Bremazocine-induced backwards walking behavior in rats is mediated via opioid kappa receptors.

Bremazocine dose-dependently induced backwards walking behavior in rats after its SC injection. Only the (-) but not the (+) enantiomer induced backwards walking. Pretreatment with either naloxone or MR 2266 reduced the bremazocine-induced backwards walking. MR 2266 was at least ten times more potent than naloxone. These findings suggest that bremazocine-induced backwards walking is mediated via an agonistic action of the drug with opioid kappa receptors. The data may contribute to the discussion concerning opioid kappa receptors and the psychotomimetic effects of some opioid analgesic drugs.