Cannabidiol in the prelimbic cortex modulates the comorbid condition between the chronic neuropathic pain and depression-like behaviour in rats: The role of medial prefrontal cortex 5-HT1A and CB1 receptors

Low-dose cannabidiol treatment prevents chronic stress-induced phenotypes and is associated with multiple synaptic changes across various brain regions

Major Depressive Disorder (MDD) is a heterogeneous and debilitating mood disorder often associated with stress. Although current treatments are available, they remain ineffective for approximately 30% of affected individuals and are frequently accompanied by undesirable side effects. Cannabidiol (CBD) has emerged as a potential and safe therapeutic option for alleviating depressive symptoms; however, the underlying molecular mechanisms through which this compound exerts its beneficial effects are not yet fully understood. In this study, we demonstrate that a very low dose of CBD (1 mg/kg) can partially reverse some sequelae induced by chronic stress, a well-established mouse model used to simulate depressive-like symptoms. Using mass spectrometry to analyze different brain regions, we observed several improvements following CBD treatment, particularly in the medial prefrontal cortex (mPFC), across multiple neurotransmission systems (including glutamatergic and serotonergic pathways). Microstructural experiments, utilizing double-labeling of F-Actin and VGlut1-positive clusters, revealed a complete restoration of mature synapses in the mPFC of mice treated with CBD. In conclusion, our findings indicate that a very low dose of CBD is effective in counteracting the adverse effects of chronic stress, possibly through the synaptic remodeling of excitatory synapses in the mPFC.

Cannabidiol reduces neuropathic pain and cognitive impairments through activation of spinal PPARγ

The purpose of this study was to evaluate the participation of spinal peroxisome proliferator-activated receptor gamma (PPARγ) in the antiallodynic effect of cannabidiol, the expression of PPARγ in sites relevant to the spinal nociceptive processing, and the effect of this cannabinoid on cognitive deficits induced by neuropathic pain in female mice. Either acute or repeated treatment with cannabidiol reduced tactile allodynia and spontaneous pain (flinching) in female neuropathic mice. Cannabidiol induced a greater effect in female mice. Pioglitazone partially reduced tactile allodynia, and this effect was fully blocked by the PPARγ antagonist GW9662. Likewise, intrathecal injection of cannabidiol reduced tactile allodynia, while PPARγ antagonist GW9662 or 5-HT1A receptor antagonist WAY-100635, but not the PPARα antagonist GW6479, partially prevented this effect. GW9662 and WAY-100635 administrated per se did not modify tactile allodynia in neuropathic female mice. Co-administration of GW9662 and WAY-100635 fully prevented the antiallodynic effect of cannabidiol in mice. Nerve injury up-regulated PPARγ expression at the spinal cord and dorsal root ganglia, while cannabidiol further enhanced nerve injury-induced up-regulation of PPARγ expression in both tissues. Repeated intrathecal injection of cannabidiol reduced tactile allodynia and several pain makers (ERK, p-ERK, p38MAPK and p-p38MAPK). In addition, this treatment restored nerve injury-induced interleukin-10 down-regulation and increased PPARγ expression at the spinal cord. Repeated treatment with cannabidiol also improved nerve injury-induced cognitive impairment in mice. These results provide compelling evidence for the involvement of PPARγ in the antiallodynic effect of cannabidiol in mice and highlight its multifaceted therapeutic potential in neuropathic pain management and its comorbidities. PERSPECTIVE: The present study reveals cannabidiol's dual effects in female mice by reducing neuropathic pain through spinal PPARγ and 5-HT1A receptor activation and ameliorating nerve injury-induced cognitive impairment. These findings may assist clinicians seeking new therapeutic approaches for managing neuropathic pain and its associated cognitive deficits.

Acute kappa opioid receptor blocking disrupts the pro-cognitive effect of cannabidiol in neuropathic rats

Cannabidiol has been shown to ameliorate neuropathic pain and its affective components. Previous studies highlighted the pharmacological interaction between the CBD and opioid system, particularly the MOR, but the understanding of the interaction between CBD and kappa opioid receptor (KOR), physiologically stimulated by the endogenous opioid dynorphin, remains elusive. We assessed the pharmacological interactions between CBD and nor-BNI, a selective KOR antagonist in a rat neuropathic pain model. We show an increase in dynorphin peptide and its KOR receptors in the hippocampus' dentate gyrus (DG) of neuropathic rats showing allodynia, and memory deficits. Consistent with these findings, neuropathic pain was associated with long-term potentiation (LTP) impairment in the entorhinal cortex-DG, also referred to as the lateral perforant pathway (LPP). Moreover, a downregulation of the endocannabinoid 2-AG and an upregulation of the cannabinoid CB1 receptors in the DG were detected in neuropathic pain animals. Either an acute KOR antagonist administration or one-week CBD treatment normalized dynorphin levels and improved affective symptoms, LTP and receptor expression, whereas only CBD showed an anti-allodynic effect. In addition, CBD normalized the SNI-induced changes in neuroplasticity as well as endocannabinoid and GABA levels in the DG. Noteworthy, the acute blockade of the KOR carried out after CBD repeated administration causes the re-installment of some neuropathic condition symptoms. As a whole, these original results indicate a critical relationship between the adaptive changes in the hippocampus produced by CBD and the need to maintain the recovered physiological dynorphin tone to preserve the therapeutic effect of CBD in neuropathic rats.

CBD and the 5-HT1A receptor: A medicinal and pharmacological review

Cannabidiol (CBD), a phytocannabinoid, has emerged as a promising candidate for addressing a wide array of symptoms. It has the ability to bind to multiple proteins and receptors, including 5-HT1AR, transient receptor potential vanilloid 1 (TRPV1), and cannabinoid receptors. However, CBD's pharmacodynamic interaction with 5-HT1AR and its medicinal outcomes are still debated. This review explores recent literature to elucidate these questions, highlighting the neurotherapeutic outcomes of this pharmacodynamic interaction and proposing a signaling pathway underlying the mechanism by which CBD desensitizes 5-HT1AR signaling. A comprehensive survey of the literature underscores CBD's multifaceted neurotherapeutic effects, which include antidepressant, anxiolytic, neuroprotective, antipsychotic, antiemetic, anti-allodynic, anti-epileptic, anti-degenerative, and addiction-treating properties, attributable in part to its interactions with 5-HT1AR. Furthermore, evidence suggests that the pharmacodynamic interaction between CBD and 5-HT1AR is contingent upon dosage. Moreover, we propose that CBD can induce desensitization of 5-HT1AR via both homologous and heterologous mechanisms. Homologous desensitization involves the recruitment of G protein-coupled receptor kinase 2 (GRK2) and β-arrestin, leading to receptor endocytosis. In contrast, heterologous desensitization is mediated by an elevated intracellular calcium level or activation of protein kinases, such as c-Jun N-terminal kinase (JNK), through the activity of other receptors.

A novel insight into the antidepressant effect of cannabidiol: possible involvement of the 5-HT1A, CB1, GPR55, and PPARγ receptors

BACKGROUND

Depression is a prevalent and disabling disorder that poses serious problems in mental health care, and rapid antidepressants are novel treatments for this disorder. Cannabidiol (CBD), a nonintoxicating phytocannabinoid, is thought to have therapeutic potential due to its important neurological and anti-inflammatory properties. Despite major advances in pharmacotherapy in experimental animals, the exact mechanism of antidepressant-like effects remains to be elucidated.

METHODS

In this paper, we review the current state of knowledge on the antidepressant properties of CBD in numerous experimental and clinical studies.

RESULTS

Accumulating evidence suggests that CBD has antidepressant properties in humans and animals with few side effects, suggesting that CBD may be a potential antidepressant. Furthermore, we discuss that CBD may therefore provide a potential treatment to exert antidepressant-like effects through various molecular targets, reducing inflammation, and enhancing neurogenesis.

CONCLUSIONS

Taken together with the growing popularity of CBD as a medicine, these findings extend the limited knowledge on the antidepressant effects of CBD. This potentially opens up new therapeutic means for the patients with depression.

The endocannabinoid system in the brain undergoes long-lasting changes following neuropathic pain

The endocannabinoid system (ECS), which is composed of endocannabinoids (eCBs), cannabinoid receptors (CBRs), and associated signaling molecules, has been identified within the brain. In neuropathic pain animal models and patients, long-lasting alterations in the ECS have been observed. These changes of neurons and glial cells in the ECS contribute to the modulation of neuropathic pain. Intervention strategies such as the activation of CBRs, the enhancement of hydrolytic enzyme function, and the inhibition of synthetizing enzymes typically alleviate neuropathic pain through CBR-dependent mechanisms. Additionally, emotions such as fear, anxiety, and depression are frequently experienced with neuropathic pain. Exogenous cannabinoids can mitigate these mood disorders via CBR signaling pathways. Therefore, the targeting of long-lasting ECS alterations represents a potential therapeutic approach for both neuropathic pain and emotional disorders. In this review, the long-lasting variations in neurons and glial cells in the ECS related to neuropathic pain and the accompanying emotional comorbidities are elucidated. Furthermore, the cellular and molecular mechanisms underlying synaptic plasticity and neural circuit activities in the brain are reviewed.

Neuromolecular and behavioral effects of cannabidiol on depressive-associated behaviors and neuropathic pain conditions in mice

BACKGROUND AND AIMS

Neuropathic pain (NP) has a high incidence in the general population, is closely related to anxiety disorders, and has a negative impact on the quality of life. Cannabidiol (CBD), as a natural product, has been extensively studied for its potential therapeutic effects on symptoms such as pain and depression (DP). However, the mechanism of CBD in improving NP with depression is not fully understood.

METHODS

First, we used bioinformatics tools to deeply mine the intersection genes associated with NP, DP, and CBD. Secondly, the core targets were screened by Protein-protein interaction network, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes analysis, molecular docking and molecular dynamics simulation. Next, the effects of CBD intervention on pain and depressive behaviors in the spinal nerve ligation (SNL) mouse model were evaluated using behavioral tests, and dose-response curves were plotted. After the optimal intervention dose was determined, the core targets were verified by Western blot (WB) and Quantitative Polymerase Chain Reaction (qPCR). Finally, we investigated the potential mechanism of CBD by Nissl staining, Immunofluorescence (IF) and Transmission Electron Microscopy (TEM).

RESULTS

A total of five core genes of CBD most associated with NP and DP were screened by bioinformatics analysis, including PTGS2, GPR55, SOD1, CYP1A2 and NQO1. Behavioral test results showed that CBD by intraperitoneal administration 5 mg/kg can significantly improve the pain behavior and depressive state of SNL mice. WB, qPCR, IF, and TEM experiments further confirmed the regulatory effects of CBD on key molecules.

CONCLUSION

In this study, we found five targets of CBD in the treatment of NP with DP. These findings provide further theoretical and experimental basis for CBD as a potential therapeutic agent.

Nitric oxide-signalling affects panic-like defensive behaviour and defensive antinociception neuromodulation in the prelimbic cerebral cortex

RATIONALE

The prelimbic division (PrL) of the medial prefrontal cortex (mPFC) is a key structure in panic.

OBJECTIVES

To evaluate the role of nitric oxide (NO) in defensive behaviour and antinociception.

METHODS

Either Nω-propyl-L-arginine (NPLA) or Carboxy-PTIO was microinjected in the PrL cortex, followed by hypothalamic treatment with bicuculline. The exploratory behaviours, defensive reactions and defensive antinociception were recorded. Encephalic c-Fos protein was immunolabelled after escape behaviour.

RESULTS

NPLA (an inhibition of nNOs) decreased panic-like responses and innate fear-induced antinociception. The c-PTIO (a membrane-impermeable NO scavenger) decreased the escape behaviour. PrL cortex pre-treatment with c-PTIO at all doses decreased defensive antinociception. c-Fos protein was labelled in neocortical areas, limbic system, and mesencephalic structures.

CONCLUSION

The NPLA and c-PTIO in the PrL/mPFC decreased the escape behaviour and defensive antinociception organised by medial hypothalamic nuclei. The oriented escape behaviour recruits neocortical areas, limbic system, and mesencephalic structures. These findings suggest that the organisation of defensive antinociception recruits NO-signalling mechanisms within the PrL cortex. Furthermore, the present findings also support the role of NO as a retrograde messenger in the PrL cortex during panic-like emotional reactions.

Cannabis constituents for chronic neuropathic pain; reconciling the clinical and animal evidence

Chronic neuropathic pain is a debilitating pain syndrome caused by damage to the nervous system that is poorly served by current medications. Given these problems, clinical studies have pursued extracts of the plant Cannabis sativa as alternative treatments for this condition. The vast majority of these studies have examined cannabinoids which contain the psychoactive constituent delta-9-tetrahydrocannabinol (THC). While there have been some positive findings, meta-analyses of this clinical work indicates that this effectiveness is limited and hampered by side-effects. This review focuses on how recent preclinical studies have predicted the clinical limitations of THC-containing cannabis extracts, and importantly, point to how they might be improved. This work highlights the importance of targeting channels and receptors other than cannabinoid CB1 receptors which mediate many of the side-effects of cannabis.

Cannabidiol (CBD): A Systematic Review of Clinical and Preclinical Evidence in the Treatment of Pain

Background/Objectives: Cannabis sativa L. is a plant that has been used for thousands of years for its industrial and medicinal properties. In recent years, there has been a rise in the study of this plant due to its bioactive compounds for pharmaceutical applications. Particularly, cannabidiol has demonstrated analgesic and non-psychoactive properties. The objective of this systematic review is to update and to gather the clinical and preclinical evidence on CBD in pain treatment. Methods: This study was performed following the PRISMA guidelines and using the following search terms "((cannabidiol) NOT (THC)) NOT (tetrahydrocannabinol)) AND (pain treatment)" in PubMed and Web of Science, with the following inclusion criteria: CBD pain treatment without THC in monotherapy, including both clinical and preclinical trials. From the initial sample of more than 500 articles, a total of 40 studies were selected, eliminating duplicate studies from the databases and considering the inclusion and exclusion criteria. On one hand, clinical trials were analyzed using CBD products without THC used in monotherapy, assigning a Jadad score to evaluate the quality/bias of the trials; on the other hand, the main preclinical trials were analyzed, grouping the results into in vivo and in vitro trials. Results: Based on the review conducted, there is sufficient clinical and preclinical evidence of CBD in pain treatment, so CBD could be an effective and safe treatment in reducing pain due to its analgesic and anti-inflammatory properties. These effects appear to be primarily mediated by the activation of TRPV-1, 5HT-1A, and CB1, with emerging therapeutic relevance in the management of osteoarthritis and chronic pain. Conclusions: Although clinical and preclinical research show promising results, clinical evidence is limited, and more studies should be performed in the future with isolated CBD.

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.

Progress and trends of research on mineral elements for depression

Objective

To explore the research progress and trends on mineral elements and depression.

Methods

After querying the MeSH database and referring to the search rules, the search terms were selected and optimized to obtain the target literature collection. We analyzed the general characteristics of the literature, conducted network clustering and co-occurrence analysis, and carried out a narrative review of crucial literature.

Results

Bipolar disorder was a dominant topic in the retrieved literature, which saw a significant increase in 2010 and 2019-2020. Most studies focused on mineral elements, including lithium, calcium, magnesium, zinc, and copper. The majority of journals and disciplines were in the fields of psychiatry, neuropsychology, neuropharmacology, nutrition, medical informatics, chemistry, and public health. The United States had the highest proportion in terms of paper sources, most-cited articles, high-frequency citations, frontier citations, and high centrality citation. Regarding the influence of academic institutions, the top five were King's College London, the Chinese Academy of Sciences, University of Barcelona, INSERM, and Heidelberg University. Frontier keywords included bipolar disorder, drinking water, (neuro)inflammation, gut microbiota, and systematic analysis. Research on lithium response, magnesium supplementation, and treatment-resistant unipolar depression increased significantly after 2013.

Conclusion

Global adverse events may have indirectly driven the progress in related research. Although the literature from the United States represents an absolute majority, its influence on academic institutions is relatively weaker. Multiple pieces of evidence support the efficacy of lithium in treating bipolar disorder (BD). A series of key discoveries have led to a paradigm shift in research, leading to increasingly detailed studies on the role of magnesium, calcium, zinc, and copper in the treatment of depression. Most studies on mineral elements remain diverse and inconclusive. The potential toxicity and side effects of some elements warrant careful attention.

Therapeutic potential of cannabidiol in depression

Major depressive disorder (MDD) is a widespread and debilitating condition affecting a significant portion of the global population. Traditional treatment for MDD has primarily involved drugs that increase brain monoamines by inhibiting their uptake or metabolism, which is the basis for the monoaminergic hypothesis of depression. However, these treatments are only partially effective, with many patients experiencing delayed responses, residual symptoms, or complete non-response, rendering the current view of the hypothesis as reductionist. Cannabidiol (CBD) has shown promising results in preclinical models and human studies. Its mechanism is not well-understood, but may involve monoamine and endocannabinoid signaling, control of neuroinflammation and enhanced neuroplasticity. This chapter will explore CBD's effects in preclinical and clinical studies, its molecular mechanisms, and its potential as a treatment for MDD.

Network analysis of monoamines involved in anxiety-like behavior in a rat model of osteoarthritis

BACKGROUND

Chronic pain is a major health problem that affects a significant number of patients, resulting in personal suffering and substantial health care costs. One of the most commonly reported causal conditions is osteoarthritis (OA). In addition to sensory symptoms, chronic pain shares an inherent overlap with mood or anxiety disorders. The involvement of the frontal cortex, striatum and nucleus accumbens, in the affective processing of pain is still poorly understood.

METHODS

Male Wistar rats were divided into two groups: MIA (monoiodoacetate injected into the knee-model of OA) and sham (NaCl). Behavioral tests assessing pain, anxiety, and depressive behavior were performed at week 1, 3, 4, 6, 8, and 10. Neurochemical assays were conducted at weeks 3, 6, and 10 post-MIA injection, followed by the neurotransmitters and their metabolites correlation matrix and network analysis.

RESULTS

OA animals developed rapid pain phenotype, whereas anxiety-like behavior accompanied the development of a pain phenotype from 6 week post-MIA injection. We did not detect any depressive-like behavior. Instead, immobility time measured in the forced swimming test transiently decreased at 3 weeks post-MIA in the OA group. We detected changes in noradrenaline and serotonin levels in analyzed structures at distinct time points. Network analysis revealed noradrenaline and serotonin neurotransmission changes in the nucleus accumbens, confirming it to be the key structure affected by chronic pain.

CONCLUSION

Animals with chronic pain exhibit symptoms of anxiety-like behavior and we identified underlying neurochemical changes using network analysis.

Cannabidiol and brain function: current knowledge and future perspectives

Cannabidiol (CBD) is a naturally occurring non-psychoactive cannabinoid found in Cannabis sativa, commonly known as cannabis or hemp. Although currently available CBD products do not meet the safety standards of most food safety authorities to be approved as a dietary supplement or food additive, CBD has been gaining widespread attention in recent years due to its various potential health benefits. While primarily known for its therapeutic effects in managing epileptic seizures, psychosis, anxiety, (neuropathic) pain, and inflammation, CBD's influence on brain function has also piqued the interest of researchers and individuals seeking to enhance cognitive performance. The primary objective of this review is to gather, synthesize, and consolidate scientifically proven evidence on the impact of CBD on brain function and its therapeutic significance in treating neurological and mental disorders. First, basic background information on CBD, including its biomolecular properties and mechanisms of action is presented. Next, evidence for CBD effects in the human brain is provided followed by a discussion on the potential implications of CBD as a neurotherapeutic agent. The potential effectiveness of CBD in reducing chronic pain is considered but also in reducing the symptoms of various brain disorders such as epilepsy, Alzheimer's, Huntington's and Parkinson's disease. Additionally, the implications of using CBD to manage psychiatric conditions such as psychosis, anxiety and fear, depression, and substance use disorders are explored. An overview of the beneficial effects of CBD on aspects of human behavior, such as sleep, motor control, cognition and memory, is then provided. As CBD products remain largely unregulated, it is crucial to address the ethical concerns associated with their use, including product quality, consistency, and safety. Therefore, this review discusses the need for responsible research and regulation of CBD to ensure its safety and efficacy as a therapeutic agent for brain disorders or to stimulate behavioral and cognitive abilities of healthy individuals.

An Overview of Cannabidiol

Cannabidiol (CBD) is one of the most interesting constituents of cannabis, garnering significant attention in the medical community in recent years due to its proven benefit for reducing refractory seizures in pediatric patients. Recent legislative changes in the United States have made CBD readily available to the general public, with up to 14% of adults in the United States having tried it in 2019. CBD is used to manage a myriad of symptoms, including anxiety, pain, and sleep disturbances, although rigorous evidence for these indications is lacking. A significant advantage of CBD over the other more well-known cannabinoid delta-9-tetrahydroncannabinol (THC) is that CBD does not produce a "high." As patients increasingly self-report its use to manage their medical conditions, and as the opioid epidemic continues to drive the quest for alternative pain management approaches, the aims of this narrative review are to provide a broad overview of the discovery, pharmacology, and molecular targets of CBD, its purported and approved neurologic indications, evidence for its analgesic potential, regulatory implications for patients and providers, and future research needs.

IUPHAR review- Preclinical models of neuropathic pain: Evaluating multifunctional properties of natural cannabinoid receptors ligands

Neuropathic pain remains prevalent and challenging to manage and is often comorbid with depression and anxiety. The new approach that simultaneously targets neuropathic pain and the associated comorbidities, such as depression and anxiety, is timely and critical, given the high prevalence and severity of neuropathic pain and the lack of effective analgesics. In this review, we focus on the animal models of neuropathic pain that researchers have used to investigate the analgesic effects of cannabidiol (CBD) and Beta-Caryophyllene (BCP) individually and in combination while addressing the impact of these compounds on the major comorbidity (e.g., depression, anxiety) associated with neuropathic pain. We also addressed the potential targets/mechanisms by which CBD and BCP produce analgesic effects in neuropathic pain models. The preclinical studies examined in this review support CBD and BCP individually and combined as potential alternative analgesics for neuropathic pain while showing beneficial effects on depression and anxiety.

Cortical Neurostimulation and N-Methyl-D-Aspartate Glutamatergic Receptor Activation in the Dysgranular Layer of the Posterior Insular Cortex Modulate Chronic Neuropathic Pain

BACKGROUND AND AIMS

The dysgranula parts of the posterior insular cortex (PIC) stimulation (PICS) has been investigated as a new putative cortical target for nonpharmacologic therapies in patients with chronic and neuropathic pain (NP). This work investigates the neural bases of insula neurostimulation-induced antinociception and glutamatergic neurochemical mechanisms recruited by the PICS in animals with neuropathy.

MATERIALS AND METHODS

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"). Either the Cascade Blue 3000 MW lysine-fixable dextran (CBD) or the biotinylated dextran amine 3000 MW (BDA) neural tract tracer was microinjected into the PIC. The electrical PICS was performed at a low frequency (20 μA, 100 Hz) for 15 seconds by a deep brain stimulation device. PIC N-methyl-D-aspartate (NMDA) receptors (NMDAR) blockade with the selective antagonist LY235959 (at 2, 4, and 8 nmol/200 nL) followed by PICS was investigated in rats with CCI.

RESULTS

PIC sends projections to the caudal pontine reticular nucleus, alpha part of the parvicellular reticular nucleus, dorsomedial tegmental area, and secondary somatosensory cortex (S2). PICS decreased both mechanical and cold allodynia in rats with chronic NP. Blockade of NMDAR in the PIC with LY235959 at 8 nmol attenuated PICS-produced antinociception.

CONCLUSION

Neuroanatomic projections from the PIC to pontine reticular nuclei and S2 may contribute to chronic NP signaling. PICS attenuates the chronic NP, and the NMDA glutamatergic system in the PIC may be involved in PICS-induced antinociception in rodents with NP conditions.

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.

Functional Dimerization of Serotonin Receptors: Role in Health and Depressive Disorders

Understanding the neurobiological underpinnings of depressive disorder constitutes a pressing challenge in the fields of psychiatry and neurobiology. Depression represents one of the most prevalent forms of mental and behavioral disorders globally. Alterations in dimerization capacity can influence the functional characteristics of serotonin receptors and may constitute a contributing factor to the onset of depressive disorders. The objective of this review is to consolidate the current understanding of interactions within the 5-HT receptor family and between 5-HT receptors and members of other receptor families. Furthermore, it aims to elucidate the role of such complexes in depressive disorders and delineate the mechanisms through which antidepressants exert their effects.

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.

Systemic Chronic Treatment with Cannabidiol in Carioca High- and Low-Conditioned Freezing Rats in the Neuropathic Pain Model: Evaluation of Pain Sensitivity

Studies have shown high comorbidity of anxiety disorder and chronic pain; generalized anxiety disorder (GAD) and neuropathic pain are among these pathologies. Cannabidiol (CBD) has been considered a promising treatment for these conditions. This study investigated whether chronic systemic treatment with CBD alters pain in high- (CHF) and low-freezing (CLF) Carioca rats (GAD model) and control rats (CTL) submitted to chronic neuropathic pain. The rats were evaluated in the sensory aspects (von Frey, acetone, and hot plate tests) before the chronic constriction injury of the ischiatic nerve (CCI) or not (SHAM) and on days 13 and 23 after surgery. Chronic treatment with CBD (5 mg/kg daily) was used for ten days, starting the 14th day after surgery. The open field test on the 22nd also evaluated locomotion and anxiety-like behavior. CBD treatment had an anti-allodynic effect on the mechanical and thermal threshold in all lineages; however, these effects were lower in the CHF and CLF lineages. Considering emotional evaluation, we observed an anxiolytic effect in CTL+CCI and CHF+CCI after CBD treatment and increased mobility in CLF+SHAM rats. These results suggest that the CBD mechanical anti-allodynic and emotional effects can depend on anxiety level.

Changes in mRNA and miRNA expression in the prelimbic cortex related to depression-like syndrome induced by chronic social defeat stress in mice

Major depressive disorder is a complex psychiatric disorder with a high prevalence rate worldwide. Previous studies have demonstrated the involvement of the prelimbic cortex (PL) in mediating depressive-like behavior, however, the exact molecular mechanism taking place in the PL remains unclear. In the present study, we conducted high-throughput sequencing of mRNAs and miRNAs in PL tissue harvested from chronic social defeat stress (CSDS) susceptible male mice. We identified 59 differentially expressed mRNAs and 6 differentially expressed miRNAs, in which 40 mRNAs and 3 miRNAs were up-regulated, while 19 mRNAs and 3 miRNAs were down-regulated. Integrated analysis of miRNA-mRNA networks suggested that GPR35 signaling might be involved in CSDS-induced depressive-like behaviors. RT-PCR and western blot assays validated that Abra, Sell and GPR35 were up-regulated. Functionally, inhibition of GPR35 in the PL ameliorated CSDS-induced depressive-like behaviors. Thus, the present study provided a global view of mRNA and miRNA profiles in the PL of male stress susceptible mice, and suggested that GPR35 signaling was associated with CSDS-induced depressive-like behaviors. These results may be valuable for further investigations of the molecular regulatory mechanisms in stress-induced depression.

Cannabidiol, a Regulator of Intracellular Calcium and Calpain

Cannabidiol (CBD) is one of the most abundant components of Cannabis and has long been used in Cannabis-based preparations. Recently, CBD has become a promising pharmacological agent because of its beneficial properties in the pathophysiology of several diseases. Although CBD is a kind of cannabinoid and acts on cannabinoid receptors (CB1 and CB2), molecular targets involved in diverse therapeutic properties of CBD have not been identified because CBD also interacts with other molecular targets. Considering that CBD alters the intracellular calcium level by which calpain activity is controlled, and both CBD and calpain are associated with various diseases related to calcium signaling, including neurological disorders, this review provides an overview of calpain and calcium signaling as possible molecular targets of CBD. As calpain is known to play an important role in the pathophysiology of neurological disease, a deeper understanding of its relationship with CBD will be meaningful. To understand the role of CBD as a calpain regulator, in silico structural analysis on the binding mode of CBD with calpain was performed.

Hippocampal CB1 receptor mediates antidepressant-like effect of synthetic cannabinoid-HU210 in acute despair reaction model in mice

Growing evidence suggests that stress may contribute to the pathophysiology of depression. The alleviation of depressive symptoms is one of the most attractive medical applications of cannabis. Here, we investigated the antidepressant-like actions of synthetic cannabinoid-HU210 in acute despair response and explored the possible underlying mechanisms. Acute stress, induced by forced-swimming, induced depression-like behavior in the sucrose preference test (SPT). HU-210 (50 μg/kg) displayed anti-depressant like effect in the forced swim test in naïve mice and decreased depression-like behavior in the SPT, induced by forced swim stress. Pretreatment with AM251, an inhibitor of CB1R or inhibition of long-term depression (LTD) at hippocampal CA3-CA1 synapses by Tat-GluR2 attenuated the antidepressant like action of HU-210. These results indicate that HU210 produces antidepressant-like effects in acute stress and its underlying mechanism may be related to CB1R activation and hence hippocampal LTD production invivo. Synthetic cannabis or cannabis-related drugs may be used as an early intervention after acute stress exposure to prevent or at least reduce depression-like behaviors.

The Therapeutic Potential of the Endocannabinoid System in Age-Related Diseases

The endocannabinoid system (ECS) dynamically regulates many aspects of mammalian physiology. ECS has gained substantial interest since growing evidence suggests that it also plays a major role in several pathophysiological conditions due to its ability to modulate various underlying mechanisms. Furthermore, cannabinoids, as components of the cannabinoid system (CS), have proven beneficial effects such as anti-inflammatory, immunomodulatory, neuromodulatory, antioxidative, and cardioprotective effects. In this comprehensive review, we aimed to describe the complex interaction between CS and most common age-related diseases such as neuro-degenerative, oncological, skeletal, and cardiovascular disorders, together with the potential of various cannabinoids to ameliorate the progression of these disorders. Since chronic inflammation is postulated as the pillar of all the above-mentioned medical conditions, we also discuss in this paper the potential of CS to ameliorate aging-associated immune system dysregulation.

Cannabidiol Reduces Short- and Long-Term High Glutamate Release after Severe Traumatic Brain Injury and Improves Functional Recovery

This study aimed to determine if orally administered cannabidiol (CBD) lessens the cortical over-release of glutamate induced by a severe traumatic brain injury (TBI) and facilitates functional recovery. The short-term experiment focused on identifying the optimal oral pretreatment of CBD. Male Wistar rats were pretreated with oral administration of CBD (50, 100, or 200 mg/kg) daily for 7 days. Then, extracellular glutamate concentration was estimated by cortical microdialysis before and immediately after a severe TBI. The long-term experiment focused on evaluating the effect of the optimal treatment of CBD (pre- vs. pre- and post-TBI) 30 days after trauma. Sensorimotor function, body weight, and mortality rate were evaluated. In the short term, TBI induced a high release of glutamate (738% ± 173%; p < 0.001 vs. basal). Oral pretreatment with CBD at all doses tested reduced glutamate concentration but with higher potency at when animals received 100 mg/kg (222 ± 33%, p < 0.01 vs. TBI), an effect associated with a lower mortality rate (22%, p < 0.001 vs. TBI). In the long-term experiment, the TBI group showed a high glutamate concentration (149% p < 0.01 vs. SHAM). In contrast, animals receiving the optimal treatment of CBD (pre- and pre/post-TBI) showed glutamate concentrations like the SHAM group (p > 0.05). This effect was associated with high sensorimotor function improvement. CBD pretreatment, but not pre-/post-treatment, induced a higher body weight gain (39% ± 2.7%, p < 0.01 vs. TBI) and lower mortality rate (22%, p < 0.01 vs. TBI). These results support that orally administered CBD reduces short- and long-term TBI-induced excitotoxicity and facilitated functional recovery. Indeed, pretreatment with CBD was sufficient to lessen the adverse sequelae of TBI.

Modulation of Endocannabinoid System Components in Depression: Pre-Clinical and Clinical Evidence

Depression is characterized by continuous low mood and loss of interest or pleasure in enjoyable activities. First-line medications for mood disorders mostly target the monoaminergic system; however, many patients do not find relief with these medications, and those who do suffer from negative side effects and a discouragingly low rate of remission. Studies suggest that the endocannabinoid system (ECS) may be involved in the etiology of depression and that targeting the ECS has the potential to alleviate depression. ECS components (such as receptors, endocannabinoid ligands, and degrading enzymes) are key neuromodulators in motivation and cognition as well as in the regulation of stress and emotions. Studies in depressed patients and in animal models for depression have reported deficits in ECS components, which is motivating researchers to identify potential diagnostic and therapeutic biomarkers within the ECS. By understanding the effects of cannabinoids on ECS components in depression, we enhance our understanding of which brain targets they hit, what biological processes they alter, and eventually how to use this information to design better therapeutic options. In this article, we discuss the literature on the effects of cannabinoids on ECS components of specific depression-like behaviors and phenotypes in rodents and then describe the findings in depressed patients. A better understanding of the effects of cannabinoids on ECS components in depression may direct future research efforts to enhance diagnosis and treatment.

Cannabinoid CB1 Receptor Involvement in the Actions of CBD on Anxiety and Coping Behaviors in Mice

The anxiolytic and antidepressant properties of cannabidiol (CBD) have been evaluated in several studies. However, the molecular mechanisms involved in these actions remain unclear. A total of 130 male mice were used. CBD’s ability to modulate emotional disturbances (anxiety and depressive-like behaviors) was evaluated at different doses in wild-type (CD1; 10, 20 and 30 mg/kg; i.p.) and knockout (CB1KO, CB2KO; GPR55KO; 20 mg/kg) mice. Moreover, CBD effects (20 mg/kg; i.p.) were evaluated in mice previously treated with the CB1r-antagonist SR141716A (2mg/kg; i.p.). Relative gene expression analyses of Cnr1 and Cnr2, Gpr55 and GABA(A)α2 and γ2 receptor subunits were performed in the amygdala (AMY) and hippocampus (HIPP) of CD1 mice. CBD (10 and 20 mg/kg) showed anxiolytic and antidepressant actions in CD1 mice, being more effective at 20 mg/kg. Its administration did not induce anxiolytic actions in CB1KO mice, contrary to CB2KO and GPR55KO. In all of them, the lack of cannabinoid receptors did not modify the antidepressant activity of CBD. Interestingly, the administration of the CB1r antagonist SR141716A blocked the anxiolytic-like activity of CBD. Real-time PCR studies revealed a significant reduction in Cnr1 and GABA(A)α2 and γ2 gene expression in the HIPP and AMY of CD1 mice treated with CBD. Opposite changes were observed in the Cnr2. Indeed, Gpr55 was increased in the AMY and reduced in the HIPP. CB1r appears to play a relevant role in modulating the anxiolytic actions of CBD. Moreover, this study revealed that CBD also modified the gene expression of GABA(A) subunits α2 and γ2 and CB1r, CB2r and GPR55, in a dose- and brain-region-dependent manner, supporting a multimodal mechanism of action for CBD.

Physical, Emotional, and Social Pain During COVID-19 Pandemic-Related Social Isolation

The socio-emotional condition during the COVID-19 pandemic subsidises the (re)modulation of interactive neural circuits underlying risk assessment behaviour at the physical, emotional, and social levels. Experiences of social isolation, exclusion, or affective loss are generally considered some of the most “painful” things that people endure. The threats of social disconnection are processed by some of the same neural structures that process basic threats to survival. The lack of social connection can be “painful” due to an overlap in the neural circuitry responsible for both physical and emotional pain related to feelings of social rejection. Indeed, many of us go to great lengths to avoid situations that may engender these experiences. Accordingly, this work focuses on pandemic times; the somatisation mentioned above seeks the interconnection and/or interdependence between neural systems related to emotional and cognitive processes such that a person involved in an aversive social environment becomes aware of himself, others, and the threatening situation experienced and takes steps to avoid daily psychological and neuropsychiatric effects. Social distancing during isolation evokes the formation of social distress, increasing the intensity of learned fear that people acquire, consequently enhancing emotional and social pain.

Major Phytocannabinoids and Their Related Compounds: Should We Only Search for Drugs That Act on Cannabinoid Receptors?

The most important discoveries in pharmacology, such as certain classes of analgesics or chemotherapeutics, started from natural extracts which have been found to have effects in traditional medicine. Cannabis, traditionally used in Asia for the treatment of pain, nausea, spasms, sleep, depression, and low appetite, is still a good candidate for the development of new compounds. If initially all attention was directed to the endocannabinoid system, recent studies suggest that many of the clinically proven effects are based on an intrinsic chain of mechanisms that do not necessarily involve only cannabinoid receptors. Recent research has shown that major phytocannabinoids and their derivatives also interact with non-cannabinoid receptors such as vanilloid receptor 1, transient receptor ankyrin 1 potential, peroxisome proliferator-activated receptor-gamma or glitazone receptor, G55 protein-coupled receptor, and nuclear receptor, producing pharmacological effects in diseases such as Alzheimer's, epilepsy, depression, neuropathic pain, cancer, and diabetes. Nonetheless, further studies are needed to elucidate the precise mechanisms of these compounds. Structure modulation of phytocannabinoids, in order to improve pharmacological effects, should not be limited to the exploration of cannabinoid receptors, and it should target other courses of action discovered through recent research.

The primary motor cortex electrical and chemical stimulation attenuates the chronic neuropathic pain by activation of the periaqueductal grey matter: The role of NMDA receptors

BACKGROUND

Motor cortex stimulation (MCS) is proper as a non-pharmacological therapy for patients with chronic and neuropathic pain (NP).

AIMS

This work aims to investigate if the MCS in the primary motor cortex (M₁) produces analgesia and how the MCS could interfere in the MCS-induced analgesia. Also, to elucidate if the persistent activation of N-methyl-d-aspartic acid receptor (NMDAr) in the periaqueductal grey matter (PAG) can contribute to central sensitisation of the NP.

METHODS

Male Wistar rats were submitted to the von Frey test to evaluate the mechanical allodynia after 21 days of chronic constriction injury (CCI) of the sciatic nerve. The MCS was performed with low-frequency (20 μA, 100 Hz) currents during 15 s by a deep brain stimulation (DBS) device. Moreover, the effect of M₁-treatment with an NMDAr agonist (at 2, 4, and 8 nmol) was investigated in CCI rats. The PAG dorsomedial column (dmPAG) was pretreated with the NMDAr antagonist LY 235959 (at 8 nmol), followed by MCS.

RESULTS

The MCS decreased the mechanical allodynia in rats with chronic NP. The M₁-treatment with an NMDA agonist at 2 and 8 nmol reduced the mechanical allodynia in CCI rats. In addition, dmPAG-pretreatment with LY 235959 at 8 nmol attenuated the mechanical allodynia evoked by MCS.

CONCLUSION

The M₁ cortex glutamatergic system is involved in the modulation of chronic NP. The analgesic effect of MCS may depend on glutamate signaling recruitting NMDAr located on PAG neurons in rodents with chronic NP.