Kindling from stimulation of a highly sensitive locus in the posterior part of the piriform cortex. Comparison with amygdala kindling and effects of antiepileptic drugs.

The piriform cortex, especially its deep anterior part, has been recently suggested to be a crucial epileptogenic site in the rat brain. We investigated the susceptibility of different parts of the piriform cortex to the development of electrical kindling as compared to that of the basolateral amygdala. A locus in the deep cell layer (layer III) of the rostral portion of the posterior piriform cortex (PPC) is described, which is considerably more sensitive to electrical stimulation than adjacent areas of the PPC, including the deep prepiriform cortex or the amygdala. The sensitive locus in the PPC can be readily kindled, and focal seizure thresholds in fully kindled rats are 60-90% lower than respective thresholds in rats kindled from other loci. Treatment of fully kindled rats with antiepileptic drugs diazepam, carbamazepine, phenobarbital, and valproate showed that anticonvulsant effects of these drugs in animals kindled from stimulation of the PPC were comparable to respective effects in animals kindled from stimulation of the basolateral amygdala, although the locus in the PPC tended to be more resistant. The data support the idea that the piriform area may contain the most sensitive neuronal tissue responsible for the generation of seizures during kindling. It remains to be determined if the described locus in the PPC is critical to the kindling process when kindling is induced from other structures within the olfactory-limbic system.