In situ Ca2+ imaging of the enteric nervous system

Reflex behaviors of the intestine are controlled by the enteric nervous system (ENS). The ENS is an integrative network of neurons and glia in two ganglionated plexuses housed in the gut wall. Enteric neurons and enteric glia are the only cell types within the enteric ganglia. The activity of enteric neurons and glia is responsible for coordinating intestinal functions. This protocol describes methods for observing the activity of neurons and glia within the intact ENS by imaging intracellular calcium (Ca(2+)) transients with fluorescent indicator dyes. Our technical discussion focuses on methods for Ca(2+) imaging in whole-mount preparations of the myenteric plexus from the rodent bowel. Bulk loading of ENS whole-mounts with a high-affinity Ca(2+) indicator such as Fluo-4 permits measurements of Ca(2+) responses in individual neurons or glial cells. These responses can be evoked repeatedly and reliably, which permits quantitative studies using pharmacological tools. Ca(2+) responses in cells of the ENS are recorded using a fluorescence microscope equipped with a cooled charge-coupled device (CCD) camera. Fluorescence measurements obtained using Ca(2+) imaging in whole-mount preparations offer a straightforward means of characterizing the mechanisms and potential functional consequences of Ca(2+) responses in enteric neurons and glial cells.