Potentiation of excitatory postsynaptic potentials by a metabotropic glutamate receptor agonist (1S,3R-ACPD) in frog spinal motoneurons.
We conducted intracellular recordings of lumbar motoneurons in the arterially-perfused frog spinal cord and investigated the effects of a metabotropic glutamate receptor agonist, (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), on excitatory postsynaptic potentials evoked by stimulation of the descending lateral column fibers (LC-EPSPs). In the absence of Mg2+, ACPD reversibly potentiated the amplitude of monosynaptic LC-EPSPs by more than 15% in 15 of 19 cells with 5 microM ACPD and in 7 of 12 cells with 0.5 microM ACPD. The EPSP amplitudes with 5 and 0.5 microM ACPD were 142 +/- 10% (mean +/- S.E.M., n = 19) and 130 +/- 13% (n = 12) of the controls. The potentiation was seen without a decrease in the input conductance. Glutamate-induced depolarizations in the absence and the presence of 0.5 microM ACPD were not significantly different in cells perfused with the low Ca(2+)-high Mg2+ solution which eliminated chemical transmission. Paired pulse facilitation of LC-EPSPs was reversibly decreased in association with the potentiation. ACPD-induced potentiation of monosynaptic LC-EPSPs was seen in 5 of 6 cells in the presence of D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), an NMDA receptor antagonist. ACPD occasionally activated polysynaptic components of LC-EPSPs which were mediated mainly via NMDA receptors. On the other hand, ACPD-induced potentiation of EPSPs was inhibited by extracellular Mg2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Gotani
H
H
Department of Physiology, Osaka City University Medical School, Japan.
Kuno
M
M
Nakamura
F
F
Matsuura
S
S
D000818:Animals; D003515:Cycloleucine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004558:Electric Stimulation; D005246:Feedback / Q000502:physiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects*; D009498:Neurotoxins / Q000494:pharmacology*; D011892:Rana catesbeiana; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists*; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D009498:Neurotoxins; D018094:Receptors, Metabotropic Glutamate; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D008274:Magnesium