Fig. 6

nptx2b Overexpression in HCRT Cells Reduces Sensitivity to the Sleep-Promoting Effect of Melatonin

(A–C) Larvae kept under 14 hr light:10 hr dark conditions (LD) were recorded under constant dim (10 lux) light (LL, gray bar represent the subjective dark period). All larvae (n = 48–52 per genotype for each treatment) demonstrate rhythmic activity under control conditions (A, p < 0.0001), but after melatonin treatment (1 μM), activity was arrhythmic and reduced while genotype effect was significant (p < 0.005), with hcrt:NPTX2b fish being more resistant than wild-type siblings (B). (C) Notably, hcrt:NPTX2b larvae are resistant while hcrtr−/− larvae are sensitive (Appelbaum et al., 2009) to melatonin.

(D–H) A similar phenotype was observed in adults under LD (n = 11 for each genotype). Sleep time of representative individuals did not increase in hcrt:NPTX2b transgenic fish (E) after melatonin (100 μM) as compared to wild-type siblings (D). Percentage increase of sleep time (F), number of wake/sleep transitions (G), and sleep bout length (H) per hour during the day and after melatonin administration are shown. Statistical comparisons were performed with t tests in adults, and repeated-measures ANOVA with grouping factor in larvae. Each value represents mean ± SEM.