Thesis Format

Integrated Article

The roles of corticotropin-releasing hormone (CRH) in stress-induced cognitive deficits in mice

Author

Xin Zhao, The University of Western OntarioFollow

Degree

Master of Science

Program

Neuroscience

Supervisor

Inoue, Wataru

2nd Supervisor

Muller, Lyle

Co-Supervisor

Abstract

Corticotropin-releasing hormone (CRH) is widely known as a hormone that mediates stress responses via the hypothalamus-pituitary-adrenal (HPA) axis. Besides its neuroendocrine release, CRH is also expressed in various neuron types distributed across brain areas. In the medial prefrontal cortex (mPFC), CRH has been shown to mediate stress-related behavioural and cognitive changes. Recently, our group showed that acute stress impaired spatial working memory in mice, and pharmacological blockade of CRHR1 in the mPFC prevented the stress-induced impairment. However, it remains unknown how stress affects the CRH-CRHR1 signalling in the mPFC relevant to spatial working memory impairment. We hypothesized that stress activates CRH-expressing interneurons in the mPFC and drives their CRH release to signal through CRHR1. We first confirmed that restraint stress increased the activity of CRH neurons in the posterior mPFC by using immunofluorescence for cFos and in vivo GCaMP6 calcium sensor-fibre photometry imaging. Next, we used a newly developed CRH sensor (GRAB_CRF) in freely behaving mice. Surprisingly, we discovered that extracellular CRH levels in the mPFC decreased during and after the restraint stress. The unexpected decrease in CRH sensor signal is possibly caused by the release of CRH-binding protein (CRHBP), and I provide supporting data that CRHBP profoundly decreases CRH sensor signal in ex vivo and in vivo. This study will help us understand how the CRH system in the mPFC mediates stress-induced working memory deficits.

Summary for Lay Audience

The medial prefrontal cortex (mPFC) is an important brain area in rodents in regulating higher cognitive functions and is sensitive to stress. Corticotropin-releasing hormone (CRH) is a well-known stress hormone that regulates the stress response. It is also a neuromodulator released in the brain to mediate stress-related behaviours and cognitive functions. Recently, our group has found that stress significantly impaired cognitive task performance in mice. Furthermore, this impairment was rescued by blocking CRH receptor type 1 (CRHR1) in the mPFC. These results indicated that CRH signalling in the mPFC is involved in stress-induced cognitive impairment. In the mPFC, a small subpopulation of neurons express CRH. Here we hypothesized that stress impairs cognitive functions by activating CRH-expressing neurons, which drives CRH release in the mPFC. To this end, I first confirmed that CRH neurons are activated by restraint stress. Next, I monitored the extracellular CRH levels in the mPFC during stress. Unexpectedly, CRH levels in the mPFC did not increase during and after the stress but decreased at the onset of the stress. We then hypothesized that there was a tonic CRH release during the baseline condition. Upon facing the stress, the CRH level was decreased by CRH-binding protein (CRHBP) which is a protein that can sequester free CRH from CRHR1. We then confirmed that CRHBP could decrease the free CRH levels in the mPFC in both ex vivo and in vivo experiments. This project will help us better understand how the mPFC CRH system mediates stress-induced cognitive impairment.

Recommended Citation

Zhao, Xin, "The roles of corticotropin-releasing hormone (CRH) in stress-induced cognitive deficits in mice" (2023). Electronic Thesis and Dissertation Repository. 9558.
https://ir.lib.uwo.ca/etd/9558

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