Developmental disruption of recurrent inhibitory feedback results in compensatory adaptation in the Renshaw cell - motor neuron circuit

Enjin A, Perry S, Hilscher MM, Nagaraja C, Larhammar M, Gezelius H, Eriksson A, Leão KE, Kullander K (2017) Developmental disruption of recurrent inhibitory feedback results in compensatory adaptation in the Renshaw cell - motor neuron circuit. J Neurosci. May 8. pii: 0949-16. doi: 10.1523/JNEUROSCI.0949-16.2017.When activating muscles, motor neurons in the spinal cord also activate Renshaw cells, which provide recurrent inhibitory feedback to the motor neurons. The tight coupling with motor neurons suggests that Renshaw cells have an integral role in movement, a role that is yet to be elucidated. Here we used the selective expression of the nicotinic cholinergic receptor alpha 2 (Chrna2) in mice to genetically target the vesicular inhibitory amino acid transporter (VIAAT) in Renshaw cells. Loss of VIAAT from Chrna2Cre expressing Renshaw cells did not impact any aspect of drug-induced fictive locomotion in the neonatal mouse, nor did it change gait, motor coordination or grip strength in adult mice of both sexes. However, motor neurons from neonatal mice lacking VIAAT in Renshaw cells received spontaneous inhibitory synaptic input with a reduced frequency, showed lower input resistance and had an increased number of proprioceptive glutamatergic and calbindin labeled putative Renshaw cell synapses on their soma and proximal dendrites. Concomitantly, Renshaw cells developed with increased excitability and a normal number of cholinergic motor neuron synapses indicating a compensatory mechanism within the recurrent inhibitory feedback circuit. Our data suggest an integral role for Renshaw cell signaling in shaping the excitability and synaptic input to motor neurons

Implementation of 3D Imaging for Two-photon Laser Scanning Microscopy

Information exchange between neural systems occurs at the level of populations of neurons. Thus in order to understand how this information exchange occurs, it is indispensible to understand the role of underlying neuronal systems. Electrophysiological techniques have enhanced our understanding of the nervous system by enabling the study of properties of single ion channels to that of ensembles of neurons. While electrophysiological measurements offer excellent temporal resolution, they lack spatial resolution as this method provides a readout of the electrical signals from single or ensembles of neurons in the vicinity of the electrodes (Scanziani et al, 2009). Imaging techniques have gained a lot of prominence because they are non-invasive and provides excellent spatial resolution (Scanziani et al, 2009). The advent of fluorescent genetically encoded optical probes and other fluorescent synthetic indicators has enabled the study of network functions of neurons (Handel et al, 2008). There are various imaging techniques but the one most suited to study network activity is Multiphoton emission (MPE) microscopy because of its ability to image at greater depths in the tissue. In particular, the most popular and extensively used method in this class is the 2-Photon Microscopy. Imaging method suntil recently have employed 2D scanning at planes normal to the light axis. It is known that processing of information occurs at local ensembles of neurons, hence obtaining population activity in a volume of interest is of greater relevance. This has been possible with the technological advancements over the past couple of years (Gobel et al,2007). The aim of this thesis is to implement a fast 3D scanning algorithm using 2-photon microscopy to measure the activity patterns of neuronal ensembles. Further, this technique could be used in order to relate the activity of neurons with the behavioral output

Functional Imaging of Spinal Locomotor Networks

Movement is necessary for the survival of most animals. The spinal cord contains neuronal networks that are capable of motor coordination and of producing different movements. In particular, a very reduced neuronal network in the spinal cord can produce simple rhythmic outputs even in the absence of descending or sensory inputs. This basic circuit was discovered by Thomas Graham Brown (reported in 1911) and is termed central pattern generator. For over a century a large number of studies have been carried out in order to identify the neuronal components that are part of these networks. In project 1 we focused on Renshaw cells, which are a population of spinal interneurons expressing the alpha-2 subunit of the nicotinic acetylcholine receptors (Chrna2). Renshaw cells are the only identified central targets for motor neuron inputs, and in turn they mediate inhibition of the motor neurons. We analyzed the activity pattern of Renshaw cells on a cell-population level in neonates when the circuit is still developing. At segment 1 of the lumbar spinal cord, Renshaw cells show significantly greater activity response to functional sensory and motor inputs from rostral compared to the caudal segments. Contrarily, the suppression of the monosynaptic stretch reflex was more pronounced when caudal roots were stimulated. Our data underline the importance of sensory input during motor circuit development and help to understand the functional organization of Renshaw cell connectivity. Several neurons that play distinct roles in locomotor central pattern generation have been identified with the help of genetics. For instance, the V0 population of spinal interneurons are identified by the expression of transcription factor developing brain homeobox 1 (Dbx1). V0 neurons are necessary for producing an alternating rhythm at all locomotor speeds. In project 2 we have looked at a population of dorsally derived ventrally projecting interneurons that express the transcription factor doublesex and mab-3 related transcription factor 3 (Dmrt3). On a behavioral level Dmrt3 neurons are involved in regulating coordination across different locomotor speeds. On a microcircuit level, we have shown that individual Dmrt3 neurons show distinct frequencies of oscillations for a constant locomotor rhythm. In addition, removal of inhibitory neurotransmission from Dmrt3 neurons results in uncoupling of rhythm in motor neurons. In project 3 the activity patterns in populations of flexor related motor neurons are characterized during fictive locomotion in neonatal mice. An interesting and intriguing finding in project 3 is the presence of multiple rhythmicities in motor neurons. Multiple rhythmicities are seen even when the locomotor output shows a constant frequency

Implementation of 3D Imaging for Two-photon Laser Scanning Microscopy

Information exchange between neural systems occurs at the level of populations of neurons. Thus in order to understand how this information exchange occurs, it is indispensible to understand the role of underlying neuronal systems. Electrophysiological techniques have enhanced our understanding of the nervous system by enabling the study of properties of single ion channels to that of ensembles of neurons. While electrophysiological measurements offer excellent temporal resolution, they lack spatial resolution as this method provides a readout of the electrical signals from single or ensembles of neurons in the vicinity of the electrodes (Scanziani et al, 2009). Imaging techniques have gained a lot of prominence because they are non-invasive and provides excellent spatial resolution (Scanziani et al, 2009). The advent of fluorescent genetically encoded optical probes and other fluorescent synthetic indicators has enabled the study of network functions of neurons (Handel et al, 2008). There are various imaging techniques but the one most suited to study network activity is Multiphoton emission (MPE) microscopy because of its ability to image at greater depths in the tissue. In particular, the most popular and extensively used method in this class is the 2-Photon Microscopy. Imaging method suntil recently have employed 2D scanning at planes normal to the light axis. It is known that processing of information occurs at local ensembles of neurons, hence obtaining population activity in a volume of interest is of greater relevance. This has been possible with the technological advancements over the past couple of years (Gobel et al,2007). The aim of this thesis is to implement a fast 3D scanning algorithm using 2-photon microscopy to measure the activity patterns of neuronal ensembles. Further, this technique could be used in order to relate the activity of neurons with the behavioral output

Helminth-based therapies for rheumatoid arthritis: a systematic review and meta-analysis

Proteins from parasitic worms have been posed as novel therapies for rheumatoid arthritis (RA) and other auto-inflammatory diseases. However, with so many potential therapeutics, it is important that drug discovery be based on the specific phyla or species which show the most promising effects. Therefore, the aim of this systematic review and meta-analysis was to evaluate the reported effects of helminthic secretory proteins and derivative therapy on RA in an animal model. Medline, Scopus and Web of Science were searched to identify studies evaluating helminthic therapy in the collagen-induced arthritis model of RA. A meta-analysis was undertaken to determine the overall effect of the proteins. Subgroup analyses were also undertaken to investigate individual treatments. Seven articles were included in the analysis. Overall, helminthic therapy significantly reduced arthritis score (SMD −1.193, 95% CI −1.525, −0.860). Subgroup analyses found a significant reduction in arthritis score following treatment with helminth protein ES-62 (SMD −1.186, 95% CI −1.633, −0.738) and phosphorylcholine-based treatment (SMD −0.997, 95% CI −1.423, −0.571). Subgroup analyses found ES-62 treatment significantly decreased IFN-γ levels (SMD −1.611, 95% CI −2.734, −0.487) and significantly increased levels of IL-10 (SMD 0.946, 95% CI 0.127, 1.765). Therapeutics from parasitic worms are a promising avenue for drug discovery, especially with all included studies reporting a significant improvement in arthritis score. Based on pooled data presented in this study, the nematode Acanthocheilonema viteae seems to be of particular interest for therapeutics

Identification of a Neuronal Receptor Controlling Anaphylaxis

Allergic reactions can in severe cases induce a state of circulatory shock referred to as anaphylaxis. Histamine, the primary mediator of this condition, is released from immune cells, and, therefore, anaphylaxis has so far been considered an immune system disorder. However, we here show that the glutamatergic receptor mGluR7, expressed on a subpopulation of both peripheral and spinal cord neurons, controls histamine-induced communication through calcium-dependent autoinhibition with implications for anaphylaxis. Genetic ablation of mGluR7, and thus altered regulation of histamine-sensing neurons, caused an anaphylaxis-like state in mGluR7(-/-) mice, which could be reversed by antagonizing signaling between neurons and mast cells but not by antagonizing a central itch pathway. Our findings demonstrate the vital role of nervous system control by mGluR7 in anaphylaxis and open up possibilities for preventive strategies for this life-threatening condition

Accelerated cerebromicrovascular senescence contributes to cognitive decline in a mouse model of paclitaxel (Taxol)-induced chemobrain

Chemotherapy-induced cognitive impairment ("chemobrain") is a frequent side-effect in cancer survivors treated with paclitaxel (PTX). The mechanisms responsible for PTX-induced cognitive impairment remain obscure, and there are no effective treatments or prevention strategies. Here, we test the hypothesis that PTX induces endothelial senescence, which impairs microvascular function and contributes to the genesis of cognitive decline. We treated transgenic p16-3MR mice, which allows the detection and selective elimination of senescent cells, with PTX (5 mg/kg/day, 2 cycles; 5 days/cycle). PTX-treated and control mice were tested for spatial memory performance, neurovascular coupling (NVC) responses (whisker-stimulation-induced increases in cerebral blood flow), microvascular density, blood-brain barrier (BBB) permeability and the presence of senescent endothelial cells (by flow cytometry and single-cell transcriptomics) at 6 months post-treatment. PTX induced senescence in endothelial cells, which associated with microvascular rarefaction, NVC dysfunction, BBB disruption, neuroinflammation, and impaired performance on cognitive tasks. To establish a causal relationship between PTX-induced senescence and impaired microvascular functions, senescent cells were depleted from PTX-treated animals (at 3 months post-treatment) by genetic (ganciclovir) or pharmacological (treatment with the senolytic drug ABT263/Navitoclax) means. In PTX treated mice, both treatments effectively eliminated senescent endothelial cells, rescued endothelium-mediated NVC responses and BBB integrity, increased capillarization and improved cognitive performance. Our findings suggest that senolytic treatments can be a promising strategy for preventing chemotherapy-induced cognitive impairment

HelioScan: a software framework for controlling in vivo microscopy setups with high hardware flexibility, functional diversity and extendibility

Intravital microscopy such as in vivo imaging of brain dynamics is often performed with custom-built microscope setups controlled by custom-written software to meet specific requirements. Continuous technological advancement in the field has created a need for new control software that is flexible enough to support the biological researcher with innovative imaging techniques and provide the developer with a solid platform for quickly and easily implementing new extensions. Here, we introduce HelioScan, a software package written in LabVIEW, as a platform serving this dual role. HelioScan is designed as a collection of components that can be flexibly assembled into microscope control software tailored to the particular hardware and functionality requirements. Moreover, HelioScan provides a software framework, within which new functionality can be implemented in a quick and structured manner. A specific HelioScan application assembles at run-time from individual software components, based on user-definable configuration files. Due to its component-based architecture, HelioScan can exploit synergies of multiple developers working in parallel on different components in a community effort. We exemplify the capabilities and versatility of HelioScan by demonstrating several in vivo brain imaging modes, including camera-based intrinsic optical signal imaging for functional mapping of cortical areas, standard two-photon laser-scanning microscopy using galvanometric mirrors, and high-speed in vivo two-photon calcium imaging using either acousto-optic deflectors or a resonant scanner. We recommend HelioScan as a convenient software framework for the in vivo imaging community