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Cited by 64Endometriosis Research and TreatmentCannabis and Cannabinoid ResearchPain Mechanisms and Treatments

Endocannabinoid involvement in endometriosis.

Open access
Dmitrieva, Natalia, Nagabukuro, Hiroshi, Resuehr, David, Zhang, Guohua, McAllister, Stacy L., McGinty, Kristina A., Mackie, Ken, Berkley, Karen J.·2010·Pain
DOI 10.1016/j.pain.2010.08.037PMC PMC2972363
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Abstract

Endometriosis is a disease common in women that is defined by abnormal extrauteral growths of uterine endometrial tissue and associated with severe pain. Partly because how the abnormal growths become associated with pain is poorly understood, the pain is difficult to alleviate without resorting to hormones or surgery, which often produce intolerable side effects or fail to help. Recent studies in a rat model and women showed that sensory and sympathetic nerve fibers sprout branches to innervate the abnormal growths. This situation, together with knowledge that the endocannabinoid system is involved in uterine function and dysfunction and that exogenous cannabinoids were once used to alleviate endometriosis-associated pain, suggests that the endocannabinoid system is involved in both endometriosis and its associated pain. Herein, using a rat model, we found that CB1 cannabinoid receptors are expressed on both the somata and fibers of both the sensory and sympathetic neurons that innervate endometriosis's abnormal growths. We further found that CB1 receptor agonists decrease, whereas CB1 receptor antagonists increase, endometriosis-associated hyperalgesia. Together these findings suggest that the endocannabinoid system contributes to mechanisms underlying both the peripheral innervation of the abnormal growths and the pain associated with endometriosis, thereby providing a novel approach for the development of badly-needed new treatments.

AI snapshot

Written from the paper’s full text.

TL;DR

In a rat model of surgically induced endometriosis, CB1 cannabinoid receptors were found on sensory and sympathetic fibers and somata innervating ectopic cysts, and CB1 receptor agonists reduced endometriosis-associated vaginal hyperalgesia while a CB1 antagonist increased it. The findings suggest the endocannabinoid system contributes to cyst innervation and endometriosis pain, supporting CB1-targeted treatment development.

Key findings

  • CB1 receptors were present on cyst-innervating fibers: most (>75%) VMAT2-positive sympathetic fibers and many (50–75%) CGRP-positive sensory fibers co-labeled with CB1; CB1-labeled fiber density was significantly higher in cysts than in eutopic uterus.
  • CB1 was also on cyst-projecting neuronal somata: 52% of Dil-labeled coeliac ganglion neurons co-labeled with CB1, and 68% of those were TH-positive; 47% of Dil-labeled DRG neurons were CB1-positive, and 24% of those were also CGRP-positive. CB1-positive DRG neurons were small to medium-sized (range 22.9–41.5 µm; median 33.6 µm).
  • The CB1/CB2 agonist WIN2 significantly increased the visceromotor reflex threshold (VMRth) in ENDO rats but had no significant effect in shamENDO rats; no tolerance was apparent after multiple treatments. ENDO ANOVA: F(5,24)=6.928, P=0.000; shamENDO ANOVA: F(5,24)=1.168, P=0.353.
  • The CB1 antagonist AM251 prevented WIN2’s reduction of hyperalgesia and, when given alone, increased referred hyperalgesia (decreased VMRth); the CB2 antagonist AM630 did not. Antagonist study ANOVA: F(11,48)=13.010, P=0.000.

Methods

  • Adult female Sprague-Dawley rats underwent surgically induced endometriosis (ENDO) or shamENDO surgery; assessments were done in proestrus, >6 weeks after surgery when hyperalgesia is fully developed and stable.
  • Immunohistochemistry and confocal microscopy examined CB1 expression in cysts, eutopic uterus, dorsal root ganglia, and coeliac ganglia; retrograde Dil labeling identified cyst-projecting neurons. Fiber quantification used blinded counts in cysts and uterus (n=8); co-labeling used 6 sections from 6 rats; triple-labeled ganglion cells used T9/T10 DRGs and CGs from 4 rats.
  • Nociception was measured by vaginal distention-induced visceromotor reflex (VMR) and EMG threshold (VMRth). WIN2 (1, 3 mg/kg), AM251 (3 mg/kg), AM630 (1 mg/kg), or vehicle were given i.p. in within-rat crossover designs; data analyzed by ANOVA and post-hoc t-tests.

Limitations

  • The paper states that the rat model parallels many aspects of endometriosis in women but has significant differences; findings are presented insofar as rat mechanisms can model human signs and symptoms.
  • The paper notes that AM251 can act as an inverse agonist, so further support for endogenous endocannabinoid involvement would require testing drugs that increase endocannabinoid levels, such as FAAH or MAGL inhibitors.
  • Evident from the methods: sample sizes were small (e.g., n=8 for fiber quantification, 6 rats for co-labeling, 4 rats for triple-labeled ganglion cells, 5 rats for retrograde labeling), and the study is entirely preclinical with no human clinical trial data.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1016/j.pain.2010.08.037

Cites

55 of 55 references verified0 citation errors · 0 not checkable

Statistics

Claims the paper makes

0 of 69 cited sources checked · 0 supported · 0 flagged

  • Findingcitation

    In the cysts, most (>75%) sympathetic fibers (VMAT2-positive) co-labeled with CB1.

    “With double-labeling fluorescence immunohistochemistry, most (> 75%) sympathetic fibers (vesicular monoamine transporter 2, VMAT2-positive) and many (50 – 75%) sensory fibers (calcitonin gene related peptide, CGRP-positive) in the cysts co-labeled with an antibody for CB1 receptors (CB1; [6]) (Fig. 1d).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [6] Bodor AL Katona I Nyíri G Mackie K Ledent C Hájos N Freund TF Endocannabinoid signaling in rat somatosensory cortex: laminar differences and involvement of specific interneuron types J Neurosci 2005 25 6845 6856 16033894 PMC6725346 source

      Not checked in the free run.

  • Findingcitation

    In the cysts, many (50-75%) sensory fibers (CGRP-positive) co-labeled with CB1.

    “With double-labeling fluorescence immunohistochemistry, most (> 75%) sympathetic fibers (vesicular monoamine transporter 2, VMAT2-positive) and many (50 – 75%) sensory fibers (calcitonin gene related peptide, CGRP-positive) in the cysts co-labeled with an antibody for CB1 receptors (CB1; [6]) (Fig. 1d).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [6] Bodor AL Katona I Nyíri G Mackie K Ledent C Hájos N Freund TF Endocannabinoid signaling in rat somatosensory cortex: laminar differences and involvement of specific interneuron types J Neurosci 2005 25 6845 6856 16033894 PMC6725346 source

      Not checked in the free run.

  • Findingown data

    The density of CB1-labeled fibers was significantly higher in the cysts than in the eutopic uterus of the same rats.

    “Although some CB1-labeled fibers were observed in the eutopic uterus of the same rats, notably, the density of the fibers was significantly higher in the cysts than uterus (Fig. 2).”
    Quote in the paperSubstantial claim
  • Findingown data

    CB1-labeled fibers in cysts were associated mainly with blood vessels and muscle fibers in the walls of the cysts, and were seen less often in the endometrial layer.

    “The fibers were associated mainly with blood vessels and muscle fibers in the walls of the cysts, and were seen less often in the endometrial layer.”
    Quote in the paperSubstantial claim
  • Findingown data

    For Dil-identified cyst-projecting DRG neurons, 47% were labeled with CB1.

    “For Dil-identified cyst-projecting DRG neurons, 47% were labeled with the CB1, some of which (24%) were also CGRP-labeled.”
    Quote in the paperSubstantial claim
  • May combine two claims. 11
  • Classified as probably not a substantial claim. 11

  • May combine two claims.

    Findingown data

    Co-administration of AM 251, but not AM 630, with WIN2 prevented WIN2's reduction of ENDO-induced hyperalgesia.

    “Co-administration of AM 251, but not of AM 630, with WIN2 prevented WIN2’s reduction of ENDO-induced hyperalgesia”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductown data

    Two observers, blinded to group and consistent (r > 85%), independently counted nerve fibers.

    “Two observers, blinded to group and consistent (r > 85%) independently counted nerve fibers in this area using criteria described elsewhere [52].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [52] Zhang G Dmitrieva N Liu Y McGinty KA Berkley KJ Endometriosis as a neurovascular condition: estrous variations in innervation, vascularization, and growth factor content of ectopic endometrial cysts in the rat Am J Physiol Regul Integr Comp Physiol 2008 294 R162 R171 17942489 PMC2365736 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The CB1 cannabinoid receptor protein is found in the rodent uterus and blastocyst.

    “The CB1 cannabinoid receptor protein (CB1) is found in the rodent uterus and blastocyst where the receptor contributes to normal fetal implantation and implantation failure [41].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [41] Paria BC Wang H Dey K Endocannabinoid signaling in synchronizing embryo development and uterine receptivity for implantation Chem Phys Lipids 2002 121 201 210 12505701 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    In control sections for CB1 immunostaining, there was no labeling.

    “Controls were omission of primary or secondary antibody and absorption of primary antiserum with its respective antigen prior to use. There was no labeling in control sections.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Cannabinoids were long used by women to alleviate dysmenorrhea.

    “The endocannabinoid system plays a key role in pain mechanisms [42], and, previously, cannabinoids were long used by women to alleviate dysmenorrhea [45].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [45] Russo E Cannabis treatments in obstetrics and gynecology: a historical review J Cannabis Ther 2002 2 5 34 source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductcitation

    All assessments were done >6 wks after surgery, when ENDO-induced hyperalgesia is fully-developed and stable.

    “All assessments were done > 6 wks after the surgery; i.e., when ENDO-induced hyperalgesia is fully-developed and stable [10,45,38].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [10] Cason AM Samuelsen CL Berkley KJ Estrous changes in vaginal nociception in a rat model of endometriosis Horm Behav 2003 44 123 131 13129484 source

      Not checked in the free run.

    • cites [45] Russo E Cannabis treatments in obstetrics and gynecology: a historical review J Cannabis Ther 2002 2 5 34 source

      Not checked in the free run.

    • cites [38] Nagabukuro H Berkley KJ Influence of endometriosis on visceromotor and cardiovascular responses induced by vaginal distention in the rat Pain 2007 132 Suppl 1 S96 S103 17544211 PMC2323582 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Studies were done when the rat was in proestrus, the estrous stage when hyperalgesia in the ENDO model is most severe.

    “Studies were done when the rat was in proestrus, the estrous stage when hyperalgesia in the ENDO model is most severe [10,45,38].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [10] Cason AM Samuelsen CL Berkley KJ Estrous changes in vaginal nociception in a rat model of endometriosis Horm Behav 2003 44 123 131 13129484 source

      Not checked in the free run.

    • cites [45] Russo E Cannabis treatments in obstetrics and gynecology: a historical review J Cannabis Ther 2002 2 5 34 source

      Not checked in the free run.

    • cites [38] Nagabukuro H Berkley KJ Influence of endometriosis on visceromotor and cardiovascular responses induced by vaginal distention in the rat Pain 2007 132 Suppl 1 S96 S103 17544211 PMC2323582 source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    The endocannabinoid system plays a key role in pain mechanisms.

    “The endocannabinoid system plays a key role in pain mechanisms [42], and, previously, cannabinoids were long used by women to alleviate dysmenorrhea [45].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [42] Rahn EJ Hohmann AG Cannabinoids as pharmacotherapies for neuropathic pain: from the bench to the bedside Neurotherapeutics 2009 6 713 737 19789075 PMC2755639 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The CB1 receptor contributes to normal fetal implantation and implantation failure in rodents.

    “The CB1 cannabinoid receptor protein (CB1) is found in the rodent uterus and blastocyst where the receptor contributes to normal fetal implantation and implantation failure [41].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [41] Paria BC Wang H Dey K Endocannabinoid signaling in synchronizing embryo development and uterine receptivity for implantation Chem Phys Lipids 2002 121 201 210 12505701 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductcitation

    The studies were approved by Florida State University's Animal Care and Use Committee and adhered to the guidelines of the Committee for Research and Ethical Issues of IASP.

    “The studies were approved by Florida State University’s Animal Care and Use Committee and adhered to the guidelines of the Committee for Research and Ethical Issues of IASP [53].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [53] Zimmermann M Ethical guidelines for investigations of experimental pain in conscious animals Pain 1983 16 109 110 6877845

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The ENDO model's surgical control (shamENDO) develops neither cysts nor pain symptoms.

    “The ENDO model’s surgical control (shamENDO) develops neither cysts nor pain symptoms [10,38].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [10] Cason AM Samuelsen CL Berkley KJ Estrous changes in vaginal nociception in a rat model of endometriosis Horm Behav 2003 44 123 131 13129484 source

      Not checked in the free run.

    • cites [38] Nagabukuro H Berkley KJ Influence of endometriosis on visceromotor and cardiovascular responses induced by vaginal distention in the rat Pain 2007 132 Suppl 1 S96 S103 17544211 PMC2323582 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    These sizes are within ranges reported by others for DRG neurons containing either CB1 or CGRP.

    “These sizes are within ranges reported by others for DRG neurons containing either CB1 [20,46] or CGRP [31].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [20] Hohmann AG Herkenham M Localization of central cannabinoid CB1 receptor messenger RNA in neuronal subpopulations of rat dorsal root ganglia: a double-label in situ hybridization study Neuroscience 1999 90 923 931 10218792 source

      Not checked in the free run.

    • cites [46] Sañudo-Peña MC Strangman NM Mackie K Walker JM Tsou K CB1 receptor localization in rat spinal cord and roots, dorsal root ganglion, and peripheral nerve Zhongguo Yao Li Xue Bao 1999 20 1115 1120 11216446

      Not checked in the free run.

    • cites [31] Lawson SN McCarthy PW Prabhakar E Eectrophysiological properties of neurones with CGRP-like immunoreactivity in rat dorsal root ganglia J Comp Neurol 1996 365 355 366 8822175 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable).

    Interpretationreasoning

    The endocannabinoid system provides a novel approach for the development of badly-needed new treatments for endometriosis.

    “Together these findings suggest that the endocannabinoid system contributes to mechanisms underlying both the peripheral innervation of the abnormal growths and the pain associated with endometriosis, thereby providing a novel approach for the development of badly-needed new treatments.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    CB1 but not CB2 receptors normally act to reduce ENDO-induced hyperalgesia.

    “suggesting that CB1 but not CB2 receptors normally act to reduce the hyperalgesia.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The endocannabinoid system contributes to mechanisms underlying both the peripheral innervation of the abnormal growths and the pain associated with endometriosis.

    “Together these findings suggest that the endocannabinoid system contributes to mechanisms underlying both the peripheral innervation of the abnormal growths and the pain associated with endometriosis, thereby providing a novel approach for the development of badly-needed new treatments.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    The endocannabinoid system is involved in reproductive function and dysfunction.

    “These findings implicate involvement of the endocannabinoid system in reproductive function and dysfunction.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [41] Paria BC Wang H Dey K Endocannabinoid signaling in synchronizing embryo development and uterine receptivity for implantation Chem Phys Lipids 2002 121 201 210 12505701 source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The rat model parallels many aspects of endometriosis in women, but there are significant differences.

    “Although the rat model parallels many aspects of endometriosis in women, there are of course significant differences [48].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [48] Stratton P Berkley KJ Chronic pelvic pain and endometriosis: translational evidence of the relationship and implications Human Reproduction Update in press PMC3072022 21106492 source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Δ9-tetrahydrocannabinol's efficacy on tail withdrawal and paw pressure tests in rats is enhanced by estradiol.

    “whereas Craft and Leitl [13] found that Δ9-tetrahydrocannabinol’s efficacy on tail withdrawal and paw pressure tests in rats is enhanced by estradiol.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [13] Craft RM Leitl MD Gonadal hormone modulation of the behavioral effects of Delta9-trahydrocannabinol in male and female rats Eur J Pharmacol 2008 578 37 42 17905227 source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    COX-2 converts the endocannabinoid 2-arachidonoylglycerol (2-AG) into prostaglandin E2 glycerol ester (PGE2-G), which is pro-nociceptive.

    “COX-2 converts the endocannabinoid 2-arachidonoylglycerol (2-AG) into prostaglandin E2 glycerol ester (PGE2-G), which is pro-nociceptive because, when administered into the footpad, it induces mechanical allodynia and thermal hyperalgesia [23].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [23] Hu SS Bradshaw HB Chen JS Tan B Walker JM Prostaglandin E2 glycerol ester, an endogenous COX-2 metabolite of 2-arachidonoylglycerol, induces hyperalgesia and modulates NFkappaB activity Br J Pharmacol 2008 153 1538 1549 18297109 PMC2437899 source

      Not checked in the free run.

19 of 19

  • The authors state this as an assumption.

    The rat model of endometriosis is a valid model for mechanisms of endometriosis-related signs and symptoms in women.

    “insofar as findings in rats can model mechanisms of endometriosis-related signs and symptoms”
1 of 1

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Statistics recomputed

Every reported test result, recomputed from its test statistic and degrees of freedom. A result shows as not adding up only once an independent check has confirmed it.

  • ConsistentF(5, 24) = 6.928reported p = 0 · recomputed p < .001

    “F(5,24) = 6.928, p = .000”

  • ConsistentF(5, 24) = 1.168reported p = .353 · recomputed p = .354

    “F(5,24) = 1.168, p = .353”

  • ConsistentF(11, 48) = 13.01reported p = 0 · recomputed p < .001

    “F(11,48) = 13.010, p = .000”

3 of 3

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Authors
Dmitrieva, N., Nagabukuro, H., Resuehr, D., Zhang, G., McAllister, S. L., McGinty, K. A., Mackie, K., & Berkley, K. J.
Affiliations
  • Florida State University (US)
  • Indiana University Bloomington (US)
Corresponding author
Berkley, Karen J.
ORCID
Venue
Pain
Publisher
Ovid Technologies (Wolters Kluwer Health)
Published
2010-12
Volume
151
Issue
3
Pages
703-710
ISSN
0304-3959 (ISSN-L)
DOI
10.1016/j.pain.2010.08.037
PMC
PMC2972363
OpenAlex
W2030621745
Semantic Scholar
32e55f5629523277c9d74017386feaad8677d6ba
Cited by
64
References
59
Citations by year
2026: 2 · 2025: 8 · 2024: 3 · 2023: 5 · 2022: 1 · 2021: 9 · 2020: 4 · 2019: 4 · 2018: 1 · 2017: 5 · 2016: 5 · 2014: 5 · 2013: 4 · 2012: 5
FWCI
4.57
Type
journal article
Language
en
Open access
Licence
www.elsevier.com/tdm/userlicense/1.0/ (tdm)
Locations
  • Pain (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
National Institutes of Health (NS011892, DA011322, DA021696)
Topics
  • Health Sciences › Medicine › Reproductive Medicine › Endometriosis Research and Treatment
  • Health Sciences › Medicine › Pharmacology › Cannabis and Cannabinoid Research
  • Health Sciences › Medicine › Physiology › Pain Mechanisms and Treatments
Keywords
endometriosis, endocannabinoid system, CB1 receptor, endometriosis-associated pain, hyperalgesia, sensory nerve fibers, sympathetic nerve fibers, peripheral innervation, CB1 receptor agonists, CB1 receptor antagonist, rat model
MeSH terms
Analysis of Variance, Animals, Disease Models, Animal, Electromyography, Endometriosis, Endometrium, Female, Hyperalgesia, Immunohistochemistry, Uterus, Calcitonin Gene-Related Peptide, Rats, Sprague-Dawley, Area Under Curve, Receptor, Cannabinoid, CB1, Vesicular Monoamine Transport Proteins, Rats

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