Levodopa analgesia in experimental neuropathic pain

Levodopa has been shown to produce analgesia in various clinical and experimental settings, but its use for chronic pain treatment has not been established. We have undertaken a study of the antiallodynic actions of levodopa in a rat model of painful mononeuropathy. When administered systemically, levodopa produced a decrease in tactile and cold allodynia lasting at least 3 h. Direct intrathecal (i.t.) levodopa injection at lumbar levels produced a similar, though shorter, antiallodynic effect. This effect was blocked by the D2-type receptor antagonist sulpiride, which supports the involvement of the spinal dopaminergic system in the analgesic action of levodopa on neuropathic pain. These results provide experimental support on the antiallodynic effect of levodopa in neuropathic pain and suggest that at least part of the analgesic action takes place in the spinal cord and involves dopaminergic D2-type receptors.