Journal of Neuroscience, Vol 9, 3058-3071, Copyright © 1989 by Society for Neuroscience
SCP-containing R20 neurons modulate respiratory pumping in Aplysia
A Alevizos, KR Weiss and J Koester
Center for Neurobiology and Behavior, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Respiratory pumping in Aplysia consists of transient, synchronous pumping
actions of the gill, siphon, mantle shelf, and parapodia. This behavior has
previously been shown to be driven by a network of coupled interneurons in
the abdominal ganglion, the R25 and the L25 cells. We describe here a pair
of electrically coupled cells, the R20 cells, which when active can
initiate respiratory pumping or increase its spontaneous rate of
occurrence. This action is mediated by a slow, long- lasting excitation of
the endogenous burst mechanism of the cells in the R25/L25 network. The R20
cells, which are located in the abdominal ganglion, also make slow
inhibitory connections to the RB cells and to the RG cells in that
ganglion, and to the gill motoneurons in the branchial ganglion. The R20
cells are immunoreactive to SCPB, a molluscan neuropeptide. Biochemical
purification studies demonstrate that each of the R20 cells synthesizes not
only SCPB, but also SCPA, a closely related molecule known to be encoded by
the same gene as SCPB. The R20 cells also synthesize in abundance several
other low-molecular- weight, methionine-containing peptides. The excitatory
actions of the R20 cells on the R25/L25 network are mimicked by SCPA and
SCPB. However, the inhibitory actions of the R20 cells on the RB cells, the
RG cells, and on the cells of the branchial ganglion are not mimicked by
the SCPs. Thus, the data support the hypothesis that the R20 cells release
SCPA and SCPB and at least one other unidentified transmitter.
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