Biology subjects

Hamou, H.

Publications and source records attributed to Hamou, H..

5 recordsLinked to original sources

bioRxiv2026

Genetic and behavioural repertoires support olfactory communication in wild capuchin monkeys

Olfaction is a key sense for many mammals, but its role in the social lives of anthropoid primates (monkeys, apes, humans) is poorly understood. Studies of chemosensory receptor genes and olfactory behaviours can provide insight into the evolution and function of olfaction across social contexts. Vomeronasal receptor (VR) genes are especially relevant to social behaviour as they are specialized for the detection of pheromones and other cues involved in social signaling, reproductive behaviour, and individual recognition in mammals. Here, we examined the population genetics and gene repertoires of VR genes in wild white-faced capuchin monkeys (Cebus imitator) from Costa Rica and Panama using DNA sourced through both host tissues and through noninvasive fluorescence-activated cell sorting of fecal samples (fecalFACS). We compared VR diversity relative to putatively neutral reference loci (NRs) to investigate evidence of selection and potential effects of demography. To complement the genetic analysis, we also conducted a detailed observational study of capuchin olfactory behaviours. Combined, we find evidence of intact VRs subject to evolutionary constraint in capuchins, providing novel evidence that members of this gene family are maintained by evolutionary constraint in wild monkeys. We further document a rich and varied ethogram of olfactory behaviours that have clear potential for communication. Overall, our study provides compelling evidence for a role of olfaction in the complex social lives of capuchin monkeys, motivating future research on the contributions of olfaction to social communication and evolution in primates and other mammals.

animal behavior and cognition↗

bioRxiv2026

Graph theory for the analysis of micro-electrode array recordings of human brain slices - framework and benchmarking

Micro-electrode array (MEA) recordings are widely used to characterize functional connectivity in neural cultures and have gained traction for the analysis of human brain slices. However, the impact of graph construction methodology on the resulting network topology has not been systematically quantified. Here, we benchmark three methods - shared spiking activity, Pearson cross-correlation, and the spike time tiling coefficient (STTC) - across 37 recordings from human cortical slice cultures classified into low, moderate, and high activity groups. We show that method choice alone produces large topological differences (Cohens d = 0.86-1.14 for clustering coefficient, d > 1.0 for node count), while higher-order features such as modularity remain stable. Each method exhibits a distinct sensitivity profile: shared spiking detects activity-dependent changes primarily through network size, correlation uniquely captures clustering differences, and STTC combines strong biological sensitivity with negligible parameter dependence across lag windows (all d < 0.1). Within shared spiking, z-score normalization dominates all other parameter choices (d > 1.0 versus bin size effects of d < 0.23), functioning as an implicit analytical null model that fundamentally reshapes the edge set rather than merely rescaling weights. Inter-method edge overlap is low (Jaccard index 0.08-0.45) and activity dependent, demonstrating that these methods identify substantially different connections from identical data. Our results reveal that methodological choices including construction method, threshold, and normalization introduce hidden degrees of freedom with effect sizes comparable to the biological signals being measured. We provide practical recommendations for parameter selection, reporting, and cross-method validation in MEA-based network neuroscience. Author SummaryWhen we record electrical activity from brain tissue using grids of electrodes, we can ask how different sites influence one another and map the tissue as a network of connections. Thanks to novel culturing methods, this approach is increasingly used to study human brain slices. However, deciding what is "connected" is not well defined. Researchers use several different methods, and it has never been clear how much this choice shapes the network they end up describing. Here we compared three widely used methods on 37 recordings from human cortical slices spanning a range of activity levels. We found that the method alone can change the apparent structure of the network as much as real biological differences do. The methods frequently disagreed about which connections exist and some technical choices, including normalization techniques, had surprisingly large effects. Because these hidden choices can rival the biological signal, we provide this benchmarking work with practical recommendations for selecting, reporting, and cross-checking methods, so that network studies of brain tissue become more transparent, comparable, and reproducible.

neuroscience↗

bioRxiv2025

Sources of Variation in Fecal Haptoglobin in a Population of Wild Capuchin Monkeys (Cebus imitator)

Non-human primates support ecosystem function by enhancing forest regeneration through seed dispersal and other key ecological roles. Unfortunately, primate populations are declining, placing renewed emphasis on monitoring the health of wild populations. Non-invasive monitoring of reliable biomarkers of inflammation and immune activation allows researchers to assess individual health status without capturing or interfering with wild animals, but studies are limited by the availability of such biomarkers that are measurable from fecal and urine samples. In the present study, we aimed to validate the measurement of fecal haptoglobin, a biomarker of inflammation, in wild white-faced capuchin monkeys (Cebus imitator), and to evaluate the relationship between fecal haptoglobin concentrations and age, sex, dominance rank, circadian effects and environmental factors including temperature and rainfall. After analytically validating the measurement of fecal haptoglobin, our results did not demonstrate a relationship between haptoglobin concentrations and age, sex, dominance rank or circadian effects. However, we found significant influences of environmental conditions on fecal haptoglobin levels, with an increase and more variation observed during drier conditions, when the animals are typically under greater environmental stress. We conclude that haptoglobin measurement is feasible in wild white-faced capuchin monkeys, and its concentrations vary in our study population, reflecting seasonal patterns of inflammation that are consistent with changes to environmental stressors associated with lower access to food and water.

physiology↗

bioRxiv2025

Non-invasive measures of DNA methylation capture molecular aging in wild capuchin monkeys

Elucidating the socio-ecological factors that shape patterns of epigenetic modification in long-lived vertebrates is of broad interest to evolutionary biologists, geroscientists, and ecologists. However, aging research in wild populations is limited due to inability to measure cellular hallmarks of aging noninvasively. Here, we demonstrate that cellular DNA methylation (DNAm) profiles from fecal samples provide an accurate and reliable molecular clock in wild capuchin monkeys. Analysis of blood, feces, and urine samples from a closely related species shows that DNAm differentiates between species and different types of biological samples. We further find age-associated differences in DNAm relevant to cellular damage, inflammation, and senescence, consistent with hallmarks conserved across humans and other mammalian species, speaking to the comparative potential. By demonstrating that DNAm can be studied non-invasively in wild animals, our research opens new avenues in the study of modifiers of the pace of aging, and increases potential for cross-population and species comparisons.

genomics↗

bioRxiv2024

Transport-Related Effects on Intrinsic and Synaptic Properties of Human Cortical Neurons: A Comparative Study

Transporting human brain tissue from the operating theater to an off-site laboratory may affect sample integrity for electrophysiological studies. This study investigated how a 30-40 minute transport influenced the intrinsic, synaptic, and morphological properties of human cortical neurons. Electrophysiological recordings were performed on Layer 2/3 (L2/3 pyramidal cells and fast-spiking (FS) interneurons from human cortical slices (n = 200 neurons from 32 surgeries), comparing on-site recordings at RWTH Aachen University Hospital and off-site at Research Centre Juelich. Action potential firing patterns remained largely preserved across both recording sites, but several differences were observed. Off-site recorded pyramidal cells showed a slightly depolarized resting membrane potential and a significantly lower rheobase current. In off-site recorded FS interneurons, we found a narrower action potential half-width and an increased amplitude, suggesting altered ion channel kinetics and/or neuromodulatory environment. Additionally, a significant reduction in large rhythmic depolarizations (LRDs) and the amplitudes of excitatory postsynaptic potentials (EPSPs) in off-site recorded FS interneurons indicated an impaired synaptic efficacy. The dendritic spine densities in apical oblique and apical tuft dendrites of off-site recorded pyramidal cells were also reduced. These findings emphasize the need for optimized transport conditions to preserve synaptic integrity, network properties, and neuronal morphology. Standardized protocols are crucial for ensuring reliable and reproducible results in studies of human cortical microcircuits. Significance StatementThis study demonstrates that transporting live human brain tissue for neuronal recordings significantly impacts the intrinsic, synaptic, and network properties of cortical neurons. By comparing on-site and off-site recordings, we found that even a brief transportation (30-40 minutes) induces increased neuronal excitability, reduced synaptic efficacy, and diminished network events such as LRDs. These alterations are likely due to the mechanical stress and washout of critical neuromodulators, which compromise tissue integrity and neuronal function. The findings underscore the necessity for optimizing transport protocols to preserve synaptic and network integrity, ensuring reliable and reproducible results in human brain research. Ultimately, this work advances our understanding of cortical microcircuitry and informs best practices for handling human brain tissue in experimental settings.

neuroscience↗