Neuropeptides are widespread signal molecules that display a great chemical and 
functional diversity. Predictions of neuropeptide cleavage from precursor 
proteins are not always correct, and thus, biochemical identification is 
essential. Single-cell analysis is valuable to identify peptides processed from 
a single precursor, but also to determine coexpression of further neuropeptides 
from other precursors. We have developed an approach to isolate single 
identified neurons from the fruit fly Drosophila melanogaster for mass 
spectrometric analysis. By using Gal4 promoter lines to drive green fluorescent 
protein under UAS control, we identified specific peptidergic neurons. These 
neurons were isolated singly under a fluorescence microscope and subjected to 
MALDI-TOF mass spectrometry. Two Gal4 lines were used here to identify 
pigment-dispersing factor (PDF) and hugin-expressing neurons. We found that the 
large PDF expressing clock neurons only give rise to a single peptide, PDF. The 
three different classes of hugin expressing neurons all display the same mass 
signal, identical to pyrokinin-2. The other peptide predicted from the hugin 
precursor, hugin gamma, was not detected in any of the cells. Single-cell 
peptidomics is a powerful tool in Drosophila neuroscience since Gal4 drivers can 
be produced for all known neuropeptide genes and thus provide detailed 
information about neuropeptide complements in neurons of interest.