Inhibitory component of the resistance reflex in the locomotor network of the crayfish.
Journal of Neurophysiology. 2002-11-01; 88(5): 2575-2588
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1. J Neurophysiol. 2002 Nov;88(5):2575-88.
Inhibitory component of the resistance reflex in the locomotor network of the
Le Bon-Jego M(1), Cattaert D.
(1)Laboratoire de Neurobiologie des Réseaux, United Mixte de Recherche 5816,
Centre National de la Recherche Scientifique, Université Bordeaux 1, Biologie
Animale, Bât B2, 33405 Talence Cedex, France.
The aim of this study was to investigate the inhibitory components of a
resistance reflex in the walking system of the crayfish. This study was performed
using an in vitro preparation of several thoracic ganglia including motor nerves
and the proprioceptor that codes movements of the second joint (coxo-basipodite
chordotonal organ-CBCO). Sinusoidal movements were imposed on the CBCO, and
intracellular responses were recorded from levator (Lev) and depressor (Dep)
motoneurons (MNs). We found that in MNs that oppose the imposed movements (e.g.,
the Lev MNs during the imposed downward movement), the response consists in a
depolarization resulting from the summation of excitatory postsynaptic potentials
(EPSPs). A movement in the opposite direction resulted in hyperpolarization
during which inhibitory postsynaptic potentials (IPSPs) summated. The inhibitory
pathway to each MN is oligosynaptic (i.e., composed of a small number of neurons
in series) and involves spiking interneurons because it was blocked in the
presence of a high-divalent cation solution. The IPSPs were mediated by a
chloride conductance because their amplitude was sensitive to the chloride
concentration of the bathing solution and because they were blocked by the
chloride channel blocker, picrotoxin. Resistance reflex IPSPs related to single
CBCO neurons could be identified. These unitary IPSPs were blocked in the
presence of 3-mercapto-propionic acid, an inhibitor of gamma-amino-butyric acid
(GABA) synthesis, indicating that they are mediated by GABA. In addition to this
GABAergic pathway, electrical stimulation of the CBCO sensory nerve induced
compound IPSPs that were blocked by glutamate pyruvate transaminase (GPT),
indicating the presence of glutamatergic inhibitory pathways. These glutamatergic
interneurons do not appear to be involved in the resistance reflex, however, as
GPT did not block the unitary IPSPs. Functionally, the resistance reflex is
mainly supported by movement-coding CBCO sensory neurons. We demonstrate that
such movement-coding CBCO neurons produce both monosynaptic EPSPs in the MNs
opposing imposed movements and oligosynaptic IPSPs in the antagonistic
motoneurons. These results highlight the similarities between the inhibitory
pathways in resistance reflex of the crayfish and in the stretch reflex of
vertebrates mediated by Ia inhibitory interneurons.
PMID: 12424295 [Indexed for MEDLINE]