Figure 4.

Electrophysiological properties of hippocampal interneurons showing the prototypic afterdischarge. A, Spiking activity in the prototypic afterdischarge cycles in individual interneurons with different electrophysiological properties (spiking ability and sag amplitude) in the strata oriens and pyramidale (left) and the strata radiatum and lacunosum moleculare (right). Each dot represents a single interneuron, and the color indicates the spiking ability [spikes/cycle; 0 (nonspiking), oscillatory responses with no spiking; No response, no oscillatory responses]. We defined an FS interneuron as >100 Hz/0.5 nA spiking and <20% sag amplitude (left, top left quadrant) (see Materials and Methods). B, Time course of the prototypic afterdischarge (top), membrane potential changes (middle), and spiking rate changes (bottom) in the interneurons with spiking oscillatory responses (compare Fig. 1C). C, Top, Representative traces illustrating an intrinsically bursting property (left, top) and a spike-pausing property (left, bottom) in response to depolarizing current injection and a preoscillatory bursting (right). Note that the preoscillatory bursting (red arrow) appeared in the interneuron, but not in the field potential (asterisk), earlier than the prototypic afterdischarge (arrowheads). Bottom, Population ratios of interneurons showing the bursting property (open), pausing property (gray), and preoscillatory bursting (red) in the interneurons with spiking and nonspiking oscillatory responses and with no oscillatory responses. D, Electrophysiological properties of interneurons showing the preoscillatory bursting activity (red) in the strata oriens and pyramidale (A, left). Most of these interneurons were categorized as FS interneurons.