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Fig. 4 Hypophyseal blood flow is regulated by oxytocin signaling (A and B) Representative hypophyseal blood flow velocity traces before and after osmotic challenge (OC). Larvae treated with the Oxtr antagonist (Oxtr ant.) L-368,899 show no change in response to the OC as compared to their control sibling. (C) Mean velocity after OC in the Oxtr ant. cohort show an increase (p = 0.0033, paired t test, n = 7) that is not observed in L-368,899-antagonist-treated siblings (p = 0.2509, paired t test, n = 7). (D and E) Single-sided amplitude spectra show that while the frequency spectra of a control cohort were affected by the OC, larvae treated with the Oxtr ant. show no difference. (F) Variability in velocities was increased following OC (p = 0.0213, paired t test, n = 7) but not in Oxtr ant.-treated siblings (p = 0.7195, paired t test, n = 7). (G and H) Representative diameter traces showing vasoconstriction following OC of control sibling but not in larvae treated with Oxtr ant. (I) No significant change in the mean capillary diameter of the Oxtr ant.-treated larvae that were subjected to OC (p = 0.3892, paired t test, n = 7) compared to a decrease in diameter in the control cohort (p = 0.0001, paired t test, n = 7). (J) The ratio between diameter change to basal diameter after OC showed a significant difference between the control and antagonist-treated cohorts (p = 0.0010, Dunn’s multiple comparison, Oxtr ant.− n = 7, Oxtr ant.+ n = 7). (K–M) Mean velocity (p = 0.2008, paired t test, n = 7), variability of velocity (p = 0.8040, paired t test, n = 7), and diameter (p = 0.8509, paired t test, n = 7) of the AMCtA did not change after OC in Oxtr ant.+ larvae. The control Oxtr ant.− larvae also did not show any difference in mean velocity (p = 0.8573, paired t test, n = 7), variability of velocity (p = 0.8533, paired t test, n = 7), or diameter (p = 0.9422, paired t test, n = 7) in the AMCtA after the OC. Data are represented as mean ± SEM.