Physiological Responses Vary with Molecular Damage Outcomes after Recovery from Constant Light

Area of Science:

• Physiology
• Endocrinology
• Stress Biology

Background:

• The Damage-Fitness model links stress, damage, and repair to health outcomes.
• Understanding how hypothalamic-pituitary-adrenal (HPA) axis flexibility influences damage post-stress recovery is limited.

Purpose of the Study:

• To investigate the mechanisms linking HPA axis responses, cellular damage, and physiological traits in zebra finches after stress recovery.
• To determine if long-term stress exposure alters HPA axis-damage relationships.

Main Methods:

• Adult female zebra finches were exposed to normal photoperiod or constant light for 23 days, followed by a recovery period.
• Path analysis was used to examine morphological and physiological traits related to cellular damage.
• HPA axis reactivity, glucose reactivity, liver 4-hydroxynonaneal, liver protein carbonyl damage, and liver glucocorticoid receptor abundance were measured.

Main Results:

• In control birds, HPA axis reactivity was condition-dependent (linked to body mass) and associated with glucose reactivity and liver 4-hydroxynonaneal.
• This condition dependency of HPA axis reactivity was lost in birds recovering from constant light exposure.
• While HPA axis reactivity remained linked to glucose reactivity, this relationship did not correlate with damage markers post-stress.
• Liver glucocorticoid receptor abundance negatively correlated with liver protein carbonyl damage in controls, but this association disappeared after constant light recovery.

Conclusions:

• Long-term stress, like constant light, can rewire interconnected physiological networks, altering relationships between HPA axis function and cellular damage markers.
• These alterations persist even after the stressor is removed and recovery occurs.
• The adaptive significance of these physiological network rewiring events for fitness and performance remains to be elucidated.