Corticosterone Treatment and Incubation Time After Contextual Fear Conditioning Synergistically Induce Fear Memory Generalization in Neuropeptide S Receptor-Deficient Mice

Abstract

Fear memory generalization is a learning mechanism that promotes flexible fear responses to novel situations. While fear generalization has adaptive value, overgeneralization of fear memory is a characteristic feature of the pathology of anxiety disorders. The neuropeptide S (NPS) receptor (NPSR) has been shown to be associated with anxiety disorders and has recently been identified as a promising target for treating anxiety disorders. Moreover, stress hormones play a role in regulating both physiological and pathological fear memories and might therefore also be involved in anxiety disorders. However, little is known about the interplay between stress hormone and the NPS system in the development of overgeneralized fear. Here, we hypothesize that NPSR-deficient mice with high corticosterone (CORT) levels during the fear memories consolidation are more prone to develop generalized fear. To address this hypothesis, NPSR-deficient mice were submitted to a contextual fear conditioning procedure. Immediately after conditioning, mice received CORT injections (2.5 or 5 mg/kg). One day and 1 month later, the mice were tested for the specificity and strength of their fear memory, their anxiety level, and their startle response. Moreover, CORT blood levels were monitored throughout the experiment. Using this protocol, a specific contextual fear memory was observed in all experimental groups, despite the 5-mg/kg CORTtreated NPSR-deficient mice. This group of mice showed a generalization of contextual fear memory and a decreased startle response, and the females of this group had significantly less body weight gain. These findings indicate that interplay between CORT and the NPS system during the consolidation of fear memories is critical for the generalization of contextual fear.

Neuropeptide‐S‐receptor deficiency affects sex‐specific modulation of safety learning by pre‐exposure to electric stimuli

“…Both stressed and nonstressed male NPSR +/− mice expressed an intermediate phenotype. Notably, the NPSR genotype neither affects reactivity to the electric stimuli during safety conditioning (see Supplementary Information, Figure S5B and 5C) nor the corticosterone response to electric stimuli as previously shown …”

“…In the expression session, freezing during the safety CS presentations was significantly reduced compared to freezing behavior to the context in both, stress and nonstressed male C57BL/6J mice ( Figure 2B; ANOVA: trial type: Information, Figure S1B). There was no main effect of the stress condition (F (1,40) = 0.06, P = .80) but a significant interaction between stress condition and trial type (F (1,40) = 32.47 P < .0001). Post-hoc Sidak's multiple comparison test revealed that freezing behavior during the safety CS presentation was significantly lower in stressed than in nonstressed male C57BL/6J mice (t [80] = 2.26, P = .05), while contextual freezing did not differ (t [80] = 1.79, P = .15).…”

“…During the acclimation session, all stressed mice showed increased freezing behavior in the novel context, which con- Figure S5B and 5C) nor the corticosterone response to electric stimuli as previously shown. 39,40 Human, as well as rodent studies investigating the role of the NPS system in anxiety-related behaviors have come to the general consensus that NPS plays an important role in the regulation of anxiety, fear and stress-related behaviors. [17][18][19][20][21] Generally, NPSR-deficient animals show a more anxious phenotype but not impaired contextual or cued fear learning.…”

Dissociative Effects of Neuropeptide S Receptor Deficiency and Nasal Neuropeptide S Administration on T-Maze Discrimination and Reversal Learning

“…These mice are a commonly used tool to investigate functions of the NPS system [ 29 , 51 , 52 ], because there is a well-investigated human polymorphism of the NPSR gene that is associated with an increased risk for panic disorders [ 53 , 54 , 55 , 56 ]. However, NPSR-deficient mice are relatively inconspicuous in most behavioral tests and only show modest, if any, changes, such as being slightly less active, more anxious, more fearful or more stress-sensitive than their wild-type littermates [ 29 , 31 , 51 , 52 , 57 , 58 , 59 ]. Novel object recognition, as well as the learning and extinction of classical conditioned fear, is not affected by NPSR deficiency [ 29 , 59 ], while safety learning is improved in male NPSR-deficient mice [ 52 ].…”

Acute stress leaves fear generalization in healthy individuals intact

“…Prefrontal and medial-temporal brain areas critically involved in fear generalization (Greenberg et al, 2013;Lissek, Bradford, et al, 2014;Lopresto et al, 2016;Onat & Büchel, 2015) are known to be particularly sensitive to stress and stress mediators (de Kloet, Joels, & Holsboer, 2005;Krugers, Karst, & Joels, 2012;Roozendaal et al, 2006). Furthermore, initial evidence in humans and animals suggests that stress and stress hormones may induce increased fear generalization (Bender, Otamendi, Calfa, & Molina, 2018;Dunsmoor, Otto, & Phelps, 2017;Kaouane et al, 2012;Kolodziejczyk & Fendt, 2020).…”