The Conditions under Which Consolidation of Serial-Order Conditioned Fear Requires De Novo Protein Synthesis in the Basolateral Amygdala Complex

Abstract

Consolidation of conditioned fear to a stimulus (S1) paired with shock requires de novo protein synthesis in the basolateral amygdala complex (BLA), whereas consolidation of conditioned fear to a stimulus (S2) paired with the fear-eliciting S1 requires DNA methylation but not de novo protein synthesis in the BLA. The present experiments merged these protocols by exposing rats to pairings of a serial S2-S1 compound and shock to examine if/when protein synthesis in the BLA is required to consolidate fear to S2. Rats received a BLA infusion of the protein synthesis inhibitor, cycloheximide, immediately after the S2-S1-shock session and were subsequently tested with S2. The infusion disrupted consolidation of fear to S2 when there had been no prior training of S1 (Experiment 1), the prior training had consisted of unpaired presentations of S1 and shock (Experiment 4), or in pairings of S1 and sucrose (Experiment 5). Consolidation of fear to S2 was unaffected by the infusion of cycloheximide but was disrupted by the DNA methyltransferase inhibitor, 5-AZA, when S1 had been previously fear-conditioned (Experiments 2a, 2b, and 3). These findings imply that what has already been learned about S1 determines the BLA processes that consolidate fear to S2. The already-fear-conditioned S1 blocks the S2-shock association that otherwise forms (and whose consolidation requires de novo protein synthesis in the BLA) while simultaneously acting as a learned source of danger for its S2 associate (whose consolidation requires DNA methylation but not de novo protein synthesis in the BLA).

Prediction Error Determines Whether NMDA Receptors in the Basolateral Amygdala Complex Are Involved in Pavlovian Fear Conditioning

“…Each experiment used the auditory and visual stimuli, counterbalanced in their roles as S1 and S2, such that the auditory stimulus was S1 and the visual stimulus was S2 for half of the subjects in each experiment, while the visual stimulus was S1 and the auditory stimulus was S2 for the remainder. The durations of S2 and S1 were 30 and 10 s, respectively, and were those used in previous studies of second-order (Lay et al, 2018) and serial-order (Leidl et al, 2018;Williams-Spooner et al, 2019) conditioning. The intensity of the foot shock was 0.8 mA, and its duration was 0.5 s.…”

Danger changes the way the brain consolidates neutral information; and does so by interacting with processes involved in the encoding of that information

“…Following the final S2-S1 pairing, rats were removed for a few minutes and returned to the chambers where rats in two groups were shocked and those in the other two were not shocked. One group in each pair then received a PRh (Experiment 1A) or BLA (Experiment 1B) infusion of the protein synthesis inhibitor, cycloheximide (CHX), as protein synthesis has been shown to be critical for the cellular changes that consolidate new information in memory (Hernandez & Abel, 2008; Johansen et al, 2011; Lay et al, 2018; Leidl et al, 2018; Rodrigues et al, 2004; Williams-Spooner et al, 2019). The other group in each pair received an infusion of vehicle (VEH) into the PRh or BLA.…”

“…Following the final S2-S1 pairing, rats were removed for a few minutes and returned to the chambers where rats in two groups were shocked and those in the other two were not shocked. One group in each pair then received a PRh (Experiment 1A) or BLA (Experiment 1B) infusion of the protein synthesis inhibitor, cycloheximide (CHX), as protein synthesis has been shown to be critical for the cellular changes that consolidate new information in memory (Hernandez & Abel, 2008;Johansen et al, 2011;Lay et al, 2018;Leidl et al, 2018;Rodrigues et al, 2004;Williams-Spooner et al, 2019). The other group in each pair received an infusion of vehicle (VEH) into the PRh or BLA.…”

Understanding Associative Learning Through Higher-Order Conditioning

“…Some instances of second-order fear conditioning consist of reinforced serial S2→S1 pairings following S1 training [i.e., S2→S1→US; Williams-Spooner et al, 2019 ; see also Mahmud et al (2019) ]. This design, like the standard non-reinforced design, results in robust learning about the second-order stimulus relative to an unpaired control ( Leidl et al, 2018 ; Williams-Spooner et al, 2019 ). In reward learning, reinforced serial S2→S1 presentations lead to higher level of responding during training compared to non-reinforced S2→S1 presentations ( Holland, 1980 ).…”