Cholecystokinin exerts an effect via the endocannabinoid system to inhibit GABAergic transmission in midbrain periaqueductal gray

Effects of perioperative dextrose infusion on preventing postoperative nausea and vomiting in patients undergoing laparoscopic surgery: a meta-analysis of randomized controlled trials

Objective

The aim of this study was to systematically examine the literature and assess the effects of perioperative dextrose infusion on the prevention of postoperative nausea and vomiting (PONV) in patients following laparoscopic surgery under general anesthesia.

Methods

We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs). Studies were eligible for inclusion if they evaluated the prevention of PONV with perioperative intravenous dextrose. Studies listed in PUBMED, Web of Science, and EMBASE databases published up to December 2020 were identified. Data were extracted and analyzed independently using a fixed-effects or random-effects model according to the heterogeneity.

Results

Six RCTs involving 526 patients were included. Our results showed that perioperative dextrose infusion not only reduced the incidence of PONV (risk ratio [RR] = 0.61, 95% confidence interval [CI]: 0.39–0.95; I² = 59%) but also decreased the requirement for antiemetics compared with the control (RR = 0.53, 95% CI: 0.42–0.66; I² = 32%). Furthermore, perioperative glucose infusion did not increase blood glucose levels compared with the control (mean difference [95% CI] = 74.55 [−20.64 to 169.73] mg/dL; I² = 100%).

Conclusion

Our study reveals that perioperative dextrose infusion may reduce the risk of PONV after laparoscopic surgery. However, additional population-based RCTs are needed to confirm this finding.

Mechanisms of endocannabinoid control of synaptic plasticity

The endogenous cannabinoid transmitter system regulates synaptic transmission throughout the nervous system. Unlike conventional transmitters, specific stimuli induce synthesis of endocannabinoids (eCBs) in the postsynaptic neuron, and these travel backwards to modulate presynaptic inputs. In doing so, eCBs can induce short-term changes in synaptic strength and longer-term plasticity. While this eCB regulation is near ubiquitous, it displays major regional and synapse specific variations with different synapse specific forms of short-versus long-term plasticity throughout the brain. These differences are due to the plethora of pre- and postsynaptic mechanisms which have been implicated in eCB signalling, the intricacies of which are only just being realised. In this review, we shall describe the current understanding and highlight new advances in this area, with a focus on the retrograde action of eCBs at CB1 receptors (CB₁Rs).

Evidence that increased cholecystokinin (CCK) in the periaqueductal gray (PAG) facilitates changes in Resident-Intruder social interactions triggered by peripheral nerve injury

Individual differences in the effects of a chronic neuropathic injury on social behaviours characterize both the human experience and pre-clinical animal models. The impacts of these changes to the well-being of the individual are often underappreciated. Earlier work from our laboratory using GeneChip® microarrays identified increased cholecystokinin (CCK) gene expression in the periaqueductal gray (PAG) of rats that showed persistent changes in social interactions during a Resident-Intruder encounter following sciatic nerve chronic constriction injury (CCI). In this study, we confirmed these gene regulation patterns using RT-PCR and identified the anatomical location of the CCK-mRNA as well as the translated CCK peptides in the midbrains of rats with a CCI. We found that rats with persistent CCI-induced changes in social behaviours had increased CCK-mRNA in neurons of the ventrolateral PAG and dorsal raphe nuclei, as well as increased CCK-8 peptide expression in terminal boutons located in the lateral and ventrolateral PAG. The functional significance of these changes was explored by microinjecting small volumes of CCK-8 into the PAG of uninjured rats and observing their Resident-Intruder social interactions. Disturbances to social interactions identical to those observed in CCI rats were evoked when injection sites were located in the rostral lateral and ventrolateral PAG. We suggest that CCI-induced changes in CCK expression in these PAG regions contributes to the disruptions to social behaviours experienced by a subset of individuals with neuropathic injury.

Cholecystokinin-Mediated Neuromodulation of Anxiety and Schizophrenia: A "Dimmer-Switch" Hypothesis

Cholecystokinin (CCK), the most abundant brain neuropeptide, is involved in relevant behavioral functions like memory, cognition, and reward through its interactions with the opioid and dopaminergic systems in the limbic system. CCK excites neurons by binding two receptors, CCK1 and CCK2, expressed at low and high levels in the brain, respectively. Historically, CCK2 receptors have been related to the induction of panic attacks in humans. Disturbances in brain CCK expression also underlie the physiopathology of schizophrenia, which is attributed to the modulation by CCK1 receptors of the dopamine flux in the basal striatum. Despite this evidence, neither CCK2 receptor antagonists ameliorate human anxiety nor CCK agonists have consistently shown neuroleptic effects in clinical trials. A neglected aspect of the function of brain CCK is its neuromodulatory role in mental disorders. Interestingly, CCK is expressed in pivotal inhibitory interneurons that sculpt cortical dynamics and the flux of nerve impulses across corticolimbic areas and the excitatory projections to mesolimbic pathways. At the basal striatum, CCK modulates the excitability of glutamate, the release of inhibitory GABA, and the discharge of dopamine. Here we focus on how CCK may reduce rather than trigger anxiety by regulating its cognitive component. Adequate levels of CCK release in the basal striatum may control the interplay between cognition and reward circuitry, which is critical in schizophrenia. Hence, it is proposed that disturbances in the excitatory/ inhibitory interplay modulated by CCK may contribute to the imbalanced interaction between corticolimbic and mesolimbic neural activity found in anxiety and schizophrenia.

Persistent Activity of Metabotropic Glutamate Receptor 5 in the Periaqueductal Gray Constrains Emergence of Chronic Neuropathic Pain

Pain sensation is powerfully modulated by signal processing in the brain, and pain becomes chronic with the dysfunction of the pain modulatory system; however, the underlying mechanisms are unclear. We found that the metabotropic glutamate receptor 5 (mGluR5) in the periaqueductal gray (PAG), the key area of endogenous pain modulation, is persistently active in normal conditions to maintain an appropriate sensory perception. In the neuropathic pain condition, Homer1a, an activity-dependent immediate early gene product, disrupted the persistent mGluR5 activity resulting in chronic pain. Remarkably a single-time blockage of the mGluR5 resulted in chronic neuropathic pain-like symptoms even in the absence of nerve injury. The decline of mGluR5 activity induced the pain modulatory dysfunction with a profound reduction of excitability of PAG neurons. These findings uncover the role of the persistent mGluR5 activity in vivo and provide new insight into how pain becomes chronic with the maladaptive coping of the PAG to pain sensation.

Whey protein supplementation reducing fasting levels of anandamide and 2-AG without weight loss in pre-menopausal women with obesity on a weight-loss diet

Background

Despite the importance of dairy proteins in modifying of metabolic abnormalities, no attention has been given to their effects on endocannabinoids.

Methods

A total number of 60 obese women were recruited in a 2-month randomized clinical trial. Following random allocation, they were assigned to one of the two groups: control (n = 30) and intervention (n = 30). Then, all the subjects followed a hypocaloric diet of 800 kcal below estimated energy needs. The intervention group received isocaloric weight-loss diet and whey protein powders (30 g/day). Baseline and 2-month fasting anthropometric, blood glucose, serum insulin, insulin resistance, lipid profile, AEA, and 2-AG were measured.

Results

The study groups were homogenous in terms of baseline characteristics (p > 0.05) except for MUFA intake (p = 0.021). There were no significant differences in energy and macronutrient intakes in the intervention group compared to the control group at the end of the study (p > 0.05). The results of the ANCOVA did not show significant reductions in body weight and BMI of the intervention group compared to the control group (p > 0.05); however, WC, body fat, FBS, AEA, 2-AG, total cholesterol, and triglyceride decreased and HDL-c significantly increased in the intervention group compared to the control group (p < 0.05).

Conclusions

In this study, the effects of simultaneous weight-loss diet and whey protein supplementation on the reduction of endocannabinoids were determined.

Trial registration

Iranian Registry of Clinical Trials IRCT2017021410181N8. Registered on March 2017.

Cannabinoids in the descending pain modulatory circuit: Role in inflammation

The legalization of cannabis in some states has intensified interest in the potential for cannabis and its constituents to lead to novel therapeutics for pain. Our understanding of the cellular mechanisms underlying cannabinoid actions in the brain have lagged behind opioids; however, the current opioid epidemic has also increased attention on the use of cannabinoids as alternatives to opioids for pain, especially chronic pain that requires long-term use. Endogenous cannabinoids are lipid signaling molecules that have complex roles in modulating neuronal function throughout the brain. In this review, we discuss cannabinoid functions in the descending pain modulatory pathway, a brain circuit that integrates cognitive and emotional processing of pain to modulate incoming sensory inputs. In addition, we highlight areas where further studies are necessary to understand cannabinoid regulation of descending pain modulation.

Effects of THC/CBD oromucosal spray on spasticity-related symptoms in people with multiple sclerosis: results from a retrospective multicenter study

INTRODUCTION

The approval of 9-δ-tetrahydocannabinol (THC)+cannabidiol (CBD) oromucosal spray (Sativex®) in Italy as an add-on medication for the management of moderate to severe spasticity in multiple sclerosis (MS) has provided a new opportunity for MS patients with drug-resistant spasticity. We aimed to investigate the improvement of MS spasticity-related symptoms in a large cohort of patients with moderate to severe spasticity in daily clinical practice.

MATERIALS AND METHODS

MS patients with drug-resistant spasticity were recruited from 30 Italian MS centers. All patients were eligible for THC:CBD treatment according to the approved label: ≥ 18 years of age, at least moderate spasticity (MS spasticity numerical rating scale [NRS] score ≥ 4) and not responding to the common antispastic drugs. Patients were evaluated at baseline (T0) and after 4 weeks of treatment (T1) with the spasticity NRS scale and were also asked about meaningful improvements in 6 key spasticity-related symptoms.

RESULTS

Out of 1615 enrolled patients, 1432 reached the end of the first month trial period (T1). Of these, 1010 patients (70.5%) reached a ≥ 20% NRS score reduction compared with baseline (initial responders; IR). We found that 627 (43.8% of 1432) patients showed an improvement in at least one spasticity-related symptom (SRSr group), 543 (86.6%) of them belonging to the IR group and 84 (13.4%) to the spasticity NRS non-responders group.

CONCLUSION

Our study confirmed that the therapeutic benefit of cannabinoids may extend beyond spasticity, improving spasticity-related symptoms even in non-NRS responder patients.

Intracerebroventricular administration of sulphated cholecystokinin octapeptide induces anxiety-like behaviour in goldfish

Sulphated cholecystokinin octapeptide (CCK-8s) is involved in feeding regulation as an anorexigenic neuropeptide in vertebrates. In rodents, i.c.v. administration of CCK-8s has been shown to affect not only feeding behaviour, but also psychomotor activity. However, there is still no information available concerning the psychophysiological effects of CCK-8s in goldfish. Therefore, in the present study, we examined the effect of synthetic goldfish (gf) CCK-8s on psychomotor activity in this species. Intracerebroventricular administration of gfCCK-8s at 0.1, 0.5 and 2.5 pmol g^-1 body weight (BW) did not affect swimming distance (locomotor activity). Because goldfish prefer the lower to the upper area of a tank, we used this as a preference test (upper/lower test) to assess anxiety-like behaviour. Intracerebroventricular administration of gfCCK-8s at 2.5 pmol g^-1 BW shortened the time spent in the upper area. The action of gfCCK-8s mimicked that of FG-7142 (the central-type benzodiazepine receptor inverse agonist, an anxiogenic agent) at 5 and 10 pmol g^-1 BW. The anxiogenic-like effect of gfCCK-8s was abolished by treatment with the CCK receptor antagonist proglumide at 50 pmol g^-1 BW. We also investigated the localisation of CCK/gastrin-like immunoreactivity in the goldfish brain. CCK/gastrin-like immunoreactivity was observed in the anxiety-related regions (the nucleus habenularis and the interpeduncular nucleus). These data indicate that gfCCK-8s potently affects psychomotor activity in goldfish, and exerts an anxiogenic-like effect via the CCK receptor-signalling pathway.

Differential effects of cholecystokinin (CCK-8) microinjection into the ventrolateral and dorsolateral periaqueductal gray on anxiety models in Wistar rats

Cholecystokinin (CCK) is one of the main neurohormone peptide systems in the brain, and a major anxiogenic mediator. The periaqueductal gray (PAG) is a key midbrain structure for defensive behaviors, which could include anxiety, fear, or even panic. The CCK system has wide distribution in the PAG, where the dorsolateral region (DL) participates in active defensive behavior and the ventrolateral region (VL) in passive defensive behavior. The aim of this study was to assess the effect of CCK-8 microinjection into DL-PAG or VL-PAG on anxiety-like behavior through two tests: elevated plus maze (EPM) and defensive burying behavior (DBB). CCK-8 (0.5 and 1.0 μg/0.5 μL) presently microinjected into the DL-PAG produced an anxiogenic-like effect on the EPM evidenced by decreasing the time spent/number of entries in open arms compared to vehicle group. Additionally, the latency to burying decreased and burying time increased on the DBB test. Contrarily, CCK-8 microinjected into the VL-PAG resulted in greater open-arm time and more open-arm entries compared to the vehicle-microinjected group. The results on the DBB test confirmed an anxiolytic-like response of CCK-8 into the VL-PAG. In conclusion, CCK-8 microinjected into DL-PAG produced anxiety-like behavior on EPM, and for first time reported on DBB. Contrarily, CCK-8 microinjected into the VL-PAG reduced anxiety-like behavior also for first time reported using both behavioral models EPM and DBB.

Cholecystokinin Switches the Plasticity of GABA Synapses in the Dorsomedial Hypothalamus via Astrocytic ATP Release

Whether synapses in appetite-regulatory brain regions undergo long-term changes in strength in response to satiety peptides is poorly understood. Here we show that following bursts of afferent activity, the neuromodulator and satiety peptide cholecystokinin (CCK) shifts the plasticity of GABA synapses in the dorsomedial nucleus of the hypothalamus of male Sprague Dawley rats from long-term depression to long-term potentiation (LTP). This LTP requires the activation of both type 2 CCK receptors and group 5 metabotropic glutamate receptors, resulting in a rise in astrocytic intracellular calcium and subsequent ATP release. ATP then acts on presynaptic P2X receptors to trigger a prolonged increase in GABA release. Our observations demonstrate a novel form of CCK-mediated plasticity that requires astrocytic ATP release, and could serve as a mechanism for appetite regulation.SIGNIFICANCE STATEMENT Satiety peptides, like cholecystokinin, play an important role in the central regulation of appetite, but their effect on synaptic plasticity is not well understood. The current data provide novel evidence that cholecystokinin shifts the plasticity from long-term depression to long-term potentiation at GABA synapses in the rat dorsomedial nucleus of the hypothalamus. We also demonstrate that this plasticity requires the concerted action of cholecystokinin and glutamate on astrocytes, triggering the release of the gliotransmitter ATP, which subsequently increases GABA release from neighboring inhibitory terminals. This research reveals a novel neuropeptide-induced switch in the direction of synaptic plasticity that requires astrocytes, and could represent a new mechanism by which cholecystokinin regulates appetite.

Endocannabinoids in Body Weight Control

Maintenance of body weight is fundamental to maintain one's health and to promote longevity. Nevertheless, it appears that the global obesity epidemic is still constantly increasing. Endocannabinoids (eCBs) are lipid messengers that are involved in overall body weight control by interfering with manifold central and peripheral regulatory circuits that orchestrate energy homeostasis. Initially, blocking of eCB signaling by first generation cannabinoid type 1 receptor (CB1) inverse agonists such as rimonabant revealed body weight-reducing effects in laboratory animals and men. Unfortunately, rimonabant also induced severe psychiatric side effects. At this point, it became clear that future cannabinoid research has to decipher more precisely the underlying central and peripheral mechanisms behind eCB-driven control of feeding behavior and whole body energy metabolism. Here, we will summarize the most recent advances in understanding how central eCBs interfere with circuits in the brain that control food intake and energy expenditure. Next, we will focus on how peripheral eCBs affect food digestion, nutrient transformation and energy expenditure by interfering with signaling cascades in the gastrointestinal tract, liver, pancreas, fat depots and endocrine glands. To finally outline the safe future potential of cannabinoids as medicines, our overall goal is to address the molecular, cellular and pharmacological logic behind central and peripheral eCB-mediated body weight control, and to figure out how these precise mechanistic insights are currently transferred into the development of next generation cannabinoid medicines displaying clearly improved safety profiles, such as significantly reduced side effects.

The effects of CCK-8S on spatial memory and long-term potentiation at CA1 during induction of stress in rats

Objectives

Cholecystokinin (CCK) has been proposed as a mediator in stress. However, it is still not fully documented what are its effects. We aimed to evaluate the effects of systemic administration of CCK exactly before induction of stress on spatial memory and synaptic plasticity at CA1 in rats.

Materials and Methods

Male Wistar rats were divided into 4 groups: the control, the control-CCK, the stress and the stress-CCK. Restraint stress was induced 6 hr per day, for 24 days. Cholecystokinin sulfated octapeptide (CCK-8S) was injected (1.6 µg/kg, IP) before each session of stress induction. Spatial memory was evaluated by Morris water maze test. Long-term potentiation (LTP) in Schaffer collateral-CA1 synapses was assessed (by 100 Hz tetanization) in order to investigate synaptic plasticity.

Results

Stress impaired spatial memory significantly (P<0.01). CCK in the control rats improved memory (P<0.05), and prevented the impairments in the stress group. With respect to the control group, both fEPSP amplitude and slope were significantly (P<0.05) decreased in the stress group. However, there were no differences between responses of the control-CCK and Stress-CCK groups compared to the control group.

Conclusion

The present results suggest that high levels of CCK-8S during induction of stress can modulate the destructive effects of stress on hippocampal synaptic plasticity and memory. Therefore, the mediatory effects of CCK in stress are likely as compensatory responses.

Gut Microbiota and the Gut-Brain Axis: New Insights in the Pathophysiology of Metabolic Syndrome

OBJECTIVE

Emerging preclinical evidence has shown that the bidirectional signaling between the gastrointestinal (GI) tract and the brain, the so-called gut-brain axis, plays an important role in both host metabolism and behavior. In this review, we discuss the potential mechanisms of the brain-gut axis in relation to the pathophysiology of metabolic syndrome.

METHODS

A selective literature review was conducted to evaluate GI and brain interactions.

RESULTS

Evidence suggests reduced microbial diversity in obesity and metabolic dysregulation. However, findings of microbiota composition in obese individuals are inconsistent, and the investigation of causality between gut microbiota and energy homeostasis is complex because multiple variables contribute to the gut microbiota composition. The microbial metabolites short chain fatty acids are found to exert numerous physiologic effects, including energy homeostasis through the regulation of GI hormones such as cholecystokinin, glucagon-like peptide 1, peptide tyrosine-tyrosine, and leptin. Preclinical studies show that modifying rodents' microbiota through fecal transplantation results in alterations of these GI hormones and subsequently an altered metabolism and behavior. However, whether and to what extent preclinical findings translate to human metabolism is unclear.

CONCLUSIONS

One of the major limitations and challenges in this field of research is interindividual variability of the microbiome. Future research needs to combine recent insights gained into tracking the dynamics of the microbiome as well as the metabolic responses. Furthermore, advanced mapping of the human microbiome is required to investigate the metabolic implications of the gut-brain axis to develop targeted interventions for obesity and metabolic syndrome.

The unappreciated roles of the cholecystokinin receptor CCK(1) in brain functioning

The CCK(1) receptor is a G-protein-coupled receptor activated by the sulfated forms of cholecystokinin (CCK), a gastrin-like peptide released in the gastrointestinal tract and mammal brain. A substantial body of research supports the hypothesis that CCK(1)r stimulates gallbladder contraction and pancreatic secretion in the gut, as well as satiety in brain. However, this receptor may also fulfill relevant roles in behavior, thanks to its widespread distribution in the brain. The strategic location of CCK(1)r in mesolimbic structures and specific hypothalamic and brainstem nuclei lead to complex interactions with neurotransmitters like dopamine, serotonin, and glutamate, as well as hypothalamic hormones and neuropeptides. The activity of CCK(1)r maintains adequate levels of dopamine and regulates the activity of serotonin neurons of raphe nuclei, which makes CCK(1)r an interesting therapeutic target for the development of adjuvant treatments for schizophrenia, drug addiction, and mood disorders. Unexplored functions of CCK(1)r, like the transmission of interoceptive sensitivity in addition to the regulation of hypothalamic hormones and neurotransmitters affecting emotional states, well-being, and attachment behaviors, may open exciting roads of research. The absence of specific ligands for the CCK(1) receptor has complicated the study of its distribution in brain so that research about its impact on behavior has been published sporadically over the last 30 years. The present review reunites all this body of evidence in a comprehensive way to summarize our knowledge about the actual role of CCK in the neurobiology of mental illness.

The endocannabinoid system, a novel and key participant in acupuncture's multiple beneficial effects

Acupuncture and its modified forms have been used to treat multiple medical conditions, but whether the diverse effects of acupuncture are intrinsically linked at the cellular and molecular level and how they might be connected have yet to be determined. Recently, an emerging role for the endocannabinoid system (ECS) in the regulation of a variety of physiological/pathological conditions has been identified. Overlap between the biological and therapeutic effects induced by ECS activation and acupuncture has facilitated investigations into the participation of ECS in the acupuncture-induced beneficial effects, which have shed light on the idea that the ECS may be a primary mediator and regulatory factor of acupuncture's beneficial effects. This review seeks to provide a comprehensive summary of the existing literature concerning the role of endocannabinoid signaling in the various effects of acupuncture, and suggests a novel notion that acupuncture may restore homeostasis under different pathological conditions by regulating similar networks of signaling pathways, resulting in the activation of different reaction cascades in specific tissues in response to pathological insults.

The effect of intravenous dextrose administration for prevention of post-operative nausea and vomiting after laparoscopic cholecystectomy: A double-blind, randomised controlled trial

Background and Aims:

Post-operative nausea and vomiting (PONV) is a common and distressing complication after laparoscopic cholecystectomy (LC). The aim of this study was to evaluate the effect of intravenous (IV) dextrose administration for the prophylaxis of PONV after LC.

Methods:

In a double-blind, randomised controlled trial, a total of 150 female patients who were scheduled for elective LC were randomly assigned into two groups (A and B). Thirty minutes before induction of anaesthesia, patients received an infusion of 500 cc lactated Ringer's solution (Group A) and 5% dextrose in lactated Ringer's solution (Group B) and over a period of 30 min. All patients rated their nausea and vomiting intensity using the verbal rating scale immediately at post-anaesthesia care unit (PACU) arrival; 30, 60, 90 and 120 min after arriving at the PACU and 6, 12 and 24 h after surgery.

Results:

There was a statistically significant time trend and group effect along with significant differences in time/group interaction effect in both groups for nausea and vomiting scores (P < 0.05). A low negative correlation coefficient was found (r = −0.394, P < 0.001) between blood glucose levels and nausea scores upon PACU arrival. Dextrose administration reduced the odds of vomiting events compared to placebo (estimate: −0.87, odds ratio = 0.42, 95% confidence interval: 0.28–0.64).

Conclusion:

Administration of IV dextrose before anaesthesia induction may be recommended as an effective, and safe method for the prophylaxis of PONV after LC.

Endocannabinoids control vesicle release mode at midbrain periaqueductal grey inhibitory synapses

KEY POINTS

The midbrain periaqueductal grey (PAG) forms part of an endogenous analgesic system which is tightly regulated by the neurotransmitter GABA. The role of endocannabinoids in regulating GABAergic control of this system was examined in rat PAG slices. Under basal conditions GABAergic neurotransmission onto PAG output neurons was multivesicular. Activation of the endocannabinoid system reduced GABAergic inhibition by reducing the probability of release and by shifting release to a univesicular mode. Blockade of endocannabinoid system unmasked a tonic control over the probability and mode of GABA release. These findings provides a mechanistic foundation for the control of the PAG analgesic system by disinhibition.

ABSTRACT

The midbrain periaqueductal grey (PAG) has a crucial role in coordinating endogenous analgesic responses to physiological and psychological stressors. Endocannabinoids are thought to mediate a form of stress-induced analgesia within the PAG by relieving GABAergic inhibition of output neurons, a process known as disinhibition. This disinhibition is thought to be achieved by a presynaptic reduction in GABA release probability. We examined whether other mechanisms have a role in endocannabinoid modulation of GABAergic synaptic transmission within the rat PAG. The group I mGluR agonist DHPG ((R,S)-3,5-dihydroxyphenylglycine) inhibited evoked IPSCs and increased their paired pulse ratio in normal external Ca²⁺ , and when release probability was reduced by lowering Ca²⁺ . However, the effect of DHPG on the coefficient of variation and kinetics of evoked IPSCs differed between normal and low Ca²⁺ . Lowering external Ca²⁺ had a similar effect on evoked IPSCs to that observed for DHPG in normal external Ca²⁺ . The low affinity GABA_A receptor antagonist TPMPA ((1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid) inhibited evoked IPSCs to a greater extent in low than in normal Ca²⁺ . Together these findings indicate that the normal mode of GABA release is multivesicular within the PAG, and that DHPG and lowering external Ca²⁺ switch this to a univesicular mode. The effects of DHPG were mediated by mGlu5 receptor engagement of the retrograde endocannabinoid system. Blockade of endocannabinoid breakdown produced a similar shift in the mode of release. We conclude that endocannabinoids control both the mode and the probability of GABA release within the PAG.

Dissecting the Signaling Pathways Involved in the Crosstalk between Metabotropic Glutamate 5 and Cannabinoid Type 1 Receptors

The metabotropic glutamate 5 receptor and the cannabinoid type 1 receptor are G protein-coupled receptors that are widely expressed in the central nervous system. Metabotropic glutamate 5 receptors, present at the postsynaptic site, are coupled to Gα_q/11 proteins and display an excitatory response upon activation, whereas the cannabinoid type 1 receptor, mainly present at presynaptic terminals, is coupled to the G_i/o protein and triggers an inhibitory response. Recent studies suggest that the glutamatergic and endocannabinoid systems exhibit a functional interaction to modulate several neural processes. In this review, we discuss possible mechanisms involved in this crosstalk and its relationship with physiologic and pathologic conditions, including nociception, addiction, and fragile X syndrome.

To Break or to Brake Neuronal Network Accelerated by Ammonium Ions?

Purpose

The aim of present study was to investigate the effects of ammonium ions on in vitro neuronal network activity and to search alternative methods of acute ammonia neurotoxicity prevention.

Methods

Rat hippocampal neuronal and astrocytes co-cultures in vitro, fluorescent microscopy and perforated patch clamp were used to monitor the changes in intracellular Ca²⁺- and membrane potential produced by ammonium ions and various modulators in the cells implicated in neural networks.

Results

Low concentrations of NH₄Cl (0.1–4 mM) produce short temporal effects on network activity. Application of 5–8 mM NH₄Cl: invariably transforms diverse network firing regimen to identical burst patterns, characterized by substantial neuronal membrane depolarization at plateau phase of potential and high-amplitude Ca²⁺-oscillations; raises frequency and average for period of oscillations Ca²⁺-level in all cells implicated in network; results in the appearance of group of «run out» cells with high intracellular Ca²⁺ and steadily diminished amplitudes of oscillations; increases astrocyte Ca²⁺-signalling, characterized by the appearance of groups of cells with increased intracellular Ca²⁺-level and/or chaotic Ca²⁺-oscillations. Accelerated network activity may be suppressed by the blockade of NMDA or AMPA/kainate-receptors or by overactivation of AMPA/kainite-receptors. Ammonia still activate neuronal firing in the presence of GABA(A) receptors antagonist bicuculline, indicating that «disinhibition phenomenon» is not implicated in the mechanisms of networks acceleration. Network activity may also be slowed down by glycine, agonists of metabotropic inhibitory receptors, betaine, L-carnitine, L-arginine, etc.

Conclusions

Obtained results demonstrate that ammonium ions accelerate neuronal networks firing, implicating ionotropic glutamate receptors, having preserved the activities of group of inhibitory ionotropic and metabotropic receptors. This may mean, that ammonia neurotoxicity might be prevented by the activation of various inhibitory receptors (i.e. by the reinforcement of negative feedback control), instead of application of various enzyme inhibitors and receptor antagonists (breaking of neural, metabolic and signaling systems).

Effects of repeated treatment with cholecystokinin sulfated octapeptide on passive avoidance memory under chronic restraint stress in male rats

Background:

Cholecystokinin (CCK), a peptide hormone found in the gut is the most abundant peptide neurotransmitter in the brain as well, and its effects on learning, memory, and anxiety have been shown. However, it is not clear whether this substance acts as a mediator for anxiety and stress induction or inhibits them. Hence, the purpose of this study was to evaluate the effects of CCK on memory function under stress conditions.

Materials and Methods:

Male Wistar rats were divided into four groups: The control, the control-CCK, the stress, and stress-CCK. To induce stress, the rats were placed within adjustable restraint chambers for 6 h daily, for 24 days. CCK-8S (cholecystokinin sulfated octapeptide was injected before induction of stress (1.6 μg/kg, intraperitoneal) for 24 days. Passive avoidance learning test was used for evaluation of learning and memory. Rats received foot electrical shock before stress induction and CCK injection and step through latencies were evaluated 1-day after the last session of stress and treatments.

Results:

Stress impaired memory significantly (P < 0.05). Although CCK per se decreased memory (P < 0.05), it prevented the memory impairments in the stress group as there was no significant difference between the control and stress-CCK groups.

Conclusion:

Stress has a profound effect on cognition and CCK probably acts as a mediator for its action. Our results showed that a high concentration of CCK during stress may be helpful in alleviating the effects of stress on the brain.

Therapeutic Basis of Clinical Pain Modulation

Pain is a hallmark of almost all bodily ailments and can be modulated by agents, including analgesics and anesthetics that suppress pain signals in the central nervous system. Defects in the modulatory systems, including the endogenous pain-inhibitory pathways, are a major factor in the initiation and chronicity of pain. Thus, pain modulation is particularly applicable to the practice of medicine. This review summarizes the existing literature on pain modulation. Here, we critically reviewed the literature from PubMed on pain modulation published primarily within the past 5 years in high impact journals. Specifically, we have discussed important anatomical landmarks of pain modulation and outlined the endogenous networks and underlying mechanisms of clinically relevant pain modulatory methods. The Gate Control Theory is briefly presented with discussion on the capacity of pain modulation to cause both hyper- and hypoalgesia. An emphasis has been given to highlight key areas in pain research that, because of unanswered questions or therapeutic potential, merit additional scientific scrutiny. The information presented in this paper would be helpful in developing novel therapies, metrics, and interventions for improved patient management.

No more pain upon Gq-protein-coupled receptor activation: role of endocannabinoids

Marijuana has been used to relieve pain for centuries. The analgesic mechanism of its constituents, the cannabinoids, was only revealed after the discovery of cannabinoid receptors (CB1 and CB2) two decades ago. The subsequent identification of the endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG), and their biosynthetic and degradation enzymes discloses the therapeutic potential of compounds targeting the endocannabinoid system for pain control. Inhibitors of the anandamide and 2-AG degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase, respectively, may be superior to direct cannabinoid receptor ligands as endocannabinoids are synthesized on demand and rapidly degraded, focusing action at generating sites. Recently, a promising strategy for pain relief was revealed in the periaqueductal gray (PAG). It is initiated by Gq-protein-coupled receptor (Gq PCR) activation of the phospholipase C-diacylglycerol lipase enzymatic cascade, generating 2-AG that produces inhibition of GABAergic transmission (disinhibition) in the PAG, thereby leading to analgesia. Here, we introduce the antinociceptive properties of exogenous cannabinoids and endocannabinoids, involving their biosynthesis and degradation processes, particularly in the PAG. We also review recent studies disclosing the Gq PCR-phospholipase C-diacylglycerol lipase-2-AG retrograde disinhibition mechanism in the PAG, induced by activating several Gq PCRs, including metabotropic glutamatergic (type 5 metabotropic glutamate receptor), muscarinic acetylcholine (M1/M3), and orexin 1 receptors. Disinhibition mediated by type 5 metabotropic glutamate receptor can be initiated by glutamate transporter inhibitors or indirectly by substance P, neurotensin, cholecystokinin and capsaicin. Finally, the putative role of 2-AG generated after activating the above neurotransmitter receptors in stress-induced analgesia is discussed.

Endocannabinoid modulation by FAAH and monoacylglycerol lipase within the analgesic circuitry of the periaqueductal grey

BACKGROUND AND PURPOSE

Endogenous cannabinoids (endocannabinoids) in the periaqueductal grey (PAG) play a vital role in mediating stress-induced analgesia. This analgesic effect of endocannabinoids is enhanced by pharmacological inhibition of their degradative enzymes. However, the specific effects of endocannabinoids and the inhibitors of their degradation are largely unknown within this pain-modulating region.

EXPERIMENTAL APPROACH

In vitro electrophysiological recordings were conducted from PAG neurons in rat midbrain slices. The effects of the major endocannabinoids and their degradation inhibitors on inhibitory GABAergic synaptic transmission were examined.

KEY RESULTS

Exogenous application of the endocannabinoid, anandamide (AEA), but not 2-arachidonoylglycerol (2-AG), produced a reduction in inhibitory GABAergic transmission in PAG neurons. This AEA-induced suppression of inhibition was enhanced by the fatty acid amide hydrolase (FAAH) inhibitor, URB597, whereas a 2-AG-induced suppression of inhibition was unmasked by the monoacylglycerol lipase (MGL) inhibitor, JZL184. In addition, application of the CB1 receptor antagonist, AM251, facilitated the basal GABAergic transmission in the presence of URB597 and JZL184, which was further enhanced by the dual FAAH/MGL inhibitor, JZL195.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that AEA and 2-AG act via disinhibition within the PAG, a cellular action consistent with analgesia. These actions of AEA and 2-AG are tightly regulated by their respective degradative enzymes, FAAH and MGL. Furthermore, individual or combined inhibition of FAAH and/or MGL enhanced tonic disinhibition within the PAG. Therefore, the current findings support the therapeutic potential of FAAH and MGL inhibitors as a novel pharmacotherapy for pain.

Neuropathic orofacial pain: cannabinoids as a therapeutic avenue

Neuropathic orofacial pain (NOP) exists in several forms including pathologies such as burning mouth syndrome (BMS), persistent idiopathic facial pain (PIFP), trigeminal neuralgia (TN) and postherpetic neuralgia (PHN). BMS and PIFP are classically diagnosed by excluding other facial pain syndromes. TN and PHN are most often diagnosed based on a typical history and presenting pain characteristics. The pathophysiology of some of these conditions is still unclear and hence treatment options tend to vary and include a wide variety of treatments including cognitive behaviour therapy, anti-depressants, anti-convulsants and opioids; however such treatments often have limited efficacy with a great amount of inter-patient variability and poorly tolerated side effects. Analgesia is one the principal therapeutic targets of the cannabinoid system and many studies have demonstrated the efficacy of cannabinoid compounds in the treatment of neuropathic pain. This review will investigate the potential use of cannabinoids in the treatment of symptoms associated with NOP.

Circulating endocannabinoids in insulin sensitive vs. insulin resistant obese postmenopausal women. A MONET group study

OBJECTIVE

To measure the circulating levels of endocannabinoids and related molecules at fasting, after acute hyperinsulinemia and after weight loss in insulin sensitive vs. insulin resistant obese postmenopausal women.

DESIGN AND METHODS

The sample consisted of 30 obese postmenopausal women (age: 58.9 ± 5.2 yrs; BMI: 32.9 ± 3.6 kg/m(2) ). Subjects underwent a 3-hour hyperinsulinaemic-euglycaemic clamp (HEC) (glucose disposal rate (M-value): 10.7 ± 3.3 mg min(-1) kg(-1) FFM) and 6-month weight loss intervention. Participants were classified as insulin sensitive obese (ISO) or insulin resistant obese (IRO) based on a predefined cutoff. Plasma levels of the endocannabinoids, anandamide (AEA), 2-arachidonoylglycerol (2-AG), and of the AEA-related compounds, palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), were measured by liquid chromatography-mass spectrometry.

RESULTS

IRO presented higher levels of 2-AG (P < 0.05) independently of the HEC and weight loss, whereas the HEC had an independent inhibitory effect on AEA, PEA, and OEA levels (P < 0.05) in both groups. Furthermore, there was an independent stimulatory effect of weight loss only on PEA levels in both groups (P < 0.05).

CONCLUSIONS

This study is the first to show that higher circulating levels of the endocannabinoid 2-AG are found in IRO compared to ISO postmenopausal women, and that weight loss is associated with an increase in PEA, a PPAR-α ligand.

Targeting the cannabinoid system for pain relief?

Marijuana has been used to relieve pain for centuries, but its analgesic mechanism has only been understood during the past two decades. It is mainly mediated by its constituents, cannabinoids, through activating central cannabinoid 1 (CB1) receptors, as well as peripheral CB1 and CB2 receptors. CB2-selective agonists have the benefit of lacking CB1 receptor-mediated CNS side effects. Anandamide and 2-arachidonoylglycerol (2-AG) are two intensively studied endogenous lipid ligands of cannabinoid receptors, termed endocannabinoids, which are synthesized on demand and rapidly degraded. Thus, inhibitors of their degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase (MAGL), respectively, may be superior to direct cannabinoid receptor ligands as a promising strategy for pain relief. In addition to the antinociceptive properties of exogenous cannabinoids and endocannabinoids, involving their biosynthesis and degradation processes, we also review recent studies that revealed a novel analgesic mechanism, involving 2-AG in the periaqueductal gray (PAG), a midbrain region for initiating descending pain inhibition. It is initiated by Gq-protein-coupled receptor (GqPCR) activation of the phospholipase C (PLC)-diacylglycerol lipase (DAGL) enzymatic cascade, generating 2-AG that produces inhibition of GABAergic transmission (disinhibition) in the PAG, thereby leading to analgesia. This GqPCR-PLC-DAGL-2-AG retrograde disinhibition mechanism in the PAG can be initiated by activating type 5 metabotropic glutamate receptor (mGluR5), muscarinic acetylcholine (M1/M3), and orexin (OX1) receptors. mGluR5-mediated disinhibition can be initiated by glutamate transporter inhibitors, or indirectly by substance P, neurotensin, cholecystokinin, capsaicin, and AM404, the bioactive metabolite of acetaminophen in the brain. The putative role of 2-AG generated after activating the above neurotransmitter receptors in stress-induced analgesia is also discussed.

Gene expression in amygdala as a function of differential trait anxiety levels in genetically heterogeneous NIH-HS rats

To identify genes involved in anxiety/fear traits, we analyzed the gene expression profile in the amygdala of genetically heterogeneous NIH-HS rats. The NIH-HS rat stock has revealed to be a unique genetic resource for the fine mapping of Quantitative Trait Loci (QTLs) to very small genomic regions, due to the high amount of genetic recombinants accumulated along more than 50 breeding generations, and for the same reason it can be expected that those genetically heterogeneous rats should be especially useful for studying differential gene expression as a function of anxiety-(or other)-related traits. We selected high- and low-anxious NIH-HS rats differing in their number of avoidances in a single 50-trial session of the two-way active avoidance task. Rats were also tested in unconditioned anxiety tests (e.g., elevated zero-maze). Three weeks after behavioural testing, the amygdala was dissected and prepared for the microarray study. There appeared 6 significantly down-regulated and 28 up-regulated genes (fold-change >|2|, FDR<0.05) between the low- and high-anxious groups, with central nervous system-related functions. Regression analyses (stepwise) revealed that differential expression of some genes could be predictive of anxiety/fear responses. Among those genes for which the present results suggest a link with individual differences in trait anxiety, six relevant genes were examined with qRT-PCR, four of which (Ucn3, Tacr3, H2-M9 and Arr3) were validated. Remarkably, some of them are characterized by sharing known functions related with hormonal HPA-axis responses to (and/or modulation of) stress, anxiety or fear, and putative involvement in related neurobehavioural functions. The results confirm the usefulness of NIH-HS rats as a good animal model for research on the neurogenetic basis of anxiety and fear, while suggesting the involvement of some neuropeptide/neuroendocrine pathways on the development of differential anxiety profiles.

Postsynaptic mGluR mediated excitation of neurons in midbrain periaqueductal grey

Metabotropic glutamate (mGlu) receptors modulate pain from within the midbrain periaqueductal grey (PAG). In the present study, the postsynaptic mGlu receptor mediated effects on rat PAG neurons were examined using whole-cell patch-clamp recordings in brain slices. The selective group I agonist DHPG (10 μM) produced an inward current in all PAG neurons tested which was associated with a near parallel shift in the current-voltage relationship. By contrast, the group II and III mGlu receptor agonists DCG-IV (1 μM) and l-AP4 (3 μM) produced an outward current in only 10-20% of PAG neurons tested. The DHPG induced current was concentration dependent (EC(50) = 1.4 μM), was reduced by the mGlu1 antagonist CPCCOEt (100 μM), and was further reduced by CPCCOEt in combination with the mGlu5 antagonist MPEP (10 μM). The glutamate transport blocker TBOA (30 μM) also produced an inward current, however, this was largely abolished by CNQX (10 μM) plus AP5 (25 μM). Slow EPSCs were evoked following train, but not single shock stimulation, which were enhanced by TBOA (30 μM). The TBOA enhancement of slow EPSCs was abolished by MPEP plus CPCCOEt. These findings indicate that endogenously released glutamate, under conditions in which neurotransmitter spill-over is enhanced, activates group I mGlu receptors to produce excitatory currents within PAG. Thus, postsynaptic group I mGlu receptors have the potential to directly modulate the analgesic, behavioural and autonomic functions of the PAG. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Cholecystokinin receptor-1 mediates the inhibitory effects of exogenous cholecystokinin octapeptide on cellular morphine dependence

Background

Cholecystokinin octapeptide (CCK-8), the most potent endogenous anti-opioid peptide, has been shown to regulate the processes of morphine dependence. In our previous study, we found that exogenous CCK-8 attenuated naloxone induced withdrawal symptoms. To investigate the precise effect of exogenous CCK-8 and the role of cholecystokinin (CCK) 1 and/or 2 receptors in morphine dependence, a SH-SY5Y cell model was employed, in which the μ-opioid receptor, CCK1/2 receptors, and endogenous CCK are co-expressed.

Results

Forty-eight hours after treating SH-SY5Y cells with morphine (10 μM), naloxone (10 μM) induced a cAMP overshoot, indicating that cellular morphine dependence had been induced. The CCK receptor and endogenous CCK were up-regulated after chronic morphine exposure. The CCK2 receptor antagonist (LY-288,513) at 1–10 μM inhibited the naloxone-precipitated cAMP overshoot, but the CCK1 receptor antagonist (L-364,718) did not. Interestingly, CCK-8 (0.1-1 μM), a strong CCK receptor agonist, dose-dependently inhibited the naloxone-precipitated cAMP overshoot in SH-SY5Y cells when co-pretreated with morphine. The L-364,718 significantly blocked the inhibitory effect of exogenous CCK-8 on the cAMP overshoot at 1–10 μM, while the LY-288,513 did not. Therefore, the CCK2 receptor appears to be necessary for low concentrations of endogenous CCK to potentiate morphine dependence in SH-SY5Y cells. An additional inhibitory effect of CCK-8 at higher concentrations appears to involve the CCK1 receptor.

Conclusions

This study reveals the difference between exogenous CCK-8 and endogenous CCK effects on the development of morphine dependence, and provides the first evidence for the participation of the CCK1 receptor in the inhibitory effects of exogenous CCK-8 on morphine dependence.