Contextual fear conditioning modulates the gene expression over time

Contextual fear conditioning (CFC) is a quick cognitive test based on the association context-aversive stimulus in which a single training leads to a long-term memory. Previously, we analyzed the gene expression in CFC rats, naïve rats, explor rats which had freely explored the experimental apparatus and shock only (SO) rats to which the same number of aversive shocks used in the CFC paradigm had been administered in the same CFC apparatus in less time to prevent the association between painful stimuli and apparatus. The analysis showed that 2 days after conditioning some genes (Napa, Pnf2, Casp3, Pdrg1, Ywhaz, Stmn1, Bpgm) were more expressed in CFC rats with respect to naive, explor and SO rats. Other genes (Actr3, Pea15,Tiprl) were more expressed in SO rats or in explor rats (Cplx1, Trim32, Ran), and the expression of the Tomm20 gene was greater in both CFC and explor rats in comparison with SO and naïve rats. Herein, we have tested the expression of these genes for longer periods, at 3, 10 and 20 days after conditioning. The expression of the transcripts was assessed by qRT-PCR. Interestingly, in CFC rats, at 3 days, the genes Tiprl and Trim32, whose expression had not been modulated at 2 days resulted more expressed with respect to naïve, explor and SO rats, whereas the gene Tomm20 was less expressed as in the SO and explor rats with respect to naïve rats. At 10 days, Trim32 gene was still more expressed in CFC rats whereas the genes Tiprl and Tomm20 returned to the constitutive level, and the gene Ran was significantly more expressed in CFC rats than in naïve, SO and explor rats. Surprisingly at 20 days, the genes Stmn1 and Tiprl again resulted significantly more expressed in CFC rats compared with naïve, SO and explor rats. Our results outline a complex modulation of gene expression in a prolonged time point of CFC post-acquisition consolidation period