Inhibitory effects of morphine on intralaminar nociceptive neurons in the cat thalamus

Abstract

We electrically stimulated the peripheral nerve and midbrain reticular formation (MRF) in the cat and recorded the response of the nociceptive neurons in the intralaminar nuclei of the thalamus. We also investigated the effects of intravenous administration of morphine on the responses obtained from these neurons. Morphine inhibited the late responses elicited by electrical stimulation of the peripheral nerve. As well, it inhibited the early responses elicited by electrical stimulation of the MRF. Administration of naloxone and cholecystokinin partially reversed these inhibitory effects of morphine. These date suggest that morphine acts at the supraspinal level.