Chemical kindling with Met-enkephalin and transfer between chemical and electrical kindling

The role played by Met-enkephalin (ME) in epileptic seizures was investigated, using 57 ME kindled rats and 10 saline injected control rats. Repeated microinjection of 10 micrograms ME into the right amygdala (AM) of male Wistar rats led to development of generalized convulsions. One week after the completion of ME kindling, 1 or 2 electrical stimulations (200-400 microA, 60 Hz, 1 sec) of the right AM of ME kindled rats resulted in generalized convulsions in 5 rats. The duration of after-discharge (AD) in the first generalized convulsion induced by electrical AM stimulation in the ME kindled rats was significantly longer than that in the first generalized convulsion induced by electrical stimulation in the saline treated control rats (P less than 0.05). One week after the completion of ME kindling, naloxone (10 or 20 mg/kg, i.p.) given 10 min before the infusion of ME into the other 3 ME kindled rats attenuated both convulsive behavior and electrographical seizures. With the progress of convulsive behavior, the frequency of wet-dog shakes (WDS) tended to decrease and was significantly lower after ME injection in the first stage 5 seizures than after the first ME injection (P less than 0.01). These results strongly suggest that ME has a potent epileptogenic effect on the rat brain which is caused by the opioid receptors. There are some differences between chemical kindling with ME and electrical kindling as indicated by the development of the AD duration and the WDS frequency.