Egr-1 mRNA expression patterns in the prefrontal cortex, hippocampus, and amygdala during variants of contextual fear conditioning in adolescent rats

Brain Res. 2014 Aug 12:1576:63-72. doi: 10.1016/j.brainres.2014.06.007. Epub 2014 Jun 26.


We report activation of the immediate-early gene Egr-1 in the lateral amygdala (LA), hippocampus (CA1), and medial prefrontal cortex (mPFC) 30-min following the training phase in the context pre-exposure facilitation effect (CPFE) and standard context fear conditioning (180 s context exposure→shock). On day one of the CPFE paradigm, postnatal day (PD) 31 rats (±1) were pre-exposed to Context A (Pre) or Context B (Alt-Pre) for 5 min followed by five additional 1-min exposures. A day later, Pre and Alt-Pre rats received a 2-s, 1.5 mA footshock immediately upon placement in Context A. Animals included in in situ hybridization were then sacrificed 30 (±3) min later. On day three, the behaviorally-tested Pre rats showed significantly more fear-conditioned freezing in Context A than Alt-Pre rats. Standard context fear conditioning groups showed much greater freezing than the Pre group, as well as no shock and immediate-shock controls. Thirty minutes after immediate shock training, Pre rats showed increased Egr-1 mRNA in the prelimbic mPFC relative to Alt-Pre rats. Standard context conditioning selectively increased Egr-1 in CA1. In the LA and mPFC, Egr-1 increased to a similar extent in no shock, immediate shock, and standard context conditioning relative to homecage controls. The present study demonstrates that Egr-1 mRNA expression has a complex relationship to fear learning in different brain regions and variants of context conditioning.

Keywords: Amygdala; CPFE; Context fear conditioning; Egr-1; Hippocampus; Prefrontal cortex.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age Factors
  • Amygdala / metabolism*
  • Amygdala / physiology
  • Animals
  • Conditioning, Classical / physiology*
  • Early Growth Response Protein 1 / biosynthesis
  • Early Growth Response Protein 1 / genetics*
  • Early Growth Response Protein 1 / physiology
  • Electroshock
  • Fear / physiology*
  • Female
  • Freezing Reaction, Cataleptic / physiology*
  • Genes, Immediate-Early*
  • Handling, Psychological
  • Hippocampus / metabolism*
  • Hippocampus / physiology
  • Male
  • Nerve Tissue Proteins / biosynthesis
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / physiology
  • Neuronal Plasticity
  • Prefrontal Cortex / metabolism*
  • Prefrontal Cortex / physiology
  • RNA, Messenger / biosynthesis*
  • RNA, Messenger / genetics
  • Rats
  • Rats, Long-Evans
  • Time Factors


  • Early Growth Response Protein 1
  • Egr1 protein, rat
  • Nerve Tissue Proteins
  • RNA, Messenger