Group I mGluRs increase locomotor network excitability in Xenopus tadpoles via presynaptic inhibition of glycinergic neurotransmission.
The group I metabotropic glutamate receptor agonist (S)-3,5-dihyroxyphenylglycine (DHPG) increases the frequency of rhythmic swimming activity in Xenopus tadpoles. This study explores the possibility that group I receptor modulation occurs in part via depression of inhibitory synaptic transmission. Applications of the glycine receptor antagonist strychnine occluded the effects of DHPG, providing preliminary evidence that group I receptors affect motor network output by reducing glycinergic transmission. This evidence was supported further by intracellular and whole-cell patch-clamp recordings from presumed motorneurons. DHPG applications produced two prominent effects: (i) during swimming activity, glycinergic mid-cycle IPSPs were reduced in amplitude; and (ii) during quiescent periods, the frequency of spontaneous miniature IPSPs was also reduced. No change in membrane potential or input resistance following group I receptor activation was detected. The reduction in fast synaptic inhibition provides a plausible explanation for the increased excitability of the locomotor network, although other contributory mechanisms activated in parallel by group I receptors cannot be discounted. Aspects of this work have been published previously in abstract form [R. J. Chapman & K. T. Sillar (2003) SFN Abstracts 277.8].
Chapman
Rebecca J
RJ
School of Biology, Bute Medical Buildings, University of St Andrews, St Andrews, Fife, UK. r.chapman@leeds.ac.uk
Issberner
Jonathan P
JP
Sillar
Keith T
KT
D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005998:Glycine / Q000378:metabolism*; D018684:Glycine Agents / Q000494:pharmacology; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D007814:Larva / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D008124:Locomotion / Q000187:drug effects / Q000502:physiology; D009415:Nerve Net / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D013116:Spinal Cord / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D013331:Strychnine / Q000494:pharmacology; D013550:Swimming / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D014982:Xenopus laevis
D018684:Glycine Agents; D018009:Receptors, Glycine; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D013331:Strychnine; D005998:Glycine