in the intact brain , intravenous ( i.v . ) injection of morphine 2 mg/kg , dextrorphan 1 mg/kg and tilidine 5 mg/kg increased the discharge rate , whereas levorphanol 1 mg/kg , pethidine 20 mg/kg and codeine 10 mg/kg reduced it .
C0026549
morphine
C0009214
codeine