In vivo Ca2+ imaging of dorsal horn neuronal populations in mouse spinal cord.

Two-photon Ca(2+) imaging allows functional studies of neuronal populations in the intact brain, but its application to the spinal cord in vivo has been limited. Here we present experimental procedures to label superficial dorsal horn populations with Ca(2+) indicator and to stabilize the spinal cord sufficiently to permit functional imaging in anaesthetized mice. Spontaneous Ca(2+) transients occurred in a small subpopulation of dorsal horn cells. Larger numbers of cells were activated by increasing electrical stimulation of primary afferent fibres. Notably, in a subset of cells we resolved Ca(2+) transients evoked by mechanical stimulation of the paw. These advances open new opportunities to study both physiology and pathology of spinal cord neural circuits in vivo.