CB1-cannabinoid-, TRPV1-vanilloid- and NMDA-glutamatergic-receptor-signalling systems interact in the prelimbic cerebral cortex to control neuropathic pain symptoms

Cannabidiol in the dorsal hippocampus attenuates emotional and cognitive impairments related to neuropathic pain: The role of prelimbic neocortex-hippocampal connections

BACKGROUND AND PURPOSE

Chronic neuropathic pain (NP) is commonly associated with cognitive and emotional impairments. Cannabidiol (CBD) presents a broad spectrum of action with a potential analgesic effect. This work investigates the CBD effect on comorbidity between chronic NP, depression, and memory impairment.

EXPERIMENTAL APPROACH

The connection between the neocortex and the hippocampus was investigated with biotinylated dextran amine (BDA) deposits in the prelimbic cortex (PrL). Wistar rats were submitted to chronic constriction injury (CCI) of the sciatic nerve and CA1 treatment with CBD (15, 30, 60 nmol).

KEY RESULTS

BDA-labeled perikarya and terminal buttons were found in CA1 and dentate gyrus. CCI-induced mechanical and cold allodynia increased c-Fos protein expression in the PrL and CA1. The number of astrocytes in PrL and CA1 increased, and the number of neuroblasts decreased in CA1. Animals submitted to CCI procedure showed increasing depressive-like behaviors, such as memory impairment. CBD (60 nmol) treatment decreased mechanical and cold allodynia, attenuated depressive-associated behaviors, and improved memory performance. Cobalt chloride (CoCl2: 1 nM), WAY-100635 (0.37 nmol), and AM251 (100 nmol) intra-PrL reversed the effect of CA1 treatment with CBD (60 nmol) on nociceptive, cognitive, and depressive behaviors.

CONCLUSION

CBD represents a promising therapeutic perspective in the pharmacological treatment of chronic NP and associated comorbidities such as depression and memory impairments. The CBD effects possibly recruit the CA1-PrL pathway, inducing neuroplasticity. CBD acute treatment into the CA1 produces functional and molecular morphological improvements.

TRPV1: Receptor structure, activation, modulation and role in neuro-immune interactions and pain

In the 1990s, the identification of a non-selective ion channel, especially responsive to capsaicin, revolutionized the studies of somatosensation and pain that were to follow. The TRPV1 channel is expressed mainly in neuronal cells, more specifically, in sensory neurons responsible for the perception of noxious stimuli. However, its presence has also been detected in other non-neuronal cells, such as immune cells, β- pancreatic cells, muscle cells and adipocytes. Activation of the channel occurs in response to a wide range of stimuli, such as noxious heat, low pH, gasses, toxins, endocannabinoids, lipid-derived endovanilloid, and chemical agents, such as capsaicin and resiniferatoxin. This activation results in an influx of cations through the channel pore, especially calcium. Intracellular calcium triggers different responses in sensory neurons. Dephosphorylation of the TRPV1 channel leads to its desensitization, which disrupts its function, while its phosphorylation increases the channel's sensitization and contributes to the channel's rehabilitation after desensitization. Kinases, phosphoinositides, and calmodulin are the main signaling pathways responsible for the channel's regulation. Thus, in this review we provide an overview of TRPV1 discovery, its tissue expression as well as on the mechanisms by which TRPV1 activation (directly or indirectly) induces pain in different disease models.

Synthesis and Antiallodynic Activity of Cannabidiol Analogue on Peripheral Neuropathy in Mice

Cannabidiol (CBD) is a substance that exerts several therapeutic actions, including analgesia. CBD is generally administered orally, but its poor water solubility and metabolism impair its bioavailability. Thus, the development of molecules with better pharmacokinetic profile from cannabidiol becomes an interesting strategy for the design of novel analgesic drugs for the relief of painful conditions that are difficult to manage clinically, such as neuropathic pain. In the present study, an unprecedented analogue of CBD (1) was synthesized and some of its physicochemical properties were evaluated in silico as well as its stability in an acid medium. Additionally, its effect was investigated in a model of neuropathic pain induced by the chemotherapy drug paclitaxel in mice, in comparison with cannabidiol itself. Cannabidiol (20 mg/kg), pregabalin (30 mg/kg), or analogue 1 (5, 10, and 20 mg/kg), administered on the 14th day after the first administration of paclitaxel, attenuated the mechanical allodynia of the sensitized animals. The antinociceptive activity of analogue 1 was attenuated by previous administration of a cannabinoid CB1 receptor antagonist, AM 251, which indicates that its mechanism of action is related to the activation of CB1 receptors. In conclusion, the CBD analogue 1 developed in this study shows great potential to be used in the treatment of neuropathic pain.

Effect of electrical and chemical (activation versus inactivation) stimulation of the infralimbic division of the medial prefrontal cortex in rats with chronic neuropathic pain

Neuropathic pain (NP) represents a complex disorder with sensory, cognitive, and emotional symptoms. The medial prefrontal cortex (mPFC) takes critical regulatory roles and may change functionally and morphologically during chronic NP. There needs to be a complete understanding of the neurophysiological and psychopharmacological bases of the NP phenomenon. This study aimed to investigate the participation of the infralimbic division (IFL) of the mPFC in chronic NP, as well as the role of the N-methyl-D-aspartic acid receptor (NMDAr) in the elaboration of chronic NP. Male Wistar rats were submitted to the von Frey and acetone tests to assess mechanical and cold allodynia after 21 days of chronic constriction injury (CCI) of the sciatic nerve or Sham-procedure ("false operated"). Electrical neurostimulation of the IFL/mPFC was performed by low-frequency stimuli (20 μA, 100 Hz) applied for 15 s by deep brain stimulation (DBS) device 21 days after CCI. Either cobalt chloride (CoCl2 at 1.0 mM/200 nL), NMDAr agonist (at 0.25, 1.0, and 2.0 nmol/200 nL) or physiological saline (200 nL) was administered into the IFL/mPFC. CoCl2 administration in the IFL cortex did not alter either mechanical or cold allodynia. DBS stimulation of the IFL cortex decreased mechanical allodynia in CCI rats. Chemical stimulation of the IFL cortex by an NMDA agonist (at 2.0 nmol) decreased mechanical allodynia. NMDA at any dose (0.25, 1.0, and 2.0 nmol) reduced the flicking/licking duration in the cold test. These findings suggest that the IFL/mPFC and the NMDAr of the neocortex are involved in attenuating chronic NP in rats.

Activation of the N-methyl-D-aspartate receptor and calcium/calmodulin-dependent protein kinase IIα signal in the rostral anterior cingulate cortex is involved in pain-related aversion in rats with peripheral nerve injury

The rostral anterior cingulate cortex (rACC) of rat brain is associated with pain-related emotions. However, the underlying molecular mechanism remains unclear. Here, we investigated the effects of the N-methyl-D-aspartate (NMDA) receptor and Ca2+/Calmodulin-dependent protein kinase type II (CaMKII)α signal on pain-related aversion in the rACC of a rat model of neuropathic pain (NP). Mechanical and thermal hyperalgesia were examined using von Frey and hot plate tests in a rat model of NP induced by spared nerve injury (SNI) of the unilateral sciatic nerve. Bilateral rACC pretreatment with the CaMKII inhibitor tat-CN21 (derived from the cell-penetrating tat sequence and CaM-KIIN amino acids 43-63) or tat-Ctrl (the tat sequence and the scrambled sequence of CN21) was performed on postoperative days 29-35 in Sham rats or rats with SNI. Spatial memory performance was tested using an eight-arm radial maze on postoperative days 34-35. Pain-related negative emotions (aversions) were evaluated using the place escape/avoidance paradigm on postoperative day 35 following the spatial memory performance test. The percentage of time spent in the light area was used to assess pain-related negative emotions (i.e., aversion). The expression levels of the NMDA receptor GluN2B subunit, CaMKIIα, and CaMKII-Threonine at position 286 (Thr286) phosphorylation in contralateral rACC specimens were detected by Western blot or real time PCR following the aversion test. Our data showed that pretreatment of the rACC with tat-CN21 increased determinate behavior but did not alter hyperalgesia or spatial memory performance in rats with SNI. In addition, tat-CN21 reversed the enhanced CaMKII-Thr286 phosphorylation and had no effect on the upregulated expression of GluN2B, CaMKIIα protein, and mRNA. Our data suggested that activation of the NMDA receptor-CaMKIIα signal in rACC is associated with pain-related aversion in rats with NP. These data may provide a new approach for the development of drugs that modulate cognitive and emotional pain aspects.

Pharmacological activation of mediodorsal thalamic GABA-A receptors modulates morphine/cetirizine-induced changes in the prefrontal cortical GFAP expression in a rat model of neuropathic pain

The present study investigated the involvement of mediodorsal thalamic (MD) GABA-A receptors in cetirizine/morphine-induced anti-allodynia using a rat model of neuropathic pain. To assess the importance of the prefrontal cortex (PFC) for chronic pain processing, its expression level changes of glial fibrillary acidic protein (GFAP) were measured following drug treatments. Each animal was subjected to chronic constriction of the sciatic nerve surgery simultaneously with the MD cannulation under stereotaxic surgery. The results showed that the administration of morphine (3-5 mg/kg) or cetirizine (1-3 mg/kg) produced significant analgesia in neuropathic rats. Systemic administration of cetirizine (2.5 and 3 mg/kg) potentiated the analgesic response to a low and intolerance dose of morphine (3 mg/kg). Intra-MD microinjection of muscimol, a selective GABA-A receptor agonist (0.005-0.01 μg/rat), increased the cetirizine/morphine-induced anti-allodynia, while muscimol by itself did not affect neuropathic pain. The neuropathic pain was associated with the increased PFC expression level of GFAP, suggesting the impact of chronic pain on PFC glial management. Interestingly, the anti-allodynia was associated with a decrease in the PFC expression level of GFAP under the drugs' co-administration. Thus, cetirizine has a significant potentiating effect on morphine response in neuropathic pain via interacting with the MD GABA-A receptors. It seems that neuropathic pain affects the prefrontal cortex GFAP signaling pathway. In clinical studies, these findings can be considered to create a combination therapy with low doses of GABA-A receptor agonist plus cetirizine and morphine to manage neuropathic pain.

Neostriatum neuronal TRPV1-signalling mediates striatal anandamide at high concentration facilitatory influence on neostriato-nigral dishinhibitory GABAergic connections

RATIONALE

Several lines of evidence have demonstrated that the cannabinoid type 1 receptor (CB₁) is found in the caudate nucleus and putamen (CPu) in addition to the substantia nigra pars reticulata (SNpr). Here, we investigated the role of endocannabinoid neuromodulation of striato-nigral disinhibitory projections on the activity of nigro-collicular GABAergic pathways that control the expression of unconditioned fear-related behavioural responses elicited by microinjections of the GABA_A receptor selective antagonist bicuculline (BIC) in the deep layers of the superior colliculus (dlSC).

METHODS

Fluorescent neural tract tracers were deposited in either CPu or in SNpr. Wistar rats received injection of vehicle, anandamide (AEA), either at low (50 pmol) or high (100 pmol) concentrations in CPu followed by bicuculline microinjections in dlSC.

RESULTS

Connections between CPu, the SNpr and dlSC were demonstrated. The GABA_A receptor blockade in dlSC elicited panic-like behaviour. AEA at the lowest concentration caused a panicolytic-like effect that was antagonised by the CPu pretreatment with AM251 at 100 pmol. AEA at the highest concentration caused a panicogenic-like effect that was antagonised by the CPu pretreatment with 6-iodonordihydrocapsaicin (6-I-CPS) at different concentrations (0.6, 6, 60 nmol).

CONCLUSION

These findings suggest that while pre-synaptic CB1-signalling subserves an indirect facilitatory effect of AEA on striato-nigral pathways causing panicolytic-like responses through midbrain tectum enhanced activity, post-synaptic TRPV₁-signalling in CPu mediates AEA direct activation of striato-nigral disinhibitory pathways resulting in increasing dlSC neurons activity and a panicogenic-like response. All these actions seem to depend on the interface with the nigro-collicular inhibitory GABAergic pathways.

Lanostane triterpenoids from Ganoderma lucidum and their inhibitory effects against FAAH

Ganoderma lucidum is a famous edible and medicinal fungus. Through a bioactive phytochemical investigation of the ethanolic extracts of the fruiting bodies of G. lucidum, twenty-nine triterpenoids, including eleven previously undescribed triterpenoids, were isolated and characterized based on spectroscopic data. The inhibitory effects of all the triterpenes against fatty acid amide hydrolase (FAAH) were found to be in the range of 30-60% at 100 μM. Methyl ganoderate A displayed the strongest inhibitory activity (61%) against FAAH. Furthermore, all compounds displayed no cytotoxicity against LOVO and MCF-7 human cancer cells. Hence, our present study provides information about G. lucidum as a functional food or pharmaceutical supplement for the treatment of neuroinflammation.

Analgesia effect of lentivirus-siSCN9A infected neurons in vincristine induced neuropathic pain rats

At present, the mechanism of siSCN9A in Vincristine (VCR)-induced neuropathic pain (NP) is still unclear. This study aimed to explore the analgesic mechanism of lentivirus-siSCN9A (LV-siSCN9A) infected neurons against NP. 40 male Sprague-Dawley (SD) rats were divided into a control group (injected with normal saline), a model group (VCR-induced NP model), a LV-SC group (NP model mice were injected with LV-SC-infected dorsal root ganglia (DRG) neuron cells under the microscope), and a LV-siSCN9A group (NP model mice were injected with LV-siSCN9A-infected DRG neuron cells under the microscope, with 10 rats in each group. The changes of mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) of rats in different groups were detected by behavior testing, the Nav1.7 changes in each group were detected by immunofluorescence double standard and Western-blot method. It was found that compared with the control group, the MWT and TWL of the rats in model group were significantly decreased (P < 0.05), and the expression levels of Nav1.7 messenger ribonucleic acid (mRNA) and proteins were significantly increased (P < 0.05). Compared with LV-SC group, the MWT and TWL of rats in LV-siSCN9A group were significantly increased (P < 0.05), the expression levels of Nav1.7 mRNA and proteins were significantly decreased (P < 0.05), and the CGRP expression of spinal dorsal horn was significantly decreased. It was concluded that the LV-siSCN9A infected neurons could play an analgesic role by down-regulating Nav1.7 expression induced by VCR in NP model.

Cannabinoid exposure as a major driver of pediatric acute lymphoid Leukaemia rates across the USA: combined geospatial, multiple imputation and causal inference study

BACKGROUND

Acute lymphoid leukaemia (ALL) is the commonest childhood cancer whose incidence is rising in many nations. In the USA, between 1975 and 2016, ALL rates (ALLRs) rose 93.51% from 1.91 to 3.70/100,000 <  20 years. ALL is more common in Caucasian-Americans than amongst minorities. The cause of both the rise and the ethnic differential is unclear, however, prenatal cannabis exposure was previously linked with elevated childhood leukaemia rates. We investigated epidemiologically if cannabis use impacted nationally on ALLRs, its ethnic effects, and if the relationship was causal.

METHODS

State data on overall, and ethnic ALLR from the Surveillance Epidemiology and End Results databank of the Centre for Disease Control (CDC) and National Cancer Institute (NCI) were combined with drug (cigarettes, alcoholism, cannabis, analgesics, cocaine) use data from the National Survey of Drug Use and Health; 74.1% response rate. Income and ethnicity data was from the US Census bureau. Cannabinoid concentration was from the Drug Enforcement Agency Data. Data was analyzed in R by robust and spatiotemporal regression.

RESULTS

In bivariate analyses a dose-response relationship was demonstrated between ALLR and Alcohol Use Disorder (AUD), cocaine and cannabis exposure, with the effect of cannabis being strongest (β-estimate = 3.33(95%C.I. 1.97, 4.68), P = 1.92 × 10^- 6). A strong effect of cannabis use quintile on ALLR was noted (Chi.Sq. = 613.79, P = 3.04 × 10^- 70). In inverse probability weighted robust regression adjusted for other substances, income and ethnicity, cannabis was independently significant (β-estimate = 4.75(0.48, 9.02), P = 0.0389). In a spatiotemporal model adjusted for all drugs, income, and ethnicity, cannabigerol exposure was significant (β-estimate = 0.26(0.01, 0.52), P = 0.0444), an effect increased by spatial lagging (THC: β-estimate = 0.47(0.12, 0.82), P = 0.0083). After missing data imputation ethnic cannabis exposure was significant (β-estimate = 0.64(0.55, 0.72), P = 3.1 × 10^- 40). 33/35 minimum e-Values ranged from 1.25 to 3.94 × 10³⁶ indicative of a causal relationship. Relaxation of cannabis legal paradigms had higher ALLR (Chi.Squ.Trend = 775.12, P = 2.14 × 10^- 112). Cannabis legal states had higher ALLR (2.395 ± 0.039 v. 2.127 ± 0.008 / 100,000, P = 5.05 × 10^- 10).

CONCLUSIONS

Data show that ALLR is associated with cannabis consumption across space-time, is associated with the cannabinoids, THC, cannabigerol, cannabinol, cannabichromene, and cannabidiol, contributes to ethnic differentials, demonstrates prominent quintile effects, satisfies criteria for causality and is exacerbated by cannabis legalization.

A NIR fluorescent probe for fatty acid amide hydrolase bioimaging and its application in development of inhibitors

Fatty acid amide hydrolase (FAAH) is primarily responsible for the inactivation of fatty acid ethanolamide (FAE) and is involved in a variety of biological functions related to diseases of the nervous system. Herein, we developed a highly selective and sensitive FAAH-activated near-infrared fluorescent probe named DAND and achieved the real-time detection and imaging of FAAH activity in complex biosystems. Moreover, a visual high-throughput screening method was established using DAND, piperine was identified as a novel inhibitor of FAAH. Based on the interaction of piperine with FAAH, a more potent FAAH inhibitor (11f) was designed and synthesized which possessed an IC₅₀ value of 0.65 μM. Furthermore, 11f could attenuate the liposaccharide (LPS)-induced activation of BV2 cells, exhibiting an excellent anti-inflammatory activity. These results indicated that DAND could be used as a promising molecular tool for exploring FAAH activity and for rapidly screening potential FAAH inhibitors. In addition, piperine and its derivatives could serve as potential candidate drugs for the treatment of neurodegenerative diseases in the future.

Probable Causes of Alzheimer’s Disease

A three-part mechanism is proposed for the induction of Alzheimer’s disease: (1) decreased blood lactic acid; (2) increased blood ceramide and adipokines; (3) decreased blood folic acid. The age-related nature of these mechanisms comes from age-associated decreased muscle mass, increased visceral fat and changes in diet. This mechanism also explains why many people do not develop Alzheimer’s disease. Simple changes in lifestyle and diet can prevent Alzheimer’s disease. Alzheimer’s disease is caused by a cascade of events that culminates in damage to the blood–brain barrier and damage to neurons. The blood–brain barrier keeps toxic molecules out of the brain and retains essential molecules in the brain. Lactic acid is a nutrient to the brain and is produced by exercise. Damage to endothelial cells and pericytes by inadequate lactic acid leads to blood–brain barrier damage and brain damage. Inadequate folate intake and oxidative stress induced by activation of transient receptor potential cation channels and endothelial nitric oxide synthase damage the blood–brain barrier. NAD depletion due to inadequate intake of nicotinamide and alterations in the kynurenine pathway damages neurons. Changes in microRNA levels may be the terminal events that cause neuronal death leading to Alzheimer’s disease. A new mechanism of Alzheimer’s disease induction is presented involving lactic acid, ceramide, IL-1β, tumor necrosis factor α, folate, nicotinamide, kynurenine metabolites and microRNA.