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Updated: Sep 23, 2026
Restraint to Induce Stress in Mice and Rats
Published on: December 6, 2024
Effects of single and repeated prolonged stress on mu-opioid receptor mRNA expression in rat gross hypothalamic and
Masato Yamamoto1, Teruhisa Komori, Takuya Matsumoto
1Department of Psychiatry, Mie University School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan. makun7@aol.com
Abstract:
This study tested the hypothesis that stress-induced opioid peptides may have stimulative and inhibitive influence on mu opioid receptor (MOR) mRNA expression and hypothalamus. Several studies have investigated the effects of stress on MOR mRNA expression in rat brain, but almost none compared the response to single versus repeated stresses. Here, we examined the effects of single and repeated stress on MOR mRNA expression in different rat brain regions using reverse transcriptase-polymerase chain reaction (RT-PCR). Following a single episode of restraint stress for 4 h (1R) or 4 h per day on 2 (2R) or 3 (3R) consecutive days, the hypothalamus and midbrain were removed immediately and MOR mRNA levels in both regions were determined by RT-PCR. Blood samples were also collected for simultaneous measurement of serum adrenocorticotropic hormone (ACTH) and corticosterone (CS). MOR mRNA expression was significantly higher in both regions in the 2R group, whereas expression levels in the 3R group did not differ from controls. In the 1R group, hypothalamic MOR expression was equivalent to that in controls, but expression was significantly higher in the midbrain. Serum ACTH levels were significantly higher only in the 1R group, whereas serum CS was significantly higher in both the 1R and 3R groups. Our findings indicate that the influence of restraint stress on MOR mRNA expression in the hypothalamus is different than in the midbrain region in rats. Endogenous opioid peptides released in response to stress may paradoxically have an effect on the HPA axis.
Insights
Restraint stress impacts mu opioid receptor (MOR) mRNA expression differently in rat brain regions. Repeated stress initially increases MOR mRNA, but prolonged stress shows no significant change, suggesting complex stress-opioid interactions.
Area of Science:
- Neuroscience
- Endocrinology
- Molecular Biology
Background:
- Stress significantly impacts the brain's neurochemical environment.
- Opioid peptides play a crucial role in stress response and neuroregulation.
- Understanding stress effects on mu opioid receptor (MOR) mRNA expression is vital for neurobiological research.
Purpose of the Study:
- To investigate the differential effects of single versus repeated restraint stress on MOR mRNA expression in specific rat brain regions.
- To compare MOR mRNA expression levels in the hypothalamus and midbrain following varying stress durations.
- To correlate stress-induced changes in MOR mRNA with hormonal responses (ACTH, corticosterone).
Main Methods:
- Utilized reverse transcriptase-polymerase chain reaction (RT-PCR) to quantify MOR mRNA levels.
- Administered single (1R) or repeated (2R, 3R) 4-hour restraint stress protocols to rats.
- Measured serum adrenocorticotropic hormone (ACTH) and corticosterone (CS) levels.
Main Results:
- MOR mRNA expression was elevated in both hypothalamus and midbrain after 2 days of stress (2R).
- 3 days of stress (3R) resulted in MOR mRNA levels similar to controls.
- Single stress (1R) increased midbrain MOR mRNA but not hypothalamic levels; only 1R showed elevated ACTH.
Conclusions:
- Restraint stress exerts region-specific effects on MOR mRNA expression in the rat brain.
- The impact of stress on MOR mRNA expression is dependent on the duration and pattern of exposure.
- Stress-induced opioid peptides may have complex, potentially paradoxical, influences on the hypothalamic-pituitary-adrenal (HPA) axis.
