Effect of olfactory bulb kindling on evoked potentials in the pyriform cortex

The potential evoked in the pyriform cortex by single-pulse stimulation of the olfactory bulb was examined before and after single and repeated elicitation of an epileptiform afterdischarge produced by stimulation of the olfactory bulb. A single afterdischarge (AD) produced a rapid (i.e. within 5 min) increase in the amplitude of an early surface-negative wave and duration of a later surface-positive wave. These effects persisted at least 48-72 h. Repeated elicitation of ADs resulted in kindling. A large increase in the amplitude of a later surface-negative wave (approximately 25 ms latency) occurred during kindling. This wave remained significantly elevated for at least 72 h after the last AD. Long-term potentiation of the early surface-negative wave was produced by kindling or two focal ADs. A short-term effect which was consistently observed following a focal or generalized AD was a prolongation of a late surface-positive wave. These effects are discussed in relation to long-term potentiation, postseizure inhibition, and kindling development.