POST-ACTIVATION POTENTIATION IN THE NEOCORTEX .3. KINDLING-INDUCED POTENTIATION IN THE CHRONIC PREPARATION

Previous experiments have shown the neocortex to be very resistant to the induction of long-term potentiation in chronic preparations. We sh ow here that kindling-induced potentiation effects can be reliably pro duced in the neocortex of awake, freely moving rats. These effects dev elop rather slowly. In sites contralateral to the stimulation electrod e, potentiation effects did not become clear until the animals had rec eived about 5 days or more of stimulation. Ipsilateral sites required even longer (approximately 10 days), and both sires required more than 13 days to reach asymptotic levels of potentiation. Both monosynaptic and polysynaptic components were present in the neocortical field pot entials. When population spikes were absent, the surface negative mono synaptic EPSP component tended to show a potentiation effect. If popul ation spikes were present, they were generally enhanced while the mono synaptic population EPSP tended to be depressed. Consequently, the app arent depression may have been due to competing field currents. The la ter polysynaptic components (15-28 ms latency to peak) always showed a potentiation effect with 5 or more kindling stimulations and is presu med to result from activation of cortico-cortical associational fibers . All of these effects were long-lasting, showing little decay over a period of several weeks.