In Vivo Calcium Imaging of Neuronal Ensembles in the Intact Dorsal Root Ganglia of a Mouse

Take an anesthetized transgenic mouse with an exposed dorsal root ganglion, or DRG, a cluster of sensory neuron cell bodies that receive input from the hind limbs.             

The neurons in the DRG express a cytoplasmic calcium indicator.

Using a confocal microscope, visualize the DRG to image the collective activity of a large number of neurons.

Without external stimulation, the low intracellular calcium level keeps the indicators in their native conformation, resulting in a faint baseline fluorescence.         

Apply a mechanical or thermal stimulus to a hind paw, generating an action potential in the sensory neurons.

The signal propagates to the DRG, where voltage-gated calcium channels in the neurons open, allowing calcium influx.

The additional calcium ions bind to the indicators, inducing a conformational change that increases fluorescence intensity.

Observe a bright fluorescence in the DRG, with the intensity corresponding to the number of stimulated neurons exhibiting calcium influx.