The combined effects of morphine and d-amphetamine on the threshold for brain stimulation reward.
The effect of morphine and d-amphetamine co-administration on the threshold for rewarding intracranial electrical stimulation was studied in rats with electrodes stereotaxically implanted in the medial forebrain bundle-lateral hypothalamic or ventral tegmental area of the brain. Thresholds were determined by means of a rate-independent psychophysical method. Individually, morphine and d-amphetamine both caused a dose-related lowering of the reward threshold. Low doses of morphine or d-amphetamine which were ineffective or minimally effective in lowering the reward threshold were then tested with various doses of either d-amphetamine or morphine, respectively. In both cases, the combined administration of morphine and d-amphetamine resulted in a lowering of the reward threshold that was greater than for the corresponding doses of morphine and d-amphetamine when given alone. Given that increased sensitivity for rewarding brain stimulation has been suggested to be an animal model of drug-induced euphoria, this effect is congruent with the reported increase in the degree of euphoria produced when amphetamine is used in conjunction with opiate drugs.
Hubner
C B
CB
Laboratory of Behavioral Pharmacology, Boston University School of Medicine, MA 02118.
Bain
G T
GT
Kornetsky
C
C
D000818:Animals; D001921:Brain; D003913:Dextroamphetamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004558:Electric Stimulation; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D012201:Reward; D012684:Sensory Thresholds / Q000187:drug effects
D009020:Morphine; D003913:Dextroamphetamine