Channelrhodopsin-2-assisted circuit mapping of long-range callosal projections.
The functions of cortical areas depend on their inputs and outputs, but the detailed circuits made by long-range projections are unknown. We show that the light-gated channel channelrhodopsin-2 (ChR2) is delivered to axons in pyramidal neurons in vivo. In brain slices from ChR2-expressing mice, photostimulation of ChR2-positive axons can be transduced reliably into single action potentials. Combining photostimulation with whole-cell recordings of synaptic currents makes it possible to map circuits between presynaptic neurons, defined by ChR2 expression, and postsynaptic neurons, defined by targeted patching. We applied this technique, ChR2-assisted circuit mapping (CRACM), to map long-range callosal projections from layer (L) 2/3 of the somatosensory cortex. L2/3 axons connect with neurons in L5, L2/3 and L6, but not L4, in both ipsilateral and contralateral cortex. In both hemispheres the L2/3-to-L5 projection is stronger than the L2/3-to-L2/3 projection. Our results suggest that laminar specificity may be identical for local and long-range cortical projections.
Petreanu
Leopoldo
L
Howard Hughes Medical Institute, Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, Virginia 20147, USA.
Huber
Daniel
D
Sobczyk
Aleksander
A
Svoboda
Karel
K
D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000378:metabolism; D001931:Brain Mapping; D003337:Corpus Callosum / Q000166:cytology / Q000378:metabolism*; D004622:Embryo, Mammalian; D005260:Female; D007839:Functional Laterality; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009415:Nerve Net / Q000378:metabolism*; D009434:Neural Pathways / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D010775:Photic Stimulation / Q000379:methods; D011247:Pregnancy; D012172:Retinaldehyde / Q000235:genetics / Q000378:metabolism*; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism*; D013003:Somatosensory Cortex / Q000166:cytology* / Q000378:metabolism
D012243:Rhodopsin; D012172:Retinaldehyde