Endocannabinoids block status epilepticus in cultured hippocampal neurons

Increased hippocampal cannabinoid 1 receptor expression is associated with protection from severe seizures in pregnant mice with reduced uterine perfusion pressure

Eclampsia, new-onset seizures in pregnancy, can complicate preeclampsia, a hypertensive pregnancy disorder. The mechanisms contributing to increased risk of seizures in preeclampsia are not fully known. One mechanism could be abnormal endocannabinoid system (ECS) activity and impaired neuromodulation. Indeed, increased placental cannabinoid receptor 1 (CB1R) expression and reduced serum anandamide, a CB1R ligand, have been reported in preeclampsia patients. We hypothesized that reduced uterine perfusion pressure (RUPP), used to mimic preeclampsia, leads to changes in hippocampal CB1R expression, and that manipulating CB1R activity will change seizure severity in RUPP mice. Pregnant mice underwent sham or RUPP surgery on gestational day (GD)13.5. On GD18.5, mice received: no drug treatment, pentylenetetrazol (PTZ, 40 mg/kg), Rimonabant (10 mg/kg) + PTZ, or 2-AG (1 mg/kg) + PTZ. Behaviors were video recorded (15 min for Rimonabant and 2-AG, followed by 30 min for PTZ), and the hippocampus was harvested. The expression of CB1R and ECS proteins was measured in hippocampal homogenates, synaptosomes, and cytosol. Hippocampal CB1R increased in homogenates and cytosolic fraction, and was unchanged in synaptosomes of RUPP mice. Increased CB1R colocalization on glutamate-releasing neurons within hippocampal CA1 was observed in RUPP mice. Rimonabant modestly increased seizure scores over time in RUPP mice. PTZ after rimonabant pretreatment increased seizure scores and duration, while reducing latency in sham mice, with little to no change in RUPP mice. Furthermore, RUPP mice had lower seizure scores over time than sham following CB1R blockade and activation. These data suggest that RUPP modifies CB1R activity prior to seizure induction, which protects mice from worse seizure outcomes.

The electrophysiological and behavioral evaluation of the peptide hemopressin and cannabinoid CB1 receptor agonist and antagonist in pentylenetetrazol model of epilepsy in rats

This study endeavoured to assess the effect of hemopressin (Hp), a nano peptide obtained from the alpha chain of hemoglobin, on chronic epileptic activity and its potential correlation with cannabinoid receptor type 1 (CB1). Male Wistar albino rats (230-260 g) were used. The kindling process was conducted by administering a sub-convulsant dose of pentylenetetrazol (PTZ) (35 mg/kg, i.p) three times a week for a maximum of 10 weeks. Tripolar electrodes and external cannula guides for intracerebroventricular (i.c.v) injections were surgically implanted in the skulls of kindled rats. On the day of the experiment, doses of Hp, AM-251, and ACEA were administered prior to the PTZ injections. Electroencephalography recordings and behavioural observations were conducted simultaneously for 30 min after the PTZ injection. The administration of Hp (0.6 μg, i.c.v) resulted in a decrease in epileptic activity. The CB1 receptor agonist ACEA (7.5 μg, i.c.v) showed an anticonvulsant effect, but the CB1 receptor antagonist AM-251 (0.5 μg, i.c.v) displayed a proconvulsant effect. The co-administration of Hp (0.6 μg, i.c.v) and ACEA (7.5 μg, i.c.v) and of Hp (0.6 μg, i.c.v) and AM-251 (0.5 μg, i.c.v) produced an anticonvulsant effect. However, when AM-251 was administered prior to Hp, it produced a proconvulsant impact that overrode Hp's intended anticonvulsant effect. Interestingly, the co-administration of Hp (0.03 μg) + AM-251 (0.125 μg) unexpectedly exhibited an anticonvulsant effect. Electrophysiological and behavioural evaluations demonstrated the anticonvulsant effect of Hp in the present model, highlighting the possibility that Hp may act as an agonist for the CB1 receptor.

Endocannabinoids at the synapse and beyond: implications for neuropsychiatric disease pathophysiology and treatment

Endocannabinoids (eCBs) are lipid neuromodulators that suppress neurotransmitter release, reduce postsynaptic excitability, activate astrocyte signaling, and control cellular respiration. Here, we describe canonical and emerging eCB signaling modes and aim to link adaptations in these signaling systems to pathological states. Adaptations in eCB signaling systems have been identified in a variety of biobehavioral and physiological process relevant to neuropsychiatric disease states including stress-related disorders, epilepsy, developmental disorders, obesity, and substance use disorders. These insights have enhanced our understanding of the pathophysiology of neurological and psychiatric disorders and are contributing to the ongoing development of eCB-targeting therapeutics. We suggest future studies aimed at illuminating how adaptations in canonical as well as emerging cellular and synaptic modes of eCB signaling contribute to disease pathophysiology or resilience could further advance these novel treatment approaches.

Anticonvulsive and anti-epileptogenesis effects of Echinacea purpurea root extract, an involvement of CB2 receptor

OBJECTIVES

Phytocannabinoids beyond the Δ9-tetrahy-drocannabinol have shown anticonvulsive effects. Also, alkylamides from Echinacea purpurea have been proved as cannabinomimetics. We examined the effect of the hydroalcoholic root extract of E. purpurea on pentylenetetrazol (PTZ)-induced tonic-clonic seizures and kindling model of epileptogenesis and the involvement of CB2 receptors as the mediator of this effect.

METHODS

Male Wistar rats (200 ± 20 g) were used. Single intraperitoneal (i.p.) injection of PTZ (80 mg/kg) was used to induce tonic-clonic seizures. The kindling model of epileptogenesis was induced by daily injections of PTZ (37 mg/kg; i.p. for 15 days). Latency and duration of the stages were monitored for analysis. The hydroalcoholic root extract of E. purpurea was injected (i.p.) 20 min before seizure induction at the doses of 10, 50, 100 and 200 mg/kg. CB2 receptor antagonist SR144528 was injected (0.1 mg/kg; i.p.) 20 min before the Echinacea injection.

RESULTS

In the tonic-clonic model, pretreatment with E. purpurea at the doses of 100 and 200 mg/kg significantly increased latencies to S2-S6, while it significantly decreased S6 duration and mortality rate. SR144528 injection before the injection of 100 mg/kg of E. purpurea significantly prevented the effects of the extract on S4-S6 latencies. In the kindling model, E. purpurea at the doses of 100 and 200 mg/kg significantly delayed epileptogenesis and decreased mortality rate, while SR144528 injection before the injection of 100 mg/kg of E. purpurea significantly blocked this effect of the extract.

CONCLUSIONS

These findings revealed the anticonvulsive and antiepileptogenesis effects of the E. purpurea root extract, which can be mediated by CB2 receptors.

Anandamide Metabolites Protect against Seizures through the TRP Channel Water Witch in Drosophila melanogaster

Endocannabinoids protect against seizures, but their mechanism of action is still unclear, as they can have effects independent of known cannabinoid receptors. Using Drosophila melanogaster, which lacks canonical cannabinoid receptors, we report that the endocannabinoids anandamide and 2-arachidonoylglycerol protect against seizures in multiple fly seizure models. Surprisingly, inhibition of anandamide catabolism renders flies insensitive to protection by anandamide, indicating that anandamide metabolites are responsible for seizure protection. Consistent with this finding, arachidonic acid, a direct metabolite of anandamide, protects against seizures. To identify downstream effectors, we test for a role of transient receptor potential (TRP) channels and find that the TRPV1 antagonist capsazepine blocks the protective effect of anandamide. Also, a targeted genetic screen of TRP channels identifies water witch as a mediator of protection by anandamide. Using a Drosophila model, we reveal the role of arachidonic acid in seizure protection and identify a cannabinoid-receptor-1/2-independent mechanism of endocannabinoid seizure protection.

Cannabidiol (CBD) Inhibited Rhodamine-123 Efflux in Cultured Vascular Endothelial Cells and Astrocytes Under Hypoxic Conditions

Despite the constant development of new antiepileptic drugs (AEDs), more than 30% of patients develop refractory epilepsy (RE) characterized by a multidrug-resistant (MDR) phenotype. The “transporters hypothesis” indicates that the mechanism of this MDR phenotype is the overexpression of ABC transporters such as P-glycoprotein (P-gp) in the neurovascular unit cells, limiting access of the AEDs to the brain. Recent clinical trials and basic studies have shown encouraging results for the use of cannabinoids in RE, although its mechanisms of action are still not fully understood. Here, we have employed astrocytes and vascular endothelial cell cultures subjected to hypoxia, to test the effect of cannabidiol (CBD) on the P-gp-dependent Rhodamine-123 (Rho-123) efflux. Results show that during hypoxia, intracellular Rho-123 accumulation after CBD treatment is similar to that induced by the P-gp inhibitor Tariquidar (Tq). Noteworthy, this inhibition is like that registered in non-hypoxia conditions. Additionally, docking studies predicted that CBD could behave as a P-gp substrate by the interaction with several residues in the α-helix of the P-gp transmembrane domain. Overall, these findings suggest a direct effect of CBD on the Rho-123 P-gp-dependent efflux activity, which might explain why the CBD add-on treatment regimen in RE patients results in a significant reduction in seizure frequency.

Levetiracetam combined with ACEA, highly selective cannabinoid CB1 receptor agonist changes neurogenesis in mouse brain

The aim of the study was to evaluate the impact of second generation antiepileptic drug levetiracetam (LEV) with arachidonyl-2'-chloroethylamide (ACEA) on proliferating neural precursor cells in mouse brain. Additionally, we established the relationship between treatment with ACEA in combination with LEV and hippocampal neurogenesis in mouse brain. All experiments were performed on male CB57/BL mice injected i.p. with LEV (10 mg/kg), ACEA (10 mg/kg) and PMSF (30 mg/kg) for 10 days. Experiments were provided in two stages: stage 1- an acute response of proliferating neural precursor cells to ACEA and LEV administration (Ki-67 staining), stage 2 - a long term response to ACEA and LEV administration (BrDU, NeuN, GFAP staining). Results indicate that ACEA + PMSF and ACEA + PMSF + LEV significantly increased the total number of Ki-67 positive cells comparing to the control group. PMSF and LEV administered alone and in combination had no significant impact on cell proliferation compared to the control group. Results from neurogenesis study indicated that ACEA + PMSF administered alone and in combination with LEV increased the total number of BrDU cells compared to the control group, although LEV on its own decreased the number of BrDU cells. Moreover, the combination of ACEA + PMSF + LEV significantly increased the total number of newborn neurons compared to the control group. In turn, LEV significantly decreased the process of neurogenesis. Astrocytes were considerably reduced in all treated groups as compare to the control mice. These data provide substantial evidence that LEV administered chronically decreases the proliferation and differentiation of newly born cells while combination of LEV + ACEA significantly increases the level of newborn neurons in the dentate subgranular zone.

Anticonvulsant-like effect of thromboxane receptor agonist U-46619 against pentylenetetrazol-induced seizures

Increasing evidence suggests that prostanoid receptors and their ligands may constitute valuable tools for development of new antiepileptic drugs. Thromboxane A₂ (TXA₂) is a major eicosanoid in cardiovascular homeostasis. TXA₂ exerts its action through the specific G protein-coupled TXA₂ receptor (TP). In addition to its crucial role in the cardiovascular system, TXA₂ and TPs play a role in the brain. Nevertheless, previously identified roles have been limited to cell protection of neurotoxicity, and the role of TPs on seizure activity was not investigated. Here we evaluated the effect of potent and selective TP agonist U-46619 on seizures induced by pentylenetetrazol (PTZ). Adult C57BL/6 mice received increasing doses of U-46619 (0, 30, 100 or 300 μg/kg). After 30 min we measured the latencies to myoclonic and generalized seizures induced by PTZ (60 mg/kg). We found that U-46619 increased the latency to PTZ-induced myoclonic jerks and tonic-clonic seizures. Moreover, U-46619 increased the immunocontent of phosphorylated Ser⁶⁵⁷ at protein kinase C (PKC) alpha subunit, indicating PKC activation in the hippocampus and cerebral cortex. Levels of TPs were not altered by the agonist. Administration of a TP antagonist, SQ 29,548, did not alter seizures and did not blunt the anticonvulsant-like effect of the agonist. In summary, we showed that a potent and selective TP agonist, U-46619, increased seizure latency in mice. Activation of PKC signaling pathways may underlie the anticonvulsant-like effect. Further investigation is needed to understand the potential of TPs in seizure treatment.

Novel drugs and early polypharmacotherapy in status epilepticus

PURPOSE

Rescue medications for status epilepticus (SE) have a relatively high rate of failure. The purpose of this review is to summarize the evidence for the efficacy of novel drugs and early polypharmacotherapy for SE.

METHOD

Literature review.

RESULTS

New drugs and treatment strategies aim to target the pathophysiology of SE in order to improve seizure control and outcomes. Changes at the synapse level during SE include a progressive decrease in synaptic GABA_A receptors and increase in synaptic NMDA receptors. These changes tend to promote self-sustaining seizures. Current SE guidelines recommend a rapid stepwise treatment using benzodiazepines in monotherapy as the first-line treatment, targeting GABA_A synaptic receptors. Novel treatment approaches target GABA_A synaptic and extrasynaptic receptors with allopregnanolone, and NMDA receptors with ketamine. Novel rescue treatments used for SE include topiramate, brivaracetam, and perampanel, which are already marketed in epilepsy. Some available drugs not marketed for use in epilepsy have been used in the treatment of SE, and other agents are being studied for this purpose. Early polytherapy, most frequently combining a benzodiazepine with a second-line drug or an NMDA receptor antagonist, might potentially increase seizure control with relatively minor increase in side effects. Although many preclinical studies support novel drugs and early polytherapy in SE, human studies are scarce and inconclusive. Currently, evidence is lacking to recommend specific combinations of these new agents.

CONCLUSIONS

Novel drugs and strategies target the underlying pathophysiology of SE with the intent to improve seizure control and outcomes.

Efficacy of CBD-enriched medical cannabis for treatment of refractory epilepsy in children and adolescents - An observational, longitudinal study

The objective of this observational study was to evaluate the efficacy of medical cannabis for the treatment of refractory epilepsy. Fifty-seven patients (age 1-20 years) with epilepsy of various etiologies were treated with Cannabis oil extract (CBD/THC ratio of 20:1) for at least 3 months (Median follow up time-18 months). Forty-Six Patients were included in the efficacy analysis. Average CBD dose was11.4 mg/kg/d. Twenty-six patients (56%) had ≤50% reduction in mean monthly seizure frequency. There was no statistically significant difference in response rate among various epilepsy etiologies, and cannabis strain used. Younger age at treatment onset (<10 years) and higher CBD dose (>11 mg/kg/d) were associated with better response to treatment. Adverse reactions were reported in 46% of patients and were the main reason for treatment cessation. Our results suggest that adding CBD-enriched cannabis extract to the treatment regimen of patients with refractory epilepsy may result in a significant reduction in seizure frequency according to parental reports. Randomized controlled trials are necessary to assess its true efficacy.

Hypothermia Reduces Mortality, Prevents the Calcium Plateau, and Is Neuroprotective Following Status Epilepticus in Rats

Status Epilepticus (SE) is a major neurological emergency and is considered a leading cause of Acquired Epilepsy (AE). We have shown that SE produces neuronal injury and prolonged alterations in hippocampal calcium levels ([Ca²⁺]_i) that may underlie the development of AE. Interventions preventing the SE-induced Ca²⁺ plateau could therefore prove to be beneficial in lowering the development of AE after SE. Hypothermia is used clinically to prevent neurological complications associated with Traumatic Brain Injury, cardiac arrest, and stroke. Here, we investigated whether hypothermia prevented the development of Ca²⁺ plateau following SE. SE was induced in hippocampal neuronal cultures (HNC) by exposing them to no added MgCl₂ solution for 3 h. To terminate SE, low Mg²⁺ solution was washed off with 31°C (hypothermic) or 37°C (normothermic) physiological recording solution. [Ca²⁺]_i was estimated with ratiometric Fura-2 imaging. HNCs washed with hypothermic solution exhibited [Ca²⁺]_i ratios, which were significantly lower than ratios obtained from HNCs washed with normothermic solution. For in vivo SE, the rat pilocarpine (PILO) model was used. Moderate hypothermia (30–33°C) in rats was induced at 30-min post-SE using chilled ethanol spray in a cold room. Hypothermia following PILO-SE significantly reduced mortality. Hippocampal neurons isolated from hypothermia-treated PILO SE rats exhibited [Ca²⁺]_i ratios which were significantly lower than ratios obtained from PILO SE rats. Hypothermia also provided significant neuroprotection against SE-induced delayed hippocampal injury as characterized by decreased FluoroJade C labeling in hypothermia-treated PILO SE rats. We previously demonstrated that hypothermia reduced Ca²⁺ entry via N-methyl-D-aspartate and ryanodine receptors in HNC. Together, our studies indicate that by targeting these two receptor systems hypothermia could interfere with epileptogenesis and prove to be an effective therapeutic intervention for reducing SE-induced AE.

Anticonvulsive effects of endocannabinoids; an investigation to determine the role of regulatory components of endocannabinoid metabolism in the Pentylenetetrazol induced tonic- clonic seizures

2-Arachidonoylglycerol (2-AG) and anandamide are two major endocannabinoids produced, released and eliminated by metabolic pathways. Anticonvulsive effect of 2-AG and CB1 receptor is well-established. Herein, we designed to investigate the anticonvulsive influence of key components of the 2-AG and anandamide metabolism. Tonic-clonic seizures were induced by an injection of Pentylenetetrazol (80 mg/kg, i.p.) in adult male Wistar rats. Delay and duration for the seizure stages were considered for analysis. Monoacylglycerol lipase blocker (JJKK048; 1 mg/kg) or alpha/beta hydroxylase domain 6 blocker (WWL70; 5 mg/kg) were administrated alone or with 2-AG to evaluate the anticonvulsive potential of these enzymes. To determine the CB1 receptor involvement, its blocker (MJ15; 3 mg/kg) was administrated associated with JJKK048 or WWL70. To assess anandamide anticonvulsive effect, anandamide membrane transporter blocker (LY21813240; 2.5 mg/kg) was used alone or associated with MJ15. Also, fatty acid amide hydrolase blocker (URB597; 1 mg/kg; to prevent intracellular anandamide hydrolysis) were used alone or with AMG21629 (transient receptor potential vanilloid; TRPV1 antagonist; 3 mg/kg). All compounds were dissolved in DMSO and injected i.p., before the Pentylenetetrazol. Both JJKK048 and WWL70 revealed anticonvulsive effect. Anticonvulsive effect of JJKK048 but not WWL70 was CB1 receptor dependent. LY2183240 showed CB1 receptor dependent anticonvulsive effect. However, URB597 revealed a TRPV1 dependent proconvulsive effect. It seems extracellular accumulation of 2-AG or anandamide has anticonvulsive effect through the CB1 receptor, while intracellular anandamide accumulation is proconvulsive through TRPV1.

Review of the neurological benefits of phytocannabinoids

Background:

Numerous physical, psychological, and emotional benefits have been attributed to marijuana since its first reported use in 2,600 BC in a Chinese pharmacopoeia. The phytocannabinoids, cannabidiol (CBD), and delta-9-tetrahydrocannabinol (Δ9-THC) are the most studied extracts from cannabis sativa subspecies hemp and marijuana. CBD and Δ9-THC interact uniquely with the endocannabinoid system (ECS). Through direct and indirect actions, intrinsic endocannabinoids and plant-based phytocannabinoids modulate and influence a variety of physiological systems influenced by the ECS.

Methods:

In 1980, Cunha et al. reported anticonvulsant benefits in 7/8 subjects with medically uncontrolled epilepsy using marijuana extracts in a phase I clinical trial. Since then neurological applications have been the major focus of renewed research using medical marijuana and phytocannabinoid extracts.

Results:

Recent neurological uses include adjunctive treatment for malignant brain tumors, Parkinson's disease, Alzheimer's disease, multiple sclerosis, neuropathic pain, and the childhood seizure disorders Lennox-Gastaut and Dravet syndromes. In addition, psychiatric and mood disorders, such as schizophrenia, anxiety, depression, addiction, postconcussion syndrome, and posttraumatic stress disorders are being studied using phytocannabinoids.

Conclusions:

In this review we will provide animal and human research data on the current clinical neurological uses for CBD individually and in combination with Δ9-THC. We will emphasize the neuroprotective, antiinflammatory, and immunomodulatory benefits of phytocannabinoids and their applications in various clinical syndromes.

Analysis of the pharmacological properties of JWH-122 isomers and THJ-2201, RCS-4 and AB-CHMINACA in HEK293T cells and hippocampal neurons

Synthetic cannabinoids are marketed as legal alternatives to Δ⁹-THC, and are a growing worldwide concern as these drugs are associated with severe adverse effects. Unfortunately, insufficient information regarding the physiological and pharmacological effects of emerging synthetic cannabinoids (ESCs) makes their regulation by government authorities difficult. One strategy used to evade regulation is to distribute isomers of regulated synthetic cannabinoids. This study characterized the pharmacological properties of a panel of ESCs in comparison to Δ⁹-THC, as well as six JWH-122 isomers relative to its parent compound (JWH-122-4). Two cell-based assays were used to determine the potency and efficacy of ESCs and a panel of reference cannabinoids. HEK293T cells were transfected with human cannabinoid receptor 1 (CB₁) and pGloSensor-22F, and the inhibition of forskolin-stimulated cyclic adenosine monophosphate (cAMP) levels was monitored in live cells. All ESCs examined were classified as agonists, with the following rank order of potency: Win 55,212-2 > CP 55,940 > JWH-122-4 > Δ⁹-THC ≈ RCS-4 ≈ THJ-2201 > JWH-122-5 > JWH-122-7 > JWH-122-2 ≈ AB-CHMINACA > JWH-122-8 > JWH-122-6 > JWH-122-3. Evaluation of ESC-stimulated Ca²⁺ transients in cultured rat primary hippocampal neurons confirmed the efficacy of four of the most potent ESCs (JWH-122-4, JWH-122-5, JWH-122-7 and AB-CHMINACA). This work helps regulatory agencies make informed decisions concerning these poorly characterized recreational drugs.

Mdivi-1 Protects Epileptic Hippocampal Neurons from Apoptosis via Inhibiting Oxidative Stress and Endoplasmic Reticulum Stress in Vitro

Mitochondrial division inhibitor 1 (mdivi-1), a selective inhibitor of the mitochondrial fission protein dynamin-related protein 1, has been proposed to have a neuroprotective effect on hippocampal neurons in animal models of epilepsy. However, the effect of mdivi-1 on epileptic neuronal death in vitro remains unknown. Therefore, we investigated the effect of mdivi-1 and the underlying mechanisms in the hippocampal neuronal culture (HNC) model of acquired epilepsy (AE) in vitro. We found that mitochondrial fission was increased in the HNC model of AE and inhibition of mitochondrial fission by mdivi-1 significantly decreased neuronal apoptosis induced by AE. In addition, mdivi-1 pretreatment significantly attenuated oxidative stress induced by AE characterized by decrease of reactive oxygen species (ROS) production and malondialdehyde level and by increase of superoxide dismutase activity. Moreover, mdivi-1 pretreatment significantly decreased endoplasmic reticulum (ER) stress markers glucose-regulated protein 78, C/EBP homologous protein expression and caspase-3 activation. Altogether, our findings suggest that mdivi-1 protected against AE-induced hippocampal neuronal apoptosis in vitro via decreasing ROS-mediated oxidative stress and ER stress.

Cannabinoids and Epilepsy

Cannabis has been used for centuries to treat seizures. Recent anecdotal reports, accumulating animal model data, and mechanistic insights have raised interest in cannabis-based antiepileptic therapies. In this study, we review current understanding of the endocannabinoid system, characterize the pro- and anticonvulsive effects of cannabinoids [e.g., Δ9-tetrahydrocannabinol and cannabidiol (CBD)], and highlight scientific evidence from pre-clinical and clinical trials of cannabinoids in epilepsy. These studies suggest that CBD avoids the psychoactive effects of the endocannabinoid system to provide a well-tolerated, promising therapeutic for the treatment of seizures, while whole-plant cannabis can both contribute to and reduce seizures. Finally, we discuss results from a new multicenter, open-label study using CBD in a population with treatment-resistant epilepsy. In all, we seek to evaluate our current understanding of cannabinoids in epilepsy and guide future basic science and clinical studies.

Chronic administration of AM251 improves albuminuria and renal tubular structure in obese rats

Modulation of the endocannabinoid system as an anti-obesity therapeutic is well established; however, the direct effects of cannabinoid receptor 1 (CB1) antagonism on renal function and structure in a model of diet-induced obesity (DIO) are unknown. The aim of this study was to characterise the renal effects of the CB1 antagonist AM251 in a model of DIO. Male Sprague-Dawley rats were fed a low- or high-fat diet (HFD: 40% digestible energy from lipids) for 10 weeks to elicit DIO (n=9). In a different cohort, rats were fed a HFD for 15 weeks. After 9 weeks consuming a HFD, rats were injected daily for 6 weeks with 3 mg/kg AM251 (n=9) or saline via i.p. injection (n=9). After 10 weeks consuming a HFD, CB1 and megalin protein expression were significantly increased in the kidneys of obese rats. Antagonism of CB1 with AM251 significantly reduced weight gain, systolic blood pressure, plasma leptin, and reduced albuminuria and plasma creatinine levels in obese rats. Importantly, there was a significant reduction in tubular cross-section diameter in the obese rats treated with AM251. An improvement in albuminuria was likely due to the reduction in tubular size, reduced leptinaemia and maintenance of megalin expression levels. In obese rats, AM251 did not alter diastolic blood pressure, sodium excretion, creatinine clearance or expression of the fibrotic proteins VEGFA, TGFB1 and collagen IV in the kidney. This study demonstrates that treatment with CB1 antagonist AM251 improves renal outcomes in obese rats.

Inhibition of monoacylglycerol lipase mediates a cannabinoid 1-receptor dependent delay of kindling progression in mice

Endocannabinoids, including 2-arachidonoylglycerol (2-AG), activate presynaptic cannabinoid type 1 receptors (CB1R) on inhibitory and excitatory neurons, resulting in a decreased release of neurotransmitters. The event-specific activation of the endocannabinoid system by inhibition of the endocannabinoid degrading enzymes may offer a promising strategy to selectively activate CB1Rs at the site of excessive neuronal activation with the overall goal to prevent the development epilepsy. The aim of this study was to investigate the impact of monoacylglycerol lipase (MAGL) inhibition on the development and progression of epileptic seizures in the kindling model of temporal lobe epilepsy. Therefore, we selectively blocked MAGL by JZL184 (8mg/kg, i.p.) in mice to analyze the effects of increased 2-AG levels on kindling acquisition and to exclude an anticonvulsive potential. Our results showed that JZL184 treatment significantly delayed the development of generalized seizures (p=0.0066) and decreased seizure (p<0.0001) and afterdischarge duration (p<0.001) in the kindling model of temporal lobe epilepsy, but caused only modest effects in fully kindled mice. Moreover, we proved that JZL184 treatment had no effects in conditional CB1R knockout mice lacking expression of the receptor in principle neurons of the forebrain. In conclusion, the data demonstrate that indirect CB1R agonism delays the development of generalized epileptic seizures but has no relevant acute anticonvulsive effects. Furthermore, we confirmed that the effects of JZL184 on kindling progression are CB1R mediated. Thus, the data indicate that the endocannabinoid 2-AG might be a promising target for an anti-epileptogenic approach.

Attenuation of kainic acid-induced status epilepticus by inhibition of endocannabinoid transport and degradation in guinea pigs

Status epilepticus (SE) is a medical emergency associated with a high rate of mortality if not treated promptly. Exogenous and endogenous cannabinoids have been shown to possess anticonvulsant properties both in vivo and in vitro. Here we study the influence of endocannabinoid metabolism on the development of kainic acid-induced SE in guinea pigs. For this purpose, the inhibitors of endocannabinoid transport, AM404, and enzymatic (fatty acid amide hydrolase) degradation, URB597, were applied. Cannabinoid CB1 receptor antagonist, AM251, was also tested. Animal behavior as well as local electric field potentials in four structures: medial septum, hippocampus, entorhinal cortex and amygdala were analyzed when AM404 (120nmol), URB597 (4.8nmol) or AM251 (20nmol) were administrated alone or together with 0.4μg of kainic acid. All substances were injected i.c.v. AM404, URB597 or AM251 administered alone did not alter markedly local field potentials of all four studied structures in the long-term compared with their basal activity. AM404 and URB597 significantly alleviated kainic acid-induced SE, decreasing behavioral manifestations, duration of seizure events and SE in general without changing the amplitude of local field potentials. AM251 did not produce distinct effects on SE in terms of our experimental paradigm. There was no apparent change of the seizure initiation pattern when kainic acid was coadministrated with AM404, URB597 or AM251. The present study provides electrophysiologic and behavioral evidences that inhibition of endocannabinoid metabolism plays a protective role against kainic acid-induced SE and may be employed for therapeutic purposes. Further investigations of the influences of cannabinoid-related compounds on SE genesis and especially epileptogenesis are required.

Upregulation of RBFOX1 in the malformed cortex of patients with intractable epilepsy and in cultured rat neurons

Mutations in RNA-binding Fox 1 (RBFOX1) are known to be associated with neurodevelopmental disorders including epilepsy, mental retardation and autism spectrum disorder. The deletion of the Rbfox1 gene in mice has been shown to result in heightened susceptibility to seizures. However, other studies have revealed mutations or the downregulation of RBFOX1 in specimens obtained from patients with epilepsy or malformations of cortical development (MCD). Generally, the expression of RBFOX1 varies according to tissue type. In this study, we demonstrated the upregulation of RBFOX1 protein in the cortex of patients with MCD and intractable epilepsy. Electrophysiological recordings of cultured rat cortical neurons with increased Rbfox1 expression also revealed a significantly increased amplitude of action potential (AP) and Na⁺ current density. Some of these neurons (26.32%) even displayed spontaneous, recurrent, epileptiform discharges (SREDs). Additionally, certain Rbfox1 target transcripts associated with epilepsy, including glutamate receptor, ionotropic, N-methyl D-aspartate 1 [Grin1, also known as N-methyl-D-aspartate receptor subunit NR1 (NMDAR1)], synaptosomal-associated protein, 25 kDa (SNAP-25 or Snap25) and sodium channel, voltage gated, type VIII, alpha subunit (Scn8a, also known as Nav1.6) were identified to be upregulated in these cultured cortical neurons with an upregulated Rbfox1 expression. These data suggest that the upregulation of RBFOX1 contributes to neuronal hyperexcitation and seizures. The upregulation of NMDAR1 (Grin1), SNAP-25 (Snap25) and Scn8a may thus be involved in Rbfox1-related neuronal hyperexcitation.

Cannabis and Endocannabinoid Signaling in Epilepsy

The antiepileptic potential of Cannabis sativa preparations has been historically recognized. Recent changes in legal restrictions and new well-documented cases reporting remarkably strong beneficial effects have triggered an upsurge in exploiting medical marijuana in patients with refractory epilepsy. Parallel research efforts in the last decade have uncovered the fundamental role of the endogenous cannabinoid system in controlling neuronal network excitability raising hopes for cannabinoid-based therapeutic approaches. However, emerging data show that patient responsiveness varies substantially, and that cannabis administration may sometimes even exacerbate seizures. Qualitative and quantitative chemical variability in cannabis products and personal differences in the etiology of seizures, or in the pathological reorganization of epileptic networks, can all contribute to divergent patient responses. Thus, the consensus view in the neurologist community is that drugs modifying the activity of the endocannabinoid system should first be tested in clinical trials to establish efficacy, safety, dosing, and proper indication in specific forms of epilepsies. To support translation from anecdote-based practice to evidence-based therapy, the present review first introduces current preclinical and clinical efforts for cannabinoid- or endocannabinoid-based epilepsy treatments. Next, recent advances in our knowledge of how endocannabinoid signaling limits abnormal network activity as a central component of the synaptic circuit-breaker system will be reviewed to provide a framework for the underlying neurobiological mechanisms of the beneficial and adverse effects. Finally, accumulating evidence demonstrating robust synapse-specific pathophysiological plasticity of endocannabinoid signaling in epileptic networks will be summarized to gain better understanding of how and when pharmacological interventions may have therapeutic relevance.

Phytocannabinoids and epilepsy

WHAT IS KNOWN AND OBJECTIVE

Antiepileptic drugs often produce serious adverse effects, and many patients do not respond to them properly. Phytocannabinoids produce anticonvulsant effects in preclinical and preliminary human studies, and appear to produce fewer adverse effects than available antiepileptic drugs. The present review summarizes studies on the anticonvulsant properties of phytocannabinoids.

METHODS

Literature search using the PubMed database to identify studies on phytocannabinoids and epilepsy.

RESULTS AND DISCUSSION

Preclinical studies suggest that phytocannabinoids, especially cannabidiol and cannabidivarin, have potent anticonvulsant effects which are mediated by the endocannabinoid system. Human studies are limited in number and quality, but suggest that cannabidiol has anticonvulsant effects in adult and infantile epilepsy and is well tolerated after prolonged administration.

WHAT IS NEW AND CONCLUSION

Phytocannabinoids produce anticonvulsant effects through the endocannabinoid system, with few adverse effects. Cannabidiol and cannabidivarin should be tested in randomized, controlled clinical trials, especially in infantile epileptic syndromes.

Post-status epilepticus treatment with the cannabinoid agonist WIN 55,212-2 prevents chronic epileptic hippocampal damage in rats

Repeated seizures are often associated with development of refractory chronic epilepsy, the most common form of which is temporal lobe epilepsy. G-protein-coupled cannabinoid receptors (CB1 and CB2 receptors) regulate neuronal excitability and have been shown to mediate acute anticonvulsant effects of cannabinoids in animal models. However, the potential of cannabinoids to prevent chronic neuronal damage and development of epilepsy remains unexplored. We hypothesized that treatment with a CB receptor agonist after an episode of status epilepticus--but before development of spontaneous recurrent seizures--might prevent the development of functional changes that lead to chronic epilepsy. Using the rat pilocarpine model, a therapeutic approach was simulated by administering the CB agonist, WIN 55,212-2 after an episode of status epilepticus. Epileptic behavior was monitored during development of spontaneous recurrent seizures for up to 6 months. Histology, neurochemistry, redox status and NMDA receptor subunit expression were assessed at 6 months after pilocarpine-induced seizures. Sub-acute treatment with WIN 55,212-2 (for 15 days starting 24h after PILO injection) dramatically attenuated the severity, duration and frequency of spontaneous recurrent seizures. Further, in contrast to vehicle-treated animals, hippocampi from WIN 55,212-2-treated animals showed: normal thiol redox state, normal NR2A and NR2B subunit expression, preservation of GABAergic neurons and prevention of abnormal proliferation of GABAergic progenitors. This study shows for the first time that, after a known inciting event, treatment with a compound targeting CB receptors has the potential to prevent the epileptogenic events that result in chronic epileptic damage.

Distinct modulation of the endocannabinoid system upon kainic acid-induced in vivo seizures and in vitro epileptiform bursting

There is clear evidence on the neuroprotective role of the endocannabinoid (eCB) signaling cascade in various models of epilepsy. In particular, increased levels of eCBs protect against kainic acid (KA)-induced seizures. However, the molecular mechanisms underlying this effect and its age-dependence are still unknown. To clarify this issue, we investigated which step of the biosynthetic and catabolic pathways of the eCBs may be responsible for the eCB-mediated neuroprotection in the hippocampus of P14 and P56-70 KA-treated rats. We found that both anandamide and N-palmitoylethanolamine, together with their biosynthetic enzyme significantly increased in the hippocampus of younger KA-treated rats, while decreasing in adults. In contrast, the levels of the other major eCB, 2-arachidonoylglycerol, similar to its biosynthetic enzyme, were higher in the hippocampus of P56-70 compared to P14 rats. In line with these data, extracellular field recordings in CA1 hippocampus showed that enhancement of endogenous AEA and 2-AG significantly counteracted KA-induced epileptiform bursting in P56-70 and P14 rats, respectively. On the contrary, while the CB1R antagonist SR141716 per se did not affect the population spike, it did worsen KA-induced bursts, confirming increased eCB tone upon KA treatment. Altogether these data indicate an age-specific alteration of the eCB system caused by KA and provide insights for the protective mechanism of the cannabinoid system against epileptiform discharges.

Anticonvulsant effects of N-arachidonoyl-serotonin, a dual fatty acid amide hydrolase enzyme and transient receptor potential vanilloid type-1 (TRPV1) channel blocker, on experimental seizures: the roles of cannabinoid CB1 receptors and TRPV1 channels

Selective blockade of anandamide hydrolysis, through the inhibition of the FAAH enzyme, has anticonvulsant effects, which are mediated by CB1 receptors. Anandamide, however, also activates TRPV1 channels, generally with an opposite outcome on neuronal modulation. Thus, we suggested that the dual FAAH and TRPV1 blockade with N-arachidonoyl-serotonin (AA-5-HT) would be efficacious in inhibiting pentylenetetrazole (PTZ)-induced seizures in mice. We also investigated the contribution of CB1 activation and TRPV1 blockade to the overt effect of AA-5-HT. In the first experiment, injection of AA-5-HT (0.3-3.0 mg/kg) delayed the onset and reduced the duration of PTZ (60 mg)-induced seizures in mice. These effects were reversed by pre-treatment with the CB1 antagonist, AM251 (1.0-3.0 mg/kg). Finally, we observed that administration of the selective TRPV1 antagonist, SB366791 (0.1-1 mg/kg), did not entirely mimic AA-5-HT effects. In conclusion, AA-5-HT alleviates seizures in mice, an effect inhibited by CB1 antagonism, but not completely mimicked by TRPV1 blockage, indicating that the overall effect of AA-5-HT seems to depend mainly on CB1 receptors. This may represent a new strategy for the development of drugs against seizures, epilepsies and related syndromes.

Cannabidivarin (CBDV) suppresses pentylenetetrazole (PTZ)-induced increases in epilepsy-related gene expression

To date, anticonvulsant effects of the plant cannabinoid, cannabidivarin (CBDV), have been reported in several animal models of seizure. However, these behaviourally observed anticonvulsant effects have not been confirmed at the molecular level. To examine changes to epilepsy-related gene expression following chemical convulsant treatment and their subsequent control by phytocannabinoid administration, we behaviourally evaluated effects of CBDV (400 mg/kg, p.o.) on acute, pentylenetetrazole (PTZ: 95 mg/kg, i.p.)-induced seizures, quantified expression levels of several epilepsy-related genes (Fos, Casp 3, Ccl3, Ccl4, Npy, Arc, Penk, Camk2a, Bdnf and Egr1) by qPCR using hippocampal, neocortical and prefrontal cortical tissue samples before examining correlations between expression changes and seizure severity. PTZ treatment alone produced generalised seizures (median: 5.00) and significantly increased expression of Fos, Egr1, Arc, Ccl4 and Bdnf. Consistent with previous findings, CBDV significantly decreased PTZ-induced seizure severity (median: 3.25) and increased latency to the first sign of seizure. Furthermore, there were correlations between reductions of seizure severity and mRNA expression of Fos, Egr1, Arc, Ccl4 and Bdnf in the majority of brain regions in the CBDV+PTZ treated group. When CBDV treated animals were grouped into CBDV responders (criterion: seizure severity ≤3.25) and non-responders (criterion: seizure severity >3.25), PTZ-induced increases of Fos, Egr1, Arc, Ccl4 and Bdnf expression were suppressed in CBDV responders. These results provide the first molecular confirmation of behaviourally observed effects of the non-psychoactive, anticonvulsant cannabinoid, CBDV, upon chemically-induced seizures and serve to underscore its suitability for clinical development.

Cellular NAD depletion and decline of SIRT1 activity play critical roles in PARP-1-mediated acute epileptic neuronal death in vitro

Intense poly(ADP-ribose) polymerase-1 (PARP-1) activation was implicated as a major cause of caspase-independent cell death in the hippocampal neuronal culture (HNC) model of acute acquired epilepsy (AE). The molecular mechanisms are quite complicated. The linkage among neuronal death, cellular nicotinamide adenine dinucleotide (NAD) levels, apoptosis-inducing factor (AIF) translocation, SIRT1 expression and activity were investigated here. The results showed that PARP-1 over-activation caused by Mg²⁺-free stimuli led to cellular NAD depletion which could block AIF translocation from mitochondria to nucleus and attenuate neuronal death. Also, SIRT1 deacetylase activity was reduced by Mg²⁺-free treatment, accompanied by elevated ratio of neuronal death, which could be rescued by NAD repletion. These data demonstrated that cellular NAD depletion and decline of SIRT1 activity play critical roles in PARP-1-mediated epileptic neuronal death in the HNC model of acute AE.

CB1 agonists, locally applied to the cortico-thalamic circuit of rats with genetic absence epilepsy, reduce epileptic manifestations

Drugs that modulate the endocannabinoid system and endocannabinoids typically play an anticonvulsant role although some proconvulsant effects have been reported both in humans and animal models. Moreover, no evidence for a role of the cannabinoid system in human absence epilepsy has been found although limited evidence of efficacy in relevant experimental animal models has been documented. This study aims to characterize the role of cannabinoids in specific areas of the cortico-thalamic network involved in oscillations that underlie seizures in a genetic animal model of absence epilepsy, the WAG/Rij rat. We assessed the effects of focal injection of the endogenous cannabinoid, anandamide (AEA), a non-selective CB receptor agonist (WIN55,212) and a selective CB1 receptor antagonist/inverse agonist (SR141716A) into thalamic nuclei and primary somatosensory cortex (S1po) of the cortico-thalamic network. AEA and WIN both reduced absence seizures independently from the brain focal site of infusion while, conversely, rimonabant increased absence seizures but only when focally administered to the ventroposteromedial thalamic nucleus (VPM). These results, together with previous reports, support therapeutic potential for endocannabinoid system modulators in absence epilepsy and highlight that attenuated endocannabinergic function may contribute to the generation and maintenance of seizures. Furthermore, the entire cortico-thalamic network responds to cannabinoid treatment, indicating that in all areas considered, CB receptor activation inhibits the pathological synchronization that subserves absence seizures. In conclusion, our result might be useful for the identification of future drug therapies in absence epilepsy.

Effects of cannabinoids and endocannabinoid hydrolysis inhibition on pentylenetetrazole-induced seizure and electroencephalographic activity in rats

Cannabinoids and drugs that increase endocannabinoid levels inhibit neuronal excitability and restrain epileptic seizures through CB1 receptor activation. Nevertheless, the results have not been entirely consistent, since pro-convulsant effects have also been reported. The present study aimed to further investigate the effects of cannabinoid-related compounds on seizures induced by pentylenetetrazole (PTZ) in rats. Video-EEG recordings were used to determine both electrographic and behavioral thresholds to ictal activity. The animals received injections of WIN-55,212-2 (0.3-3 mg/kg, non-selective) or ACEA (1-4 mg/kg, CB1-selective), two synthetic cannabinoids, or URB-597 (0.3-3 mg/kg), an anandamide-hydrolysis inhibitor (FAAH enzyme inhibitor), followed by PTZ. Both WIN-55,212-2 (1 mg/kg) and ACEA (1-4 mg/kg) reduced the threshold for myoclonic seizures and enhanced epileptiform EEG activity, typical pro-convulsive effects. On the contrary, URB-597 (1 mg/kg) had an anti-convulsive effect, as it increased the threshold for the occurrence of minimal seizures and reduced EEG epileptiform activity. None of the drugs tested altered the tonic-clonic maximal seizure threshold. These data suggest that the effects of CB1 signaling upon seizure activity may depend on how this receptor is activated. Contrary to direct agonists, drugs that increase anandamide levels seem to promote an optimal tonus and represent a promising strategy for treating myoclonic seizures.

Effect of ACEA--a selective cannabinoid CB1 receptor agonist on the protective action of different antiepileptic drugs in the mouse pentylenetetrazole-induced seizure model

Endogenous cannabinoid ligands and cannabinoid CB1 receptor agonists have been shown to exert anticonvulsant effects in various experimental models of epilepsy. The purpose of this study was to determine the effects of arachidonyl-2'-chloroethylamide (ACEA-a highly selective cannabinoid CB1 receptor agonist) on the protective action of clonazepam, ethosuximide, phenobarbital, and valproate against pentylenetetrazole (PTZ)-induced clonic seizures in mice. To ascertain any pharmacokinetic contribution of ACEA to the observed interactions between tested drugs, free (non-protein bound) plasma and total brain concentrations of the antiepileptic drugs were estimated. Additionally, acute adverse-effect profiles of the combination of ACEA and different classical antiepileptic drugs (clonazepam, ethosuximide, phenobarbital and valproate) with respect to motor performance, long-term memory and skeletal muscular strength were measured. Results indicated that ACEA (10mg/kg, i.p.) co-administered with phenylmethylsulfonyl fluoride (PMSF-a substance protecting ACEA against degradation by the fatty-acid hydrolase; 30mg/kg, i.p.) significantly potentiated the anticonvulsant activity of ethosuximide, phenobarbital and valproate in the mouse PTZ-induced clonic seizure model by reducing their median effective doses (ED(50) values) from 122.8mg/kg to 71.7mg/kg (P<0.01; for ethosuximide), from 13.77mg/kg to 5.26mg/kg (P<0.05; for phenobarbital), and from 142.7mg/kg to 87.3mg/kg (P<0.05; for valproate), respectively. In contrast, ACEA (10mg/kg, i.p.) in combination with PMSF (30mg/kg, i.p.) had no impact on the protective action of clonazepam against PTZ-induced seizures in mice. However, ACEA (10mg/kg)+PMSF (30mg/kg) considerably increased free plasma and total brain concentrations of ethosuximide and valproate in mice suggesting a pharmacokinetic nature of interaction between drugs. In contrast, free plasma and total brain concentrations of clonazepam and phenobarbital remained unchanged after ACEA+PMSF administration and thus, indicating pharmacodynamic interactions. Moreover, none of the examined combinations of ACEA (10mg/kg, i.p.)+PMSF (30mg/kg, i.p.) with clonazepam, ethosuximide, phenobarbital, and valproate (at their ED(50) values from the PTZ-induced seizure test) affected motor coordination in the chimney test, long-term memory in the passive avoidance task, and muscular strength in the grip-strength test in mice, indicating no possible acute adverse effects in animals. In conclusion, pharmacodynamic enhancement of the anticonvulsant potency of phenobarbital by ACEA+PMSF is worthy of recommendation for further clinical settings. Pharmacokinetic interactions of ACEA+PMSF with ethosuximide and valproate seem to be responsible for a significant suppression of PTZ-induced seizures in mice. The combination of ACEA+PMSF with clonazepam seems to be neutral from a preclinical viewpoint.

Marijuana, endocannabinoids, and epilepsy: potential and challenges for improved therapeutic intervention

Phytocannabinoids isolated from the cannabis plant have broad potential in medicine that has been well recognized for many centuries. It is presumed that these lipid soluble signaling molecules exert their effects in both the central and peripheral nervous system in large part through direct interaction with metabotropic cannabinoid receptors. These same receptors are also targeted by a variety of endogenous cannabinoids including 2-arachidonoyl glycerol and anandamide. Significant effort over the last decade has produced an enormous advance in our understanding of both the cellular and the synaptic physiology of endogenous lipid signaling systems. This increase in knowledge has left us better prepared to carefully evaluate the potential for both natural and synthetic cannabinoids in the treatment of a variety of neurological disorders. In the case of epilepsy, long standing interest in therapeutic approaches that target endogenous cannabinoid signaling systems are, for the most part, not well justified by available clinical data from human epileptics. Nevertheless, basic science experiments have clearly indicated a key role for endogenous cannabinoid signaling systems in moment to moment regulation of neuronal excitability. Further it has become clear that these systems can both alter and be altered by epileptiform activity in a wide range of in vitro and in vivo models of epilepsy. Collectively these observations suggest clear potential for effective therapeutic modulation of endogenous cannabinoid signaling systems in the treatment of human epilepsy, and in fact, further highlight key obstacles that would need to be addressed to reach that goal.

Inverse relationship of cannabimimetic (R+)WIN 55, 212 on behavior and seizure threshold during the juvenile period

Cannabinoids have anti-convulsant effects in both in vivo and in vitro models of status epilepticus. Since the development of spontaneous seizures and neuronal vulnerability are age-dependent, we hypothesized that the anti-convulsant effects of cannabimimetics are also age-dependent. We administered a single injection of varied doses of (R+)WIN 55,212 (0.5, 1, 5 mg/kg) to postnatal (P) day 20 rats 90 min prior to induction of kainate (KA)-induced status epilepticus. The highest dose of (R+)WIN 55,212 (5 mg/kg) resulted in rapid onset of behavioral stupor, loss of balance, stiffening and immobility while standing on hind legs or laying flat in prone position; lower doses had minimal or no behavioral effect. After KA administration, seizure scores and electroencephalography (EEG) recordings were inversely related to (R+)WIN 55,212 dosage whereby higher doses were associated with high seizures scores and synchronous epileptiform activity and low doses with low seizure scores and diminished spiking in the EEG. Immunohistochemistry revealed a dose-dependent reduction in CB1 receptor expression with increasing concentrations of (R+)WIN 55,212 in presence or absence of KA seizures. Nissl and NeuN staining showed hippocampal injury was attenuated only when seizures were mild following low doses of WIN 55,212 (0.5, 1 mg/kg), consistent with the level of CB1 expression. Since low doses abolished seizures without psychotropic side-effects further study may facilitate a groundbreaking cannabamimetic therapeutic strategy to treat early-life seizures. Higher doses had adverse effects on behavior and failed to prevent seizures and protect CA1 neurons possibly due to inactivation or loss of CB1 receptors.

Acetaminophen inhibits status epilepticus in cultured hippocampal neurons

Status epilepticus (SE) is a major neurological disorder and SE survivors often develop acquired epilepsy and cognitive deficits. Thus, it is important to stop SE and limit brain damage. However, rapid pharmacoresistance develops to anticonvulsants as seizure duration lengthens. Recently, acetaminophen was reported to increase endocannabinoid levels by its conversion to AM 404. Further, cannabinoids are potent anticonvulsants. Here we investigated whether acetaminophen would block SE-like activity in hippocampal neurons. Exposure of cultured hippocampal neurons to a low Mg2+ medium elicits high-frequency epileptiform discharges that exceed 3 Hz (in-vitro SE). Acetaminophen (500 μM) blocks the SE-like activity. CB1 receptor antagonist SR 141716A (1 μM) blocked this inhibitory effect of acetaminophen on SE, indicating that acetaminophen was mediating its anticonvulsant effects through CB1 receptors.

Prolonged cannabinoid exposure alters GABA(A) receptor mediated synaptic function in cultured hippocampal neurons

Developing cannabinoid-based medication along with marijuana's recreational use makes it important to investigate molecular adaptations the endocannabinoid system undergoes following prolonged use and withdrawal. Repeated cannabinoid administration results in development of tolerance and produces withdrawal symptoms that may include seizures. Here we employed electrophysiological and immunochemical techniques to investigate the effects of prolonged CB1 receptor agonist exposure on cultured hippocampal neurons. Approximately 60% of CB1 receptors colocalize to GABAergic terminals in hippocampal cultures. Prolonged treatment with the cannabinamimetic WIN 55,212-2 (+WIN, 1 μM, 24 h) caused profound CB1 receptor downregulation accompanied by neuronal hyperexcitability. Furthermore, prolonged +WIN treatment resulted in increased GABA release as indicated by increased mIPSC frequency, a diminished GABAergic inhibition as indicated by reduction in mIPSC amplitude and a reduction in GABA(A) channel number. Additionally, surface staining for the GABA(A) β(2/3) receptor subunits was decreased, while no changes in staining for the presynaptic vesicular GABA transporter were observed, indicating that GABAergic terminals remained intact. These findings demonstrate that agonist-induced downregulation of the CB1 receptor in hippocampal cultures results in neuronal hyperexcitability that may be attributed, in part, to alterations in both presynaptic GABA release mechanisms and postsynaptic GABA(A) receptor function demonstrating a novel role for cannabinoid-dependent presynaptic control of neuronal transmission.

Synthetic cannabinoid WIN 55,212-2 mesylate enhances the protective action of four classical antiepileptic drugs against maximal electroshock-induced seizures in mice

The aim of this study was to determine the effect of WIN 55,212-2 mesylate (WIN--a non-selective cannabinoid CB1 and CB2 receptor agonist) on the protective action of four classical antiepileptic drugs (carbamazepine, phenytoin, phenobarbital, and valproate) in the mouse maximal electroshock seizure (MES) model. The results indicate that WIN (10 mg/kg, i.p.) significantly enhanced the anticonvulsant action of carbamazepine, phenytoin, phenobarbital and valproate in the MES test in mice. WIN (5 mg/kg) potentiated the anticonvulsant action of carbamazepine and valproate, but not that of phenytoin or phenobarbital in the MES test in mice. However, WIN administered alone and in combination with carbamazepine, phenytoin, phenobarbital and valproate significantly reduced muscular strength in mice in the grip-strength test. In the passive avoidance task, WIN in combination with phenobarbital, phenytoin and valproate significantly impaired long-term memory in mice. In the chimney test, only the combinations of WIN with phenobarbital and valproate significantly impaired motor coordination in mice. In conclusion, WIN enhanced the anticonvulsant action of carbamazepine, phenytoin, phenobarbital and valproate in the MES test. However, the utmost caution is advised when combining WIN with classical antiepileptic drugs due to impairment of motor coordination and long-term memory and/or reduction of skeletal muscular strength that might appear during combined treatment.

Selective reduction of cholecystokinin-positive basket cell innervation in a model of temporal lobe epilepsy

Perisomatic inhibition from basket cells plays an important role in regulating pyramidal cell output. Two major subclasses of CA1 basket cells can be identified based on their expression of either cholecystokinin (CCK) or parvalbumin. This study examined their fates in the mouse pilocarpine model of temporal lobe epilepsy. Overall, immunohistochemical labeling of GABAergic boutons in the pyramidal cell layer of CA1 was preserved in the mouse model. However, CCK-labeled boutons in this layer were chronically reduced, whereas parvalbumin-containing boutons were conserved. Immunohistochemistry for cannabinoid receptor 1 (CB(1)), another marker for CCK-containing basket cells, also labeled fewer boutons in pilocarpine-treated mice. Hours after status epilepticus, electron microscopy revealed dark degenerating terminals in the pyramidal cell layer with lingering CCK and CB(1) immunoreactivity. In mice with recurrent seizures, carbachol-induced enhancement of spontaneous IPSCs (sIPSCs) originating from CCK-containing basket cells was accordingly reduced in CA1 pyramidal cells. By suppressing sIPSCs from CCK-expressing basket cells, a CB(1) agonist reverted the stimulatory effects of carbachol in naive mice to levels comparable with those observed in cells from epileptic mice. The agatoxin-sensitive component of CA1 pyramidal cell sIPSCs from parvalbumin-containing interneurons was increased in pilocarpine-treated mice, and miniature IPSCs were reduced, paralleling the decrease in CCK-labeled terminals. Altogether, the findings are consistent with selective reduction in perisomatic CA1 pyramidal cell innervation from CCK-expressing basket cells in mice with spontaneous seizures and a greater reliance on persisting parvalbumin innervation. This differential alteration in inhibition may contribute to the vulnerability of the network to seizure activity.

Δ⁹-Tetrahydrocannabivarin suppresses in vitro epileptiform and in vivo seizure activity in adult rats

PURPOSE

We assessed the anticonvulsant potential of the phytocannabinoid Δ⁹-tetrahydrocannabivarin (Δ⁹-THCV) by investigating its effects in an in vitro piriform cortex (PC) brain slice model of epileptiform activity, on cannabinoid CB1 receptor radioligand-binding assays and in a generalized seizure model in rats.

METHODS

Δ⁹-THCV was applied before (10 μm Δ⁹-THCV) or during (10-50 μm Δ⁹-THCV) epileptiform activity induced by Mg²(+) -free extracellular media in adult rat PC slices and measured using multielectrode array (MEA) extracellular electrophysiologic techniques. The actions of Δ⁹-THCV on CB1 receptors were examined using [³H]SR141716A competition binding and [³⁵S]GTPγS assays in rat cortical membranes. Effects of Δ⁹-HCV (0.025-2.5 mg/kg) on pentylenetetrazole (PTZ)-induced seizures in adult rats were also assessed.

RESULTS

After induction of stable spontaneous epileptiform activity, acute Δ⁹ -THCV application (≥ 20 μm) significantly reduced burst complex incidence and the amplitude and frequency of paroxysmal depolarizing shifts (PDSs). Furthermore, slices pretreated with 10 μm Δ⁹-THCV prior to induction of epileptiform activity exhibited significantly reduced burst complex incidence and PDS peak amplitude. In radioligand-binding experiments, Δ⁹-THCV acted as a CB1 receptor ligand, displacing 0.5 nm [³H]SR141716A with a Ki∼290 nm, but exerted no agonist stimulation of [³⁵S]GTPγS binding. In PTZ-induced seizures in vivo, 0.25 mg/kg Δ⁹-THCV significantly reduced seizure incidence.

DISCUSSION

These data demonstrate that Δ⁹-THCV exerts antiepileptiform and anticonvulsant properties, actions that are consistent with a CB1 receptor-mediated mechanism and suggest possible therapeutic application in the treatment of pathophysiologic hyperexcitability states.

Cerebrospinal fluid levels of the endocannabinoid anandamide are reduced in patients with untreated newly diagnosed temporal lobe epilepsy

PURPOSE

The endocannabinoid system is involved in excitatory/inhibitory balance mechanisms within the central nervous system (CNS). Growing evidence shows that its perturbation leads to development of epileptic seizures in experimental models, thus indicating that endocannabinoids play an intrinsic protective role in suppressing pathologic neuronal excitability. Experimental data also demonstrate that the endocannabinoid anandamide (AEA) can antagonize epileptic discharges in hippocampal tissue. The objective of our study was to measure endocannabinoids levels in the cerebrospinal fluid (CSF) of drug-naive patients affected by temporal lobe epilepsy (TLE).

METHODS

We measured the levels of both AEA and the other endocannabinoid, 2-arachidonoylglycerol (2-AG), in the CSF of drug-naive patients with TLE.

RESULTS

A significant reduction of AEA was found in the CSF of patients with compared with healthy controls (epileptic patients = 2.55 +/- 1.78 pmol/ml; healthy controls = 11.65 +/- 7.53 pmol/ml; n = 9 for both groups, p < 0.01). 2-AG levels, however, were not affected (epileptic patients = 209.5 +/- 146.56; healthy controls = 159.6 +/- 110.2) (n = 6 for both groups, p = 0.48).

DISCUSSION

Our findings seem to be consistent with experimental evidence demonstrating a significant prevention of epileptic seizures induced by endocannabinoids in models of epilepsy. Furthermore, they support the hypothesis that AEA may be involved in its pathogenesis, suggesting a hypothetical primary impairment of the endocannabinoid system in untreated TLE. The actual role of this in vivo dysregulation still remains unclear.

Pursuing paradoxical proconvulsant prophylaxis for epileptogenesis

There are essentially two potential treatment options for any acquired disorder: symptomatic or prophylactic. For acquired epilepsies that follow a variety of different brain insults, there remains a complete lack of prophylactic treatment options, whereas at the same time these epilepsies are notoriously resistant, once they have emerged, to symptomatic treatments with antiepileptic drugs. The development of prophylactic strategies is logistically challenging, both for basic researchers and clinicians. Nevertheless, cannabinoid-targeting drugs provide a very interesting example of a system within the central nervous system (CNS) that can have very different acute and long-term effects on hyperexcitability and seizures. In this review, we outline research on cannabinoids suggesting that although cannabinoid antagonists are acutely proconvulsant, they may have beneficial effects on long-term hyperexcitability following brain insults of multiple etiologies, making them promising candidates for further investigation as prophylactics against acquired epilepsy. We then discuss some of the implications of this finding on future attempts at prophylactic treatments, specifically, the very short window within which prevention may be possible, the possibility that traditional anticonvulsants may interfere with prophylactic strategies, and the importance of moving beyond anticonvulsants-even to proconvulsants-to find the ideal preventative strategy for acquired epilepsy.