Penicillin-induced epileptic phenomena in the rabbit's neocortex II. Laminar specific generation of interictal spikes after the application of penicillin to different cortical depths.

To elucidate the generation mechanisms of interictal spikes we analyzed the electrical events in the different layers of the rabbit's neocortex after application of penicillin to distinct cortical layers. Field potentials (FP) recorded simultaneously from all layers with a 16-fold micro-electrode-assembly were subjected to current-source-density analysis (CSD), which allows a more accurate description of local electrical events. To demonstrate the influence of neocortical architectonics on the generation of interictal spikes, 3 different areas-area occipitalis 1, precentralis 1 and 2, according to Fleischhauer et al., were studied. Interictal spikes develop regardless of the depth of PNC application. Moreover the appearance of spikes does not seem to depend exclusively on the diffusion of PNC into a distinct cortical layer (i.e. layers IV and V). The CSD analysis indicated that different generation mechanisms within the different cortical layers underly the spikes. According to CSD configurations maximum sinks occur at depths where the dendrites join closely to form bundles. This finding supports the importance of dendrites for the generation of interictal spikes. Finally, the distribution of CSD patterns is similar in all 3 neocortical areas studied, if PNC is applied to the same cortical depth.