ANTAGONISM OF THE BEHAVIORAL EFFECTS OF MORPHINE AND METHADONE BY NARCOTIC ANTAGONISTS IN THE PIGEON

¹ Department of Pharmacology, University of North Carolina at Chapel Hill; Department of Pharmacology, Downstate Medical Center, State University of New York at Brooklyn

The effects of narcotics and narcotic antagonists, alone and in combination, were studied on the schedule-controlled behavior of the pigeon. Morphine and methadone increased the rate of responding under the fixed-interval component of a multiple fixed-interval, fixed-ratio schedule at low dose levels in some birds, and at higher dose levels they decreased the rates of responding under both components in all birds. The effects of narcotic antagonists were much like the effects of morphine and methadone. Naloxone, which has been considered to be a relatively pure narcotic antagonist, affected the schedule-controlled behavior of the pigeon in the same way as other narcotic antagonists and with a greater potency than some. Narcotic antagonists blocked both the rate-increasing and rate-decreasing effects of morphine. The order of potency of the narcotic antagonists for blocking the rate-decreasing effects of morphine was: naloxone = cyclasocine > nalorphine > pentazocine. This antagonism of the rate-decreasing effect of morphine seemed to be specific for narcotic analgesics, since naloxone and cyclazocine blocked the effects of methadone as well as morphine, but naloxone did not block the rate-decreasing effects of chlorpromazine and cyclazocine. Although d-amphetamine could reverse the rate-decreasing effects of morphine, the degree of reversal was proportional to the rate-increasing effects of d-amphetamine, which was unlike the antagonism of the rate-decreasing effects of morphine by narcotic antagonists. The rate-increasing effects of morphine and d-amphetamine were additive, rather than antagonistic.

This article has been cited by other articles:

				T. Asai and I. Power Naloxone Inhibits Gastric Emptying in the Rat Anesth. Analg., January 1, 1999; 88(1): 204 - 208. [Abstract] [Full Text] [PDF]

				L. R. Gerak and C. P. France Changes in Sensitivity to the Rate-Decreasing Effects of Opioids in Pigeons Treated Acutely or Chronically with l-alpha -Acetylmethadol J. Pharmacol. Exp. Ther., May 1, 1997; 281(2): 799 - 809. [Abstract] [Full Text]