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Neurobiology of Disease Nov 2021Group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, in the spinal cord are implicated in nociceptive transmission and plasticity through G...
Group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, in the spinal cord are implicated in nociceptive transmission and plasticity through G protein-mediated second messenger cascades leading to the activation of various protein kinases such as extracellular signal-regulated kinase (ERK). In this study, we demonstrated that cytohesin-2, a guanine nucleotide exchange factor for ADP ribosylation factors (Arfs), is abundantly expressed in subsets of excitatory interneurons and projection neurons in the superficial dorsal horn. Cytohesin-2 is enriched in the perisynapse on the postsynaptic membrane of dorsal horn neurons and forms a protein complex with mGluR5 in the spinal cord. Central nervous system-specific cytohesin-2 conditional knockout mice exhibited reduced mechanical allodynia in inflammatory and neuropathic pain models. Pharmacological blockade of cytohesin catalytic activity with SecinH3 similarly reduced mechanical allodynia and inhibited the spinal activation of Arf6, but not Arf1, in both pain models. Furthermore, cytohesin-2 conditional knockout mice exhibited reduced mechanical allodynia and ERK1/2 activation following the pharmacological activation of spinal mGluR1/5 with 3,5-dihydroxylphenylglycine (DHPG). The present study suggests that cytothesin-2 is functionally associated with mGluR5 during the development of mechanical allodynia through the activation of Arf6 in spinal dorsal horn neurons.
Topics: ADP-Ribosylation Factor 1; ADP-Ribosylation Factor 6; Animals; GTPase-Activating Proteins; Hyperalgesia; Inflammation; MAP Kinase Signaling System; Methoxyhydroxyphenylglycol; Mice; Mice, Knockout; Neuralgia; Post-Synaptic Density; Posterior Horn Cells; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Spinal Cord; Spinal Cord Dorsal Horn; Triazoles
PubMed: 34390832
DOI: 10.1016/j.nbd.2021.105466 -
Clinical Autonomic Research : Official... Jun 2021Ampreloxetine is a novel, selective, long-acting norepinephrine reuptake (NET) inhibitor being investigated as a once-daily oral treatment for symptomatic neurogenic...
PURPOSE
Ampreloxetine is a novel, selective, long-acting norepinephrine reuptake (NET) inhibitor being investigated as a once-daily oral treatment for symptomatic neurogenic orthostatic hypotension (nOH) in patients with autonomic synucleinopathies. The purpose of this study was to characterize the pharmacokinetic and pharmacodynamic profiles of ampreloxetine in this target population.
METHODS
Patients with nOH were enrolled in a multicenter, phase II clinical trial of ampreloxetine (NCT02705755). They received escalating doses over 5 days in the clinical research unit, followed by 20 weeks of open-label treatment and then a 4-week withdrawal. As neurochemical biomarkers of NET inhibition, we assayed plasma concentrations of norepinephrine (NE) and its main intraneuronal metabolite 3,4-dihydroxyphenylglycol (DHPG) pre- and post-ampreloxetine.
RESULTS
Thirty-four patients with nOH were enrolled. Plasma ampreloxetine concentrations increased with repeated escalating doses, with peak concentrations observed 6-9 h post-drug administration. The median ampreloxetine dose in the 20-week treatment phase was 10 mg once daily. Plasma ampreloxetine concentrations reached steady state by 2 weeks, with stable plasma levels over 24 h. No influence of age or renal function on ampreloxetine plasma concentrations was observed. On treatment, compared to baseline, plasma NE significantly increased by 71% (p < 0.005), plasma DHPG significantly declined by 22% (p < 0.05), and the NE:DHPG ratio significantly increased (p < 0.001).
CONCLUSIONS
Persistent elevation of plasma NE levels accompanied by reduced DHPG levels after ampreloxetine suggests reduced neuronal reuptake and metabolism of NE in postganglionic efferent sympathetic neurons. The findings are consistent with long-lasting NET inhibition, which may increase vasoconstrictor tone, supporting once-daily ampreloxetine dosing in patients with nOH.
Topics: Autonomic Nervous System; Humans; Hypotension, Orthostatic; Methoxyhydroxyphenylglycol; Norepinephrine
PubMed: 33782836
DOI: 10.1007/s10286-021-00800-x -
Molecular Autism Oct 2020Mutations in TSC2 are the most common cause of tuberous sclerosis (TSC), a disorder with a high incidence of autism and intellectual disability. TSC2 regulates mRNA...
BACKGROUND
Mutations in TSC2 are the most common cause of tuberous sclerosis (TSC), a disorder with a high incidence of autism and intellectual disability. TSC2 regulates mRNA translation required for group 1 metabotropic glutamate receptor-dependent synaptic long-term depression (mGluR-LTD) and behavior, but the identity of mRNAs responsive to mGluR-LTD signaling is largely unknown.
METHODS
We utilized Tsc2 mice as a mouse model of TSC and prepared hippocampal slices from these animals. We induced mGluR-LTD synaptic plasticity in slices and processed the samples for RNA-seq and ribosome profiling to identify differentially expressed genes in Tsc2 and following mGluR-LTD synaptic plasticity.
RESULTS
Ribosome profiling reveals that in Tsc2 mouse hippocampal slices, the expression of several mRNAs was dysregulated: terminal oligopyrimidine (TOP)-containing mRNAs decreased, while FMRP-binding targets increased. Remarkably, we observed the opposite changes of FMRP binding targets in Fmr1 hippocampi. In wild-type hippocampus, induction of mGluR-LTD caused rapid changes in the steady-state levels of hundreds of mRNAs, many of which are FMRP targets. Moreover, mGluR-LTD failed to promote phosphorylation of eukaryotic elongation factor 2 (eEF2) in TSC mice, and chemically mimicking phospho-eEF2 with low cycloheximide enhances mGluR-LTD in TSC mice.
CONCLUSION
These results suggest a molecular basis for bidirectional regulation of synaptic plasticity and behavior by TSC2 and FMRP. Our study also suggests that altered mGluR-regulated translation elongation contributes to impaired synaptic plasticity in Tsc2 mice.
Topics: Animals; Fragile X Mental Retardation Protein; Fragile X Syndrome; Hippocampus; Methoxyhydroxyphenylglycol; Mice, Inbred C57BL; Neuronal Plasticity; Peptide Elongation Factor 2; Protein Binding; Protein Biosynthesis; RNA 5' Terminal Oligopyrimidine Sequence; Receptors, Metabotropic Glutamate; Ribosomes; Signal Transduction; Tuberous Sclerosis Complex 2 Protein
PubMed: 33054857
DOI: 10.1186/s13229-020-00384-9 -
Cells Feb 2020The cation channel subunit TRPC1 is strongly expressed in central neurons including neurons in the CA1 region of the hippocampus where it forms complexes with TRPC4 and...
The cation channel subunit TRPC1 is strongly expressed in central neurons including neurons in the CA1 region of the hippocampus where it forms complexes with TRPC4 and TRPC5. To investigate the functional role of TRPC1 in these neurons and in channel function, we compared current responses to group I metabotropic glutamate receptor (mGluR I) activation and looked for major differences in dendritic morphology in neurons from and mice. mGluR I stimulation resulted in the activation of a voltage-dependent nonselective cation current in both genotypes. Deletion of TRPC1 resulted in a modification of the shape of the current-voltage relationship, leading to an inward current increase. In current clamp recordings, the percentage of neurons that responded to depolarization in the presence of an mGluR I agonist with a plateau potential was increased in mice. There was also a small increase in the minor population of CA1 neurons that have more than one apical dendrite in mice. We conclude that TRPC1 has an inhibitory effect on receptor-operated nonselective cation channels in hippocampal CA1 neurons probably as a result of heterotetramer formation with other TRPC isoforms, and that TRPC1 deletion has only minor effects on dendritic morphology.
Topics: Animals; CA1 Region, Hippocampal; Male; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; Mice, Knockout; Neurons; Receptors, Metabotropic Glutamate; TRPC Cation Channels
PubMed: 32085504
DOI: 10.3390/cells9020459 -
CNS Neuroscience & Therapeutics Feb 2024To investigate the role of mGluR1α in cerebellar unipolar brush cells (UBC) in mediating vestibular compensation (VC), using mGluR1α agonist and antagonist to modulate...
AIMS
To investigate the role of mGluR1α in cerebellar unipolar brush cells (UBC) in mediating vestibular compensation (VC), using mGluR1α agonist and antagonist to modulate ON UBC neurons, and explore the mGluR1/IP3/extracellular signal-regulated kinase (ERK) signaling pathway.
METHODS
First, AAV virus that knockdown ON UBC (mGluR1α) were injected into cerebellar UBC by stereotactic, and verified by immunofluorescence and western blot. The effect on VC was evaluated after unilateral labyrinthectomy (UL). Second, saline, (RS)-3,5-dihydroxyphenylglycine (DHPG), and LY367385 were injected into tubes implanted in rats at different time points after UL separately. The effect on ON UBC neuron activity was evaluated by immunofluorescence. Then, Phosphoinositide (PI) and p-ERK1/2 levels of mGluR1α were analyzed by ELISA after UL. The protein levels of p-ERK and total ERK were verified by western blot. In addition, the effect of mGluR1α activation or inhibition on VC-related behavior was observed.
RESULTS
mGluR1α knockdown induced VC phenotypes. DHPG increased ON UBC activity, while LY367385 reduced ON UBC activity. DHPG group showed an increase in PI and p-ERK1/2 levels, while LY367385 group showed a decrease in PI and p-ERK1/2 levels in cerebellar UBC of rats. The western blot results of p-ERK and total ERK confirm and support the observations. DHPG alleviated VC-related behavior phenotypes, while LY367385 exacerbated vestibular decompensation-like behavior induced by UL.
CONCLUSION
mGluR1α activity in cerebellar ON UBC is crucial for mediating VC through the mGluR1/IP3/ERK signaling pathway, which affects ON UBC neuron activity and contributes to the pathogenesis of VC.
Topics: Rats; Animals; Extracellular Signal-Regulated MAP Kinases; Signal Transduction; Benzoates; Glycine; Methoxyhydroxyphenylglycol; Receptors, Metabotropic Glutamate
PubMed: 37622292
DOI: 10.1111/cns.14419 -
BMC Research Notes Apr 2018Norepinephrine (NE), a sympathetic neurotransmitter, is often measured in plasma as an index of sympathetic activity. To better understand NE dynamics, it is important...
OBJECTIVE
Norepinephrine (NE), a sympathetic neurotransmitter, is often measured in plasma as an index of sympathetic activity. To better understand NE dynamics, it is important to measure its principal metabolite, 3,4-dihydroxyphenylglycol (DHPG), concurrently. Our aim was to present a method, developed in the course of a translational research study, to measure NE and DHPG in human plasma using high performance liquid chromatography with electrochemical detection (HPLC-ED).
RESULTS
After pre-purifying plasma samples by alumina extraction, we used HPLC-ED to separate and quantify NE and DHPG. In order to remove uric acid, which co-eluted with DHPG, a sodium bicarbonate wash was added to the alumina extraction procedure, and we oxidized the column eluates followed by reduction because catechols are reversibly oxidized whereas uric acid is irreversibly oxidized. Average recoveries of plasma NE and DHPG were 35.3 ± 1.0% and 16.3 ± 1.1%, respectively, and there was no detectable uric acid. Our estimated detection limits for NE and DHPG were approximately 85 pg/mL (0.5 pmol/mL) and 165 pg/mL (0.9 pmol/mL), respectively. The measurement of NE and DHPG in human plasma has wide applicability; thus, we describe a method to quantify plasma NE and DHPG in a laboratory setting as a useful tool for translational and clinical research.
Topics: Chromatography, High Pressure Liquid; Electrochemical Techniques; Heart Failure; Humans; Methoxyhydroxyphenylglycol; Norepinephrine; Sympathetic Nervous System; Translational Research, Biomedical
PubMed: 29673396
DOI: 10.1186/s13104-018-3352-3 -
Cell Reports Nov 2021A core network of widely expressed proteins within the glutamatergic post-synapse mediates activity-dependent synaptic plasticity throughout the brain, but the specific...
A core network of widely expressed proteins within the glutamatergic post-synapse mediates activity-dependent synaptic plasticity throughout the brain, but the specific proteomic composition of synapses differs between brain regions. Here, we address the question, how does proteomic composition affect activity-dependent protein-protein interaction networks (PINs) downstream of synaptic activity? Using quantitative multiplex co-immunoprecipitation, we compare the PIN response of in vivo or ex vivo neurons derived from different brain regions to activation by different agonists or different forms of eyeblink conditioning. We report that PINs discriminate between incoming stimuli using differential kinetics of overlapping and non-overlapping PIN parameters. Further, these "molecular logic rules" differ by brain region. We conclude that although the PIN of the glutamatergic post-synapse is expressed widely throughout the brain, its activity-dependent dynamics show remarkable stimulus-specific and brain-region-specific diversity. This diversity may help explain the challenges in developing molecule-specific drug therapies for neurological disorders.
Topics: Animals; Blinking; Brain; Conditioning, Eyelid; Excitatory Amino Acid Agonists; Female; Male; Methoxyhydroxyphenylglycol; Mice; N-Methylaspartate; Neuronal Plasticity; Protein Interaction Maps; Proteome; Synapses
PubMed: 34852231
DOI: 10.1016/j.celrep.2021.110076 -
Neuropharmacology Jan 2018mGlu5 receptors are involved in mechanisms of activity-dependent synaptic plasticity, and are targeted by drugs developed for the treatment of CNS disorders. We report...
mGlu5 receptors are involved in mechanisms of activity-dependent synaptic plasticity, and are targeted by drugs developed for the treatment of CNS disorders. We report that mGlu3 receptors, which are traditionally linked to the control of neurotransmitter release, support mGlu5 receptor signaling in neurons and largely contribute to the robust mGlu5 receptor-mediated polyphosphoinositide hydrolysis in the early postnatal life. In cortical pyramidal neurons, mGlu3 receptor activation potentiated mGlu5 receptor-mediated somatic Ca mobilization, and mGlu3 receptor-mediated long-term depression in the prefrontal cortex required the endogenous activation of mGlu5 receptors. The interaction between mGlu3 and mGlu5 receptors was also relevant to mechanisms of neuronal toxicity, with mGlu3 receptors shaping the influence of mGlu5 receptors on excitotoxic neuronal death. These findings shed new light into the complex role played by mGlu receptors in physiology and pathology, and suggest reconsideration of some of the current dogmas in the mGlu receptor field.
Topics: Amino Acids; Animals; Animals, Newborn; Astrocytes; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Central Nervous System; Embryo, Mammalian; Excitatory Amino Acid Agents; Female; Gene Expression Regulation, Developmental; Humans; Hydrolysis; Long-Term Potentiation; Male; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred C57BL; N-Methylaspartate; Neurons; Phosphatidylinositol Phosphates; Rats; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate
PubMed: 29079293
DOI: 10.1016/j.neuropharm.2017.10.026 -
Journal of Psychopharmacology (Oxford,... Oct 2014Suppressing anxiety and fear memory relies on bidirectional projections between the medial prefrontal cortex and the amygdala. Positive allosteric modulators of mGluR5...
Suppressing anxiety and fear memory relies on bidirectional projections between the medial prefrontal cortex and the amygdala. Positive allosteric modulators of mGluR5 improve cognition in animal models of schizophrenia and retrieval of newly formed associations such as extinction of fear-conditioned behaviour. The increase in neuronal network activities of the medial prefrontal cortex is influenced by both mGluR1 and mGluR5; however, it is not well understood how they modulate network activities and downstream information processing. To map mGluR5-mediated network activity in relation to its emergence as a viable cognitive enhancer, we tested group I mGluR compounds on medial prefrontal cortex network activity via multi-electrode array neuronal spiking and whole-cell patch clamp recordings. Results indicate that mGluR5 activation promotes feed-forward inhibition that depends on recruitment of neuronal activity by carbachol-evoked up states. The rate of neuronal spiking activity under the influence of carbachol was reduced by the mGluR5 positive allosteric modulator, N-(1,3-Diphenyl-1H-pyrazolo-5-yl)-4-nitrobenzamide (VU-29), and enhanced by the mGluR5 negative allosteric modulator, 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine hydrochloride (MTEP). Spontaneous inhibitory post-synaptic currents were increased upon application of carbachol and in combination with VU-29. These results emphasize a bias towards tonic mGluR5-mediated inhibition that might serve as a signal-to-noise enhancer of sensory inputs projected from associated limbic areas onto the medial prefrontal cortex neuronal microcircuit.
Topics: Action Potentials; Allosteric Regulation; Animals; Benzamides; Carbachol; Drug Synergism; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Inhibitory Postsynaptic Potentials; Male; Methoxyhydroxyphenylglycol; Neural Pathways; Prefrontal Cortex; Pyrazoles; Pyridines; Rats; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Thiazoles
PubMed: 25031220
DOI: 10.1177/0269881114542856 -
The Journal of Physiology Jan 2017The midbrain periaqueductal grey (PAG) forms part of an endogenous analgesic system which is tightly regulated by the neurotransmitter GABA. The role of endocannabinoids...
KEY POINTS
The midbrain periaqueductal grey (PAG) forms part of an endogenous analgesic system which is tightly regulated by the neurotransmitter GABA. The role of endocannabinoids in regulating GABAergic control of this system was examined in rat PAG slices. Under basal conditions GABAergic neurotransmission onto PAG output neurons was multivesicular. Activation of the endocannabinoid system reduced GABAergic inhibition by reducing the probability of release and by shifting release to a univesicular mode. Blockade of endocannabinoid system unmasked a tonic control over the probability and mode of GABA release. These findings provides a mechanistic foundation for the control of the PAG analgesic system by disinhibition.
ABSTRACT
The midbrain periaqueductal grey (PAG) has a crucial role in coordinating endogenous analgesic responses to physiological and psychological stressors. Endocannabinoids are thought to mediate a form of stress-induced analgesia within the PAG by relieving GABAergic inhibition of output neurons, a process known as disinhibition. This disinhibition is thought to be achieved by a presynaptic reduction in GABA release probability. We examined whether other mechanisms have a role in endocannabinoid modulation of GABAergic synaptic transmission within the rat PAG. The group I mGluR agonist DHPG ((R,S)-3,5-dihydroxyphenylglycine) inhibited evoked IPSCs and increased their paired pulse ratio in normal external Ca , and when release probability was reduced by lowering Ca . However, the effect of DHPG on the coefficient of variation and kinetics of evoked IPSCs differed between normal and low Ca . Lowering external Ca had a similar effect on evoked IPSCs to that observed for DHPG in normal external Ca . The low affinity GABA receptor antagonist TPMPA ((1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid) inhibited evoked IPSCs to a greater extent in low than in normal Ca . Together these findings indicate that the normal mode of GABA release is multivesicular within the PAG, and that DHPG and lowering external Ca switch this to a univesicular mode. The effects of DHPG were mediated by mGlu5 receptor engagement of the retrograde endocannabinoid system. Blockade of endocannabinoid breakdown produced a similar shift in the mode of release. We conclude that endocannabinoids control both the mode and the probability of GABA release within the PAG.
Topics: Animals; Calcium; Endocannabinoids; Female; GABA Antagonists; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Male; Methoxyhydroxyphenylglycol; Periaqueductal Gray; Phosphinic Acids; Piperidines; Pyrazoles; Pyridines; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Synapses; gamma-Aminobutyric Acid
PubMed: 27461371
DOI: 10.1113/JP272292