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Meiser S, Sleeboom JM, Arkhypchuk I, Sandbote K, Kretzberg J. Cell anatomy and network input explain differences within but not between leech touch cells at two different locations. Front Cell Neurosci 2023; 17:1186997. [PMID: 37565030 PMCID: PMC10411907 DOI: 10.3389/fncel.2023.1186997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 07/06/2023] [Indexed: 08/12/2023] Open
Abstract
Mechanosensory cells in the leech share several common features with mechanoreceptors in the human glabrous skin. Previous studies showed that the six T (touch) cells in each body segment of the leech are highly variable in their responses to somatic current injection and change their excitability over time. Here, we investigate three potential reasons for this variability in excitability by comparing the responses of T cells at two soma locations (T2 and T3): (1) Differential effects of time-dependent changes in excitability, (2) divergent synaptic input from the network, and (3) different anatomical structures. These hypotheses were explored with a combination of electrophysiological double recordings, 3D reconstruction of neurobiotin-filled cells, and compartmental model simulations. Current injection triggered significantly more spikes with shorter latency and larger amplitudes in cells at soma location T2 than at T3. During longer recordings, cells at both locations increased their excitability over time in the same way. T2 and T3 cells received the same amount of synaptic input from the unstimulated network, and the polysynaptic connections between both T cells were mutually symmetric. However, we found a striking anatomical difference: While in our data set all T2 cells innervated two roots connecting the ganglion with the skin, 50% of the T3 cells had only one root process. The sub-sample of T3 cells with one root process was significantly less excitable than the T3 cells with two root processes and the T2 cells. To test if the additional root process causes higher excitability, we simulated the responses of 3D reconstructed cells of both anatomies with detailed multi-compartment models. The anatomical subtypes do not differ in excitability when identical biophysical parameters and a homogeneous channel distribution are assumed. Hence, all three hypotheses may contribute to the highly variable T cell responses, but none of them is the only factor accounting for the observed systematic difference in excitability between cells at T2 vs. T3 soma location. Therefore, future patch clamp and modeling studies are needed to analyze how biophysical properties and spatial distribution of ion channels on the cell surface contribute to the variability and systematic differences of electrophysiological phenotypes.
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Affiliation(s)
- Sonja Meiser
- Department of Neuroscience, Computational Neuroscience, Faculty VI, University of Oldenburg, Oldenburg, Germany
| | - Jana Marie Sleeboom
- Department of Neuroscience, Computational Neuroscience, Faculty VI, University of Oldenburg, Oldenburg, Germany
- Institute of Physiology II, Faculty of Medicine, University Clinic Bonn (UKB), University of Bonn, Bonn, Germany
| | - Ihor Arkhypchuk
- Department of Neuroscience, Computational Neuroscience, Faculty VI, University of Oldenburg, Oldenburg, Germany
| | - Kevin Sandbote
- Department of Neuroscience, Computational Neuroscience, Faculty VI, University of Oldenburg, Oldenburg, Germany
| | - Jutta Kretzberg
- Department of Neuroscience, Computational Neuroscience, Faculty VI, University of Oldenburg, Oldenburg, Germany
- Department of Neuroscience, Cluster of Excellence Hearing4all, Faculty VI, University of Oldenburg, Oldenburg, Germany
- Research Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany
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Ashaber M, Tomina Y, Kassraian P, Bushong EA, Kristan WB, Ellisman MH, Wagenaar DA. Anatomy and activity patterns in a multifunctional motor neuron and its surrounding circuits. eLife 2021; 10:e61881. [PMID: 33587033 PMCID: PMC7954528 DOI: 10.7554/elife.61881] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 02/12/2021] [Indexed: 12/27/2022] Open
Abstract
Dorsal Excitor motor neuron DE-3 in the medicinal leech plays three very different dynamical roles in three different behaviors. Without rewiring its anatomical connectivity, how can a motor neuron dynamically switch roles to play appropriate roles in various behaviors? We previously used voltage-sensitive dye imaging to record from DE-3 and most other neurons in the leech segmental ganglion during (fictive) swimming, crawling, and local-bend escape (Tomina and Wagenaar, 2017). Here, we repeated that experiment, then re-imaged the same ganglion using serial blockface electron microscopy and traced DE-3's processes. Further, we traced back the processes of DE-3's presynaptic partners to their respective somata. This allowed us to analyze the relationship between circuit anatomy and the activity patterns it sustains. We found that input synapses important for all the behaviors were widely distributed over DE-3's branches, yet that functional clusters were different during (fictive) swimming vs. crawling.
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Affiliation(s)
- Mária Ashaber
- Division of Biology and Biological Engineering, California Institute of TechnologyPasadenaUnited States
| | - Yusuke Tomina
- Division of Biology and Biological Engineering, California Institute of TechnologyPasadenaUnited States
| | - Pegah Kassraian
- Division of Biology and Biological Engineering, California Institute of TechnologyPasadenaUnited States
| | - Eric A Bushong
- Division of Biological Sciences, University of California, San DiegoSan DiegoUnited States
| | - William B Kristan
- Division of Biological Sciences, University of California, San DiegoSan DiegoUnited States
| | - Mark H Ellisman
- National Center for Microscopy and Imaging Research, University of California, San DiegoSan DiegoUnited States
- Department of Neurosciences, UCSD School of MedicineSan DiegoUnited States
| | - Daniel A Wagenaar
- Division of Biology and Biological Engineering, California Institute of TechnologyPasadenaUnited States
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Kuo DH, De-Miguel FF, Heath-Heckman EAC, Szczupak L, Todd K, Weisblat DA, Winchell CJ. A tale of two leeches: Toward the understanding of the evolution and development of behavioral neural circuits. Evol Dev 2020; 22:471-493. [PMID: 33226195 DOI: 10.1111/ede.12358] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Revised: 10/23/2020] [Accepted: 11/02/2020] [Indexed: 11/29/2022]
Abstract
In the animal kingdom, behavioral traits encompass a broad spectrum of biological phenotypes that have critical roles in adaptive evolution, but an EvoDevo approach has not been broadly used to study behavior evolution. Here, we propose that, by integrating two leech model systems, each of which has already attained some success in its respective field, it is possible to take on behavioral traits with an EvoDevo approach. We first identify the developmental changes that may theoretically lead to behavioral evolution and explain why an EvoDevo study of behavior is challenging. Next, we discuss the pros and cons of the two leech model species, Hirudo, a classic model for invertebrate neurobiology, and Helobdella, an emerging model for clitellate developmental biology, as models for behavioral EvoDevo research. Given the limitations of each leech system, neither is particularly strong for behavioral EvoDevo. However, the two leech systems are complementary in their technical accessibilities, and they do exhibit some behavioral similarities and differences. By studying them in parallel and together with additional leech species such as Haementeria, it is possible to explore the different levels of behavioral development and evolution.
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Affiliation(s)
- Dian-Han Kuo
- Department of Life Science, National Taiwan University, Taipei, Taiwan
| | - Francisco F De-Miguel
- Instituto de Fisiología Celular - Neurociencias, Universidad Nacional Autónoma de México, México City, México
| | | | - Lidia Szczupak
- Departamento de Fisiología Biología Molecular y Celular, Universidad de Buenos Aires, and IFIBYNE UBA-CONICET, Buenos Aires, Argentina
| | - Krista Todd
- Department of Neuroscience, Westminster College, Salt Lake City, Utah, USA
| | - David A Weisblat
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Christopher J Winchell
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
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Segura OM, Abdulnoor L, Hua VV, Solano MJ, Macagno ER, Baker MW. Purinergic modulation of neuronal gap junction circuits in the CNS of the leech. J Neurosci Res 2020; 98:1232-1249. [PMID: 32096570 DOI: 10.1002/jnr.24599] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 01/25/2020] [Accepted: 02/05/2020] [Indexed: 11/08/2022]
Abstract
Gap junctions (GJs) are widely distributed in brains across the animal kingdom. To visualize the GJ- coupled networks of two major mechanosensory neurons in the ganglia of medicinal leeches, we injected these cells with the GJ-permeable tracer Neurobiotin. When diffusion time was limited to only 30 min, tracer coupling was highly variable for both cells, suggesting a possible modulation of GJ permeability. In invertebrates the innexins (homologs of vertebrate pannexins) form the GJs. Because extracellular adenosine triphosphate (ATP) modulates pannexin and leech innexin hemichannel permeability and is released by leech glial cells following injury, we tested the effects of bath application of ATP after the injection of Neurobiotin and observed a significant increase in the number of neurons tracer coupled to the sensory neurons. This effect required the elevation of intracellular Ca2+ and could be produced by bath application of caffeine. Conversely, scavenging endogenous extracellular ATP with the ATPase apyrase decreased the number of coupled cells. ATP also increased electrical conductance and tracer permeability between the bilateral Retzius neurons. This modulatory effect of ATP on GJ coupling was blocked by siRNA knockdown of a P1-like adenosine receptor. Finally, exposure of leech ganglia to extracellular ATP induced a characteristic low frequency (<0.3 Hz) rhythmic bursting activity that was roughly synchronous among multiple neurons, a behavior that was significantly attenuated by the GJ blocker octanol. These findings highlight the mediation by ATP of a robust physiological mechanism for modifying neuronal circuits by rapidly recruiting neurons into active networks and entraining synchronized bursting activity.
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Affiliation(s)
- Oliva Mota Segura
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Lina Abdulnoor
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Vinh-Vincent Hua
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Martha J Solano
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Eduardo R Macagno
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA
| | - Michael W Baker
- Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA.,Department of Psychology, Mount Saint Vincent University, Halifax, Nova Scotia, Canada
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Smith D, Starborg T. Serial block face scanning electron microscopy in cell biology: Applications and technology. Tissue Cell 2019; 57:111-122. [DOI: 10.1016/j.tice.2018.08.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 08/22/2018] [Accepted: 08/26/2018] [Indexed: 10/28/2022]
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Pipkin JE, Bushong EA, Ellisman MH, Kristan Jr. WB. Verifying, Challenging, and Discovering New Synapses Among Fully EM-Reconstructed Neurons in the Leech Ganglion. Front Neuroanat 2018; 12:95. [PMID: 30487738 PMCID: PMC6246621 DOI: 10.3389/fnana.2018.00095] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 10/18/2018] [Indexed: 12/14/2022] Open
Abstract
Neural circuits underpin the production of animal behavior, largely based upon the precise pattern of synaptic connectivity among the neurons involved. For large numbers of neurons, determining such "connectomes" by direct physiological means is difficult, as physiological accessibility is ultimately required to verify and characterize the function of synapses. We collected a volume of images spanning an entire ganglion of the juvenile leech nervous system via serial blockface electron microscopy (SBEM). We validated this approach by reconstructing a well-characterized circuit of motor neurons involved in the swimming behavior of the leech by locating the synapses among them. We confirm that there are multiple synaptic contacts between connected pairs of neurons in the leech, and that these synapses are widely distributed across the region of neuropil in which the neurons' arbors overlap. We verified the anatomical existence of connections that had been described physiologically among longitudinal muscle motor neurons. We also found that some physiological connections were not present anatomically. We then drew upon the SBEM dataset to design additional physiological experiments. We reconstructed an uncharacterized neuron and one of its presynaptic partners identified from the SBEM dataset. We subsequently interrogated this cell pair via intracellular electrophysiology in an adult ganglion and found that the anatomically-discovered synapse was also functional physiologically. Our findings demonstrate the value of combining a connectomics approach with electrophysiology in the leech nervous system.
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Affiliation(s)
- Jason E. Pipkin
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, United States
| | - Eric Allen Bushong
- National Center for Microscopy and Imaging Research, University of California, San Diego, La Jolla, CA, United States
| | - Mark H. Ellisman
- National Center for Microscopy and Imaging Research, University of California, San Diego, La Jolla, CA, United States
- Department of Neuroscience, University of California, San Diego, La Jolla, CA, United States
| | - William B. Kristan Jr.
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, United States
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Northcutt AJ, Fischer EK, Puhl JG, Mesce KA, Schulz DJ. An annotated CNS transcriptome of the medicinal leech, Hirudo verbana: De novo sequencing to characterize genes associated with nervous system activity. PLoS One 2018; 13:e0201206. [PMID: 30028871 PMCID: PMC6054404 DOI: 10.1371/journal.pone.0201206] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 07/10/2018] [Indexed: 11/19/2022] Open
Abstract
The medicinal leech is one of the most venerated model systems for the study of fundamental nervous system principles, ranging from single-cell excitability to complex sensorimotor integration. Yet, molecular analyses have yet to be extensively applied to complement the rich history of electrophysiological study that this animal has received. Here, we generated the first de novo transcriptome assembly from the entire central nervous system of Hirudo verbana, with the goal of providing a molecular resource, as well as to lay the foundation for a comprehensive discovery of genes fundamentally important for neural function. Our assembly generated 107,704 contigs from over 900 million raw reads. Of these 107,704 contigs, 39,047 (36%) were annotated using NCBI's validated RefSeq sequence database. From this annotated central nervous system transcriptome, we began the process of curating genes related to nervous system function by identifying and characterizing 126 unique ion channel, receptor, transporter, and enzyme contigs. Additionally, we generated sequence counts to estimate the relative abundance of each identified ion channel and receptor contig in the transcriptome through Kallisto mapping. This transcriptome will serve as a valuable community resource for studies investigating the molecular underpinnings of neural function in leech and provide a reference for comparative analyses.
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Affiliation(s)
- Adam J. Northcutt
- Division of Biological Sciences, University of Missouri-Columbia, Columbia, Missouri, United States of America
| | - Eva K. Fischer
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Joshua G. Puhl
- Department of Entomology and Graduate Program in Neuroscience, University of Minnesota, Saint Paul, Minnesota, United States of America
| | - Karen A. Mesce
- Department of Entomology and Graduate Program in Neuroscience, University of Minnesota, Saint Paul, Minnesota, United States of America
| | - David J. Schulz
- Division of Biological Sciences, University of Missouri-Columbia, Columbia, Missouri, United States of America
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Tomina Y, Wagenaar DA. A double-sided microscope to realize whole-ganglion imaging of membrane potential in the medicinal leech. eLife 2017; 6:29839. [PMID: 28944754 PMCID: PMC5656430 DOI: 10.7554/elife.29839] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 09/25/2017] [Indexed: 12/15/2022] Open
Abstract
Studies of neuronal network emergence during sensory processing and motor control are greatly facilitated by technologies that allow us to simultaneously record the membrane potential dynamics of a large population of neurons in single cell resolution. To achieve whole-brain recording with the ability to detect both small synaptic potentials and action potentials, we developed a voltage-sensitive dye (VSD) imaging technique based on a double-sided microscope that can image two sides of a nervous system simultaneously. We applied this system to the segmental ganglia of the medicinal leech. Double-sided VSD imaging enabled simultaneous recording of membrane potential events from almost all of the identifiable neurons. Using data obtained from double-sided VSD imaging, we analyzed neuronal dynamics in both sensory processing and generation of behavior and constructed functional maps for identification of neurons contributing to these processes. In every animal, networks of nerve cells work together to interpret signals from the environment and to coordinate responses. Being able to record the activity of all the neurons in a brain at once would greatly advance our understanding of how the brain works. Yet it is not possible to do this for a human brain, which contains several billion neurons. The medicinal leech, on the other hand, has a much simpler nervous system. It has 21 brain-like units called segmental ganglia, which control how the parts of its body move, and each one contains about 400 neurons arranged on a single layer. The activity of large populations of neurons can be monitored using a technique called fluorescent imaging. Most fluorescent dyes, however, are not sensitive enough to report low levels of activity or fast enough to track individual nerve impulses. Also, current microscopy techniques only allow one surface to be imaged at any one time. These limitations constrain the kinds of questions that neuroscientists can ask about how networks of nerve cells function. Tomina and Wagenaar have now developed a double-sided fluorescent microscope system that allows a ganglion in a medicinal leech to be viewed from both sides at once. Using a new generation of dyes, which rapidly change their brightness as individual neurons become active or are inhibited, subtle changes in the activity of hundreds of individual neurons were monitored at the same time. In a test of the system, Tomina and Wagenaar recorded activity for different leech behaviors, like bending, swimming and crawling. For the first time, the relationships between neurons on both sides of the ganglion could be seen. This new technique for examining the activity in neuronal circuitry will allow complex networks of neurons to be studied in more detail. The data that these images generate could then be analyzed mathematically to better understand how the brain processes information from its senses and generates behavior.
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Affiliation(s)
- Yusuke Tomina
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States
| | - Daniel A Wagenaar
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States
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