Letter

Nature 457, 1142-1145 (26 February 2009) | doi:10.1038/nature07709; Received 19 August 2008; Accepted 4 December 2008; Published online 18 January 2009

The subcellular organization of neocortical excitatory connections

Leopoldo Petreanu1, Tianyi Mao1, Scott M. Sternson1 & Karel Svoboda1

  1. Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia 20147, USA

Correspondence to: Karel Svoboda1 Correspondence and requests for materials should be addressed to K.S. (Email: svobodak@janelia.hhmi.org).

Understanding cortical circuits will require mapping the connections between specific populations of neurons1, as well as determining the dendritic locations where the synapses occur2. The dendrites of individual cortical neurons overlap with numerous types of local and long-range excitatory axons, but axodendritic overlap is not always a good predictor of actual connection strength3, 4, 5. Here we developed an efficient channelrhodopsin-2 (ChR2)-assisted method6, 7, 8 to map the spatial distribution of synaptic inputs, defined by presynaptic ChR2 expression, within the dendritic arborizations of recorded neurons. We expressed ChR2 in two thalamic nuclei, the whisker motor cortex and local excitatory neurons and mapped their synapses with pyramidal neurons in layers 3, 5A and 5B (L3, L5A and L5B) in the mouse barrel cortex. Within the dendritic arborizations of L3 cells, individual inputs impinged onto distinct single domains. These domains were arrayed in an orderly, monotonic pattern along the apical axis: axons from more central origins targeted progressively higher regions of the apical dendrites. In L5 arborizations, different inputs targeted separate basal and apical domains. Input to L3 and L5 dendrites in L1 was related to whisker movement and position, suggesting that these signals have a role in controlling the gain of their target neurons9. Our experiments reveal high specificity in the subcellular organization of excitatory circuits.

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