Kindling of the massa intermedia of the thalamus in rats

The kindling response of the massa intermedia (MI) was assessed in rats. Clinical manifestation of the MI kindling was generally similar to that of limbic kindling, and positive transfer to the amygdala (AM) was obtained following MI kindling. However, MI kindling showed (1) a relatively high after discharge threshold which sometimes increased during the course of kindling, (2) a seizure stage instability with frequent regression to earlier stages, (3) a failure to establish a generalized seizure triggering threshold with an 'all-or-none' property, and (4) a generalized tonic-clonic seizure, which was quite different from a kindled limbic seizure, during early phase of kindling. Furthermore, the MI stimulation caused violent beating movement of the forelimbs, jumping, or running regardless of presence/absence of afterdischarge. The findings suggest that mechanisms other than a simple activation of limbic structures are involved in the process of MI kindling.