Journal of Neuroscience, Vol 6, 2509-2520, Copyright © 1986 by Society for Neuroscience
Actions of opioids on primate spinothalamic tract neurons
WS Willcockson, J Kim, HK Shin, JM Chung and WD Willis
The effects of iontophoretically applied opiates were tested on 24
spinothalamic tract cells in 12 anesthetized monkeys. The drugs used were
chosen because of their agonist actions on different classes of opiate
receptors (mu, morphine; kappa, dynorphin; delta, methionine
enkephalinamide; sigma, N-allylnormetazocine or SKF 10047 and
phencyclidine). The actions of the opiate drugs were generally inhibitory,
although excitatory or mixed effects were sometimes seen, especially with
morphine and dynorphin. Drug effects could change, depending on the
position of the iontophoretic electrode array or on the current employed.
Naloxone sometimes antagonized the action of the opiate drugs used, but
naloxone did not seem to be a drug suited for iontophoretic application. A
number of explanations are discussed to explain the variable actions of the
opiate drugs.