Effects of morphine or naloxone on kainic acid neurotoxicity.

Intraperitoneal or subcutaneous administration of kainic acid (KA) (5–15 mg/kg) to adult rats included a syndrome of wef wet dog shakes (WDS), convulsions and brain damage. Components of the syndrome were evoked in a dose-related manner with low doses inducing WDS only and progressively higher doses being associated with an increasing incidence of naloxone (4 mg/kg) 5 minutes prior to KA (12 mg/kg) resulted in a moderate reduction in the incidence of WDS, convulsions and brain damage. Administering morphine (5 or 10 mg/kg) 10 minutes prior to KA (7 mg/kg) markedly enhanced the neurotoxicity of KA as was evidenced in an increase in the incidence of convulsions and brain damage from 7% (KA alone) to 100% (morphine + KA). KA, a structural analog of the putative excitatory transmitter glutamate (Glu), is thought to exert its excitotoxic activity through Glu excitatory receptors. Additional studies are needed to elucidate the mechanism by which morphine and naloxone respectively enhance and suppress KA neurotoxicity and to clarify whether interaction of these agents at either opioid or Glu receptors plays a role in such phenomena.