Electrophysiological and Morphological Classification of Inhibitory Interneurons in Layer II/III of the Rat Visual Cortex

Electrophysiological and Morphological Classification of Inhibitory Interneurons in Layer II/III of the Rat Visual Cortex

Interneuron diversity is one of the key factors to hinder understanding the mechanism of cortical neural network functions even with their important roles. We characterized inhibitory interneurons in layer II/III of the rat primary visual cortex, using patch-clamp recording and confocal reconstruction, and classified inhibitory interneurons into fast spiking (FS), late spiking (LS), burst spiking (BS), and regular spiking non-pyramidal (RSNP) neurons according to their electrophysiological characteristics. Global parameters to identify inhibitory interneurons were resting membrane potential (<FONT FACE= 바탕 >＞&#8291;70 mV) and action potential (AP) width (<FONT FACE= 바탕 >＜0.9 msec at half amplitude). FS could be differentiated from LS, based on smaller amplitude of the AP (<FONT FACE= 바탕 >＜∼50 mV) and shorter peak-to-trough time (P-T time) of the afterhyperpolarization (<FONT FACE= 바탕 >＜4 msec). In addition to the shorter AP width, RSNP had the higher input resistance (<FONT FACE= 바탕 >＞200 M<FONT FACE= 바탕 >Ω) and the shorter P-T time (<FONT FACE= 바탕 >＜20 msec) than those of regular spiking pyramidal neurons. Confocal reconstruction of recorded cells revealed characteristic morphology of each subtype of inhibitory interneurons. Thus, our results provide at least four subtypes of inhibitory interneurons in layer II/III of the rat primary visual cortex and a classification scheme of inhibitory interneurons.