Cannabinoids in Audiogenic Seizures: From Neuronal Networks to Future Perspectives for Epilepsy Treatment

Abstract

Introduction

Epilepsy is a neurological disorder characterized by the presence of epileptic seizures and their behavioral, physiological, and social consequences (Fisher et al., 2014; Kanner, 2017). Despite the great variety of antiepileptic drugs (Löscher, 2017) one third of patients remain pharmacoresistant and cannot have their seizures under control with the available pharmacological treatment (Kwan and Brodie, 2010), indicating that new therapeutic and pharmacological targets are needed. In that context, the endocannabinoid system (ES) has been receiving especial attention in the epilepsy research scenario. The ES comprises the cannabinoids receptors type 1 (CB1R) and type 2 (CB2R) and their endogenous bindings, the endocannabinoids. CB1R has been receiving especial attention in epilepsy due to seizure control in several preclinical models and can also be modulated by phytocannabinoids (Wallace et al., 2003; Lutz, 2004; Blair, 2006; Huizenga et al., 2017; Britch et al., 2020). Moreover, anticonvulsant effects were associated with Cannabis-derived compounds, especially the cannabidiol (CBD), reinforcing the role of cannabinoids in epileptic seizures (Friedman and Devinsky, 2015; Rosenberg et al., 2017; Lazarini-Lopes et al., 2020b). CBD, a phytocannabinoid present in Cannabis sp. (Jacob and Todd, 1940; Mechoulam and Shvo, 1963), has receiving especial attention due to its anticonvulsant properties in animal models of the epilepsies (Jones et al., 2012; Do Val-da Silva et al., 2017; Lazarini-Lopes et al., 2020b) and also in humans with pharmacoresistant epilepsy (Press et al., 2015; Devinsky et al., 2016, 2017). Although CBD anticonvulsant mechanisms of action seem to be related with a great diversity of cellular and molecular targets, which include components of the ES, the possible existence of synergistic effects between CBD and conventional anticonvulsant drugs may not be ignored (Mencher and Wang, 2005; Devinsky et al., 2014; Gaston et al., 2017). Additionally, although CBD has limited effects at cannabinoids receptors, CBD can modulate CB1R activity by indirect mechanisms of action (Britch et al., 2020). Therefore, the ES arise as important endogenous mechanism for seizure control (Alger, 2004; Hofmann and Frazier, 2013).

Animal models are essential for the development and screening of new anticonvulsant drugs and to evaluate their effects on the brain and on behavior (Löscher, 2011, 2017). Since epilepsies are greatly diverse in etiology, the differences between seizure induction protocols are extremely important to help understanding neuronal alterations associated with each type of seizure induction and, consequently, their clinical applications (Löscher, 2017). Audiogenic seizures (AS) are induced by intense sound stimulation (~100–120 dB) in susceptible animals and are used to study epilepsies-related mechanisms such as neuronal pathways and endogenous alterations associated with seizure susceptibility (Garcia-Cairasco et al., 2017). Audiogenic susceptible rodent strains are widely used around the world, beginning with the oldest colony, the Krushinsky-Molodkina (KM) rats in Russia (Poletaeva et al., 2017), followed by the Genetically Epilepsy-Prone Rats (GEPR) in the United States (Reigel et al., 1986; Dailey et al., 1989), the DBA/1 and DBA/2 mice (Jensen et al., 1983; Faingold et al., 2010), the Wistar Audiogenic Rat (WAR) in Brazil (Doretto et al., 2003; Garcia-Cairasco et al., 2017), among others (Ross and Coleman, 2000).

Acute AS are considered a model of generalized tonic-clonic seizures, with seizures characterized by an initial wild running phase with jumping and atonic falls followed by tonic or tonic-clonic seizures (Faingold, 1988; Terra and Garcia-Cairasco, 1992; Garcia-Cairasco et al., 1996, 2017; Ross and Coleman, 2000). However, when animals are chronically exposed to the AS protocol, called Audiogenic Kindling (AuK) (Marescaux et al., 1987), some audiogenic susceptible animals develop limbic seizures, characterized by the appearance of new behaviors such as facial and forelimb clonus, usually followed by elevation and falling (Naritoku et al., 1992; Garcia-Cairasco et al., 1996), similar to those described by Racine’s scale (Racine, 1972). While brainstem sensory motor structures are primarily involved in the acute AS expression (Faingold, 1988; Terra and Garcia-Cairasco, 1992), cortical and limbic structures are associated with behavioral, EEG, and histological alterations during the AuK, indicating an expansion of the initially brainstem-dependent seizure networks to limbic regions and networks (Marescaux et al., 1987; Naritoku et al., 1992; Garcia-Cairasco et al., 1996; Moraes et al., 2000; Galvis-Alonso et al., 2004). Therefore, the AuK is as a model of temporal lobe recruitment and consequently of temporal lobe epilepsy (Moraes et al., 2000; Romcy-Pereira and Garcia-Cairasco, 2003). Other quite important characteristic is that genetic and chronic models, like susceptible strains and the AuK, can be used also to study the comorbidities, usually from neuropsychiatric origin, associated with epilepsies (Garcia-Cairasco et al., 2017).

Therefore, the purpose of the present study was to review the neuronal networks associated with AS expression. Additionally, we reviewed the effects of ES modulation and Cannabis-derived compounds in AS. We discussed cannabinoids modulation in AS neuronal pathways and the future perspectives of cannabinoids in AS and comorbidities.

Neuronal Networks Involved in Audiogenic Seizures

Since AS are evoked by a high-intensity acoustic stimulus, the primary auditory pathway has been the first cluster of structures to be evaluated in audiogenic susceptible rodent strains. In this context, several research groups have detected peripheral alterations associated with AS susceptibility, such as hearing loss (Saunders et al., 1972; Glenn et al., 1980; Faingold et al., 1990), unbalance between GABAergic and Glutamatergic neurotransmissions between the inner hair cells and the cochlear nerve (Altschuler et al., 1989; Bobbin et al., 1990; Lefebvre et al., 1991), and tinnitus followed by intensity sound exposure (Heffner and Harrington, 2002; Chen et al., 2013). Similarly, anatomical and morphological alterations in the organ of Corti and in the inner and outer hair cells of the GEPRs have already been observed (Penny et al., 1983, 1986). However, despite the importance of peripheral alterations in the onset of AS, the present review will focus on brain sites involved on the onset, maintenance, and expression of AS, specifically in the brainstem (acute AS) and limbic areas (AuK).

Endocannabinoid System and CB1R in Audiogenic Seizures Network

The ES is classically composed by endogenous receptors, CB1R and CB2R (Matsuda et al., 1990; Munro et al., 1993), and their endogenous ligands, anandamide, and 2-arachydonil glycerol (Devane et al., 1992; Mechoulam et al., 1995; Sugiura et al., 1995). It is widely accepted that the ES modulates neuronal activity through its retrograde action based “on-demand” endocannabinoid synthesis and release (Lutz, 2004; Alger and Kim, 2011; Castillo et al., 2012; Fitzgerald et al., 2012). However, before discussing the role of the ES modulation on seizure control in audiogenic models, it is worth to note how these cannabinoids receptors are distributed on the brain, especially on structures important to AS expression.

Autoradiography assays were used to assess CB1R distribution in several brain structures (Herkenham et al., 1990, 1991). The most intense binding was observed in the cerebellum and forebrain structures, such as several cortical and hippocampal areas. The frontal cortex presented the greater density of CB1R compared to other cortical regions, while the dorsal hippocampus seems to present more CB1R than the ventral hippocampus. The amygdaloid complex presented a moderate binding, with exception of the central nucleus that showed the lowest CB1R levels. Brainstem structures, like PAG, BRF, SC, IC, and hypothalamus presented lower levels of CB1R and sparse binding when compared to the forebrain. Like in brainstem structures, the spinal cord showed sparse binding, specifically in the dorsal horn. It is worth to note that the SNr, but not the SNc, showed the highest density levels of CB1R in the entire rat brain (Herkenham et al., 1990, 1991). Similar expression patterns were observed in others species of mammals, such as dogs, Rhesus monkeys, and humans (Herkenham et al., 1990).

Tsou et al. (1998) used immunohistochemical analysis to assess CB1R distribution in the rat brain. These authors showed CB1R in axons, dendrites, and in soma of neurons in several brain structures. Intense and widely CB1R distribution were detected in forebrain structures, such as cortical areas, as well as in amygdala, and hippocampal formation, although very restricted immunostaining were present in the brainstem, in structures like the PAG and SC. Additionally, the SNr presented a very intense immunostaining (Tsou et al., 1998), confirming those previous results observed by Herkenham’s research group.

Changes in CB1R expression and functionality have already been detected in animal models of epileptic seizures and in humans with chronic seizures (Maglóczky et al., 2010; Karlócai et al., 2011; Rocha et al., 2020). Goffin et al. (2011) assessed CB1R expression in tissue from humans with TLE and observed increased CB1R receptors expression in the seizure onset area, while CB1R expression was decreased in other areas, like the insular cortex, suggesting that different alterations in cannabinoid receptors expression could be associated with seizures expression and brain hyperexcitability (Goffin et al., 2011). However, data of CB1R expression in audiogenic strains are scarce. Increased CB1R expression was observed in the inner molecular layer of WARs, when compared to control Wistars. Additionally, in WARs, acute and chronic AS increased CB1R expression in several hippocampal layers and in specific amygdala subnuclei, the basolateral, lateral, and basomedial nuclei. Acute AS also induced changes in CB1R in the central and medial amygdala nuclei. Moreover, it is worth to note that, changes in CB1R expression in lateral, basolateral, and basomedial amygdala nuclei were correlated with limbic seizure severity during the AuK (Lazarini-Lopes et al., 2020a). See Figure 1 for a representative view of CB1R expression in limbic and cortical structures of audiogenic susceptible rats from the WAR strain.

Figure 1

Representative CB1R immunostaining in limbic and cortical brain structures of Wistar Audiogenic Rats (WAR). It is possible to observe the increased CB1R immunostaining in limbic (hippocampus and amygdala) and cortical areas of WARs after acute audiogenic seizures (WAR AS) and chronic audiogenic seizures (WAR AuK). Wistar represents a control non-audiogenic strain. Image obtained from Lazarini-Lopes et al. (2020a).

Wistar Albino rats from Rijswijk (WAG/Rij strain) develop absence seizures along their life (van Luijtelaar and Coenen, 1986; van Luijtelaar and Sitnikova, 2006) and a subpopulation of WAG/Rij rats can also develop AS with limbic recruitment during the AuK (Vinogradova, 2008). These animals present endogenous alterations in the ES, like reduced CB1R mRNA, demonstrated by in situ hybridization, in the hippocampus and thalamic nuclei, brain regions associated with the genesis of absence seizures (Van Rijn et al., 2010). Therefore, further characterization of CB1R expression and functionality in brainstem and limbic sites in audiogenic WAG/Rij rats can bring important information regarding the susceptibility to AS in the WAG/Rij subpopulation.

Pharmacological CB1R activation in the intermediate layers of SC induced a robust turning behavior, these effects may be associated with modulation of GABAergic input from SNr to SC (Sañudo-Peña et al., 2000). In the SNr, CB1R are located in presynaptic terminals from the striatonigral pathways, they modulate GABA release from the nigrotectal GABAergic projections (Wallmichrath and Szabo, 2002), which may play an important role on seizure propagation and expression (Iadarola and Gale, 1982; Gale, 1986). Miller and Walker (1995) explored how the ES modulates SNr activity. WIN 55,212-2, systemically administered in normal Sprague-Dawley rats increased spontaneous firing rate in neurons from the SNr. In addition, WIN 55,212-2 also attenuated the inhibition of neuronal firing in the SNr induced by striatum electrical stimulation. In the same study, bicuculline antagonized the effects of striatum stimulation, suggesting that WIN 55,212-2 effects on SNr activity were dependent on GABAergic neurotransmission (Miller and Walker, 1995), although specific neurons and projections associated with these effects still need to be verified. Therefore, the GABAergic signaling from SNr to mesencephalic tectum may be, somehow, enhanced by cannabinoids administration, increasing the inhibitory tonus generated by this endogenous anticonvulsant system. Although, this hypothesis still needs to be further elucidated, measuring GABA release and also CB1R activity in the SNr.

Based on these previous evidences, we proposed a schematic representation of how brainstem and forebrain structures with different distribution of CB1R might modulate AS susceptibility and expression (Figure 2).

Endocannabinoid System Modulation in Audiogenic Seizures

Although cannabinoids induce modulation have already been shown as capable of epileptic seizures in several animal models (Rosenberg et al., 2017; Lazarini-Lopes et al., 2020b), studies evaluating the role of the ES on AS experimental models are still scarce. See Table 1 for main results from the literature.

Vinogradova et al. (2011) showed that acute and chronic treatment with SR141716, a CB1R antagonist, presented pro-epileptic effects in audiogenic Wistar rats and facilitated the AuK progression. These authors reported that acute treatment with SR141716 in susceptible rats increased AS duration and severity and induced the appearance of limbic seizures behaviors. Interestingly, the treatment with the CB1R antagonist did not modify AS susceptibility in normal rats, but in susceptible animals that developed resistance to AS, the seizures reappeared after SR141716 administration (Vinogradova et al., 2011). It is worth to notice that similar results were observed in a patient that was free of seizures for more than 20 years, but after administration of CB1R antagonist for obesity treatment the seizures reappeared. In that case, when the CB1R antagonist treatment was interrupted, the seizures disappeared (Braakham et al., 2009).

Conversely, a single administration of WIN 55,212-2, a CB1R agonist, presented long-term, but not acute effects, against AS, increasing the latency to the onset of post-tonic clonus in KM rats (Vinogradova and Van Rijn, 2015). Moreover, pharmacological treatments with different cannabinoid receptors agonists were capable of attenuating AS in DBA/2 mice, reducing wild running, clonus, and tonus behaviors. These anticonvulsant effects were blocked by previous administration of NIDA-41020, a selective CB1R antagonist (Citraro et al., 2016). Additionally, these authors also demonstrated that when ineffective doses of cannabinoid receptors agonists were co-administered with classical anticonvulsant drugs, such as carbamazepine, gabapentin, phenobarbital, and valproate, the anticonvulsant effects of all these drugs were potentiated (Citraro et al., 2016). In GEPR-3s, systemic administration of WIN 55,212-2, was effective against AS, suppressing seizures in 9/10 animals and attenuating seizure severity in 1/10 rats. Similarly, central administration of CP 55940, a CB1/2 agonist, directly into the DLSC of GEPR-3s, suppressed seizures in 6/9 rats, reduced seizure severity in 2/9, and had no effect in 1/9. Additionally, intra-DLSC administration of SR141716 did not modify AS in control GEPRs and did not antagonize the anticonvulsant effects induced by systemic WIN 55,212-2 (Santos et al., 2020). Also using GEPRs, Samineni et al. (2011) showed that central injection of AM251, a CB1R antagonist, directly into the ventrolateral PAG, attenuated post-ictal analgesia in GEPR-9s. These data suggest that AS results in increased endocannabinoid levels in the PAG, which may mediate post-ictal analgesia (Samineni et al., 2011). Since the last study did not look at seizure expression after CB1R modulation, it should be interesting to assess the role of CB1R from PAG in AS expression in GEPRs and other audiogenic strains.

Using the Fmr1 knockout mice to mimic the fragile X syndrome, authors observed that pharmacological blockade of CB1R rescued several pathological alterations, including the increased susceptibility to AS. Additionally, blockade of CB2R also induced anxiolytic behavior in the elevated plus maze (Busquets-Garcia et al., 2013). In the WAG/Rij strain, a model of absence seizures with a subpopulation also susceptible to AS, systemic administration of WIN 55,212-2 reduced the number of spontaneous spike-wave discharges, but increased seizure duration, in WAG/Rijs, whereas administration of AM251 attenuated the effects of CB1R activation (Van Rijn et al., 2010). Reduced number and duration of spike-wave discharges were observed after central (intra-thalamic nucleus) anandamide or WIN 55,212-2 administration (Citraro et al., 2013). However, it is unclear if the pharmacological modulation of CB1R, or endocannabinoids, can attenuate AS in the WAG/Rij strain and the exploration of this research field, assessing acute and chronic AS in WAG/Rij rats, can bring important information and insights about ES functionality in two different types of seizures (absence and audiogenic) in the same strain.

Cannabis-Derived Compounds in Audiogenic Seizures

After 40 years of the demonstration of CBD as anticonvulsant in humans (Cunha et al., 1980), the interest in medical Cannabis-derived compounds, especially CBD, has substantially increased, as an alternative treatment for pharmacoresistant epilepsy (Porter and Jacobson, 2013; Press et al., 2015; Devinsky et al., 2016, 2017). In 2018, the United States Food and Drug Administration (FDA) approved its first Cannabis-derived drug, the Epidiolex, a highly purified CBD oil solution (Corroon and Kight, 2018). This compound presents important therapeutic effect, especially in treatment-resistant epilepsy (Devinsky et al., 2018; Hausman-Kedem et al., 2018). However, although some studies have already demonstrated significant effects of Epidiolex against seizures, longitudinal studies to investigate long-term efficacy and safety are necessary, especially to assess its effects on cognitive and hormonal functions after chronic administration (Sekar and Pack, 2019).

In the basic research, CBD exerts not only anticonvulsant effects (Gobira et al., 2015; Kaplan et al., 2017; Klein et al., 2017; Lazarini-Lopes et al., 2020b), but also presents additional prominent effects important for epilepsy treatment, such as neuroprotective (Campos et al., 2016; Do Val-da Silva et al., 2017) and anti-inflammatory effects (Costa et al., 2004; Esposito et al., 2011). Because the epilepsies usually are accompanied by neuropsychiatric comorbidities, it is also important to know that CBD has antipsychotic, anxiolytic, and antidepressant effects (Zuardi et al., 1991; Crippa et al., 2011; Linge et al., 2016). As previously reported for pharmacological modulation of cannabinoid receptors, studies regarding Cannabis-derived compounds in AS are limited. See Table 1 for main results.

CBD anticonvulsant effects against AS were firstly demonstrated by Carlini’s research group during the 70’s, in Brazil, when audiogenic susceptible Wistar rats were treated with CBD and then exposed to high-intensity sound stimulation. CBD drastically reduced the incidence of AS, decreasing the expression of wild running followed by tonic-clonic seizures from 60 to 10% after an acute acoustic stimulation (Carlini et al., 1973). Using audiogenic susceptible rats, Consroe and Wolkin (1977), evaluated CBD effects in a great variety of epileptic seizure models, including AS. After three consecutive screenings for AS to confirm seizure susceptibility, CBD treatment was capable of preventing AS in a posterior stimulus. Moreover, the same research group showed that not only CBD, but also its analogs, prevented AS in 70% of animals after intravenous administration (Consroe et al., 1981). However, these studies did not discuss additional information regarding behavioral seizure profile or brain sites associated with CBD effects.

Cannabidivarin (CBDV), a CBD analog, presented dose-dependent protective effects against AS in DBA/2 mice, reducing the percentage of animals that developed tonic seizures, dropping to zero the mortality, and increasing the number of animals seizure-free (Hill et al., 2012). Similarly, Cannabis-derived botanical drug compounds rich in CBD were capable of reducing clonic seizures, and the co-administration of CBD and CBDV had synergic effects against generalized AS in DBA/2 mice, reducing wild running and clonic behaviors and blocking tonic seizures. This result is particularly interesting because although the authors confirmed CBD protective effects against AS, CBD anticonvulsant effects were independent of CB1R mechanisms (Hill et al., 2013). Gu et al. (2019) investigated CBD effects against AS in an animal model of Angelman Syndrome. In this model, mice are susceptible to AS, expressing wild running and tonic-clonic behaviors in response to intense sound stimulation (125 dB). CBD pretreatment presented dose-response effect, attenuating seizure expression, blocking tonic-clonic behaviors, and preventing seizure behaviors in more than 80% of Angelman Syndrome-mice tested (Gu et al., 2019). Furthermore, (–) Δ⁹-tetrahydrocannabinol (THC) protect animals against AS. Authors observed a dose-dependent effect of THC, attenuating wild running, tonic, and clonic seizures (Boggan et al., 1973).

The current data about Cannabis-derived compounds on AS, especially CBD, CBDV, and THC, are convergent, suggesting attenuation of wild running and tonic-clonic behaviors in acute AS. Nevertheless, cannabinoids in the context of chronic AS still need to be explored. Chronic seizure protocols, like the AuK, allow the study of drugs with anticonvulsant effects and potential antiepileptogenic effects associated with seizures progression during the chronic protocol (Simonato et al., 2014). Therefore, exploration of this research field using audiogenic strains could bring important information, especially regarding cannabinoids and the epileptogenic process.

Conclusion and Future Perspectives

Although with some paradoxical puzzling data, AS susceptibility in several of the mentioned networks converge to a more hyperexcitable brainstem state, either by an increase in glutamatergic neurotransmission or by a decrease in GABAergic signaling. Intra-collicular circuits receive and integrate information and send projections to extra-collicular afferent and efferent pathways and excessive excitatory activity into IC, SC, PAG, and BRF seems to be related with AS expression. On the other hand, GABA signaling into SNr is believed to be part of an endogenous anticonvulsant system that seems to be modulated by the ES, especially by CB1R, which could be an important clue to explain the neuronal basis of cannabinoids effects in AS.

Genetic strains used to study AS present advantages over chemical models, such as pilocarpine- and kainic acid-induced Status Epilepticus, where extended lesions are displayed by the animals (Leite et al., 2002; Castro et al., 2011; Furtado et al., 2011), but the neuroplasticity in AS is not accompanied by huge structural abnormalities (Galvis-Alonso et al., 2004). Other important characteristic of genetic models of AS is the absence of possible pharmacological interaction between cannabinoids and convulsant drugs. The AS model does not require previous invasive protocols for seizure induction (i.e., stereotaxic surgery or drug administration) and the trigger is an external high intensity stimulus directly controlled by the researcher. Because of these advantages, audiogenic strains seem to be interesting and appropriate approaches for epilepsies studies (Faingold et al., 2014).

Treatment with CB1R agonists, as well as with Cannabis-derived compounds, like CBD and CBDV, presented anticonvulsant activity against acute AS. The most prominent effects are associated with tonic behaviors, but wild running and clonus were also attenuated by these treatments. CB1R location in brainstem and forebrain structures also supports ES modulation on AS, especially into the SNr, amygdala, hippocampus, and cortex, the brain sites with most intense CB1R expression. Although there is a lack of studies investigating CBD and ES on chronic seizures in protocols like the AuK, the current data suggest that this is a prominent research area of study for epilepsies treatment. Since chronic protocols of AS allow the study of the epileptogenic process, the AuK could be an interesting tool to assess the role of the ES and Cannabis-derived compounds on limbic and forebrain recruitment.

Moreover, CBD anticonvulsant effects are associated with a great variety of mechanisms of action, such as GPR55, TRPV1, 5-HT_1A, BK channels, increased GABAergic neurotransmission, changes in calcium signaling, an indirect modulation of CB1R (Devinsky et al., 2014; Britch et al., 2020; Lazarini-Lopes et al., 2020b). In that context, antagonism of TRPV1 receptors suppressed AS in female GEPR-3s and attenuated seizures in male GEPR-3s (Cho et al., 2018). Therefore, the exploration of these mechanisms associated with cannabinoids in audiogenic strains is an interesting approach that should be further investigated. Furthermore, recent clinical data indicate that, regardless of the CBD low affinity for 5-HT1A receptors, at high concentration, CBD reduced the constitutive activity of receptors coupled to Gi/o receptors and these effects were reversed in the presence of 5-HT_1A antagonist, suggesting that CBD can act as a 5-HT_1A inverse agonist (Martínez-Aguirre et al., 2020). Therefore, the linking behind CBD anticonvulsant effects and the serotonergic system, should be further investigated in audiogenic strains.

Recent data showed that CBD attenuated seizures and restored the impaired hippocampal GABAergic neurotransmission observed in an animal model of Dravet-Syndrome (Kaplan et al., 2017). Likewise, audiogenic susceptible animals from the WAR strain present reduced GABAergic activity in the hippocampus (Cunha et al., 2018b) and the evaluation of CBD effects at GABAergic hippocampal network of WARs and other audiogenic strains could bring important information regarding CBD effects on epileptogenic process. Similarly, characterization of endocannabinoids levels and CB1R expression and functionality in brainstem and forebrain networks could help to explain the susceptibility to brainstem and limbic seizures in audiogenic strains. Data about CB1R expression in audiogenic susceptible strains are still very limited, but the current data suggest that endogenous alterations in CB1R could be related with seizure susceptibility, corroborating clinical data. Moreover, chronic alcohol exposure impairs CB1R functionality in the basolateral amygdala nucleus, which in turn, affects GABAergic signaling in this structure (Varodayan et al., 2016). Therefore, it should be an interesting approach to investigate changes in endocannabinoids levels and functionality in AS induced by ethanol withdrawal.

Finally, CBD presents different physiological and pharmacological mechanisms of action associated with its anticonvulsant effects and improvement of epilepsy-related neuropsychiatric comorbidities in basic and clinical research (Bergamaschi et al., 2011; Devinsky et al., 2014; Campos et al., 2017; Patra et al., 2020). Anxiety- and depressive-like behaviors are associated with genetic predisposition to seizure in strains like WAR, GEPR, KM, and audiogenic-susceptible WAG/Rij rats (Sarkisova and Kulikov, 2006; Castro et al., 2017; Sarkisova et al., 2017; Aguilar et al., 2018). However, the assessment of cannabinoids in epilepsy related comorbidities is an under-explored research field. Therefore, the ES in brainstem and limbic structures should be investigated not only in seizure susceptibility and expression, but also in neuropsychiatric comorbidities related to epilepsies.

Author Contributions

WL-L, RD, and NG-C conceived the original idea. WL-L wrote the manuscript. RD, AC, RS-J, and NG-C provided critical reviews, and assisted in the writing and background research. RS-J and WL-L prepared the figures. WL-L prepared the table. NG-C reviewed the manuscript and included additional recommendations. All authors approved the final version.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Footnotes

References