Figure 4.

Carrying out the fluoxetine pre-treatment in the absence of light decreases its effectiveness

(A) Experimental timeline: Fluoxetine is added to tadpoles' rearing solution at 16:00 and then tadpoles are maintained either on the regular 12:12 light/dark schedule (left time-line) or on a 24 h dark schedule (right time-line) until testing. Tadpoles are tested 24 h later, at 16:00 on the following day.

(B and C) Dot plots showing the average percent of developmental stage 48 and (C) stage 49 control and fluoxetine-exposed tadpoles (green dots) when the fluoxetine exposure was carried out on a 12:12 light dark schedule and when the exposure was carried out entirely in darkness (24-h dark schedule). The total number of trials is shown in parentheses. Notice that the fluoxetine effect on preference for light is markedly attenuated when the pre-treatment is carried out in the dark, suggesting that endogenous levels of serotonin release are relatively lower in the dark. Also notice that the control tadpoles that were housed in the dark for 24 h before testing display a modest decrease in preference for light, suggesting that normal serotonin release during the day shapes the strength of preference for light (B and C, A Kruskal-Wallis non-parametric statistical test was used to determine if at least one experimental group was statistically different from the others. This was followed by a pairwise non-parametric Mann-Whitney test to compare specific groups; ∗∗p < 0.01, ∗∗∗p < 0.001 as determined by Mann-Whitney U test). Error bars represent SEM.