Methods of reverse transcription polymerase chain reaction (RT-PCR), intrathecal injection and antisense drugs were used to study the effects of nitric oxide (NO) on the scores of morphine-withdrawal syndrome and the expression of NMDA1AR mRNA in rat spinal cord and brainstem. Intrathecal injection of NOS antisense oligonucleotides (AS-ONs) significantly decreased the scores of morphine-withdrawal symptoms. The effect of nNOS AS-ONs was greater than that of eNOS AS-ONs. The expression of NMDA1AR mRNA in the spinal cord and brainstem increased in morphine-dependent rats and increased to a greater extent in morphine-withdrawal rats. Intrathecal injection of nNOS AS-ONs significantly inhibited the increased expression of NMDA1AR mRNA in the spinal cord and brainstem of morphine-withdrawal rats. Intrathecal injection of eNOS antisense oligonucleotides inhibited the expression of NMDA1AR mRNA in the spinal cord of morphine-withdrawal rats, but did not in the brainstem. It is suggested that NO mediates morphine-withdrawal reaction and participates in modulating the expression of NMDA1AR mRNA in morphine-withdrawal rats.