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The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 476-479
Copyright ©2001 by the American Physiological Society
RAPID COMMUNICATION
Department of Biology, Center for Neural Communication and Computation, Georgia State University, Atlanta, Georgia 30303
Clemens, Stefan and
Paul S. Katz.
Identified Serotonergic Neurons in the Tritonia
Swim CPG Activate Both Ionotropic and Metabotropic Receptors. J. Neurophysiol. 85: 476-479, 2001. Although
G-protein-coupled (metabotropic) receptors are known to modulate the
production of motor patterns, evidence from the escape swim central
pattern generator (CPG) of the nudibranch mollusk, Tritonia
diomedea, suggests that they might also participate in the
generation of the motor pattern itself. The dorsal swim interneurons
(DSIs), identified serotonergic neurons intrinsic to the
Tritonia swim CPG, evoke dual component synaptic potentials onto other CPG neurons and premotor interneurons. Both the fast and
slow components were previously shown to be due to serotonin (5-HT)
acting at distinct postsynaptic receptors. We find that blocking or
facilitating metabotropic receptors in a postsynaptic premotor
interneuron differentially affects the fast and slow synaptic responses
to DSI stimulation. Blocking G-protein activation by iontophoretically
injecting the GDP-analogue guanosine
5'-O-(2-thiodiphosphate) (GDP-
-S) did not significantly
affect the DSI-evoked fast excitatory postsynaptic potential (EPSP) but
decreased the amplitude of the slow component more than 50%. Injection
of the GTP analogues guanosine 5'-O-(3-thiotriphosphate)
(GTP-
-S) and 5'-guanylyl-imidodiphosphate, to prolong
G-protein activation, had mixed effects on the fast component but
increased the amplitude and duration of the slow component of the
DSI-evoked response and, with repeated DSI stimulation, led to a
persistent depolarization. These results indicate that the fast
component of the biphasic synaptic potential evoked by a serotonergic
CPG neuron onto premotor interneurons is mediated by ionotropic
receptors (5-HT-gated ion channels), whereas the slow component is
mediated by G-protein-coupled receptors. A similar synaptic activation
of metabotropic receptors might also be found within the CPG itself,
where it could exert a direct influence onto motor pattern generation.
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