Many studies report that the electroconvulsive seizure (ECS) administered immediately after the training (fear conditioning) impairs the memory formation. In contrast, there are only few studies asking whether or not the ECS before the training influence the learning. Here, we trained mice by fear conditioning and investigated which timing of the ECS abrogates the memory formation. Contextual and auditory memories were tested 1 h, 24 h, and 8 d after the conditioning to assess the formation of short-(STM) and long-term memories (LTM). The ECS 2 h before the conditioning caused a decrease in contextual-freezing, but did not affect the auditory-freezing, when the memory was tested 24 h after the conditioning. However, the ECS 2 h before the conditioning did not decrease in either contextual-or auditory-freezing, when the memory was tested 1 h after the conditioning. In addition, the ECS 2 h before the conditioning did not affect the contextual-or auditory-freezing, when the memory was tested 8 days after the conditioning. The data suggest that the ECS 2 h before the conditioning inhibits the transition from the contextual STM to the LTM one. As the ECS strongly induces various immediate-early genes, some of the gene products might be involved in the abrogation of the transition of the STM to the LTM.
The hippocampus is functionally segregated along the dorso-ventral axis in rodents. The dorsal hippocampus is involved in spatial memory whereas the ventral is in emotional responses. Consistently, each region receives afferents from distinct brain regions. Furthermore, within the dentate gyrus (DG), the proximal and distal portions of granule cell (GC) dendrites receive medial and lateral perforant pathway axons, respectively, which are originating from different regions of the entorhinal cortex. Differences in dendritic morphology and spine density presumably reflect differences in activities of their partner axon termini. Here, we investigate the morphological features of the GC in the dorsal and the ventral DG, and their responses to social defeat stress as an example of emotional inputs. Visualization of single neurons by microinjection of Lucifer Yellow revealed that the branching patterns of GC dendrites are distinct between dorsal and ventral DGs; the peak of the number of intersections in Sholl analyses localized more proximal in the dorsal than in the ventral DG. Spine density of ventral DG was higher than dorsal DG. Social defeat stress was found to suppress the dendritic branching and spine densities of GCs both in dorsal and ventral DGs to similar extent. Mushroom and thin spines decreased significantly whereas stubby spines did not. The data suggest that the dendritic branching pattern and spine density of GCs are distinct between the dorsal and ventral hippocampus, but undergo uniform morphological remodeling in response to an emotional stress.
LBS
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.