Citation

McMurray KMJ, Gray A, Horn P, Sah R. Neuroscience 2020; ePub(ePub): ePub.

Affiliation

Department of Pharmacology & Systems Physiology, University of Cincinnati, United States; Veterans Administration (VA) Medical Centre, Cincinnati, OH 45237, United States. Electronic address: sahr@uc.edu.

Copyright

(Copyright © 2020, International Brain Research Organization, Publisher Elsevier Publishing)

DOI

10.1016/j.neuroscience.2019.12.009

PMID

31930959

Abstract

There is considerable interest in pre-trauma individual differences that may contribute to increased risk for developing post-traumatic stress disorder (PTSD). Identification of underlying vulnerability factors that predict differential responses to traumatic experiences is important. Recently, the relevance of homeostatic perturbations in shaping long-term behavior has been recognized. Sensitivity to CO₂ inhalation, a homeostatic threat to survival, was shown to associate with the later development of PTSD symptoms in veterans. Here, we investigated whether behavioral sensitivity to CO₂ associates with PTSD-relevant behaviors and alters forebrain fear circuitry in mice. Mice were exposed to 5% CO₂ or air inhalation and tested one week later on acoustic startle and footshock contextual fear conditioning, extinction and reinstatement. CO₂ inhalation evoked heterogenous freezing behaviors (high freezing CO₂-H and low freezing CO₂-L) that significantly associated with fear conditioning and extinction behaviors. CO₂-H mice elicited potentiated conditioned fear and delayed extinction while behavioral responses in CO₂-L mice were similar to the air group. Persistent neuronal activation marker ΔFosB immunostaining revealed altered regional neuronal activation within the hippocampus, amygdala and medial pre-frontal cortex that correlated with conditioned fear and extinction. Inter-regional co-activation mapping revealed disruptions in the coordinated activity of hippocampal dentate-amygdala-infralimbic regions and infralimbic-prelimbic associations in CO₂-H mice that may explain their enhanced fear phenotype. In conclusion, our data support an association of behavioral sensitivity to interoceptive threats such as CO₂ with altered fear responding to exteroceptive threats and suggest that "CO₂-sensitive" individuals may be susceptible to developing PTSD.

Copyright © 2019 IBRO. Published by Elsevier Ltd. All rights reserved.

Language: en

Keywords

CO(2) sensitivity; PTSD; extinction; fear; startle