The interaction between kappa-opioid agonist, U-50, 488H, and kainic acid: behavioral and histological assessments

The effects of a selective kappa-agonist, U-50,488H, on systemic kainic acid-induced behavioral and histological changes were studied in rats. U-50,488H inhibited kainic acid-induced wet dog shakes in a naloxone reversible manner; however, U-50,488H did not protect rats against kainic acid-evoked behavioral seizures. As revealed by histological analysis, kainic acid caused edema and severe neuronal damage in several brain regions, notably in CA1 but also in the CA3 fields of both hippocampi. Pretreatment of rats with U-50,488H markedly protected hippocampal neurons, especially those in CA1, against kainic acid-induced neurotoxicity. Naloxone by itself had little effect on kainic acid-induced seizures or hippocampal neuron loss. Naloxone plus U-50,488H resulted in less severe seizures and, consequently, less hippocampal cell loss than after kainic acid alone. These data indicate that U-50,488H can markedly attenuate the neurotoxic and behavioral consequences of systemic kainic acid administration. However, the mechanism of these effects requires further study with more specific opioid antagonists.