Long‐lasting increased pain sensitivity in rat following exposure to heroin for the first time

TLDR

A single dose of an opiate can precipitate acute dependence, evidenced by somatic signs triggered by an antagonist. The study aimed to determine whether a first exposure to heroin can induce pain facilitation (hyperalgesia) in opiate‑naïve rats. In opiate‑naïve rats, a single heroin injection produced initial analgesia followed by prolonged allodynia that persisted for days, and this effect was blocked by the NMDA antagonist MK‑801, indicating that early allodynia reflects neural plasticity associated with dependence development.

Abstract

Abstract Acute dependence, defined as a precipitation of somatic signs by an antagonist, may occur after a single administration of an opiate drug. Because hyperalgesia is a consistent sign of the withdrawal syndrome, we tested the effectiveness of heroin, an opiate used by addicts, to induce pain facilitation even after a first exposure to the drug. In opiate‐naive rats, subcutaneous injection of heroin induced analgesia followed by allodynia, a decrease in pain threshold. This latter phenomenon was observed in the absence of noxious stimuli and lasted several days. An N ‐methyl‐ d ‐aspartate (NMDA) receptor antagonist, MK‐801 prevented such long‐lasting allodynia. These results suggest that allodynia is an early sign reflecting neural plasticity associated with the development of dependence.