BEHAVIOR INDUCES EXPRESSION OF THE PLASTICITY-RELATED IMMEDIATE-EARLY GENE ARC IN EXCITATORY HIPPOCAMPAL AND CORTICAL NEURONS, BUT NOT IN ASTROCYTES OR INHIBITORY NEURONS

A. Vazdarjanova¹*; V. Ramirez-Amaya¹; V.L. Sutherland¹; M.K. Chawla¹; P.F. Worley²; C.A. Barnes¹; J.F. Guzowski³

1. NSMA, Univ Arizona, Tucson, AZ, USA
2. Neurosci, Johns Hopkins, Baltimore, MD, USA
3. Neurosci, Univ New Mexico, Albuquerque, NM, USA

The activity-regulated cytoskeletal associated protein (Arc or Arg 3.1) is a key protein implicated in synaptic plasticity and memory consolidation. It is quickly induced and dynamically-regulated by novel learning experiences, as revealed by a sensitive fluorescence in situ hybridization method known as catFISH. It is not known, however, which cell types express Arc in the mammalian central nervous system. Using double fluorescent immunohistochemistry for Arc/GFAP and Arc/NeuronN in animals that explored a novel environment for 5 minutes or received electro convulsive shock (MECS), we observed that Arc protein expression is co-localized only with NeuronN, but not GFAP-positive cells during the time of the highest levels of Arc protein expression. Thus, it appears that only neurons express Arc, which is consistent with the idea that Arc is involved in neuronal plasticity in networks activated by behavior. Furthermore, double catFISH for Arc and GAD65/67 in the same rats revealed that, although Arc can be expressed in GAD-positive cells with a strong stimulus (MECS), exploration of a novel environment does not induce Arc in inhibitory neurons in the hippocampus and cortex. Additionally, triple labeling for Arc, GAD65/67, and -CAMKII reveals that Arc is expressed in a subpopulation of -CAMKII-positive cells in the same brain regions. Taken together, our findings demonstrate that under behaviorally-relevant conditions Arc is expressed specifically by excitatory hippocampal and cortical cells. As the cell types that contain Arc readily show plasticity, our findings lend further support to the idea that Arc is integral to synaptic modification that accompanies learning.
Support Contributed By: AG09219, MH064357, MH060123 & HFSP LT00112-2002-C

plasticity, gene expression, excitatory neurons, Arc