Induction of immediate early genes in the mouse auditory cortex after auditory cued fear conditioning to complex...

Immediate early genes (IEGs) are widely used as markers to delineate neuronal circuits because they show fast and transient expression induced by various behavioral paradigms. In this study, we investigated the expression of the IEGs c-fos and Arc in the auditory cortex of the mouse after auditory cued fear conditioning using quantitative polymerase chain reaction and microarray analysis. To test for the specificity of the IEG induction, we included several control groups that allowed us to test for factors other than associative learning to sounds that could lead to an induction of IEGs. We found that both c-fos and Arc showed strong and robust induction after auditory fear conditioning. However, we also observed increased expression of both genes in any control paradigm that involved shocks, even when no sounds were presented. Using mRNA microarrays and comparing the effect of the various behavioral paradigms on mRNA expression levels, we did not find genes being selectively upregulated in the auditory fear conditioned group. In summary, our results indicate that the use of IEGs to identify neuronal circuits involved specifically in processing of sound cues in the fear conditioning paradigm can be limited by the effects of the aversive unconditional stimulus and that activity levels in a particular primary sensory cortical area can be strongly influenced by stimuli mediated by other modalities.