Specific molecular mass detection of endogenously released neuropeptides using in vivo microdialysis mass spectrometry

The specific molecular detection of the endogenous neuropeptides methionine ([Met](5)) enkephalin and neurotensin released in vivo in rat brain has been accomplished using microdialysis and mass spectrometry. Microdialysis probes were implanted in specific brain regions and were used to collect samples from brain extracellular fluids in unanesthetized, freely moving animals. Microelectrospray/tandem mass spectrometry was used-to achieve molecular-specific identification of the neuropeptides with a sensitivity in the amol/mu l range. Measurements of the amounts; of neuropeptides in the dialysates obtained from studies of KCl-stimulated release showed that [Met](5)-enkephalin from the globus pallidus/ventral pallidum region was present at a level of approximately 4-6 fmol/10 mu l of dialysate and neurotensin from the hypothalamus of approximately 500 amol in 10 mu l of dialysate. In this manuscript, we present the first data of a mass- and molecular-specific detection and quantitation of individual neuropeptides released in response to either intracerebrally or systemically administered compounds.