Figure 3. Aging in zebrafish is associated with sleep alterations, reduced intrinsic circadian rhythm of activity and cognitive performance, and these effects are counteracted by repeated overnight melatonin administration.

A: Change in percentage of sleep time at daytime (ZT 5–7) and at night (ZT 18–20), with or without 30-min melatonin (+MLT) pre-treatment in 1- and 4-year old zebrafish, relative to mean sleep time in 1-year old zebrafish during the day represented as 100%. B: Percentage of distance traveled at daytime and at night under constant dim light conditions in 1-year old (1-dL) and 4-year old (4-dL) zebrafish at baseline and after melatonin administration (1-dL-MLT and 4-dL-MLT), relative to 1-dL at daytime, represented as 100%. In A and B:* p< 0.05 relative to the same age and treatment condition at daytime; $ p<0.05 and $$ p<0.001, relative to the same age and time in the absence of melatonin treatment; # p< 0.05 and ## p<0.001, relative to the same time and treatment condition in the young group. C: Generalization of conditioned response after exposure to 2 days of different light conditions (LD or dL), with or without overnight melatonin administration in 1- and 4-year old zebrafish. Percentage of choosing the red arm of the T-maze at baseline (white), 2 days after the end of conditioning (diagonal) and 2 days after the end of conditioning with overnight melatonin treatment (black with dots). * p< 0.0001 relative to the same age and light condition at baseline; $ p<0.01, relative to the same age and light condition without melatonin treatment, # p<0.05 relative to the same age and treatment condition in LD. Data presented as group mean (SEM); N=8–10 fish per data point; Proc Mixed for all comparisons.