Evaluation of interactions between cannabinoid compounds and diazepam in electroshock-induced seizure model in mice

Abstract

Several studies have shown that cannabinoids have anticonvulsant properties that are mediated through activation of the cannabinoid CB1 receptors. In addition, endogenous cannabinoid compounds (endocannabinoids) regulate synaptic transmission and dampen seizure activity via activation of the same receptors. The aim of this study was to evaluate the possible interactions between antiepileptic effects of cannabinoid compounds and diazepam using electroshock-induced model of seizure in mice. Electroconvulsions were produced by means of an alternating current (ear-clip electrodes, fixed current intensity 35 mA, stimulus duration 0.2 s) and tonic hindlimb extension was taken as the endpoint. All experiments were performed on groups of ten mice and the number of animals who did not display seizure reported as percent protection. Intraperitoneal (i.p.) administration of diazepam (0.25-2 mg/kg) and CB1 receptor agonist WIN55212-2 (0.5-4 mg/kg) dose dependently produced an antiepileptic effect evaluated in terms of increased percentage of protection against electroshock-induced seizure. Logistic regression analysis indicated synergistic interactions in anticonvulsant action after co-administration of diazepam and WIN55212-2 in fixed-ratio combination of 3:1 (diazepam:WIN55212-2), while an additive effect was resulted after co-administration of 1:1 and 1:3 fixed-ratio combinations. Administration of various doses of the endocannabinoid reuptake inhibitor, AM404, did not produce any effect on electroshock-induced seizure. Moreover, co-administration of AM404 and diazepam did not produce significant interaction in antiepileptic properties of these compounds. Administration of the fatty acid amide hydrolase inhibitor, URB597, produced significant antiepileptic effect. Co-administration of URB597 and diazepam led to an antagonistic interaction in protection against shock-induced seizure. Co-administration of different doses of the cannabinoid CB1 receptor antagonist, AM251 did not alter the antiepileptic effect of diazepam in the electroshock-induced seizure test. These results demonstrate that endocannabinoid system participates in the modulation of seizure and combination of small doses of exogenous CB1 receptor agonists with diazepam may have effective consequences in seizure control. Furthermore, inhibiting the endocannabinoid degradation could be more efficacious in modulating seizure than preventing their uptake. This study also suggests that the effects of cannabinoids on epilepsy depend on the relative cannabinoid responsiveness of GABAergic and glutamatergic neurotransmission. While, the antiepileptic effects of cannabinoid compounds are likely by affecting excitatory glutamate neurotransmission, the antagonistic interaction between cannabinoid compounds and diazepam to protect seizure is due to the cannabinoid action on inhibitory GABAergic system.

Modulation of Anticonvulsant Effects of Cannabinoid Compounds by GABA-A Receptor Agonist in Acute Pentylenetetrazole Model of Seizure in Rat

“…This finding is consistent with other studies demonstrating WIN55212-2 produced an anticonvulsant effect in both in vivo [17] and in vitro [2] models of seizure. Moreover, these data complement our previous study showed WIN55212-2 produced protective effect in electroshock-induced seizure in mice [18]. Activation of cannabinoid CB1 receptor reduces the release of the excitatory neurotransmitter glutamate in CNS neurons [19].…”

“…Pre-treatment of rats with FAAH inhibitor URB597 did not produce significant change in the latency of seizure occurrence in PTZ-induced model of seizure, although previous work in this laboratory revealed a protective effect of URB597 against electroshock-induced seizure [18]. This could be in part due to the differences in the mechanism of seizure induction in these two models which affect different ion channels and receptors.…”

“…In conclusion, considering the results of the present study and our previously published data [18], it could be suggested that an interactions between cannabinoidergic and GABAergic systems exists during seizure. Understanding the different mechanism of action of the two putative endocannabinoids anandamide and 2-AG, and exogenous cannabinoid compounds in protection against seizure is important in analyzing the interaction between GABAergic agonists and cannabinoids in different animal models of seizure.…”

Effects of WIN 55,212-2 (a non-selective cannabinoid CB1 and CB2 receptor agonist) on the protective action of various classical antiepileptic drugs in the mouse 6 Hz psychomotor seizure model

“…Accumulating experimental evidence indicates that one of the synthetic cannabimimetic compounds [i.e., WIN 55,212-2 mesylate (WIN)—a highly potent non-selective cannabinoid CB 1 and CB 2 receptor agonist] potentiated the anticonvulsant activity of some classical antiepileptic drugs (i.e., diazepam, carbamazepine, phenytoin, phenobarbital and valproate) and second-generation antiepileptic drugs (i.e., lamotrigine, pregabalin and topiramate) in the mouse maximal electroshock-induced tonic seizure (MES) model (Luszczki et al 2011b, 2013; Naderi et al 2008). WIN also enhanced the anticonvulsant activity of ethosuximide, phenobarbital and valproate in the mouse pentylenetetrazole-induced clonic seizure (PTZ) model (Luszczki et al 2011a).…”

The Pharmacological Basis of Cannabis Therapy for Epilepsy

“…WIN55212, a CB 1 receptor agonist with effects similar to THC, was given at low doses in tandem with low doses of ethosuximide (Luszczki et al, 2011a), phenobarbital (Luszczki et al, 2011a(Luszczki et al, , 2011b, valproate (Luszczki et al, 2011a(Luszczki et al, , 2011b, carbamazepine (Luszczki et al, 2011b), phenytoin (Luszczki et al, 2011b), and diazepam (Naderi et al, 2008) to produce enhanced anticonvulsant effects in mice. In a similar fashion, the synthetic CB 1 receptor agonist arachidonyl-29-chloroethylamide was tested with low dose injections of naltrexone (Bahremand et al, 2008) and phenobarbital (Luszczki et al, 2010) to produce an additive anticonvulsant effect in mice.…”