Satellite workshop of the Japan Neuroscience Meeting : Okazaki 2006
第35回生理研コンファレンス / 統合脳 国際シンポジウム/日本神経科学会大会サテライトワークショップ(岡崎)

Direction selectivity and arrangement of neurons in single barrel columns in the rat somatosensory cortex examined with in vivo two-photon calcium imaging

1Koji Ikezoe, 2Yoshiya Mori, 3, 4Kazuo Kitamura, 2, 4Hiroshi Tamura, 2, 4Ichiro Fujita
1Grad. Sch. Engineering Science, 2Grad. Sch. Frontier Biosciences, and 3Grad. Sch. Medicine, Osaka University, Osaka, Japan
4CREST, JST, Saitama, Japan

Tactile inputs from whiskers are mapped in an array of barrel columns in the rodent primary somatosensory cortex. Previous extracelluar single-unit recording studies suggested a subcolumnar functional organization within individual barrel columns. Here, we investigated how neurons with different direction selectivities are spatially arranged within a single barrel column using in vivo two-photon calcium imaging. We loaded a region (250-300 μm in diameter) in layer II/III of a barrel column, whose principal whisker was C2 or D2, with a calcium indicator (Oregon Green 488 BAPTA-1 AM) in juvenile Sprague-Dawley rats (postnatal day 15-21) anesthetized with urethane. We recorded [Ca2+] transients in response to a single deflection of the principal whisker in the rostral-to-caudal and caudal-to-rostral directions. Significant changes in [Ca2+] were observed in 90-100% of the neurons examined. The duration of the responses to a single principal whisker stimulation was approximately 1 s. Although most neurons responded to both directions of the whisker deflection, the direction preference of the neural population was biased for the rostral-to-caudal direction. In most cases, the direction preference of the neurons did not systematically change across a barrel column, although it changed gradually across a barrel column in one animal. The results suggest that nearly all neurons in layer II/III of the barrel cortex represent whisker inputs. Variability of the arrangement of neurons with the direction preference in different experiments is likely due to differences in the relative position of imaged areas to a barrel column, the rate of transition of direction preference and the direction of the whisker stimulus. We are now optimizing the experiments by systematically changing the imaging areas and the direction of the whisker stimulus.

Supported by CREST, JST, Japan