Opioid-independent hyperalgesia induced in mice by pentobarbitone at low dosage.

The abdominal constriction (writhing) test was used to investigate the effect of pentobarbitone on nociception in mice. At dosages of 10, 20 and 30 mg/kg, pentobarbitone produced marked increases in nociceptive scores. The extent of the enhancement of nociception was uninfluenced by naloxone or swim-stress. The swim-stress induced analgesia but, in contrast to previous results using other tests for nociception, the analgesia was wholly non-opioid with the abdominal constriction test.