Pentylenetetrazol-induced seizures produce an increased release of IR-Met-enkephalin from rat striatum in vitro

In this work we analyzed the immunoreactive-methionine-enkephalin (IR-Met-enkephalin) levels in several brain regions of rats sacrificed during the tonic extension, induced by acute treatment with pentylenetetrazol (PTZ). The results show an increase of IR-Met-enkephalin content in striatum but not in amygdala, hypothalamus, septum, hippocampus and cortex. To characterize whether this elevation of enkephalin levels in striatum corresponded to the releasable pool, we studied the intro efflux of this peptide in striatal slices of rats sacrificed during the seizures, in acute PTZ and in PTZ-kindled rats (kindling group I). In addition, PTZ-kindled rats were analyzed 24 h after the last stimulus (kindling group II). The striatal slices of acute group and kindling group I displayed a significant increase in the evoked release of IR-Met-enkephalin. However, no significant changes occurred from striatal slices of kindling group II animals. In vitro superfusion of GABA (100 μM) produced a 63% decrease in IR-Met-enkephalin released from striatal slices in both saline and acute PTZ-treated rats. Several studies suggest that opioid peptides may be released in the ictal phase of seizure in order to mediate some transient postictal behavior. Our results suggest that of several brain regions tested, only the striatal IR-Met-enkephalin may be released during the ictus to mediate postical behavior in the acute PTZ treated and in PTZ-kindled rats. This effect may be regulated by the GABA system.