Pentylenetetrazol kindling produces a long-lasting elevation of IR-Met-enkephalin but not IR-Leu-enkephalin in rat brain.

Pentylenetetrazol (PTZ) kindling was induced in male Wistar rats by daily i.p. injections of 40 mg/kg of the convulsant agent. IR-Met-enkephalin and IR-Leu-enkephalin were quantified in several brain regions 16 days after the last stimulus. In addition other rats received another PTZ dose on the sixteenth day and the samples were analyzed 1 and 24 h later. The results showed a long-lasting elevation in amygdala, septum, hypothalamus and hippocampus of IR-Met-enkephalin only. These brain structures also showed a decrease of IR-Met-enkephalin 1 h after the PTZ-induced seizure, but reached newly elevated levels 24 h later. IR-Leu-enkephalin levels only showed a decrease in striatum 1 h after PTZ-induced convulsions. The data suggest that Met-enkephalin is related to permanent changes in brain function induced by PTZ kindling, while Leu-enkephalin may depend on the occurrence of epileptic seizures.