Chemogenetic activation of CRF neurons as a model of chronic stress produces sex-specific physiological and behavioral effects

Abstract

Trauma and chronic stress exposure are the strongest predictors of lifetime neuropsychiatric disease presentation. These disorders often have significant sex biases, with females having higher incidences of affective disorders such as major depression, anxiety, and PTSD. Understanding the mechanisms by which stress exposure heightens disease vulnerability is essential for developing novel interventions. Current rodent stress models consist of a battery of sensory, homeostatic, and psychological stressors that are ultimately integrated by corticotropin-releasing factor (CRF) neurons to trigger corticosteroid release. These stress paradigms, however, often differ between research groups in the type, timing, and duration of stressors utilized. These inconsistencies, along with the variability of individual animals’ perception and response to each stressor, present challenges for reproducibility and translational relevance. Here, we hypothesized that a more direct approach using chemogenetic activation of CRF neurons would recapitulate the effects of traditional stress paradigms and provide a high-throughput method for examining stress-relevant phenotypes. Using a transgenic approach to express the Gq-coupled Designer Receptor Exclusively Activated by Designer Drugs (DREADD) receptor hM3Dq in CRF-neurons, we found that the DREADD ligand clozapine-N-oxide (CNO) produced an acute and robust activation of the hypothalamic-pituitary-adrenal (HPA) axis, as predicted. Interestingly, chronic treatment with this method of direct CRF activation uncovered a novel sex-specific dissociation of glucocorticoid levels with stress-related outcomes. Despite hM3Dq-expressing females producing greater corticosterone levels in response to CNO than males, hM3Dq-expressing males showed significant typical physiological stress sensitivity with reductions in body and thymus weights. hM3Dq-expressing females while resistant to the physiological effects of chronic CRF activation, showed significant increases in baseline and fear-conditioned freezing behaviors. These data establish a novel mouse model for interrogating stress-relevant phenotypes and highlight sex-specific stress circuitry distinct for physiological and limbic control that may underlie disease risk.

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“…CRF is a key regulator of the body’s stress response and is closely associated with various psychiatric disorders, including depression. Overproduction of CRF is a mechanism that activates the HPA axis ( Montgomery et al, 2023 ). Furthermore, cortisol (CORT), which acts downstream of the HPA axis, plays a significant role in the pathogenesis of depression.…”

An Interaction between Brain-Derived Neurotrophic Factor and Stress-Related Glucocorticoids in the Pathophysiology of Alzheimer’s Disease

“…It is recognized that females have higher incidences of affective disorders, including anxiety, PTSD, and major depression, although mechanisms under the sex biases remain unclear. Montgomery et al (2023) showed an acute activation of the HPA axis by clozapine-N-oxide (CNO) in the transgenic mice expressing the Gq-coupled Designer Receptor exclusively stimulated by the Designer Drugs (DREADD) receptor hM3Dq in corticotropin-releasing factor (CRF, or CRH) neurons and found a novel sex-specific dissociation of GCs levels using the CRH activation method [29]. Although hM3Dq-expressing males displayed physiological stress sensitivity, including reductions in body and thymus weights, the corticosterone levels in response to CNO in the hM3Dq females were greater than those in males.…”

“…Although hM3Dq-expressing males displayed physiological stress sensitivity, including reductions in body and thymus weights, the corticosterone levels in response to CNO in the hM3Dq females were greater than those in males. The hM3Dq female animals also showed significant increases in baseline and fear-conditioned freezing behaviors, suggesting a possible contribution of activation of CRH neurons to sex-specific behaviors [29]. You et al (2023) used a predator scent stimulus (PSS) paradigm where mice were exposed to a volatile predator cue (e.g., cat odor) as a psychological stressor and found that appetite changes were caused by PSS [30].…”

Stress-activated brain-gut circuits disrupt intestinal barrier integrity and social behaviour

“…To test whether PVH CRH + neurons can control enteric immunity and barrier function, we expressed the excitatory designer receptor exclusively activated by designer drugs (DREADD) hM3Dq in the PVH of Crh Cre mice. Similar to a previously established method to induce stress responses by chronically activating CRH + cells 25 , we performed chemogenetic activation of PVH CRH + neurons by administering clozapine N-oxide (CNO) once daily for 10 consecutive days, to mimic conditions during the 10 day CSDS paradigm ( Fig. 4h , i ).…”