Carnita Lincoln, “The Role of the Nucleus Reuniens in Memory Consolidation and Visualization of its Projections”
Mentor: Karyn Frick, Psychology

Concurrent activity in both the dorsal hippocampus (DH) and medial prefrontal cortex (mPFC) is necessary for the consolidation of spatial memory in mice and it is hypothesized that other brain regions might mediate communication between the two. Because the nucleus reuniens of the thalamus has been shown to facilitate communication between the DH and mPFC, the goal of this study was to determine whether the nucleus reuniens (RE) is also necessary for spatial memory consolidation. To inactivate the RE, we used a technique called DREADDs (designer receptors exclusively activated by designer drugs) which uses a viral vector to express a synthetic receptor that inhibits neuron activity after application of a synthetic, selective drug. Female mice were trained in an object placement memory task, RE was inactivated, and memory tested 4 hours later. Inactivation of the RE impaired object placement memory. Because this inactivation method targets the entire RE, which projects to multiple brain regions, we next want to specifically inactivate projections from RE to either the DH or mPFC. We tested retrograde Cre viral construct combined with Green Fluorescent Protein that allows us to label neurons that project to a specific brain region and target these neurons for inactivation. The retrograde Cre was infused into the mPFC, DH, or RE of young female mice, and brains were collected 3, 4, or 6 weeks later to determine the extent of viral expression. Brains were flash frozen, sectioned using a cryostat, mounted on slides, and imaged using a fluorescent microscope. Imaging allowed us to identify which projection cells expressed the virus and determine an optimal expression time (3, 4, or 6 weeks). The results from this and future studies will allow us to better understand the circuitry underlying memory formation and may lead to advances in treatments for memory consolidation.

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