Contextual fear conditioning with a time interval induces CREB phosphorylation in the dorsal hippocampus and amygdala nuclei that depend on prelimbic cortex activity

Abstract

In temporal associations, a conditioned stimulus (CS) is separated by a time interval from the unconditioned stimulus (US), which activates the prelimbic cortex (PL) to maintain a CS representation over time. However, it is unknown whether the PL participates, besides the encoding, in the memory consolidation, and thus directly, with activity‐dependent changes or indirectly, by modulation of activity‐dependent changes in other brain regions. We investigated brain regions supporting the consolidation of associations with intervals and the influence of PL activity in this consolidation process. For this, we observed in Wistar rats the effect of pre‐training PL inactivation by muscimol in CREB (cAMP response element‐binding protein) phosphorylation, which is essential for memory consolidation, in subdivisions of the medial prefrontal cortex (mPFC), hippocampus, and amygdala 3 h after the training in the contextual fear conditioning (CFC) or CFC with 5‐s interval (CFC‐5s), fear associations without or with an interval between the CS and US, respectively. Both the CFC‐5s and CFC training increased phosphorylation of CREB in the PL and infralimbic cortex (IL); lateral (LA) and basolateral (BLA) amygdala; dorsal CA1 (dCA1); dorsal (dDG), and ventral dentate gyrus, and the CFC‐5s training in the central amygdala (CEA). PL activity was necessary for the CREB phosphorylation in the PL, BLA, CEA, dCA1, and dDG only in animals trained in the CFC‐5s. The cingulate cortex, ventral CA1, and ventral subiculum did not have learning‐induced phosphorylation of CREB. These results suggest that the mPFC, hippocampus, and amygdala support the consolidation of associations with or without intervals and that PL activity influences consolidation in the dorsal hippocampus and amygdala in temporal associations. Thereby, the PL contributes directly and indirectly by modulation to memory consolidation. The time interval engaged the PL early in recent memory consolidation. Results expanded PL's role beyond the time interval and remote memory consolidation.

Temporal association activates projections from the perirhinal cortex and ventral CA1 to the prelimbic cortex and from the prelimbic cortex to the basolateral amygdala

“…Considering that BLA is the site of CS-US convergence (Barot et al 2009), this finding suggests that the PL may convey the contextual CS associated with the US in the BLA. In line, a functional connection between the PL and the BLA accompanied CFC-5s learning (Santos et al 2023), and the PL→BLA connection was required or accompanied trace fear conditioning, but not CFC (Song et al 2005;Kirry et al 2020;Kitamura et al 2017). Olfactory or AFC also induced post-training changes in the PL-BLA functional connection required for the expression of the CR (Garcia et al 1999;Vouimba et al 2011;Arruda-Carvalho and Clem 2014;Karalis et al 2016).…”

“…Experiments were performed on thirty-six male Wistar rats 10 weeks old at the start et al 2007) to ensure adequate power to detect effect sizes previously observed using the CFC-5s training (Santos et al 2023).…”

“…CFC-5s was conducted as previously described (Santos et al 2017;Santos et al 2020;Santos et al 2023). Rats were pre-exposed to the conditioning chamber for 5 min, placed in the transport cage beside the conditioning chamber for a 5-second interval, and then re-exposed to the conditioning chamber, delivering one immediate footshock (0.8 mA, 1 s).…”

“…CFC was performed as previously described (Santos et al 2017;Santos et al 2020;Santos et al 2023). We placed the rats in the conditioning chamber for 5 min delivering one (which was not certified by peer review) is the author/funder.…”

“…A functional connection between the DH and the PL accompanied CFC-5s learning. Pre-training PL inactivation impaired CFC-5s learning and reduced CFC-5s-induced phosphorylation of CREB in the DH(Santos et al 2023). The PER was a hub, a brain region with increased importance, in the functional network of CFC learned in the absence of the DH, that is, with a dorsal hippocampal lesion, suggesting that the PER may replace the DH exercising a similar function(Coelho et al…”