Activation of pharmacologically distinct metabotropic glutamate receptors depresses reticulospinal-evoked monosynaptic EPSPs in the lamprey spinal cord

1996 ◽  
Vol 76 (6) ◽  
pp. 3834-3841 ◽  
Author(s):  
P. Krieger ◽  
A. el Manira ◽  
S. Grillner
Keyword(s):  
Spinal Cord ◽  
Synaptic Transmission ◽  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Input Resistance ◽  
Spinal Neurons ◽  
Metabotropic Glutamate ◽  
Apparent Change ◽  
Glutamatergic Synaptic Transmission ◽  
Presynaptic Mechanisms

1. Different metabotropic glutamate receptors (mGluRs) can modulate synaptic transmission in different regions in the CNS, but their roles at individual synaptic connections have not been detailed. We used paired intracellular recordings from reticulospinal axons and their postsynaptic target neurons in the lamprey spinal cord to investigate the effects of mGluR activation on glutamatergic synaptic transmission. 2. The mGluR agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxyylic acid [(1S,3R)-ACPD] and L(+)-2-amino-4-phosphonobutyric acid (L-AP4) both reduced the amplitude of monosynaptic excitatory postsynaptic potentials (EPSPs) elicited by stimulation of single reticulospinal axons. The depression of monosynaptic unitary EPSPs occurred without any apparent change in the input resistance of postsynaptic neurons. Furthermore, the mGluR agonists did not affect the amplitude of (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced depolarizations. Taken together, these results thus suggest that (1S,3R)-ACPD and L-AP4 depress reticulospinal synaptic transmission via presynaptic mechanisms. 3. (2S,1'S,2'S)-2-(carboxycyclopropyl) glycine (L-CCG-I), which selectively activates group II mGluRs, also reduced the amplitude of reticulospinal-evoked EPSPs without any apparent change in the input resistance or membrane potential of the postsynaptic neuron. 4. The mGluR antagonist alpha-methyl-L-AP4 blocked the depression induced by L-AP4 but not that induced by (1S,3R)-ACPD. Furthermore, the effects of coapplication of (1S,3R)-ACPD and L-AP4 were additive, suggesting that they inhibit synaptic transmission by an action on pharmacologically distinct mGluRs. 5. These results provide evidence for the colocalization of at least two different subtypes of presynaptic mGluRs on a single reticulospinal axon in the lamprey. These presynaptic mGluRs could serve as glutamatergic autoreceptors limiting the extent of reticulospinal-mediated excitation of spinal neurons.

scholarly journals Ethanol tachyphylaxis in spinal cord motorneurons: role of metabotropic glutamate receptors

2003 ◽  
Vol 138 (8) ◽  
pp. 1417-1424 ◽  
Author(s):  
Hui-Fang Li ◽  
Meng-Ya Wang ◽  
Jessica Knape ◽  
Joan J Kendig
Keyword(s):  
Spinal Cord ◽  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Metabotropic Glutamate

Activation of metabotropic glutamate receptors induces long-term depression of GABAergic inhibition in hippocampus

1993 ◽  
Vol 69 (3) ◽  
pp. 1000-1004 ◽  
Author(s):  
Y. B. Liu ◽  
J. F. Disterhoft ◽  
N. T. Slater
Keyword(s):  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Hippocampal Slices ◽  
Input Resistance ◽  
Nmda Receptor Antagonist ◽  
Metabotropic Glutamate ◽  
Epileptiform Discharges ◽  
Bath Application

1. The long-term enhancement of synaptic excitability in CA1 hippocampal pyramidal neurons produced by activation of metabotropic glutamate receptors (mGluRs) was studied in rabbit hippocampal slices in vitro. 2. Bath application of the mGluR agonist (1S,3R)-1-aminocyclopentane-1,3- dicarboxylic acid (1S,3R-ACPD) (5-20 microM) for 20 min produced a reversible depolarization of membrane potentiatil, blockade of spike accommodation, and increase in input resistance of CA1 neurons. However, a long-lasting increase in synaptic excitability was observed: single stimuli applied to the Schaffer collateral commisural fiber pathway evoked epileptiform discharges in the presence of 1S,3R-ACPD and after the washout of 1S,3R-ACPD, persistent paroxysmal depolarization shifts (PDSs) were evoked by afferent stimulation. A long-lasting enhancement of synaptic excitability was also observed in the presence of the NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), which blocked the stimulation-evoked PDS and associated afterdischarges. 3. When biphasic, monosynaptically evoked inhibitory post-synaptic potentials (IPSPs) were recorded in the presence of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10–15 microM) and D-AP5 (20 microM), the bath application of 1S,3R-ACPD produced a significant reduction (approximately 50%) of both components of the IPSP, which persisted after the washout of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for Functional Metabotropic Glutamate Receptors in the Dorsal Cochlear Nucleus

1997 ◽  
Vol 77 (4) ◽  
pp. 1889-1905 ◽  
Author(s):  
Scott C. Molitor ◽  
Paul B. Manis
Keyword(s):  
Synaptic Transmission ◽  
Dicarboxylic Acid ◽  
Glutamate Receptors ◽  
Cochlear Nucleus ◽  
Metabotropic Glutamate Receptors ◽  
Dorsal Cochlear Nucleus ◽  
Evoked Responses ◽  
Field Potentials ◽  
Metabotropic Glutamate ◽  
Field Response

Molitor, Scott C. and Paul B. Manis. Evidence for functional metabotropic glutamate receptors in the dorsal cochlear nucleus. J. Neurophysiol. 77: 1889–1905, 1997. The parallel fibers (PFs) of the dorsal cochlear nucleus (DCN) molecular layer use glutamate as a neurotransmitter. Although metabotropic glutamate receptors (mGluRs) have been identified on cells postsynaptic to the PFs, little is known about the effects of mGluR activation in PF synaptic transmission in the DCN. To investigate these effects, PF-evoked field potentials were recorded from the DCN in guinea pig brain stem slice preparations. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated components of the field response were reversibly depressed by bathing the slice in the mGluR agonists (±)-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD) or (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD]. A similar depression was produced by the mGluR1/5 agonist (RS)-3,5-dihydroxyphenylglycine, but not by the mGluR2/3 agonist (2S,1′S,2′S)-2-(carboxycyclopropyl)glycine or by the mGluR4/6/7/8 agonist l(+)-2-amino-4-phosphonobutyric acid. In addition to the AMPA component, an N-methyl-d-aspartate (NMDA) receptor-dependent component of the field potentials could be identified when the slices were bathed in a low magnesium solution. Under these conditions, the ACPD-induced depression of the AMPA component did not completely recover, whereas the depression of the NMDA component usually recovered and potentiated in some slices. Intracellular recordings of PF-evoked responses were obtained to ascertain which neuronal populations were affected by mGluR activation. Activation of mGluRs produced a reversible depression of PF-evoked responses in cartwheel cells that was not accompanied by any changes in paired-pulse facilitation. The PF-evoked responses recorded from pyramidal cells were unaffected by mGluR activation. Both cell types exhibited a reversible depolarization during (1S,3R)-ACPD application. Subsequent experiments explored the involvement of protein kinases in mediating the effects of mGluRs. The protein kinase C (PKC) activator phorbol-12,13-diacetate partially inhibited the mGluR-mediated depression of the field response;however, the PKC inhibitor 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide or the protein kinaseA inhibitor N-[2-(( p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide had little effect on the actions of (1S,3R)-ACPD. These results demonstrate that functional mGluRs are present at PF synapses and are capable of modulating PF synaptic transmission in the DCN.

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