Sigma effects of nalorphine in the chronic spinal dog.

The effects of graded doses of nalorphine and morphine were studied in nondependent chronic spinal dogs. Morphine and low doses of nalorphine produced behavioral changes characterized by indifference, whereas the largest dose of nalorphine produced canine delirium indistinguishable from that produced by SKF-10, 047 or cyclazocine. Nalorphine depressed the flexor reflex; however, a plateau was observed. The data suggest that nalorphine is a partial agonist of the kappa type and a sigma agonist in addition to being a competitive antagonist at the mu receptor, and further, that the dysphoric and hallucinogenic effects of nalorphine-like drugs are due to their sigma activity.