Distributed Amine Modulation of Graded Chemical Transmission in the Pyloric
Network of the Lobster Stomatogastric Ganglion.
Johnson, Bruce R., Jack H. Peck and Ronald M. Harris-Warrick.
Section of Neurobiology and Behavior, S.G. Mudd Hall, Cornell University,
Ithaca, NY 14853, Department of Psychology, Ithaca College, Ithaca, NY
14850.
APStracts 2:0090N, 1995.
SUMMARY AND CONCLUSIONS
1. In the pyloric network of the lobster stomatogastric ganglion, graded
synapses organize the network output. The amines dopamine (DA), serotonin
(5HT) and octopamine (Oct) each elicit a distinctive motor pattern from a
quiescent pyloric network. We have been examining the effects of these amines
on the graded synaptic strengths between the six major types of neurons of
this network to understand how amine modulation of synaptic strength
contributes to the amine-induced motor patterns. Here, we tested amine
affectsat ten different graded chemical synapses of the pyloric network. We
show that each amine has a statistically different spectrum of distributed
effects across the network synapses. 2. Under our control conditions (isolated
pairs of neurons, removal of modulatory input), most of the graded chemical
synapses were weak and some synapses were nonfunctional. The output synapses
of the Ventricular Dilator (VD) neuron were significantly stronger than the
other synapses. 3. Dopamine altered the synaptic strength of every graded
chemical synapse. This amine strengthened the weak chemical output synapses of
the anterior burster (AB), lateral pyloric (LP) and pyloric constrictor (PY)
neurons and weakened (and in some cases abolished) the strong chemical output
synapses of the VD neuron. The AB˙AE Inferior Cardiac (IC) neuron and PY IC
graded chemical synapses were non-functional under our control conditions; DA
activated these silent synapses. 4. Serotonin enhanced the AB's output
chemical synapses but weakened all the other graded chemical synapses
examined. Octopamine's effects were much weaker than those of the other two
amines. It enhanced AB LP and the LP's output synapses and weakly
strengthened the AB PY, VD LP and VD PY synapses. 5. The amines alter the
input resistance of many of the pyloric neurons, and this could contribute to
the observed changes in synaptic strength by altering passive current flow
between input and output sites in the cells. However, the input resistance
changes were relatively small compared to the changes in synaptic strength
andcannot alone account for the synaptic modulation. In some cases, the sign
of the input resistance change was inconsistent with the change in synaptic
strength. Thus, the amines appear to modify synaptic transmssion directly in
this system. 6. This study completes our description of amine effects on all
the graded synapses of the pyloric network. We summarize our present and
earlier work to show that modulators can reconfigure the entire synaptic
organization of a neural network by acting at many distributed synaptic sites.
Modulators may be critical for normal network operation because they not only
quantitatively change the synaptic gain but also qualitatively abolish and
create functional synaptic interactions. Such modulatory actions contribute
tothe flexible outputs produced from anatomically defined neural networks.
Received 17 October 1994; accepted in final form 22 February 1995.
APS Manuscript Number J642-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.