Acute ethanol administration affects memory reactivation: a look at the neuronal density and apoptosis in the rat hippocampus

This study is an attempt to examine whether administration of ethanol after memory reactivation will modulate expression of memory in rats or not. We further examined whether this administration alters the number of tunnel positive cells in hippocampus.Adult male Wistar rats were trained in a fear conditioning system using two 1 s , 0.6 mA shock with an interval of 180 s. 24 h later the rats were returned to the chamber for reactivation, and then they were injected with ethanol (0.5, 1, 1.5 mg/kg) or saline, ip. Again, one, seven and fourteen days after reactivation, the rats were returned to the context for 5 min. The freezing time (absence of all movements except respiration) was scored in seconds.In the second experiment, after test 1, the animals were anesthetized and a transcardial perfuse with phosphate buffer and paraformaldehyde 4% was conducted. After post-fixation of brains 5-μm sections were stained with cresyl violet.Finally, paraffin-embedded sections of 10 μm were cut out throughout the tissue and each sample was processed with TUNEL. The number of apoptotic cells in a 130 μm-long segment of the hippocampal CA1 and CA3 fields and dentate gyrus was counted.The data demonstrate that ethanol exposure impairs post retrieval processes. Rats receiving ethanol (1.5 mg/kg) showed lower freezing levels during the first test. Moreover, ethanol decreases the density of CA1, CA3 and DG cells and increases the density of apoptotic cells in all regions of hippocampus. Therefore, ethanol exposure impairs reconsolidation of contextual fear conditioning probably via decreasing the density of CA1, CA3 and DG cells.