Fig. 6

Neonatal peripheral inflammatory pain diminished the oxytocin receptor expression in the hippocampus of the juvenile brain. Immunohistochemical staining measured the expression and distribution of the oxytocin receptor in the CA1, CA2, and CA3 regions of the hippocampus. P21 rats were subjected to formalin injections or saline injections at P3–P5 age. a Oxytocin receptor-positive cells (green) and NeuN-positive cells (red, shown as purple due to overlay with blue of Hoechst 33342 nuclei staining) in the hippocampus from the control and formalin groups. The first row in each group shows oxytocin receptor only, and the next row shows the overlay images of all three immunostainings. Scale bars = 50 μM. b, c Quantified data from experiments in a. The numbers of oxytocin receptor/NeuN double-positive cells per survey area under × 20 magnification. These double-labeled cells in both CA1 and CA2 were significantly less in male rats in the formalin group comparing to male controls (b). A trend of reduced oxytocin receptor level was also seen in CA3. In female rats of the formalin group, a significant reduction of oxytocin-positive neurons was only seen in the CA1 region, although there was a trend of reduction in CA2 (c). *P < 0.05 vs. control, ***P < 0.001 vs. control; n = 6–7 per group