Using pain measurement and immunohistochemistry

we have observed that the intrathecal injection (it) SP produced dose-related pain response. A larger dose of SP (5μg

1eμg) could reduce the pain thresho1d and evoke c-fos expression

but no obvious effect was produced by a smaller dose of SP (0. 5μg

1μg). Morphine (it) not only increased the pain threshold

but also inhibited pain response and c-fos expression of spinal cord induced by it SP

the effects could be reversed by naloxone