A contribution to the understanding of the effects of 4-aminopyridine on rat hippocampal slices /

The aim of the work presented in this thesis was to study the effects of 4-aminopyridine (4-AP, 5-100 $ mu$M) on rat hippocampal slices maintained in vitro. Two types of synchronous potentials were evoked by 4-AP: epileptiform bursts and GABA-mediated potentials. Bursts were initiated in CA3 by giant excitatory postsynaptic potentials (EPSPs) mediated by quisqualate/kainate receptors and involving recurrent excitatory pathways. This epileptiform activity occurred despite the presence of potentiated inhibitory postsynaptic potentials (IPSPs) and could propagate to CAl. The second type of activity occurred in all regions of the hippocampal slice and consisted of long-lasting depolarizations (LLDs) mediated by a Cl$ sp-$ efflux through dendritic GABA$ sb{ rm A}$ receptor ionophores. As resection experiments and pharmacological studies indicated that the propagation of LLDs did not require synaptic transmission, we propose that a novel coupling mechanism between GABAergic interneurons involving (K$ sp+ rbrack sb0$ accumulation and redistribution is revealed by 4-AP