Figure 1.

(a) Surgical procedures: After anesthesia by intraperitoneal injection of sodium pentobarbital (40 mg/kg), a 1-cm incision was made along the upper margin of the right vibrissa pad of the rat to separate and expose the infraorbital nerve; (b) Mechanical pain threshold measurement: The rat was placed using a reticulated rat cage and waited until the rats were silent; the test subjects used the von Frey fiber filament to stimulate the rat’s surgical side whiskers.