Society for Neuroscience 2006
Oct. 14-18, 2006 in Atlanta, Georgia

Response properties and arrangement of neurons in a barrel column in rat somatosensory cortex revealed with in vivo two-photon calcium imaging

Presentation Start/End Time: Sunday, Oct 15, 2006, 8:00 AM - 9:00 AM

Authors: *K. IKEZOE1, Y. MORI2, K. KITAMURA3,4, H. TAMURA2,4, I. FUJITA2,4;
1Grad. Sch. Engineering Science, Osaka University, Toyonaka, Osaka, JAPAN, 2Grad. Sch. Frontier Biosciences, Osaka University, Toyonaka, Osaka, JAPAN, 3Grad. Sch. Medicine, Osaka University, Suita, 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. Extracellular recording techniques, however, allow only a limited number of neurons to be studied in a single experiment, and have inevitable sampling biases and uncertain localization of recorded neurons. Here, we used in vivo two-photon calcium imaging to investigate the percentage of neurons in a single barrel column that represent a whisker deflection and how neurons with different direction selectivities are spatially arranged within a single barrel column. We loaded a region (250-300 m 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 fluorescent responses to deflection of the principal whisker in the rostral-to-caudal and caudal-to-rostral directions. It has been shown that changes in fluorescence correlate with changes in the intracellular calcium concentration, which in turn reflect neuronal spike responses. Significant changes in fluorescence were observed in 90-100% of the neurons loaded with the indicator in response to deflection of the principal whisker. The responses lasted for 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. The arrangement of neurons was not consistent across experiments. This may be due to differences in the relative position of imaged areas to a barrel column, age of animals, or other factors.