Biology subjects

Medalla, M.

Publications and source records attributed to Medalla, M..

8 recordsLinked to original sources

bioRxiv2026

Multimodal characterization of putative pan-inhibitory viral constructs in macaque monkeys

Transgenic approaches and validated viral vector toolboxes have advanced our understanding of how inhibitory neurons shape cognition and motor control in mice and other rodents. However, such advances have been elusive in non-human primates (NHPs). While many studies demonstrate expression of reporter proteins, few studies have provided clear quantitative evidence of whether these viral constructs can be reliably used for assessment of in vivo and in vitro function in primates, which, in turn, has hindered widespread adoption by NHP researchers. Here, we characterize putative pan-inhibitory cell targeting vectors engineered with regions from the Dlx5-6 intergenic domain. Pan-inhibitory viral vectors are attractive because they enable ground-truth optotagging and modulation of multiple inhibitory subtypes in the same animal and, when combined with machine learning approaches, enable cell-type classifiers for NHPs. We combined in vivo anesthetized electrophysiological recordings, in vitro slice electrophysiology, and immunohistochemistry across seven rhesus macaque monkeys to assess the specificity, completeness and efficacy of three constructs in multiple sensory and higher-order association cortices. The vectors reliably restricted transgene expression to inhibitory neurons (81-97%). However, of the local GABAergic neurons only 32-64% expressed the transgene, depending on the construct. This incompleteness arose in part from uneven coverage across subtypes, with strong transgene expression in parvalbumin-positive interneurons (~60-90%), sparse expression in calbindin-positive interneurons (~1-7%), and near-complete avoidance of calretinin-positive interneurons. A construct pairing DLX2.0 with ChrimsonR was excellent for in vivo optotagging, while h56D paired with bReaChES most effectively suppressed neural activity in vivo. In the slice, activating terminals of transgene-expressing neurons optically evoked inhibitory currents in coupled pyramidal neurons confirming transsynaptic functionality of these constructs and their use for inhibitory circuit-specific synaptic assessments and manipulation. Collectively, the results provide rigorous functional characterization, and quantitative guidance for NHP researchers seeking to deploy GABAergic cell-type-specific tools in their experiments.

neuroscience↗

bioRxiv2026

Entorhinal Cortex Wolframin-1-expressing neurons propagate tau to CA1 neurons and impair hippocampal memory

Tau pathology emerges early in Alzheimers disease within entorhinal cortex layer II (ECII) and reaches hippocampal CA1, but how this circuit-level spread translates into sex-dependent vulnerability remains unclear. Using a circuit-defined model in which P301L human tau is expressed selectively in Wolframin-1 (Wfs1+) ECII neurons and propagates to CA1, we found that the extent and proximal-distal distribution of tau-positive CA1 neurons were comparable in males and females. Despite similar propagation, females exhibited broad hippocampal-dependent cognitive impairment (working memory, object recognition, fear acquisition, trace associative memory, and contextual fear memory), whereas males showed a selective deficit in trace associative memory. Consistent with these behavioral outcomes, CA1 pyramidal neurons in tau-propagated females displayed reduced excitability (slower action potential kinetics, reduced firing during depolarizing steps) and reduced spontaneous excitatory postsynaptic current (EPSC) amplitude, while males showed subtler intrinsic changes with altered EPSC kinetics. Bulk RNA sequencing of entorhinal cortex and CA1 revealed robust immune pathway engagement after tau propagation, with males showing a stronger Th1/Th2 and neuroinflammatory signature and CTLA4-associated signaling changes, whereas females showed prominent complement-phagosome pathway enrichment and a female-specific increase in Clec7a+ microglia density in CA1. CD4+ T-cell infiltration into CA1 was detected in both sexes. Together, these results indicate that sex-specific neuroimmune programs, rather than differences in tau propagation load, shape CA1 electrophysiological dysfunction and the breadth of memory impairment following early entorhinal-to-hippocampal tau spread.

neuroscience↗

bioRxiv2025

Transcriptional and functional profiles of muscarinic receptor-expressing neurons in primate lateral prefrontal and anterior cingulate cortices

Acetylcholine modulates anterior cingulate (ACC) and lateral prefrontal (LPFC) cortices for cognitive-motivational integration, via specific m1-m4 muscarinic receptors (mAChR) encoded by CHRM1-4 genes. Single-nucleus RNA sequencing and mRNA-protein histology in macaques revealed CHRM3 to be the most enriched mAChR gene in neurons, while m1 predominates at the protein level, likely due to nuclear retention of CHRM3 and cytoplasmic trafficking of CHRM1. CHRM3 and CHRM1 showed strong co-expression and functional overlap, and were transcriptomically-distinct from CHRM2, which was uniquely enriched in deep layer excitatory and PVALB+ inhibitory neurons. Although CHRM+ cell distributions were similar between areas, CHRM1-3+ excitatory neurons in ACC exhibited upregulation of synaptic plasticity genes relative to LPFC. Functional in vitro experiments confirm a more robust cholinergic-mediated decrease in excitatory:inhibitory synaptic ratio in ACC than in LPFC neurons, accompanied by compensatory changes in spine morphology. These findings highlight region-specific acetylcholine signaling essential for flexible processing, learning and memory.

neuroscience↗

bioRxiv2024

Mesenchymal Cell-Derived Extracellular Vesicles Ameliorate Age-Related Deficits in Working Memory as well as Brain MRI and CSF in vivo Biomarkers of Neurodegeneration in Rhesus Monkeys.

Normal aging in humans and non-human primates is associated with a decline in cognitive functions. Subject-wise differences in cognitive decline can be attributed to different degrees of damage to cortical white matter (WM) which is largely affected by neuroinflammation during aging. Mesenchymal stromal cell-derived extracellular vesicles (MSC-EVs) have recently been identified as a potential immunomodulatory therapeutic for brain damage and Alzheimers disease (AD) and related dementias by suppressing neuroinflammation. Here, we evaluated the efficacy of MSC-EVs for slowing or ameliorating cognitive decline during aging in rhesus monkeys, a well-studied model of normal aging that is free of extensive AD pathology. We report that late middle-aged monkeys treated with MSC-EVs every two weeks for 18 months showed improved performance on a task of spatial working memory relative to vehicle control monkeys. In addition, we used diffusion magnetic resonance imaging (MRI) and resting state functional MRI to evaluate structural white matter and functional network changes in vivo. Imaging data revealed that MSC-EV treatment preserved prefrontal and temporal WM structural integrity and large-scale functional network connectivity that are correlated with early, increased CSF levels of amyloid beta protein. Amyloid beta levels at 12 months are also correlated with improved cognitive performance at the end of the 18 months of treatment. These findings suggest that MSC-EVs can mitigate age-related cognitive decline by potentially enhancing the CSF clearance of neurodegenerative proteins, which correlates with greater WM integrity and functional brain connectivity.

neuroscience↗

bioRxiv2023

Comparative Features of Calretinin, Calbindin and Parvalbumin Expressing Interneurons in Mouse and Monkey Primary Visual and Frontal Cortices

Much is known about differences in pyramidal cells across cortical areas and species, but studies of interneurons have focused on comparisons within single cortical areas and/or species. Here we quantified the distribution and somato-dendritic morphology of interneurons expressing one or more of the calcium binding proteins (CaBPs) calretinin (CR), calbindin (CB) and/or parvalbumin (PV) in mouse (Mus musculus) versus rhesus monkey (Macaca mulatta) in two functionally and cytoarchitectonically distinct regions- the primary visual and frontal cortical areas. The density, laminar distribution and morphology of interneurons were assessed in serial brain sections using immunofluorescent multi-labeling, stereological counting and 3D reconstructions. There were significantly higher densities of CB+ and PV+ neurons in visual compared to frontal areas in both species. The main species difference was the significantly greater density and proportion of CR+ interneurons and lower extent of CaBP co-expression in monkey compared to mouse cortices. Cluster analyses revealed that the somato-dendritic morphology of layer 2-3 inhibitory interneurons is more dependent on CaBP expression than on species and area. Only modest effects of species were observed for CB+ and PV+ interneuron morphologies, while CR+ neurons showed no difference. By contrast to pyramidal cells which show highly distinctive area- and species-specific features, here we found more subtle differences in the distribution and features of interneurons across areas and species. These data yield insight into how nuanced differences in the population organization and properties of neurons may underlie specializations in cortical regions to confer species and area-specific functional capacities. Key PointsO_LISomato-dendritic morphology of distinct interneurons did not substantially scale and vary across areas and species- differences were mainly dependent on CaBP expression. C_LIO_LICortical diversity in inhibitory function across areas and species is thus likely to be derived from differential laminar distribution and densities of distinct interneuron subclasses. C_LIO_LIIn contrast to pyramidal cells which differ widely in distribution and morphology across areas and species, the features of interneurons appears to be relatively more conserved across areas and species. C_LI

neuroscience↗

bioRxiv2023

Neuronal properties of pyramidal cells in lateral prefrontal cortex of the aging rhesus monkey brain are associated with performance deficits on spatial working memory but not executive function.

Age-related declines in cognitive abilities occur as early as middle-age in humans and rhesus monkeys. Specifically, performance by aged individuals on tasks of executive function (EF) and working memory (WM) is characterized by greater frequency of errors, shorter memory spans, increased frequency of perseverative responses, impaired use of feedback and reduced speed of processing. However, how aging precisely differentially impacts specific aspects of these cognitive functions and the distinct brain areas mediating cognition are not well understood. The prefrontal cortex (PFC) is known to mediate EF and WM and is an area that shows a vulnerability to age-related alterations in neuronal morphology. In the current study, we show that performance on EF and WM tasks exhibited significant changes with age and these impairments correlate with changes in biophysical properties of L3 pyramidal neurons in lateral LPFC (LPFC). Specifically, there was a significant age-related increase in excitability of Layer 3 LPFC pyramidal neurons, consistent with previous studies. Further, this age-related hyperexcitability of LPFC neurons was significantly correlated with age-related decline on a task of WM, but not an EF task. The current study characterizes age-related performance on tasks of WM and EF and provides insight into the neural substrates that may underlie changes in both WM and EF with age.

neuroscience↗

bioRxiv2022

Single cell transcriptomic profiling of tauopathy in a novel 3D neuron-astrocyte coculture model

The use of iPSC derived brain organoid models to study neurodegenerative disease has been hampered by a lack of systems that accurately and expeditiously recapitulate pathogenesis in the context of neuron-glial interactions. Here we report development of a system, termed AstTau, which propagates toxic human tau oligomers in iPSC derived neuron-astrocyte spheroids. The AstTau system develops much of the neuronal and astrocytic pathology observed in tauopathies including misfolded, phosphorylated, oligomeric, and fibrillar tau, strong neurodegeneration, and reactive astrogliosis. Single cell transcriptomic profiling combined with immunochemistry characterizes a model system that can more closely recapitulate late-stage changes in adult neurodegeneration. The transcriptomic studies demonstrate striking changes in neuroinflammatory and heat shock protein (HSP) chaperone systems in the disease process. Treatment with the HSP90 inhibitor PU-H71 was used to address the putative dysfunctional HSP chaperone system and produced a strong reduction of pathology and neurodegeneration, highlighting the potential of AstTau as a rapid and reproducible tool for drug discovery.

neuroscience↗

bioRxiv2021

Non-linear Dimensionality Reduction on Extracellular Waveforms Reveals Physiological, Functional, and Laminar Diversity in Premotor Cortex

Cortical circuits are thought to contain a large number of cell types that coordinate to produce behavior. Current in vivo methods rely on clustering of specified features of extracellular waveforms to identify putative cell types, but these capture only a small amount of variation. Here, we develop a new method (WaveMAP) that combines non-linear dimensionality reduction with graph clustering to identify putative cell types. We apply WaveMAP to extracellular waveforms recorded from dorsal premotor cortex of macaque monkeys performing a decision-making task. Using WaveMAP, we robustly establish eight waveform clusters and show that these clusters recapitulate previously identified narrow- and broad-spiking types while revealing previously unknown diversity within these subtypes. The eight clusters exhibited distinct laminar distributions, characteristic firing rate patterns, and decision-related dynamics. Such insights were weaker when using feature-based approaches. WaveMAP therefore provides a more nuanced understanding of the dynamics of cell types in cortical circuits. SignificanceHow different cell types sculpt activity patterns in brain areas associated with decision-making is a fundamentally unresolved problem in neuroscience. In monkeys, and other species where transgenic access is not yet possible, identifying physiological types in vivo relies on only a few discrete user-specified features of extracellular waveforms to identify cell types. Here, we show that non-linear dimensionality reduction with graph clustering applied to the entire extracellular waveform can delineate many different putative cell types and does so in an interpretable manner. We show that this method reveals previously undocumented physiological, functional, and laminar diversity in the dorsal premotor cortex of monkeys, a key brain area implicated in decision-making.

neuroscience↗