<p class="first" id="d8093033e111">The context preexposure facilitation effect (CPFE)
is a contextual fear conditioning
paradigm in which learning about the context, acquiring the context-shock association,
and retrieving/expressing contextual fear are temporally dissociated into three distinct
phases (context preexposure, immediate-shock training, and retention). The current
study examined changes in the expression of plasticity-associated immediate early
genes (IEGs) during context and contextual fear memory formation on the preexposure
and training days of the CPFE, respectively. Using adolescent Long-Evans rats, preexposure
and training day expression of the IEGs c-Fos, Arc, Egr-1, and Npas4 in the medial
prefrontal cortex (mPFC), dorsal hippocampus (dHPC), and basolateral amygdala (BLA)
was analyzed using qPCR as an extension of previous studies from our lab examining
Egr-1 via in situ hybridization (Asok, Schreiber, Jablonski, Rosen, & Stanton,
2013;
Schreiber, Asok, Jablonski, Rosen, & Stanton, 2014). In Expt. 1, context preexposure
induced expression of c-Fos, Arc, Egr-1 and Npas4 significantly above that of home-cage
(HC) controls in all three regions. In Expt. 2, immediate-shock was followed by a
post-shock freezing test, resulting in increased mPFC c-Fos expression in a group
preexposed to the training context but not a control group preexposed to an alternate
context, indicating expression related to associative learning. This was not seen
with other IEGs in mPFC or with any IEG in dHPC or BLA. Finally, when the post-shock
freezing test was omitted in Expt. 3, training-related increases were observed in
prefrontal c-Fos, Arc, Egr-1, and Npas4, hippocampal c-Fos, and amygdalar Egr-1 expression.
These results indicate that context exposure in a post-shock freezing test re-engages
IEG expression that may obscure associatively-induced expression during contextual
fear conditioning. Additionally, these studies suggest a key role for long-term synaptic
plasticity in the mPFC in supporting the CPFE.
</p>