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di Biase L, Pecoraro PM, Carbone SP, Caminiti ML, Di Lazzaro V. Levodopa-Induced Dyskinesias in Parkinson's Disease: An Overview on Pathophysiology, Clinical Manifestations, Therapy Management Strategies and Future Directions. J Clin Med 2023; 12:4427. [PMID: 37445461 DOI: 10.3390/jcm12134427] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2023] [Revised: 06/18/2023] [Accepted: 06/27/2023] [Indexed: 07/15/2023] Open
Abstract
Since its first introduction, levodopa has become the cornerstone for the treatment of Parkinson's disease and remains the leading therapeutic choice for motor control therapy so far. Unfortunately, the subsequent appearance of abnormal involuntary movements, known as dyskinesias, is a frequent drawback. Despite the deep knowledge of this complication, in terms of clinical phenomenology and the temporal relationship during a levodopa regimen, less is clear about the pathophysiological mechanisms underpinning it. As the disease progresses, specific oscillatory activities of both motor cortical and basal ganglia neurons and variation in levodopa metabolism, in terms of the dopamine receptor stimulation pattern and turnover rate, underlie dyskinesia onset. This review aims to provide a global overview on levodopa-induced dyskinesias, focusing on pathophysiology, clinical manifestations, therapy management strategies and future directions.
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Affiliation(s)
- Lazzaro di Biase
- Fondazione Policlinico Universitario Campus Bio-Medico, Via Alvaro del Portillo, 200, 00128 Roma, Italy
- Brain Innovations Lab, Università Campus Bio-Medico di Roma, Via Álvaro del Portillo, 21, 00128 Rome, Italy
| | - Pasquale Maria Pecoraro
- Fondazione Policlinico Universitario Campus Bio-Medico, Via Alvaro del Portillo, 200, 00128 Roma, Italy
- Unit of Neurology, Neurophysiology, Neurobiology and Psichiatry, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21, 00128 Roma, Italy
| | - Simona Paola Carbone
- Fondazione Policlinico Universitario Campus Bio-Medico, Via Alvaro del Portillo, 200, 00128 Roma, Italy
- Unit of Neurology, Neurophysiology, Neurobiology and Psichiatry, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21, 00128 Roma, Italy
| | - Maria Letizia Caminiti
- Fondazione Policlinico Universitario Campus Bio-Medico, Via Alvaro del Portillo, 200, 00128 Roma, Italy
- Unit of Neurology, Neurophysiology, Neurobiology and Psichiatry, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21, 00128 Roma, Italy
| | - Vincenzo Di Lazzaro
- Fondazione Policlinico Universitario Campus Bio-Medico, Via Alvaro del Portillo, 200, 00128 Roma, Italy
- Unit of Neurology, Neurophysiology, Neurobiology and Psichiatry, Department of Medicine and Surgery, Università Campus Bio-Medico di Roma, Via Alvaro del Portillo, 21, 00128 Roma, Italy
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Rescue of striatal long-term depression by chronic mGlu5 receptor negative allosteric modulation in distinct dystonia models. Neuropharmacology 2021; 192:108608. [PMID: 33991565 DOI: 10.1016/j.neuropharm.2021.108608] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 04/28/2021] [Accepted: 05/06/2021] [Indexed: 12/16/2022]
Abstract
An impairment of long-term synaptic plasticity is considered as a peculiar endophenotype of distinct forms of dystonia, a common, disabling movement disorder. Among the few therapeutic options, broad-spectrum antimuscarinic drugs are utilized, aimed at counteracting abnormal striatal acetylcholine-mediated transmission, which plays a crucial role in dystonia pathophysiology. We previously demonstrated a complete loss of long-term synaptic depression (LTD) at corticostriatal synapses in rodent models of two distinct forms of isolated dystonia, resulting from mutations in the TOR1A (DYT1), and GNAL (DYT25) genes. In addition to anticholinergic agents, the aberrant excitability of striatal cholinergic cells can be modulated by group I metabotropic glutamate receptor subtypes (mGlu1 and 5). Here, we tested the efficacy of the negative allosteric modulator (NAM) of metabotropic glutamate 5 (mGlu) receptor, dipraglurant (ADX48621) on striatal LTD. We show that, whereas acute treatment failed to rescue LTD, chronic dipraglurant rescued this form of synaptic plasticity both in DYT1 mice and GNAL rats. Our analysis of the pharmacokinetic profile of dipraglurant revealed a relatively short half-life, which led us to uncover a peculiar time-course of recovery based on the timing from last dipraglurant injection. Indeed, striatal spiny projection neurons (SPNs) recorded within 2 h from last administration showed full expression of synaptic plasticity, whilst the extent of recovery progressively diminished when SPNs were recorded 4-6 h after treatment. Our findings suggest that distinct dystonia genes may share common signaling pathway dysfunction. More importantly, they indicate that dipraglurant might be a potential novel therapeutic agent for this disabling disorder.
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He C, Zhao X, Li H, Wang F, Zhang J, Wang Y, Han Y, Yuan C, Niu Q. Regulation of mGluR1 on the Expression of PKC and NMDAR in Aluminum-Exposed PC12 Cells. Neurotox Res 2021; 39:634-644. [PMID: 33464538 DOI: 10.1007/s12640-020-00319-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 11/16/2020] [Accepted: 11/30/2020] [Indexed: 12/12/2022]
Abstract
Aluminum demonstrates clear neurotoxicity and can cause Alzheimer's disease (AD)-like symptoms, including cognitive impairment. One toxic effect of aluminum is a decrease in synaptic plasticity, but the specific mechanism remains unclear. In this study, PC12 cells were treated with Al(mal)3 to construct a toxic cell model. (S)-3,5-Dihydroxyphenylglycine (DHPG), α-methyl-4-carboxyphenylglycine (MCPG), and mGluR1-siRNA were used to interfere with the expression of metabotropic glutamate receptor subtype 1 (mGluR1). Polymerase chain reaction and western blotting were used to investigate the expression of mGluR1, protein kinase C (PKC), and N-methyl-D-aspartate receptor (NMDAR) subunits. ELISA was used to detect PKC enzyme activity. In PC12 cells, mRNA and protein expressions of PKC and NMDAR subunits were inhibited by Al(mal)3. Aluminum may further regulate the expression of NMDAR1 and NMDAR2B through mGluR1 to regulate PKC enzyme activity, thereby affecting learning and memory functions. Furthermore, the results implied that the mGluR1-PKC-NMDAR signaling pathway may predominately involve positive regulation. These findings provide new targets for studying the neurotoxic mechanism of aluminum.
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Affiliation(s)
- Chanting He
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China.,Key Lab of Environmental Hazard & Health of Shanxi Province, Shanxi Medical University, Taiyuan, 030001, Shanxi, China.,Key Lab of Cellular Physiology of Education Ministry, Shanxi Medical University, Taiyuan, 030001, Shanxi, China.,Department of Anatomy, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Xiaoyan Zhao
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Huan Li
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Fei Wang
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Jingsi Zhang
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Yanni Wang
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Yingchao Han
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Chunman Yuan
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China
| | - Qiao Niu
- Department of Occupational Health, School of Public Health, Shanxi Medical University, Taiyuan, 030001, Shanxi, China. .,Key Lab of Environmental Hazard & Health of Shanxi Province, Shanxi Medical University, Taiyuan, 030001, Shanxi, China. .,Key Lab of Cellular Physiology of Education Ministry, Shanxi Medical University, Taiyuan, 030001, Shanxi, China.
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Astrocyte Signaling Gates Long-Term Depression at Corticostriatal Synapses of the Direct Pathway. J Neurosci 2020; 40:5757-5768. [PMID: 32541069 DOI: 10.1523/jneurosci.2369-19.2020] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Revised: 05/04/2020] [Accepted: 05/05/2020] [Indexed: 12/19/2022] Open
Abstract
Despite extensive research into understanding synaptic mechanisms of striatal plasticity, the functional role played by astrocytes in this region remains to be fully elucidated. It was recently demonstrated that high-frequency stimulation (HFS) of cortical inputs induced long-term depression (LTD) mediated by adenosine A1 receptor (A1R) activation at corticostriatal synapses of the direct pathway [cortico-striatal projection neuron (dSPN)] in the dorsolateral striatum (DLS). Because astrocyte-derived adenosine has been shown to regulate synaptic transmission in several brain areas, we investigated whether this form of neuron-astrocyte signaling contributes to synaptic plasticity in the DLS of male and female mice. We found that cortical HFS increases calcium (Ca2+) levels in striatal astrocytes through activation of metabotropic glutamate receptor type 5 (mGluR5) signaling and that this astrocyte-mediated response is necessary for A1R-mediated LTD. Consistent with this, astrocyte activation with Gq designer receptors exclusively activated by designer drugs (DREADDs) induced A1R-mediated synaptic depression at cortico-dSPN synapses. Together, these results indicate that astrocytes are integral elements of striatal A1R-mediated LTD.SIGNIFICANCE STATEMENT Abnormal striatal circuit function is implicated in several disorders such as Parkinson's disease and Huntington's disease. Thus, there is a need to better understand the mechanisms supporting proper striatal activity. While extensive work has revealed the many important contributions from neurons in striatal function, far less is known about the role of astrocytes in this brain area. We show that long-term depression (LTD) at corticostriatal synapses of the direct pathway is not strictly a neuronal phenomenon; astrocytes respond to corticostriatal stimulation and this astrocyte response is necessary for LTD. This research adds to the accumulating evidence that astrocytes are active and integral players in synaptic communication, and that neuron-astrocyte interactions are key cellular processes involved in brain function.
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Mechanisms Underlying Long-Term Synaptic Zinc Plasticity at Mouse Dorsal Cochlear Nucleus Glutamatergic Synapses. J Neurosci 2020; 40:4981-4996. [PMID: 32434779 DOI: 10.1523/jneurosci.0175-20.2020] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 05/13/2020] [Accepted: 05/15/2020] [Indexed: 11/21/2022] Open
Abstract
In many brain areas, such as the neocortex, limbic structures, and auditory brainstem, synaptic zinc is released from presynaptic terminals to modulate neurotransmission. As such, synaptic zinc signaling modulates sensory processing and enhances acuity for discrimination of different sensory stimuli. Whereas sensory experience causes long-term changes in synaptic zinc signaling, the mechanisms underlying this long-term synaptic zinc plasticity remain unknown. To study these mechanisms in male and female mice, we used in vitro and in vivo models of zinc plasticity observed at the zinc-rich glutamatergic dorsal cochlear nucleus (DCN) parallel fiber synapses onto cartwheel cells. High-frequency stimulation of DCN parallel fiber synapses induced LTD of synaptic zinc signaling (Z-LTD), evidenced by reduced zinc-mediated inhibition of EPSCs. Low-frequency stimulation induced LTP of synaptic zinc signaling (Z-LTP), evidenced by enhanced zinc-mediated inhibition of EPSCs. Pharmacological manipulations of Group 1 metabotropic glutamate receptors (G1 mGluRs) demonstrated that G1 mGluR activation is necessary and sufficient for inducing Z-LTD and Z-LTP. Pharmacological manipulations of Ca2+ dynamics indicated that rises in postsynaptic Ca2+ are necessary and sufficient for Z-LTD induction. Electrophysiological measurements assessing postsynaptic expression mechanisms, and imaging studies with a ratiometric extracellular zinc sensor probing zinc release, supported that Z-LTD is expressed, at least in part, via reductions in presynaptic zinc release. Finally, exposure of mice to loud sound caused G1 mGluR-dependent Z-LTD at DCN parallel fiber synapses, thus validating our in vitro results. Together, our results reveal a novel mechanism underlying activity- and experience-dependent plasticity of synaptic zinc signaling.SIGNIFICANCE STATEMENT In the neocortex, limbic structures, and auditory brainstem, glutamatergic nerve terminals corelease zinc to modulate excitatory neurotransmission and sensory responses. Moreover, sensory experience causes bidirectional, long-term changes in synaptic zinc signaling. However, the mechanisms of this long-term synaptic zinc plasticity remain unknown. Here, we identified a novel Group 1 mGluR-dependent mechanism that causes bidirectional, long-term changes in synaptic zinc signaling. Our results highlight new mechanisms of brain adaptation during sensory processing, and potentially point to mechanisms of disorders associated with pathologic adaptation, such as tinnitus.
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Li W, Pozzo-Miller L. Dysfunction of the corticostriatal pathway in autism spectrum disorders. J Neurosci Res 2019; 98:2130-2147. [PMID: 31758607 DOI: 10.1002/jnr.24560] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 11/04/2019] [Accepted: 11/05/2019] [Indexed: 12/14/2022]
Abstract
The corticostriatal pathway that carries sensory, motor, and limbic information to the striatum plays a critical role in motor control, action selection, and reward. Dysfunction of this pathway is associated with many neurological and psychiatric disorders. Corticostriatal synapses have unique features in their cortical origins and striatal targets. In this review, we first describe axonal growth and synaptogenesis in the corticostriatal pathway during development, and then summarize the current understanding of the molecular bases of synaptic transmission and plasticity at mature corticostriatal synapses. Genes associated with autism spectrum disorder (ASD) have been implicated in axonal growth abnormalities, imbalance of the synaptic excitation/inhibition ratio, and altered long-term synaptic plasticity in the corticostriatal pathway. Here, we review a number of ASD-associated high-confidence genes, including FMR1, KMT2A, GRIN2B, SCN2A, NLGN1, NLGN3, MET, CNTNAP2, FOXP2, TSHZ3, SHANK3, PTEN, CHD8, MECP2, DYRK1A, RELN, FOXP1, SYNGAP1, and NRXN, and discuss their relevance to proper corticostriatal function.
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Affiliation(s)
- Wei Li
- Department of Neurobiology, The University of Alabama at Birmingham, Birmingham, AL, USA
| | - Lucas Pozzo-Miller
- Department of Neurobiology, The University of Alabama at Birmingham, Birmingham, AL, USA
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Laukkanen V, Kärkkäinen O, Kautiainen H, Tiihonen J, Storvik M. Increased [³H]quisqualic acid binding density in the dorsal striatum and anterior insula of alcoholics: A post-mortem whole-hemisphere autoradiography study. Psychiatry Res Neuroimaging 2019; 287:63-69. [PMID: 30991250 DOI: 10.1016/j.pscychresns.2019.04.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 04/05/2019] [Accepted: 04/07/2019] [Indexed: 01/28/2023]
Abstract
The function of group I metabotropic glutamate receptors mGluR1 and mGluR5 is involved in the hyperglutamatergic state caused by chronic alcohol. Preclinical studies suggest that group I mGluR modulation could serve as a novel treatment of alcoholism. Considering the wide role of glutamatergic neurochemistry in addiction, group I mGluR binding was studied in brain areas involved in decision-making, learning and memory. Post-mortem whole hemisphere autoradiography was used to study the binding density of [³H]quisqualic acid, a potent group I mGluR agonist, in 9 Cloninger type 1 alcoholics, 8 Cloninger type 2 alcoholics and 10 controls. Binding was studied in the dorsal striatum, hippocampus and cortex. Alcoholics displayed a trend towards increased [³H]quisqualic acid binding in all brain areas. The most robust findings were in the putamen (p = 0.006) and anterior insula (p = 0.005), where both alcoholic subtypes displayed increased binding compared to the controls. These findings suggest altered group I mGluR function in alcoholic subjects in the dorsal striatum, which is involved in habitual learning, and in the anterior insula, which has a pivotal role in the perception of bodily sensations. Increased [³H]quisqualic acid binding might suggest a beneficial impact of mGluR1/5 modulators in the treatment of alcoholism.
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Affiliation(s)
- Virpi Laukkanen
- Department of Forensic Psychiatry, University of Eastern Finland, Niuvanniemi Hospital, Niuvankuja 65, FI-70240 Kuopio, Finland; Department of Psychiatry, Kuopio University Hospital, P.O. Box 100, FI-70029 Kuopio, Finland.
| | - Olli Kärkkäinen
- Department of Pharmacology and Toxicology, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland
| | - Hannu Kautiainen
- Unit of Primary Health Care, Helsinki University Central Hospital, P.O. Box 705, FI-00029 HUS, Helsinki, Finland; Department of General Practice, Helsinki University, P.O. Box 20, FI-00014 Helsinki, Finland
| | - Jari Tiihonen
- Department of Forensic Psychiatry, University of Eastern Finland, Niuvanniemi Hospital, Niuvankuja 65, FI-70240 Kuopio, Finland; Department of Clinical Neuroscience, Karolinska Institutet, Karolinska Hospital, 17176 Stockholm, Sweden
| | - Markus Storvik
- Department of Psychiatry, Kuopio University Hospital, P.O. Box 100, FI-70029 Kuopio, Finland
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Caverzasio S, Amato N, Manconi M, Prosperetti C, Kaelin-Lang A, Hutchison WD, Galati S. Brain plasticity and sleep: Implication for movement disorders. Neurosci Biobehav Rev 2018; 86:21-35. [DOI: 10.1016/j.neubiorev.2017.12.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 12/15/2017] [Accepted: 12/18/2017] [Indexed: 12/31/2022]
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Combining Dopaminergic Facilitation with Robot-Assisted Upper Limb Therapy in Stroke Survivors: A Focused Review. Am J Phys Med Rehabil 2017; 95:459-74. [PMID: 26829074 PMCID: PMC4866584 DOI: 10.1097/phm.0000000000000438] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Despite aggressive conventional therapy, lasting hemiplegia persists in a large percentage of stroke survivors. The aim of this article is to critically review the rationale behind targeting multiple sites along the motor learning network by combining robotic therapy with pharmacotherapy and virtual reality–based reward learning to alleviate upper extremity impairment in stroke survivors. Methods for personalizing pharmacologic facilitation to each individual’s unique biology are also reviewed. At the molecular level, treatment with levodopa was shown to induce long-term potentiation-like and practice-dependent plasticity. Clinically, trials combining conventional therapy with levodopa in stroke survivors yielded statistically significant but clinically unconvincing outcomes because of limited personalization, standardization, and reproducibility. Robotic therapy can induce neuroplasticity by delivering intensive, reproducible, and functionally meaningful interventions that are objective enough for the rigors of research. Robotic therapy also provides an apt platform for virtual reality, which boosts learning by engaging reward circuits. The future of stroke rehabilitation should target distinct molecular, synaptic, and cortical sites through personalized multimodal treatments to maximize motor recovery.
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mGluR1 and mGluR5 Synergistically Control Cholinergic Synaptic Transmission in the Thalamic Reticular Nucleus. J Neurosci 2017; 36:7886-96. [PMID: 27466334 DOI: 10.1523/jneurosci.0409-16.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 06/08/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Acetylcholine (ACh) signaling is involved in a wide range of processes, including arousal, attention, and learning. An increasing number of studies indicate that cholinergic control of these functions is highly deterministic, mediated by synaptic afferents that generate reliable and precise responses in postsynaptic neurons. However, mechanisms that govern plastic changes of cholinergic synaptic strength are poorly understood, even though they are likely critical in shaping the impact of cholinergic inputs on neuronal networks. We have recently shown that in the thalamic reticular nucleus (TRN), synaptic release of ACh generates excitatory-inhibitory biphasic postsynaptic responses, mediated by the activation of α4β2 nicotinic (nAChRs) and M2 muscarinic receptors (mAChRs), respectively. Here, using voltage-clamp recordings from TRN neurons in thalamocortical slices of mice, we demonstrate that the activation of Group I metabotropic glutamate receptors (mGluRs) by ambient or synaptically released glutamate evokes transient increases of nicotinic EPSCs. Additionally, we find that the selective Group I mGluR agonist DHPG [(S)-3,5-dihydroxyphenylglycine] evokes long-term potentiation of nicotinic EPSCs (mGluR-nLTP), dependent on increases in postsynaptic Ca(2+) concentration and the activation of phospholipase C. Both the induction and the maintenance of mGluR-nLTP require synergistic activation of mGluR1 and mGluR5. Together, our results show that postsynaptic Group I mGluRs are critically involved in the regulation of cholinergic synaptic strength on different time scales, suggesting that cholinergic control of local thalamic circuits is highly context-dependent and regulated by the overall levels of glutamatergic afferent activity. SIGNIFICANCE STATEMENT Cholinergic signaling controls information processing and plasticity in neuronal circuits, but the mechanisms underlying the regulation of cholinergic synaptic strength on different time scales are unknown. Here we identify mGluR1 and mGluR5 as key elements in the dynamic regulation of cholinergic synaptic inputs onto neurons of the TRN. Our findings highlight potential mechanisms that regulate cholinergic signaling in the mammalian brain.
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Sumit M, Takayama S, Linderman JJ. New insights into mammalian signaling pathways using microfluidic pulsatile inputs and mathematical modeling. Integr Biol (Camb) 2017; 9:6-21. [PMID: 27868126 PMCID: PMC5259548 DOI: 10.1039/c6ib00178e] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Temporally modulated input mimics physiology. This chemical communication strategy filters the biochemical noise through entrainment and phase-locking. Under laboratory conditions, it also expands the observability space for downstream responses. A combined approach involving microfluidic pulsatile stimulation and mathematical modeling has led to deciphering of hidden/unknown temporal motifs in several mammalian signaling pathways and has provided mechanistic insights, including how these motifs combine to form distinct band-pass filters and govern fate regulation under dynamic microenvironment. This approach can be utilized to understand signaling circuit architectures and to gain mechanistic insights for several other signaling systems. Potential applications include synthetic biology and biotechnology, in developing pharmaceutical interventions, and in developing lab-on-chip models.
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Affiliation(s)
- M Sumit
- Biointerface Institute, North Campus Research Complex, University of Michigan, 2800 Plymouth Road, Ann Arbor, MI 48109, USA. and Biophysics Graduate Program, University of Michigan, Ann Arbor, MI 48109, USA
| | - S Takayama
- Biointerface Institute, North Campus Research Complex, University of Michigan, 2800 Plymouth Road, Ann Arbor, MI 48109, USA. and Michigan Centre for Integrative Research in Critical Care, North Campus Research, Complex, University of Michigan, 2800 Plymouth Road, Ann Arbor, MI 48109, USA and Department of Biomedical Engineering, University of Michigan, 1107 Carl A., Gerstacker Building, 2200, Bonisteel Blvd, Ann Arbor, MI 48109, USA and Macromolecular Science and Engineering Program, University of Michigan, 2300, Hayward Street, Ann Arbor, MI 48109, USA
| | - J J Linderman
- Department of Biomedical Engineering, University of Michigan, 1107 Carl A., Gerstacker Building, 2200, Bonisteel Blvd, Ann Arbor, MI 48109, USA and Department of Chemical Engineering, University of Michigan, Building 26, 2800 Plymouth Road, Ann Arbor, MI 48109, USA.
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Suryavanshi PS, Gupta SC, Yadav R, Kesherwani V, Liu J, Dravid SM. Glutamate Delta-1 Receptor Regulates Metabotropic Glutamate Receptor 5 Signaling in the Hippocampus. Mol Pharmacol 2016; 90:96-105. [PMID: 27231330 DOI: 10.1124/mol.116.104786] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 05/24/2016] [Indexed: 11/22/2022] Open
Abstract
The delta family of ionotropic glutamate receptors consists of glutamate delta-1 (GluD1) and glutamate delta-2 receptors. We have previously shown that GluD1 knockout mice exhibit features of developmental delay, including impaired spine pruning and switch in the N-methyl-D-aspartate receptor subunit, which are relevant to autism and other neurodevelopmental disorders. Here, we identified a novel role of GluD1 in regulating metabotropic glutamate receptor 5 (mGlu5) signaling in the hippocampus. Immunohistochemical analysis demonstrated colocalization of mGlu5 with GluD1 punctas in the hippocampus. Additionally, GluD1 protein coimmunoprecipitated with mGlu5 in the hippocampal membrane fraction, as well as when overexpressed in human embryonic kidney 293 cells, demonstrating that GluD1 and mGlu5 may cooperate in a signaling complex. The interaction of mGlu5 with scaffold protein effector Homer, which regulates mechanistic target of rapamycin (mTOR) signaling, was abnormal both under basal conditions and in response to mGlu1/5 agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) in GluD1 knockout mice. The basal levels of phosphorylated mTOR and protein kinase B, the signaling proteins downstream of mGlu5 activation, were higher in GluD1 knockout mice, and no further increase was induced by DHPG. We also observed higher basal protein translation and an absence of DHPG-induced increase in GluD1 knockout mice. In accordance with a role of mGlu5-mediated mTOR signaling in synaptic plasticity, DHPG-induced internalization of surface α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunits was impaired in the GluD1 knockout mice. These results demonstrate that GluD1 interacts with mGlu5, and loss of GluD1 impairs normal mGlu5 signaling potentially by dysregulating coupling to its effector. These studies identify a novel role of the enigmatic GluD1 subunit in hippocampal function.
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Affiliation(s)
| | - Subhash C Gupta
- Department of Pharmacology, Creighton University, Omaha, Nebraska
| | - Roopali Yadav
- Department of Pharmacology, Creighton University, Omaha, Nebraska
| | - Varun Kesherwani
- Department of Pharmacology, Creighton University, Omaha, Nebraska
| | - Jinxu Liu
- Department of Pharmacology, Creighton University, Omaha, Nebraska
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Electrophysiological CNS-processes related to associative learning in humans. Behav Brain Res 2015; 296:211-232. [PMID: 26367470 DOI: 10.1016/j.bbr.2015.09.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Revised: 09/01/2015] [Accepted: 09/07/2015] [Indexed: 11/22/2022]
Abstract
The neurophysiology of human associative memory has been studied with electroencephalographic techniques since the 1930s. This research has revealed that different types of electrophysiological processes in the human brain can be modified by conditioning: sensory evoked potentials, sensory induced gamma-band activity, periods of frequency-specific waves (alpha and beta waves, the sensorimotor rhythm and the mu-rhythm) and slow cortical potentials. Conditioning of these processes has been studied in experiments that either use operant conditioning or repeated contingent pairings of conditioned and unconditioned stimuli (classical conditioning). In operant conditioning, the appearance of a specific brain process is paired with an external stimulus (neurofeedback) and the feedback enables subjects to obtain varying degrees of control of the CNS-process. Such acquired self-regulation of brain activity has found practical uses for instance in the amelioration of epileptic seizures, Autism Spectrum Disorders (ASD) and Attention Deficit Hyperactivity Disorder (ADHD). It has also provided communicative means of assistance for tetraplegic patients through the use of brain computer interfaces. Both extra and intracortically recorded signals have been coupled with contingent external feedback. It is the aim for this review to summarize essential results on all types of electromagnetic brain processes that have been modified by classical or operant conditioning. The results are organized according to type of conditioned EEG-process, type of conditioning, and sensory modalities of the conditioning stimuli.
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14
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Picconi B, Calabresi P. Targeting metabotropic glutamate receptors as a new strategy against levodopa-induced dyskinesia in Parkinson's disease? Mov Disord 2014; 29:715-9. [PMID: 24591264 DOI: 10.1002/mds.25851] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Revised: 09/18/2013] [Accepted: 02/06/2014] [Indexed: 11/10/2022] Open
Abstract
Levodopa-induced dyskinesias (LIDs) represent one major motor disability of Parkinson's disease (PD) therapy. Thus, research effort is still devoted to finding agents that may improve parkinsonism and concomitantly reduce or avoid dyskinesia. Rodent and nonhuman primate models provide useful tools to study the molecular and neuronal bases of LIDs. Among the various strategies investigated recently, the use of drugs targeting metabotropic glutamate receptors has received large attention. In particular, use of antagonists of the subtype 5 of metabotropic glutamate receptors revealed promising preclinical and clinical results.
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15
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Hawes SL, Gillani F, Evans RC, Benkert EA, Blackwell KT. Sensitivity to theta-burst timing permits LTP in dorsal striatal adult brain slice. J Neurophysiol 2013; 110:2027-36. [PMID: 23926032 DOI: 10.1152/jn.00115.2013] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Long-term potentiation (LTP) of excitatory afferents to the dorsal striatum likely occurs with learning to encode new skills and habits, yet corticostriatal LTP is challenging to evoke reliably in brain slice under physiological conditions. Here we test the hypothesis that stimulating striatal afferents with theta-burst timing, similar to recently reported in vivo temporal patterns corresponding to learning, evokes LTP. Recording from adult mouse brain slice extracellularly in 1 mM Mg(2+), we find LTP in dorsomedial and dorsolateral striatum is preferentially evoked by certain theta-burst patterns. In particular, we demonstrate that greater LTP is produced using moderate intraburst and high theta-range frequencies, and that pauses separating bursts of stimuli are critical for LTP induction. By altering temporal pattern alone, we illustrate the importance of burst-patterning for LTP induction and demonstrate that corticostriatal long-term depression is evoked in the same preparation. In accord with prior studies, LTP is greatest in dorsomedial striatum and relies on N-methyl-d-aspartate receptors. We also demonstrate a requirement for both Gq- and Gs/olf-coupled pathways, as well as several kinases associated with memory storage: PKC, PKA, and ERK. Our data build on previous reports of activity-directed plasticity by identifying effective values for distinct temporal parameters in variants of theta-burst LTP induction paradigms. We conclude that those variants which best match reports of striatal activity during learning behavior are most successful in evoking dorsal striatal LTP in adult brain slice without altering artificial cerebrospinal fluid. Future application of this approach will enable diverse investigations of plasticity serving striatal-based learning.
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Affiliation(s)
- Sarah L Hawes
- Molecular Neuroscience Department, The Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia
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16
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Lesch KP, Merker S, Reif A, Novak M. Dances with black widow spiders: dysregulation of glutamate signalling enters centre stage in ADHD. Eur Neuropsychopharmacol 2013; 23:479-91. [PMID: 22939004 DOI: 10.1016/j.euroneuro.2012.07.013] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Revised: 07/10/2012] [Accepted: 07/24/2012] [Indexed: 11/26/2022]
Abstract
Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder with impairments across the lifespan. The persistence of ADHD is associated with considerable liability to neuropsychiatric co-morbidity such as depression, anxiety and substance use disorder. The substantial heritability of ADHD is well documented and recent genome-wide analyses for risk genes revealed synaptic adhesion molecules (e.g. latrophilin-3, LPHN3; fibronectin leucine-rich repeat transmembrane protein-3, FLRT3), glutamate receptors (e.g. metabotropic glutamate receptor-5, GRM5) and mediators of intracellular signalling pathways (e.g. nitric oxide synthase-1, NOS1). These genes encode principal components of the molecular machinery that connects pre- and postsynaptic neurons, facilitates glutamatergic transmission, controls synaptic plasticity and empowers intersecting neural circuits to process and refine information. Thus, identification of genetic variation affecting molecules essential for the formation, specification and function of excitatory synapses is refocusing research efforts on ADHD pathogenesis to include the long-neglected glutamate system.
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Affiliation(s)
- K P Lesch
- Division of Molecular Psychiatry, Laboratory of Translational Neuroscience, ADHD Clinical Research Network, Department of Psychiatry, Psychosomatics and Psychotherapy, University of Würzburg, Füchsleinstr. 15, 97080 Würzburg, Germany.
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17
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Kim B, Hawes SL, Gillani F, Wallace LJ, Blackwell KT. Signaling pathways involved in striatal synaptic plasticity are sensitive to temporal pattern and exhibit spatial specificity. PLoS Comput Biol 2013; 9:e1002953. [PMID: 23516346 PMCID: PMC3597530 DOI: 10.1371/journal.pcbi.1002953] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Accepted: 01/12/2013] [Indexed: 11/18/2022] Open
Abstract
The basal ganglia is a brain region critically involved in reinforcement learning and motor control. Synaptic plasticity in the striatum of the basal ganglia is a cellular mechanism implicated in learning and neuronal information processing. Therefore, understanding how different spatio-temporal patterns of synaptic input select for different types of plasticity is key to understanding learning mechanisms. In striatal medium spiny projection neurons (MSPN), both long term potentiation (LTP) and long term depression (LTD) require an elevation in intracellular calcium concentration; however, it is unknown how the post-synaptic neuron discriminates between different patterns of calcium influx. Using computer modeling, we investigate the hypothesis that temporal pattern of stimulation can select for either endocannabinoid production (for LTD) or protein kinase C (PKC) activation (for LTP) in striatal MSPNs. We implement a stochastic model of the post-synaptic signaling pathways in a dendrite with one or more diffusionally coupled spines. The model is validated by comparison to experiments measuring endocannabinoid-dependent depolarization induced suppression of inhibition. Using the validated model, simulations demonstrate that theta burst stimulation, which produces LTP, increases the activation of PKC as compared to 20 Hz stimulation, which produces LTD. The model prediction that PKC activation is required for theta burst LTP is confirmed experimentally. Using the ratio of PKC to endocannabinoid production as an index of plasticity direction, model simulations demonstrate that LTP exhibits spine level spatial specificity, whereas LTD is more diffuse. These results suggest that spatio-temporal control of striatal information processing employs these Gq coupled pathways.
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Affiliation(s)
- BoHung Kim
- School of Mechanical Engineering, University of Ulsan, Ulsan, South Korea
- The Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia, United States of America
| | - Sarah L. Hawes
- The Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia, United States of America
| | - Fawad Gillani
- The Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia, United States of America
| | - Lane J. Wallace
- College of Pharmacy, Ohio State University, Columbus, Ohio, United States of America
| | - Kim T. Blackwell
- The Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia, United States of America
- * E-mail:
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18
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Hovelsø N, Sotty F, Montezinho LP, Pinheiro PS, Herrik KF, Mørk A. Therapeutic potential of metabotropic glutamate receptor modulators. Curr Neuropharmacol 2012; 10:12-48. [PMID: 22942876 PMCID: PMC3286844 DOI: 10.2174/157015912799362805] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2010] [Revised: 01/10/2011] [Accepted: 03/04/2011] [Indexed: 12/21/2022] Open
Abstract
Glutamate is the main excitatory neurotransmitter in the central nervous system (CNS) and is a major player in complex brain functions. Glutamatergic transmission is primarily mediated by ionotropic glutamate receptors, which include NMDA, AMPA and kainate receptors. However, glutamate exerts modulatory actions through a family of metabotropic G-protein-coupled glutamate receptors (mGluRs). Dysfunctions of glutamatergic neurotransmission have been implicated in the etiology of several diseases. Therefore, pharmacological modulation of ionotropic glutamate receptors has been widely investigated as a potential therapeutic strategy for the treatment of several disorders associated with glutamatergic dysfunction. However, blockade of ionotropic glutamate receptors might be accompanied by severe side effects due to their vital role in many important physiological functions. A different strategy aimed at pharmacologically interfering with mGluR function has recently gained interest. Many subtype selective agonists and antagonists have been identified and widely used in preclinical studies as an attempt to elucidate the role of specific mGluRs subtypes in glutamatergic transmission. These studies have allowed linkage between specific subtypes and various physiological functions and more importantly to pathological states. This article reviews the currently available knowledge regarding the therapeutic potential of targeting mGluRs in the treatment of several CNS disorders, including schizophrenia, addiction, major depressive disorder and anxiety, Fragile X Syndrome, Parkinson’s disease, Alzheimer’s disease and pain.
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Affiliation(s)
- N Hovelsø
- Department of Neurophysiology, H. Lundbeck A/S, Ottiliavej 9, 2500 Copenhagen-Valby, Denmark
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19
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Ciruela F, Fernández-Dueñas V, Llorente J, Borroto-Escuela D, Cuffí ML, Carbonell L, Sánchez S, Agnati LF, Fuxe K, Tasca CI. G protein-coupled receptor oligomerization and brain integration: focus on adenosinergic transmission. Brain Res 2012; 1476:86-95. [PMID: 22575562 DOI: 10.1016/j.brainres.2012.04.056] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2012] [Accepted: 04/30/2012] [Indexed: 10/28/2022]
Abstract
The control of glutamatergic corticostriatal transmission is essential for the induction and expression of plasticity mechanisms in the striatum, a phenomenon thickly regulated by G protein-coupled receptors (GPCRs). Interestingly, in addition to dopamine receptors, adenosine and metabotropic glutamate receptors also play a key role in striatal functioning. The existence of a supramolecular organization (i.e. oligomer) containing dopamine, adenosine and metabotropic glutamate receptors in the striatal neurons is now being widely accepted by the scientific community. Indeed, these oligomers may enhance the diversity and performance by which extracellular striatal signals are transferred to the G-proteins in the process of receptor transduction, and also may allow unpredictable receptor-receptor allosteric regulations. Overall, here we want to review how formations of adenosine, dopamine and metabotropic glutamate receptors-containing oligomers impinge into striatal functioning in both normal and pathological conditions. This article is part of a Special Issue entitled: Brain Integration.
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Affiliation(s)
- Francisco Ciruela
- Unitat de Farmacologia, Departament Patologia i Terapèutica Experimental, Facultat de Medicina, Universitat de Barcelona, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
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20
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Herman EJ, Bubser M, Conn PJ, Jones CK. Metabotropic glutamate receptors for new treatments in schizophrenia. Handb Exp Pharmacol 2012:297-365. [PMID: 23027420 DOI: 10.1007/978-3-642-25758-2_11] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Metabotropic glutamate receptors (mGluRs) represent exciting targets for the development of novel therapeutic agents for schizophrenia. Recent studies indicate that selective activation of specific mGluR subtypes may provide potential benefits for not only the positive symptoms, but also the negative symptoms and cognitive impairments observed in individuals with schizophrenia. Although optimization of traditional orthosteric agonists may still offer a feasible approach for the activation of mGluRs, important progress has been made in the discovery of novel subtype-selective allosteric ligands, including positive allosteric modulators (PAMs) of mGluR2 and mGluR5. These allosteric mGluR ligands have improved properties for clinical development and have served as key preclinical tools for a more in-depth understanding of the potential roles of these different mGluR subtypes for the treatment of schizophrenia.
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Affiliation(s)
- E J Herman
- Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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21
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Metabotropic Glutamate Receptor–Dopamine Interactions in the Basal Ganglia Motor Circuit. ACTA ACUST UNITED AC 2011. [DOI: 10.1201/b11284-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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22
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Klug J, Deutch A, Colbran R, Winder D. Synaptic Triad in the Neostriatum. DOPAMINE – GLUTAMATE INTERACTIONS IN THE BASAL GANGLIA 2011. [DOI: 10.1201/b11284-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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23
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Xie K, Martemyanov KA. Control of striatal signaling by g protein regulators. Front Neuroanat 2011; 5:49. [PMID: 21852966 PMCID: PMC3151604 DOI: 10.3389/fnana.2011.00049] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2011] [Accepted: 07/23/2011] [Indexed: 12/03/2022] Open
Abstract
Signaling via heterotrimeric G proteins plays a crucial role in modulating the responses of striatal neurons that ultimately shape core behaviors mediated by the basal ganglia circuitry, such as reward valuation, habit formation, and movement coordination. Activation of G protein-coupled receptors (GPCRs) by extracellular signals activates heterotrimeric G proteins by promoting the binding of GTP to their α subunits. G proteins exert their effects by influencing the activity of key effector proteins in this region, including ion channels, second messenger enzymes, and protein kinases. Striatal neurons express a staggering number of GPCRs whose activation results in the engagement of downstream signaling pathways and cellular responses with unique profiles but common molecular mechanisms. Studies over the last decade have revealed that the extent and duration of GPCR signaling are controlled by a conserved protein family named regulator of G protein signaling (RGS). RGS proteins accelerate GTP hydrolysis by the α subunits of G proteins, thus promoting deactivation of GPCR signaling. In this review, we discuss the progress made in understanding the roles of RGS proteins in controlling striatal G protein signaling and providing integration and selectivity of signal transmission. We review evidence on the formation of a macromolecular complex between RGS proteins and other components of striatal signaling pathways, their molecular regulatory mechanisms and impacts on GPCR signaling in the striatum obtained from biochemical studies and experiments involving genetic mouse models. Special emphasis is placed on RGS9-2, a member of the RGS family that is highly enriched in the striatum and plays critical roles in drug addiction and motor control.
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Affiliation(s)
- Keqiang Xie
- The Scripps Research Institute Jupiter, FL, USA
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24
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Tsui A, Isacson O. Functions of the nigrostriatal dopaminergic synapse and the use of neurotransplantation in Parkinson's disease. J Neurol 2011; 258:1393-405. [PMID: 21544566 DOI: 10.1007/s00415-011-6061-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2011] [Revised: 04/12/2011] [Accepted: 04/14/2011] [Indexed: 10/18/2022]
Abstract
While pharmaceutical options remain the overwhelmingly accepted treatment of choice for neurological and psychiatric diseases, significant accomplishments in regenerative neuroscience research have demonstrated the potential of cellular and synaptic functional repair in future therapies. Parkinson's disease stands out as an example in which repair by dopaminergic neurons appears a viable potential therapy. This article describes the basic neurobiological underpinnings of the rationale for cell therapy for Parkinson's disease and the challenges ahead for the use of regenerative medicine in the treatment for this disease.
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Affiliation(s)
- Alex Tsui
- University of Oxford Medical School, John Radcliffe Hospital, Oxford, UK.
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25
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Characterization of the selective mGluR1 antagonist, JNJ16259685, in rodent models of movement and coordination. Pharmacol Biochem Behav 2011; 98:181-7. [DOI: 10.1016/j.pbb.2010.11.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 11/22/2010] [Accepted: 11/23/2010] [Indexed: 11/23/2022]
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26
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Ciruela F, Gómez-Soler M, Guidolin D, Borroto-Escuela DO, Agnati LF, Fuxe K, Fernández-Dueñas V. Adenosine receptor containing oligomers: their role in the control of dopamine and glutamate neurotransmission in the brain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:1245-55. [PMID: 21316336 DOI: 10.1016/j.bbamem.2011.02.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Revised: 02/02/2011] [Accepted: 02/05/2011] [Indexed: 02/05/2023]
Abstract
While the G protein-coupled receptor (GPCR) oligomerization has been questioned during the last fifteen years, the existence of a multi-receptor complex involving direct receptor-receptor interactions, called receptor oligomers, begins to be widely accepted. Eventually, it has been postulated that oligomers constitute a distinct functional form of the GPCRs with essential receptorial features. Also, it has been proven, under certain circumstances, that the GPCR oligomerization phenomenon is crucial for the receptor biosynthesis, maturation, trafficking, plasma membrane diffusion, and pharmacology and signalling. Adenosine receptors are GPCRs that mediate the physiological functions of adenosine and indeed these receptors do also oligomerize. Accordingly, adenosine receptor oligomers may improve the molecular mechanism by which extracellular adenosine signals are transferred to the G proteins in the process of receptor transduction. Importantly, these adenosine receptor-containing oligomers may allow not only the control of the adenosinergic function but also the fine-tuning modulation of other neurotransmitter systems (i.e. dopaminergic and glutamatergic transmission). Overall, we underscore here recent significant developments based on adenosine receptor oligomerization that are essential for acquiring a better understanding of neurotransmission in the central nervous system under normal and pathological conditions.
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Affiliation(s)
- Francisco Ciruela
- Departament de Patologia i Terapèutica Experimental, Universitat de Barcelona, 08097 L'Hospitalet de Llobregat, Spain.
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27
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Incentive learning underlying cocaine-seeking requires mGluR5 receptors located on dopamine D1 receptor-expressing neurons. J Neurosci 2010; 30:11973-82. [PMID: 20826661 DOI: 10.1523/jneurosci.2550-10.2010] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Understanding the psychobiological basis of relapse remains a challenge in developing therapies for drug addiction. Relapse in cocaine addiction often occurs following exposure to environmental stimuli previously associated with drug taking. The metabotropic glutamate receptor, mGluR5, is potentially important in this respect; it plays a central role in several forms of striatal synaptic plasticity proposed to underpin associative learning and memory processes that enable drug-paired stimuli to acquire incentive motivational properties and trigger relapse. Using cell type-specific RNA interference, we have generated a novel mouse line with a selective knock-down of mGluR5 in dopamine D1 receptor-expressing neurons. Although mutant mice self-administer cocaine, we show that reinstatement of cocaine-seeking induced by a cocaine-paired stimulus is impaired. By examining different aspects of associative learning in the mutant mice, we identify deficits in specific incentive learning processes that enable a reward-paired stimulus to directly reinforce behavior and to become attractive, thus eliciting approach toward it. Our findings show that glutamate signaling through mGluR5 located on dopamine D1 receptor-expressing neurons is necessary for incentive learning processes that contribute to cue-induced reinstatement of cocaine-seeking and which may underpin relapse in drug addiction.
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28
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The mGluR5 antagonist MTEP dissociates the acquisition of predictive and incentive motivational properties of reward-paired stimuli in mice. Neuropsychopharmacology 2010; 35:1807-17. [PMID: 20375996 PMCID: PMC3055484 DOI: 10.1038/npp.2010.48] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
An environmental stimulus paired with reward (a conditioned stimulus; CS) can acquire predictive properties that signal reward availability and may also acquire incentive motivational properties that enable the CS to influence appetitive behaviors. The neural mechanisms involved in the acquisition and expression of these CS properties are not fully understood. The metabotropic glutamate receptor, mGluR5, contributes to synaptic plasticity underlying learning and memory processes. We examined the role of mGluR5 in the acquisition and expression of learning that enables a CS to predict reward (goal-tracking) and acquire incentive properties (conditioned reinforcement). Mice were injected with vehicle or the mGluR5 antagonist, MTEP (3 or 10 mg/kg), before each Pavlovian conditioning session in which a stimulus (CS+) was paired with food delivery. Subsequently, in the absence of the primary food reward, we determined whether the CS+ could reinforce a novel instrumental response (conditioned reinforcement) and direct behavior toward the place of reward delivery (goal-tracking). MTEP did not affect performance during the conditioning phase, or the ability of the CS+ to elicit a goal-tracking response. In contrast, 10 mg/kg MTEP given before each conditioning session prevented the subsequent expression of conditioned reinforcement. This dose of MTEP did not affect conditioned reinforcement when administered before the test, in mice that had received vehicle before conditioning sessions. Thus, mGluR5 has a critical role in the acquisition of incentive properties by a CS, but is not required for the expression of incentive learning, or for the CS to acquire predictive properties that signal reward availability.
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29
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Xiao MY, Gustafsson B, Niu YP. Metabotropic glutamate receptors in the trafficking of ionotropic glutamate and GABA(A) receptors at central synapses. Curr Neuropharmacol 2010; 4:77-86. [PMID: 18615134 DOI: 10.2174/157015906775202986] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Revised: 08/23/2005] [Accepted: 09/30/2005] [Indexed: 01/08/2023] Open
Abstract
The trafficking of ionotropic glutamate (AMPA, NMDA and kainate) and GABA(A) receptors in and out of, or laterally along, the postsynaptic membrane has recently emerged as an important mechanism in the regulation of synaptic function, both under physiological and pathological conditions, such as information processing, learning and memory formation, neuronal development, and neurodegenerative diseases. Non-ionotropic glutamate receptors, primarily group I metabotropic glutamate receptors (mGluRs), co-exist with the postsynaptic ionotropic glutamate and GABA(A) receptors. The ability of mGluRs to regulate postsynaptic phosphorylation and Ca(2+) concentration, as well as their interactions with postsynaptic scaffolding/signaling proteins, makes them well suited to influence the trafficking of ionotropic glutamate and GABA(A) receptors. Recent studies have provided insights into how mGluRs may impose such an influence at central synapses, and thus how they may affect synaptic signaling and the maintenance of long-term synaptic plasticity. In this review we will discuss some of the recent progress in this area: i) long-term synaptic plasticity and the involvement of mGluRs; ii) ionotropic glutamate receptor trafficking and long-term synaptic plasticity; iii) the involvement of postsynaptic group I mGluRs in regulating ionotropic glutamate receptor trafficking; iv) involvement of postsynaptic group I mGluRs in regulating GABA(A) receptor trafficking; v) and the trafficking of postsynaptic group I mGluRs themselves.
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Affiliation(s)
- Min-Yi Xiao
- Institute of Physiology and Pharmacology, Göteborg University, Box 432, 405 30 Göteborg, Sweden.
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30
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Lesage A, Steckler T. Metabotropic glutamate mGlu1 receptor stimulation and blockade: therapeutic opportunities in psychiatric illness. Eur J Pharmacol 2010; 639:2-16. [PMID: 20371230 DOI: 10.1016/j.ejphar.2009.12.043] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2009] [Revised: 12/15/2009] [Accepted: 12/18/2009] [Indexed: 12/26/2022]
Abstract
Metabotropic glutamate mGlu(1) receptors play a modulatory role in the nervous system. They enhance cell excitability, modulate synaptic neurotransmission and are involved in synaptic plasticity. During the last 10 years, several selective metabotropic glutamate mGlu(1) receptor competitive antagonists and potentiators have been discovered. These pharmacological tools, together with early and later work in metabotropic glutamate mGlu(1) receptor mutant mice have allowed studying the role of the receptor in various aspects of psychiatric illnesses such as anxiety, depression and schizophrenia. We here review the data on selective metabotropic glutamate mGlu(1) receptor antagonists in support of their potential as anxiolytic and antidepressant treatments. We propose a rationale for the development of metabotropic glutamate mGlu(1) receptor positive allosteric modulators for the treatment of schizophrenia. Potential side effects of blockade and activation of metabotropic glutamate mGlu(1) receptors are addressed, with special focus on the differential effects of metabotropic glutamate mGlu(1) receptor antagonists in cognition models with positive reinforcement versus those that use aversive learning procedures. Further development of negative allosteric modulators and more drug-like positive allosteric modulators will be required in order to decipher the therapeutic efficacy and safety margin of these compounds in the clinic.
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Affiliation(s)
- Anne Lesage
- Department of CNS-Neuroscience, Research and Early Development, Johnson and Johnson Research and Development, Turnhoutseweg 30, 2340 Beerse, Belgium.
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31
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Olive MF. Cognitive effects of Group I metabotropic glutamate receptor ligands in the context of drug addiction. Eur J Pharmacol 2010; 639:47-58. [PMID: 20371237 DOI: 10.1016/j.ejphar.2010.01.029] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Revised: 01/14/2010] [Accepted: 01/20/2010] [Indexed: 01/03/2023]
Abstract
Glutamate plays a pivotal role in regulating drug self-administration and drug-seeking behavior, and the past decade has witnessed a substantial surge of interest in the role of Group I metabotropic glutamate receptors (mGlu(1) and mGlu(5) receptors) in mediating these behaviors. As will be reviewed here, Group I mGlu receptors are involved in normal and drug-induced synaptic plasticity, drug reward, reinforcement and relapse-like behaviors, and addiction-related cognitive processes such as maladaptive learning and memory, behavioral inflexibility, and extinction learning. Animal models of addiction have revealed that antagonists of Group I mGlu receptors, particularly the mGlu(5) receptor, reduce self-administration of virtually all drugs of abuse. Since inhibitors of mGlu5 receptor function have now entered clinical trials for other medical conditions and appear to be well-tolerated, a key question that remains unanswered is - what changes in cognition are produced by these compounds that result in reduced drug intake and drug-seeking behavior? Finally, in contrast to mGlu(5) receptor antagonists, recent studies have indicated that positive allosteric modulation of mGlu(5) receptors actually enhances synaptic plasticity and improves various aspects of cognition, including spatial learning, behavioral flexibility, and extinction of drug-seeking behavior. Thus, while inhibition of Group I mGlu receptor function may reduce drug reward, reinforcement, and relapse-related behaviors, positive allosteric modulation of the mGlu5 receptor subtype may actually enhance cognition and potentially reverse some of the cognitive deficits associated with chronic drug use.
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Affiliation(s)
- M Foster Olive
- Center for Drug and Alcohol Programs, Department of Psychiatry, Medical University of South Carolina, 67 President Street, MSC 861, Charleston, SC 29425, USA.
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32
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Cocaine-mediated synaptic potentiation is absent in VTA neurons from mGlu5-deficient mice. Int J Neuropsychopharmacol 2010; 13:133-41. [PMID: 19545477 DOI: 10.1017/s1461145709990162] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Drugs of abuse have the ability to instantiate plastic adaptations within the central nervous system, and this property may relate to the development and persistence of addiction. In this context, a single exposure to cocaine in rodents may induce synaptic plasticity by increasing the AMPA/NMDA receptor excitatory post-synaptic current (EPSC) amplitude ratio in dopaminergic cells of the ventral tegmental area (VTA). Here, we examine the role of the metabotropic glutamate 5 (mGlu5) receptor in this regard using a genetic mouse model. The control AMPA/NMDA EPSC ratio is reduced in mGlu5-deficient mice compared to wild-types. Moreover, cocaine-induced enhancement of this EPSC ratio is also absent in mutant mice, which suggests that mGlu5 receptors are required for single-dose cocaine-induced plasticity onto VTA cells. While the temporal profile of hyperactivity to acute cocaine is altered in mGlu5-deficient mice; these mice still develop and express sensitized psychomotor responses to cocaine. These data suggest that the mGlu5 receptor is required for cocaine-induced plasticity in VTA dopaminergic cells. In contrast, the mGlu5 receptor may not be essential for psychostimulant behavioural sensitization; although it probably impacts other aspects drug addiction, such as motivation to self-administer.
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Cheng S, Zhang J, Zhu P, Ma Y, Xiong Y, Sun L, Xu J, Zhang H, He J. The PDZ domain protein CAL interacts with mGluR5a and modulates receptor expression. J Neurochem 2010; 112:588-98. [DOI: 10.1111/j.1471-4159.2009.06454.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Bird MK, Lawrence AJ. The promiscuous mGlu5 receptor--a range of partners for therapeutic possibilities? Trends Pharmacol Sci 2009; 30:617-23. [PMID: 19892412 DOI: 10.1016/j.tips.2009.09.008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2009] [Revised: 09/23/2009] [Accepted: 09/23/2009] [Indexed: 01/20/2023]
Abstract
The issue of non-specific effects for potential therapeutics is particularly salient in neurological/psychiatric disorders, where adverse drug reactions could impair critical brain functions. The issue of specificity is not limited to candidate molecules, as receptor targets themselves often influence physiological as well as pathological outcomes. Metabotropic glutamate receptor 5 (mGlu5) is an example of a "promiscuous" receptor target that has been implicated in addiction, but also many other processes. However, if receptor modulation could be restricted to specific pathways/brain regions, mGlu5 may still prove to be a viable therapeutic target for various indications. Using this premise, a number of possible methods to refine drug development strategy are discussed, including exploiting specific interactions of mGlu5 with other receptors to narrow the influence of pharmacological agents, and also the use of RNA interference targeted to specific cells/regions of the brain.
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Affiliation(s)
- Michael K Bird
- Florey Neuroscience Institutes, University of Melbourne, Parkville, Victoria, 3010, Australia
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She WC, Quairiaux C, Albright MJ, Wang YC, Sanchez DE, Chang PS, Welker E, Lu HC. Roles of mGluR5 in synaptic function and plasticity of the mouse thalamocortical pathway. Eur J Neurosci 2009; 29:1379-96. [PMID: 19519626 DOI: 10.1111/j.1460-9568.2009.06696.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The group I metabotropic glutamate receptor 5 (mGluR5) has been implicated in the development of cortical sensory maps. However, its precise roles in the synaptic function and plasticity of thalamocortical (TC) connections remain unknown. Here we first show that in mGluR5 knockout (KO) mice bred onto a C57BL6 background cytoarchitectonic differentiation into barrels is missing, but the representations for large whiskers are identifiable as clusters of TC afferents. The altered dendritic morphology of cortical layer IV spiny stellate neurons in mGluR5 KO mice implicates a role for mGluR5 in the dendritic morphogenesis of excitatory neurons. Next, in vivo single-unit recordings of whisker-evoked activity in mGluR5 KO adults demonstrated a preserved topographical organization of the whisker representation, but a significantly diminished temporal discrimination of center to surround whiskers in the responses of individual neurons. To evaluate synaptic function at TC synapses in mGluR5 KO mice, whole-cell voltage-clamp recording was conducted in acute TC brain slices prepared from postnatal day 4-11 mice. At mGluR5 KO TC synapses, N-methyl-D-aspartate (NMDA) currents decayed faster and synaptic strength was more easily reduced, but more difficult to strengthen by Hebbian-type pairing protocols, despite a normal developmental increase in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated currents and presynaptic function. We have therefore demonstrated that mGluR5 is required for synaptic function/plasticity at TC synapses as barrels are forming, and we propose that these functional alterations at the TC synapse are the basis of the abnormal anatomical and functional development of the somatosensory cortex in the mGluR5 KO mouse.
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Affiliation(s)
- Wei-Chi She
- Department of Pediatrics, The Cain Foundation Laboratories, Baylor College of Medicine, Houston, TX 77030, USA
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Ferraguti F, Crepaldi L, Nicoletti F. Metabotropic glutamate 1 receptor: current concepts and perspectives. Pharmacol Rev 2009; 60:536-81. [PMID: 19112153 DOI: 10.1124/pr.108.000166] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Almost 25 years after the first report that glutamate can activate receptors coupled to heterotrimeric G-proteins, tremendous progress has been made in the field of metabotropic glutamate receptors. Now, eight members of this family of glutamate receptors, encoded by eight different genes that share distinctive structural features have been identified. The first cloned receptor, the metabotropic glutamate (mGlu) receptor mGlu1 has probably been the most extensively studied mGlu receptor, and in many respects it represents a prototypical subtype for this family of receptors. Its biochemical, anatomical, physiological, and pharmacological characteristics have been intensely investigated. Together with subtype 5, mGlu1 receptors constitute a subgroup of receptors that couple to phospholipase C and mobilize Ca(2+) from intracellular stores. Several alternatively spliced variants of mGlu1 receptors, which differ primarily in the length of their C-terminal domain and anatomical localization, have been reported. Use of a number of genetic approaches and the recent development of selective antagonists have provided a means for clarifying the role played by this receptor in a number of neuronal systems. In this article we discuss recent advancements in the pharmacology and concepts about the intracellular transduction and pathophysiological role of mGlu1 receptors and review earlier data in view of these novel findings. The impact that this new and better understanding of the specific role of these receptors may have on novel treatment strategies for a variety of neurological and psychiatric disorders is considered.
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Affiliation(s)
- Francesco Ferraguti
- Department of Pharmacology, Innsbruck Medical University, Peter-Mayr Strasse 1a, Innsbruck A-6020, Austria.
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De Leonibus E, Managò F, Giordani F, Petrosino F, Lopez S, Oliverio A, Amalric M, Mele A. Metabotropic glutamate receptors 5 blockade reverses spatial memory deficits in a mouse model of Parkinson's disease. Neuropsychopharmacology 2009; 34:729-38. [PMID: 18704096 DOI: 10.1038/npp.2008.129] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Visuo-spatial deficits are the most consistently reported cognitive abnormalities in Parkinson's disease (PD), and they are frequently associated to motor symptoms in the early stages of the disease when dopamine loss is moderate and still restricted to the caudate-putamen. The metabotropic glutamate receptor 5 (mGluR5) antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), has beneficial effects on motor symptoms in animal models of PD. However, the effects of MPEP on the cognitive deficits of the disease have never been investigated. Thus, the purpose of this study was to explore its therapeutic potentials by investigating its effects on the visuo-spatial deficits induced by 6-hydroxydopamine (6-OHDA) lesions of dorsal striatum in CD1 mice. The results demonstrated that systemic injections of MPEP (6, 12, and 24 mg/kg, i.p.) impair visuo-spatial discrimination in intact mice at high concentrations, whereas lower doses (1.5 and 3 mg/kg, i.p.) were void of effects. Nevertheless, when an ineffective dose (MPEP 3 mg/kg) was injected, either acutely or subchronically (8 days), it antagonized the visuo-spatial discrimination deficit induced by bilateral dopamine lesion of the striatum. Furthermore, the same treatment increased contralateral turning induced by L-DOPA in mice bearing unilateral 6-OHDA lesion. These results confirm the therapeutic potential of mGluR5 blockade on motor symptoms induced by reduced striatal dopamine function. Further, they demonstrate that mGluR5 blockade may also have beneficial effects on cognitive deficits induced by dopamine depletion.
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Affiliation(s)
- Elvira De Leonibus
- Dipartimento di Genetica e Biologia Molecolare C.Darwin, Università degli Studi di Roma La Sapienza, Rome, Italy
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Group I metabotropic glutamate receptors control metaplasticity of spinal cord learning through a protein kinase C-dependent mechanism. J Neurosci 2009; 28:11939-49. [PMID: 19005059 DOI: 10.1523/jneurosci.3098-08.2008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Neurons within the spinal cord can support several forms of plasticity, including response-outcome (instrumental) learning. After a complete spinal transection, experimental subjects are capable of learning to hold the hindlimb in a flexed position (response) if shock (outcome) is delivered to the tibialis anterior muscle when the limb is extended. This response-contingent shock produces a robust learning that is mediated by ionotropic glutamate receptors (iGluRs). Exposure to nociceptive stimuli that are independent of limb position (e.g., uncontrollable shock; peripheral inflammation) produces a long-term (>24 h) inhibition of spinal learning. This inhibition of plasticity in spinal learning is itself a form of plasticity that requires iGluR activation and protein synthesis. Plasticity of plasticity (metaplasticity) in the CNS has been linked to group I metabotropic glutamate receptors (subtypes mGluR1 and mGluR5) and activation of protein kinase C (PKC). The present study explores the role of mGluRs and PKC in the metaplastic inhibition of spinal cord learning using a combination of behavioral, pharmacological, and biochemical techniques. Activation of group I mGluRs was found to be both necessary and sufficient for metaplastic inhibition of spinal learning. PKC was activated by stimuli that inhibit spinal learning, and inhibiting PKC activity restored the capacity for spinal learning. Finally, a PKC inhibitor blocked the metaplastic inhibition of spinal learning produced by a group I mGluR agonist. The data strongly suggest that group I mGluRs control metaplasticity of spinal learning through a PKC-dependent mechanism, providing a potential therapeutic target for promoting use-dependent plasticity after spinal cord injury.
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Distinct roles of group I mGlu receptors in striatal function. Neuropharmacology 2008; 55:392-5. [PMID: 18602651 DOI: 10.1016/j.neuropharm.2008.05.020] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Revised: 05/16/2008] [Accepted: 05/23/2008] [Indexed: 11/20/2022]
Abstract
In the recent past, evidence accumulated in favour of a central role of group I metabotropic glutamate (mGlu) receptors, mGlu1 and mGlu5, in the modulation of cell excitability both of striatal medium spiny projection neurons (MSNs) and interneuronal population. Electrophysiological and pharmacological studies have clearly shown that activation of mGlu1 and mGlu5 receptors exerts distinct actions, depending on the neuronal subtype involved. MGlu5 receptor activation mediates the potentiation of NMDA responses in MSNs, and underlies the retrograde inhibitory signaling by endocannabinoids at corticostriatal synapses. Conversely, both group I mGlu receptors are involved in long-term synaptic plasticity of MSNs. Likewise, either mGlu1 or mGlu5 receptors are engaged in shaping the excitability of large cholinergic interneurons, playing different roles in the membrane responses. Differently, although GABAergic parvalbumin-positive, fast-spiking interneurons have been shown to express both group I receptors, only mGlu1 receptor seems to mediate membrane and synaptic responses. This review provides a brief survey of the cellular and synaptic actions of group I mGlu receptors, and discusses the potential relevance of these findings in neostriatal function and motor control.
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40
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Wang W, Zhang Z, Shang J, Jiang ZZ, Wang S, Liu Y, Zhang LY. Activation of group I metabotropic glutamate receptors induces long-term depression in the hippocampal CA1 region of adult rats in vitro. Neurosci Res 2008; 62:43-50. [PMID: 18602428 DOI: 10.1016/j.neures.2008.06.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2007] [Revised: 06/05/2008] [Accepted: 06/09/2008] [Indexed: 10/21/2022]
Abstract
Previous studies have implicated that long-term depression (LTD) was developmentally regulated since LTD can be readily induced by low frequency stimulation (LFS) in acute hippocampal slices prepared from juvenile but not adult animals. Here, we have examined the LTD induced by LFS (1Hz, 900 pulses) paired with a certain pattern at the Schaffer collateral-CAl synapse in adult hippocampal slices. We found that, in the 90-day-old rat hippocampus, LTD could be induced reliably by LFS paired with stronger stimulus intensity than that used during baseline recording. However, this synaptic depression could be completely abolished by application of metabotropic glutamate receptor (mGluR) antagonist (S)-amethyl-4-carboxyphenylglycine (MCPG) which had no effect on that induced by the same protocol in the 16-day-old rat hippocampus. Furthermore, preincubation with group I mGluR antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP) and (S)-2-methyl-4-carboxyphenylglycine (LY367385), also completely prevented the LFS-induced LTD. In contrast, group II mGluR antagonist (2S)-a-ethylglutamic acid (EGLU), N-methyl-d-aspartate (NMDA) receptor antagonist APV and voltage-gated calcium channel antagonist nimodipine had no effect on the LFS-induced LTD. Taken together, these observations suggest that LFS paired with strong stimulus strength can efficiently induce group I mGluR-dependent LTD in the adult hippocampal CA1 region, proving insight into the functional significance of hippocampal mGluR-mediated LTD in learning and memory.
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Affiliation(s)
- Wei Wang
- National Drug Screening Laboratory, New Drug Screening Center, China Pharmaceutical University, Nanjing, China
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41
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Le Vasseur M, Ran I, Lacaille JC. Selective induction of metabotropic glutamate receptor 1– and metabotropic glutamate receptor 5–dependent chemical long-term potentiation at oriens/alveus interneuron synapses of mouse hippocampus. Neuroscience 2008; 151:28-42. [DOI: 10.1016/j.neuroscience.2007.09.071] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Revised: 08/29/2007] [Accepted: 09/26/2007] [Indexed: 10/22/2022]
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Sergeeva OA, Doreulee N, Chepkova AN, Kazmierczak T, Haas HL. Long-term depression of cortico-striatal synaptic transmission by DHPG depends on endocannabinoid release and nitric oxide synthesis. Eur J Neurosci 2007; 26:1889-94. [PMID: 17868368 DOI: 10.1111/j.1460-9568.2007.05815.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
In models of early stage Parkinson's disease (PD), motor deficits are accompanied by excessive activation of striatal glutamate receptors. Metabotropic glutamate group I receptors (mGluR I) play an important but not well-understood role in PD progression. In mouse brain slices, bath application of the mGluR I agonist (RS)-DHPG (3,5-dihydroxyphenylglycine, 100 microm for 20 min) caused a long-term depression of corticostriatal transmission (LTD(DHPG)), which was reversed by three mGluR I antagonists: LY 367385, CPCCOEt and MPEP. LTD(DHPG) required nitric oxide (NO) synthesis as it was blocked by the broad-spectrum NO synthase (NOS) inhibitor Nomega-nitro-l-arginine (NL-Arg) and impaired under blockade of neuronal NOS and in endothelial NOS-deficient mice. Release of endocannabinoids (eCB) was critically involved in this form of striatal plasticity givem that the CB1 receptor antagonist AM251 prevented LTD(DHPG), while the CB1 agonist ACEA elicited LTD. The NO synthesis necessary for LTD(DHPG) induction occurred downstream of CB1 activation as ACEA-evoked LTD was also abolished by NL-Arg. These findings are relevant for the pathophysiology of PD, as they link the overactivation of group I mGluRs and striatal NO production.
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Affiliation(s)
- O A Sergeeva
- Department of Neurophysiology, Heinrich-Heine-University, D-40001, Dusseldorf, Germany.
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43
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Ferré S, Agnati LF, Ciruela F, Lluis C, Woods AS, Fuxe K, Franco R. Neurotransmitter receptor heteromers and their integrative role in 'local modules': the striatal spine module. BRAIN RESEARCH REVIEWS 2007; 55:55-67. [PMID: 17408563 PMCID: PMC2039920 DOI: 10.1016/j.brainresrev.2007.01.007] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 01/17/2007] [Accepted: 01/18/2007] [Indexed: 12/01/2022]
Abstract
'Local module' is a fundamental functional unit of the central nervous system that can be defined as the minimal portion of one or more neurons and/or one or more glial cells that operates as an independent integrative unit. This review focuses on the importance of neurotransmitter receptor heteromers for the operation of local modules. To illustrate this, we use the striatal spine module (SSM), comprised of the dendritic spine of the medium spiny neuron (MSN), its glutamatergic and dopaminergic terminals and astroglial processes. The SSM is found in the striatum, and although aspects such as neurotransmitters and receptors will be specific to the SSM, some general principles should apply to any local module in the brain. The analysis of some of the receptor heteromers in the SSM shows that receptor heteromerization is associated with particular elaborated functions in this local module. Adenosine A(2A) receptor-dopamine D(2) receptor-glutamate metabotropic mGlu(5) receptor heteromers are located adjacent to the glutamatergic synapse of the dendritic spine of the enkephalin MSN, and their cross-talk within the receptor heteromers helps to modulate postsynaptic plastic changes at the glutamatergic synapse. A(1) receptor-A(2A) receptor heteromers are found in the glutamatergic terminals and the molecular cross-talk between the two receptors in the heteromer helps to modulate glutamate release. Finally, dopamine D(2) receptor-non-alpha(7) nicotinic acetylcholine receptor heteromers, which are located in dopaminergic terminals, introduce the new concept of autoreceptor heteromer.
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Affiliation(s)
- Sergi Ferré
- Behavioral Neuroscience Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Department of Health and Human Services, Nathan Shock Drive, Baltimore, MD 21224, USA.
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44
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Group I mGluRs and long-term depression: potential roles in addiction? Mol Neurobiol 2007; 36:232-44. [PMID: 17955198 DOI: 10.1007/s12035-007-0037-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2006] [Accepted: 01/10/2007] [Indexed: 01/16/2023]
Abstract
Addiction is an enormous societal problem. A number of recent studies have focused on adaptations at glutamatergic synapses that may play a role in the behavioral responses to drugs of abuse. These studies have largely focused on NMDA receptor-dependent forms of synaptic plasticity such as NMDA receptor-dependent long-term potentiation (LTP) and long-term depression (LTD). A growing body of evidence, however, suggests that metabotropic glutamate receptors (mGluRs) also play important roles in the behavioral responses to drugs of abuse and participate in producing synaptic plasticity at glutamate synapses. In this review, we focus first on the evidence supporting a role for mGluRs in addiction and then on the properties of mGluR-dependent forms of synaptic plasticity, focusing in particular on Gq-linked receptor-induced LTD.
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Centonze D, Rossi S, Prosperetti C, Gasperi V, De Chiara V, Bari M, Tscherter A, Febbraro F, Bernardi G, Maccarrone M. Endocannabinoids limit metabotropic glutamate 5 receptor-mediated synaptic inhibition of striatal principal neurons. Mol Cell Neurosci 2007; 35:302-10. [PMID: 17434747 DOI: 10.1016/j.mcn.2007.03.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2006] [Revised: 03/07/2007] [Accepted: 03/08/2007] [Indexed: 11/27/2022] Open
Abstract
Synaptic transmission in the striatum is regulated by metabotropic glutamate (mGlu) receptors through pre- and postsynaptic mechanisms. We investigated the involvement of mGlu 1 and 5 receptors in the control of both excitatory and inhibitory transmission in the striatum. The mGlu 1 and 5 receptor agonist 3,5-DHPG failed to affect glutamate transmission, while it caused a biphasic effect on GABA transmission, characterized by early increase and late decrease in the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) recorded from striatal principal neurons. Both mGlu 1 and 5 receptors were involved in the early response to 3,5-DHPG, through membrane depolarization of striatal GABAergic interneurons and action potential generation. The 3,5-DHPG-mediated late depression of inhibitory inputs to striatal principal neurons was conversely secondary to mGlu 5 receptor activation and subsequent endocannabinoid release. In conclusion, we have identified an mGlu-dependent mechanism of GABA transmission regulation of potential relevance for physiological neuronal activity.
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Affiliation(s)
- Diego Centonze
- Clinica Neurologica, Dipartimento di Neuroscienze, Università Tor Vergata, Rome, Italy.
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46
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El-Kouhen O, Lehto SG, Pan JB, Chang R, Baker SJ, Zhong C, Hollingsworth PR, Mikusa JP, Cronin EA, Chu KL, McGaraughty SP, Uchic ME, Miller LN, Rodell NM, Patel M, Bhatia P, Mezler M, Kolasa T, Zheng GZ, Fox GB, Stewart AO, Decker MW, Moreland RB, Brioni JD, Honore P. Blockade of mGluR1 receptor results in analgesia and disruption of motor and cognitive performances: effects of A-841720, a novel non-competitive mGluR1 receptor antagonist. Br J Pharmacol 2006; 149:761-74. [PMID: 17016515 PMCID: PMC2014656 DOI: 10.1038/sj.bjp.0706877] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE To further assess the clinical potential of the blockade of metabotropic glutamate receptors (mGluR1) for the treatment of pain. EXPERIMENTAL APPROACH We characterized the effects of A-841720, a novel, potent and non-competitive mGluR1 antagonist in models of pain and of motor and cognitive function. KEY RESULTS At recombinant human and native rat mGluR1 receptors, A-841720 inhibited agonist-induced calcium mobilization, with IC50 values of 10.7+/-3.9 and 1.0 +/- 0.2 nM, respectively, while showing selectivity over other mGluR receptors, in addition to other neurotransmitter receptors, ion channels, and transporters. Intraperitoneal injection of A-841720 potently reduced complete Freund's adjuvant-induced inflammatory pain (ED50 = 23 micromol kg(-1)) and monoiodoacetate-induced joint pain (ED50 = 43 micromol kg(-1)). A-841720 also decreased mechanical allodynia observed in both the sciatic nerve chronic constriction injury and L5-L6 spinal nerve ligation (SNL) models of neuropathic pain (ED50 = 28 and 27 micromol kg(-1), respectively). Electrophysiological studies demonstrated that systemic administration of A-841720 in SNL animals significantly reduced evoked firing in spinal wide dynamic range neurons. Significant motor side effects were observed at analgesic doses and A-841720 also impaired cognitive function in the Y-maze and the Water Maze tests. CONCLUSIONS AND IMPLICATIONS The analgesic effects of a selective mGluR1 receptor antagonist are associated with motor and cognitive side effects. The lack of separation between efficacy and side effects in pre-clinical models indicates that mGluR1 antagonism may not provide an adequate therapeutic window for the development of such antagonists as novel analgesic agents in humans.
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Affiliation(s)
- O El-Kouhen
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - S G Lehto
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - J B Pan
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - R Chang
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - S J Baker
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - C Zhong
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - P R Hollingsworth
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - J P Mikusa
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - E A Cronin
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - K L Chu
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - S P McGaraughty
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - M E Uchic
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - L N Miller
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - N M Rodell
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - M Patel
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - P Bhatia
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - M Mezler
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Ludwigshafen, Germany
| | - T Kolasa
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - G Z Zheng
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - G B Fox
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - A O Stewart
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - M W Decker
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - R B Moreland
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - J D Brioni
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
| | - P Honore
- Neuroscience Research, Global Pharmaceutical Research Division, Abbott Laboratories Abbott Park, IL, USA
- Author for correspondence:
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47
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Gerdjikov TV, Beninger RJ. Place preference induced by nucleus accumbens amphetamine is impaired by local blockade of Group II metabotropic glutamate receptors in rats. BMC Neurosci 2006; 7:43. [PMID: 16734896 PMCID: PMC1501036 DOI: 10.1186/1471-2202-7-43] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2006] [Accepted: 05/30/2006] [Indexed: 11/10/2022] Open
Abstract
Background The nucleus accumbens (NAc) plays a critical role in amphetamine-produced conditioned place preference (CPP). In previous studies, NAc basal and amphetamine-produced DA transmission was altered by Group II mGluR agents. We tested whether NAc amphetamine CPP depends on Group II mGluR transmission. Results NAc injections (0.5 μl/side) of the Group II mGluR antagonist (2 S)- a-ethylglutamic acid (EGLU: 0.01–0.8 μg but not 0.001 μg) impaired CPP. The drug did not block the acute locomotor effect of amphetamine. Conclusion Results suggest that Group II mGluRs may be necessary for the establishment of NAc amphetamine-produced CPP. These receptors may also mediate other forms of reward-related learning dependent on this structure.
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Affiliation(s)
- Todor V Gerdjikov
- Department of Psychology, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Richard J Beninger
- Department of Psychology, Queen's University, Kingston, ON K7L 3N6, Canada
- Department of Psychiatry, Queen's University, Kingston, ON K7L 3N6, Canada
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48
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Bonsi P, Cuomo D, Picconi B, Sciamanna G, Tscherter A, Tolu M, Bernardi G, Calabresi P, Pisani A. Striatal metabotropic glutamate receptors as a target for pharmacotherapy in Parkinson’s disease. Amino Acids 2006; 32:189-95. [PMID: 16715415 DOI: 10.1007/s00726-006-0320-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2005] [Accepted: 01/12/2006] [Indexed: 11/26/2022]
Abstract
Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopamine (DA)-containing neurons in the substantia nigra pars compacta (SNc). The symptoms are resting tremor, slowness of movement, rigidity and postural instability. Evidence that an imbalance between dopaminergic and cholinergic transmission takes place within the striatum led to the utilization of DA precursors, DA receptor agonists and anticholinergic drugs in the symptomatic therapy of PD. However, upon disease progression the therapy becomes less effective and debilitating effects such as dyskinesias and motor fluctuations appear. Hence, the need for the development of alternative therapeutic strategies has emerged. Several observations in different experimental models of PD suggest that blockade of excitatory amino acid transmission exerts antiparkinsonian effects. In particular, recent studies have focused on metabotropic glutamate receptors (mGluRs). Drugs acting on group I and II mGluRs have indeed been proven useful in ameliorating the parkinsonian symptoms in animal models of PD and therefore might represent promising therapeutic targets. This beneficial effect could be due to the reduction of both glutamatergic and cholinergic transmission. A novel target for drugs acting on mGluRs in PD therapy might be represented by striatal cholinergic interneurons. Indeed, the activation of mGluR2, highly expressed on this cell type, is able to reduce calcium-dependent plateau potentials by interfering with somato-dendritic N-type calcium channel activity, in turn reducing ACh release in the striatum. Similarly, the blockade of both group I mGluR subtypes reduces cholinergic interneuron excitability, and decreases striatal ACh release. Thus, targeting mGluRs located onto cholinergic interneurons might result in a beneficial pharmacological effect in the parkinsonian state.
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Affiliation(s)
- P Bonsi
- Laboratorio di Neurofisiologia, I.R.C.C.S. Fondazione Santa Lucia - C.E.R.C., European Brain Research Institute, Rome, Italy
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Page G, Khidir FAL, Pain S, Barrier L, Fauconneau B, Guillard O, Piriou A, Hugon J. Group I metabotropic glutamate receptors activate the p70S6 kinase via both mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK 1/2) signaling pathways in rat striatal and hippocampal synaptoneurosomes. Neurochem Int 2006; 49:413-21. [PMID: 16549223 DOI: 10.1016/j.neuint.2006.01.020] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Revised: 01/18/2006] [Accepted: 01/19/2006] [Indexed: 10/24/2022]
Abstract
Group I metabotropic glutamate receptors (mGluRs) have been demonstrated to play a role in synaptic plasticity via a rapamycin-sensitive mRNA translation signaling pathway. Various growth factors can stimulate this pathway, leading to the phosphorylation and activation of mammalian target of rapamycin (mTOR), a serine/threonine protein kinase that modulates the activity of several translation regulatory factors, such as p70S6 kinase. However, little is known about the cellular and molecular mechanisms that bring the plastic changes of synaptic transmission after stimulation of group I mGluRs. Here, we investigated the role of the mTOR-p70S6K and the ERK1/2-p70S6K pathways in rat striatal and hippocampal synaptoneurosomes after group I mGluR stimulation. Our findings show that (S)-3,5-dihydroxyphenylglycine (DHPG) increases significantly the activation of mTOR and p70S6K (Thr389, controlled by mTOR) in both brain areas. The mTOR activation is dose-dependent and requires the stimulation of mGluR1 subtype receptors as for the p70S6K activation observed in striatum and hippocampus. In addition, the p70S6K (Thr421/Ser424) activation via the ERK1/2 activation is increased and involved also mGluR1 receptors. These results demonstrate that group I mGluRs are coupled to mTOR-p70S6K and ERK1/2-p70S6K pathways in striatal and hippocampal synaptoneurosomes. The translational factor p70S6K could be involved in the group I mGluRs-modulated synaptic efficacy.
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Affiliation(s)
- Guylène Page
- Research Group on Brain Aging (EA 3808), University of Poitiers, Cedex, France.
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Dhami GK, Ferguson SSG. Regulation of metabotropic glutamate receptor signaling, desensitization and endocytosis. Pharmacol Ther 2006; 111:260-71. [PMID: 16574233 DOI: 10.1016/j.pharmthera.2005.01.008] [Citation(s) in RCA: 155] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2005] [Accepted: 01/25/2005] [Indexed: 11/24/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) comprise a unique family of G protein-coupled receptors (GPCR) that can be classified into 3 groups based on G protein coupling specificity and sequence similarity. Group I mGluRs (mGluR1 and mGluR5) are coupled to the heterotrimeric G protein Galpha(q/11) and trigger the release of calcium from intracellular stores. In the present review, we discuss the molecular mechanisms involved in the desensitization and endocytosis of group I mGluRs. Group I mGluRs desensitize in response to both second-messenger-dependent protein kinases and G protein-coupled receptor kinases (GRK). However, GRK2-mediated mGluR1 desensitization appears to be both phosphorylation- and beta-arrestin-independent. In addition to GRK-mediated uncoupling of mGluRs from heterotrimeric G proteins, the huntingtin-interacting protein, optineurin, also contributes to mGluR1 and mGluR5 desensitization. The G protein-uncoupling activity of optineurin appears to be facilitated by the presence of polyglutamine-expanded mutant huntingtin but not wild-type huntingtin. Group I mGluRs also undergo both agonist-dependent and -independent endocytosis in both heterologous cell expression systems and primary neuronal cultures. The present review overviews the current understanding of the contribution of second messenger-dependent protein kinases, beta-arrestins and a novel Ral/phospholipase D2 (PLD2)-mediated endocytic pathway to the regulation of Group I mGluR endocytosis. Overall, the regulation of Group I mGluR desensitization and endocytosis appears to be mediated by the same molecular intermediates as have been described for more typical GPCR such as the beta(2)-adrenergic receptor. However, there appears to be subtle, but important, differences in the mechanisms by which these intermediates are employed to regulate Group I mGluR desensitization and endocytosis.
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Affiliation(s)
- Gurpreet K Dhami
- Cell Biology Research Group, Robarts Research Institute, London, Ontario, Canada N6A 5K8
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