Canada

Introduction: Rats with complete spinal cord injury (SCI) exhibit good plantar stepping in the upright posture 5weeks after complete SCI without any training. Spontaneous reorganization of spinal circuits transmitting afferent input from the sole of the foot via the Tibial nerve (TIB) is a main contributor to this locomotor recovery. The purpose of this study was to examine changes in afferent pathways of the TIB at different times after SCI. Methods: Cord dorsum potential responses to graded electrical TIB stimulation were measured in 17 rats at different levels of the lumbar spinal cord. Intra-spinal field potentials were recorded (6 rats) after graded TIB stimulation. The amplitude of the different components of these potentials were normalized and compared in rats with intact cords (x), injured cords at 1 week (y) and at 5 weeks (z) post SCI. Results: The TIB group I muscle afferents evoked maximal response at the L4-L5 level in both intact and spinalized animals. The group II muscle afferents evoked surface potentials that decreased at L4 at 1 week after SCI compared to responses in intact rats. By 5 weeks post SCI, the group II responses became similar to those seen in the intact rats coinciding with upright walking development. Intraspinal field potentials from the dorsal horn also showed a similar reduction and recovery pattern. Conclusion: The reduction observed in cord dorsum and intraspinal field potentials evoked by group II afferent stimulation of the TIB at 1 week SCI suggests that dorsal horn interneurons with group II input are compromised at this time.

CAN-ACN 2021

Afferent input &quot;re-organization&quot; after a complete thoracic spinal cord injury in rats

locomotor recovery

groupii afferents

groupi afferents

tibial nerve

afferents

spinal cord injury

Colleagues and Friends:

I am very happy to welcome you to the 14th annual Canadian Neuroscience Meeting, and to the first virtual edition of our meeting. I want to highlight the important work the CAN meeting chair, **Roger Thompson** and co-chair, **Alyson Fournier**, did to put together the great program we are offering this year. Moving to a virtual format required a complete re-design of the program, and both Roger and Alyson did a splendid job in providing us with an appealing and well adapted program for our first virtual event. I wish to thank them for this very important effort.

Highlights of this year’s scientific meeting include invited speakers **Michael Hausser, Franck Polleux, Gwyneth Card, Magdalena Götz**and Brain Prize winner **Huda Zoghbi**. Plenary and parallel symposia, proposed by our members complete our diverse [scientific program.](https://can-acn.org/meeting-2021/program-2021/)

The 2021 Advocacy session, chaired and organized by CAN advocacy committee chair **Karun Singh**, will feature a special lecture and question period with Member of Parliament and past Science Minister **Kirsty Duncan**. This will be followed by a short overview of CAN’s advocacy activities over the last year. We invite you to participate in this session for insight from Dr. Duncan on the workings of Parliament Hill, and to learn more about what CAN has been doing to promote neuroscience research in Canada.

We are also excited to host **Lisa Willis** in the Equity Diversity and Inclusion session, organized by EDI committee chair **Jibran Khokhar**.

A special highlight of our meeting will be the lectures by award-winning young neuroscientists. We are please to host the CAN 2020 Young Investigator Award winner **Mihaela Iordanova**, and CAN 2021 Young Investigator Award winners **Aaron Phillips** and **Tabrez Siddiqui**. Highlights will also include presentation by the top three winners of the CAN-CIHR-INMHA Brain Star Award winners, **Claire Gizowski, Nuria Daviu Abant** and **Lukas Tamayo-Orrego**.

Independently organized satellite symposia complement and complete this exciting program, check them out here: https://can-acn.org/meeting-2021/2021-satellite-symposia/

Some of the most engaging sessions are always the poster sessions featuring the work of our trainees, so make sure to log in to Gather Town during the poster sessions to chat with the presenters.
We hope you enjoy this program, and look forward to welcoming you, virtually.

Shernaz Bamji

President of the Canadian Association for Neuroscience

![](https://assets.underline.io/uploads/markdown_image/1/image/b9aea25343a87d5aac3b9367dc780974.jpg)



Please head to https://can-acn.org/meeting-2021/registration-2021/ to register. 

14th Canadian Neuroscience Meeting from August 23rd-25th

Afferent input "re-organization" after a complete thoracic spinal cord injury in rats

poster

Sodium-dependent high affinity glutamate transporters are essential in mitigating the toxic effects of extracellular glutamate accumulation. Glutamate uptake is primarily mediated by astrocytes, although glial coverage is reported to be four times higher postsynaptically than presynaptically. The functional consequences of this synapse asymmetry in glial coverage is poorly understood, but it implies the presynapse is more vulnerable to glutamate uptake impairments than the postsynapse in brain diseases with compromised glutamate uptake, such as Alzheimer disease (AD). Here, we developed a novel approach to quantify the unique glutamate clearance dynamics in presynaptic and postsynaptic microenvironments in the hippocampus of the 3xTg mouse model of AD through a combination of intensity-based glutamate sensing fluorescent reporter (iGluSnFR) and two-photon microscopy. By 6-months, an age corresponding to the emergence of an AD-like phenotype in the 3xTg mouse, glutamate clearance in presynaptic microenviornments was impaired while clearance in postsynaptic microenvironments was unimpaired in 3xTg mice. This impairment is mediated by GLT-1 as confirmed by 2 observations: DHK application to acute hippocampal slices increases glutamate clearance time in presynaptic microenvironments, but the extent of this increase is lesser in 3xTg mice compared to control mice; and EAAT2 overexpression via ceftriaxone speeds up glutamate clearance in presynaptic microenvironments. This implies that glutamate transporters have different capabilities depending on the specific microenvironment within a given region, and in the context of AD, suggests that the emergence of presynaptic microenvironment glutamate clearance deficits may correlate with the emergence of AD-like synaptic pathology

Glutamate uptake asymmetry in a mouse model of alzheimer disease

One of the most vulnerable neuronal cell types in the mammalian brain are cerebellar Purkinje cells (PC). In many ataxias, certain PCs show remarkable resilience to disease, with only a subpopulation of PCs typically vulnerable to the same insult. Recently we have found that certain PCs located in the anterior region of the cerebellar vermis are more likely to die than those located in the posterior region in Christianson syndrome (CS) ataxia. We now wish to investigate what leads to PC vulnerabilities versus resilience in CS ataxia. CS is a rare X-linked neurodevelopmental and neurodegenerative disorder caused by loss of function mutations in NHE6, an endosomal Na+/H+ exchanger responsible for regulating pH in recycling endosomes of the endocytic pathway. Loss of NHE6 results in over acidification of endosomes leading to mistrafficking of cargo which could affect neuronal function. PCs have a unique ability to fire high frequency action potentials, even in the absence of synaptic input and motor control. Using electrophysiology techniques we investigated if PCs in the anterior region have alterations in intrinsic firing prior to cell death and motor deficits in CS. Using a mouse model of CS (NHE6KO), we observed a significant decrease in PC intrinsic firing ability in the anterior region at age P40, an age which precedes manifestation of PC death and motor impairment. Given these results, we are testing therapeutic approaches targeting intrinsic firing in vulnerable PCs with the goal of restoring firing output and prevent behavioral deficits.

Purkinje cell intrinsic firing deficits precede cell death and motor impairment in a mouse model of Christianson syndrome

Amyotrophic lateral sclerosis (ALS) is a moto-neuron disorder in which an RNA-binding protein, TDP-43, mislocalizes and pathologically accumulates from its normal nuclear locale to the cytosol. Given that the subcellular localization and expression of TDP-43 is tightly regulated and affected by its protein-protein interactions (PPIs), we posit that identifying novel interactors of wild-type and mutant TDP-43 could reveal insight into networks involved in driving ALS pathogenesis. Using CRISPR/Cas9, our lab has generated knockin cell lines expressing GFP-tagged wildtype (WT) and an ALS-causing mutant (Q331K) TDP-43, in the endogenous TARDBP locus (coding for TDP-43). We have shown that the Q331K mutation causes loss-of-function and mislocalization of TDP-43. We have performed immunoprecipitation-mass spectrometry (IP-MS) on these cell lines to elucidate interactors of WT- and Q331K, TDP-43. Our data has shown that there is an overall loss of interactors with the Q331K mutation. We have analyzed these data using bioinformatic approaches to shortlist and validate 14 candidates. From this, 4 interactors have shown robust interaction with TDP-43 via IP-western blot. We are using cellular and biochemical assays to assess the effects of knockdown and overexpression of these top 4 hits on TDP-43 localization and loss-of-function. Using this unbiased approach, we will identify TDP-43 PPIs and characterize their roles in cellular functions in the context of ALS, giving insight into pathways involved in driving neurodegeneration.

Mapping and characterizing ALS-linked TDP-43 protein-protein interactions

The 15q13.3 microdeletion syndrome is a highly penetrant copy number variant (CNV) associated with epilepsy, autism spectrum disorder, schizophrenia, and intellectual disability. Within the deletion are seven protein coding genes, including the deubiquitinase and driver gene, OTUD7A. We used a proximity proteomics assay in neurons to determine the binding partners to OTUD7A and found enrichment in proteins localized to the axon and axon initial segment (AIS). Using neurons generated from our cohort of 15q13.3 patient-derived induced pluripotent stem cells (iPSCs), we sought to understand the role of OTUD7A at the axon in 2D and 3D models of the CNV. 15q13.3 and mutant OTUD7A patient-derived neurons were generated from iPSCs and assayed for early growth and axonal properties using immunofluorescence techniques. We found that OTUD7A interacts with the axon growth protein, Ankyrin B, and AIS regulator, Ankyrin G. We examined 15q13.3 neurons at an early timepoint during axon outgrowth and found an immature phenotype among three 15q13.3 probands. We then looked at a mature timepoint to find aberrant localization of Ankyrin G at the AIS. To better profile the developmental trajectory of the 15q13.3 CNV, we are examining cerebral organoids at various timepoints to investigate neural progenitor proliferation, cellular migration, and maturation in a 3D system across development.

Investigating neurodevelopmental and axonal defects in human models of the 15q13.3 microdeletion disorder

Lysosomes are acidic organelles that contain a myriad of hydrolytic enzymes. In neurons, lysosomes traffic throughout the axons and dendrites to deliver catabolic enzymes to distal regions of the cell and maintain local degradative demands. Of the various lysosomal enzymes, glucocerebrosidase (GBA) is of particular interest due to its relationship with synucleinopathies such as Parkinson's Disease and Dementia with Lewy Bodies. Mutations in GBA are the most common genetic risk factor for synucleinopathies, but the mechanistic relationship is unclear. GBA cleaves the glycolipid glucosylceramide (GC) into glucose and ceramide, but mutations in GBA, or its catalytic inhibition, can disrupt the composition of the lysosomal membrane. The lysosomal membrane serves as the platform to which trafficking complexes are recruited and activated. Thus, we investigated if the prolonged catalytic inhibition of GBA by Conduritol B Epoxide (CBE) could interfere with lysosomal trafficking dynamics in axons. In human iPSC-derived cortical neurons treated with CBE for 10 days, we did not observe a change in the motile fraction, velocity, or run length of LAMP1-GFP vesicles. Additionally, we did not find any alterations in lysosomal size or density in the axon, dendrites, or neuronal cell bodies, despite complete inhibition of enzymatic activity. These results suggest that CBE-mediated inhibition of GBA in neurons does not directly impact lysosomal dynamics or size in the time course of our experiments.

Lysosomal transport dynamics in GBA-inhibited iPSC-derived human neurons

The previous study from our group has identified that after peripheral nerve injury there is an increase of kynurenine in the plasma, which seems to be involved in the maintenance of neuropathic pain. However, the mechanisms which peripheral kynurenine (Kyn) mediates neuropathic pain is unknown. Therefore, the aim of the present study was to test the hypothesis that peripheral Kyn reaches the spinal cord and maintain neuropathic pain by KMO metabolism, leading to downstream nociceptive metabolites. Methods: Spared Nerve Injury (SNI) model of neuropathic pain was induced in C57BL/6 mice and the following test and methods were used: von Frey filaments nociceptive test, Real-time PCR and western blotting, inhibition of KMO activity. This study was approved by the Local Ethical Commission in Animal Research (045/2013). Results: SNI induced mechanical allodynia in a time-dependent manner, which peaked from 7 up to 21 days. SNI- induced mechanical allodynia was associated with an increase in the expression of KMO in the spinal cord, mainly at day 10 and 14 after injury. KMO expression was restricted to spinal cord astrocytes. Functionally, pharmacological inhibitor against KMO injected intrathecally after SNI, reduced mechanical allodynia. Also, kyn injected systemically (i.v) promoted mechanical allodynia, which was educed when KMO was pharmacologically inhibited. In summary, these results indicated that after peripheral nerve injury spinal astrocytes-expressing KMO plays a critical role in the development of neuropathic pain. In conclusion, the kynurenine metabolic pathway is a critical link in the neuroimmune response after peripheral nerve injury in the maintenance of neuropathy.

Meningeal dendritic cells interactions with astrocytes elevate the kynurenine metabolic pathway to sustain neuropathic pain

Multiple sclerosis (MS) is a neurodegenerative disease which is largely associated with progressive disability. It is characterized by multiple focal demyelinating lesions where the extent of myelin loss correlates with the advancement of disease and also age. Substantial work has focused on preventing demyelination from occurring, but the alleviation of MS symptoms through regeneration of myelin, or remyelination, remains an under-researched area. Remyelination is associated with less clinical disability and linearly declines with age. This process is dependent upon microglia, the resident immune mediators of the central nervous system (CNS). Microglia are a heterogeneous phenotype, forming subpopulations that vary across development, anatomical regions and disease. Using advanced analytical tools and bioinformatic techniques, we show that a subpopulation of microglia arises at the onset of remyelination in a mouse model of MS which presents acute demyelination followed by spontaneous, but robust, remyelination. These remyelination-associated microglia (RAM) change their transcriptional signature throughout remyelination, moving from an Igf1/Irf7 dominated phenotype to one that is characterized by genes responsible for regeneration, such as Meg3. We have validated this by showing the expression of Igf1 and Irf7 within mouse lesions using RNA scope. We are currently sequencing microglia from aged, lesioned environments to assess how microglia responses differ through ageing

Phenotypic profiling of microglia across remyelination and ageing

The lateral entorhinal cortex (LEC) is the site of tau accumulation in early stages of Alzheimer's disease and has projections downstream to the dentate gyrus (DG) of the hippocampus. The pathological form of tau has the ability to propagate across synapses, spreading to connected brain regions and correlating with memory deficits and synaptic loss. The DG is the site of ongoing adult neurogenesis, with new granule neurons added showing enhanced plasticity and increased survival compared to older neurons. Thus, we are interested in examining neuron age for vulnerability to tau pathology in the LEC-DG circuit. We use an inducible cre-recombinase transgenic mouse model to label neurons born at different ages (development vs. adulthood) with TdTomato, and viral AAV tau injections into the LEC to mimic early tau pathology. Following a 4-month incubation, animals are tested for memory deficits with Novel Object Recognition (NOR) and Novel Place Recognition (NPR) and tissue is immunohistochemically processed to analyze tau levels and cellular morphology in TdTomato-labelled DG neurons. We assess synaptic changes in DG neurons via measuring dendritic spines, dendritic complexity and mossy fibre boutons. Preliminary findings show a trend for tau animals to perform worse on NOR compared to healthy controls, while no difference found for NPR. Morphological results show adult-born neurons have an increase in immature thin dendritic spines and decrease in mushroom spines (mature, functional spines) in tau animals relative to healthy controls, as well as reduced mossy fibre bouton filopodia length. Our initial results demonstrate the effect of tau on the LEC-DG circuit, with altered synaptic connectivity and memory performance.

Vulnerability to tau pathology in the entorhinal-hippocampal circuit

Neurodegeneration (NDG), hallmarked by neuronal cell body and axonal loss, occurs in progressive Multiple Sclerosis (MS) in the absence of overt relapses and inflammatory episodes. Heterogeneous nuclear ribonucleoprotein A1 (A1) is an RNA binding protein that is key in cellular RNA metabolism, but is mislocalized from nuclei to cytoplasm in the neurons from brains of people with progressive MS, and from spinal cords of mice with experimental autoimmune encephalomyelitis (EAE), a model for MS. We hypothesized that this mislocalization impacts the A1 RNA binding profile to promote NDG. To test this, we compared the A1 RNA binding profile from the spinal cords of naïve mice to those of mice with EAE, using crosslinking-immunoprecipitation/RNA sequencing (CLIPseq). We confirmed that the global RNA transcriptome from EAE mouse spinal cords is distinct from that of naïve mice, and further found that severity of EAE disease resulted in a greater alteration in the global transcriptome, with a number of differentially-expressed genes involved in neurodegeneration. We have also generated a first-of-its-kind profile of homeostatic A1 RNA targets in spinal cord. Further, the A1 RNA binding profile is drastically dysregulated in EAE mouse spinal cords, losing interaction with ~40% of homeostatically bound RNAs and instead enriching for non-coding RNAs. We are in the process of mapping the A1 binding "footprint" on these RNAs to provide insight into its specificity. Together, these data will form the foundation of our understanding of the role A1 dysfunction plays in NDG in MS.

RNA binding of heterogeneous nuclear ribonucleoprotein A1 is dysregulated in a mouse model of Multiple Sclerosis

To provide us with a complete sensory experience, our brain naturally merges information from our various senses (e.g., vision and hearing). The brain's ability to integrate auditory and visual information is not static; studies have shown that recent sensory experience can influence the accuracy and sensitivity of one's perception. To better understand the neural mechanisms underlying this process, we set out to develop and validate rodent models of audiovisual temporal and synchrony perception. Rats were trained on one of two perceptual judgment tasks: (1) a temporal order judgment (TOJ) task where rats reported whether the auditory or visual stimulus was presented first, or (2) a synchrony judgment (SJ) task where rats reported whether the auditory and visual stimulus were presented at the same moment in time or different times. To test for sensory adaption, rats were passively exposed to either synchronous or asynchronous stimuli prior to undergoing an experimental test session. Consistent with human studies, both tasks showed a psychophysical relationship between stimuli timing offsets and performance. Interestingly, prior disclosure to asynchronous audiovisual stimuli resulted in a shift of the psychophysical curve in the direction of the stimulus offset in rats performing the TOJ task, but not the SJ task. Additional testing is underway using the SJ task to further investigate synchrony perception in rats. Our collective results suggest that rats represent a suitable model for future studies aimed at studying the neural mechanisms underlying audiovisual perception.

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Glutamate uptake asymmetry in a mouse model of alzheimer disease

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