Oxidation and Cognitive Impairment in the Aging Zebrafish.

BACKGROUND: The zebrafish has become an established model organism in aging research giving insight into general aging processes in vertebrates. Oxidative stress in aging may damage proteins and lipids in brain cells. Enhanced levels of oxidized macromolecules exert neurotoxic effects that could lead to disturbances in neuronal functioning and cognitive skills. OBJECTIVE: This study aims to investigate a possible relation between oxidative stress and learning deficits during aging in zebrafish. METHODS: We tested zebrafish of different ages in a color discrimination paradigm for associative learning and in a hole board task for spatial learning abilities. Afterwards, we determined the levels of oxidized lipids and proteins as well as the amount of lipofuscin in the learning-relevant brain regions of animals of the same age. RESULTS: While young zebrafish at the age of 1 year successfully completed both learning tasks, cognitive abilities were significantly impaired in older animals. Learning deficits occurred at the age of 2 years, where we also detected significantly increased levels of lipofuscin and oxidized proteins in the zebrafish medial and lateral pallial areas of the dorsal telencephalon. CONCLUSION: These data suggest that enhanced oxidative stress may contribute to behavioral and cognitive impairments in the aging zebrafish.

Acute administration of THC impairs spatial but not associative memory function in zebrafish.

RATIONALE: The present study examined the effect of acute administration of endocannabinoid receptor CB1 ligand ∆-9-tetrahydrocannabinol (THC) on intracellular signalling in the brain and retrieval from two different memory systems in the zebrafish (Danio rerio). METHODS: First, fish were treated with THC and changes in the phosphorylation level of mitogen-activated protein (MAP) kinases Akt and Erk in the brain were determined 1 h after drug treatment. Next, animals of a second group learned in a two-alternative choice paradigm to discriminate between two colours, whereas a third group solved a spatial cognition task in an open-field maze by use of an ego-allocentric strategy. After memory acquisition and consolidation, animals were pharmacologically treated using the treatment regime as in the first group and then tested again for memory retrieval. RESULTS: We found an enhanced Erk but not Akt phosphorylation suggesting that THC treatment specifically activated Erk signalling in the zebrafish telencephalon. While CB1 agonist THC did not affect behavioural performance of animals in the colour discrimination paradigm, spatial memory was significantly impaired. The effect of THC on spatial learning is probably specific, since neither motor activity nor anxiety-related behaviour was influenced by the drug treatment. That indicates a striking influence of the endocannabinoid system (ECS) on spatial cognition in zebrafish. CONCLUSIONS: The results are very coincident with reports on mammals, demonstrating that the ECS is functional highly conserved during vertebrate evolution. We further conclude that the zebrafish provides a promising model organism for ongoing research on the ECS.