Effects of tetrahydrocannabinols on kindled amygdaloid seizures and photogenic seizures in Senegalese baboons, Papio papio

Cannabinoid treatments in epilepsy and seizure disorders

Cannabis has been used to treat convulsions and other disorders since ancient times. In the last few decades, preclinical animal studies and clinical investigations have established the role of cannabidiol (CBD) in treating epilepsy and seizures and support potential therapeutic benefits for cannabinoids in other neurological and psychiatric disorders. Here, we comprehensively review the role of cannabinoids in epilepsy. We briefly review the diverse physiological processes mediating the central nervous system response to cannabinoids, including Δ9-tetrahydrocannabinol (Δ9-THC), cannabidiol, and terpenes. Next, we characterize the anti- and proconvulsive effects of cannabinoids from animal studies of acute seizures and chronic epileptogenesis. We then review the clinical literature on using cannabinoids to treat epilepsy, including anecdotal evidence and case studies as well as the more recent randomized controlled clinical trials that led to US Food and Drug Administration approval of CBD for some types of epilepsy. Overall, we seek to evaluate our current understanding of cannabinoids in epilepsy and focus future research on unanswered questions.

Delta-8, a Cannabis-Derived Tetrahydrocannabinol Isomer: Evaluating Case Report Data in the Food and Drug Administration Adverse Event Reporting System (FAERS) Database

Purpose

The aim of this study was to characterize the frequency of adverse effects where delta-8 tetrahydrocannabinol (D8-THC) was identified as a possible suspect drug in the FDA Adverse Event Reporting System (FAERS) database.

Methods

A case-series design was used.

Results

A total of 183 cases listed D8-THC as a suspect drug in FAERS as of June 30, 2021. The most common events included dyspnea, respiratory disorder, and seizure. The reporting odds ratios were consistently and significantly greater than 2, a 2-fold increase from 2019 to 2021, indicating a potential safety signal.

Conclusion

The first report of D8-THC, in the FAERS database, as a suspect drug appears to be in 2011. Overall, there are 183 total cases listing D8-THC as a suspect drug in the FAERS database as of June 30, 2021. Of the 183 cases, most were respiratory in nature.

Antiseizure effects of the cannabinoids in the amygdala-kindling model

OBJECTIVE

Focal impaired awareness seizures (FIASs) are the most common seizure type in adults and are often refractory to medication. Management of FIASs is clinically challenging, and new interventions are needed for better seizure control. The amygdala-kindling model is a preclinical model of FIASs with secondary generalization. The present study assessed the efficacy of cannabidiol (CBD), ∆9-tetrahydrocannabinol (THC), and a combination of CBD and THC in a 15:1 ratio at suppressing focal and secondarily generalized seizures in the amygdala-kindled rat.

METHODS

Fully kindled, male Sprague Dawley rats, with bipolar electrodes implanted in the right amygdala, were given either CBD (0-320 mg/kg), THC (0-40 mg/kg), or a combination of CBD and THC (15:1 ratio, multiple doses) intraperitoneally. Suprathreshold kindling stimulation was administered 1 h (THC) or 2 h (CBD) after drug injection, and outcomes were assessed using focal electroencephalographic recording and the Racine seizure scale.

RESULTS

CBD alone produced a partial suppression of both generalized seizures (median effective dose [ED₅₀ ] = 283 mg/kg) and focal seizures (ED₄₀ = 320 mg/kg) at doses that did not produce ataxia. THC alone also produced partial suppression of generalized (ED₅₀ = 10 mg/kg) and focal (ED₅₀ = 30 mg/kg) seizures, but doses of 10 mg/kg and above produced hypolocomotion, although not ataxia. The addition of a low dose of THC to CBD (15:1) left-shifted the CBD dose-response curve, producing much lower ED₅₀ s for both generalized (ED₅₀ = 26 + 1.73 mg/kg) and focal (ED₅₀ = 40 + 2.66 mg/kg) seizures. No ataxia or hypolocomotion was seen at these doses of the CBD + THC combination.

SIGNIFICANCE

CBD and THC both have antiseizure properties in the amygdala-kindling model, although THC produces suppression of the amygdala focus only at doses that produce hypolocomotion. The addition of small amounts of THC greatly improves the effectiveness of CBD. A combination of CBD and THC might be useful for the management of FIASs.

Therapeutic effects of cannabinoids in animal models of seizures, epilepsy, epileptogenesis, and epilepsy-related neuroprotection

The isolation and identification of the discrete plant cannabinoids in marijuana revived interest in analyzing historical therapeutic claims made for cannabis in clinical case studies and anecdotes. In particular, sources as old as the 11th and 15th centuries claimed efficacy for crude marijuana extracts in the treatment of convulsive disorders, prompting a particularly active area of preclinical research into the therapeutic potential of plant cannabinoids in epilepsy. Since that time, a large body of literature has accumulated describing the effects of several of the >100 individual plant cannabinoids in preclinical models of seizures, epilepsy, epileptogenesis, and epilepsy-related neuroprotection. We surveyed the literature for relevant reports of such plant cannabinoid effects and critically reviewed their findings. We found that acute CB₁R agonism in simple models of acute seizures in rodents typically produces anti-convulsant effects whereas CB₁R antagonists exert converse effects in the same models. However, when the effects of such ligands are examined in more complex models of epilepsy, epileptogenesis and neuroprotection, a less simplistic narrative emerges. Here, the complex interactions between (i) brain regions involved in a given model, (ii) relative contributions of endocannabinoid signaling to modulation of synaptic transmission in such areas, (iii) multi-target effects, (iv) cannabinoid type 1 and type 2 receptor signaling interactions and, (v) timing, (vi) duration and (vii) localization of ligand administration suggest that there is both anti-epileptic therapeutic potential and a pro-epileptic risk in up- and down-regulation of endocannabinoid signaling in the central nervous system. Factors such receptor desensitization and specific pharmacology of ligands used (e.g. full vs partial agonists and neutral antagonists vs inverse agonists) also appear to play an important role in the effects reported. Furthermore, the effects of several plant cannabinoids, most notably cannabidiol (CBD) and cannabidavarin (CBDV), in models of seizures, epilepsy, epileptogenesis, and neuroprotection are less ambiguous, and consistent with reports of therapeutically beneficial effects of these compounds in clinical studies. However, continued paucity of firm information regarding the therapeutic molecular mechanism of CBD/CBDV highlights the continued need for research in this area in order to identify as yet under-exploited targets for drug development and raise our understanding of treatment-resistant epilepsies. The recent reporting of positive results for cannabidiol treatment in two Phase III clinical trials in treatment-resistant epilepsies provides pivotal evidence of clinical efficacy for one plant cannabinoid in epilepsy. Moreover, risks and/or benefits associated with the use of unlicensed Δ⁹-THC containing marijuana extracts in pediatric epilepsies remain poorly understood. Therefore, in light of these paradigm-changing clinical events, the present review's findings aim to drive future drug development for newly-identified targets and indications, identify important limitations of animal models in the investigation of plant cannabinoid effects in the epilepsies, and focuses future research in this area on specific, unanswered questions regarding the complexities of endocannabinoid signaling in epilepsy. This article is part of a Special Issue titled Cannabinoids and Epilepsy.

Cannabinoids as hippocampal network administrators

Extensive pioneering studies performed in the hippocampus have greatly contributed to our knowledge of an endogenous cannabinoid system comprised of the molecular machinery necessary to process endocannabinoid lipid messengers and their associated cannabinoid receptors. Moreover, a foundation of knowledge regarding the function of hippocampal circuits, and its role in supporting synaptic plasticity has facilitated our understanding of the roles cannabinoids play in the diverse behaviors in which the hippocampus participates, in both normal and pathological states. In this review, we present an historical overview of research pertaining to the hippocampal cannabinoid system to provide context in which to understand the participation of the hippocampus in cognition, behavior, and epilepsy. We also examine potential roles for the hippocampal formation in mediating dysfunctional behavior, and assert that these phenomena reflect disordered physiological activity within the hippocampus and its interactions with other brain regions after exposure to synthetic cannabinoids, and the phytocannabinoids found in marijuana, such as Δ⁹-THC and cannabidiol. In this regard, we examine contemporary hypotheses concerning the hippocampal endocannabinoid system's participation in psychotic disorders, schizophrenia, and epilepsy, and examine cannabinoid-sensitive cellular mechanisms contributing to coherent network oscillations as potential contributors to these disorders. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

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.

Marijuana: A Time-Honored but Untested Treatment for Epilepsy

The biology of the endocannabinoid system in the brain provides a possible basis for a beneficial pharmacological effect of marijuana on seizures. However, evidence for efficacy of cannabis treatment of epilepsy is anecdotal because no acceptable randomized controlled trials have been done. Proper dosage and means of administration remain unknown. Cannabis is safer than other controlled substances, including tobacco or alcohol, and appears to be relatively safe compared with most pharmaceuticals used to treat epilepsy. This is a review of this topic from a Canadian perspective.

The case for medical marijuana in epilepsy

Charlotte, a little girl with SCN1A-confirmed Dravet syndrome, was recently featured in a special that aired on CNN. Through exhaustive personal research and assistance from a Colorado-based medical marijuana group (Realm of Caring), Charlotte's mother started adjunctive therapy with a high concentration cannabidiol/Δ(9) -tetrahydrocannabinol (CBD:THC) strain of cannabis, now known as Charlotte's Web. This extract, slowly titrated over weeks and given in conjunction with her existing antiepileptic drug regimen, reduced Charlotte's seizure frequency from nearly 50 convulsive seizures per day to now 2-3 nocturnal convulsions per month. This effect has persisted for the last 20 months, and Charlotte has been successfully weaned from her other antiepileptic drugs. We briefly review some of the history, preclinical and clinical data, and controversies surrounding the use of medical marijuana for the treatment of epilepsy, and make a case that the desire to isolate and treat with pharmaceutical grade compounds from cannabis (specifically CBD) may be inferior to therapy with whole plant extracts. Much more needs to be learned about the mechanisms of antiepileptic activity of the phytocannabinoids and other constituents of Cannabis sativa.

Prevention of plasticity of endocannabinoid signaling inhibits persistent limbic hyperexcitability caused by developmental seizures

Depolarization-induced suppression of inhibition (DSI) is an endocannabinoid-mediated short-term plasticity mechanism that couples postsynaptic Ca2+ rises to decreased presynaptic GABA release. Whether the gain of this retrograde synaptic mechanism is subject to long-term modulation by glutamatergic excitatory inputs is not known. Here, we demonstrate that activity-dependent long-term DSI potentiation takes place in hippocampal slices after tetanic stimulation of Schaffer collateral synapses. This activity-dependent, long-term plasticity of endocannabinoid signaling was specific to GABAergic synapses, as it occurred without increases in the depolarization-induced suppression of excitation. Induction of tetanus-induced DSI potentiation in vitro required a complex pathway involving AMPA/kainate and metabotropic glutamate receptor as well as CB1 receptor activation. Because DSI potentiation has been suggested to play a role in persistent limbic hyperexcitability after prolonged seizures in the developing brain, we used these mechanistic insights into activity-dependent DSI potentiation to test whether interference with the induction of DSI potentiation prevents seizure-induced long-term hyperexcitability. The results showed that the in vitro, tetanus-induced DSI potentiation was occluded by previous in vivo fever-induced (febrile) seizures, indicating a common pathway. Accordingly, application of CB1 receptor antagonists during febrile seizures in vivo blocked the seizure-induced persistent DSI potentiation, abolished the seizure-induced upregulation of CB1 receptors, and prevented the emergence of long-term limbic hyperexcitability. These results reveal a new form of activity-dependent, long-term plasticity of endocannabinoid signaling at perisomatic GABAergic synapses, and demonstrate that blocking the induction of this plasticity abolishes the long-term effects of prolonged febrile seizures in the developing brain.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Activation of the cannabinoid type-1 receptor mediates the anticonvulsant properties of cannabinoids in the hippocampal neuronal culture models of acquired epilepsy and status epilepticus

Cannabinoids have been shown to have anticonvulsant properties, but no studies have evaluated the effects of cannabinoids in the hippocampal neuronal culture models of acquired epilepsy (AE) and status epilepticus (SE). This study investigated the anticonvulsant properties of the cannabinoid receptor agonist R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolol[1,2,3 de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone (WIN 55,212-2) in primary hippocampal neuronal culture models of both AE and SE. WIN 55,212-2 produced dose-dependent anticonvulsant effects against both spontaneous recurrent epileptiform discharges (SRED) (EC50 = 0.85 microM) and SE (EC50 = 1.51 microM), with total suppression of seizure activity at 3 microM and of SE activity at 5 microM. The anticonvulsant properties of WIN 55,212-2 in these preparations were both stereospecific and blocked by the cannabinoid type-1 (CB1) receptor antagonist N-(piperidin-1-yl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride (SR141716A; 1 microM), showing a CB1 receptor-dependent pathway. The inhibitory effect of WIN 55,212-2 against low Mg2+-induced SE is the first observation in this model of total suppression of SE by a selective pharmacological agent. The clinically used anticonvulsants phenytoin and phenobarbital were not able to abolish low Mg2+-induced SE at concentrations up to 150 microM. The results from this study show CB1 receptor-mediated anticonvulsant effects of the cannabimimetic WIN 55,212-2 against both SRED and low Mg2+-induced SE in primary hippocampal neuronal cultures and show that these in vitro models of AE and SE may represent powerful tools to investigate the molecular mechanisms mediating the effects of cannabinoids on neuronal excitability.

The sleep lipid oleamide may represent an endogenous anticonvulsant: an in vitro comparative study in the 4-aminopyridine rat brain-slice model

cis-Oleamide (cOA) is a putative endocannabinoid, which modulates GABA(A) receptors, Na+ channels and gap-junctions (important targets for clinical and experimental anticonvulsants). Here we address the hypothesis that cOA possesses seizure limiting properties and might represent an endogenous anticonvulsant. Field potentials were recorded from the rat hippocampus and visual cortex. The effects of cOA, were compared to carbamazepine (CBZ), pentobarbital (PB) and carbenoxolone (CRX) on 4-Aminopyridine(4AP)-induced epileptiform discharges. CBZ (100 microM), PB (50 microM) and CRX (100 microM), but not cOA (64 microM), significantly attenuated the duration of the evoked epileptiform discharges in CA1. Interictal activity in CA3 was significantly depressed by CRX and cOA (irreversible by AM251), increased by CBZ and remained unaffected by PB. CBZ, PB and CRX abolished spontaneous ictal events and attenuated evoked ictal discharges in the visual cortex. cOA did not abolish spontaneous ictal events, but significantly (albeit weakly) reduced the duration of evoked ictal events. cOA and CRX, in contrast to CBZ or PB, caused a significant delay in the development of the evoked (tonic phase) epileptiform discharges. The weak effects of cOA seem independent of cannabinoid (CB1) receptors. Enzymatic cleavage and lack of specific antagonists for cOA confound simple interpretations of its actions in slices. Its high lipophilicity, imposing a permeability barrier, may also explain the lack of anticonvulsant activity. The effects of cOA may well be masked by release of the endogenous ligand upon ictal depolarisation as we demonstrate here for established endocannabinoids. cOA does not possess profound antiepileptic actions in our hands compared to CBZ, PB or CRX.

Local pressure application of cannabinoid agonists increases spontaneous activity of rat substantia nigra pars reticulata neurons without affecting response to iontophoretically-applied GABA

This study tested the hypothesis that cannabinoid agonists, applied locally into the pars reticulata of substantia nigra (SNpr), could modulate striatonigral transmission, without affecting the response of SNpr neurons to iontophoretically-applied GABA. Multibarreled glass capillary electrode assemblies were used for extracellular recording of the spontaneous electrical activity of single SNpr cells in anesthetized rats. Local pressure ejection of the cannabinoid agonists Win 55212-2 (WIN2) and CP 55940 increased SNpr spontaneous firing rate by 13-46%, similar to the effects of systemic injections. Neither WIN2 nor CP 55940 had an effect on the slowing of SNpr neuron activity in response to iontophoretic GABA. Local pressure application of Win 55212-3 (the much less active enantiomer of WIN2) produced an insignificant decrease in SNpr firing rate. Similarly, locally applied vehicle (45% 2-hydroxypropyl-beta-cyclodextrin) produced insignificant decreases in SNpr firing. A second application of cannabinoid agonist produced a much smaller effect, suggesting desensitization. Increasing the interval between CP 55940 applications to 45 min showed recovery of sensitivity to the agonist. Local application of the cannabinoid antagonist, SR 141716A, significantly decreased spontaneous cell firing by 34%. CP 55940, when given immediately following or concurrently with the antagonist application failed to produce the expected increase in discharge rate over baseline. A second application of CP 55940 45 min later produced a 26% increase in firing rate. Bicuculline methiodide (BMI) was applied locally causing a significant increase in SNpr cell firing. CP 55940, when locally administered concurrently with bicuculline methiodide, had no further effect on the firing rate of the cell. Based on the reported presynaptic localization of cannabinoid receptors in SNpr, these findings suggest that cannabinoids act within the SNpr to modulate striatonigral neurotransmission presynaptically. The effect of SR 141716A suggests that an endogenous cannabinoid may mediate striato-nigral transmission.

The ontogeny of delta-9-tetrahydrocannabinol responsiveness in the rabbit

An autosomal recessive condition (thc/thc) in our closed colony of New Zealand White rabbits (Uaz:NZW-thc) results in nonfatal, behavioral convulsions following intravenous (i.v.) injections of delta-9-tetrahydrocannabinol (THC) and other psychoactive cannabinoids of marijuana. The ontogeny of the convulsive response was evaluated in potential THC-seizure-susceptible (SS) rabbits from postnatal Days (PN) 15-548. Ages of nonsusceptibility (PN 15-23), partial susceptibility (PN 24-38), and complete susceptibility (PN 39-548) were found. Also, open-field activity was determined in PN 14-25 THC-SS and THC-seizure-resistant (SR) rabbits. Administration of THC during the seizure-insensitive period resulted in genotype-dependent alternations in photocell activity and sprawling.

Effects of marihuana cannabinoids on seizure activity in cobalt-epileptic rats

Rats rendered chronically epileptic by bilateral implantation of cobalt into frontal cortices were simultaneously prepared with permanent electrodes for longitudinal recording of the electroencephalogram (EEG) and electromyogram (EMG). Delta-8-tetrahydrocannabinol (delta-8-THC; 10 mg/kg), delta-9-tetrahydrocannabinol (delta-9-THC; 10 mg/kg), cannabidiol (CBD; 60 mg/kg), or polyvinylpyrrolidone (PVP) vehicle (2 ml/kg) was administered IP twice daily from day 7 through 10 after cobalt implantation, at which time generalized seizure activity in non-treated cobalt-epileptic rats was maximal. Relative to PVP-treated controls, CBD did not alter the frequency of appearance of seizures during the course of repeated administration. In contrast, both delta-8-THC and delta-9-THC markedly reduced the incidence of seizures on the first and second days of administration. Interictal spiking during this period, on the other hand, was actually enhanced. On the third and fourth days, tolerance to the effect on seizures was evident, with a return of seizure frequency of THC-treated rats to values not significantly different from those of controls. Unlike the effect on seizures, no tolerance developed to the marked suppression of rapid eye movement (REM) sleep induces by delta-8-THC and delta-9-THC. REM sleep remained reduced in the treated animals during the first 2 days after termination of THC administration. In contrast, REM sleep time was unaffected by repeated administration of CBD. These results suggest that delta-8-THC and delta-9-THC exert their initial anticonvulsant effect by limiting the spread of epileptogenic activity originating from the cobalt focus.

Electrophysiologic properties of the cannabinoids

The effects of the psychoactive cannabinoid delta 9-tetrahydrocannabinol (THC) and the nonpsychoactive cannabinoid cannabidiol (CBD) were investigated comparatively on electrically caused transcallosal cortical evoked responses, electrically induced limbic after discharges, photically evoked cortical afterdischarges, spontaneous cortical focal epileptic potentials, and spinal monosynaptic reflexes. In each system, THC produced central excitation; for example, the drug's responses ranged from enhancement of synaptic transmission to precipitation of frank convulsions. In addition to central nervous system stimulation, THC usually elicited depression; the qualitative character of the effect of the drug was dependent upon the dosage and the test system. In contrast to THC, cannabidiol generated no CNS excitation: it was either depressant or inert in these test systems. The results clearly demonstrate the complexity of the CNS properties of THC and the selectivity of the depressant properties of cannabidiol; moreover, the data illustrate the wide range of neuropharmacologic responses that potentially any cannabinoid can effect.

The cannabinoids as potential antiepileptics

Comparative studies of the anticonvulsant properties of the cannabinoids and prototype antiepileptic drugs in numerous animal seizure models demonstrate that (1) as an anticonvulsant, cannabidiol (CBD), in contrast to delta 9-tetrahydrocannabinol (THC), is relatively selective in terms of both central nervous system (CNS), depressant and excitatory properties; (2) the potency of cannabidiol, unlike that of phenytoin and phenobarbital, varies greatly with the species; (3) the large potency difference between the cannabinoids and the antiepileptics in the mouse appears to be due to dispositional differences, because brain concentrations of all the drugs are very similar; (4) tolerance to the anticonvulsant properties of cannabidiol is not a prominent feature; in three seizure models, tolerance developed in one, but "reverse tolerance" developed in the other two; and (5) the results of a study of the electrophysiologic mechanisms of action indicate that cannabidiol produces some unique effects and that its spectrum of antiepileptic activity may be different from that of the prototype drugs. The anticonvulsant nature of cannabidiol suggests that it has a therapeutic potential in at least three of the four major types of epilepsy: grand mal, cortical focal, and complex partial seizures.

Excitatory and depressant effects of delta 9-tetrahydrocannabinol and cannabidiol on cortical evoked responses in the conscious rat

The influences of delta 9-tetrahydrocannabinol (THC) and cannabidiol on electrically evoked cortical potentials of conscious rats with chronically implanted electrodes were investigated. Specifically, the cannabinoids' effects on a transcallosal evoked response were compared with those of ethosuximide, phenytoin, and pentylenetetrazol. THC produced dose-related opposite effects: Low doses increased the amplitude of the response, whereas higher doses reduced the response. Other drugs that can cause or exacerbate seizures, i. e., phenytoin and pentylenetetrazol, also increased the amplitude of the cortical response. In contrast, cannabidiol, over a wide dosage range, caused only depression. Ethosuximide, like cannabidiol, elicited a depressant effect. The data indicate that under the conditions of the present investigation, cannabidiol shares electrophysiological properties with ethosuximide but not with phenytoin, and that cannabidiol is a relatively selective, centrally acting drug. In addition, our findings support the suggestion that augmentation of neurotransmission in central pathways may contribute to the convulsant actions of THC, and the cannabinoids' depressant effects may, at least partially, account for their anticonvulsant actions.

Frontal kindling in rabbits and its influence on visual and auditory evoked response

Frontal kindling in rabbits, prolongation of the duration of afterdischarge concomitant and clinical manifestations and the epileptic foci (primary and independent secondary foci) were revealed. Auditory and visual evoked responses were recorded after completion of the kindling phenomenon. 1. Electrical stimulations, 300 microA, 60 Hz. 1 msec in duration, 2 sec train, were applied once a day. Clinical manifestations were divided into five stages: 1) the arrest of behavior or no response, 2) the adversive movement with a tonic and/or clonic convulsion of left paw, 3) the adversive movement following mastication, facial spasms and postictal stupor, 4) falling down abruptly and generalized convulsive seizure, and 5) generalized seizure followed by rotatory movement, vocalization and myoclonus. The appearance of five generalized convulsions was defined as a completion of the kindling phenomenon. 2. The duration of afterdischarge increased stepwisely from 2--3 sec to more than 400 sec. However, there was no constant duration of AD even though the animal showed generalized convulsion after completion of the kindling phenomenon. 3. Visual and auditory evoked responses were recorded after completion of kindling. There was a change in the auditory evoked response but not in the visual. A shortening of the latency of P2 component (73.3 msec in peak latency), N2 component (146.7 msec in peak latency) and amplification of the amplitude of N2 component were noticed. Thus, the intermittent weak electrical stimulation on the frontal cortex in rabbits induced generalized convulsion and produced primary and independent secondary epileptic focus on EEG, and the change of auditory evoked response was recognized in kindled animals.

The influence of cannabidiol and delta 9-tetrahydrocannabinol on cobalt epilepsy in rats

The mechanisms of the anticonvulsant activity of cannabidiol (CBD) and the central excitation of delta 9-tetrahydrocannabinol (delta 9-THC) were investigated electrophysiologically with conscious, unrestrained cobalt epileptic rats. The well-known antiepileptics, trimethadione (TMO), ethosuximide (ESM), and phenytoin (PHT), were included as reference drugs. Direct measurements were made of spontaneously firing, epileptic potentials from a primary focus on the parietal cortex and convulsions were monitored visually. ESM and TMO decreased the frequency of focal potentials, but PHT and CBD exerted no such effect. Although CBD did not suppress the focal abnormality, it did abolish jaw and limb clonus; in contrast, delta 9-THC markedly increased the frequency of focal potentials, evoked generalized bursts of polyspikes, and produced frank convlusions. 11-OH-delta 9-THC, the major metabolite of delta 9-THC, displayed only one of the excitatory properties of the parent compound: production of bursts of polyspikes. In contrast to delta 9-THC and its 11-OH metabolite, CBD, even in very high doses, did not induce any excitatory effects or convulsions. The present study provides the first evidence that CBD exerts anticonvulsant activity against the motor manifestations of a focal epilepsy, and that the mechanism of the effect may involve a depression of seizure generation or spread in the CNS.

An electrophysiological analysis of the anticonvulsant action of cannabidiol on limbic seizures in conscious rats

The effects of cannabidiol (CBD) on electrically evoked kindled seizures were studied in conscious, unrestrained rats with chronically implanted cortical and limbic electrodes, and the results were compared with those of delta 9-tetrahydrocannabinol (delta 9-THC), phenytoin (PHT), and ethosuximide (ESM). All drugs were anticonvulsant, but there were marked differences in their effects on afterdischarge (AD) threshold, duration, and amplitude. CBD, like PHT and delta 9-THC, elevated the AD threshold; in contrast, ESM decreased the threshold but suppressed AD spread. CBD, however, also resembled ESM inasmuch as both drugs decreased AD duration and amplitude. Electrophysiologically, the antiseizure effects of CBD were a combination of those of PHT and ESM. The combination of effects may account for the observation that CBD was the most efficacious of the drugs tested against limbic ADs and convulsions. Other properties of CBD were also noted: For example, compared with delta 9-THC, it is a much more selective anticonvulsant vis-à-vis motor toxicity. CBD also lacks the CNS excitatory effects produced by delta 9-THC, PHT, and ESM. These characteristics, combined with its apparently unique set of electrophysiological properties, support the suggestion that CBD has therapeutic potential as an antiepileptic.

Antiepileptic and prophylactic effects of tetrahydrocannabinols in amygdaloid kindled rats

The antiepileptic and prophylactic effects of delta9-tetrahydrocannabinol (delta9-THC) and delta8-THC were examined in rats that developed generalized seizures in response to intermittent electrical stimulation of the amygdala (kindling). Both isomers of the THC were able to acutely suppress kindled seizures, but consistent antiepileptic effects were obtained only with high, toxic dosages. Tolerance to the antiepileptic effects of THC developed very rapidly when the drugs were give repeatedly, and there was evidence that the repeated administration of a high dosage of delta9-THC resulted in a state of acute physical dependence. Administration of the isomers of THC during seizure development resulted in a suppression of kindling, suggestive of a prophylactic effect. The rate of rekindling after withdrawal of the drugs was not significantly different from that of vehicle-treated control rats, however, indicating that a genuine prophylactic effect was not obtained.