Intrathecal neurokinin A facilitates the spinal nociceptive flexor reflex evoked by thermal and mechanical stimuli and synergistically interacts with substance P.

The neuropeptide neurokinin A was injected intrathecally and its effect on the spinal nociceptive flexor reflex was examined. The reflex, which was evoked by electrical, thermal or mechanical stimulation of the foot and was recorded from the ipsilateral hamstring muscles, was substantially facilitated by 7 pmol intrathecally injected neurokinin A. The facilitatory effect of neurokinin A to thermal stimulation was, however, significantly stronger than to electrical or mechanical stimuli. Furthermore, co-administration of neurokinin A with substance P induced a significant synergistic facilitation of the reflex. It is suggested that neurokinin A, like substance P, may be released in association with activation of polymodal C-nociceptors.