Journal of Neuroscience, Vol 12, 3545-3553, Copyright © 1992 by Society for Neuroscience
Modulation of peptide release from single identified Aplysia neurons in culture
MD Whim and PE Lloyd
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Aplysia neurons B1 and B2 contain large amounts of the neuropeptides SCPA
and SCPB. When grown in culture, individual B1 and B2 cells incorporate
35S-methionine into the SCPs, which can be released in a stimulus- and
calcium-dependent fashion (Lloyd et al., 1986). We now show that single
cells can be stimulated in a manner to evoke release of the SCPs that
declines only slightly with repeated stimulation. This has allowed us to
examine the ability of several physiologically relevant agonists to
modulate the stimulus-evoked release of the SCPs. Bath application of
either FMRFamide or 5-HT resulted in a significant decrease in the amount
of SCPs released by intracellular stimulation of B1 or B2. The action of
5-HT was dose dependent with an inhibition of release of approximately 70%
at a concentration of 100 microM. SCPA did not significantly affect
release. The bath application of several compounds that are expected to
elevate intracellular levels of cAMP were also found to depress release. To
investigate the possibility that the agonists inhibited the release of the
SCPs via a hyperpolarization of membrane potential (and perhaps a loss of
spikes in the neurites), we examined the actions of 5-HT, FMRFamide, and
SCPA on several electrophysiological parameters intended to monitor the
level of cell excitability. Surprisingly, even though 5-HT depressed the
release of the SCPs from both cells, it depolarized and increased the
excitability of B1, and hyperpolarized and decreased the excitability of
B2. Furthermore, in contrast to the effects seen in culture, 5-HT
depolarized both B1 and B2 in situ.(ABSTRACT TRUNCATED AT 250 WORDS)