Journal of Neuroscience, Vol 8, 3085-3093, Copyright © 1988 by Society for Neuroscience
Proprioceptive inputs to nonspiking local interneurons contribute to local reflexes of a locust hindleg
M Burrows, GJ Laurent and LH Field
Department of Zoology, University of Cambridge, England.
Local reflexes of a leg of the locust Schistocerca gregaria (Forskal) can
be elicited by selective stimulation of a proprioceptor (the femoral
chordotonal organ) at the femorotibial joint. Motor neurons are either
excited or inhibited, so that a coordinated reflex response of a leg
results. At the same time, some nonspiking local interneurons are either
excited or inhibited by the inputs from these proprioceptive afferents.
Altering the membrane potential of an individual, nonspiking interneuron
can either increase or decrease the response of the participating motor
neurons to the proprioceptive stimulus and thereby alter the gain of the
reflex. To determine the pathways, and to understand the role of the
nonspiking interneurons in mediating these reflex effects, recordings were
made simultaneously from these interneurons and afferent neurons. The
excitation of a particular nonspiking local interneuron is produced
monosynaptically by the afferent neurons. Chemically mediated EPSPs
consistently follow sensory spikes with a latency that is the same as that
for the known parallel, direct connections made by these sensory neurons
with motor neurons (Burrows, 1987a). The chordotonal afferents and the
branches of the local interneurons project to the same regions of neuropil.
In contrast, the simplest inhibitory pathway is disynaptic, involving
spiking local interneurons. The afferents make direct excitatory
connections with some of these spiking interneurons, which then make direct
inhibitory connections with a nonspiking interneuron. Interactions between
the local interneurons add to the complexity of the pathways.(ABSTRACT
TRUNCATED AT 250 WORDS)
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