Egr-1 increases in the prefrontal cortex following training in the context preexposure facilitation effect (CPFE) paradigm

Abstract

The context pre-exposure facilitation effect (CPFE) is a modified form of standard contextual fear conditioning that dissociates learning about the context during a preexposure phase from learning the context-shock association during an immediate shock training phase conducted on separate days. Fear conditioning in the CPFE is an associative process in which only animals that are preexposed to the same context they are later given an immediate shock in demonstrate freezing when tested for conditioned fear memory. Previous research has shown that the hippocampus and amygdala are necessary for different phases of the CPFE, but whether other brain regions are also involved is unknown. The present study examined expression of the immediate-early gene early growth response gene 1 (Egr-1; also called Zif268, Ngfi-a, Krox-24) in the dorsal hippocampus, lateral nucleus of the amygdala, retrosplenial cortex, and several prefrontal cortex regions (infralimbic and prelimbic medial prefrontal cortex, anterior cingulate, and orbitofrontal cortex) following each phase of the CPFE in juvenile rats. Animals preexposed to the conditioning context displayed fear conditioned freezing during a retention test whereas rats preexposed to an alternate context did not. Following context preexposure, Egr-1 mRNA was elevated in context and alternate context exposed animals compared to home-cage control rats in almost all regions analyzed. Following the context-shock training phase, fear conditioned rats displayed significantly more Egr-1 mRNA expression in the infralimbic, prelimbic, and orbitofrontal cortices compared to the alternate context preexposed control rats. These differences in Egr-1 expression were not found in amygdala between the preexposed context and alternate context rats. No sex differences were observed following preexposure or training in any regions analyzed. The findings suggest that increased expression of Egr-1 within the prefrontal cortex is associated with contextual fear conditioning in the CPFE paradigm.