The behavioral effectsof naloxone in pigeons receiving repeated morphine injections varied with the log dose of naloxone administered and were correlated with the physiological abstinence sign of weight loss. Pigeons key pecked under a conjunctive response-initiated fixed-interval 2-min interresponse time > x seconds schedule of food presentation. Repeated daily administration of increasing doses of morphine, 9 to 90 mg/kg/day, produced sustained decreases in overall rate of key pecking across all doses over a period of 24 to 25 wk. In order to investigate the effects of naloxone administration on response rate and patterning, the subjects were maintained on 90 mg/kg/day of morphine, and naloxone was administered in 2 ascending dose series. Naloxone altered overall rate in a dose-related manner. In the first series of naloxone challenges, low doses (0.01 and 0.03 mg/kg) slightly increased overall rate; higher doses decreased overall rate, with complete response suppression occurring at 0.30 to 1.00 mg/kg. Naloxone decreased overall rate at lower doses in the second administration series than in the first. Increases in total session pause time paralleled the naloxone-produced decreases in overall rate. Naloxone generally altered running rate of key pecking in an all-or-none fashion. Marked decreases in overall response rate at moderate naloxone doses were due primarily to increased pausing between reinforcer delivery and initiation of the next interval component and not to decreases in running rate. Body weight loss increased as a function of increasing naloxone dose. At high doses, subjects lost 2 to 12 g during 1-hr experimental sessions.
|Number of pages||10|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 1978|