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.
Laboratory of Behavioral Pharmacology, Boston University School of Medicine, MA 02118.
C B
CB
Hubner
G T
GT
Bain
C
C
Kornetsky
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