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Anatomical and electrophysiological mechanisms for asymmetrical excitatory propagation in the rat insular cortex: In vivo optical imaging and whole‐cell patch‐clamp studies
Author(s) -
Adachi Kazunori,
Fujita Satoshi,
Yoshida Atsushi,
Sakagami Hiroshi,
Koshikawa Noriaki,
Kobayashi Masayuki
Publication year - 2013
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.23246
Subject(s) - neuroscience , excitatory postsynaptic potential , biology , postsynaptic potential , electrophysiology , inhibitory postsynaptic potential , barrel cortex , somatosensory system , stimulation , anatomy , anterograde tracing , central nervous system , biochemistry , receptor
The insular cortex (IC) integrates limbic information from the amygdala and hypothalamic nucleus to multimodal sensory inputs, including visceral, gustatory, and somatosensory information. However, the functional framework of excitation in the IC is still unknown. We performed optical imaging and single pyramidal neuronal staining using a whole‐cell patch‐clamp technique in urethane‐anesthetized rats to elucidate the precise anatomical and physiological features of IC pyramidal neurons, which regulate cortical information processing via their horizontal connections. Optical imaging revealed that electrical stimulation of the granular (GI) or dysgranular (DI) IC elicited characteristic excitatory propagations along the rostrocaudal axis parallel to the rhinal fissure, with a preference toward the rostral direction. Spatial patterns of the dendrites and axons of layer II/III pyramidal cells in the DI/GI support these functional features of excitation; for example, rostrocaudal axonal arbors tend to extend with a rostral directional preference. The mean length of the axons from the soma to the farthest site rostrally was ∼50% longer than that of the caudal length. Pyramidal cells in the DI/GI exhibited spontaneous membrane oscillation in the UP and DOWN states. Similarly to the evoked signals obtained by optical imaging, repetitive electrical stimulation of the caudal IC ∼1 mm away from the recorded cells (five pulses at 50 Hz) induced the summation of evoked excitatory postsynaptic potentials during the DOWN state and profound inhibitory postsynaptic potentials during the UP state. Clarification of the excitation feature with its cellular basis provides new clues about the functional mechanisms of the asymmetric propagation of neural activities in the IC. J. Comp. Neurol. 521:1598–1613, 2013. © 2012 Wiley Periodicals, Inc.