Pain Mechanisms and Sensory NeuroscienceReseach PaperSpatiotemporal profiles of transcallosal connections in rat insular cortex revealed by in vivo optical imaging
Highlights
▶Gustatory cortex (GC) is reciprocally connected with contralateral GC. ▶Contra- and ipsilateral GC stimulation evoked similar spatial patterns of excitation. ▶Transcallosal excitation was frequently followed by GABAB-mediated hyperpolarization. ▶Transcallosal GC projections may support the detection of weak gustatory inputs.
Section snippets
Experimental procedures
Experiments were approved by the Animal Experimentation Committee of Nihon University and were performed in accordance with the institutional guidelines of the National Institute of Health Guide for the Care and Use of Laboratory Animals. The present study used totally 63 male rats. All efforts were made to minimize animal suffering and to reduce the number of animals used.
Anatomical evidence of transcallosal inputs to the DI
In the sensory cortex, including visual and somatosensory areas, the main source of transcallosal projections is the pyramidal or stellate cells in layer II/III and V (Koralek et al., 1990, Martínez-García et al., 1994). The transcallosal projections of the GC have a similar anatomical profile, as reported by Hayama and Ogawa (2001). Before starting the optical imaging experiments, we confirmed that the pyramidal neurons in the DI/GI project to layers II/III of the contralateral DI/GI in our
Putative neural circuits through the corpus callosum
The spatial patterns of excitatory propagation evoked by contralateral stimulation demonstrated that the area of excitation was relatively limited; that is, most of the excitation area was within the IC. Taken together with the present anatomical findings, transcallosal fibers project almost symmetrically to the IC of the other hemisphere. Hayama and Ogawa (2001) demonstrated that in the DI/GI, pyramidal cells are the source of transcallosal axons, and most of these target the contralateral
Acknowledgments
We thank Prof. Atsushi Yoshida for instruction in FG and BDA histochemistry. This work was supported by KAKENHI 20592188 to M.K. and 22791802 to S.F. from the Japanese Ministry of Education, Culture, Sports, Science and Technology; Nihon University Joint Grant Research Grant to M.K.; the Promotion and Mutual Aid Corporation for Private Schools of Japan to N.K. and M.K.; and Grant for the Promotion of Multi-disciplinary Research Projects entitled “Translational Research Network on Orofacial
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