DIFFERENTIAL ARC EXPRESSION IN THE LATERAL VERSUS BASAL AMYGDALA NUCLEI FOLLOWING ELECTROCONVULSIVE SEIZURE, BUT NOT SPATIAL EXPLORATION

 A. Vazdarjanova¹*; S. Rosi¹; N. Insel¹; V. Ramirez-Amaya^1,2; K. Olson¹; J.F. Guzowski³; P.F. Worley⁴; C.A. Barnes¹

1. NSMA , Univ Arizona, Tucson, AZ, USA
2. Instit Fisiol Cel UNAM, Mexico DF, Mexico
3. Neuroscience, Univ New Mexico, Albuquerque, NM, USA
4. Neuroscience & Neuroloy, Johns Hopkins Univ, Baltimore, MD, USA

Expression of the activity-regulated cytoskeleton-associated protein Arc or Arg 3.1 is induced by both electroconvulsive seizure (MECS) and by learning. In the hippocampal CA areas and in neocortex, Arc mRNA expression is tightly regulated, such that characteristic foci of transcription in the nucleus of hippocampal and neocortical neurons can be observed between 2-16 min after neuronal activation, after which time the mRNA translocates to the cytoplasm. These temporal characteristics of Arc expression have made it a useful tool to study changes in the composition of neuronal ensembles activated by two behavioral experiences, separated by ~30 min, a method known as catFISH ( cellular compartment analysis with temporal resolution by fluorescence in situ hybridization). Here we report that exploration of a novel environment induced a rapid (<5 min) and relatively short-lived (<45 min) period of Arc transcription in both the lateral and basal amygdala nuclei. In contrast, MECS induced sustained transcription (>2, but <4 hrs) only in basal amygdala neurons. These results suggest that behaviorally-induced Arc expression in the basolateral amygdala is tightly regulated, as observed in hippocampal and neocortical pyramidal neurons, and that Arc catFISH can be used to study neuronal ensembles in the basolateral amygdala activated by behavior. The observed sustained Arc transcription in basal, but not lateral, amygdala neurons following MECS may result from either recurring epileptiform activity, or from properties of Ca 2+ loading and compartmentalization selectively involving basal amygdala neurons. Thus, the lateral and basal amygdala nuclei may be differentially involved in sustaining seizure-related neural activity.

Support Contributed By: AG009219, AG010546, MH064357 & HFSP LT00112-2002-C

Key words: immediate early genes, activity-regulated cytoskeleton-associated protein, basolateral, learning