Physiological bases of the synchronized population spikes and slow wave of the magnetic field generated by a guinea-pig longitudinal CA3 slice preparation.
OBJECTIVE
The physiological bases of evoked magnetic fields were examined in a guinea-pig hippocampal slice preparation, motivated by new concepts in central nervous system (CNS) electrophysiology brought about by discoveries of active conductances in the dendrites and soma of neurons.


METHODS
Their origins were elucidated by comparing them with intracellular and extracellular field potentials.


RESULTS
With excitatory synaptic transmissions blocked, the magnetic signal elicited by an electrical stimulus applied to the pyramidal cell layer consisted of a spike and a depolarizing afterpotential-like waveform. With the excitatory synaptic transmissions intact, but with inhibitory synaptic transmissions blocked, the magnetic signal was bi- or triphasic depending on whether the cell layer or the apical dendrite area of the pyramidal cells was, respectively, depolarized. In both cases the signal consisted of a train of synchronized population spikes superimposed on a brief wave followed by a longer, slow wave. The spike train was correlated with synaptically mediated intracellular spikes. The underlying currents for the slow wave were directed from the apical to the basal side for both types of stimulation. It was most likely generated by depolarization of the apical dendrites, caused by recurrent excitatory synaptic activation.


CONCLUSIONS
This analysis illustrates how synaptic connections and intrinsic conductances in a disinhibited mammalian CNS structure can generate spikes and waves of the magnetic field and electrical potential.
Wu
J
J
Department of Neurology, University of New Mexico School of Medicine, Albuquerque 87131, USA.
Okada
Y C
YC
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D004867:Equipment Design; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006168:Guinea Pigs; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D015225:Magnetoencephalography / Q000295:instrumentation; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D013779:Tetrodotoxin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate