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Lenert ME, Burton MD. Sensory neuron LKB1 mediates ovarian and reproductive function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.28.534533. [PMID: 37034663 PMCID: PMC10081243 DOI: 10.1101/2023.03.28.534533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/20/2023]
Abstract
Treatments for reproductive disorders in women primarily consist of hormone replacement therapy, which can have negative health impacts. Bidirectional communication between sensory neurons and innervated organs is an emerging area of interest in tissue physiology with potential relevance for reproductive disorders. Indeed, the metabolic activity of sensory neurons can have profound effects on reproductive phenotypes. To investigate this phenomenon, we utilized a murine model with conditional deletion in sensory neurons of liver kinase B1 (LKB1), a serine/threonine kinase that regulates cellular metabolism. Female mice with this LKB1 deletion (Nav1.8cre;LKB1fl/fl) had significantly more pups per litter compared to wild-type females. Interestingly, the LKB1 genotype of male breeders had no effect on fertility outcomes, thus indicating a female-specific role of sensory neuron metabolism in fertility. LKB1 deletion in sensory neurons resulted in reduced ovarian innervation from dorsal root ganglia neurons and increased follicular turnover compared to littermate controls. In summary, LKB1 expression in peripheral sensory neurons plays an important role in modulating fertility of female mice via ovarian sensory innervation.
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Affiliation(s)
- Melissa E Lenert
- Neuroimmunology and Behavior Laboratory, Department of Neuroscience, School of Behavioral and Brain Sciences, Center for Advanced Pain Studies (CAPS), The University of Texas at Dallas, Richardson, TX 75080
| | - Michael D Burton
- Neuroimmunology and Behavior Laboratory, Department of Neuroscience, School of Behavioral and Brain Sciences, Center for Advanced Pain Studies (CAPS), The University of Texas at Dallas, Richardson, TX 75080
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Spencer NJ, Hibberd T, Xie Z, Hu H. How should we define a nociceptor in the gut-brain axis? Front Neurosci 2022; 16:1096405. [PMID: 36601592 PMCID: PMC9806170 DOI: 10.3389/fnins.2022.1096405] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2022] [Accepted: 12/05/2022] [Indexed: 12/23/2022] Open
Abstract
In the past few years, there has been extraordinary interest in how the gut communicates with the brain. This is because substantial and gathering data has emerged to suggest that sensory nerve pathways between the gut and brain may contribute much more widely in heath and disease, than was originally presumed. In the skin, the different types of sensory nerve endings have been thoroughly characterized, including the morphology of different nerve endings and the sensory modalities they encode. This knowledge is lacking for most types of visceral afferents, particularly spinal afferents that innervate abdominal organs, like the gut. In fact, only recently have the nerve endings of spinal afferents in any visceral organ been identified. What is clear is that spinal afferents play the major role in pain perception from the gut to the brain. Perhaps surprisingly, the majority of spinal afferent nerve endings in the gut express the ion channel TRPV1, which is often considered to be a marker of "nociceptive" neurons. And, a majority of gut-projecting spinal afferent neurons expressing TRPV1 are activated at low thresholds, in the "normal" physiological range, well below the normal threshold for detection of painful sensations. This introduces a major conundrum regarding visceral nociception. How should we define a "nociceptor" in the gut? We discuss the notion that nociception from the gut wall maybe a process encrypted into multiple different morphological types of spinal afferent nerve ending, rather than a single class of sensory ending, like free-endings, suggested to underlie nociception in skin.
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Affiliation(s)
- Nick J. Spencer
- Visceral Neurophysiology Laboratory, College of Medicine and Public Health, Flinders Health and Medical Research Institute, Flinders University, Bedford Park, SA, Australia,*Correspondence: Nick J. Spencer,
| | - Tim Hibberd
- Visceral Neurophysiology Laboratory, College of Medicine and Public Health, Flinders Health and Medical Research Institute, Flinders University, Bedford Park, SA, Australia
| | - Zili Xie
- Department of Anesthesiology, The Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, St. Louis, MO, United States
| | - Hongzhen Hu
- Department of Anesthesiology, The Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, St. Louis, MO, United States
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Dodds KN, Kyloh MA, Travis L, Cox M, Hibberd TJ, Spencer NJ. Anatomical distribution of CGRP-containing lumbosacral spinal afferent neurons in the mouse uterine horn. Front Neurosci 2022; 16:1012329. [PMID: 36248657 PMCID: PMC9554138 DOI: 10.3389/fnins.2022.1012329] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Accepted: 09/09/2022] [Indexed: 11/16/2022] Open
Abstract
Sensory stimuli from the uterus are detected by spinal afferent neurons whose cell bodies arise from thoracolumbar and lumbosacral dorsal root ganglia (DRG). Using an in vivo survival surgical technique developed in our laboratory to remove select DRG from live mice, we recently quantified the topographical distribution of thoracolumbar spinal afferents innervating the mouse uterine horn, revealed by loss of immunoreactivity to calcitonin gene-related peptide (CGRP). Here, we used the same technique to investigate the distribution of lumbosacral uterine spinal afferents, in which L5-S1 DRG were unilaterally removed from adult female C57BL/6J mice (N = 6). Following 10–12 days recovery, CGRP immunoreactivity was quantified along the length of uterine horns using fluorescence immunohistochemistry. Relative to myometrial thickness, overall CGRP density in uterine tissues ipsilateral to L5-S1 DRG removal was reduced compared to the DRG-intact, contralateral side (P = 0.0265). Regionally, however, myometrial CGRP density was unchanged in the cranial, mid, and caudal portions. Similarly, CGRP-expressing nerve fiber counts, network lengths, junctions, and the proportion of area occupied by CGRP immunoreactivity were unaffected by DRG removal (P ≥ 0.2438). Retrograde neuronal tracing from the caudal uterine horn revealed fewer spinal afferents here arise from lumbosacral than thoracolumbar DRG (P = 0.0442) (N = 4). These data indicate that, unlike thoracolumbar DRG, lumbosacral spinal afferent nerves supply relatively modest sensory innervation across the mouse uterine horn, with no regional specificity. We conclude most sensory information between the mouse uterine horn and central nervous system is likely relayed via thoracolumbar spinal afferents.
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Kyloh MA, Hibberd TJ, Castro J, Harrington AM, Travis L, Dodds KN, Wiklendt L, Brierley SM, Zagorodnyuk VP, Spencer NJ. Disengaging spinal afferent nerve communication with the brain in live mice. Commun Biol 2022; 5:915. [PMID: 36104503 PMCID: PMC9475039 DOI: 10.1038/s42003-022-03876-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Accepted: 08/23/2022] [Indexed: 11/24/2022] Open
Abstract
Our understanding of how abdominal organs (like the gut) communicate with the brain, via sensory nerves, has been limited by a lack of techniques to selectively activate or inhibit populations of spinal primary afferent neurons within dorsal root ganglia (DRG), of live animals. We report a survival surgery technique in mice, where select DRG are surgically removed (unilaterally or bilaterally), without interfering with other sensory or motor nerves. Using this approach, pain responses evoked by rectal distension were abolished by bilateral lumbosacral L5-S1 DRG removal, but not thoracolumbar T13-L1 DRG removal. However, animals lacking T13-L1 or L5-S1 DRG both showed reduced pain sensitivity to distal colonic distension. Removal of DRG led to selective loss of peripheral CGRP-expressing spinal afferent axons innervating visceral organs, arising from discrete spinal segments. This method thus allows spinal segment-specific determination of sensory pathway functions in conscious, free-to-move animals, without genetic modification. A surgical method in mice can selectively remove dorsal root ganglia (DRG) at specific spinal levels without interfering with other nerves, providing insight on thoracolumbar vs. lumbosacral DRG contributions to pain signalling and behaviour.
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Brierley SM, Grundy L, Castro J, Harrington AM, Hannig G, Camilleri M. Guanylate cyclase-C agonists as peripherally acting treatments of chronic visceral pain. Trends Pharmacol Sci 2022; 43:110-122. [PMID: 34865885 PMCID: PMC8760167 DOI: 10.1016/j.tips.2021.11.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 10/28/2021] [Accepted: 11/02/2021] [Indexed: 02/03/2023]
Abstract
Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by abdominal pain and altered bowel habit that affects ~11% of the global population. Over the past decade, preclinical and clinical studies have revealed a variety of novel mechanisms relating to the visceral analgesic effects of guanylate cyclase-C (GC-C) agonists. Here we discuss the mechanisms by which GC-C agonists target the GC-C/cyclic guanosine-3',5'-monophosphate (cGMP) pathway, resulting in visceral analgesia as well as clinically relevant relief of abdominal pain and other sensations in IBS patients. Due to the preponderance of evidence we focus on linaclotide, a 14-amino acid GC-C agonist with very low oral bioavailability that acts within the gut. Collectively, the weight of experimental and clinical evidence supports the concept that GC-C agonists act as peripherally acting visceral analgesics.
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Affiliation(s)
- Stuart M. Brierley
- Visceral Pain Research Group, College of Medicine and Public Health, Flinders Health and Medical Research Institute (FHMRI), Flinders University, Bedford Park, South Australia, 5042, AUSTRALIA.,Hopwood Centre for Neurobiology, Lifelong Health Theme, South Australian Health and Medical Research Institute (SAHMRI), North Terrace, Adelaide, South Australia 5000, AUSTRALIA.,Discipline of Medicine, University of Adelaide, North Terrace, Adelaide, South Australia 5000, AUSTRALIA.,Corresponding Author: Prof. Stuart M. Brierley, Ph.D. Visceral Pain Research Group, Level 7, South Australian Health and Medical Research Institute (SAHMRI), North Terrace, Adelaide, SA 5000, AUSTRALIA.
| | - Luke Grundy
- Visceral Pain Research Group, College of Medicine and Public Health, Flinders Health and Medical Research Institute (FHMRI), Flinders University, Bedford Park, South Australia, 5042, AUSTRALIA.,Hopwood Centre for Neurobiology, Lifelong Health Theme, South Australian Health and Medical Research Institute (SAHMRI), North Terrace, Adelaide, South Australia 5000, AUSTRALIA
| | - Joel Castro
- Visceral Pain Research Group, College of Medicine and Public Health, Flinders Health and Medical Research Institute (FHMRI), Flinders University, Bedford Park, South Australia, 5042, AUSTRALIA.,Hopwood Centre for Neurobiology, Lifelong Health Theme, South Australian Health and Medical Research Institute (SAHMRI), North Terrace, Adelaide, South Australia 5000, AUSTRALIA
| | - Andrea M. Harrington
- Visceral Pain Research Group, College of Medicine and Public Health, Flinders Health and Medical Research Institute (FHMRI), Flinders University, Bedford Park, South Australia, 5042, AUSTRALIA.,Hopwood Centre for Neurobiology, Lifelong Health Theme, South Australian Health and Medical Research Institute (SAHMRI), North Terrace, Adelaide, South Australia 5000, AUSTRALIA
| | | | - Michael Camilleri
- Clinical Enteric Neuroscience Translational and Epidemiologic Research Program, Mayo Clinic, Rochester, MN, USA
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