Central excitatory properties of delta 9-tetrahydrocannabinol and its metabolites in iron-induced epileptic rats

The Potential Proconvulsant Effects of Cannabis: a Scoping Review

INTRODUCTION

Cannabis' effect on seizure activity is an emerging topic that remains without consensus and merits further investigation. We therefore performed a scoping review to identify the available evidence and knowledge gaps within the existing literature on cannabis product exposures as a potential cause of seizures in humans.

METHODS

A scoping review was conducted in accordance with the PRISMA Extension for Scoping Reviews guidelines. The PubMed and Scopus databases were searched over a 20-year period from the date of the database query (12/21/2020). Inclusion criteria were (1) English language original research articles, (2) inclusion of human subjects, and (3) either investigation of seizures as a part of recreational cannabinoid use OR of exogenous cannabinoids as a cause of seizures.

RESULTS

A total of 3104 unique articles were screened, of which 68 underwent full-text review, and 13 met inclusion/exclusion criteria. Ten of 11 studies evaluating acute cannabis exposures reported a higher seizure incidence than would be expected based on the prevalence of epilepsy in the general and pediatric populations (range 0.7-1.2% and 0.3-0.5% respectively). The remaining two studies demonstrated increased seizure frequency and/or seizure-related hospitalization in recreational cannabis users and those with cannabis use disorder.

CONCLUSIONS

This scoping review demonstrates that a body of literature describing seizures in the setting of cannabis exposure exists, but it has several limitations. Ten identified studies showed a higher than expected incidence of seizures in populations exposed to cannabis products. Based on the Bradford Hill criteria, delta-9 tetrahydrocannabinol (THC) may be the causative xenobiotic for this phenomenon.

Cannabidiol in the Treatment of Epilepsy: A Focused Review of Evidence and Gaps

Approximately one third of epilepsy patients do not become seizure free with antiseizure medications. This treatment gap motivates research for new therapeutic options, such as cannabidiol (CBD). CBD differs from other cannabis derivatives because of its consistent efficacy and lack of a psychoactive effect. CBD can be recommended as adjunctive therapy in patients with Dravet and Lennox-Gastaut syndromes. The most common adverse effects (AEs) are drowsiness, reduced appetite, diarrhea, and vomiting. Transaminase elevation is the most common AE that leads to CBD discontinuation. Coadministration with valproate may increase the risk of hepatotoxicity. The combination of CBD and clobazam may increase both the effectiveness and the risk of AEs associated with these drugs. The most striking gaps in knowledge are the efficacy and optimal dose of CBD for adults with focal epilepsies, the long-term safety of CBD use, and strategies to improve access to CBD for people living with epilepsy.

Cannabinoid Receptors: An Update on Cell Signaling, Pathophysiological Roles and Therapeutic Opportunities in Neurological, Cardiovascular, and Inflammatory Diseases

The identification of the human cannabinoid receptors and their roles in health and disease, has been one of the most significant biochemical and pharmacological advancements to have occurred in the past few decades. In spite of the major strides made in furthering endocannabinoid research, therapeutic exploitation of the endocannabinoid system has often been a challenging task. An impaired endocannabinoid tone often manifests as changes in expression and/or functions of type 1 and/or type 2 cannabinoid receptors. It becomes important to understand how alterations in cannabinoid receptor cellular signaling can lead to disruptions in major physiological and biological functions, as they are often associated with the pathogenesis of several neurological, cardiovascular, metabolic, and inflammatory diseases. This review focusses mostly on the pathophysiological roles of type 1 and type 2 cannabinoid receptors, and it attempts to integrate both cellular and physiological functions of the cannabinoid receptors. Apart from an updated review of pre-clinical and clinical studies, the adequacy/inadequacy of cannabinoid-based therapeutics in various pathological conditions is also highlighted. Finally, alternative strategies to modulate endocannabinoid tone, and future directions are also emphasized.

Cannabis for Pediatric Epilepsy

Epilepsy is a chronic disease characterized by recurrent unprovoked seizures. Up to 30% of children with epilepsy will be refractory to standard anticonvulsant therapy, and those with epileptic encephalopathy can be particularly challenging to treat. The endocannabinoid system can modulate the physiologic processes underlying epileptogenesis. The anticonvulsant properties of several cannabinoids, namely Δ-tetrahydrocannabinol and cannabidiol (CBD), have been demonstrated in both in vitro and in vivo studies. Cannabis-based therapies have been used for millennia to treat a variety of diseases including epilepsy. Several studies have shown that CBD, both in isolation as a pharmaceutical-grade preparation or as part of a CBD-enriched cannabis herbal extract, is beneficial in decreasing seizure frequency in children with treatment-resistant epilepsy. Overall, cannabis herbal extracts appear to provide greater efficacy in decreasing seizure frequency, but the studies assessing cannabis herbal extract are either retrospective or small-scale observational studies. The two large randomized controlled studies assessing the efficacy of pharmaceutical-grade CBD in children with Dravet and Lennox-Gastaut syndromes showed similar efficacy to other anticonvulsants. Lack of data regarding appropriate dosing and pediatric pharmacokinetics continues to make authorization of cannabis-based therapies to children with treatment-resistant epilepsy challenging.

Cannabis for the treatment of paediatric epilepsy? An update for Canadian paediatricians

The plant Cannabis sativa produces over 140 known cannabinoids. These chemicals generate considerable interest in the medical research community for their possible application to several intractable disease conditions. Recent reports have prompted parents to strongly consider Cannabis products to treat their children with drug resistant epilepsy. Physicians, though, are reluctant to prescribe Cannabis products due to confusion about their regulatory status and limited clinical data supporting their use. We provide the general paediatrician with a brief review of cannabinoid biology, the literature regarding their use in children with drug resistant epilepsy, the current Health Canada and Canadian Paediatric Society recommendations and also the regulations from the physician regulatory bodies for each province and territory. Given the complexities of conducting research on Cannabis products for children with epilepsy, we also discuss outstanding research objectives that must be addressed to support Cannabis products as an accepted treatment option for children with refractory epilepsy.

Cannabinoids disrupt memory encoding by functionally isolating hippocampal CA1 from CA3

Much of the research on cannabinoids (CBs) has focused on their effects at the molecular and synaptic level. However, the effects of CBs on the dynamics of neural circuits remains poorly understood. This study aims to disentangle the effects of CBs on the functional dynamics of the hippocampal Schaffer collateral synapse by using data-driven nonparametric modeling. Multi-unit activity was recorded from rats doing an working memory task in control sessions and under the influence of exogenously administered tetrahydrocannabinol (THC), the primary CB found in marijuana. It was found that THC left firing rate unaltered and only slightly reduced theta oscillations. Multivariate autoregressive models, estimated from spontaneous spiking activity, were then used to describe the dynamical transformation from CA3 to CA1. They revealed that THC served to functionally isolate CA1 from CA3 by reducing feedforward excitation and theta information flow. The functional isolation was compensated by increased feedback excitation within CA1, thus leading to unaltered firing rates. Finally, both of these effects were shown to be correlated with memory impairments in the working memory task. By elucidating the circuit mechanisms of CBs, these results help close the gap in knowledge between the cellular and behavioral effects of CBs.

Research into cannabinoids (CBs) over the last several decades has found that they induce a large variety of oftentimes opposing effects on various neuronal receptors and processes. Due to this plethora of effects, disentangling how CBs influence neuronal circuits has proven challenging. This paper contributes to our understanding of the circuit level effects of CBs by using data driven modeling to examine how THC affects the input-output relationship in the Schaffer collateral synapse in the hippocampus. It was found that THC functionally isolated CA1 from CA3 by reducing feedforward excitation and theta information flow while simultaneously increasing feedback excitation within CA1. By elucidating the circuit mechanisms of CBs, these results help close the gap in knowledge between the cellular and behavioral effects of CBs.

Endocannabinoid Signaling Regulates Sleep Stability

The hypnogenic properties of cannabis have been recognized for centuries, but endogenous cannabinoid (endocannabinoid) regulation of vigilance states is poorly characterized. We report findings from a series of experiments in mice measuring sleep with polysomnography after various systemic pharmacological manipulations of the endocannabinoid system. Rapid, unbiased scoring of vigilance states was achieved using an automated algorithm that we devised and validated. Increasing endocannabinoid tone with a selective inhibitor of monoacyglycerol lipase (JZL184) or fatty acid amide hydrolase (AM3506) produced a transient increase in non-rapid eye movement (NREM) sleep due to an augmentation of the length of NREM bouts (NREM stability). Similarly, direct activation of type 1 cannabinoid (CB1) receptors with CP47,497 increased NREM stability, but both CP47,497 and JZL184 had a secondary effect that reduced NREM sleep time and stability. This secondary response to these drugs was similar to the early effect of CB1 blockade with the antagonist/inverse agonist AM281, which fragmented NREM sleep. The magnitude of the effects produced by JZL184 and AM281 were dependent on the time of day this drug was administered. While activation of CB1 resulted in only a slight reduction in gamma power, CB1 blockade had dramatic effects on broadband power in the EEG, particularly at low frequencies. However, CB1 blockade did not significantly reduce the rebound in NREM sleep following total sleep deprivation. These results support the hypothesis that endocannabinoid signaling through CB1 is necessary for NREM stability but it is not necessary for sleep homeostasis.

Striatal GABAergic and cortical glutamatergic neurons mediate contrasting effects of cannabinoids on cortical network synchrony

Activation of type 1 cannabinoid receptors (CB1R) decreases GABA and glutamate release in cortical and subcortical regions, with complex outcomes on cortical network activity. To date there have been few attempts to disentangle the region- and cell-specific mechanisms underlying the effects of cannabinoids on cortical network activity in vivo. Here we addressed this issue by combining in vivo electrophysiological recordings with local and systemic pharmacological manipulations in conditional mutant mice lacking CB1R expression in different neuronal populations. First we report that cannabinoids induce hypersynchronous thalamocortical oscillations while decreasing the amplitude of faster cortical oscillations. Then we demonstrate that CB1R at striatonigral synapses (basal ganglia direct pathway) mediate the thalamocortical hypersynchrony, whereas activation of CB1R expressed in cortical glutamatergic neurons decreases cortical synchrony. Finally we show that activation of CB1 expressed in cortical glutamatergic neurons limits the cannabinoid-induced thalamocortical hypersynchrony. By reporting that CB1R activations in cortical and subcortical regions have contrasting effects on cortical synchrony, our study bridges the gap between cellular and in vivo network effects of cannabinoids. Incidentally, the thalamocortical hypersynchrony we report suggests a potential mechanism to explain the sensory "high" experienced during recreational consumption of marijuana.

Phytocannabinoids as novel therapeutic agents in CNS disorders

The Cannabis sativa herb contains over 100 phytocannabinoid (pCB) compounds and has been used for thousands of years for both recreational and medicinal purposes. In the past two decades, characterisation of the body's endogenous cannabinoid (CB) (endocannabinoid, eCB) system (ECS) has highlighted activation of central CB(1) receptors by the major pCB, Δ(9)-tetrahydrocannabinol (Δ(9)-THC) as the primary mediator of the psychoactive, hyperphagic and some of the potentially therapeutic properties of ingested cannabis. Whilst Δ(9)-THC is the most prevalent and widely studied pCB, it is also the predominant psychotropic component of cannabis, a property that likely limits its widespread therapeutic use as an isolated agent. In this regard, research focus has recently widened to include other pCBs including cannabidiol (CBD), cannabigerol (CBG), Δ(9)tetrahydrocannabivarin (Δ(9)-THCV) and cannabidivarin (CBDV), some of which show potential as therapeutic agents in preclinical models of CNS disease. Moreover, it is becoming evident that these non-Δ(9)-THC pCBs act at a wide range of pharmacological targets, not solely limited to CB receptors. Disorders that could be targeted include epilepsy, neurodegenerative diseases, affective disorders and the central modulation of feeding behaviour. Here, we review pCB effects in preclinical models of CNS disease and, where available, clinical trial data that support therapeutic effects. Such developments may soon yield the first non-Δ(9)-THC pCB-based medicines.

Inhibitory role of Acorus calamus in ferric chloride-induced epileptogenesis in rat

The roots and rhizomes of Acorus calamus (Family: Araceae) have been used in the ancient systems of medicine for the treatment of various neurological disorders. Of the various methods used for inducing experimental epileptic models, the intracortical administration of ferric chloride (FeCl(3)) into sensorimotor cortex induces recurrent seizures and epileptic discharge similar to human post-traumatic epilepsy through the generation of free radicals. The present study focuses on the effect of Acorus calamus on the behavioral, electroencephalographic, and antioxidant changes in FeCl(3)-induced rat epileptogenesis. Topical administration of FeCl(3) (5 microL; 100 mM) into the sensorimotor cortex of rats showed an increase in the wet dog shake behavior, spike wave discharges together with an significant increase in antioxidant enzyme activity, such as superoxide dismutase and catalase, resulting in an increase in the level of lipid peroxidation in cerebral cortex. Pretreatment with Acorus calamus (200 mg/kg b.w., p.o. for 14 days) and also diazepam (DZ, 20 mg/kg b.w., i.p.) decreased the WDS behavior, spike wave discharges with single isolated positive waves, and a significant decrease in activity of superoxide dismutase and level of lipid peroxidation was observed in cerebral cortex with respect to those observed in FeCl(3)-induced epileptic group. Data presented in this study clearly show that Acorus calamus possesses the ability for preventing the development of FeCl(3)-induced epileptogenesis by modulating antioxidant enzymes, which in turn exhibit the potentiality of Acorus calamus to be developed as an effective anti-epileptic drug.

Identification of the endogenous cannabinoid system through integrative pharmacological approaches

Scientific progress in the biological sciences increasingly relies on an integration of behavioral, pharmacological, cellular, and molecular approaches, particularly in translating basic research observations into therapeutic potential. The strength of in vivo model systems lies in the direct assessment of physiological function. However, they only allow indirect evidence for mechanism of action. Frequently, in vitro models provide just the opposite. A combination of both in vitro and in vivo approaches are often essential for establishing the underlying mechanisms of a specific pharmacological effect. In recent times, an endogenous cannabinoid system has been characterized due to the combined efforts of chemists, pharmacologists, molecular and cellular biologists, and biochemists. This endogenous cannabinoid system is providing a basis for systematically addressing the pharmacological controversies surrounding marijuana. The description of this endogenous cannabinoid system and the strategies for establishing the physiological function of this system are the subjects of this article.

Effect of [dl]-alpha-tocopherol on FeCl2-induced lipid peroxidation in rat amygdala

Peroxidative injury of neural membrane lipids can be initiated by iron-containing blood products, chelated ferrous or ferric ions, and low valence iron in aqueous solution. Lipid peroxidation was measured following focal injection of 3 microliters of 100 mM FeCl2 into rat amygdala. Acute parenteral administration of [dl]-alpha-tocopherol as the alcohol limited the quantity of peroxidation products generated. These data suggest a potential role for alpha-tocopherol administration in limiting brain injury responses.

Differential effects of delta-9-tetrahydrocannabinol and its 11-hydroxy metabolite on sodium current in neuroblastoma cells

Whole-cell voltage-clamp techniques were used to study the comparative effects of delta-9-tetrahydrocannabinol (THC) and its principal metabolite, 11-hydroxy-delta-9-tetrahydrocannabinol (11-OH-THC), on the voltage-gated sodium current in neuroblastoma cells. The parent compound markedly depressed the inward sodium current with minimal reduction of the outward current, demonstrating that the effects of the drug were related to the membrane potential. In addition, THC reduced the reversal potential, indicating that the drug modified the ion selectivity of the channel. 11-OH-THC similarly depressed inward sodium current; however, in marked contrast to the effects of the parent compound, the drug equally depressed the outward voltage-gated sodium current, indicating that its effects were not related to the membrane potential. Furthermore, 11-OH-THC differed from THC in that it did not alter the reversal potential. The results demonstrate that THC and its 11-OH metabolite both reduce inward sodium current, but their effects on the outward current and ion selectivity are distinctly different. The sum of the actions of these two cannabinoids on the voltage-gated sodium channel provides a plausible cellular basis for THC's depression of action potentials in vivo and for some of its central depressant effects.

Oxygen free radicals and brain dysfunction

Oxygen free radicals, any chemical moiety containing an oxygen atom with an unpaired electron in the outer orbital shell, are generated during many normal biochemical reactions in living tissue. The unpaired electron makes these compounds highly reactive and they can initiate disruptive peroxidation reactions with various substrates important to the survival of cells such as proteins, lipids and nucleic acids. A fairly complex defense system has evolved to protect living tissue from free radicals and to minimize the damage they might cause. Neurons are especially vulnerable to free radical attack and impaired defenses or exposure to excess free radicals can lead to neuronal death. Free radicals contribute to neuronal loss in cerebral ischemia and hemorrhage and may be involved in the degeneration of neurons in epilepsy, schizophrenia, tardive dyskinesia, normal aging, Parkinson's Disease and Alzheimer's Disease. The development of drugs that limit or prevent the attack of free radicals on neurons would be an important advance in the treatment of these conditions.

Iron-induced lipid peroxidation and brain injury responses

Head trauma with cerebral contusion causes extravasation of red blood cells, followed by hemolysis and deposition of iron-containing blood products within the neuropil. Liberation of heme compounds is associated with deposition of hemosiderin, and with gliosis, neuronal loss and occasionally the development of seizures. In this experiment we injected components of red blood cell contents into rat amygdala, and then measured the rate of appearance of products of lipid peroxidation. Injection of microliter volumes of hemin and hemoglobin, with hematoprotoporphyrin and rodent plasma injection and contralateral uninjected tissue as controls, showed that the presence of the iron moiety within the protoporphyrin ring was required to initiate and propagate peroxidation. Free radical reactions initiated by iron or heme deposited within the neuropil may be a fundamental reaction associated with brain injury responses, and possibly with posttraumatic epileptogenesis.

Post-traumatic epilepsy: cellular mechanisms and implications for treatment

Epilepsy complicates severe head trauma. Development of persistent seizures appears to correlate with the extent of trauma. Although early reports suggested that prophylactic administration of antiepileptic drugs would prevent epileptogenesis, controlled studies have failed to corroborate this assumption. Head trauma initiates a sequence of responses that includes altered blood flow and vasoregulation, disruption of the blood-brain barrier, increases in intracranial pressure, focal or diffuse ischemia, hemorrhage, inflammation, necrosis, and disruption of fiber tracts. The presence of an intracranial hematoma has a robust association with the development of post-traumatic epilepsy. Extravasation of blood is followed by hemolysis and deposition of heme-containing compounds into the neuropil, initiating a sequence of univalent redox reactions and generating various free radical species, including superoxides, hydroxyl radicals, peroxides, and perferryl ions. Free radicals initiate peroxidation reactions by hydrogen abstraction from methylene groups adjacent to double bonds of fatty acids and lipids within cellular membranes. Intrinsic enzymatic mechanisms for control of free radical reactions include activation of catalase, peroxidase, and superoxide dismutase. Steroids, proteins, and tocopherol also terminate peroxidative reactions. Tocopherol and selenium are effective in preventing tissue injury initiated by ferrous chloride and heme compounds. Treatment strategies for prevention or prophylaxis of post-traumatic epilepsy must await absolute knowledge of mechanisms. Antioxidants and chelators may be useful, given the speculation that peroxidative reactions may be an important component of brain injury responses. However, potential treatment strategies involving gamma-aminobutyric acid (GABA) agonists, NMDA receptor antagonists, and barbiturates need further scientific assessment.

Lipid peroxidation and glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase, and glucose-6-phosphate dehydrogenase activities in FeCl3-induced epileptogenic foci in the rat brain

This study investigated the relationship between lipid peroxidation, subsequent activation of antioxidative enzymes, and development of iron-induced epilepsy in the rat. Epileptic foci were produced in rat cerebral cortex by intracortical injection of ferric chloride (FeCl3). The epileptic foci were identified by electrocorticography (ECoG). Epileptiform ECoG activity was shown to occur in the contralateral homotopic cerebral cortex as well. We measured levels of lipid peroxides and changes in the activities of the enzymes: superoxide dismutase (SOD), glutathione peroxidase (GP), glutathione reductase (GR), catalase (CA), and glucose-6-phosphate dehydrogenase (G6P) in the epileptogenic focus (both ipsilateral and contralateral) at days 3, 8, 15, and 23 after FeCl3 injection. Biochemical estimations were made in subcellular fractions, and changes in the ipsilateral site were compared with those in the contralateral site. The results of this study showed that large increases in lipid peroxidation were associated with development and buildup of the ECoG epileptiform discharges. Lipid peroxides increased in the ipsilateral focus by approximately 100% as compared with control. In the contralateral site, however, the increase in lipid peroxides was marginal only. The increase in lipid peroxidation was concomitant with development of the high level of epileptiform activity. The time course of changes in lipid peroxidation paralleled the time course of development and persistence of the epileptiform activity. Regarding changes in the enzyme activities accompanying development of iron epilepsy, the data showed that although SOD and G6P increased by approximately 60% and GR increased by approximately 40%, the increases in the enzyme GP and CA were much lower, less than 20%. Thus, comparatively less increase in CA and GP activities produces a deficiency of these two enzymes in the iron (ipsilateral) focus. Among the various biochemical disturbances that have been identified as involved in epileptogenesis, peroxidative injury resulting from lipid peroxidation in neural plasma membrane may be causally related to development of paroxysmal epileptiform activity in the iron focus. Since GP is an enzyme of major importance in detoxification of lipid peroxides in the brain, based on the results presented in this article, it appears reasonable to suggest that GP deficiency causes lipid peroxidation to increase tremendously during iron epileptogenesis.

Effects of delta-9-tetrahydrocannabinol, 11-hydroxy-delta-9-tetrahydrocannabinol and cannabidiol on neuromuscular transmission in the frog

Intracellular recording techniques were used on neuromuscular junctions of the sartorius muscle of the frog, in vitro, to define the synaptic pharmacology of delta-9-tetrahydrocannabinol (THC), 11-hydroxy-THC and cannabidiol (CBD). The frequency of miniature endplate potentials was increased by THC, decreased by CBD and was unaffected by 11-hydroxy-THC, whereas the amplitude of the miniature endplate potentials was depressed by all three cannabinoids. In addition, the mean quantum content of the endplate potential (m) was first increased and then decreased by THC and 11-hydroxy-THC, but CBD produced only depression. Changes in m and the frequency of the miniature endplate potential indicated presynaptic sites of drug action and reduction of the amplitude of the miniature endplate potential suggested a postsynaptic site. The findings suggest possible mechanisms of action for the central excitatory and depressant properties of the cannabinoids.

The role of iron-induced hippocampal peroxidation in acute epileptogenesis

Intracortical injection of iron salts causes lipid peroxidation, focal edema, necrosis, gliosis, and the development of behavioral and electrographic seizures. Tocopherol pretreatment prevents the histopathologic perturbations associated with iron injection, and appears to accelerate the resolution of focal accumulation of peroxidation products. In this experiment, rats were pretreated with 500 mg/kg DL-alpha-tocopherol acetate prior to the injection of 3 microliter of 100 mM FeCl2 into the dorsal hippocampus, or induction of convulsive seizures by s.c. injection of 0.8 mg/100 g bicucullin. Tocopherol pretreatment prevented the occurrence of convulsive seizures in a significant number of iron-salts injected animals. Lipid peroxidation measured in the dissected hippocampus was significantly increased in untreated rats developing iron-induced seizures and in rats treated with tocopherol, but developing convulsive seizures. Tocopherol failed to prevent bicucullin-induced seizures. Further, convulsive seizures induced by bicucullin failed to alter hippocampal fluorescence levels. Hence, we concluded that the epileptogenic effects of hippocampal injection of iron salts appear to be related to the induction of peroxidation of neural lipids within the injection site.

Prolonged CNS hyperexcitability in mice after a single exposure to delta-9-tetrahydrocannabinol

A single exposure to delta-9-tetrahydrocannabinol (THC) resulted in a "rebound" hyperexcitability in the CNS in mice, which was assessed in terms of the susceptibility of the CNS to electrically-induced convulsions. The magnitude of the hyperexcitability was dose-related (25-150 mg/kg, i.p.), as measured 24 hr after treatment. The time-course study of the effect indicated a peak-effect at 24 hr after administration of the drug, with a duration of the effect for as long as 196 hr. The time course of the rebound hyperexcitability to THC was compared to that for phenobarbital, which peaked at 48 hr after administration of the drug and returned to the control value by 96 hr. Tolerance developed rapidly to the motor-toxic effect of THC, but after 23 days of daily treatment there was no evidence of tolerance to the rebound hyperexcitability. The functional significance of the hyperexcitable state was assessed in two tests; electrical kindling to minimal convulsions was enhanced, even when the kindling procedure was initiated 120 hr after exposure to the drug; and the anticonvulsant activity of phenytoin was blocked when mice were treated with the anticonvulsant 96 hr after a single exposure to THC. The results suggest that the rebound response from a single exposure to THC represents a functionally significant prolonged increase in excitability of the CNS.

Influence of 11-hydroxy-delta-9-tetrahydrocannabinol on spinal motoneurons in cat

Intracellular recording techniques were used on spinal motoneurons in the cat in order to define the synaptic pharmacology of 11-hydroxy-delta-9-tetrahydrocannabinol (11-hydroxy-delta-9-THC), the principal metabolite of delta-9-tetrahydrocannabinol (delta-9-THC). The 11-hydroxy derivative increased the amplitude of excitatory postsynaptic potentials; such an excitatory response did not appear to be the result of changes in afferent input. The increase in excitatory postsynaptic potentials, however, may be accounted for by a rise in membrane resistance. The cannabinoid also concomitantly produced synaptic depression, as indicated by a rise in the firing threshold for the motoneuron action potential. The responses to 11-hydroxy derivative suggest synaptic sites and mechanisms of action; for instance, the data indicate that the cannabinoid affected postsynaptic conductance. Finally, the similarity between the synaptic effects of the 11-hydroxy derivative and those of delta-9-THC suggest that the metabolite may contribute to the pharmacological properties of its parent compound.

The effect of tocopherol and dimethyl sulfoxide on focal edema and lipid peroxidation induced by isocortical injection of ferrous chloride

Addition of iron salts to suspensions of subcellular organelles or polyunsaturated fatty acids results in the formation of oxidative free radicals with subsequent initiation of lipid peroxidation. Pretreatment of rats with anti-oxidants prevents peroxidation following isocortical ferrous chloride injection, and increases the rate of resolution of iron-induced focal edema. In this experiment, treatment of rats at the time of injection of 5 microliters of 100 mM FeCl2 with tocopherol and DMSO caused decreased formation of brain peroxidation at the injection site, as measured by formation of MDA. Tocopherol failed to change the quantity of tissue fluid accumulation. However, DMSO alone, or combined with tocopherol, hastened the resolution of brain edema. Tocopherol may terminate peroxidation reactions by donation of a phenolic hydrogen, forming a quinone of tocopherol. DMSO has many pharmacologic effects; however, inhibition of initiation reactions by scavenging hydroxyl radicals, and direct and indirect effects on focal edema accumulation may account for our observations.

In vivo lipid peroxidation in rat brain following intracortical Fe2+ injection

Cerebral contusion, cortical laceration, intracerebral hematoma formation, and hemorrhagic cortical infarction cause extravasation of red blood cells, followed by hemolysis, decompartmentalization of iron, formation and deposition of hemosiderin, and an increased incidence of epilepsy. In this experiment, 10 microliter of an aqueous solution containing 100 mmol/L FeCl2, 100 mmol/L CoCl2, or 0.9% (wt/vol) NaCl were injected at a depth of 1.8 mm into rat isocortex. The rate of formation of fluorescent compounds was measured in chloroform-methanol extracts of isocortical homogenates. Significant increases in the quantity of fluorescent products of lipid peroxidation were found 120 min after the injection of 100 mmol/L FeCl2. Cobaltous chloride and saline injection had no effect on the levels of fluorescent products found in the cortical homogenates. Although the intracortical deposition of aqueous solutions containing CoCl2 or FeCl2 in rodent cortex causes acute epileptiform discharges, the epileptogenic effect of CoCl2 is transient, while the injection of iron salts causes persistent seizures. Since CoCl2 injection failed to cause formation of lipid peroxidation products while the isocortical injection of iron caused significant increase in fluorescence within the injected hemisphere, we suggest that the occurrence of iron-induced lipid peroxidation may be of importance in initiation of recurrent seizures in the rat.

Effect of phenytoin and corticosteroids on seizures and lipid peroxidation in experimental posttraumatic epilepsy

Head trauma, intracerebral hematoma formation, and hemorrhagic cerebral infarction cause extravasation of the intravascular contents, red blood cell (RBC) hemolysis, hemosiderin deposition within the neuropil, and an increased incidence of epilepsy. Reports conflict regarding the efficacy of the administration of prophylactic anticonvulsant drugs to head-injured patients to prevent the development of posttraumatic epilepsy. In this study, rats received a 10-microliter injection of 100 mM FeCl2 at a depth of 1.8 mm into the isocortex, or an equal volume of saline. Rats were then treated with 30 mg/kg methylprednisolone (MPS), 90 mg/kg MPS, 100 mg/kg phenytoin, or with an equal volume of propylene glycol. Behavioral or electroencephalographic (EEG) seizures occurred in all control-treated iron-injected rats within 93 +/- 6 minutes of injection. Brain injury responses as measured by the occurrence of fluorescent product formation from iron-induced lipid peroxidation showed 6.6 +/- 0.8 units/gm in the saline-injected animals, and 16.7 +/- 2.5 units/gm in the control-treated iron-injected rats. Of the 90-mg/kg MPS-treated rats, 8% had seizures; fluorescence in those animals was 5.7 +/- 0.5 units/gm. Phenytoin treatment prevented the occurrence of convulsive and EEG seizures; however, lipid peroxidation was unaffected (16.5 +/- 4.1 units/gm). If posttraumatic epilepsy develops because of RBC extravasation, hemolysis, parenchymal deposition of heme compounds, and initiation of lipid peroxidation, then treatments designed to prevent peroxidation may be more effective for epilepsy prophylaxis than administration of anticonvulsant drugs that mask convulsive seizures while biochemical brain injury continues.

Effects of antiperoxidants on FeCl2-induced lipid peroxidation and focal edema in rat brain

Head trauma with contusion or cortical laceration and hemorrhage causes focal edema with encephalomalacia and gliosis. Because cerebral hemorrhage ultimately results in deposition of heme compounds and iron into the neuropil, we injected an aqueous solution of iron salts to simulate the decompartmentalization of iron after trauma. We pretreated animals with saline or with 600 mg/kg alpha-tocopherol plus 5 ppm selenium added to the drinking water. Formation of lipid peroxidation products was significantly inhibited within the iron injection site in the antiperoxidant-pretreated rats at 30, 60, and 120 min after injection of iron into the isocortex. The antiperoxidants failed to prevent formation of focal brain edema at the injection site between 1 and 8 h after injection; however, significantly less edema was present in the alpha-tocopherol + selenium-pretreated animals 24 and 48 h after injection. The efficacy of antiperoxidants in preventing lipid peroxidation, and enhancing the resolution of ferrous-induced focal brain edema suggest that tocopherol + selenium administration caused free radical quenching and termination of lipid peroxidation, and increased membrane stabilization, an effect similar to the action of glucocorticoids.

Effects of delta 9-tetrahydrocannabinol on cat spinal motoneurons

The influence of delta 9-tetrahydrocannabinol (delta 9-THC) on cat spinal motoneurons was investigated with intracellular recording techniques in order to identify possible mechanisms of action of the drug's central excitatory and depressant properties. delta 9-THC increased the amplitude of the excitatory postsynaptic potentials (EPSPs) and decreased the amplitude of the inhibitory postsynaptic potentials (IPSPs); these excitatory effects do not appear to be the result of changes in the afferent input. However, an observed increase in membrane resistance may account for, or contribute to, the enhanced EPSPs. The cannabinoid also concomitantly caused depression, as evidenced by a rise in the firing threshold for the motoneuron action potential. The responses of the motoneuron to the drug suggest synaptic sites and mechanisms of action.

Formation of superoxide radicals after FeCl3 injection into rat isocortex

Subpial injection of aqueous solutions of iron salts into rat isocortex induces recurrent epileptiform discharges with focal brain edema, cavitary necrosis and gliosis. Since aqueous iron or heme compounds cause peroxidation of lipids, we studied the sequence of changes in the formation of free radicals, and superoxide radicals, in rat isocortex injected with 5 microliter of 100 mM FeCl3. Electron spin resonance measurements of whole rat brain showed a transient increase in heme-bound Fe3+. Superoxide radicals were increased in a cylinder of tissue obtained at the injection site 5 min and 15 min after completion of the injection. This study shows that iron salts injected into rat isocortex cause transient formation of free radicals. We suggest that decompartmentalization of iron compounds may be of importance in trauma-related brain injury responses.

Influence of different barbiturate anesthetics on delta-9-tetrahydrocannabinol effects on spinal monosynaptic reflexes

Two barbiturates, pentobarbital and methohexital, were used as general anesthetics to evaluate their interactions with the effects of delta-9-tetrahydrocannabinol (delta-9-THC) on spinal monosynaptic reflexes in cats with transected spinal cords and ischemically destroyed brains. In animals initially anesthetized with pentobarbital, delta-9-THC over a wide dosage range produced only an enhancement of the reflex, whereas in methohexital-treated animals only depression was elicited. Because delta-9-THC is known to produce both excitatory and depressant effects in conscious animals, the results of the present study demonstrate that the choice of anesthetic may determine which effects manifest themselves. Therefore, if anesthesia is used in the investigation of any cannabinoid, the possibility of such interactions must be considered when interpreting the results.