Lab Animal Stress Corticosterone Measuring Welfare Rodents

Stress in laboratory animals is a critical factor influencing both
animal welfare and the reliability of experimental results.
Corticosterone, a glucocorticoid hormone, is a widely recognized
biomarker for assessing stress in rodents, particularly mice and rats.
This article delves into the importance of corticosterone measurements,
their applications, and complementary markers that offer a holistic
understanding of stress in laboratory animals.

Why Measure Corticosterone?

Corticosterone is secreted by the adrenal cortex in response to stress,
making it an effective indicator of physiological stress levels in
rodents. Measuring corticosterone helps researchers understand acute
stress responses, monitor chronic stress exposure, and establish
baseline levels that ensure experiment validity. Different methods exist
to measure corticosterone, including plasma, urine, feces, and even
non-invasive imaging techniques, each with advantages and limitations.

Methods of Measuring Corticosterone

Plasma and Serum Analysis 🩺

Blood sampling is one of the most common methods for measuring
corticosterone, often conducted using an enzyme-linked immunosorbent
assay (ELISA) or radioimmunoassay (RIA). Despite its popularity, this
method is invasive and can induce stress, potentially confounding the
results. Acclimating animals to handling or using anesthesia can
mitigate stress, resulting in more accurate baseline measurements (Fomby
et al., 2004).

Urine and Feces Analysis 💩

Non-invasive methods, such as measuring corticosterone metabolites in
urine and feces, are increasingly favored for reducing stress during
sample collection. These approaches provide reliable adrenocortical
activity data, reflecting diurnal variations and responses to
pharmacological challenges (Lepschy et al., 2007). For example, enzyme
immunoassay (EIA) has been validated for measuring corticosterone
metabolites in rats, making it an effective tool for assessing
adrenocortical responses.

Hair or Fur Samples 🧑‍🔬

Corticosterone accumulates in hair or fur, offering a marker for chronic
stress exposure over longer periods. This method is beneficial for
longitudinal studies, where understanding cumulative stress is crucial.

Salivary Corticosterone 💧

Salivary corticosterone collection provides a minimally invasive
approach to assess acute stress. Although it offers a real-time measure,
careful technique is necessary to avoid contamination or insufficient
sampling.

Non-Invasive Imaging

Recent advancements have led to the development of genetically encoded
stress indicators for non-invasive imaging of corticosterone in living
animals. This technique enables real-time monitoring of stress responses
without blood sampling, significantly reducing distress (Kim et al.,
2005).

Factors Influencing Corticosterone Levels

Corticosterone levels can vary depending on multiple factors, including
sex, time of day, and type of stressor. For example, a meta-analysis
found that sex, time since lights were on, and type of control can
significantly influence basal corticosterone concentrations in mice (Van
Der Mierden et al., 2020). Additionally, the kinetics of corticosterone
release vary depending on the stressor type, with the magnitude and
duration correlating with the severity of the stress experienced (2019).

Complementary Stress Markers

While corticosterone is a critical indicator of stress, combining it
with other physiological and behavioral markers provides a more
comprehensive assessment of animal welfare.

Behavioral Assessments

Behavioral changes, such as increased anxiety, altered locomotor
activity, and changes in nesting behavior, can signal stress. These
behavioral indicators are often used alongside corticosterone
measurements to provide a holistic understanding of animal well-being
(Hohlbaum et al., 2018).

Physiological Indicators

Other physiological changes, like variations in body weight, food
intake, heart rate, blood pressure, and immune function, can also
indicate stress. Elevated corticosterone has been linked to reduced body
growth and altered immune responses in animals such as broiler chickens
(Post et al., 2003).

Molecular Markers

Molecular indicators, such as changes in stress-related gene expression
(e.g., CRH, ACTH) or alterations in neurotransmitter levels, can provide
insights into the biological underpinnings of stress. These are valuable
for more profound analyses of the hypothalamic-pituitary-adrenal (HPA)
axis.

Applications in Laboratory Animal Research

Corticosterone measurements have diverse applications in laboratory
animal research:

– Assessing Welfare: Routine monitoring can help identify

environmental stressors, such as overcrowding, insufficient
enrichment, or improper handling practices.

– Improving Study Designs: Minimizing stress is crucial for

improving the consistency and reproducibility of experimental
results.

– Developing Interventions: Corticosterone data is essential for

testing the efficacy of stress-reducing interventions like
environmental enrichment or refined handling methods.

Challenges and Future Directions

The future of corticosterone monitoring lies in developing more refined,
non-invasive methods. Advancements like wearable sensors or microchip
technology could enhance stress monitoring while minimizing animal
discomfort. Moreover, careful experimental controls are essential when
interpreting corticosterone data, as levels can fluctuate based on
circadian rhythms and individual animal variability.

Corticosterone is a pivotal marker for assessing stress in laboratory
rodents. While plasma and serum analyses are traditional methods,
non-invasive approaches such as fecal analysis and advanced imaging are
gaining prominence. Complementing corticosterone data with behavioral,
physiological, and molecular markers provides a comprehensive framework
for evaluating stress and ensuring animal welfare in research settings.
By leveraging these diverse indicators, researchers can improve both the
ethical standards of animal experimentation and the reliability of their
findings.

References

– Van Der Mierden, S., Leenaars, C., Boyle, E., Ripoli, F., Gass, P.,

Durst, M., Goerlich-Jansson, V., Jirkof, P., Keubler, L., Talbot,
S., Habedank, A., Lewejohann, L., Tolba, R., & Bleich, A. (2020).
Measuring endogenous corticosterone in laboratory mice – a mapping
review, meta-analysis, and open source database. ALTEX.

– (2019). Grading Distress of Different Animal Models for

Gastrointestinal Diseases Based on Plasma Corticosterone Kinetics.
Animals : an Open Access Journal from MDPI, 9.

– Kim, S., Ozawa, T., & Umezawa, Y. (2005). Genetically encoded stress

indicator for noninvasively imaging endogenous corticosterone in
living mice. Analytical chemistry, 77 20, 6588-93.

– Lepschy, M., Touma, C., Hrubý, R., & Palme, R. (2007). Non-invasive

measurement of adrenocortical activity in male and female rats.
Laboratory Animals, 41, 372 – 387.

– Fomby, L., Wheat, T., Hatter, D., Tuttle, R., & Black, C. (2004).

Use of CO2/O2 anesthesia in the collection of samples for serum
corticosterone analysis from Fischer 344 rats. Contemporary topics
in laboratory animal science, 43 2, 8-12.

– Hohlbaum, K., Bert, B., Dietze, S., Palme, R., Fink, H., &

Thône-Reineke, C. (2018). Impact of repeated anesthesia with
ketamine and xylazine on the well-being of C57BL/6JRj mice. PLoS
ONE, 13.

– Touma, C., Sachser, N., Möstl, E., & Palme, R. (2003). Effects of

sex and time of day on metabolism and excretion of corticosterone in
urine and feces of mice. General and comparative endocrinology, 130
3, 267-78.

– Post, J., Rebel, J., & Huurne, A. (2003). Physiological effects of

elevated plasma corticosterone concentrations in broiler chickens.
Poultry science, 82 8, 1313-8.

Join the conversation 💬: What other stress markers do you use in your
research? Share your insights and experiences to help advance the
understanding and management of stress in laboratory animals.

Stay tuned for more scientific insights into laboratory animal welfare
and research innovations! 🚀