Journal of Neuroscience, Vol 4, 1300-1311, Copyright © 1984 by Society for Neuroscience
Proctolin in the lobster: the distribution, release, and chemical characterization of a likely neurohormone
TL Schwarz, GM Lee, KK Siwicki, DG Standaert and EA Kravitz
A radioimmunoassay, immunohistochemical techniques, and high pressure
liquid chromatography (HPLC) methods have been developed for the study of
the pentapeptide proctolin in the lobster Homarus americanus.
Proctolin-like immunoreactivity is present in nearly every portion of the
lobster nervous system; immunoreactivity is found in the brain, in each of
the ganglia and connectives of the ventral nerve cord, and in many of the
nerve roots that emerge from the cord. The greatest amounts are found in
the pericardial organs, which are well known neurosecretory structures, and
these structures have been selected for more detailed study. The
immunoreactive material in the pericardial organs appears to be authentic
proctolin. This material co-migrates with synthetic proctolin in two HPLC
systems. Furthermore, a peptide that is purified from pericardial organs by
HPLC is indistinguishable from synthetic proctolin in high resolution fast
atom bombardment mass spectrometry. Cytochemistry reveals that the surface
of the pericardial organs is densely covered with immunoreactive
varicosities. No cell bodies that stain for proctolin are found in the
pericardial organs, and the cells that give rise to the varicosities have
not yet been located. The nerve endings in pericardial organs are capable
of releasing proctolin-like material when depolarized in the presence of
Ca++. These findings suggest that proctolin is a neurohormone in the
lobster.