Introduction: This research investigates an anomalous pyramidal cell type, dubbed "deep cells" in the subiculum of the hippocampus. Deep cells are structurally unique in that they completely lack radial oblique dendrites. This work will use in-vivo calcium imaging to elucidate how this remarkable change in structure effects neuronal function in vivo in the subiculum and its possible role during behaviour. Methods: Our lab has constructed a transgenic cre line to access this deep cell type. I use this mouse line to image deep cells during spatial navigation and novel object tasks. During these experiments, I use wire-free 1-photon miniscopes to image the dorsal subiculum while mice undergo an open field task with two local objects, repeated over several timepoints. Results: Data from this project show that deep cells act on very slow timescales and have robust, sustained activity that appear to respond to encounters with novel, local objects . Deep cells show large increases in activity after interaction with a novel object on day one and this activity is substantially reduced by day four. Intriguingly, this cellular signature is still reduced 100 days after initial introduction. In comparison to control cells, deep cells show novel object-centered activity and no classic spatial phenotypes expected from pyramidal cells in the subiculum. Conclusion: This data leaves us with intriguing evidence of a seemingly spatially uninvolved, novelty driven and morphologically distinct cell type previously undescribed in the subiculum. Future work will be integral to identifying the role of this cell in memory processes/dysfunction and the role of this novel cell type in other brain regions.

An investigation into an anomalous pyramidal cell type: atypical morphology and sustained cellular activity to novel stimuli

uthorDespite being implicated in various functions, the structural organization of the claustrum remains largely unknown. It is crucial that we first understand the intrinsic neural organization of the claustrum to better elucidate its functional complexity. Thus, we sought to investigate the transcriptomic breakdown of the claustrum through single cell RNA-sequencing (scRNA-seq). In our analysis, we uncovered a previously unknown excitatory neuronal subtype, suggesting the claustrum is composed of 2 transcriptomically distinct excitatory neurons. To investigate the spatial organization of these subtypes, we used multiplexed single-molecule fluorescence in situ hybridization (smFISH), targeting RNA from 12 different marker genes in individual brain sections. We found that the gene expression patterns of the claustral neurons correlated strongly with the scRNA-seq predictions, organizing into a "core-shell" spatial configuration that was consistent across the anterior-posterior axis. To determine if these transcriptomic signatures corresponded to specific projection neuron populations within the claustrum, multicolour retrograde tracing in conjunction with smFISH was performed. Here, we found the core and shell subtypes correlated with distinct projection targets from the retrosplenial cortex and lateral entorhinal cortex, respectively. Thus, the claustrum exhibits a "core-shell" spatial organization with distinct molecular and circuit properties, which may drive its functional complexity. This spatial heterogeneity can be used in the future to examine subtype-specific function.

Spatially patterned excitatory neuron subtypes and circuits within the claustrum

Subiculum pyramidal neurons form the main output of the hippocampus, and are classically viewed as giving rise to memory by branched structures that receive proximal and distal input. Here, we identified a sparse pyramidal cell subpopulation within the subiculum that diverges from classical pyramidal neuron characteristics across connectivity, morphology, and intrinsic activity. Via transcriptomics, we identified a sparse excitatory neuron population that occupies the deepest layer of the subiculum, and generated a new transgenic mouse line that allows cre-mediated cell-type-specific access of these deep cells. Combining this transgenic line with cell-type-specific viral tracing tools, we discovered that this deep cell population forms dedicated projections to the anterior thalamic nuclei, a key brain region in spatial working memory. Moreover, these deep cells lack radial oblique dendrites typical of classical subiculum pyramidal cells. Motivated by this unique local and long-range structure of these cells, we investigated potential differences in intrinsic function via whole cell patch-clamp recordings. Recording results revealed that these deep cells exhibited an increased input resistance compared to classical pyramidal cells in the subiculum. Altogether, our data provides evidence for a previously unknown subiculum pyramidal cell subtype that exhibits unique structural and intrinsic characteristics, which could indicate a potentially specialized role in spatial memory. Future work will be integral to identifying the functional correlates of this atypical population.

Atypical subiculum pyramidal neurons form dedicated projections and exhibit morphological and electrophysiological differences

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PS-2-B -  Neural Excitability, Synapses, and Glia: Cellular Mechanisms

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

CAN-ACN 2021

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

Join us in Gather.Town to view the posters and interact live with friends and colleagues

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Sarah Erwin

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An investigation into an anomalous pyramidal cell type: atypical morphology and sustained cellular activity to novel stimuli

Spatially patterned excitatory neuron subtypes and circuits within the claustrum

Atypical subiculum pyramidal neurons form dedicated projections and exhibit morphological and electrophysiological differences

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