Identified serotonergic neurons in the Tritonia swim CPG activate both ionotropic and metabotropic receptors.
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-beta-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-gamma-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.
Clemens
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Department of Biology, Center for Neural Communication and Computation, Georgia State University, Atlanta, Georgia 30303, USA. bioscl@panther.gsu.edu
Katz
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PS
D000818:Animals; D002490:Central Nervous System / Q000166:cytology / Q000502:physiology*; D004558:Electric Stimulation; D004924:Escape Reaction / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000008:administration & dosage; D006153:Guanosine Diphosphate / Q000008:administration & dosage / Q000031:analogs & derivatives*; D006165:Guanylyl Imidodiphosphate / Q000008:administration & dosage; D066298:In Vitro Techniques; D007323:Instinct; D007395:Interneurons / Q000166:cytology / Q000378:metabolism*; D007478:Iontophoresis; D008564:Membrane Potentials / Q000187:drug effects; D008974:Mollusca; D017470:Receptors, Glutamate / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D013550:Swimming / Q000502:physiology; D013873:Thionucleotides / Q000008:administration & dosage
D017470:Receptors, Glutamate; D018094:Receptors, Metabotropic Glutamate; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D012701:Serotonin; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D019204:GTP-Binding Proteins