoidance (IA) memory. We first examined the effect of lesion to the ACC on long-term memory retrieval. Chemical lesion to the ACC by quinolinic acid severely impaired retrieval of 15-day and 29-day memories for one-trial step-through IA. We then investigated the effect of inactivation of the ACC on short- and long-term memory retrieval. Pre-retrieval inactivation of the ACC by local infusion of muscimol, a selective GABAa receptor agonist, produced severe deficit in 1-day, 4-day and 7-day memories, but had no effect on 2-hour and 6-hour memories. The present results provide evidence that the ACC is important for retrieval of long-term, but not short-term, fear memory for IA. Part II: The medial prefrontal cortex is required for retrieval of long-term memory for one-trial inhibitory avoidance in ratsNeural mechanism underlying memory retrieval has been extensively studied in the hippocampus and amygdala. However, little is known about the role of the prefrontal cortex in memory retrieval. The present study investigated the role of the rat medial prefrontal cortex (mPFC) in retrieval of memory for one-trial step-through inhibitory avoidance (IA). Our results showed that, 1) inactivation of the mPFC by local infusion of the GABA_A-receptor agonist muscimol caused a severe deficit in retrieval of 1-day and 7-day but not 2-hour IA memory; 2) the protein level of phospho-ERK1/2 in the mPFC were significantly increased following retrieval of 1-day and 7-day IA memory, so did the numbers of phospho-ERK (pERK) and phospho-CREB (pCREB) positive neurons; 3) intra-mPFC infusion of the ERK kinase inhibitor PD98095 30 min prior to retrieval significantly reduced both protein levels and/or positive neurons of phospho-ERK1/2 and phospho-CREB, and severely impaired retrieval of 7-day IA memory. The present study provides evidence that the retrieval of long-lasting memory for inhibitory avoidance requires the mPFC and involves the ERK-CREB signaling cascade in this cortical region.