TIME COURSE OF ARC PROTEIN EXPRESSION IN THE HIPPOCAMPUS AFTER SPATIAL EXPLORATION

V. Ramirez-Amaya¹*; A. Vazdarjanov¹; F.P. Houston1; K. Olson¹; P.F. Worley²; C.A. Barnes¹

1. NSMA, Univ Arizona, Tucson, AZ, USA
2. Neurosci, Johns Hopkins, Baltimore, MD, USA

Spatial exploration is known to induce the expression of Arc mRNA in the CA1, CA3 and DG regions of the hippocampus, and several cortical regions. Because Arc mRNA can be localized to either the nucleus or the cytoplasm of the cell with a precise timecourse after behavioral induction, two experiences can be observed simultaneously in the network, and this observation forms the basis of the catFISH brain imaging method. Arc is also known to be an important factor for learning-related plasticity in the hippocampus. To better understand the downstream function of Arc, the dynamics of the expression of the protein product of Arc was studied here. Male Fisher-344 rats (9 mo) were exposed twice to a particular environment for 5 min (environment A) using 5 different intervals between the two environment exposures (A-A 60, A-A 120, A-A 180, A-A 240 and A-A 360 min). Also included are caged controls (Caged) and animals exposed for only 5 min once (A Ctrl). Using fluorescence immuno-histochemistry combined with fluorescence in situ hybridization the expression of Arc mRNA was found to be colocalized with Arc protein, validating the use of immunohistochemistry to measure Arc protein. Arc protein expression in CA1 and CA3 is robust at 60 min, declined at 120 min, and did not differ from controls at the 180, 240, and 360 min time points. In the DG, however, the protein is expressed robustly at 60 min and the expression is maintained through 360 min at levels above controls. These results suggest that the kinetics of the protein product of Arc are different in the DG and CA regions, and indicates behaviorally-induced Arc may tag synapses for a longer period in DG than in CA1.
Support Contributed By: AG09219, MH46357 & HFSP LT00112-2002-C

Arg3.1, Immediate Early Genes, Synaptic Plasticity, Place Cells