Papers of the Week – Editors’ Picks

Anterolateral system (ALS) projection neurons underlie perception of pain, itch and skin temperature. These cells are heterogeneous, and there have therefore been many attempts to define functional populations. A recent study identified two classes of ALS neuron in mouse superficial dorsal horn (SDH) based on expression of the G protein-coupled receptors Tacr1 or Gpr83. It was reported that cells expressing these receptors formed largely non-overlapping populations, and that ~60% of ALS cells in SDH expressed Tacr1. An additional finding was that while Tacr1- and Gpr83-expressing ALS cells projected to several brain nuclei, their axons did not reach the ventral posterolateral (VPL) thalamic nucleus, which is reciprocally connected to the primary somatosensory cortex. These results were surprising, because we had reported that ~90% of SDH ALS neurons in the mouse possess the neurokinin 1 receptor (NK1r), which is encoded by Tacr1, and in addition the VPL is thought to receive input from lamina I ALS cells. Here we use retrograde and anterograde labelling in Tacr1CreERT2 and Gpr83CreERT2 mice to reinvestigate the expression of the receptors by ALS neurons and to reassess their projection patterns. We find that ~90% of ALS neurons in SDH express Tacr1, with 40-50% expressing Gpr83. We also show that axons of both Tacr1- and Gpr83-expressing ALS neurons reach the VPL. These results suggest that ALS neurons in the SDH that express these GPCRs show considerable overlap, and that they are likely to contribute to the sensory-discriminative dimension of pain through their projections to VPL.

Endometriosis is a chronic, estrogen-dependent, inflammatory disease defined by endometrial-like tissue (lesions) outside the uterine lining. It affects up to 10% of women worldwide, and 9 million women in the US, during reproductive years.

Helicobacter pylori (H. pylori) manipulates the host immune system to establish a persistent colonization, posing a serious threat to human health, but the mechanisms remain poorly understood. Here we integrate single-cell RNA sequencing and TCR profiling for analyzing 187,192 cells from 11 H. pylori-negative and 12 H. pylori-positive individuals to describe the human gastric ecosystem reprogrammed by H. pylori infection, as manifested by impaired antigen presentation and phagocytosis function. We further delineate a monocyte-to-C1QC macrophage differentiation trajectory driven by H. pylori infection, while T cell responses exhibit broad functional impairment and hyporesponsiveness with restricted clonal expansion capacity. We also identify an HLA-DRs- and CTLA4-expressing T cell population residing in H. pylori-inhabited stomach that potentially contribute to immune evasion. Together, our findings provide single-cell resolution information into the immunosuppressive microenvironment shaped by H. pylori infection, offering critical insights for developing novel therapeutic approaches to eliminate this globally prevalent pathogen.

Pain sensation often involves mechanical modalities. Mechanically activated (MA) ion channels on sensory neurons underly responsiveness to mechanical stimuli. MA current properties have mainly been derived from rodent sensory neurons. This study aimed to address gaps in knowledge regarding MA current properties in trigeminal (TG) neurons of a higher order species, common marmoset non-human primates (NHP). MA currents triggered by a piezo-actuator were recorded in patch clamp configuration . MA responses were associated with action potential (AP) properties, such as width, dV/dt on the falling phase, and presence/absence of AP firing in NHP TG neurons. According to responsiveness to mechanical stimuli and AP properties, marmoset TG neurons were clustered into 4 S-type and 5 M-type groups. S-type TG neurons had broader AP with two dV/dt peaks on the AP falling phase. Only one S-type group of NHP TG neurons produced small MA currents. M-type TG neurons had narrow AP without two dV/dt peaks on the AP falling phase. M-type NHP TG neurons, except one group, showed MA currents. We additionally used immunohistochemistry to confirm presence of known sensory neuronal types such as un-myelinated peptidergic CGRP/trpV1, un-myelinated non-peptidergic MrgprD and CGRP/trpV1, and myelinated peptidergic CGRP/trpV1 and non-peptidergic CGRP and PV NHP TG neurons. Overall, marmoset TG neurons and associated MA currents have many similarities compared to reported data from mouse sensory neurons. However, there are notable differences such as lower percentage of small NHP TG neurons responding to mechanical stimuli, and absence fast inactivating MA currents. Understanding the mechanical responses in trigeminal (TG) neurons is pivotal for elucidating the mechanisms of somatosensation and gaining insights into the cellular basis of acute and chronic pain in head and neck area. Mechanically activated (MA) currents have mainly been characterized in rodent sensory neurons. However, extrapolating these findings to humans may have significant implications. Thus, identifying specific properties of MA currents from non-human primates (NHPs) is of fundamental importance, underscoring the relevance of this study. MA currents triggered by a piezo-actuator were studied in NHP TG neurons using patch-clamp electrophysiology. Based on electrical properties of neurons, 9 distinct types of NHP TG neurons were identified. Overall, NHP TG neurons have many similarities with reported properties of mouse dorsal root ganglion (DRG) and TG neurons. However, there are notable differences such as a low percentage of neurons responding to mechanical stimuli among the smaller TG neurons and an absence of fast inactivating MA currents.

The purpose of this review is to provide an update on the clinical course and management of migraine in women.

Somatosensory neurons encode detailed information about touch and temperature and are the peripheral drivers of pain. Here by combining functional imaging with multiplexed in situ hybridization, we determined how heat and mechanical stimuli are encoded across neuronal classes and how inflammation transforms this representation to induce heat hypersensitivity, mechanical allodynia and continuing pain. Our data revealed that trigeminal neurons innervating the cheek exhibited complete segregation of responses to gentle touch and heat. By contrast, heat and noxious mechanical stimuli broadly activated nociceptor classes, including cell types proposed to trigger select percepts and behaviours. Injection of the inflammatory mediator prostaglandin E2 caused long-lasting activity and thermal sensitization in select classes of nociceptors, providing a cellular basis for continuing inflammatory pain and heat hypersensitivity. We showed that the capsaicin receptor TRPV1 (ref. ) has a central role in heat sensitization but not in spontaneous nociceptor activity. Unexpectedly, the responses to mechanical stimuli were minimally affected by inflammation, suggesting that tactile allodynia results from the continuing firing of nociceptors coincident with touch. Indeed, we have demonstrated that nociceptor activity is both necessary and sufficient for inflammatory tactile allodynia. Together, these findings refine models of sensory coding and discrimination at the cellular and molecular levels, demonstrate that touch and temperature are broadly but differentially encoded across transcriptomically distinct populations of sensory cells and provide insight into how cellular-level responses are reshaped by inflammation to trigger diverse aspects of pain.

In this issue of Neuron, Xu et al. demonstrate that activating GPR37L1, a G-protein-coupled receptor that negatively regulates astrocytes, suppresses the onset and maintenance of neuropathic pain, an intractable chronic pain caused by nerve damage, thereby serving as a therapeutic target.

The mu-opioid receptor (MOR), a member of the G-protein-coupled receptor superfamily, is pivotal in pain modulation and analgesia. Biased agonism at MOR offers a promising avenue for developing safer opioid therapeutics by selectively engaging specific signaling pathways. This study presents a comprehensive analysis of biased agonists using a newly curated database, BiasMOR, comprising 166 unique molecules with annotated activity data for GTPγS, cAMP, and β-arrestin assays. Advanced structure-activity relationship (SAR) analyses, including network similarity graphs, maximum common substructures, and activity cliff identification, reveal critical molecular features underlying bias signaling. Modelability assessments indicate high suitability for predictive modeling, with RMODI indices exceeding 0.96 and SARI indices highlighting moderately continuous SAR landscapes for cAMP and β-arrestin assays. Interaction patterns for biased agonists are discussed, including key residues such as D, Y, and Y. Comparative studies of enantiomer-specific interactions further underscore the role of ligand-induced conformational states in modulating signaling pathways. This work underscores the potential of combining computational and experimental approaches to advance the understanding of MOR-biased signaling, paving the way for safer opioid therapies. The database provided here will serve as a starting point for designing biased mu opioid receptor ligands and will be updated as new data become available. Increasing the repertoire of biased ligands and analyzing molecules collectively, as the database described here, contributes to pinpointing structural features responsible for biased agonism that can be associated with biological effects still under debate.