RT Journal Article SR Electronic T1 An Antisense Oligonucleotide Reverses the Footshock-Induced Expression of Fos in the Rat Medial Prefrontal Cortex and the Subsequent Expression of Conditioned Fear-Induced Immobility JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 5666 OP 5673 DO 10.1523/JNEUROSCI.19-13-05666.1999 VO 19 IS 13 A1 Bret A. Morrow A1 John D. Elsworth A1 Fiona M. Inglis A1 Robert H. Roth YR 1999 UL http://www.jneurosci.org/content/19/13/5666.abstract AB The immediate-early genes, including c-fos, have been proposed to be involved in learning and memory. In this report, we examine stress-induced Fos-like immunoreactivity (Fos-li) in subregions of the prefrontal cortex during a conditioned fear paradigm. During the acquisition phase, the rats were conditioned to fear a formerly neutral tone by pairing the tone with a mild footshock. The rats were then tested for fearful behavior by reexposure to the tone without additional footshock. During acquisition, Fos-li was increased in the medial prefrontal cortex (infralimbic and prelimbic) but not the anterior cingulate and M1 motor cortex. However, during the extinction phase, no significant increase in Fos-li was observed in any region. These findings indicate that acquisition, but not extinction, of conditioned fear is associated with an increase in Fos-li in subregions of the medial prefrontal cortex. In other animals, an antisense oligonucleotide directed against the c-fos mRNA was injected into the infralimbic/prelimbic cortex 12 or 72 hr before the acquisition session. Antisense treatment given 12, but not 72, hr earlier suppressed Fos production without altering behavior during the acquisition session. Three days after the acquisition session, rats were tested for fearful behavior as before. The antisense oligonucleotide blockade of Fos production during acquisition was associated with a significantly less fearful response during the extinction session. These results support a role for Fos in the medial prefrontal cortex during the acquisition of aversive learning.