Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.05.13.093237v1?rss=1 Authors: Subramaniyan, M., Manivannan, S., Chelur, V., Tsetsenis, T., Jiang, E., Dani, J. A. Abstract: The hippocampus is essential for spatial learning and memory. To assess learning we used contextual fear conditioning (cFC), where animals learn to associate a place with aversive events such as foot-shocks. Candidate memory mechanisms for cFC are long-term potentiation and long-term depression, but there is little direct evidence of those mechanisms operating in the hippocampus in vivo following cFC. Also, little is known about the behavioral state changes induced by cFC. To address these shortcomings, we used motion tracking and recorded local field potentials in freely behaving mice by placing a stimulating electrode in the left dorsal CA1 region and positioning recording electrodes in the right dorsal CA1 region. Synaptic strength in the commissural pathway was monitored by measuring field excitatory postsynaptic potentials (fEPSPs) before and after cFC. After cFC, the commissural pathway's synaptic strength was potentiated. Although recordings were conducted during the wake phase of the light/dark cycle, the mice slept more in the post-conditioning period than in the pre-conditioning period. Relative to awake periods, in non-rapid eye movement (NREM) sleep the fEPSPs were larger in both pre- and post-conditioning periods. Therefore, to avoid sleep-related fEPSP changes confounding the effects of cFC learning, we accounted for the effects of sleep and still found long-term potentiation of the commissural pathway, but no significant long-term depression. Synaptic strength changes were not found in the no-shock, control group that simply explored the fear-conditioning chamber, indicating that exploration of the novel place did not produce the measurable effects caused by cFC. These results show that following cFC, the CA1 commissural pathway is potentiated, likely contributing to the functional integration of the left and right hippocampi in fear memory consolidation. In addition, the cFC paradigm produces significant changes in an animal's behavioral state, which are observable as proximal changes in sleep patterns. Copy rights belong to original authors. Visit the link for more info