Cellular and Molecular Neurobiology

Author: Nahir Guadalupe Gazal | Email: nggazal@immf.uncor.edu

Nahir Gazal ^1°, María Castellanos-Montiel ^2°, Guillermina Bruno ^1°, Lale Gursu ^2°, Ghazal Haghi ^2°, Gilles Maussion ^2°, Thomas Durcan ^2°, Nicolás Unsain ^1°

1° Instituto de Investigación Médica Mercedes y Martín Ferreyra (INIMEC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Córdoba, Córdoba, Argentina
2° Early Drug Discovery Unit, Montreal Neurologial Institute-Hospital, Canadá

The membrane-associated periodic skeleton (MPS) is a protein structure of actin “rings” located transversely to the axon and separated every 190 nm by “spacers” of α/β-spectrin tetramers. In mature neurons, the MPS is organized along almost the entire axonal shaft that correlates with βII-spectrin’s homogenous distribution. During the maturation of human induced Pluripotent Stem Cells (hiPSCs) in culture, we observed an intriguing interruption in the otherwise uniform distribution of βII-spectrin along axons, referred to as βII-spectrin gaps (βIIs-gaps). These appear as stretches devoid of βII-spectrin. To determine if βIIs-gaps are associated with axonal constriction or loss, phase contrast and co-immunofluorescence analysis against various cytoskeletal and membrane proteins demonstrated that the lack of βII-spectrin is specific and that the axon shows no changes in those areas. Consequently, we subjected 2-week-old cultures to acute stress using sub-lethal doses of staurosporine, arsenite and L-glutamate. Remarkably, a significant increase in the occurrence of axons with βIIs-gaps under staurosporine treatment was observed. STED microscopy of βII-spectrin showed that the MPS is unaffected outside of the βIIs-gaps. Staurosporine was also found to induce βIIs-gaps in dorsal root ganglion neurons, but not in hippocampal neurons, derived from mouse embryos. We believe the study of βIIs-gaps will provide valuable insights into the formation and dynamics of the MPS in axons.

Cellular and Molecular Neurobiology

Author: Natali Rasetto | Email: rasettonatali@gmail.com

Natalí Belén Rasetto ^1°, Damiana Giacomini ^1°, Ariel Berardino ^2°, Tomás Vega Waichman ^2°, Maximiliano Beckel ^2°, Daniela Di Bella ^3°, Juliana Brown ^3°, Paola Arlotta ^3°, Ariel Chernomoretz ^2°, Alejandro Schinder ^1°

1° Laboratory of Neuronal Plasticity, Leloir Institute-CONICET, Buenos Aires, Argentina.
2° Laboratory of Integrative Systems Biology, Leloir Institute-CONICET, Buenos Aires, Argentina
3° Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA, USA.

Adult hippocampal neurogenesis plays a critical role in spatial memory formation, context discrimination, and clearance of memory traces. In the mouse dentate gyrus, the maturation of adult-born granule cells lasts several weeks and can be divided in 4 phases based on electrophysiological and morphological features. However, the molecular mechanisms underlying the progression through those discrete phases are still unknown. We have proposed that maturation is driven by sequential changes in the gene expression program, and should be revealed by transcriptome analysis. We thus set up an approach for high-throughput single-nuclei RNA sequencing applying Chromium 10X Genomics technology to interrogate the transcriptomic profile of new granule cells at different ages. We used Ascl1CreERT2;CAGfloxStopSun1sfGFP mice to allow conditional expression of Sun-1/sfGFP in the nuclear membrane of developing granule cells at identified ages and isolate fluorescent nuclei using FACS. Clusterization of two separate datasets identified multiple partitions that define a pathway from radial glia-like cells to mature neurons. Several clusters represent intermediate stages of maturation that were previously unknown. The emergence of novel transcriptional markers for the intermediate states was validated by in situ hybridization using RNAscope. These results are beginning to reveal key players involved in neuronal maturation and function with high temporal resolution.

Neuroendocrinology and Neuroimmunology

Author: Ivana Maria Gomez | Email: ivanamariagomez@gmail.com

Ivana Maria Gomez ^1°, Franco Barrile ^1°, Gimena Fernandez ^1°, Daniel Castrogiovanni ^1°, Maia Uriarte ^1°, Mario Perelló ^1°, Pablo Nicolás De Francesco ^1°

1° Laboratorio de Neurofisiología, Instituto Multidisciplinario de Biología Celular (IMBICE)

Hypothalamic tanycytes are polarized ependymoglial cells that line the ventral part of the third ventricle (V3) and emit processes through the hypothalamic parenchyma and median eminence contacting blood vessels, neurons and other glial cells. We recently described that tanycytes internalize the orexigenic hormone ghrelin trough clathrin-mediated endocytosis. Here, we study its uptake and transport direction in these cells with a fluorescent ghrelin tracer (Fr-ghr) using in vivo, ex vivo and in vitro strategies.
First, we centrally injected mice with Fr-ghr and observed a fluorescent signal in tanycytes 15 min post-injection that was reduced by 87% at 30 min and returned to control values at 60 min. We then studied mouse hypothalamic explants incubated with Fr-ghrelin on their outer side (contacting terminals) or within the V3 (contacting soma), and observed fluorescence within tanycytes only in the second condition. Finally, we used primary cultures of rat hypothalamic tanycytes incubated with a 5-min pulse of Fr-ghr to quantify the intracellular redistribution of fluorescent signal over time. We observed that the signal was mostly found in somas after the 5 min pulse, and significantly increased in processes and terminals after 10 min. After 30 min, fluorescence decreased in the whole cell.
This evidence shows that tanycytes internalize ghrelin in their CSF-contacting soma and transport it to their terminals, possibly playing a role in CSF ghrelin clearance.

Cognition, Behavior, and Memory

Author: Juliette López Hanotte | Email: julietteloha@gmail.com

Juliette López Hanotte ^1°, Facundo Peralta ^1°, María Angeles Carrillo-de Sauvage ^2°, Carole Escartin ^2°, Paula Cecilia Reggiani ^1°

1° Universidad Nacional de La Plata, Instituto de Investigaciones Bioquímicas de La Plata, Argentina.
2° Université Paris-Saclay, CEA, CNRS, Laboratoire des Maladies Neurodégénératives, Fontenay-aux-Roses, France

Male rodents have been the default model organism in neuroscience research, including for the intracerebroventricular (icv) streptozotocin (STZ)-induced Alzheimer’s disease (AD) model. Our objective was to compare the effect of icv-STZ injection in male and female rats with and without ovaries. Male rats were separated into control and STZ groups. Fourteen days before STZ injection, half of female rats were ovariectomized (OVX), or left with intact ovaries (Female group), and then separated into control or STZ groups on the same day as male rats. Two weeks later, behavioral tests were conducted for spatial memory (Barnes Maze) and depressive-like behavior (Forced swimming test). Immunofluorescence analyses were performed in the hippocampus. STZ affected spatial memory and increased depressive behavior in male, but not in female rats. We assessed GFAP expression and JAK2/STAT3 signaling activation, and we found sex differences on astrocyte reaction to STZ, with astrocyte reactivity evidence only in male rats. Also, STZ induced synapse loss in male rats, although it did not affect the expression of astrocyte proteins relevant for synapses, independent of the sex. We conclude that STZ affected differentially male and female rats, and OVX did not render the rats more vulnerable to STZ. Therefore, experimental design changes should be considered in order to set up a female sporadic AD model, and sex differences in the icv-STZ model should be addressed and further studied.

Development

Author: Christell Tatiana Becerra Flores | Email: 174203@unsaac.edu.pe

Christell Becerra ^1°, Carlos Medina-Saldívar ^1°, Enver M. Oruro ^2°, Grace E. Pardo ^1°, Luis F. Pacheco-Otálora ¹

1° Laboratorio de Investigación en Neurociencias Universidad Andina del Cusco
2° Laboratorio de Neurocomputación, Simulación Social y Sistemas Complejos Universidad Andina del Cusco

Background: In rat pups, home odor preference is present at postnatal day (P) 5; however, the ability to discriminate home nest odors from other nests appears on P10. The developmental shift in GABA signaling in the piriform cortex (PCX) could be a possible explanation at the neuronal level for why P10 pups discriminate their nest odor from other similar nests but not younger pups.
Methods: To test this hypothesis, we used a computational model of the PCx for rat pups constructed with our experimental data, including data from P5 and P10 PCx GABA synaptic input profile, then simulated the home-odor processing discrimination. During both periods, we also studied the expression of the KCC2 chloride extruder in the PCX using RT-qPCR and Western blotting.
Results: The results show that the number of active neurons and evoked spikes in response to two highly similar odors were higher than for the other nest in the P10 circuit, but this comparison was identical in the P5 circuit, suggesting discrimination odor ability in the P10 circuit but not in P5. Moreover, gene and protein expression of KCC2 was significantly upregulated in P10 compared to P5, suggesting a shift of GABAergic transmission from depolarizing to hyperpolarizing.
Conclusions: Our results support the idea that the ability to discriminate between closely associated nest odors in P10 rat pups may be attributed to the developmental shift in GABAergic signaling in the PCx between P5 and P10.

Chronobiology

Author: Juan Ignacio Ispizua | Email: ispizua.juan@gmail.com

Juan Ignacio Ispizua 1°, Magdalena Fernandez-Acosta 1°, Maria Fernanda Ceriani 1°

1° Laboratorio de Genética del Comportamiento, IIBBA – Fundación Instituto Leloir, CABA, Argentina.

The small lateral ventral neurons (s-LNvs) are a core pacemaker in the D. melanogaster circadian network. They rhythmically release the neuropeptide Pigment Dispersing Factor (PDF), acting as a synchronizer for the rest of the clock. In phase with the rhythm of PDF levels, s-LNvs dorsal termini adopt different structures during the day. This property, named circadian structural plasticity, relies on a functional glial clock; but the nature of this reliance is unknown. In this work, we delve into this interaction .
Using GFP reconstitution assays, we found that s-LNvs termini contact two glial subtypes in a circadian manner: astrocytes and ensheathing glia (EG). Then, we found that short-term adult-specific blockage of gliotransmission in either cell type dampens structural remodelling without affecting PDF neuropeptide levels: even a 12 hours silencing of the astrocytes compromises neuronal remodeling .
Lastly, knocking down maverick (a ligand of the BMP pathway that may act as gliotransmitter) in astrocytes has a similar effect on the remodelling as blocking vesicle release; on the other hand, MAV KD has no effect when downregulated in the EG.
Our results suggest that glial subtypes contribute to shape neuronal terminals differently: while communication from both astrocytes and EG is important for structural remodeling, different gliotransmitters may be recruited to mediate this effect.

Cognition, Behavior, and Memory

Author: luciano cavallino | Email: lcavallino@hotmail.com

Luciano Cavallino ^1°, Florencia Scaia ^2°, Andrea Pozzi ^2°, Eugenia Pedreira ^1°

1° Laboratorio de Neurociencias de la memoria, Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
2° Laboratorio de Neuroendocrinología y comportamiento en peces y anfibios, DBBE, IBBEA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, CABA, Argentina. Intendente Güiraldes 2160, Pabellón 2, Piso 4º, Laboratorio26 (C1428EHA). Fax: +54 1145763384

In male zebrafish, Danio rerio, we observed that there is a memory of an agonistic encounter against a particular opponent, which generates a behavioral modulation in successive encounters. This effect is prevented by treatment with an amnesic agent (MK-801) after the first encounter. Evaluating the neuronal activation through C-fos protein quantification in thelencephalic nuclei, significant differences were found between the fish with social interaction and the control group (isolated fish without interaction), showing greater neuronal activation in the ventral nucleus of the ventral telencephalic region (Vv) when the individuals had social interaction. The same trend was observed in the dorsal nucleus of the ventral region (Vd) and in the medial nucleus of the dorsal region (Dm). In the lateral nucleus of the dorsal telencephalic area (Dl), a greater activation was observed in fish previously exposed to MK-801 (they interact against an opponent of which they would have no memory) than in fish treated with water (they interact with an opponent of which they would have memory). We also found differences in the correlation between nuclei (Vv,Vd,Dm,Dl) for each treatment (water, MK-801 and control group), evaluating not only the activation of each nucleus but also the interaction between them. Finally, we did not observe a clear relationship between the levels of aggressiveness shown by individuals and neuronal activation.

Theoretical and Computational Neuroscience

Author: Catalina María Galván | Email: catalinamgalvan@gmail.com

Catalina M. Galván ^1°, Ruben D. Spies ^1°, Diego H. Milone ^2°, Victoria Peterson ^1°

1° Instituto de Matemática Aplicada del Litoral, IMAL, UNL, CONICET, Argentina
2° Instituto de Investigación en Señales, Sistemas e Inteligencia Computacional, sinc, FICH-UNL/CONICET, Argentina

Reducing calibration time is crucial for enhancing the usability of brain-computer interfaces based on motor imagery. Due to the high inter-user variability of electroencephalography (EEG) signals, a user traditionally has to endure long and tedious calibration sessions to collect enough personalized training data before using the system. This need has become even more evident with the advent of deep learning decoding models, whose performance strongly depends on the volume of data available for training. Inter-user transfer learning, where other users’ data is used to train the model, reduces the required amount of personalized training data. In this context, self-supervised learning strategies can be used to pretrain the first stages of the model on a pretext task and then adapt it to the task of interest through fine-tuning with a few data from the target user.
Here, we propose a self-supervised learning approach based on a fully convolutional encoder-decoder network. The reconstruction of EEG segments of a channel is used as the pretext task. Then an ensemble of the pre-trained encoders per EEG channel, followed by a classification block, conforms the final decoding model. This model is fine-tuned with a small dataset of the target user in the final MI-classification task.

Sensory and Motor Systems

Author: Facundo Fainstein | Email: facu.fainstein@gmail.com

Facundo Fainstein ^1°, Ana Amador ^1°, Franz Goller ^2°, Gabriel B. Mindlin ^3°

1° Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, Ciudad Universitaria, 1428 Buenos Aires, Argentina, and CONICET – Universidad de Buenos Aires, Instituto de Física Interdisciplinaria y Aplicada (INFINA), Ciudad Universitaria, 1428 Buenos Aires, Argentina.
2° Institute of Zoophysiology, University of Münster, Münster 48143, Germany and School of Biological Sciences, University of Utah, Salt Lake City, Utah 84112, USA
3° Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, Ciudad Universitaria, 1428 Buenos Aires, Argentina, and CONICET – Universidad de Buenos Aires, Instituto de Física Interdisciplinaria y Aplicada (INFINA), Ciudad Universitaria, 1428 Buenos Aires, Argentina, and Universidad Rey Juan Carlos, Departamento de Matemática Aplicada, Madrid, Spain.

Activation of circuits in the forebrain during sleep has been linked to the consolidation of memories, including motor memories. However, the specific motor patterns reproduced during sleep remain largely elusive in any system. Single-cell measurements in these brain areas in songbirds have not allowed the detection of specific song patterns and a precise study of variants not observed during daytime performance. It has recently been discovered that in zebra finches this activity can be detected in the muscles of the vocal organ. Interestingly, this activity was not simultaneous with song-like respiratory events, which were thought to be inhibited. In this work we show that domestic canaries (Serinus canaria) exhibit spontaneous song-like activity in respiratory muscles and in air sac pressure fluctuations. These events are frequent predominantly towards the end of the night, shorter than daytime vocalizations but with similar rhythmic patterns. We find that the syllable sequences observed during the night deviate from the most probable sequences during daytime vocalizations. More generally, this result contributes to a program aimed at quantitatively studying dreamt complex motor patterns.

Neuroendocrinology and Neuroimmunology

Author: Ana Paula Toselli | Email: ana.paula.toselli@mi.unc.edu.ar

Ana Paula Toselli ^1°, Antonella Pollano ^1°, Marta M. Suárez ^1°, Ma. Angélica Rivarola ^1°2°, Carlos Wilson ^3°, Franco R. Mir ^1°4°

1° Cátedra de Fisiología Animal – Facultad de Ciencias Exactas, Físicas y Naturales – Universidad Nacional de Córdoba.
2° INICSA – Instituto de Investigaciones en Ciencias de la Salud – CONICET – Facultad de Ciencias Médicas – Universidad Nacional de Córdoba.
3° Centro de Investigación en Medicina Traslacional Severo Amuchástegui – Instituto Universitario de Ciencias Biomédicas de Córdoba.
4° Cátedra de Fisiología Animal – Departamento de Ciencias Exactas, Físicas y Naturales – Universidad Nacional de La Rioja.

Exposure to adverse life events can contribute to the development of depression. The dentate gyrus (DG) of the hippocampus, known for its remarkable plasticity through neurogenesis, is one of the regions sensitive to such alterations. Hypotheses like match/mismatch attempt to elucidate how the relationship between early-life experiences and later adulthood plays a crucial role in stress coping strategies. In this study, we aimed to investigate the impact of early maternal separation (SMT) and chronic variable stress (CVS), both individually and combined, on the neural precursor population. Male rats underwent 4.5 hours of SMT between postnatal days 1 to 21. Subsequently, between postnatal days 50 to 74, the rats were exposed to a CVS protocol and concurrently treated with either the antidepressant Tianeptine (TIA) at 10 mg/kg or vehicle. The number of neural precursors in the subgranular zone of the DG was quantified using immunohistochemistry targeting SOX2 and confocal microscopy. Our findings revealed that only CVS exposure led to a significant 46% reduction in the neural precursor cell population. Furthermore, this impact was morphologically distinct, with the supra-pyramidal zone being the most affected. Interestingly, TIA was effective in restoring the number of neural precursors to control levels only in the infrapyramidal zone. Collectively, our results cannot be explained by the match/mismatch hypothesis, suggesting that alternative hypotheses must be considered.