Nitric oxide modulates local reflexes of the tailfan of the crayfish

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Description/Abstract

Electrical stimulation of sensory neurons
that innervate receptors on the tailfan of crayfish
evokes a reflex response of motor neurons that produce
movements of the blades of the tailfan, the uropods. We
analyzed the modulatory effects of nitric oxide (NO) on
the spike frequency of the reflex response. Bath application
of L-arginine and SNAP, which elevate endogenous
and exogenous NO levels, increased the frequency
of the evoked response, whereas the application of LNAME
and PTIO, which reduce NO levels, decreased
the frequency of the response. To determine through
what pathway and target NO exerted these effects we
bath applied ODQ, an inhibitor of soluble guanylyl cyclase
(sGC), which decreased the frequency of response,
and 8-br-cGMP, which increased the spike frequency of
response. To provide further evidence that NO acts via
sGC, we elevated NO levels with L-arginine while simultaneously
inhibiting sGC with ODQ. This application
reduced the response to control levels, indicating that
NO in the terminal ganglion of crayfish acts via sGC to
modulate cGMP levels, which in turn regulate the responses
of the uropod motor neurons.