Propagation of epileptiform activity in the hippocampus can be driven by non-synaptic mechanisms

Most studies of epileptic waves of brain activity assume that propagation is based on synaptic transmission and few of them consider the involvement of synapse-independent effects. Epileptiform propagation can be better observed in the unfolded hippocampus as both transverse and longitudinal pathways have been preserved. In order to better monitor the propagation of epileptiform activity, we used a custom-made micro-electrode penetrating array. The results show that 4-AP-induced epileptiform activity propagates in both the longitudinal and transverse directions. Further experiments using low Ca²⁺/4-AP and mefloquine/4-AP indicated that propagation does not depend on either chemical or electrical synaptic transmission. All the propagation speeds were measured to be approximately around 0.1 m/s, a value that is not compatible with ionic diffusion or pure axonal conduction. Taken together our results and previous studies, evidence suggests that ephaptic effect might be a non-synaptic mechanism for the epileptiform propagation in the hippocampus.