title: Genesis of MEG signals in a mammalian CNS structure.
abstract: Neuromagnetic signals of guinea pig hippocampal slices were characterized and compared with the extracellular field potential to elucidate the genesis of magnetoencephalographic signals in a mammalian CNS structure. The spatial distribution of magnetic evoked field (MEF) directed normal to bath surface was similar for transverse CA1, longitudinal CA1 and longitudinal CA3 slices in the presence of 0.1 mM picrotoxin (PTX) which blocks inhibitory synaptic transmission. Their MEFs were produced by currents along the longitudinal axis of the pyramidal cells. Comparisons of the MEF with the laminar potential profile revealed that the MEF was generated by intracellular longitudinal currents. The dipolar component of the intracellular currents was the dominant factor generating the MEF even at a distance of 2 mm from the slice. The MEF from a slice in Ringer's solution without PTX became similar in temporal waveform with time to the MEF in the presence of PTX, indicating the predominance of excitatory connections in generating the MEF and the existence of highly synchronous populations activities across the slice even in PTX-free Ringer's solution. The presence of such highly synchronous population activities underlying the MEFs was verified directly with field potentials recorded across the slice. A systematic variation of the stimulation site revealed a characteristic waveform for each site. The variation of the with stimulation site suggested the contribution of many factors, both synaptic and voltage-sensitive conductances, to the overall waveform of the MEF.
authors.affiliation: Department of Neurology, University of New Mexico School of Medicine, Albuquerque 87131, USA.
authors.forename: Y C
authors.initials: YC
authors.lastname: Okada
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: S
authors.initials: S
authors.lastname: Kyuhou
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D004569:Electroencephalography; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007552:Isotonic Solutions / Q000494:pharmacology; D015225:Magnetoencephalography; D010852:Picrotoxin / Q000494:pharmacology; D011930:Reaction Time; D000077331:Ringer's Solution
chemical_list: D000697:Central Nervous System Stimulants; D007552:Isotonic Solutions; D010852:Picrotoxin; D000077331:Ringer's Solution