Abstract
The effects of intraperitoneal (IP), intracerebroventricular (ICV) and intrathecal (IT) opiates were studied in the rat neuropathic pain model of Kim and Chung. Dose dependent reduction of allodynia was observed after IP and ICV morphine, but not after IT morphine, IT or ICV c[ d-pen2 d-pen5]enkephalin (DPDPE) (δ agonist), or IT or ICV U50488H (κ agonist). The effects of ICV morphine were blocked by IP naloxone, but not by IT methysergide, phentolamine or 8-sulfophenyltheophylline. Catalepsy (immobility) was observed after IT, ICV and IT morphine but this was not reliably associated with a reduction of allodynia. IP and ICV morphine may thus reduce tactile allodynia via supraspinal, but not spinal, μ opioid receptors.
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