Transfer kindling between sites in the entorhinal cortex-perforant path-dentate gyrus system

Repeated electrical stimulation of forebrain sites can lead to an enhanced epileptogenic response (the kindling phenomenon). When stimulation is subsequently applied to related sites, these developments occur more rapidly (the transfer effect). Axonal pathways do not support epileptiform discharge, so it is generally assumed that the kindling develops, when these pathways are stimulated, in the target structures of those pathways. Consequently, transfer kindling should be immediate, or at least very rapid. Primary and 'transfer' kindling effects were examined in the excitatory, monosynaptically coupled, entorhinal cortex-dentate gyrus system. Transfer kindling was begun following either a 24 h delay or a 4 week delay between the last primary site convulsion and the start of transfer kindling in the secondary site. A 4 week delay between kindling sites was chosen to minimize the effects of a previously reported transient suppression of transfer kindling and the increased inhibition that has been shown to develop in the dentate gyrus as a result of kindling the perforant path. Although there was a significant transfer to the dentate gyrus following perforant path stimulation, the dentate gyrus still required a mean of 18.5 (24 h delay) and 20.3 (4 week delay) stimulations to reach criterion. In the entorhinal cortex, there was a significant positive transfer following primary kindling of the perforant path only in the group in which transfer kindling was begun after a 4 week delay. When the perforant path itself was the transfer site, there was a significant savings in number of afterdischarges needed to reach criterion following dentate gyrus kindling but no savings following entorhinal cortex kindling.(ABSTRACT TRUNCATED AT 250 WORDS)