151
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Sitko AA, Goodrich LV. Making sense of neural development by comparing wiring strategies for seeing and hearing. Science 2021; 371:eaaz6317. [PMID: 33414193 PMCID: PMC8034811 DOI: 10.1126/science.aaz6317] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The ability to perceive and interact with the world depends on a diverse array of neural circuits specialized for carrying out specific computations. Each circuit is assembled using a relatively limited number of molecules and common developmental steps, from cell fate specification to activity-dependent synaptic refinement. Given this shared toolkit, how do individual circuits acquire their characteristic properties? We explore this question by comparing development of the circuitry for seeing and hearing, highlighting a few examples where differences in each system's sensory demands necessitate different developmental strategies.
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Affiliation(s)
- A A Sitko
- Department of Neurobiology, Harvard Medical School, Boston, MA, USA
| | - L V Goodrich
- Department of Neurobiology, Harvard Medical School, Boston, MA, USA.
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152
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Yamagata M, Yan W, Sanes JR. A cell atlas of the chick retina based on single-cell transcriptomics. eLife 2021; 10:e63907. [PMID: 33393903 PMCID: PMC7837701 DOI: 10.7554/elife.63907] [Citation(s) in RCA: 72] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 01/01/2021] [Indexed: 12/14/2022] Open
Abstract
Retinal structure and function have been studied in many vertebrate orders, but molecular characterization has been largely confined to mammals. We used single-cell RNA sequencing (scRNA-seq) to generate a cell atlas of the chick retina. We identified 136 cell types plus 14 positional or developmental intermediates distributed among the six classes conserved across vertebrates - photoreceptor, horizontal, bipolar, amacrine, retinal ganglion, and glial cells. To assess morphology of molecularly defined types, we adapted a method for CRISPR-based integration of reporters into selectively expressed genes. For Müller glia, we found that transcriptionally distinct cells were regionally localized along the anterior-posterior, dorsal-ventral, and central-peripheral retinal axes. We also identified immature photoreceptor, horizontal cell, and oligodendrocyte types that persist into late embryonic stages. Finally, we analyzed relationships among chick, mouse, and primate retinal cell classes and types. Our results provide a foundation for anatomical, physiological, evolutionary, and developmental studies of the avian visual system.
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Affiliation(s)
- Masahito Yamagata
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
| | - Wenjun Yan
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
| | - Joshua R Sanes
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard UniversityCambridgeUnited States
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153
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Optimized culture of retinal ganglion cells and amacrine cells from adult mice. PLoS One 2020; 15:e0242426. [PMID: 33284815 PMCID: PMC7721191 DOI: 10.1371/journal.pone.0242426] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2020] [Accepted: 11/02/2020] [Indexed: 01/22/2023] Open
Abstract
Cell culture is widely utilized to study the cellular and molecular biology of different neuronal cell populations. Current techniques to study enriched neurons in vitro are primarily limited to embryonic/neonatal animals and induced pluripotent stem cells (iPSCs). Although the use of these cultures is valuable, the accessibility of purified primary adult neuronal cultures would allow for improved assessment of certain neurological diseases and pathways at the cellular level. Using a modified 7-step immunopanning technique to isolate for retinal ganglion cells (RGCs) and amacrine cells (ACs) from adult mouse retinas, we have successfully developed a model of neuronal culture that maintains for at least one week. Isolations of Thy1.2+ cells are enriched for RGCs, with the isolation cell yield being congruent to the theoretical yield of RGCs in a mouse retina. ACs of two different populations (CD15+ and CD57+) can also be isolated. The populations of these three adult neurons in culture are healthy, with neurite outgrowths in some cases greater than 500μm in length. Optimization of culture conditions for RGCs and CD15+ cells revealed that neuronal survival and the likelihood of neurite outgrowth respond inversely to different culture media. Serially diluted concentrations of puromycin decreased cultured adult RGCs in a dose-dependent manner, demonstrating the potential usefulness of these adult neuronal cultures in screening assays. This novel culture system can be used to model in vivo neuronal behaviors. Studies can now be expanded in conjunction with other methodologies to study the neurobiology of function, aging, and diseases.
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154
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Tsuboi A. LRR-Containing Oncofetal Trophoblast Glycoprotein 5T4 Shapes Neural Circuits in Olfactory and Visual Systems. Front Mol Neurosci 2020; 13:581018. [PMID: 33192298 PMCID: PMC7655536 DOI: 10.3389/fnmol.2020.581018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 09/22/2020] [Indexed: 01/19/2023] Open
Abstract
In mammals, the sensory experience can regulate the development of various brain structures, including the cortex, hippocampus, retina, and olfactory bulb (OB). Odor experience-evoked neural activity drives the development of dendrites on excitatory projection neurons in the OB, such as mitral and tufted cells, as well as inhibitory interneurons. OB interneurons are generated continuously in the subventricular zone and differentiate into granule cells (GCs) and periglomerular cells (PGCs). However, it remains unknown what role each type of OB interneuron plays in controlling olfactory behaviors. Recent studies showed that among the various types of OB interneurons, a subtype of GCs expressing oncofetal trophoblast glycoprotein 5T4 is required for simple odor detection and discrimination behaviors. Mouse 5T4 (also known as Tpbg) is a type I membrane glycoprotein whose extracellular domain contains seven leucine-rich repeats (LRRs) sandwiched between characteristic LRR-N and LRR-C regions. Recently, it was found that the developmental expression of 5T4 increases dramatically in the retina just before eye-opening. Single-cell transcriptomics further suggests that 5T4 is involved in the development and maintenance of functional synapses in a subset of retinal interneurons, including rod bipolar cells (RBCs) and amacrine cells (ACs). Collectively, 5T4, expressed in interneurons of the OB and retina, plays a key role in sensory processing in the olfactory and visual systems.
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Affiliation(s)
- Akio Tsuboi
- Graduate School of Frontier Biosciences, Osaka University, Suita, Japan
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155
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Egger V, Diamond JS. A17 Amacrine Cells and Olfactory Granule Cells: Parallel Processors of Early Sensory Information. Front Cell Neurosci 2020; 14:600537. [PMID: 33250720 PMCID: PMC7674606 DOI: 10.3389/fncel.2020.600537] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 10/05/2020] [Indexed: 12/16/2022] Open
Abstract
Neurons typically receive synaptic input in their dendritic arbor, integrate inputs in their soma, and send output action potentials through their axon, following Cajal's law of dynamic polarization. Two notable exceptions are retinal amacrine cells and olfactory granule cells (GCs), which flout Cajal's edict by providing synaptic output from the same dendrites that collect synaptic input. Amacrine cells, a diverse cell class comprising >60 subtypes, employ various dendritic input/output strategies, but A17 amacrine cells (A17s) in particular share further interesting functional characteristics with GCs: both receive excitatory synaptic input from neurons in the primary glutamatergic pathway and return immediate, reciprocal feedback via GABAergic inhibitory synapses to the same synaptic terminals that provided input. Both neurons thereby process signals locally within their dendrites, shaping many parallels, signaling pathways independently. The similarities between A17s and GCs cast into relief striking differences that may indicate distinct processing roles within their respective circuits: First, they employ partially dissimilar molecular mechanisms to transform excitatory input into inhibitory output; second, GCs fire action potentials, whereas A17s do not. Third, GC signals may be influenced by cortical feedback, whereas the mammalian retina receives no such retrograde input. Finally, A17s constitute just one subtype within a diverse class that is specialized in a particular task, whereas the more homogeneous GCs may play more diverse signaling roles via multiple processing modes. Here, we review these analogies and distinctions between A17 amacrine cells and granule cells, hoping to gain further insight into the operating principles of these two sensory circuits.
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Affiliation(s)
- Veronica Egger
- Department of Neurophysiology, Institute of Zoology, Universität Regensburg, Regensburg, Germany
| | - Jeffrey S. Diamond
- Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
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156
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Kim T, Shen N, Hsiang JC, Johnson KP, Kerschensteiner D. Dendritic and parallel processing of visual threats in the retina control defensive responses. SCIENCE ADVANCES 2020; 6:6/47/eabc9920. [PMID: 33208370 PMCID: PMC7673819 DOI: 10.1126/sciadv.abc9920] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 10/01/2020] [Indexed: 05/03/2023]
Abstract
Approaching predators cast expanding shadows (i.e., looming) that elicit innate defensive responses in most animals. Where looming is first detected and how critical parameters of predatory approaches are extracted are unclear. In mice, we identify a retinal interneuron (the VG3 amacrine cell) that responds robustly to looming, but not to related forms of motion. Looming-sensitive calcium transients are restricted to a specific layer of the VG3 dendrite arbor, which provides glutamatergic input to two ganglion cells (W3 and OFFα). These projection neurons combine shared excitation with dissimilar inhibition to signal approach onset and speed, respectively. Removal of VG3 amacrine cells reduces the excitation of W3 and OFFα ganglion cells and diminishes defensive responses of mice to looming without affecting other visual behaviors. Thus, the dendrites of a retinal interneuron detect visual threats, divergent circuits downstream extract critical threat parameters, and these retinal computations initiate an innate survival behavior.
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Affiliation(s)
- T Kim
- John F. Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA
- Graduate Program in Neuroscience, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - N Shen
- John F. Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - J-C Hsiang
- John F. Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA
- Graduate Program in Neuroscience, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - K P Johnson
- John F. Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA
- Graduate Program in Neuroscience, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - D Kerschensteiner
- John F. Hardesty, MD Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA.
- Department of Neurosciences, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Hope Center for Neurological Disorders, Washington University School of Medicine, Saint Louis, MO 63110, USA
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157
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Kerstein PC, Leffler J, Sivyer B, Taylor WR, Wright KM. Gbx2 Identifies Two Amacrine Cell Subtypes with Distinct Molecular, Morphological, and Physiological Properties. Cell Rep 2020; 33:108382. [PMID: 33207201 PMCID: PMC7713908 DOI: 10.1016/j.celrep.2020.108382] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 08/21/2020] [Accepted: 10/22/2020] [Indexed: 01/21/2023] Open
Abstract
Our understanding of nervous system function is limited by our ability to identify and manipulate neuronal subtypes within intact circuits. We show that the Gbx2CreERT2-IRES-EGFP mouse line labels two amacrine cell (AC) subtypes in the mouse retina that have distinct morphological, physiological, and molecular properties. Using a combination of RNA-seq, genetic labeling, and patch clamp recordings, we show that one subtype is GABAergic that receives excitatory input from On bipolar cells. The other population is a non-GABAergic, non-glycinergic (nGnG) AC subtype that lacks the expression of standard neurotransmitter markers. Gbx2+ nGnG ACs have smaller, asymmetric dendritic arbors that receive excitatory input from both On and Off bipolar cells. Gbx2+ nGnG ACs also exhibit spatially restricted tracer coupling to bipolar cells (BCs) through gap junctions. This study identifies a genetic tool for investigating the two distinct AC subtypes, and it provides a model for studying synaptic communication and visual circuit function. Investigations into neural circuit development and function are limited by the lack of genetic tools to label and perturb individual neuronal subtypes. Using the Gbx2CreERT2 mouse line, Kerstein et al. identify two amacrine cell subtypes in the mouse retina and explore their distinct molecular, morphological, and physiological characteristics.
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Affiliation(s)
- Patrick C Kerstein
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA
| | - Joseph Leffler
- School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Neuroscience Graduate Program, Oregon Health and Science University, Portland, OR 97239, USA
| | - Benjamin Sivyer
- Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science University, Portland, OR 97239, USA; Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, OR 97239, USA
| | - W Rowland Taylor
- School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Kevin M Wright
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA; Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science University, Portland, OR 97239, USA.
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158
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Heterogeneous Presynaptic Distribution of Munc13 Isoforms at Retinal Synapses and Identification of an Unconventional Bipolar Cell Type with Dual Expression of Munc13 Isoforms: A Study Using Munc13-EXFP Knock-in Mice. Int J Mol Sci 2020; 21:ijms21217848. [PMID: 33105896 PMCID: PMC7660176 DOI: 10.3390/ijms21217848] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 10/19/2020] [Accepted: 10/20/2020] [Indexed: 12/19/2022] Open
Abstract
Munc13 isoforms are constituents of the presynaptic compartment of chemical synapses, where they govern important steps in preparing synaptic vesicles for exocytosis. The role of Munc13-1, -2 and -3 is well documented in brain neurons, but less is known about their function and distribution among the neurons of the retina and their conventional and ribbon-type chemical synapses. Here, we examined the retinae of Munc13-1-, -2-, and -3-EXFP knock-in (KI) mice with a combination of immunocytochemistry, physiology, and electron microscopy. We show that knock-in of Munc13-EXFP fusion proteins did not affect overall retinal anatomy or synapse structure, but slightly affected synaptic transmission. By labeling Munc13-EXFP KI retinae with specific antibodies against Munc13-1, -2 and -3, we found that unlike in the brain, most retinal synapses seem to operate with a single Munc13 isoform. A surprising exception to this rule was type 6 ON bipolar cells, which expressed two Munc13 isoforms in their synaptic terminals, ubMunc13-2 and Munc13-3. The results of this study provide an important basis for future studies on the contribution of Munc13 isoforms in visual signal processing in the mammalian retina.
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159
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Seifert M, Baden T, Osorio D. The retinal basis of vision in chicken. Semin Cell Dev Biol 2020; 106:106-115. [PMID: 32295724 DOI: 10.1016/j.semcdb.2020.03.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 03/31/2020] [Accepted: 03/31/2020] [Indexed: 12/20/2022]
Abstract
The Avian retina is far less known than that of mammals such as mouse and macaque, and detailed study is overdue. The chicken (Gallus gallus) has potential as a model, in part because research can build on developmental studies of the eye and nervous system. One can expect differences between bird and mammal retinas simply because whereas most mammals have three types of visual photoreceptor birds normally have six. Spectral pathways and colour vision are of particular interest, because filtering by oil droplets narrows cone spectral sensitivities and birds are probably tetrachromatic. The number of receptor inputs is reflected in the retinal circuitry. The chicken probably has four types of horizontal cell, there are at least 11 types of bipolar cell, often with bi- or tri-stratified axon terminals, and there is a high density of ganglion cells, which make complex connections in the inner plexiform layer. In addition, there is likely to be retinal specialisation, for example chicken photoreceptors and ganglion cells have separate peaks of cell density in the central and dorsal retina, which probably serve different types of behaviour.
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Affiliation(s)
- M Seifert
- Sussex Neuroscience, School of Life Sciences, University of Sussex, UK.
| | - T Baden
- Sussex Neuroscience, School of Life Sciences, University of Sussex, UK; Institute for Ophthalmic Research, University of Tuebingen, Germany
| | - D Osorio
- Sussex Neuroscience, School of Life Sciences, University of Sussex, UK
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160
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Maddox JW, Randall KL, Yadav RP, Williams B, Hagen J, Derr PJ, Kerov V, Della Santina L, Baker SA, Artemyev N, Hoon M, Lee A. A dual role for Ca v1.4 Ca 2+ channels in the molecular and structural organization of the rod photoreceptor synapse. eLife 2020; 9:e62184. [PMID: 32940604 PMCID: PMC7561352 DOI: 10.7554/elife.62184] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 09/09/2020] [Indexed: 02/06/2023] Open
Abstract
Synapses are fundamental information processing units that rely on voltage-gated Ca2+ (Cav) channels to trigger Ca2+-dependent neurotransmitter release. Cav channels also play Ca2+-independent roles in other biological contexts, but whether they do so in axon terminals is unknown. Here, we addressed this unknown with respect to the requirement for Cav1.4 L-type channels for the formation of rod photoreceptor synapses in the retina. Using a mouse strain expressing a non-conducting mutant form of Cav1.4, we report that the Cav1.4 protein, but not its Ca2+ conductance, is required for the molecular assembly of rod synapses; however, Cav1.4 Ca2+ signals are needed for the appropriate recruitment of postsynaptic partners. Our results support a model in which presynaptic Cav channels serve both as organizers of synaptic building blocks and as sources of Ca2+ ions in building the first synapse of the visual pathway and perhaps more broadly in the nervous system.
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Affiliation(s)
- J Wesley Maddox
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Kate L Randall
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Ravi P Yadav
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
| | - Brittany Williams
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Jussara Hagen
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Paul J Derr
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
| | - Vasily Kerov
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
| | - Luca Della Santina
- Department of Ophthalmology, University of California, San FranciscoSan FranciscoUnited States
| | - Sheila A Baker
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Department of Biochemistry, University of IowaIowa CityUnited States
- Department of OphthalmologyIowa CityUnited States
| | - Nikolai Artemyev
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Department of OphthalmologyIowa CityUnited States
| | - Mrinalini Hoon
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Department of Ophthalmology and Visual Science, University of Wisconsin-MadisonMadisonUnited States
| | - Amy Lee
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
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161
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Korshunov KS, Blakemore LJ, Trombley PQ. Illuminating and Sniffing Out the Neuromodulatory Roles of Dopamine in the Retina and Olfactory Bulb. Front Cell Neurosci 2020; 14:275. [PMID: 33110404 PMCID: PMC7488387 DOI: 10.3389/fncel.2020.00275] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 08/04/2020] [Indexed: 01/28/2023] Open
Abstract
In the central nervous system, dopamine is well-known as the neuromodulator that is involved with regulating reward, addiction, motivation, and fine motor control. Yet, decades of findings are revealing another crucial function of dopamine: modulating sensory systems. Dopamine is endogenous to subsets of neurons in the retina and olfactory bulb (OB), where it sharpens sensory processing of visual and olfactory information. For example, dopamine modulation allows the neural circuity in the retina to transition from processing dim light to daylight and the neural circuity in the OB to regulate odor discrimination and detection. Dopamine accomplishes these tasks through numerous, complex mechanisms in both neural structures. In this review, we provide an overview of the established and emerging research on these mechanisms and describe similarities and differences in dopamine expression and modulation of synaptic transmission in the retinas and OBs of various vertebrate organisms. This includes discussion of dopamine neurons’ morphologies, potential identities, and biophysical properties along with their contributions to circadian rhythms and stimulus-driven synthesis, activation, and release of dopamine. As dysregulation of some of these mechanisms may occur in patients with Parkinson’s disease, these symptoms are also discussed. The exploration and comparison of these two separate dopamine populations shows just how remarkably similar the retina and OB are, even though they are functionally distinct. It also shows that the modulatory properties of dopamine neurons are just as important to vision and olfaction as they are to motor coordination and neuropsychiatric/neurodegenerative conditions, thus, we hope this review encourages further research to elucidate these mechanisms.
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Affiliation(s)
- Kirill S Korshunov
- Department of Biological Science, Florida State University, Tallahassee, FL, United States.,Program in Neuroscience, Florida State University, Tallahassee, FL, United States
| | - Laura J Blakemore
- Department of Biological Science, Florida State University, Tallahassee, FL, United States.,Program in Neuroscience, Florida State University, Tallahassee, FL, United States
| | - Paul Q Trombley
- Department of Biological Science, Florida State University, Tallahassee, FL, United States.,Program in Neuroscience, Florida State University, Tallahassee, FL, United States
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162
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Imamura F, Ito A, LaFever BJ. Subpopulations of Projection Neurons in the Olfactory Bulb. Front Neural Circuits 2020; 14:561822. [PMID: 32982699 PMCID: PMC7485133 DOI: 10.3389/fncir.2020.561822] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 08/12/2020] [Indexed: 12/17/2022] Open
Abstract
Generation of neuronal diversity is a biological strategy widely used in the brain to process complex information. The olfactory bulb is the first relay station of olfactory information in the vertebrate central nervous system. In the olfactory bulb, axons of the olfactory sensory neurons form synapses with dendrites of projection neurons that transmit the olfactory information to the olfactory cortex. Historically, the olfactory bulb projection neurons have been classified into two populations, mitral cells and tufted cells. The somata of these cells are distinctly segregated within the layers of the olfactory bulb; the mitral cells are located in the mitral cell layer while the tufted cells are found in the external plexiform layer. Although mitral and tufted cells share many morphological, biophysical, and molecular characteristics, they differ in soma size, projection patterns of their dendrites and axons, and odor responses. In addition, tufted cells are further subclassified based on the relative depth of their somata location in the external plexiform layer. Evidence suggests that different types of tufted cells have distinct cellular properties and play different roles in olfactory information processing. Therefore, mitral and different types of tufted cells are considered as starting points for parallel pathways of olfactory information processing in the brain. Moreover, recent studies suggest that mitral cells also consist of heterogeneous subpopulations with different cellular properties despite the fact that the mitral cell layer is a single-cell layer. In this review, we first compare the morphology of projection neurons in the olfactory bulb of different vertebrate species. Next, we explore the similarities and differences among subpopulations of projection neurons in the rodent olfactory bulb. We also discuss the timing of neurogenesis as a factor for the generation of projection neuron heterogeneity in the olfactory bulb. Knowledge about the subpopulations of olfactory bulb projection neurons will contribute to a better understanding of the complex olfactory information processing in higher brain regions.
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Affiliation(s)
- Fumiaki Imamura
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA, United States
| | - Ayako Ito
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA, United States
| | - Brandon J LaFever
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA, United States
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