Journal of Neuroscience, Vol 10, 448-457, Copyright © 1990 by Society for Neuroscience
Suppressive control of the crustacean pyloric network by a pair of identified interneurons. I. Modulation of the motor pattern
JR Cazalets, F Nagy and M Moulins
Laboratoire de Neurobiologie et Physiologie Comparees, CNRS et Universite de Bordeaux, Arcachon, France.
A pair of identified neuromodulatory neurons, the pyloric suppressor (PS)
neurons, can individually and strongly modify the activity of the pyloric
network in the stomatogastric nervous system of the lobster Homarus
gammarus. The PS neurons are identified by the location of their somata in
the inferior ventricular nerve, their axonal projections, and their effects
on pyloric network activity in vitro. Discharge of a PS neuron evokes large
EPSPs in the pyloric dilator (PD) neurons and a long-lasting cessation of
rhythmic activity in the neurons that control movements of the pyloric
filter: PD, lateral pyloric (LP), and pyloric (PY). This cessation of
rhythmic activity can outlast by several 10s of seconds a brief discharge
of PS lasting only a few seconds. The different neurons of the pyloric
filter do not exhibit the same sensitivity to the suppressive effects of
PS, with the LP neuron being the most sensitive. Tonic discharge in PS
induces graded alterations in the pyloric pattern, depending on its firing
frequency. At low (less than 5 Hz) discharge frequencies, PS provokes
changes in phase relationships and duration of bursting in pyloric neurons.
A slight increase in PS frequency suppresses the rhythmic activity of some
pyloric neurons, resulting in a switch from a triphasic to a biphasic
pattern. At higher (greater than 10 Hz) PS firing frequencies, rhythmic
activity in all the pyloric neurons, including the pacemakers (PD, anterior
burster), is abolished, except in cells (ventricular dilator, inferior
cardiac) controlling the pyloric valve. We conclude that a central pattern
generator is not only subject to activating modulatory control, but may
also be the target of suppressive inputs that are themselves able to
provoke functional reconfigurations of the network.
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