In search of stress: analysis of stress-related markers in mice after hindlimb unloading and social isolation

ABSTRACT

Objectives

Hindlimb unloading (HU), widely used to simulate microgravity effects, is known to induce a stress response. However, as single-housed animals are usually used in such experiments, social isolation (SI) stress can affect experimental results. In the present study, we aimed to delineate stressful effects of 3-day HU and SI in mice.

Methods

Three animal groups, HU, SI, and group-housed (GH) control mice, were recruited. A comprehensive analysis of stress-related markers was performed using ELISA, western blotting, and immunohistochemistry.

Results

Our results showed that blood corticosterone and activity of glucocorticoid receptors and cAMP response element-binding protein (CREB) in the hippocampus of SI and HU animals did not differ from GH control. However, SI mice demonstrated upregulation of the hippocampal corticotropin-releasing hormone (CRH), inducible NO synthase (iNOS), vesicular glutamate transporter 1 (VGLUT1), and glutamate decarboxylases 65/67 (GAD65/67) along with activation of Fos-related antigen 1 (Fra-1) in the amygdala confirming the expression of stress. In HU mice, the same increase in GAD65/67 and Fra-1 indicated the contribution of SI. The special HU effect was expressed only in neurogenesis attenuation.

Discussion

Thus, our data indicated that 3-day HU could not be characterized as physiological stress, but SI stress contributed to the negative effects of HU.

KEYWORDS:

• Hippocampus
• corticosterone
• glucocorticoid receptors
• Fra-1
• CREB
• iNOS
• CRH
• neurogenesis

Acknowledgments

Part of the analysis was performed at the Research Resource Center #441590 of Sechenov Institute of Evolutionary Physiology and Biochemistry, the Russian Academy of Sciences.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Conceptualization, M.V.G.; methodology, M.V.G. and A.A.N.; validation, M.V.G. and A.A.N.; formal analysis, E.A.O., Y.S.G., and A.A.N.; investigation, Y.S.G., S.D.N., and E.A.O.; data curation, E.V.C. and A.A.N.; writing – original draft preparation, A.A.N. and MVG.; writing – review and editing, M.V.G. and A.A.N.; visualization, E.A.O. and S.D.N.; funding acquisition, M.V.G. All authors have read and agreed to the published version of the manuscript.

Data availability statement

The data are available on reasonable request to the corresponding author.

Institutional review board statement

The animal study protocol was approved by the Institutional Ethics Committee of Sechenov Institute of Evolutionary Physiology and Biochemistry Russian Academy of Sciences (# 12-2/2021, 23.12.2021).

Additional information

Funding

This research was funded by RFBR, grant #20-015-00062, and by a Russian Government program #075-967-23-00.