Brain dysfunction during warming is linked to oxygen limitation in larval zebrafish
Anna H Andreassen1, Petter Hall1, Pouya Khatibzadeh1
1Department of Biology, Faculty of Natural Sciences, Norwegian University of Science and Technology, Trondheim, 7491 Norway.
Summary
The upper thermal limit in zebrafish is not caused by brain depolarization. Instead, insufficient oxygen impairs brain function, leading to reduced neural activity and loss of response to stimuli.
Area of Science:
- Physiology
- Neuroscience
- Climate Change Biology
Background:
- Understanding animal thermal tolerance is vital for predicting responses to heat waves.
- Mechanisms limiting upper thermal tolerance in animals, especially fish, are poorly understood.
- A hypothesis suggests brain thermal tolerance and global brain depolarization limit fish upper thermal limits.
Purpose of the Study:
- To investigate the physiological mechanisms underlying the upper thermal tolerance limit (CTmax) in larval zebrafish (Danio rerio).
- To determine if global brain depolarization causes CTmax in zebrafish.
- To explore the role of oxygen availability in thermal tolerance and brain function.
Main Methods:
- Developed methods for measuring CTmax in larval zebrafish.
- Simultaneously recorded brain activity using GCaMP6s calcium imaging.
- Manipulated water oxygen levels during controlled warming experiments.
Main Results:
- CTmax occurred before global brain depolarization, refuting the hypothesis.
- CTmax coincided with a decline in spontaneous neural activity and loss of visual response.
- Oxygen availability significantly affected neural activity and CTmax.
Conclusions:
- Upper thermal tolerance in zebrafish larvae is limited by insufficient oxygen availability.
- Impaired brain function due to hypoxia, not brain depolarization, determines CTmax.
- Oxygen levels are critical for maintaining neural function and thermal limits in fish.
