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Contextual fear conditioning alter microglia number and morphology in the rat dorsal hippocampus


Chaaya, N and Jacques, A and Belmer, A and Beecher, K and Ali, SA and Chehrehasa, F and Battle, AR and Johnson, LR and Bartlett, SE, Contextual fear conditioning alter microglia number and morphology in the rat dorsal hippocampus, Frontiers in Cellular Neuroscience, 13 Article 214. ISSN 1662-5102 (2019) [Refereed Article]

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Copyright 2019 Chaaya, Jacques, Belmer, Beecher, Ali, Chehrehasa, Battle, Johnson and Bartlett. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License (

DOI: doi:10.3389/fncel.2019.00214


Contextual fear conditioning is a Pavlovian conditioning paradigm capable of rapidly creating fear memories to contexts, such as rooms or chambers. Contextual fear conditioning protocols have long been utilized to evaluate how fear memories are consolidated, maintained, expressed, recalled, and extinguished within the brain. These studies have identified the lateral portion of the amygdala and the dorsal portion of the hippocampus as essential for contextual fear memory consolidation. The current study was designed to evaluate how two different contextual fear memories alter amygdala and hippocampus microglia, brain derived neurotrophic factor (BDNF), and phosphorylated cyclic-AMP response element binding (pCREB). We find rats provided with standard contextual fear conditioning to have more microglia and more cells expressing BDNF in the dentate gyrus as compared to a context only control group. Additionally, standard contextual fear conditioning altered microglia morphology to become amoeboid in shape - a common response to central nervous system insult, such as traumatic brain injury, infection, ischemia, and more. The unpaired fear conditioning procedure (whereby non-reinforced and non-overlapping auditory tones were provided at random intervals during conditioning), despite producing equivalent levels of fear as the standard procedure, did not alter microglia, BDNF or pCREB number in any dorsal hippocampus or lateral amygdala brain regions. Despite this, the unpaired fear conditioning protocol produced some alterations in microglia morphology, but less compared to rats provided with standard contextual fear conditioning. Results from this study demonstrate that contextual fear conditioning is capable of producing large alterations to dentate gyrus plasticity and microglia, whereas unpaired fear conditioning only produces minor changes to microglia morphology. These data show, for the first time, that Pavlovian fear conditioning protocols can induce similar responses as trauma, infection or other insults within the central nervous system.

Item Details

Item Type:Refereed Article
Keywords:BDNF, contextual fear conditioning, dentate gyrus, hippocampus and amygdala, microglia
Research Division:Biomedical and Clinical Sciences
Research Group:Neurosciences
Research Field:Cellular nervous system
Objective Division:Health
Objective Group:Public health (excl. specific population health)
Objective Field:Mental health
UTAS Author:Johnson, LR (Associate Professor Luke Johnson)
ID Code:145081
Year Published:2019
Web of Science® Times Cited:13
Deposited By:Psychology
Deposited On:2021-06-29
Last Modified:2022-08-23
Downloads:13 View Download Statistics

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