By using matrix-assisted laser desorptiony
ionization time-of-flight MS, individual peptidergic neurons
from Aplysia are assayed. A semiquantitative method is developed
for comparing single-cell profiles by using spectral
normalization, and peptides are localized to specific cells by
mass spectrometric cell mapping. In addition to all previously
identified products of the egg-laying hormone (ELH) gene,
other peptides are formed from proteolytic hydrolysis of
Leu-Leu residues within ELH and acidic peptide (AP). AP
exhibits further processing to yield AP1–20 and AP9–27. These
peptides appear to be colocalized in vesicles with ELH,
transported to specific neuronal targets, and released in a
Ca21-dependent manner. A differential peptide distribution is
observed at a specific target cell, and a low-frequency variation
of AP, [Thr21]AP, is detected in a single animal