Biology subjects

Davis, O. C.

Publications and source records attributed to Davis, O. C..

6 recordsLinked to original sources

bioRxiv2026

Chronic lower limb pain is not associated with a loss of inhibitory neurons in the human lumbar spinal dorsal horn

The spinal dorsal horn is the primary processing site of nociceptive sensory input from the periphery. Excitatory spinal interneurons releasing glutamate can amplify this information before it is sent to the brain, whereas inhibitory neurons releasing GABA and/or glycine can suppress the outflow of nociceptive signals. An imbalance favoring excitation is thought to underlie certain aspects of chronic pain. Although rodent studies have identified spinal mechanisms underlying hyperalgesia and allodynia, little is known about the anatomical changes associated with chronic pain in the human spinal cord, a gap in knowledge we sought to address in this study. Using immunohistochemistry and in situ hybridization on lumbar spinal cord tissue recovered from organ donors, we characterized neuronal size and density across the human dorsal horn and confirmed the presence of the human equivalent of the lateral spinal nucleus in many individuals. Chronic lower limb pain was not associated with changes in neuronal density in the dorsal horn. Likewise, the ratio of excitatory (SLC17A6+) to inhibitory (PAX2+) neurons remained consistent across laminae for age, sex and chronic pain state, providing no evidence for selective loss of inhibitory neurons with chronic pain in humans. We found no differences in the size or density of the postsynaptic markers Homer1 and gephyrin between groups, suggesting glutamatergic and GABAergic postsynaptic sites remain structurally stable. These findings provide a thorough evaluation of cellular anatomy of the human dorsal horn and form a foundation for future studies investigating neuronal changes that may contribute to chronic pain in humans.

neuroscience↗

bioRxiv2025

A molecular map of the human spinal dorsal and ventral horn defines arrangement of neuronal types and glial sex differences

The spinal cord is the gateway for somatosensory and nociceptive information to the brain and a key locus for sensory-motor integration. Studies in mice have advanced our understanding of spinal cord circuitry, and transcriptomic studies have begun to characterize the human spinal cord; however, major gaps in knowledge persist. We conducted single-nucleus sequencing of lumbar spinal cord tissue from 11 adult organ donors and annotated spinal cord cell types with high resolution spatial transcriptomics. We identified 34 spatially and transcriptionally defined neuronal classes and detected sex-specific cell types and states across multiple glial populations. Electrophysiological recordings from dorsal horn neurons revealed firing patterns for neuronal subtypes and group I mGluR-dependent plasticity. Our work defines previously unknown aspects of human spinal cord molecular anatomy and physiology.

neuroscience↗

bioRxiv2025

Glutamatergic and GABAergic synapses in the human spinal dorsal horn revealed with immunohistochemistry

Primary afferent neurons detect sensory stimuli in the periphery and transmit this information to the dorsal horn of the spinal cord, where it is extensively processed by excitatory and inhibitory spinal controls before being sent to higher brain centres. Immunohistochemical analysis of the synaptic architecture of these spinal circuits has been notoriously difficult in formaldehyde-fixed tissue and often requires antigen retrieval techniques to reveal antigen binding epitopes. To avoid the damage this harsh treatment can induce, studies have used antibodies raised against scaffolding proteins Homer1 and gephyrin, which anchor glutamate and GABA receptors to the membrane, respectively, to identify synaptic associations in rodent spinal cord underlying pain and itch transmission. In contrast, few studies have attempted to visualise spinal cord synapses in the human, partly due to a lack of high-quality tissue with low postmortem intervals. In this study, we reveal both excitatory and inhibitory synapses at a high resolution in human lumbar spinal cord tissue using antibodies to Homer1 and gephyrin and show that the basic organisation of these proteins within the dorsal horn is similar to that seen in the rodent. We show these postsynaptic markers are highly colocalised with glutamate and GABA receptor subunits and are in close apposition to presynaptic markers, confirming their specificity. Finally, we use Homer1-immunolabelling to demonstrate that primary afferents can form complex synaptic arrangements in human. We conclude that these antibodies can be used as reliable tools for the study of the human CNS and we have used them to reveal insight into the microanatomy of somatosensory connections in the human spinal cord that can be expanded upon in future studies.

neuroscience↗

bioRxiv2025

Decreased KCC2 expression in the human spinal dorsal horn associated with chronic pain and long-term opioid use

Loss of GABAergic and glycinergic inhibitory efficacy in the spinal dorsal horn is associated with neuropathic pain and opioid-induced hyperalgesia in rodent models. Downregulation of the KCC2 chloride extrusion transporter is a key mechanism underlying this decreased inhibitory efficacy, but to-date there is no evidence supporting or opposing this hypothesis in humans. Here we demonstrate that KCC2 expression is decreased in superficial dorsal horn neurons of organ donors who died with a documented history of pain, or of long-term opioid use. We show profoundly decreased KCC2 dorsal horn membrane expression in a primary cohort associated with either chronic pain or opioid use, and in a replication cohort of mixed chronic pain and opioid use history. These results show that decreased dorsal horn inhibitory efficacy likely promotes chronic pain in humans and support the development of therapeutics augmenting KCC2 function as a treatment for chronic pain and opioid use disorders.

neuroscience↗

bioRxiv2023

Calretinin-expressing islet cells: a source of pre- and post-synaptic inhibition of non-peptidergic nociceptor input to the mouse spinal cord

Unmyelinated non-peptidergic nociceptors (NP afferents) arborise in lamina II of the spinal cord and receive GABAergic axoaxonic synapses, which mediate presynaptic inhibition. However, until now the source of this axoaxonic synaptic input was not known. Here we provide evidence that it originates from a population of inhibitory calretinin-expressing interneurons (iCRs), which correspond to lamina II islet cells. The NP afferents can be assigned to 3 functionally distinct classes (NP1-3). NP1 afferents have been implicated in pathological pain states, while NP2 and NP3 afferents also function as pruritoceptors. Our findings suggest that all 3 of these afferent types innervate iCRs and receive axoaxonic synapses from them, providing feedback inhibition of NP input. The iCRs also form axodendritic synapses, and their targets include cells that are themselves innervated by the NP afferents, thus allowing for feedforward inhibition. The iCRs are therefore ideally placed to control the input from non-peptidergic nociceptors and pruritoceptors to other dorsal horn neurons, and thus represent a potential therapeutic target for the treatment of chronic pain and itch.

neuroscience↗

bioRxiv2022

The matrisome of the murine and human dorsal root ganglion: a transcriptomal approach

The extracellular matrix (ECM) is a dynamic structure composed of a large number of molecules that can be divided into six different categories and are collectively called the matrisome. The ECM plays pivotal roles in physiological and pathological processes in many tissues, including the nervous system. Intriguingly, alterations in ECM molecules/pathways are often associated with painful human conditions and murine experimental pain models. Nevertheless, mechanistic insight into the interplay of normal or defective ECM and pain is largely lacking. To expand the knowledge on ECM composition and synthesis in the peripheral nervous system, we used a transcriptomal approach to investigate the expression and cellular origin of matrisome genes in murine and human dorsal root ganglia (DRG), containing the cell bodies of sensory neurons. Bulk RNA sequencing data showed that over 60% of all matrisome genes were expressed in both murine and human DRG, with proportionally more core matrisome genes (glycoproteins, collagens, and proteoglycans) expressed compared to matrisome-associated genes (ECM-affiliated genes, ECM regulators and secreted factors). Examination of the cellular origin of matrisome expression by single cell RNA sequencing on murine DRG revealed that core matrisome genes, especially collagens, were expressed by vascular leptomeningeal-like (fibroblast) cell types whereas matrisome-associated genes were mainly expressed by neuronal cell types. We analyzed cell-cell communication networks with the CellChat R package and predicted an important role for the Collagen signaling pathway in connecting vascular cell types and nociceptors in murine tissue, which we confirmed by analysis of spatial transcriptomic data from human DRG. RNAscope in situ hybridization and immunohistochemistry confirmed expression of collagens in fibroblasts surrounding nociceptors in human DRG. This study supports the idea that the DRG matrisome may contribute to neuronal signaling in both mouse and human. The identification of the cellular distribution of murine and human matrisome genes provides a framework to study the role of the ECM in peripheral nervous tissue and its effects on pain signaling. HighlightsO_LITranscriptomal analyses of mouse and human dorsal root ganglia (DRG) revealed that over 60% of matrisome genes are expressed by murine and human dorsal root ganglia (DRG), with over 85% of the genes with orthologues overlapping between both species. C_LIO_LIMatrisome-associated genes had the highest expression in both species and included conserved expression of annexins, S100 calcium binding proteins and cathepsins. C_LIO_LICollagens and collagen receptors are expressed by distinct cell types in murine and human DRG, suggesting that the collagen signaling pathway could be involved in cell-cell signaling. C_LI

neuroscience↗