de Paiva, J. P. Q. | bioRxiv Science

bioRxiv2020

The Posterior Insular Cortex is Necessary for the Consolidation of Tone Fear

The insular cortex (IC) is notably implicated in emotional and cognitive processing; however, little is known regarding to what extent its two main subregions play functionally distinct roles on memory consolidation of conditioned fear tasks. Here we verified the effects of temporary functional inactivation of the anterior (aIC) and posterior IC (pIC) on contextual and tone fear memory. Rats received post-training bilateral infusions of the GABAA receptor agonist muscimol into either the aIC or pIC and were tested 48 and 72 hours after the conditioning session to assess contextual (CFC) and tone (TFC) fear conditioning, respectively. Inactivation of the aIC during memory consolidation did not affect fear memory for CFC or TFC. On the other hand, post-training inactivation of the pIC impaired TFC but not CFC. Our findings indicate that the pIC is a necessary part of the neural circuitry related to the consolidation of cued-fear memories. HighlightsO_LIWe studied the role of the anterior (aIC) and posterior (pIC) insula in fear memory C_LIO_LIPost-training inactivation of aIC and pIC did not impact contextual fear conditioning C_LIO_LIThe pIC but not aIC is necessary for the consolidation of tone fear conditioning C_LI

animal behavior and cognition↗

bioRxiv2019

Relationship between footshock intensity, post-training corticosterone release and contextual fear memory specificity over time

Overgeneralized fear has long been implicated in generalized anxiety and post-traumatic stress disorder, however, time-dependent mechanisms underlying memory retrieval are still not completely understood. Previous studies have revealed that stronger fear conditioning training protocols are associated with both increased post-training corticosterone (CORT) levels and fear responses at later retrieval tests. Here we used discriminative contextual fear conditioning (CFC) to investigate the relationship between post-training CORT levels and memory specificity in different retrieval timepoints. Wistar rats were exposed to CFC training with increasing footshock intensities (0.3, 0.6 or 1.0mA) and had their blood collected 30 min afterwards to measure post-training plasma CORT. After 2, 14 or 28 days, rats were tested for memory specificity either in the training or in the novel context. Regression analysis was used to verify linear and non-linear interactions between CORT levels and freezing. Higher footshock intensities increased post-training CORT levels and freezing times during tests in all timepoints. Moreover, stronger trainings elicited faster memory generalization, which was associated with higher CORT levels during memory consolidation. The 0.3mA training maintained memory specificity up to 28 days. Additionally, linear regressions suggest that the shift from specific to generalized memories is underway at 14 days after training. These results are consistent with the hypotheses that stronger training protocols elicit a faster generalization rate, and that this process is associated with increased post-training CORT release.\n\nHIGHLIGHTSStronger contextual fear conditioning (CFC) elicits higher plasma corticosterone (CORT).\n\nStrong CFC and high CORT levels increase the rate of memory generalization.\n\nWeak CFC and low CORT levels retain memory specificity up to 28 days.\n\nPost-training plasma CORT is linearly associated with remote generalized fear.

animal behavior and cognition↗