Contrasting organizational versus activational effects of OXT neurons in adult social affiliation. A, Experimental timeline: fish were MTZ treated at different developmental stages, allowed to grow until adulthood and then tested for social affiliation. B, MTZ treatments during the first two weeks of life affect adult social affiliation. Social affiliation score = %T_shoal/(%T_shoal + %T_empty). Eight independent cohorts were treated at 4–6 d old, and only one cohort at later time points. Therefore, to obtain comparable sample sizes among the different age-treatment groups and a more representative sample, the data for 4- to 6-d-old MTZ treatment shown in this graph were generated by a MC simulation with 1000 iterations of samples of 15 individuals of each group (4- to 6-d-old MTZ treated vs untreated; see Materials and Methods, Statistical analysis, for details). C, D, Effect of early (4- to 6-d-old) MTZ treatment on (C) adult social affiliation and (D) total distance moved of eight independent cohorts of either MTZ treated at 4–6 d old (NTR+, MTZ+) or untreated control fish (NTR+, MTZ–); (E) adult social affiliation and (F) total distance moved of control cohorts not expressing the transgene, 4- to 6-d-old MTZ treated (NTR–, MTZ+) or untreated (NTR–, MTZ–). One-tailed p values were considered in B, C because there was an a priori directional hypothesis that MTZ treatment would ablate OXT neurons in fish expressing the oxt:GAL4;UAS-NTR-mCherry transgene and induce a decrease in social affiliation behavior. Data are presented as mean ± SEM. CoH, cohort. Full squares (purple or dark gray): untreated fish (MTZ–); open square or light gray: MTZ-treated fish (MTZ+).