Journal of Neuroscience, Vol 7, 522-532, Copyright © 1987 by Society for Neuroscience
Proctolin in identified serotonergic, dopaminergic, and cholinergic neurons in the lobster, Homarus americanus
KK Siwicki, BS Beltz and EA Kravitz
In order to explore the functions of the peptide proctolin in the lobster
nervous system, 3 classes of neurons showing proctolin-like
immunocytochemical staining were selected for study. These neurons were
identified on the basis of physiological and/or morphological criteria,
isolated by dissections, and analyzed with biochemical methods to determine
whether they contained authentic proctolin and which classical
neurotransmitters coexisted with the peptide. Pairs of large
proctolin-immunoreactive neurons in fifth thoracic and first abdominal
ganglia were identified as serotonin-immunoreactive neurons (Beltz and
Kravitz, 1983, 1987) by staining serial sections of the ganglia alternately
with the 2 antisera. Physiologically identified cells, dissected from the
ganglia and analyzed with high-performance liquid chromatography (HPLC),
contained approximately 20 microM proctolin and 0.5 mM serotonin. A large
proctolin-immunoreactive neuron in the circumesophageal ganglion was
identified as the lobster homolog of a dopaminergic neurosecretory cell
found in other crustaceans (Cooke and Goldstone, 1970). The large lobster
cell stained with antityrosine hydroxylase antiserum, and synthesized
3H-dopamine from 3H-tyrosine. Dissected cell bodies, analyzed by HPLC,
contained approximately 25 microM proctolin. Proctolin-immunoreactive
sensory neurons were identified as large stained fibers that terminated in
sensory dendrites of the oval organ mechanoreceptor in the scaphognathite
(Pasztor, 1979; Pasztor and Bush, 1982). The largest sensory fiber was
isolated for biochemical studies. It synthesized 3H-acetylcholine from
3H-choline and, by HPLC analysis, was found to contain approximately 3
microM proctolin. Thus, proctolin coexists with different conventional
transmitters in several classes of identified lobster neurons.
Investigations of the actions of proctolin in these different contexts
should contribute to a more complete understanding of the diverse functions
of neuropeptides and their roles as cotransmitters.
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