Arc Expression in the Entorhinal Cortex of the Behaving Animal

• Main Author: Clasen, Sara Jean
• Language: en
• Published: The University of Arizona. 2010
• Online Access: http://hdl.handle.net/10150/146072

The hippocampus is a brain structure critical for learning and memory and receives a major input from the entorhinal cortex, which is itself divided into medial and lateral divisions. The medial division (MEC) contains grid cells, so named because the locations in space that increase any specific cell's ring rate are distributed as a triangular lattice-shaped grid [1]. The neurons of the lateral division (LEC) do not exhibit spatially selective firing [2], but may instead be involved in providing the hippocampus with information about the objects in the environment based on its anatomical connections with the perirhinal cortex [3]. The immediate-early gene Arc codes for a protein involved in synaptic plasticity and its expression is induced in principal cell populations by active behavior. In this experiment Arc is used to mark neuronal activation in LEC to test the hypothesis that these regions process different information about the rat's experience. Rats were trained to run on a circular track; on the day of the experiment, animals were divided into four groups: caged controls (negative control group); maximal electroconvulsive shock controls (positive control group); an A/A group which ran on a track populated with the same set of objects for two sessions separated by 20 minutes, and then sacrificed; and an A/B group which encountered two distinct sets of objects for each session. Arc expression was increased in the A/A and A/B groups relative to the caged controls; the pattern of Arc-labeled neuron proportions was altered in the A/B group relative to the A/A group, but no firm evidence of object-selective neurons was found. This may be due to low statistical power, sampling limitations, or unknown confounds.