Journal of Neuroscience, Vol 7, 2884-2893, Copyright © 1987 by Society for Neuroscience
Suppression of oscillatory activity in crustacean pyloric neurons: implication of GABAergic inputs
JR Cazalets, I Cournil, M Geffard and M Moulins
Generation of rhythmic pyloric motor output in the crustacean
stomatogastric ganglion results from synaptic connections and cellular
properties of a 14-cell network of pyloric neurons. These cellular
properties are under the influences of modulatory inputs, which act, for
the most part, in an activating mode, i.e., they enhance the bursting
properties of the pyloric neurons and/or their ability to express their
regenerative properties. Here we attempt to demonstrate that the pyloric
motor output is also under the control of suppressive afferent inputs that
are able to stop the pyloric rhythm in a long- lasting manner.
Immunohistochemistry, using GABA antibodies, indicates that GABAergic-like
fibers are present in both the stomatogastric ganglion and its afferent
nerve. Bath-applied GABA suppresses spontaneous pyloric rhythmic activity.
This is due to an inability of the pyloric pacemakers to express their
bursting properties. The suppressive effect of GABA is blocked by
picrotoxin and mimicked by muscimol. Isolating the pyloric neurons from all
descending spiking influences with tetrodotoxin demonstrates that
exogenously applied GABA acts directly on the pyloric neurons. To confirm
the existence of a physiological suppressive system for the pyloric motor
pattern, we show that the stimulation of an afferent nerve, known to
contain GABA-like fibers, also causes the cessation of rhythmic activity
and the inability of the pyloric neurons to express their bursting
properties.