Journal of Neuroscience, Vol 5, 1412-1417, Copyright © 1985 by Society for Neuroscience
Changes from enkephalin-like to gastrin/cholecystokinin-like immunoreactivity in snail neurons
BP Gesser and LI Larsson
Coexistence of regulatory peptides is reported with increasing frequency in
the mammalian neuroendocrine system. We have investigated the possible
presence of such coexistence in the invertebrate Lymnaea stagnalis and have
found evidence for concurrence of enkephalin- and gastrin/cholecystokinin
(CCK)-like peptides in identified neurosecretory neurons. Our
immunocytochemical studies reveal, however, that some of these neurons show
variations in their content of immunoreactive peptides depending upon
season or age. Thus, the light green cells of the Lymnaea cerebral
ganglion, known to produce a body growth-stimulating hormone, contain
enkephalin-like immunoreactivity during spring and gastrin/CCK-like
immunoreactivity during fall. During winter, these cells contain both
enkephalin-like and gastrin/CCK-like immunoreactivities. In another group
of neurosecretory neurons, the caudodorsal cells, known to produce an
ovulation hormone, age-dependent changes were noted. Thus, in young
animals, these cells contain enkephalin-like immunoreactivity; in animals
of intermediate age, they contain both enkephalin- and gastrin/CCK-like
immunoreactivity and, in older animals, only gastrin/CCK-like
immunoreactivity can be detected in these cells. Interestingly, the
mediodorsal bodies, which are endocrine organs also implicated in
regulating sexual function of Lymnaea, show age-dependent variations in
immunocytochemically detectable enkephalin- and gastrin/CCK-like
immunoreactivity which parallels that found in the caudodorsal cells. The
changes noted in the light green cells and the caudodorsal cells are
detected both in the cell bodies and in the terminals of these cells,
suggesting that the immunoreactivity represents secretory material. The
relation, if any, between the immunoreactivities detected and the growth
and reproduction of Lymnaea remains to be established, as do the factors
responsible for the observed age- and season-dependent variations.