Fig. 6

HDC gene knockout or H₁ receptor antagonist mepyramine abolished the inhibitory effect of histidine on spinal microglial activation. Histidine (200 mg/kg, i.p.) administered once daily through 0–7 days PO did not inhibit microglial activation in HDC^−/− mice (a, b). Mepyramine (200 ng/rat, i.t.) abolished the inhibitory effect of histidine on microglial activation (c, d). Scale bar = 200 μm (bottom) and 20 μm (insets). ***P < 0.001, compared with the vehicle-treated group