Abstract
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.
Footnotes
- Received January 9, 1970.
- Accepted June 15, 1970.
- © 1970 by The Williams & Wilkins Co.
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