Involvement of ATP-sensitive potassium channels and the opioid system in the anticonvulsive effect of zolpidem in mice

Epilepsy & Behavior 62 (2016) 291–296

Contents lists available at ScienceDirect

Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh

Involvement of ATP-sensitive potassium channels and the opioid system in the anticonvulsive effect of zolpidem in mice Mehdi Sheikhi a,b, Armin Shirzadian a,b, Amir Dehdashtian a,b, Shayan Amiri b, Sattar Ostadhadi a,b, Mehdi Ghasemi c, Ahmad Reza Dehpour a,b,⁎ a b c

Experimental Medicine Research Center, Tehran University of Medical Sciences, Tehran, Iran Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Department of Neurology, University of Massachusetts School of Medicine, Worcester, MA 01655, USA

a r t i c l e

i n f o

Article history: Received 19 May 2016 Revised 5 July 2016 Accepted 6 July 2016 Available online xxxx Keywords: Zolpidem Seizure Opioid KATP channel Morphine Pentylentetrazole Mice

a b s t r a c t Zolpidem is a hypnotic medication that mainly exerts its function through activating γ-aminobutyric acid (GABA)A receptors. There is some evidence that zolpidem may have anticonvulsive effects. However, the mechanisms underlying this effect have not been elucidated yet. In the present study, we used the pentylentetrazole (PTZ)-induced generalized seizure model in mice to investigate whether zolpidem can affect seizure threshold. We also further evaluated the roles of ATP-sensitive potassium (KATP) channels as well as μ-opioid receptors in the effects of zolpidem on seizure threshold. Our data showed that zolpidem in a dose-dependent manner increased the PTZ-induced seizure threshold. The noneffective (i.e., did not significantly alter the PTZ-induced seizure threshold by itself) doses of KATP channel blocker (glibenclamide) and nonselective opioid receptor antagonist (naloxone) were able to inhibit the anticonvulsive effect of zolpidem. Additionally, noneffective doses of either KATP channel opener (cromakalim) or nonselective μ-opioid receptor agonist (morphine) in combination with a noneffective dose of zolpidem exerted a significant anticonvulsive effect on PTZ-induced seizures in mice. A combination of noneffective doses of naloxone and glibenclamide, which separately did not affect zolpidem effect on seizure threshold, inhibited the anticonvulsive effects of zolpidem. These results suggest a role for KATP channels and the opioid system, alone or in combination, in the anticonvulsive effects of zolpidem. © 2016 Elsevier Inc. All rights reserved.

1. Introduction Zolpidem is an effective nonbenzodiazepine sedative hypnotic medication that activates benzodiazepine binding sites on γ-aminobutyric acid (GABA)A receptors [1,2]. The selective affinity of zolpidem for α1containing GABAA receptors causes different effects including sedation, muscle relaxation, and anxiolytic effects, which represents different pharmacological profiles from the classic benzodiazepines. Additionally, there is some evidence that zolpidem can act as a potent anticonvulsant in animal studies [3]. Zolpidem has approximately 10-fold lower affinity for the α2 and α3 subunit-containing GABAA receptors than benzodiazepines and with no appreciable affinity for α5 subunit-containing receptors [4,5]. There is a consensus among researchers that, except for anxiolytic effects of zolpidem, other effects of zolpidem such as sedation, amnesia, and potential anticonvulsant properties are mainly due to its effect on α1-containing GABAA receptors [1,2,6–10]; however,

⁎ Corresponding author at: Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Tel.: +98 21 8897 3652; fax: +98 21 6640 2569. E-mail addresses: [email protected], [email protected] (M. Ghasemi), [email protected] (A.R. Dehpour).

http://dx.doi.org/10.1016/j.yebeh.2016.07.014 1525-5050/© 2016 Elsevier Inc. All rights reserved.

the exact underlying mechanism of action of zolpidem in increasing seizure threshold has not been completely understood. It is well established that central opioidergic neurotransmission plays a crucial role in modulating seizure threshold [11–15]. Opioid receptor agonists depending on the doses used exert both anticonvulsive and proconvulsive effects in different models of experimental seizures [13–17]. Low doses of the nonselective μ-opioid receptor agonist morphine have an anticonvulsive effect, while higher doses increase the seizure susceptibility induced by GABA-transmission blockers (i.e., picrotoxin, bicuculline, pentylentetrazole [PTZ]) and in isoniazid models of seizures [16,18]. It has been shown that μ-opioid receptors are responsible for both anticonvulsive and proconvulsive effects of morphine on chemical and electrical models of seizures and, accordingly, naloxone, as a nonselective opioid receptor antagonist, reverses these effects [16]. Although several investigations have shown that GABAergic neurotransmission could participate in seizure modulation in association with the central opioidergic system [19,20], whether the possible anticonvulsive effects of zolpidem, as a GABAA receptor agonist, could be modulated by the opioidergic system has not yet been assessed in the recent studies. The ATP-sensitive potassium (KATP) channels are a group of potassium channels that are sensitive to alterations in the intracellular concentration of the ATP and the ATP/ADP ratio, linking the electrical activity of

292

M. Sheikhi et al. / Epilepsy & Behavior 62 (2016) 291–296

the cell to its metabolic state [21,22]. They are expressed in many excitable cells such as cardiac myocytes, pancreatic β cells, vascular smooth muscles, skeletal muscles, and neurons [23–27]. These channels are also expressed pre- and postsynaptically in some brain regions such as hippocampus [28,29]. Increasing lines of evidence have demonstrated that KATP channels play an important role in control of seizure threshold in in vivo and in vitro models [15,29–35]. Activation of KATP channels prolongs seizure onset through inhibition of excitatory neurotransmitters (e.g., glutamate) [36]. It has been shown that the lack and overexpression of KATP channels are respectively responsible for reducing the threshold of generalized seizure and increasing the threshold for kainite-induced seizures [32,36]. Additionally, several lines of evidence have suggested the involvement of KATP channels in the central and/or peripheral actions of nonselective μ-opioid receptor agonists (e.g., morphine). In the central nervous system (CNS), these actions include the following: antinociceptive effect, tolerance, withdrawal, hyperthermia, noradrenaline turnover-enhancing effect, morphine state-dependent memory of passive avoidance, and bicuculline (a competitive GABAA receptor antagonist)-induced convulsions [34,37–42]. Thus, KATP channel modulators play a major role in the effects of morphine on neurotransmitter release in the CNS [43] and may be involved in their effects on modulation of the central GABAergic transmission. To the best of our knowledge, there is no published evidence regarding the possible involvement of KATP channels, directly or indirectly through involving other systems such as opioid systems, in the central effects of zolpidem, as a GABAA receptor agonist, such as its possible anticonvulsive effects. Therefore, in the present study, we first evaluated the effects of zolpidem on the seizure threshold in a mouse model of clonic seizures induced by PTZ, and then we evaluated whether the μ-opioidergic receptors as well as KATP channels could potentially be involved in the anticonvulsive effects of zolpidem on the PTZ-induced seizures in mice. Of note, PTZ is a noncompetitive GABAA receptor antagonist [44]. The onset and intensity of PTZ-induced seizure can be modified by drugs having anticonvulsive and/or proconvulsive effects [44,45]. There is an intravenous (i.v.) PTZ seizure threshold model which is used as a laboratory evaluation for anticonvulsive drugs [46], and we used this model in our present study. 2. Materials and methods 2.1. Chemicals Drugs used were as follows: cromakalim, glibenclamide, pentylenetetrazole (Sigma, Bristol, UK), morphine (Sigma, Bristol, UK), and naloxone (Sigma, Bristol, UK). Glibenclamide was dissolved in 1% of DMSO. Cromakalim and morphine were dissolved in saline. All injections were administered at a volume of 5 ml/kg. Appropriate vehicle controls were performed for each experiment. Morphine, naloxone, cromakalim, and glibenclamide were administered intraperitoneally (i.p.). To assess clonic seizure experiments, PTZ was administered intravenously at a constant rate of 1 ml/min to unrestrained animals. The doses were chosen based on previously published studies [1,15,31,47–49] and pilot experiments.

2.3. Determination of clonic seizure threshold Pentylentetrazole-induced clonic seizure threshold was determined by inserting a 30-gauge butterfly needle into the tail vein of mice which was fixed by adhesive tape and the infusion of PTZ (0.5%) at a constant rate of 1 ml/min to animals using a 40-cm flexible tube as a connector between infusion pump syringe and butterfly needle which provides an unrestrained freely moving condition. Infusion was halted when forelimb clonus followed by full clonus of the body was observed. A minimal dose of PTZ (mg/kg of mice weight) needed to induce clonic seizure was considered as an index of seizure threshold. As such, seizure threshold is dependent on PTZ dose administered and time-related [1,15,31,47–49]. 2.4. Experimental protocol We investigated the effect of three different doses of zolpidem (1, 3, and 10 mg/kg) [50,51] on PTZ-induced seizures compared with the seizure threshold of the control group, which had been given normal saline. Also in separate groups of animals, zolpidem at a dose of 10 mg/kg was injected 5, 15, and 30 min before the PTZ infusion to acquire the best time of action for our subsequent experiments. Next, for the determination of probable contribution of KATP channels in the anticonvulsive activity of zolpidem, we administered different doses of the KATP channel blocker glibenclamide (0.3, 0.1, and 1 mg/kg) [15,49] 30 min prior injection of zolpidem (10 mg/kg) and 60 min prior to PTZ-induced seizure threshold measurement. In an additional set of experiments, we further assessed the interaction between zolpidem and KATP channels in seizure threshold alteration in mice. We administered the noneffective dose of the KATP channel opener cromakalim (10 μg/kg) [52] 15 min before the administration of the noneffective dose of zolpidem (1 mg/kg, i.p.). The seizure threshold was then assessed 30 min after zolpidem injection. In order to assess the interaction between the opioid system and zolpidem in provoking the anticonvulsive effects, noneffective doses of the opioid receptor antagonist naloxone (0.03, 0.1, and 1 mg/kg, i.p.) [53] were injected 15 min prior to zolpidem (10 mg/kg) and 45 min before PTZ infusion. Finally, we evaluated the potential interaction between KATP channels and opioid system in modulating to anticonvulsive effect of zolpidem. Thus, glibenclamide (0.03 mg/kg, i.p.) or naloxone (0.03 mg/kg, i.p.), separately or combined together, was injected prior to the injection of zolpidem (10 mg/kg, i.p.). 2.5. Statistical analysis Data are expressed as mean ± S.E.M. of clonic seizure threshold in each experimental group. The one-way or two-way analysis of variance (ANOVA) followed by Newman–Keuls post hoc test was used to analyze the data. In all experiments, a P value less than 0.05 was considered statistically significant. 3. Results

2.2. Experimental animals

3.1. Anticonvulsive effect of zolpidem

Male NMRI mice weighing 20–25 g (Pasteur Institute) were used throughout this study. Animals were housed in groups of 4–5 and were allowed free access to food and water except for the short time that animals were removed from their cages for testing. All behavioral experiments were conducted during the period between 10:00 a.m. and 13:00 p.m. with normal room light (12-h regular light/dark cycle) and temperature (22 ± 1 °C). All procedures were carried out in accordance with the institutional guidelines for animal care and use. Each group consisted of 8–10 animals.

Fig. 1A shows the effect of zolpidem (1, 3, and 10 mg/kg, i.p.) on PTZinduced seizure threshold 30 min after zolpidem injection. Doses of 3 mg/kg and 10 mg/kg of zolpidem significantly increased the threshold (P b 0.001 and P b 0.0001, respectively; F3,16 = 102.1), whereas zolpidem at 1 mg/kg did not show significant anticonvulsive effects. As depicted in Fig. 1, the maximum dose of zolpidem for an anticonvulsive effect was observed at 10 mg/kg. Fig. 1B also shows the effects of zolpidem (10 mg/kg, i.p.) on seizure threshold when administered 5, 15, and 30 min before the PTZ injection. The maximum response time

M. Sheikhi et al. / Epilepsy & Behavior 62 (2016) 291–296

Fig. 1. (A) Comparison of PTZ-induced clonic-seizure threshold in mice at different doses of zolpidem (1, 3, and 10 mg/kg, i.p.) and its vehicle (saline). ***P b 0.001 and ****P b 0.0001 compared with saline group. (B) Comparison of PTZ-induced clonicseizure threshold in mice at different times after injection of zolpidem at 10 mg/kg (i.v.) and vehicle (saline) on the seizure threshold. ****P b 0.0001 compared with saline group, according to one-way analysis of variance, followed by Newman–Keuls post hoc test. Each point represents the mean ± S.E.M. of 10 mice. Minimal dose of PTZ (mg/kg of mice weight) needed to induce clonic seizure was considered as an index of seizure threshold. *P b 0.05 and ***P b 0.001 compared with saline-treated group,

in the PTZ-induced seizure threshold was 30 min (P b 0.0001) after zolpidem administration (Fig. 1B).

3.2. Effects of KATP channel modulators on anticonvulsive property of zolpidem In the next step, we examined the role of a KATP channel blocker in the anticonvulsive effects of zolpidem. Fig. 2A shows administration of 0.03, 0.1, and 1 mg/kg of the selective KATP channel blocker glibenclamide 30 min prior to zolpidem and 60 min prior to PTZ administration. Glibenclamide at doses of 0.1 mg/kg (P b 0.05) and 1 mg/kg (P b 0.01) significantly prevented the anticonvulsive effect of zolpidem (F5,22 = 93.77; P b 0.01), whereas a lower dose of glibenclamide (0.03 mg/kg) did not significantly affect the anticonvulsive effects of zolpidem on PTZ-induced seizures in mice. It is noteworthy that glibenclamide itself at these doses did not have any significant effect on the seizure threshold induced by PTZ. As shown in Fig. 2B, we also found that the selective KATP channel opener cromakalim at 10 μg/kg (i.p.) when administered 15 min before the administration of a noneffective dose of zolpidem (1 mg/kg, i.p.) resulted in a significant elevation of seizure threshold (F3,17 = 10.50; P b 0.01). At this dose, cromakalim itself did not have any significant effect on the PTZ-induced seizure threshold.

293

Fig. 2. (A) Effects of pretreatment with glibenclamide (gli, 0.03, 0.1, and 1 mg/kg, i.p.) or its vehicle (DMSO) on the anticonvulsant effects of zolpidem (Zol, 10 mg/kg, i.p.) on PTZinduced seizure threshold. Each point represents the mean ± S.E.M. of 10 mice. ****P b 0.0001 compared with DMSO/saline group. #P b 0.05 and ##P b 0.01 compared with DMSO/zolpidem (10 mg/kg, i.p.) group. (B) Effects of pretreatment (15 min prior either zolpidem or saline) with noneffective dose of cromakalim (crmk, 10 μg/kg, i.p.) or its vehicle (saline) on noneffective dose of zolpidem (Zol, 1 mg/kg, i.p.) on PTZ-induced seizure threshold. Each point represents the mean ± S.E.M. of 10 mice. **P b 0.01 compared with either saline/saline or saline/zolpidem group. Data were analyzed by one-way analysis of variance, followed by Newman–Keuls post hoc test. Minimal dose of PTZ (mg/kg of mice weight) needed to induce clonic seizure was considered as an index of seizure threshold.

3.3. Effects of opioid receptor modulators on the anticonvulsive property of zolpidem Fig. 3A shows the effects of different doses of the μ-opioid receptor antagonist naloxone on the anticonvulsive effects of zolpidem (10 mg/kg, i.p.) on the PTZ-induced seizure threshold. Naloxone (0.03, 0.1, and 1 mg/kg) was administered intraperitoneally (i.p.) 15 min before zolpidem and 45 min before the PTZ infusion. Naloxone at doses of 0.1 and 1 mg/kg significantly prevented the anticonvulsive effects of zolpidem (P b 0.01 and P b 0.001, respectively; F5,22 = 71.64). At these doses, naloxone itself had no significant effects on PTZ-induced seizure threshold. As depicted in Fig. 3B, combined treatment with a noneffective dose of morphine (1 mg/kg) and noneffective dose of zolpidem (1 mg/kg) significantly increased the seizure threshold induced by PTZ (F3,14 = 22.39, P b 0.001). 3.4. Effect of combined KATP channel and opioid receptor antagonists on anticonvulsive effects of zolpidem As depicted in Fig. 4, noneffective doses of glibenclamide (0.03 mg/kg, i.p.) and naloxone (0.03 mg/kg, i.p.) did not alter the anticonvulsive

294

M. Sheikhi et al. / Epilepsy & Behavior 62 (2016) 291–296

Fig. 4. Effects of subeffective doses of naloxone (NX, 0.03 mg/kg, i.p.) and glibenclamide (gli, 0.03 mg/kg, i.p.), alone or in combination, on the anticonvulsant effects of zolpidem (Zol, 10 mg/kg, i.p.) on PTZ-induced seizure threshold. Each point represents the mean ± S.E.M. of 10 mice. ****P b 0.0001 compared with saline/DMSO/saline group; ## P b 0.01 compared to corresponding saline/DMSO/zolpidem group. Data were analyzed by one-way analysis of variance, followed by Newman–Keuls post hoc test. Minimal dose of PTZ (mg/kg of mice weight) needed to induce clonic seizure was considered as an index of seizure threshold.

Fig. 3. (A) Effects of pretreatment with different doses of naloxone (NX, 0.03, 0.1, and 1 mg/kg, i.p.) and its vehicle (saline) on the anticonvulsant effects of zolpidem (Zol, 10 mg/kg, i.p.) on PTZ-induced seizure threshold. Each point represents the mean ± S.E.M. of 10 mice. ****P b 0.0001, compared with saline/saline group. #P b 0.05 and ### P b 0.001 compared with saline/zolpidem (10 mg/kg, i.p.) group. (B) Effects of pretreatment (15 min prior to either zolpidem or saline) with noneffective dose of morphine (1 mg/kg, i.p.) or its vehicle (saline) on noneffective dose of zolpidem (Zol, 1 mg/kg, i.p.) on PTZ-induced seizure threshold. Each point represents the mean ± S.E.M. of 10 mice. ***P b 0.001, compared with either saline/saline or saline/zolpidem group. Data were analyzed by one-way analysis of variance, followed by Newman–Keuls post hoc test. Minimal dose of PTZ (mg/kg of mice weight) needed to induce clonic seizure was considered as an index of seizure threshold.

effects of zolpidem (10 mg/kg, i.p.) separately. However, when the combination of glibenclamide (0.03 mg/kg, i.p.) and naloxone (0.03 mg/kg, i.p.) was administered before zolpidem (10 mg/kg, i.p.), they prevented the anticonvulsive effect of zolpidem on PTZ-induced seizure threshold (F11,44 = 117.5, P b 0.01). 4. Discussion The present study demonstrated the dose-dependent anticonvulsive effects of zolpidem on PTZ-induced seizures in mice. Our data revealed that the noneffective doses (0.1 and 1 mg/kg) of the KATP channel blocker glibenclamide (which individually had no significant effect on the PTZ-induced seizure threshold) prevented the anticonvulsive effects of zolpidem. We also showed that this effect of zolpidem was blocked by the selective KATP channel opener cromakalim. On the other hand, pretreatment with the nonselective opioid receptor antagonist naloxone decreased the anticonvulsive effects of zolpidem. Pretreatment with the opioid receptor agonist morphine also enhanced the

anticonvulsive effects of zolpidem on seizure threshold. Additionally, the combination of noneffective doses of naloxone and glibenclamide significantly decreased the effects of zolpidem on the seizure threshold. According to these results, it seems that the anticonvulsive effects of zolpidem are mediated through both KATP channels and opioid receptors. Zolpidem is a well tolerated, safe, and acceptable medication with minimal risk of dependence and abuse. Selective affinity for GABAA receptors causes different pharmacological profiles compared with classic benzodiazepines [1,2]. It has been suggested that zolpidem has an anticonvulsive effect and might be a better anticonvulsive drug than previously thought; thus, this effect should not be overlooked [3,54,55]. Our data are in accordance with the results of a recent study that has shown the anticonvulsive property of zolpidem in the PTZ-induced seizure model [3]. Previous investigation has also demonstrated the protective effect of zolpidem against tonic seizures induced by PTZ, maximal electroshock, and clonic seizures induced by isoniazid [1,55]. Administration with the GABAA antagonist picrotoxin demonstrated protective activity in induced seizures [56]. Zolpidem also exerts a strong antiabscence activity in WAG/Rij rats which mimics the effect of midazolam, a potent hypnotic drug [54]. Although GABAergic transmission is well established in regulating seizure threshold in the CNS [57] and may explain the anticonvulsive effects of zolpidem, as a GABAA receptor agonist, the possible role of other neurotransmitter systems or ion channels in this effect of zolpidem has not been investigated yet. Our data for the first time, to our knowledge, suggested a role for involvement of KATP channels in the anticonvulsive effects of zolpidem. It is well-known that KATP channels play a very important role in the modulation of seizure threshold [58], as demonstrated by a variety of in vivo and in vitro models [15,31,49,59,60]. Reducing the risk of overstimulation of glutamate transmission at CA3 synapses by the functional KATP channel subunits Kir6.1/SUR1 has been demonstrated to be an endogenous cellular protective event against seizures [61]. Other studies also suggested that changes in the gene and protein expression of KATP channel subunits in the hippocampus of rats subjected to picrotoxininduced kindling are key in the induction and maintenance of kindling in the rat brain [62]. Mice lacking Kir6.2−/−, a subunit of KATP channels, are more vulnerable to hypoxia and have a reduced threshold for generalized seizures [63]. The KATP channels can also modulate the

M. Sheikhi et al. / Epilepsy & Behavior 62 (2016) 291–296

effects of other systems on seizure threshold. For instance, these channels are involved in the biphasic effects of morphine (the nonselective μ-opioid receptor agonist) on PTZ-induced seizure threshold in mice [15]. In the present study, the selective KATP channel blocker glibenclamide inhibited and the selective KATP channel opener cromakalim potentiated the anticonvulsive effects of zolpidem in the PTZ model of generalized seizures in mice. To the best of our knowledge, there is no published evidence of an effect of zolpidem on KATP channels themselves. Given the fact that zolpidem is a GABAA receptor agonist, it is possible that interaction with the GABAergic system and KATP channels may be involved in the increased seizure threshold induced by PTZ in mice. Accordingly, there is some evidence that KATP channels may modulate GABAergic transmission in different brain regions such as hippocampus, hypothalamus, caudate nucleus, and striatum [64–70]. For instance, these channels are present both pre- and postsynaptically on GABAergic hippocampal neurons and affect both presynaptic GABA release as well as the postsynaptic GABA response [67,68]. Thus, it is plausible that interaction between the GABAergic system and KATP channels in certain brain regions that are involved in epileptogenesis, such as hippocampus, participates in the anticonvulsive effects of zolpidem. Morphine expresses biphasic effects on PTZ-induced clonic seizures with an anticonvulsive profile associated with increased central GABAergic transmission [16,71]. Also, continued activation of opioid receptors is associated with seizures via GABA inhibitory pathways. Morphine can modulate seizure susceptibility and be proconvulsive in higher doses [15,34,72,73]. There is evidence supporting the role of μopioid system activation in various seizure models induced by PTZ, bicuculline. N-methyl-D-aspartate (NMDA) and pilocarpine have more general modulatory effects on other seizure models [15,34,72,73]. In our study, we also showed that opioid neurotransmission could be involved in the anticonvulsant effects of zolpidem. There is some evidence that opioidergic neurotransmission may contribute to some other effects of zolpidem such as pain control [74]. By using the hotplate analgesic assay in mice, Pick et al. found that antinociceptive effects of zolpidem are inhibited by pretreatment with naloxone [74], suggesting the possible interaction of zolpidem with the opioid system. In our study, we also showed that combined noneffective doses of KATP channels and opioid receptor blockers significantly decreased the anticonvulsant effects of zolpidem. These data suggest that interaction between the KATP channels and opioid system in the CNS may contribute to the effects of zolpidem on seizure threshold. In fact, there is evidence that μ-opioid receptors increase K+ conductance in cellular studies [75]. Morphine can hyperpolarize neuronal cells and reduce their activity through μ1 and μ2 receptors which are coupled to KATP channels [76]. Our previous studies also demonstrated that KATP channels can modulate the effects of the opioid system in PTZ-induced seizures in mice [15]. These systems also have interactions in other behavioral models such as antinociception and conditioned place preference [77–79]. Taken together, the interactions between the opioid system and KATP channels seem to be an important contributor in the modulation of anticonvulsant effects of zolpidem in the mouse model of PTZ-induced seizures. In summary, our present data demonstrated anticonvulsant effects of zolpidem in the PTZ-induced seizure model in mice. We also found that both the opioidergic system and KATP channels, alone or in combination with each other, could be involved in the anticonvulsant effects of zolpidem. However, more studies using different seizure models are clearly required to investigate whether these systems are involved in the anticonvulsant effects of zolpidem.

Conflict of interest The authors have no conflict of interest regarding the current manuscript and presented data.

295

References [1] Depoortere H, Zivkovic B, Lloyd KG, Sanger DJ, Perrault G, Langer SZ, et al. Zolpidem, a novel nonbenzodiazepine hypnotic. I. Neuropharmacological and behavioral effects. J Pharmacol Exp Ther 1986;237:649–58. [2] Sanger DJ, Benavides J, Perrault G, Morel E, Cohen C, Joly D, et al. Recent developments in the behavioral pharmacology of benzodiazepine (omega) receptors: evidence for the functional significance of receptor subtypes. Neurosci Biobehav Rev 1994;18:355–72. [3] Vlainic J, Pericic D. Zolpidem is a potent anticonvulsant in adult and aged mice. Brain Res 2010;1310:181–8. [4] Pritchett DB, Seeburg PH. Gamma-aminobutyric acidA receptor alpha 5-subunit creates novel type II benzodiazepine receptor pharmacology. J Neurochem 1990; 54:1802–4. [5] Smith AJ, Alder L, Silk J, Adkins C, Fletcher AE, Scales T, et al. Effect of alpha subunit on allosteric modulation of ion channel function in stably expressed human recombinant gamma-aminobutyric acid(A) receptors determined using (36)Cl ion flux. Mol Pharmacol 2001;59:1108–18. [6] Crestani F, Martin JR, Mohler H, Rudolph U. Mechanism of action of the hypnotic zolpidem in vivo. Br J Pharmacol 2000;131:1251–4. [7] Perrault G, Morel E, Sanger DJ, Zivkovic B. Differences in pharmacological profiles of a new generation of benzodiazepine and non-benzodiazepine hypnotics. Eur J Pharmacol 1990;187:487–94. [8] McKernan RM, Rosahl TW, Reynolds DS, Sur C, Wafford KA, Atack JR, et al. Sedative but not anxiolytic properties of benzodiazepines are mediated by the GABA(A) receptor alpha1 subtype. Nat Neurosci 2000;3:587–92. [9] Kralic JE, O'Buckley TK, Khisti RT, Hodge CW, Homanics GE, Morrow AL. GABA(A) receptor alpha-1 subunit deletion alters receptor subtype assembly, pharmacological and behavioral responses to benzodiazepines and zolpidem. Neuropharmacology 2002;43:685–94. [10] Heldt SA, Ressler KJ. Amygdala-specific reduction of alpha1-GABAA receptors disrupts the anticonvulsant, locomotor, and sedative, but not anxiolytic, effects of benzodiazepines in mice. J Neurosci 2010;30:7139–51. [11] Hong JS. Hippocampal opioid peptides and seizures. Epilepsy Res Suppl 1992;7: 187–95. [12] Simonato M, Romualdi P. Dynorphin and epilepsy. Prog Neurobiol 1996;50:557–83. [13] Ghasemi M, Shafaroodi H, Nazarbeiki S, Meskar H, Ghasemi A, Bahremand A, et al. Inhibition of NMDA receptor/NO signaling blocked tolerance to the anticonvulsant effect of morphine on pentylenetetrazole-induced seizures in mice. Epilepsy Res 2010;91:39–48. [14] Roshanpour M, Ghasemi M, Riazi K, Rafiei-Tabatabaei N, Ghahremani MH, Dehpour AR. Tolerance to the anticonvulsant effect of morphine in mice: blockage by ultralow dose naltrexone. Epilepsy Res 2009;83:261–4. [15] Shafaroodi H, Asadi S, Sadeghipour H, Ghasemi M, Ebrahimi F, Tavakoli S, et al. Role of ATP-sensitive potassium channels in the biphasic effects of morphine on pentylenetetrazole-induced seizure threshold in mice. Epilepsy Res 2007;75:63–9. [16] Lauretti GR, Ahmad I, Pleuvry BJ. The activity of opioid analgesics in seizure models utilizing N-methyl-DL-aspartic acid, kainic acid, bicuculline and pentylenetetrazole. Neuropharmacology 1994;33:155–60. [17] Foote F, Gale K. Proconvulsant effect of morphine on seizures induced by pentylenetetrazol in the rat. Eur J Pharmacol 1984;105:179–84. [18] Homayoun H, Khavandgar S, Dehpour AR. The involvement of endogenous opioids and nitricoxidergic pathway in the anticonvulsant effects of foot-shock stress in mice. Epilepsy Res 2002;49:131–42. [19] Bodnar RJ. Endogenous opiates and behavior: 2014. Peptides 2016;75:18–70. [20] Simmons ML, Chavkin C. Endogenous opioid regulation of hippocampal function. Int Rev Neurobiol 1996;39:145–96. [21] Mannhold R. KATP channel openers: structure–activity relationships and therapeutic potential. Med Res Rev 2004;24:213–66. [22] Aguilar-Bryan L, Clement JP, Gonzalez G, Kunjilwar K, Babenko A, Bryan J. Toward understanding the assembly and structure of KATP channels. Physiol Rev 1998;78: 227–45. [23] Noma A. ATP-regulated K+ channels in cardiac muscle. Nature 1983;305:147–8. [24] Findlay I, Dunne MJ, Petersen OH. ATP-sensitive inward rectifier and voltage- and calcium-activated K+ channels in cultured pancreatic islet cells. J Membr Biol 1985;88:165–72. [25] Kakei M, Noma A, Shibasaki T. Properties of adenosine–triphosphate-regulated potassium channels in guinea-pig ventricular cells. J Physiol 1985;363:441–62. [26] Standen NB, Quayle JM, Davies NW, Brayden JE, Huang Y, Nelson MT. Hyperpolarizing vasodilators activate ATP-sensitive K+ channels in arterial smooth muscle. Science 1989;245:177–80. [27] Spruce AE, Standen NB, Stanfield PR. Voltage-dependent ATP-sensitive potassium channels of skeletal muscle membrane. Nature 1985;316:736–8. [28] de Weille JR, Lazdunski M. Regulation of the ATP-sensitive potassium channel. Ion Channels 1990;2:205–22. [29] Zawar C, Plant TD, Schirra C, Konnerth A, Neumcke B. Cell-type specific expression of ATP-sensitive potassium channels in the rat hippocampus. J Physiol 1999;514(Pt 2): 327–41. [30] Yamada K, Inagaki N. Neuroprotection by KATP channels. J Mol Cell Cardiol 2005;38: 945–9. [31] Niaki SE, Shafaroodi H, Ghasemi M, Shakiba B, Fakhimi A, Dehpour AR. Mouth breathing increases the pentylenetetrazole-induced seizure threshold in mice: a role for ATP-sensitive potassium channels. Epilepsy Behav 2008;13:284–9. [32] Yamada K, Ji JJ, Yuan H, Miki T, Sato S, Horimoto N, et al. Protective role of ATPsensitive potassium channels in hypoxia-induced generalized seizure. Science 2001;292:1543–6.

296

M. Sheikhi et al. / Epilepsy & Behavior 62 (2016) 291–296

[33] Gandolfo G, Gottesmann C, Bidard JN, Lazdunski M. K+ channels openers prevent epilepsy induced by the bee venom peptide MCD. Eur J Pharmacol 1989;159: 329–30. [34] Narita M, Takahashi Y, Suzuki T, Misawa M, Nagase H. An ATP-sensitive potassium channel blocker abolishes the potentiating effect of morphine on the bicucullineinduced convulsion in mice. Psychopharmacology (Berl) 1993;110:500–2. [35] Katsumori H, Ito Y, Higashida H, Hashii M, Minabe Y. Anti- and proconvulsive actions of levcromakalim, an opener of ATP-sensitive K+ channel, in the model of hippocampus-generating partial seizures in rats. Eur J Pharmacol 1996;311:37–44. [36] Hernandez-Sanchez C, Basile AS, Fedorova I, Arima H, Stannard B, Fernandez AM, et al. Mice transgenically overexpressing sulfonylurea receptor 1 in forebrain resist seizure induction and excitotoxic neuron death. Proc Natl Acad Sci U S A 2001;98: 3549–54. [37] Narita M, Suzuki T, Misawa M, Nagase H, Nabeshima A, Ashizawa T, et al. Role of central ATP-sensitive potassium channels in the analgesic effect and spinal noradrenaline turnover-enhancing effect of intracerebroventricularly injected morphine in mice. Brain Res 1992;596:209–14. [38] Raffa RB, Martinez RP. The ‘glibenclamide-shift’ of centrally-acting antinociceptive agents in mice. Brain Res 1995;677:277–82. [39] Gonzalez LG, Portillo E, Del Pozo E, Baeyens JM. Changes in [(3)H]glibenclamide binding to mouse forebrain membranes during morphine tolerance. Eur J Pharmacol 2001;418:29–37. [40] Robles LI, Barrios M, Baeyens JM. ATP-sensitive K+ channel openers inhibit morphine withdrawal. Eur J Pharmacol 1994;251:113–5. [41] Narita M, Suzuki T, Misawa M, Nagase H. Role of central ATP-sensitive potassium channels in the hyperthermic effect of morphine in mice. Psychopharmacology (Berl) 1992;109:239–40. [42] Zarrindast MR, Jafari MR, Shafaghi B, Djahanguiri B. Influence of potassium channel modulators on morphine state-dependent memory of passive avoidance. Behav Pharmacol 2004;15:103–10. [43] Sarne Y, Fields A, Keren O, Gafni M. Stimulatory effects of opioids on transmitter release and possible cellular mechanisms: overview and original results. Neurochem Res 1996;21:1353–61. [44] Loscher W, Schmidt D. Which animal models should be used in the search for new antiepileptic drugs? A proposal based on experimental and clinical considerations. Epilepsy Res 1988;2:145–81. [45] Loscher W. Preclinical assessment of proconvulsant drug activity and its relevance for predicting adverse events in humans. Eur J Pharmacol 2009;610:1–11. [46] Loscher W, Fiedler M. The role of technical, biological, and pharmacological factors in the laboratory evaluation of anticonvulsant drugs. VII. Seasonal influences on anticonvulsant drug actions in mouse models of generalized seizures. Epilepsy Res 2000;38:231–48. [47] Rayatzadeh H, Nouri M, Ghasemi M, Kebriaeezadeh A, Mehr SE, Dehpour AR. Effect of metal chelating agents on pentylenetetrazole-induced seizure threshold in cholestatic mice. Seizure 2009;18:51–6. [48] Shafaroodi H, Ghasemi M, Dehpour AR. Elevation of pentylenetetrazole-induced seizure threshold in cholestatic mice: interaction between opioid and cannabinoid systems. J Gastroenterol Hepatol 2008;23:e251–7. [49] Shafaroodi H, Barati S, Ghasemi M, Almasirad A, Moezi L. A role for ATP-sensitive potassium channels in the anticonvulsant effects of triamterene in mice. Epilepsy Res 2016;121:8–13. [50] Fahey JM, Grassi JM, Reddi JM, Greenblatt DJ. Acute zolpidem administration produces pharmacodynamic and receptor occupancy changes at similar doses. Pharmacol Biochem Behav 2006;83:21–7. [51] Vlainić J, Peričić D. Effects of acute and repeated zolpidem treatment on pentylenetetrazole-induced seizure threshold and on locomotor activity: comparison with diazepam. Neuropharmacology 2009;56:1124–30. [52] Ghasemi M, Shafaroodi H, Karimollah AR, Gholipour T, Nezami BG, Ebrahimi F, et al. ATP-sensitive potassium channels contribute to the time-dependent alteration in the pentylenetetrazole-induced seizure threshold in diabetic mice. Seizure 2010; 19:53–8. [53] Hassanipour M, Shirzadian A, Boojar MM-A, Abkhoo A, Abkhoo A, Delazar S, et al. Possible involvement of nitrergic and opioidergic systems in the modulatory effect of acute chloroquine treatment on pentylenetetrazol induced convulsions in mice. Brain Res Bull 2016;121:124–30. [54] Depoortere H, Francon D, van Luijtelaar EL, Drinkenburg WH, Coenen AM. Differential effects of midazolam and zolpidem on sleep–wake states and epileptic activity in WAG/Rij rats. Pharmacol Biochem Behav 1995;51:571–6.

[55] Sanger DJ, Morel E, Perrault G. Comparison of the pharmacological profiles of the hypnotic drugs, zaleplon and zolpidem. Eur J Pharmacol 1996;313:35–42. [56] Pericic D, Vlainic J, Strac DS. Sedative and anticonvulsant effects of zolpidem in adult and aged mice. J Neural Transm 2008;115:795–802. [57] Kaila K, Ruusuvuori E, Seja P, Voipio J, Puskarjov M. GABA actions and ionic plasticity in epilepsy. Curr Opin Neurobiol 2014;26:34–41. [58] Olson TM, Terzic A. Human K(ATP) channelopathies: diseases of metabolic homeostasis. Pflugers Arch 2010;460:295–306. [59] D'Adamo MC, Catacuzzeno L, Di Giovanni G, Franciolini F, Pessia M. K(+) channelepsy: progress in the neurobiology of potassium channels and epilepsy. Front Cell Neurosci 2013;7:134. [60] Rubaiy HN. The therapeutic agents that target ATP-sensitive potassium channels. Acta Pharm 2016;66:23–34. [61] Soundarapandian MM, Wu D, Zhong X, Petralia RS, Peng L, Tu W, et al. Expression of functional Kir6.1 channels regulates glutamate release at CA3 synapses in generation of epileptic form of seizures. J Neurochem 2007;103:1982–8. [62] Jiang K, Shui Q, Xia Z, Yu Z. Changes in the gene and protein expression of K(ATP) channel subunits in the hippocampus of rats subjected to picrotoxin-induced kindling. Brain Res Mol Brain Res 2004;128:83–9. [63] Minami K, Miki T, Kadowaki T, Seino S. Roles of ATP-sensitive K+ channels as metabolic sensors: studies of Kir6.x null mice. Diabetes 2004;53(Suppl. 3):S176–80. [64] Crepel V, Rovira C, Ben-Ari Y. The K+ channel opener diazoxide enhances glutamatergic currents and reduces GABAergic currents in hippocampal neurons. J Neurophysiol 1993;69:494–503. [65] Emmanouilidou E, Minakaki G, Keramioti MV, Xylaki M, Balafas E, ChrysanthouPiterou M, et al. GABA transmission via ATP-dependent K+ channels regulates alpha-synuclein secretion in mouse striatum. Brain 2016;139:871–90. [66] Margaill I, Miquet JM, Doble A, Blanchard JC, Boireau A. KATP channels modulate GABA release in hippocampal slices in the absence of glucose. Fundam Clin Pharmacol 1992;6:295–300. [67] Matsumoto N, Komiyama S, Akaike N. Pre- and postsynaptic ATP-sensitive potassium channels during metabolic inhibition of rat hippocampal CA1 neurons. J Physiol 2002; 541:511–20. [68] Ohno-Shosaku T, Sawada S, Yamamoto C. ATP-sensitive K+ channel activators suppress the GABAergic inhibitory transmission by acting on both presynaptic and postsynaptic sites in rat cultured hippocampal neurons. Neurosci Lett 1993;159: 139–42. [69] Schwanstecher C, Panten U. Identification of an ATP-sensitive K+ channel in spiny neurons of rat caudate nucleus. Pflugers Arch 1994;427:187–9. [70] Chan O, Lawson M, Zhu W, Beverly JL, Sherwin RS. ATP-sensitive K(+) channels regulate the release of GABA in the ventromedial hypothalamus during hypoglycemia. Diabetes 2007;56:1120–6. [71] Foote F, Gale K. Morphine potentiates seizures induced by GABA antagonists and attenuates seizures induced by electroshock in the rat. Eur J Pharmacol 1983;95: 259–64. [72] Lutfy K, Woodward RM, Keana JF, Weber E. Inhibition of clonic seizure-like excitatory effects induced by intrathecal morphine using two NMDA receptor antagonists: MK-801 and ACEA-1011. Eur J Pharmacol 1994;252:261–6. [73] Turski L, Ikonomidou C, Cavalheiro EA, Kleinrok Z, Czuczwar SJ, Turski WA. Effects of morphine and naloxone on pilocarpine-induced convulsions in rats. Neuropeptides 1985;5:315–8. [74] Pick CG, Chernes Y, Rigai T, Rice KC, Schreiber S. The antinociceptive effect of zolpidem and zopiclone in mice. Pharmacol Biochem Behav 2005;81:417–23. [75] North RA. Twelfth Gaddum memorial lecture. Drug receptors and the inhibition of nerve cells. Br J Pharmacol 1989;98:13–28. [76] Ocana M, Del Pozo E, Barrios M, Baeyens JM. Subgroups among mu-opioid receptor agonists distinguished by ATP-sensitive K+ channel-acting drugs. Br J Pharmacol 1995;114:1296–302. [77] Ahmadi S, Azarian S, Ebrahimi SS, Rezayof A. ATP-sensitive potassium channels and L-type calcium channels are involved in morphine-induced hyperalgesia after nociceptive sensitization in mice. Basic Clin Neurosci 2014;5:191–8. [78] Ahmadi S, Ebrahimi SS, Oryan S, Rafieenia F. Blockades of ATP-sensitive potassium channels and L-type calcium channels improve analgesic effect of morphine in alloxan-induced diabetic mice. Pathophysiology 2012;19:171–7. [79] Zarrindast MR, Sattari-Naeini M, Khalilzadeh A. Involvement of glucose and ATP-sensitive potassium (K+) channels on morphine-induced conditioned place preference. Eur J Pharmacol 2007;573:133–8.