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Fujiyama F, Karube F, Hirai Y. Globus pallidus is not independent from striatal direct pathway neurons: an up-to-date review. Mol Brain 2024; 17:34. [PMID: 38849935 PMCID: PMC11157709 DOI: 10.1186/s13041-024-01107-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Accepted: 05/28/2024] [Indexed: 06/09/2024] Open
Abstract
Striatal projection neurons, which are classified into two groups-direct and indirect pathway neurons, play a pivotal role in our understanding of the brain's functionality. Conventional models propose that these two pathways operate independently and have contrasting functions, akin to an "accelerator" and "brake" in a vehicle. This analogy further elucidates how the depletion of dopamine neurons in Parkinson's disease can result in bradykinesia. However, the question arises: are these direct and indirect pathways truly autonomous? Despite being distinct types of neurons, their interdependence cannot be overlooked. Single-neuron tracing studies employing membrane-targeting signals have shown that the majority of direct pathway neurons terminate not only in the output nuclei, but also in the external segment of the globus pallidus (GP in rodents), a relay nucleus of the indirect pathway. Recent studies have unveiled the existence of arkypallidal neurons, which project solely to the striatum, in addition to prototypic neurons. This raises the question of which type of GP neurons receive these striatal axon collaterals. Our morphological and electrophysiological experiments showed that the striatal direct pathway neurons may affect prototypic neurons via the action of substance P on neurokinin-1 receptors. Conversely, another research group has reported that direct pathway neurons inhibit arkypallidal neurons via GABA. Regardless of the neurotransmitter involved, it can be concluded that the GP is not entirely independent of direct pathway neurons. This review article underscores the intricate interplay between different neuronal pathways and challenges the traditional understanding of their independence.
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Affiliation(s)
- Fumino Fujiyama
- Laboratory of Cytology and Histology, Faculty of Medicine, Hokkaido University, Sapporo, Japan.
| | - Fuyuki Karube
- Laboratory of Cytology and Histology, Faculty of Medicine, Hokkaido University, Sapporo, Japan.
| | - Yasuharu Hirai
- Laboratory of Cytology and Histology, Faculty of Medicine, Hokkaido University, Sapporo, Japan
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Jones JA, Peña J, Likhotvorik RI, Garcia-Castañeda BI, Wilson CJ. Comparison of unitary synaptic currents generated by indirect and direct pathway neurons of the mouse striatum. J Neurophysiol 2024; 131:914-936. [PMID: 38596834 DOI: 10.1152/jn.00066.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 04/05/2024] [Accepted: 04/07/2024] [Indexed: 04/11/2024] Open
Abstract
Two subtypes of striatal spiny projection neurons, iSPNs and dSPNs, whose axons form the "indirect" and "direct" pathways of the basal ganglia, respectively, both make synaptic connections in the external globus pallidus (GPe) but are usually found to have different effects on behavior. Activation of the terminal fields of iSPNs or dSPNs generated compound currents in almost all GPe neurons. To determine whether iSPNs and dSPNs have the same or different effects on pallidal neurons, we studied the unitary synaptic currents generated in GPe neurons by action potentials in single striatal neurons. We used optogenetic excitation to elicit repetitive firing in a small number of nearby SPNs, producing sparse barrages of inhibitory postsynaptic currents (IPSCs) in GPe neurons. From these barrages, we isolated sequences of IPSCs with similar time courses and amplitudes, which presumably arose from the same SPN. There was no difference between the amplitudes of unitary IPSCs generated by the indirect and direct pathways. Most unitary IPSCs were small, but a subset from each pathway were much larger. To determine the effects of these unitary synaptic currents on the action potential firing of GPe neurons, we drove SPNs to fire as before and recorded the membrane potential of GPe neurons. Large unitary potentials from iSPNs and dSPNs perturbed the spike timing of GPe neurons in a similar way. Most SPN-GPe neuron pairs are weakly connected, but a subset of pairs in both pathways are strongly connected.NEW & NOTEWORTHY This is the first study to record the synaptic currents generated by single identified direct or indirect pathway striatal neurons on single pallidal neurons. Each GPe neuron receives synaptic inputs from both pathways. Most striatal neurons generate small synaptic currents that become influential when occurring together, but a few are powerful enough to be individually influential.
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Affiliation(s)
- James A Jones
- Department of Neuroscience, Developmental and Regenerative Biology, University of Texas at San Antonio, San Antonio, Texas, United States
- Vollum Institute, Oregon Health and Science University, Portland, Oregon, United States
| | - Jacob Peña
- Department of Neuroscience, Developmental and Regenerative Biology, University of Texas at San Antonio, San Antonio, Texas, United States
| | - Rostislav I Likhotvorik
- Department of Neuroscience, Developmental and Regenerative Biology, University of Texas at San Antonio, San Antonio, Texas, United States
| | - Brandon I Garcia-Castañeda
- Department of Neuroscience, Developmental and Regenerative Biology, University of Texas at San Antonio, San Antonio, Texas, United States
| | - Charles J Wilson
- Department of Neuroscience, Developmental and Regenerative Biology, University of Texas at San Antonio, San Antonio, Texas, United States
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Giossi C, Rubin JE, Gittis A, Verstynen T, Vich C. Rethinking the external globus pallidus and information flow in cortico-basal ganglia-thalamic circuits. Eur J Neurosci 2024. [PMID: 38659055 DOI: 10.1111/ejn.16348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 02/27/2024] [Accepted: 03/19/2024] [Indexed: 04/26/2024]
Abstract
For decades, the external globus pallidus (GPe) has been viewed as a passive way-station in the indirect pathway of the cortico-basal ganglia-thalamic (CBGT) circuit, sandwiched between striatal inputs and basal ganglia outputs. According to this model, one-way descending striatal signals in the indirect pathway amplify the suppression of downstream thalamic nuclei by inhibiting GPe activity. Here, we revisit this assumption, in light of new and emerging work on the cellular complexity, connectivity and functional role of the GPe in behaviour. We show how, according to this new circuit-level logic, the GPe is ideally positioned for relaying ascending and descending control signals within the basal ganglia. Focusing on the problem of inhibitory control, we illustrate how this bidirectional flow of information allows for the integration of reactive and proactive control mechanisms during action selection. Taken together, this new evidence points to the GPe as being a central hub in the CBGT circuit, participating in bidirectional information flow and linking multifaceted control signals to regulate behaviour.
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Affiliation(s)
- Cristina Giossi
- Departament de Ciències Matemàtiques i Informàtica, Universitat de les Illes Balears, Palma, Illes Balears, Spain
- Institute of Applied Computing and Community Code, Universitat de les Illes Balears, Palma, Illes Balears, Spain
| | - Jonathan E Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Aryn Gittis
- Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Department of Biology, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
| | - Timothy Verstynen
- Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Department of Psychology & Neuroscience Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
| | - Catalina Vich
- Departament de Ciències Matemàtiques i Informàtica, Universitat de les Illes Balears, Palma, Illes Balears, Spain
- Institute of Applied Computing and Community Code, Universitat de les Illes Balears, Palma, Illes Balears, Spain
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Giossi C, Rubin JE, Gittis A, Verstynen T, Vich C. Rethinking the external globus pallidus and information flow in cortico-basal ganglia-thalamic circuits. ARXIV 2023:arXiv:2312.14267v2. [PMID: 38196745 PMCID: PMC10775352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 01/11/2024]
Abstract
For decades the external globus pallidus (GPe) has been viewed as a passive way-station in the indirect pathway of the cortico-basal ganglia-thalamic (CBGT) circuit, sandwiched between striatal inputs and basal ganglia outputs. According to this model, one-way descending striatal signals in the indirect pathway amplify the suppression of downstream thalamic nuclei by inhibiting GPe activity. Here we revisit this assumption, in light of new and emerging work on the cellular complexity, connectivity, and functional role of the GPe in behavior. We show how, according to this new circuit-level logic, the GPe is ideally positioned for relaying ascending and descending control signals within the basal ganglia. Focusing on the problem of inhibitory control, we illustrate how this bidirectional flow of information allows for the integration of reactive and proactive control mechanisms during action selection. Taken together, this new evidence points to the GPe as being a central hub in the CBGT circuit, participating in bidirectional information flow and linking multifaceted control signals to regulate behavior.
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Affiliation(s)
- Cristina Giossi
- Departament de Matemàtiques i Informàtica, Universitat de les Illes Balears, Palma, Spain
- Institute of Applied Computing and Community Code, Palma, Spain
| | - Jonathan E Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Center for the Neural Basis of Cognition, Pittsburgh, Carnegie Mellon University, Pennsylvania, United States of America
| | - Aryn Gittis
- Center for the Neural Basis of Cognition, Pittsburgh, Carnegie Mellon University, Pennsylvania, United States of America
- Department of Biology, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America
| | - Timothy Verstynen
- Center for the Neural Basis of Cognition, Pittsburgh, Carnegie Mellon University, Pennsylvania, United States of America
- Department of Psychology & Neuroscience Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America
| | - Catalina Vich
- Departament de Matemàtiques i Informàtica, Universitat de les Illes Balears, Palma, Spain
- Institute of Applied Computing and Community Code, Palma, Spain
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