Tag Archives: antinociception

Role of the cannabinoid signaling in the brain orexin- and ghrelin-induced visceral antinociception in conscious rats.

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Journal of Pharmacological Sciences

“We hypothesized that the cannabinoid (CB) system may mediate the brain orexin- or ghrelin-induced visceral antinociception. Intraperitoneal injection of either CB1/2 agonist, WIN 55212 or O-Arachidonoyl ethanolamine increased the threshold volume of colonic distension-induced abdominal withdrawal reflex in rats, suggesting CB could induce visceral antinociception. Pretreatment with either the CB1 or CB2 antagonist potently blocked the centrally injected orexin-A-induced antinociceptive action against colonic distension while CB2 but not CB1 antagonist blocked the brain ghrelin-induced visceral antinociception. These results suggest that the cannabinoid signaling may be involved in the central orexin- or ghrelin-induced antinociceptive action in a different mechanistic manner.”

 https://www.ncbi.nlm.nih.gov/pubmed/29958814
https://www.sciencedirect.com/science/article/pii/S1347861318301002?via%3Dihub

Brain endocannabinoid signaling exhibits remarkable complexity.

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Image result for Brain Res Bull.

“The endocannabinoid (eCB) signaling system is one of the most extensive of the mammalian brain. Despite the involvement of only few specific ligands and receptors, the system encompasses a vast diversity of triggered mechanisms and driven effects. It mediates a wide range of phenomena, including the regulation of transmitter release, neural excitability, synaptic plasticity, impulse spread, long-term neuronal potentiation, neurogenesis, cell death, lineage segregation, cell migration, inflammation, oxidative stress, nociception and the sleep cycle. It is also known to be involved in the processes of learning and memory formation. This extensive scope of action is attained by combining numerous variables. In a properly functioning brain, the correlations of these variables are kept in a strictly controlled balance; however, this balance is disrupted in many pathological conditions. However, while this balance is known to be disrupted by drugs in the case of addicts, the stimuli and mechanisms influencing the neurodegenerating brain remain elusive. This review examines the multiple factors and phenomena affecting the eCB signaling system in the brain. It evaluates techniques of controlling the eCB system to identify the obstacles in their applications and highlights the crucial interdependent variables that may influence biomedical research outcomes.”

https://www.ncbi.nlm.nih.gov/pubmed/29953913

Cannabinoid receptor type 1 in the brain regulates the affective component of visceral pain in mice.

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“Endocannabinoids acting through cannabinoid receptor type 1 (CB1) are major modulators of peripheral somatic and visceral nociception. Although only partially studied, some evidence suggests a particular role of CB1 within the brain in nociceptive processes.

As the endocannabinoid system regulates affect and emotional behaviors, we hypothesized that cerebral CB1 influences affective processing of visceral pain-related behaviors in laboratory animals.

To study nocifensive responses modulated by supraspinal CB1, we used conditional knock-out mice lacking CB1 either in cortical glutamatergic neurons (Glu-CB1-KO), or in forebrain GABAergic neurons (GABA-CB1-KO), or in principle neurons of the forebrain (CaMK-CB1-KO). These mutant mice and mice treated with the CB1 antagonist SR141716 were tested for different pain-related behaviors. In an acetic acid-induced abdominal constriction test, supraspinal CB1 deletions did not affect nocifensive responses. In the cerulein-model of acute pancreatitis, mechanical allodynia or hyperalgesia were not changed, but Glu-CB1- and CaMK-CB1-KO mice showed significantly increased facial grimacing scores indicating increased affective responses to this noxious visceral stimulus. Similarly, these brain-specific CB1 KO mice also showed significantly changed thermal nociception in a hot-plate test.

These results reveal a novel, and important role of CB1 expressed by cortical glutamatergic neurons in the affective component of visceral nociception.”

https://www.ncbi.nlm.nih.gov/pubmed/29885522

https://www.sciencedirect.com/science/article/pii/S0306452218303919

Ventilatory-depressant effects of opioids alone and in combination with cannabinoids in rhesus monkeys.

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“Pain is a serious health problem that is commonly treated with opioids, although the doses of opioids needed to treat pain are often similar to those that decrease respiration. Combining opioids with drugs that relieve pain through non-opioid mechanisms can decrease the doses of opioids needed for analgesia, resulting in an improved therapeutic window, but only if the doses of opioids that decrease respiration are not similarly decreased. Using small doses of opioids to treat pain has the potential to reduce the number of overdoses and deaths.

This study investigated whether the cannabinoid receptor agonists Δ9-tetrahydrocannabinol (Δ9-THC) and CP 55,940 modify the ventilatory-depressant effects of morphine and fentanyl in three monkeys.

In summary, cannabinoid receptor agonists, which increase the potency of opioids to produce antinociception, did not increase their potency to depress ventilation. Thus, the therapeutic window is greater for opioids when they are combined with cannabinoid receptor agonists, indicating a possible advantage for these drug mixtures in treating pain.”

https://www.ncbi.nlm.nih.gov/pubmed/29807027

https://www.sciencedirect.com/science/article/pii/S0014299918303108

Cannabinoid 1 receptors are expressed in nociceptive primary sensory neurons.

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 Neuroscience

“Expression of cannabinoid 1 (CB1) and vanilloid 1 (VR1) receptor proteins was studied in adult, cultured rat dorsal root ganglion neurons. Immunostaining of CB1 receptors alone produced labelling in 57+/-2% of the cultured dorsal root ganglion neurons (n=3 cultures). The area of the labelled cells was between 200 and 800 microm(2) with an average of 527+/-68 microm(2). VR1 immunolabelling revealed immunopositivity in 42+/-6% of the total population of dorsal root ganglion neurons. Cells showing VR1-like immunopositivity had an area between 200 and 600 microm(2). The mean area of the VR1-like immunopositive neurons was 376+/-61 microm(2). Double immunostaining with antisera raised against the CB1 and VR1 receptor proteins, showed a high degree of co-expression between CB1 and VR1 receptors. An average of 82+/-3% of the CB1-like immunopositive cells also showed VR1-like immunoreactivity (n=3 cultures) while 98+/-2% of the VR1-like immunolabelled neurons showed CB1 receptor-like immunostaining (n=3 cultures). Our data suggests that nociceptive primary sensory neurons co-express CB1 and VR1 receptors to a very high degree. We propose that this may provide an anatomical basis for a powerful combination of VR1 mediated excitation and CB1-mediated inhibition of nociceptive responses at central and peripheral terminals of nociceptive primary afferents.”

https://www.ncbi.nlm.nih.gov/pubmed/11036202

https://www.sciencedirect.com/science/article/abs/pii/S0306452200003894

Possible mechanisms of cannabinoid-induced antinociception in the spinal cord.

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European Journal of Pharmacology

“Anandamide is an endogenous ligand at both the inhibitory cannabinoid CB(1) receptor and the excitatory vanilloid receptor 1 (VR1). The CB(1) receptor and vanilloid VR1 receptor are expressed in about 50% and 40% of dorsal root ganglion neurons, respectively. While all vanilloid VR1 receptor-expressing cells belong to the calcitonin gene-related peptide-containing and isolectin B4-binding sub-populations of nociceptive primary sensory neurons, about 80% of the cannabinoid CB(1) receptor-expressing cells belong to those sub-populations. Furthermore, all vanilloid VR1 receptor-expressing cells co-express the cannabinoid CB(1) receptor.

In agreement with these findings, neonatal capsaicin treatment that induces degeneration of capsaicin-sensitive, vanilloid VR1 receptor-expressing, thin, unmyelinated, nociceptive primary afferent fibres significantly reduced the cannabinoid CB(1) receptor immunostaining in the superficial spinal dorsal horn.

Synthetic cannabinoid CB(1) receptor agonists, which do not have affinity at the vanilloid VR1 receptor, and low concentrations of anandamide both reduce the frequency of miniature excitatory postsynaptic currents and electrical stimulation-evoked or capsaicin-induced excitatory postsynaptic currents in substantia gelatinosa cells in the spinal cord without any effect on their amplitude. These effects are blocked by selective cannabinoid CB(1) receptor antagonists. Furthermore, the paired-pulse ratio is increased while the postsynaptic response of substantia gelatinosa neurons induced by alpha-amino-3-hydroxy-5-methylisoxasole-propionic acid (AMPA) in the presence of tetrodotoxin is unchanged following cannabinoid CB(1) receptor activation.

These results strongly suggest that the cannabinoid CB(1) receptor is expressed presynaptically and that the activation of these receptors by synthetic cannabinoid CB(1) receptor agonists or low concentration of anandamide results in inhibition of transmitter release from nociceptive primary sensory neurons. High concentrations of anandamide, on the other hand, increase the frequency of miniature excitatory postsynaptic currents recorded from substantia gelatinosa neurons. This increase is blocked by ruthenium red, suggesting that this effect is mediated through the vanilloid VR1 receptor.

Thus, anandamide at high concentrations can activate the VR1 and produce an opposite, excitatory effect to its inhibitory action produced at low concentrations through cannabinoid CB(1) receptor activation. This “dual”, concentration-dependent effect of anandamide could be an important presynaptic modulatory mechanism in the spinal nociceptive system.”

https://www.ncbi.nlm.nih.gov/pubmed/11698030

https://www.sciencedirect.com/science/article/pii/S0014299901013097?via%3Dihub

Effects of cannabinoid type 2 receptor agonist AM1241 on morphine-induced antinociception, acute and chronic tolerance, and dependence in mice.

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“Morphine is a potent opioid analgesic used to alleviate moderate or severe pain but the development of drug tolerance and dependence limits its use in pain management.

Previous studies showed that cannabinoid type 2 (CB2) receptor ligands may modulate opioid effects. However, there is no report of the effect of CB2 receptor agonist on acute morphine tolerance and physical dependence. We therefore investigated the effect of a CB2 receptor agonist (AM1241) on morphine-induced morphine tolerance and physical dependence in mice.

Our findings suggest that coadministration of the CB2 receptor agonist and morphine could increase morphine antinociception and reduce morphine tolerance and physical dependence in mice.

PERSPECTIVE:

Combination of a CB2 agonist and morphine may provide a new strategy for better treatment of acute and chronic pain, and prevention of opioid tolerance and dependence. This may also provide a clue for the treatment of opioid tolerance and dependence in clinic.”

https://www.ncbi.nlm.nih.gov/pubmed/29729431

https://www.sciencedirect.com/science/article/pii/S1526590018301597

“Antinociceptive Synergy between 9 -Tetrahydrocannabinol and Opioids after Oral Administration” http://jpet.aspetjournals.org/content/jpet/304/3/1010.full.pdf

Molecular and cellular basis of cannabinoid and opioid interactions.

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 Pharmacology Biochemistry and Behavior

“Cannabinoids and opioids have been shown to possess several similar pharmacological effects, including analgesia and stimulation of brain circuitry that are believed to underlie drug addiction and reward. In recent years, these phenomena have supported the possible existence of functional links in the mechanisms of action of both types of drugs.

The present review addresses the recent advances in the study of biochemical and molecular mechanisms underlying opioid and cannabinoid interaction. Several hypothesis have been formulated to explain this cross-modulation including the release of opioid peptides by cannabinoids or endocannabinoids by opioids and interaction at the level of receptor and/or their signal transduction mechanisms.

Moreover it is important to consider that the nature of cannabinoid and opioid interaction might differ in the brain circuits mediating reward and in those mediating other pharmacological properties, such as antinociception.

Further studies are needed since a better knowledge of the opioid-cannabinoid interaction may lead to exciting therapeutic possibilities.”

https://www.ncbi.nlm.nih.gov/pubmed/15927245

https://www.sciencedirect.com/science/article/pii/S0091305705001450?via%3Dihub

Opioids and cannabinoids interactions: involvement in pain management.

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“Among several pharmacological properties, analgesia is the most common feature shared by either opioid or cannabinoid systems.

Cannabinoids and opioids are distinct drug classes that have been historically used separately or in combination to treat different pain states.

Indeed, it is widely known that activation of either opioid or cannabinoid systems produce antinociceptive properties in different pain models.

Moreover, several biochemical, molecular and pharmacological studies support the existence of reciprocal interactions between both systems, suggesting a common underlying mechanism.

Further studies have demonstrated that the endogenous opioid system could be involved in cannabinoid antinociception and recent data have also provided evidence for a role of the endogenous cannabinoid system in opioid antinociception.

These interactions may lead to additive or even synergistic antinociceptive effects, emphasizing their clinical relevance in humans in order to enhance analgesic effects with lower doses and consequently fewer undesirable side effects.

Thus, the present review is focused on bidirectional interactions between opioids and cannabinoids and their potent repercussions on pain modulation.”

https://www.ncbi.nlm.nih.gov/pubmed/20017728

http://www.eurekaselect.com/71318/article

Current evidence of cannabinoid-based analgesia obtained in preclinical and human experimental settings.

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European Journal of Pain

“Cannabinoids have a long record of recreational and medical use and become increasingly approved for pain therapy. This development is based on preclinical and human experimental research summarized in this review.

Cannabinoid CB1 receptors are widely expressed throughout the nociceptive system. Their activation by endogenous or exogenous cannabinoids modulates the release of neurotransmitters. This is reflected in antinociceptive effects of cannabinoids in preclinical models of inflammatory, cancer and neuropathic pain, and by nociceptive hypersensitivity of cannabinoid receptor-deficient mice.

Cannabis-based medications available for humans mainly comprise Δ9 -tetrahydrocannabinol (THC), cannabidiol (CBD) and nabilone.

During the last 10 years, six controlled studies assessing analgesic effects of cannabinoid-based drugs in human experimental settings were reported. An effect on nociceptive processing could be translated to the human setting in functional magnetic resonance imaging studies that pointed at a reduced connectivity within the pain matrix of the brain. However, cannabinoid-based drugs heterogeneously influenced the perception of experimentally induced pain including a reduction in only the affective but not the sensory perception of pain, only moderate analgesic effects, or occasional hyperalgesic effects. This extends to the clinical setting.

While controlled studies showed a lack of robust analgesic effects, cannabis was nearly always associated with analgesia in open-label or retrospective reports, possibly indicating an effect on well-being or mood, rather than on sensory pain. Thus, while preclinical evidence supports cannabinoid-based analgesics, human evidence presently provides only reluctant support for a broad clinical use of cannabinoid-based medications in pain therapy.

SIGNIFICANCE:

Cannabinoids consistently produced antinociceptive effects in preclinical models, whereas they heterogeneously influenced the perception of experimentally induced pain in humans and did not provide robust clinical analgesia, which jeopardizes the translation of preclinical research on cannabinoid-mediated antinociception into the human setting.”

https://www.ncbi.nlm.nih.gov/pubmed/29160600

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