Antinociception in thermal, mechanical and chemical pain tests

What acts on it

1. The antinociceptive effect of acetaminophen at an oral dose lacking hypolocomotor activity was absent in fatty acid amide hydrolase and TRPV1 knockout mice in the formalin, tail immersion and von Frey tests, that dose did not affect global brain contents of prostaglandin E2 or endocannabinoids, intracerebroventricular injection of AM404 produced a TRPV1-mediated antinociceptive effect in the formalin test, and pharmacological inhibition of brain TRPV1 by intracerebroventricular capsazepine abolished the antinociceptive effect of oral acetaminophen.

   Human transient receptor potential vanilloid 1 / TRPV1 → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
   Experimental context and source evidence

   availability_state

   machinery_impairment Imported condition classification; unverified.

   evidence_span

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   experimental_model

   Formalin, tail immersion and von Frey tests in fatty acid amide hydrolase and TRPV1 knockout mice with intracerebroventricular injection

   exposure

   Oral acetaminophen at a dose lacking hypolocomotor activity, with intracerebroventricular AM404 and capsazepine

   limitations

   Two separate knockouts and a central antagonist all point the same way, and the dose was chosen to avoid sedation confounding the pain tests. Brain prostaglandin E2 was unchanged at that dose, which is a notable negative.

   nutrient_topic

   Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol

   organism

   Mouse

   plain_language

   Remove the channel and the painkiller stops working, while putting the metabolite straight into the brain works.

   primary_references

   [apap-p20862299] TRPV1 in brain is involved in acetaminophen-induced antinociception. (2010). https://pubmed.ncbi.nlm.nih.gov/20862299/ DOI: 10.1371/journal.pone.0012748

   tissue_or_cell_type

   Brain

   trigger_kind

   machinery_impairment Imported condition classification; unverified.

   Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 311–322

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Formalin, tail immersion and von Frey tests in fatty acid amide hydrolase and TRPV1 knockout mice with intracerebroventricular injection · source_derived_draft · unverified_draft

   ### apap-analgesia-needs-trpv1 The antinociceptive effect of acetaminophen at an oral dose lacking hypolocomotor activity was absent in fatty acid amide hydrolase and TRPV1 knockout mice in the formalin, tail immersion and von Frey tests, that dose did not affect global brain contents of prostaglandin E2 or endocannabinoids, intracerebroventricular injection of AM404 produced a TRPV1-mediated antinociceptive effect in the formalin test, and pharmacological inhibition of brain TRPV1 by intracerebroventricular capsazepine abolished the antinociceptive effect of oral acetaminophen. Condition category: machinery_impairment nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Remove the channel and the painkiller stops working, while putting the metabolite straight into the brain works. organism: Mouse tissue_or_cell_type: Brain experimental_model: Formalin, tail immersion and von Frey tests in fatty acid amide hydrolase and TRPV1 knockout mice with intracerebroventricular injection limitations: Two separate knockouts and a central antagonist all point the same way, and the dose was chosen to avoid sedation confounding the pain tests. Brain prostaglandin E2 was unchanged at that dose, which is a notable negative. exposure: Oral acetaminophen at a dose lacking hypolocomotor activity, with intracerebroventricular AM404 and capsazepine evidence_span: {"source_cache": "artifacts/paracetamol-research/20862299.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2cb3934d80d1a7a6632c49f2007cb6e203b3851706a4ffeb43fda2bb655fa8f2", "start_char": 0, "end_char": 1701, "text_sha256": "2cb3934d80d1a7a6632c49f2007cb6e203b3851706a4ffeb43fda2bb655fa8f2"} [apap-p20862299] TRPV1 in brain is involved in acetaminophen-induced antinociception. (2010). https://pubmed.ncbi.nlm.nih.gov/20862299/ DOI: 10.1371/journal.pone.0012748

   Complete structured claim and evidence

2. In thermal, mechanical and chemical pain tests the specific cannabinoid receptor 1 antagonist AM-251 abolished the analgesic action of acetaminophen, which was also lost in cannabinoid receptor 1 knockout mice, yet acetaminophen was shown unable to bind to those receptors demonstrating an indirect involvement, inhibition of fatty acid amide hydrolase suppressed the effect, and the antinociceptive activity of a cannabinoid receptor 1 agonist was itself inhibited by lesion of bulbospinal serotonergic pathways and by spinal 5-HT receptor antagonists, leading the authors to propose a sequence of metabolism to AM404, indirect cannabinoid receptor involvement, reinforcement of serotonergic bulbospinal pathways and action at spinal serotonergic receptors.

   Human cannabinoid receptor 1 / CB1 / CNR1 → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
   Experimental context and source evidence

   evidence_span

   {"source_cache": "artifacts/paracetamol-research/18485596.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f", "start_char": 0, "end_char": 1545, "text_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f"}

   experimental_model

   Thermal, mechanical and chemical pain tests in cannabinoid receptor 1 knockout mice with receptor binding and pathway lesions

   exposure

   Acetaminophen with AM-251, cannabinoid receptor 1 deletion, fatty acid amide hydrolase inhibition and serotonergic pathway lesion

   limitations

   The binding experiment is what makes the receptor involvement indirect rather than direct, which is the substantive point. The proposed sequence is the authors’ synthesis.

   nutrient_topic

   Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol

   organism

   Mouse

   plain_language

   The drug needs the cannabinoid receptor but never touches it, which is what a metabolite doing the work looks like.

   primary_references

   [apap-p18485596] Endocannabinoid and serotonergic systems are needed for acetaminophen-induced analgesia. (2008). https://pubmed.ncbi.nlm.nih.gov/18485596/ DOI: 10.1016/j.pain.2008.03.030

   tissue_or_cell_type

   Brain and spinal cord

   Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 337–348

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Thermal, mechanical and chemical pain tests in cannabinoid receptor 1 knockout mice with receptor binding and pathway lesions · source_derived_draft · unverified_draft

   ### apap-cb1-needed-but-not-bound In thermal, mechanical and chemical pain tests the specific cannabinoid receptor 1 antagonist AM-251 abolished the analgesic action of acetaminophen, which was also lost in cannabinoid receptor 1 knockout mice, yet acetaminophen was shown unable to bind to those receptors demonstrating an indirect involvement, inhibition of fatty acid amide hydrolase suppressed the effect, and the antinociceptive activity of a cannabinoid receptor 1 agonist was itself inhibited by lesion of bulbospinal serotonergic pathways and by spinal 5-HT receptor antagonists, leading the authors to propose a sequence of metabolism to AM404, indirect cannabinoid receptor involvement, reinforcement of serotonergic bulbospinal pathways and action at spinal serotonergic receptors. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The drug needs the cannabinoid receptor but never touches it, which is what a metabolite doing the work looks like. organism: Mouse tissue_or_cell_type: Brain and spinal cord experimental_model: Thermal, mechanical and chemical pain tests in cannabinoid receptor 1 knockout mice with receptor binding and pathway lesions limitations: The binding experiment is what makes the receptor involvement indirect rather than direct, which is the substantive point. The proposed sequence is the authors’ synthesis. exposure: Acetaminophen with AM-251, cannabinoid receptor 1 deletion, fatty acid amide hydrolase inhibition and serotonergic pathway lesion evidence_span: {"source_cache": "artifacts/paracetamol-research/18485596.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f", "start_char": 0, "end_char": 1545, "text_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f"} [apap-p18485596] Endocannabinoid and serotonergic systems are needed for acetaminophen-induced analgesia. (2008). https://pubmed.ncbi.nlm.nih.gov/18485596/ DOI: 10.1016/j.pain.2008.03.030

   Complete structured claim and evidence

3. Prostanoid production by rat aorta, heart, lung and whole blood was inhibited by all drugs tested with the order of potency SC560 greater than naproxen greater than acetaminophen greater than or equal to rofecoxib while in brain and cerebellum no differences among drug potencies were found, Western blotting using a commercially available antibody raised against canine COX-3 failed to detect any immunoreactive proteins, and the authors conclude that cyclooxygenase-1 and -2 are the functional forms present in the rat tissues tested, that acetaminophen is not a selective inhibitor of cyclooxygenase activities in the central nervous system, and that expression of an active cyclooxygenase protein from COX-3 messenger RNA in the rat is apparently impossible.

   COX-3 / COX-1b, a cyclooxygenase-1 transcript retaining intron 1 → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
   Experimental context and source evidence

   evidence_span

   {"source_cache": "artifacts/paracetamol-research/15148345.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c", "start_char": 0, "end_char": 1940, "text_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c"}

   experimental_model

   Comparison of acetaminophen, rofecoxib, naproxen and SC560 across rat aorta, heart, lung, brain, cerebellum and whole blood

   exposure

   Four drugs of differing isoform selectivity, with transcript and protein detection including an anti-canine-COX-3 antibody

   limitations

   Tests the proposal functionally across tissues and looks for the protein directly. A rat study, and a negative Western blot is weaker evidence than a positive one.

   nutrient_topic

   Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol

   organism

   Rat

   plain_language

   Nobody could find the protein, and in brain the drug showed no special selectivity at all.

   primary_references

   [apap-p15148345] Cyclooxygenases 1, 2, and 3 and the production of prostaglandin I2: investigating the activities of acetaminophen and cyclooxygenase-2-selective inhibitors in rat tissues. (2004). https://pubmed.ncbi.nlm.nih.gov/15148345/ DOI: 10.1124/jpet.103.063875

   tissue_or_cell_type

   Multiple tissues

   Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 233–244

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Comparison of acetaminophen, rofecoxib, naproxen and SC560 across rat aorta, heart, lung, brain, cerebellum and whole blood · source_derived_draft · unverified_draft

   ### apap-no-cox3-protein-found Prostanoid production by rat aorta, heart, lung and whole blood was inhibited by all drugs tested with the order of potency SC560 greater than naproxen greater than acetaminophen greater than or equal to rofecoxib while in brain and cerebellum no differences among drug potencies were found, Western blotting using a commercially available antibody raised against canine COX-3 failed to detect any immunoreactive proteins, and the authors conclude that cyclooxygenase-1 and -2 are the functional forms present in the rat tissues tested, that acetaminophen is not a selective inhibitor of cyclooxygenase activities in the central nervous system, and that expression of an active cyclooxygenase protein from COX-3 messenger RNA in the rat is apparently impossible. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Nobody could find the protein, and in brain the drug showed no special selectivity at all. organism: Rat tissue_or_cell_type: Multiple tissues experimental_model: Comparison of acetaminophen, rofecoxib, naproxen and SC560 across rat aorta, heart, lung, brain, cerebellum and whole blood limitations: Tests the proposal functionally across tissues and looks for the protein directly. A rat study, and a negative Western blot is weaker evidence than a positive one. exposure: Four drugs of differing isoform selectivity, with transcript and protein detection including an anti-canine-COX-3 antibody evidence_span: {"source_cache": "artifacts/paracetamol-research/15148345.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c", "start_char": 0, "end_char": 1940, "text_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c"} [apap-p15148345] Cyclooxygenases 1, 2, and 3 and the production of prostaglandin I2: investigating the activities of acetaminophen and cyclooxygenase-2-selective inhibitors in rat tissues. (2004). https://pubmed.ncbi.nlm.nih.gov/15148345/ DOI: 10.1124/jpet.103.063875

   Complete structured claim and evidence

4. In rats using the hot plate test the analgesic effect of paracetamol was prevented by two antagonists at cannabinoid CB1 receptors, AM281 and SR141716A, at doses that prevent the analgesic activity of the cannabinoid CB1 agonist HU210, suggesting that paracetamol-induced antinociception involves the cannabinoid system.

   AM251, a cannabinoid receptor 1 antagonist → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
   Experimental context and source evidence

   evidence_span

   {"source_cache": "artifacts/paracetamol-research/16438952.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f", "start_char": 0, "end_char": 509, "text_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f"}

   experimental_model

   Hot plate test in rats with two cannabinoid receptor antagonists

   exposure

   Paracetamol with AM281 and SR141716A at doses that prevent the action of a cannabinoid agonist

   limitations

   A short report with the antagonist doses anchored to a positive control. One pain test in one species.

   nutrient_topic

   Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol

   organism

   Rat

   plain_language

   Two different blockers of the cannabinoid receptor each stopped the painkiller working.

   primary_references

   [apap-p16438952] The analgesic activity of paracetamol is prevented by the blockade of cannabinoid CB1 receptors. (2006). https://pubmed.ncbi.nlm.nih.gov/16438952/ DOI: 10.1016/j.ejphar.2005.12.015

   tissue_or_cell_type

   Whole animal

   Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 350–361

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Hot plate test in rats with two cannabinoid receptor antagonists · source_derived_draft · unverified_draft

   ### apap-two-antagonists-block-it In rats using the hot plate test the analgesic effect of paracetamol was prevented by two antagonists at cannabinoid CB1 receptors, AM281 and SR141716A, at doses that prevent the analgesic activity of the cannabinoid CB1 agonist HU210, suggesting that paracetamol-induced antinociception involves the cannabinoid system. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Two different blockers of the cannabinoid receptor each stopped the painkiller working. organism: Rat tissue_or_cell_type: Whole animal experimental_model: Hot plate test in rats with two cannabinoid receptor antagonists limitations: A short report with the antagonist doses anchored to a positive control. One pain test in one species. exposure: Paracetamol with AM281 and SR141716A at doses that prevent the action of a cannabinoid agonist evidence_span: {"source_cache": "artifacts/paracetamol-research/16438952.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f", "start_char": 0, "end_char": 509, "text_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f"} [apap-p16438952] The analgesic activity of paracetamol is prevented by the blockade of cannabinoid CB1 receptors. (2006). https://pubmed.ncbi.nlm.nih.gov/16438952/ DOI: 10.1016/j.ejphar.2005.12.015

   Complete structured claim and evidence