LONG-LASTING INCREASED PAIN SENSITIVITY IN RAT FOLLOWING EXPOSURE TO HEROIN FOR THE FIRST TIME

Acute dependence, defined as a precipitation of somatic signs by an an tagonist, may occur after a single administration of an opiate drug. B ecause hyperalgesia is a consistent sign of the withdrawal syndrome, w e tested the effectiveness of heroin, an opiate used by addicts, to in duce pain facilitation even after a first exposure to the drug. In opi ate-naive rats, subcutaneous injection of heroin induced analgesia fol lowed by allodynia, a decrease in pain threshold. This latter phenomen on was observed in the absence of noxious stimuli and lasted several d ays. An N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 preven ted such longlasting allodynia, These results suggest that allodynia i s an early sign reflecting neural plasticity associated with the devel opment of dependence.