Shedding light on learning and memory: optical interrogation of the synaptic circuitry

Modulating neuroinflammation and cognitive function in postoperative cognitive dysfunction via CCR5-GPCRs-Ras-MAPK pathway targeting with microglial EVs

AIMS

Postoperative cognitive dysfunction (POCD) is prevalent among the elderly, characterized primarily by cognitive decline after surgery. This study aims to explore how extracellular vesicles (EVs) derived from BV2 microglial cells, with and without the C-C chemokine receptor type 5 (CCR5), affect neuroinflammation, neuronal integrity, and cognitive function in a POCD mouse model.

METHODS

We collected EVs from LPS-stimulated BV2 cells expressing CCR5 (EVsM1) and from BV2 cells with CCR5 knockdown (EVsM1-CCR5). These were administered to POCD-induced mice. Protein interactions between CCR5, G-protein-coupled receptors (GPCRs), and Ras were analyzed using structure-based docking and co-immunoprecipitation (Co-IP). We assessed the phosphorylation of p38 and Erk, the expression of synaptic proteins PSD95 and MAP2, and conducted Morris Water Maze tests to evaluate cognitive function.

RESULTS

Structure-based docking and Co-IP confirmed interactions between CCR5, GPR, and Ras, suggesting a CCR5-GPCRs-Ras-MAPK pathway involvement in neuroinflammation. EVsM1 heightened neuroinflammation, reduced synaptic integrity, and impaired cognitive function in POCD mice. In contrast, EVsM1-CCR5 reduced neuroinflammatory markers, preserved synaptic proteins, enhanced dendritic spine structure, and improved cognitive outcomes.

CONCLUSION

EVsM1 induced neuroinflammation via the CCR5-GPCRs-Ras-MAPK pathway, with EVsM1-CCR5 showing protective effects on POCD progression, suggesting a new therapeutic strategy for POCD management via targeted modification of microglial EVs.

Structural characterization of two nanobodies targeting the ligand-binding pocket of human Arc

The activity-regulated cytoskeleton-associated protein (Arc) is a complex regulator of synaptic plasticity in glutamatergic neurons. Understanding its molecular function is key to elucidate the neurobiology of memory and learning, stress regulation, and multiple neurological and psychiatric diseases. The recent development of anti-Arc nanobodies has promoted the characterization of the molecular structure and function of Arc. This study aimed to validate two anti-Arc nanobodies, E5 and H11, as selective modulators of the human Arc N-lobe (Arc-NL), a domain that mediates several molecular functions of Arc through its peptide ligand binding site. The structural characteristics of recombinant Arc-NL-nanobody complexes were solved at atomic resolution using X-ray crystallography. Both anti-Arc nanobodies bind specifically to the multi-peptide binding site of Arc-NL. Isothermal titration calorimetry showed that the Arc-NL-nanobody interactions occur at nanomolar affinity, and that the nanobodies can displace a TARPγ2-derived peptide from the binding site. Thus, both anti-Arc-NL nanobodies could be used as competitive inhibitors of endogenous Arc ligands. Differences in the CDR3 loops between the two nanobodies indicate that the spectrum of short linear motifs recognized by the Arc-NL should be expanded. We provide a robust biochemical background to support the use of anti-Arc nanobodies in attempts to target Arc-dependent synaptic plasticity. Function-blocking anti-Arc nanobodies could eventually help unravel the complex neurobiology of synaptic plasticity and allow to develop diagnostic and treatment tools.

SHANK3 Mutations Associated with Autism and Schizophrenia Lead to Shared and Distinct Changes in Dendritic Spine Dynamics in the Developing Mouse Brain

Autism Spectrum Disorders (ASD) and schizophrenia are distinct neurodevelopmental disorders that share certain symptoms and genetic components. Both disorders show abnormalities in dendritic spines, which are the main sites of excitatory synaptic inputs. Recent studies have identified the synaptic scaffolding protein Shank3 as a leading candidate gene for both disorders. Mutations in the SHANK3 gene have been linked to both ASD and schizophrenia; however, how patient-derived mutations affect the structural plasticity of dendritic spines during brain development is unknown. Here we use live two photon in vivo imaging to examine dendritic spine structural plasticity in mice with SHANK3 mutations associated with ASD and schizophrenia. We identified shared and distinct phenotypes in dendritic spine morphogenesis and plasticity in the ASD-associated InsG3680 mutant mice and the schizophrenia-associated R1117X mutant mice. No significant changes in dendritic arborization were observed in either mutant, raising the possibility that synaptic dysregulation may be a key contributor to the behavioral defects previously reported in these mice. These findings shed light on how patient-linked mutations in SHANK3 affect dendritic spine dynamics in the developing brain, which provides insight into the synaptic basis for the distinct phenotypes observed in ASD and schizophrenia.

Dendritic Spines in Learning and Memory: From First Discoveries to Current Insights

The central nervous system is composed of neural ensembles, and their activity patterns are neural correlates of cognitive functions. Those ensembles are networks of neurons connected to each other by synapses. Most neurons integrate synaptic signal through a remarkable subcellular structure called spine. Dendritic spines are protrusions whose diverse shapes make them appear as a specific neuronal compartment, and they have been the focus of studies for more than a century. Soon after their first description by Ramón y Cajal, it has been hypothesized that spine morphological changes could modify neuronal connectivity and sustain cognitive abilities. Later studies demonstrated that changes in spine density and morphology occurred in experience-dependent plasticity during development, and in clinical cases of mental retardation. This gave ground for the assumption that dendritic spines are the particular locus of cerebral plasticity. With the discovery of synaptic long-term potentiation, a research program emerged with the aim to establish whether dendritic spine plasticity could explain learning and memory. The development of live imaging methods revealed on the one hand that dendritic spine remodeling is compatible with learning process and, on the other hand, that their long-term stability is compatible with lifelong memories. Furthermore, the study of the mechanisms of spine growth and maintenance shed new light on the rules of plasticity. In behavioral paradigms of memory, spine formation or elimination and morphological changes were found to correlate with learning. In a last critical step, recent experiments have provided evidence that dendritic spines play a causal role in learning and memory.

Usability of Memes and Humorous Resources in Virtual Learning Environments

This research consists of a quantitative analysis of the perspective of a group of university professors from different areas of knowledge and from 19 different Latin American countries on the use of humor and memes in virtual learning environments (VLEs) in higher education. The data have been obtained from an own-design survey, and the answers have been analyzed in a descriptive and inferential way with the aim of knowing the opinion of the 401 participants (professors) about the didactic effectiveness of humor and the benefits and employability of memes in virtual classrooms. The analysis differentiates the sample by the professors’ area of knowledge as the main variable, and by gender, age and teaching experience. As results, the participants give a high evaluation of humorous didactic resources, particularly memes, although the evaluation of their usability in the classroom is intermediate. In this sense, it is shown that the area of knowledge has a significant influence on opinions in this regard.

Beyond dimension reduction: Stable electric fields emerge from and allow representational drift

It is known that the exact neurons maintaining a given memory (the neural ensemble) change from trial to trial. This raises the question of how the brain achieves stability in the face of this representational drift. Here, we demonstrate that this stability emerges at the level of the electric fields that arise from neural activity. We show that electric fields carry information about working memory content. The electric fields, in turn, can act as "guard rails" that funnel higher dimensional variable neural activity along stable lower dimensional routes. We obtained the latent space associated with each memory. We then confirmed the stability of the electric field by mapping the latent space to different cortical patches (that comprise a neural ensemble) and reconstructing information flow between patches. Stable electric fields can allow latent states to be transferred between brain areas, in accord with modern engram theory.

Synaptic modifications in learning and memory - A dendritic spine story

Synapses are specialized sites where neurons connect and communicate with each other. Activity-dependent modification of synaptic structure and function provides a mechanism for learning and memory. The advent of high-resolution time-lapse imaging in conjunction with fluorescent biosensors and actuators enables researchers to monitor and manipulate the structure and function of synapses both in vitro and in vivo. This review focuses on recent imaging studies on the synaptic modification underlying learning and memory.