The Journal of Neuroscience, October 15, 2002, 22(20):9078-9085
A Lateral Excitatory Network in the Escape Circuit of Crayfish
Jens
Herberholz,
Brian L.
Antonsen, and
Donald H.
Edwards
Department of Biology, Georgia State University, Atlanta, Georgia
30302-4010
A phasic stimulus directed to the rear of a crayfish
(Procambarus clarkii) creates mechanosensory input to
the lateral giant (LG) interneuron, a command neuron for escape. A
single LG spike is necessary and sufficient to produce a highly
stereotyped tail flip that thrusts the animal away from the source of
stimulation. Here we describe a lateral excitatory network among
primary afferent axons in the last abdominal ganglion of crayfish that
produces nonlinear amplification of the sensory input to the command
circuitry for escape. The lateral excitation is mediated by electrical
synapses between central terminals of primary mechanosensory afferents. The network enables stimulated afferents to recruit unstimulated afferents that contribute additional input to LG and to mechanosensory interneurons that also converge on LG. When depolarized, the LG neuron
increases its own inputs from primary afferents and primary interneurons by facilitating the recruitment of both. Conversely, hyperpolarization of LG reduces the excitability of primary afferents and primary interneurons. The crayfish's decision to escape,
previously thought to lie exclusively in the synaptic integrative
properties of LG, is now seen to depend on the interactions between LG
dendritic postsynaptic potentials and the responses of primary afferent terminals in the lateral excitatory network.
Key words:
crayfish; escape; lateral giant neuron; afferents; interneurons; lateral excitation
Copyright © 2002 Society for Neuroscience 0270-6474/02/22209078-08$05.00/0
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