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Introduction: Despite its recent reputation as prosocial neurohormone, the most important physiological role of oxytocin (OT) is stimulating uterine contractions. Though it is well known that plasma OT concentrations change drastically during delivery, it remains unexplored whether and how OT receptors in the maternal brain are activated. We examined whether the responses of cells in the central amygdala (CeA), an OT receptor-rich limbic site involved in pain and fear memory regulation, to exogenously applied OT analogue, Thr-Gly-OT (TGOT), varies depending on delivery. Methods: Intracellular Ca2+ dynamics of the CeA cells were visualized in brain slices from female rats at virgin (VG), during pregnancy term days 16¬¬¬–21 (PT), within 24 hours after delivery (G0), and within one to three days after delivery (G3). The Ca2+ responses to 1 µM TGOT, 20 mM KCl (high K), and 300 µM ADP were compared. Results: We found that fraction of cells responding to TGOT, high K, and ADP differed significantly between the four delivery-associated terms. In particular, the fraction of cells responding to TGOT (TGOT responders) significantly increased from VG and PT at G0 and G3. Furthermore, the significant positive correlation between TGOT and high K response in TGOT-and-high K responders was reduced at G0, while that between TGOT and ADP responses in TGOT-and-ADP responders was increased at G0. Conclusion: These results indicate that the responses of CeA cells to an OT receptor agonist markedly change around delivery, which might play a role in controlling the labor-related pain and post-delivery emotional complications.

S. Karger AG, Basel