The Journal of Neurophysiology Vol. 85 No. 2 February 2001, pp. 495-505
Copyright ©2001 by the American Physiological Society

Electrophysiological and Morphological Characterization of Neurons Within Neocortical Ectopias

Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269

Gabel, Lisa A. and Joseph J. LoTurco. Electrophysiological and Morphological Characterization of Neurons Within Neocortical Ectopias. J. Neurophysiol. 85: 495-505, 2001. Focal developmental abnormalities in neocortex, including ectopic collections of neurons in layer I (ectopias), have been associated with behavioral and neurological deficits. In this study, we used infrared differential interference contrast microscopy and whole cell patch-clamp to complete the first characterization of neurons within and surrounding neocortical ectopias. Current-clamp recordings revealed that neurons within ectopias display multiple types of action potential firing patterns, and biocytin labeling indicated that ~20% of the cells in neocortical ectopias can be classified as nonpyramidal cells and the rest as atypically oriented pyramidal cells. All cells had spontaneous excitatory (glutamatergic) and inhibitory (GABAergic) postsynaptic currents. Exhibitory postsynaptic currents consisted of both N-methyl-D-aspartate (NMDA) receptor-mediated and AMPA/kainate (A/K) receptor-mediated currents. The NMDA receptor-mediated component had decay time constants of 15.35 ± 2.2 (SE) ms, while the A/K component had faster decay kinetics of 7.6 ± 1.7 ms at 20 mV. GABA_A receptor-mediated synaptic currents in ectopic cells reversed at potentials near the Cl equilibrium potential and had decay kinetics of 16.65 ± 1.3 ms at 0 mV. Furthermore we show that cells within ectopias receive direct excitatory and inhibitory input from adjacent normatopic cortex and can display a form of epileptiform activity.