Involvement of delta-opioid receptors in pentylenetetrazol kindling development and kindling-related processes in rats.

The role of delta-opioid receptors on the development of kindling induced by the convulsant pentylenetetrazol (37.5 mg kg(-1) i.p.) was investigated in rats. Besides the seizure development, the kindling induced enhancement of glutamate binding and the kindling-induced learning deficit were examined. A clear depression of kindling development by blocking of delta-opioid receptors by intracerebroventricular administration of naltrindole (10 nmol/5 microl) was found. In an acute convulsion test performed 8 days after kindling completion, animals pretreated with naltrindole during kindling induction showed lower seizure stages compared to saline-pretreated kindled animals. The kindling-induced increase in hippocampal glutamate binding was completely prevented by naltrindole, whereas the kindling-induced learning deficit was not influenced. The learning performance of control animals pretreated with naltrindole was very low. It was hypothesized that the various consequences of kindling induction could be influenced separately. Summarizing the results, an involvement of the delta-opioid system in mechanisms underlying chemical kindling was clearly demonstrated. Interactions of endogenous opioid systems with glutamatergic transmission were suggested.