Cross-sensitization to the excitatory effect of morphine in post-dependent rats.
Time-effects of morphine, methadone, meperidine and pentazocine upon locomotor activity were investigated in naive and in post-dependent rats. Dependence was induced by daily injection of 20 mg/kg (i.p.) of morphine for 30 days. Tests were run starting from 1 month after withdrawal from morphine. Morphine produced a greater increase in activity in post-dependent than in naive rats. Marked cross-sensitization to the excitatory effect occurred with methadone but not with pentazocine. The motility pattern of meperidine was similar in naive and in post-dependent animals. The findings presented here suggest that: different mechanisms underlie the excitatory actions of opiates; the narcotic character of a drug can be detected by challenging this drug in rats previously dependent on morphine.
D000818:Animals; D008297:Male; D008614:Meperidine / Q000494:pharmacology; D008691:Methadone / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence / Q000503:physiopathology*; D009043:Motor Activity / Q000187:drug effects; D010423:Pentazocine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D009020:Morphine; D008614:Meperidine; D010423:Pentazocine; D008691:Methadone