Microdialysis combined with a sensitive radioimmunoassay. A technique for studying in vivo release of neuropeptides.

Microdialysis in combination with radioimmunoassay was used to study in vivo release of neuropeptides in the rat brain. Microdialysis is a novel brain perfusion technique, by which molecules in the extracellular space may be monitored. This study describes the application to neuropeptide research. A radioimmunoassay procedure was adapted so that substance P- and neurokinin A-like immunoreactivity could be measured in samples collected during in vivo release experiments. The detection limits of substance P and neurokinin A were below 0.1 fmol/100-microliters sample and the IC50 approximately 1 fmol/sample for both peptides. Potassium, introduced via the microdialysis probe, was found to induce a concentration-dependent increase of the extracellular concentration of neurokinin A-like immunoreactivity.