Shuttlebox avoidance in rhesus monkeys: effects on plasma cortisol and beta-endorphin

Area of Science:

• Neuroscience
• Behavioral Endocrinology
• Animal Behavior

Background:

• Stress response in animals is influenced by prior experiences.
• Cortisol and beta-endorphin are key stress hormones.
• Shuttlebox paradigms are used to study stress and avoidance learning.

Purpose of the Study:

• To investigate the influence of prior shuttlebox experience on plasma cortisol and beta-endorphin levels in monkeys.
• To compare hormonal responses between extensively pretrained and inexperienced monkeys under different shuttlebox conditions.

Main Methods:

• Monkeys with varying shuttlebox experience (extensive pretraining vs. minimal) were exposed to a shuttlebox under three conditions: no shock, inescapable shock, or re-exposure without shock.
• Plasma cortisol and beta-endorphin levels were measured immediately after exposure.
• Baseline hormone levels were also measured in home cages for pretrained animals.

Main Results:

• Inexperienced monkeys showed similar cortisol elevations from mere box exposure as from exposure plus shock.
• Pretrained monkeys exhibited smaller cortisol increases with box exposure alone compared to shock exposure.
• Plasma beta-endorphin levels showed sporadic elevations and were lower at baseline in pretrained animals.
• Pretrained animals had lower baseline cortisol levels compared to controls.

Conclusions:

• Behavioral factors, particularly prior experience and learned avoidance, significantly modulate acute stress hormone responses (cortisol) in monkeys.
• Learned behavioral strategies may influence the physiological impact of stressful environments.
• The study highlights the role of behavioral history in shaping neuroendocrine responses to stress.