Journal of Neuroscience, Vol 9, 1443-1451, Copyright © 1989 by Society for Neuroscience
Positive feedback by autoexcitatory neuropeptides in neuroendocrine bag cells of Aplysia
RO Brown and E Mayeri
Department of Physiology, University of California, San Francisco 94143.
Neurohormones are often secreted in large amounts from neuroendocrine cells
during episodes of synchronous, repetitive spike activity. We report
evidence that this pattern of activity in the neuroendocrine bag cells of
Aplysia involves positive feedback by autoexcitatory transmitters.
Intracellular stimulation of individual bag cells caused slow depolarizing
afterpotentials and synchronous afterdischarges in the entire population of
bag cells. Application of the bathing medium collected during bag cell
activity mimicked these responses. Application of alpha-, beta-, or
gamma-bag cell peptides (BCPs), 3 structurally related neuropeptides
released from bag cells, also mimicked these responses. These
autoexcitatory BCPs fulfill most of the strict criteria necessary for
classification as neurotransmitters in this system. This is the first
biological activity reported for beta- and gamma-BCPs and brings to 4 the
number of bag cell neuropeptides derived from the egg-laying hormone/BCP
precursor that are putative cotransmitters. Positive feedback by
autoexcitatory transmission may provide a general mechanism for the
generation of episodic activity in neuroendocrine systems.