Subcolumnar structures in local inputs of pyramidal neurons onto corticothalamic neurons in rat barrel cortex.

Yasuhiro Tanaka, Yasuyo Tanaka, Michiteru Konno, Fumino Fujiyama, Keiko Okamoto-Furuta, Takahiro Sonomura, Hiroshi Kameda, Hiroyuki Hioki, Takahiro Furuta, Kouichi Nakamura, Takeshi Kaneko

Department of Morphological Brain Science, Graduate school of medicine, Kyoto University, Kyoto, Japan

The thalamocortical reciprocal circuit is an essential cortical input/output organization.   Despite the pivotal position of corticothalamic neurons in the reciprocal circuit, however, it is poorly understood how the excitatory local connections to corticothalamic neurons is organized.  We retrogradely labeled almost all dendrites of layer (L) 6 corticothalamic neurons in rat barrel cortex with newly developed adenoviral vector.  Subsequently, we intracellularly stained single L2/3, L4, L5, or L6 pyramidal neurons, and examined the number and the distribution of their boutons apposed to dendrites of corticothalamic neurons.  The results suggested that the largest near and far sources of excitatory connections onto a L6 corticothalamic neuron are L6 corticothalamic neurons and L6 putative corticocortical neurons, respectively.  It was also suggested that a L6 corticothalamic neuron receives many connections from vertically-aligned L4 neurons.  This vertical and horizontal input organization of L6 corticothalamic neurons is of potential importance in shaping cortical modulation of thalamic excitability.