MEMBRANE PROPERTIES, AMINO ACID RECEPTORS, AND LOCAL CIRCUITS

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Electrophysiological studies will be conducted on slices from developing human neocortex to examine intrinsic electrophysiological properties of cortical neurons, the pharmacology of excitatory and inhibitory amino acid receptors, and the characteristics of local synaptic circuits. The proposed experiments will be performed on human cortical tissue surgically removed for treatment of catastrophic childhood epilepsy. For tissue from each patient, direct comparisons will be made between the most abnormal area and the least abnormal area. The relative normality of the tissue samples will be evaluated from clinical data, such as intraoperative electrocorticography (ECoG), positron emission tomography (PET), pathology, etc. The experimental methods will include: (1) intracellular recording with current- and voltage-clamp techniques using sharp and patch electrodes, (2) bath and microapplication of pharmacological agonists and antagonists, and (3) intracellular staining. The experiments will test specific hypotheses about the cellular mechanisms of catastrophic childhood epilepsy and about changes in neocortical neurophysiology that occur during human development. Particular emphasis will be on analyses of: (1) current-evoked action potentials and spike bursts and their underlying voltage-dependent Na+ and Ca2+ conductances, (2) N-methyl-D-aspartate (NMDA) receptors, (3) GABA-mediated synaptic inhibition, and (4) local excitatory circuits. Each specific aim includes hypotheses concerning the underlying cellular mechanism(s) of catastrophic childhood epilepsy and developmental changes in the electrophysiology of human cortical neurons. Particular emphasis, especially at the beginning of the grant, will be aimed at testing the hypothesis that epileptogenic and/or developmental changes in human neocortex involve alterations in the number or properties of NMDA receptors or decreases in GABAA-mediated inhibition. Long-term studies will determine possible changes in local excitatory circuits among neocortical pyramidal cells. Alterations in the anatomy of neocortical neurons, which could be associated with epileptogenesis and/or development, will be examined in neurons stained intracellularly with biocytin. The goal is to provide fundamental new information on the electrophysiological characteristics of human cortical neurons, how these properties change during development, and how they are involved in and/or altered during catastrophic childhood epilepsy.