The structure of spontaneous locomotion in zebrafish larvae and mice during the active phase of the circadian cycle (light for zebrafish larvae, dark for mice).

(A) Representative sequence of spontaneous activity (20 s) recorded at 6 dpf in one control and one larva exposed to 1 mg/L PFOS. In the control larva, the spontaneous activity consists of short, evenly spread bouts of swimming. In the larva exposed to 1 mg/L PFOS, the spontaneous activity consists of clusters of intense activity separated by extended periods of inactivity. Background noise (displacement below 0.2 mm/frame) shaded in gray; inset in top panel – magnification of a representative bout of spontaneous activity. (B) Quantification of frequency of spontaneous bouts of activity. Note the dramatic decrease in bout frequency induced by exposure to 1 mg/L PFOS. (C) Average distance moved during one spontaneous bout of activity. Zebrafish larvae exposed to 1 mg/L PFOS have a hyperactive phenotype characterized by a 2.5 fold higher distance swum during spontaneous bouts of activity. (D) Illustrative sequence of spontaneous locomotion during the active phase of the circadian cycle in one control and one mouse exposed to 3 mg/kg/dy PFOS during gestation. The spontaneous locomotor activity (visits) in the homecage is integrated over consecutive, non-overlapping 10 min bins and spline-interpolated for clarity. (E, F) Similar to the pattern found in zebrafish larvae, the mice exposed to 3 mg/kg PFOS display less frequent (E), but more intense (F) bouts of activity. B, C, E, F – one-way ANOVA followed by Dunnett's post-hoc test; * p<0.05 PFOS exposed vs. control. The number of independent observations is indicated at the bottom of each column in B, C, E and F.