THE EFFECTS OF LESIONS OF THE POSTERIOR PIRIFORM CORTEX ON AMYGDALA KINDLING IN THE RAT

The piriform cortex (PC) is thought to be critically involved in the genesis of forebrain (limbic type) seizures, including limbic kindled seizures. More recent studies have shown that the posterior PC is particularly sensitive to kindling stimulation, suggesting that the posterior PC contains specific generating sites which may be important for the stepwise progression of kindling. In the present experiments, we used microinjections of ibotenate to study the effect of selective lesions of the posterior PC on amygdala kindling in rats. Large unilateral lesions of the posterior PC and adjacent endopiriform nucleus markedly decreased the susceptibility of the ipsilateral basolateral amygdala to electrical stimulation, thus indicating that the posterior PC may normally contribute to regulation of physiologic excitability in amygdala. During kindling, rats with large lesions of the PC stayed longer in the initial phase of kindling (stage 1) than sham-lesioned controls, consistent with involvement of the posterior PC in the early stages of seizure propagation during kindling acquisition. However, the PC lesions were not capable of blocking or even severely retarding kindling. Following kindling development, rats with large lesions of the posterior PC had significantly higher focal seizure thresholds than kindled rats without lesion or rats with only small PC lesions, which suggests that the posterior PC is involved in the mechanisms which are responsible for the marked increase in seizure susceptibility induced by kindling. Taken together, the data substantiate that PC structures play a facilitatory role in kindling.