Classic Papers
Explore Classic Papers of the Week as identified by the PRF editorial team.
Opposite regulation of medullary pain-related projection neuron excitability in acute and chronic pain
Enhancer AAVs for targeting spinal motor neurons and descending motor pathways in rodents and macaque
Experimental access to cell types within the mammalian spinal cord is severely limited by the availability of genetic tools. To enable access to spinal motor neurons (SMNs) and SMN subtypes, we generated single-cell multiome datasets from mouse and macaque spinal cords and discovered putative enhancers for each neuronal population. We cloned these enhancers into adeno-associated viral vectors driving a reporter fluorophore and functionally screened them in the mouse. We extensively characterized the most promising candidate enhancers in rat and macaque and developed an optimized pan-SMN enhancer virus. Additionally, we generated derivative viruses expressing iCre297T recombinase or ChR2-EYFP for labeling and functional studies, and we created a single vector with combined enhancer elements to achieve simultaneous labeling of layer 5 extratelencephalic projecting neurons and SMNs. This unprecedented SMN toolkit will enable future investigations of cell type function across species and potential therapeutic interventions for human neurodegenerative diseases.
Rejuvenation alleviates prolonged postsurgical pain in aging mice by mitigating inflammaging.
As individuals age, they often experience persistent, unresolved pain, impacting their quality of life. Aging as a process is accompanied by “inflammaging,” a state of chronic, low-grade systemic inflammation contributing to various diseases. Understanding the functional link between inflammaging and age-related development of pain is crucial for identifying novel therapeutic targets. We hypothesized that the circulatory milieu plays a role in regulating pain and that inflammaging contributes to changes in pain behavior with age. To test these hypotheses, we monitored nociception and postsurgical pain in male and female mice aged 3 and 24 months and analyzed their serum proteome, including cytokine/chemokine profiles. Our results demonstrated that compared with young mice, aging mice were hyposensitive to mechanical stimulation, yet their pain response to incision was aggravated and prolonged. Serum proteomic analysis revealed sex-specific inflammaging patterns. To explore the link between inflammaging and age-related alteration in pain behavior, we applied a rejuvenation strategy by transferring serum from 3-month-old mice to 19- to 21-month-old mice. Young serum normalized mechanical sensitivity in aged mice, alleviated postsurgical mechanical pain, and promoted recovery. Alongside the improvements in pain behavior phenotype, young serum recalibrated the aging serum profile. It reduced age-associated increases of cytokine/chemokine levels in male mice and rescued age-related, female-selective downregulation of inflammatory pathways such as liver X receptor/retinoid X receptor activation, D24-dehydrocholesterol reductase, and complement signaling. Our findings suggest that the circulatory environment, notably inflammaging, plays a significant role in altered pain behavior of aging mice. The sex-specific signature of age-dependent systemic inflammation highlights the importance of investigating inflammaging through the lens of sexual dimorphism.
Projection-TAGs enable multiplex projection tracing and multi-modal profiling of projection neurons
Single-cell multiomic techniques have sparked immense interest in developing a comprehensive multi-modal map of diverse neuronal cell types and their brain-wide projections. However, investigating the complex wiring diagram, spatial organization, transcriptional, and epigenetic landscapes of brain-wide projection neurons is hampered by the lack of efficient and easily adoptable tools. Here we introduce Projection-TAGs, a retrograde AAV platform that allows multiplex tagging of projection neurons using RNA barcodes. By using Projection-TAGs, we performed multiplex projection tracing of the cortex and high-throughput single-cell profiling of the transcriptional and epigenetic landscapes of the cortical projection neurons in female mice. Projection-TAGs can be leveraged to obtain a snapshot of activity-dependent recruitment of distinct projection neurons and their molecular features in the context of a specific stimulus. Given its flexibility, usability, and compatibility, we envision that Projection-TAGs can be readily applied to build a comprehensive multi-modal map of brain neuronal cell types and their projections.
Discovery of a functionally selective serotonin receptor (5-HTR) agonist for the treatment of pain.
The heterotrimeric G protein-coupled serotonin receptor 5-HT receptor (5-HTR) mediates antinociception and may serve as a valuable target for the treatment of pain. Starting from a chemical library, we evolved ST171, a bitopic 5-HTR agonist that revealed highly potent and functionally selective G signaling without G activation and marginal β-arrestin recruitment. ST171 is effective in acute and chronic pain models. Cryo-electron microscopy structures of ST171 bound to 5-HTR in complex with the G protein compared to the canonical agonist befiradol bound to complexes of 5-HTR with G or G revealed that the ligands occupy different exo-sites. The individual binding poses are associated with ligand-specific receptor conformations that were further studied by molecular dynamics simulations, allowing us to better understand ligand bias, a phenomenon that may be crucial to the discovery of more effective and safe G protein-coupled receptor drugs.
Microglial pruning of glycinergic synapses disinhibits spinal PKCγ interneurons to drive pain hypersensitivity in mice.
Microglial activation is linked to neuroinflammation in neuropathic pain. Recently, microglia-mediated synaptic pruning has received mounting attention. However, the exact role of spinal microglia in modulating neuropathic pain-associated neural circuits remains unclear. To investigate this question, we used pharmacological, optogenetic, and genetic manipulations combined with behavioral tests, confocal imaging, and patch-clamp studies in a murine spared nerve injury (SNI) model of neuropathic pain. We demonstrate that spinal microglia pruned inhibitory presynaptic terminals in SNI mice, contributing to the disinhibition of spinal protein kinase C γ (PKCγ) interneurons and facilitating neurotransmission from low-threshold Aβ fibers. Single-cell RNA sequencing revealed that SNI-associated microglial subpopulations exhibited high expression of liver X receptor, apolipoprotein E (), and complement C1q. Global knockout of , microglia-specific knockdown of , or treatment with anti-C1q monoclonal antibody reversed SNI-induced pruning of spinal inhibitory synapses, prevented the disinhibition of PKCγ interneurons, and reduced pain hypersensitivity. Our study suggests that destabilization of neural networks through microglia-mediated pruning of inhibitory synapses in the spinal cord contributes to the development of neuropathic pain in mice.
Environmental microbiomes drive chemotactile sensation in octopus
Microbial communities coat nearly every surface in the environment and have co-existed with animals throughout evolution. Whether animals exploit omnipresent microbial cues to navigate their surroundings is not well understood. Octopuses use “taste-by-touch” chemotactile receptors (CRs) to explore the seafloor, but how they distinguish meaningful surfaces from the rocks and crevices they encounter is unknown. Here, we report that secreted signals from microbiomes of ecologically relevant surfaces activate CRs to guide octopus behavior. Distinct molecules isolated from individual bacterial strains located on prey or eggs bind single CRs in subtly different structural conformations to elicit specific mechanisms of receptor activation, ion permeation and signal transduction, and maternal care and predation behavior. Thus, microbiomes on ecological surfaces act at the level of primary sensory receptors to inform behavior. Our study demonstrates that uncovering interkingdom interactions is essential to understanding how animal sensory systems evolved in a microbe-rich world.
Lamellar Schwann cells in the Pacinian corpuscle potentiate vibration perception
Pacinian corpuscles are among the most sensitive mechanoreceptors found in vertebrates, and they are tuned to vibrations in the highest perceptible frequency range (100 to 2000 Hz). One of their anatomical hallmarks is the onion-like cell layers surrounding the central axon. The innermost layers consist of ~60 densely packed lamellar Schwann cells (LSCs), whose function remains largely unknown. Using high-resolution three-dimensional electron microscopy, we found that LSCs do not form concentric rings, but complex, multilayered, and intertwining assemblies that are connected via a high density of desmosomes and gap junctions. LSCs make multiple converging contacts with the afferent axon via desmosomes. Using optogenetic manipulations of LSCs, we demonstrate not only that their activation drives reliable time-locked spiking in the axon but also that their inactivation significantly elevates the thresholds in situ and increases perceptual thresholds behaviorally. Together, these findings provide evidence that LSCs are a key element of somatosensory processing, actively potentiating mechanosensitivity in Pacinian corpuscles.