Abstract
Chemical calcium indicators have been commonly used to monitor calcium (Ca(2+)) activity in cell bodies, i.e., somata, of isolated dorsal root ganglion neurons. Recent studies have shown that dorsal root ganglion somata play an essential role in soma-glia interactions and actively participate in the transmission of nociceptive signals. It is therefore desirable to develop methods to study Ca(2+) activity in neurons and glia in intact dorsal root ganglia. In our previous studies, we found that incubation of intact dorsal root ganglia with acetoxymethyl dye resulted in efficient Ca(2+) dye loading into glial cells but limited dye loading into neurons. Here, we introduce a useful method to load Ca(2+) dyes in intact dorsal root ganglion neurons through electroporation. We found that electroporation greatly facilitated loading of Fluo-4 acetoxymethyl, Oregon green bapta-1-488 acetoxymethyl, and Fluo-4 pentapotassium salt into dorsal root ganglion neurons. In contrast, electroporation did not further facilitate dye loading into glia. Using electroporation followed by incubation of acetoxymethyl form Ca(2+) dye, we can load acetoxymethyl Ca(2+) dye well in both neurons and glia. With this approach, we found that inflammation induced by complete Freund's adjuvant significantly increased the incidence of neuron-glia interactions in dorsal root ganglia. We also confirmed the actions of capsaicin and morphine on Ca(2+) responses in dorsal root ganglion neurons. Thus, by promoting the loading of Ca(2+) dye in neurons and glia through electroporation and incubation, Ca(2+) activities in neurons and neuron-glia interactions can be well studied in intact dorsal root ganglia.