Abstract
The presence of columnar organization is most apparent in the rodent primary somatosensory cortex receiving inputs arising from whiskers, as revealed by a barrel structure in layer IV. By contrast, it is unclear whether the columnar organization exists or not in the insular cortex, the primary gustatory area. In the present study, we have performed optical imaging to investigate spatiotemporal patterns of excitation spread in the insular cortex in comparison with the barrel cortex. Slice preparations were incubated with a voltage-sensitive dye (RH414) for 1 hr. Following electrical stimulation applied to layer IV, excitation spread vertically from layer IV to layers II/III in the insular cortex, similar to the pattern seen in the barrel cortex. Then, the excitation spread horizontally in layers II/III in the both cortices. However, the extent of horizontal spread and the intensity of excitation in layers II/III were smaller and lower, respectively, in the insular than in the barrel cortex. An application of bicuculline (5-20 μM), a GABAA receptor antagonist, enlarged the extent and prolonged the time course of excitation spread in the insular cortex as well as in the barrel cortex. These results suggest that although there is a columnar organization in the insular cortex, horizontal excitatory connections are less abundant in the insular cortex than in the barrel cortex while there is no prominent difference in GABAA receptor-mediated lateral inhibition in layers II/III. [Jpn J Physiol 54 Suppl:S146 (2004)]
