Figure 2

c-fos expression stimulated by injection of formalin in the hindpaw increases with postnatal age in the lateral parabrachial nucleus (PB) but not in the superficial dorsal horn. A, Neuronal density in lamina I of dorsal horn decreases with postnatal age. B, Immunohistochemistry for c-fos (green) and NeuN (red) in the dorsal horn of a P3 rat two hours after injection of formalin in the hindpaw. Co-localization of c-fos with NeuN in the same section of dorsal horn can be seen in yellow. Scale bar, 100 μm. C, Percentage of NeuN-positive lamina I neurons that expressed c-fos after injection of formalin in the hindpaw in P3 (N = 3), P10 (N = 5), P20 (N = 3) and adult (N = 5) rats. Injection of formalin in the neonatal rat hindpaw induced similar level of stimulation of lamina I neurons to that in the adult rat. D, Neuronal density in the lateral PB remained constant with postnatal age. E, Immunohistochemistry for c-fos (green) and NeuN (red) in the lateral PBN of a P3 rat at 2 h after injection of formalin in the hindpaw. Co-localization of c-fos with NeuN in the same section of the lateral PB can be seen in yellow. Scale bar, 200 μm. F, Percentage of NeuN-positive lateral PBN neurons that expressed c-fos after injection of formalin in the hindpaw in P3 (N = 3), P10 (N = 2), P20 (N = 3) and adult (N = 4) rats. Data show mean ± SEM. * p < 0.05.