Analgesic doses of morphine do not reduce noxious stimulus‐evoked release of immunoreactive neurokinins in the dorsal horn of the spinal cat

1 Antibody microprobes were used to detect immunoreactive neurokinin A release in the dorsal spinal cord of barbiturate‐anaesthetized spinal cats. 2 Noxious mechanical stimulation of the ipsilateral hind paw and electrical stimulation (suprathreshold for unmyelinated primary afferent fibres) of the ipsilateral tibial nerve evoked immunoreactive neurokinin A release. 3 Systemic morphine, 5 mg kg−1, i.v., did not block immunoreactive neurokinin A release in response to these stimuli. 4 Subsequent naloxone administration, 0.5 mg kg−1, i.v., did not alter this stimulus‐evoked release. 5 Basal levels of immunoreactive neurokinin A were unaltered by morphine or naloxone. 6 These results suggest that the analgesic effects of morphine at the spinal cord level are not brought about by activation of presynaptic opiate receptors on neurokinin A containing afferent terminals.