Effects of zonisamide on neurotransmitter exocytosis associated with ryanodine receptors

ML218 modulates calcium binding protein, oxidative stress, and inflammation during ischemia-reperfusion brain injury in mice

Cerebral ischemia disrupts calcium homeostasis in the brain causing excitotoxicity, oxidative stress, inflammation, and neuronal cell apoptosis. During ischemic conditions, T-type calcium channel channels contribute to increase in intracellular calcium ions in both neurons and glial cells therefore, the current study hypothesizes the antagonism of these channels using ML218, a novel specific T-Type inhibitor in experimental model of cerebral ischemia-reperfusion (CI/R) brain injury. CI/R injury was induced in Swiss Albino mice by occlusion of common carotid arteries followed by reperfusion. Animals were assessed for learning and memory (MWM), motor coordination (Rota rod), neurological function (neurological deficit score), cerebral infarction, edema, and histopathological alterations. Biochemical assessments were made for calcium binding proteins (Calmodulin- CaM, calcium/calmodulin-dependent protein kinase II-CaMKII, S100B), oxidative stress (4-hydroxy 2-nonenal-4-HNE, glutathione-GSH, inflammation (nuclear factor kappa-light-chain-enhancer of activated B-p65-NF-kB, tumor necrosis factor-TNF-α, interleukin-IL-10) inducible nitric oxide synthase (iNOS) levels, and acetylcholinesterase activity (AChE) in brain supernatants. Furthermore, serum levels of NF-kB, iNOS, and S100B were also assessed. CI/R animals showed impairment in learning, memory, motor coordination, and neurological function along with increase in cerebral infarction, edema, and histopathological alterations. Furthermore, increase in brain calcium binding proteins, oxidative stress, inflammation, and AChE activity along with serum NF-kB, iNOS, and S100B levels were recorded in CI/R animals. Administration of ML218 (5 mg/kg and 10 mg/kg; i.p.) was observed to recuperate CI/R induced impairments in behavioral, biochemical, and histopathological analysis. Hence, it may be concluded that ML218 mediates neuroprotection during CI/R via decreasing brain and serum calcium binding proteins, inflammation, iNOS, and oxidative stress markers.

Clinical efficacy and tolerability of zonisamide monotherapy in dogs with newly diagnosed idiopathic epilepsy: Prospective open-label uncontrolled multicenter trial

BACKGROUND

Zonisamide (ZNS) is a newer generation antiseizure medication (ASM) used to treat epilepsy in dogs and cats. However, scientific and clinical information, particularly regarding monotherapy, is limited.

OBJECTIVES

To evaluate the antiseizure efficacy and tolerability of ZNS monotherapy in dogs with newly diagnosed idiopathic epilepsy (IE).

ANIMALS

Study included 56 client-owned dogs newly diagnosed with IE.

METHODS

This was a prospective multicenter, open-label, uncontrolled study. All dogs were ASM-naïve and had ≥2 seizures within 12 weeks. Dogs were administered 2.7-14.4 mg/kg ZNS PO q12h and followed up for ≥12 weeks. Data from the 12-week maintenance treatment period were compared with those from the 4- to 12-week pretreatment period for efficacy evaluation. Data from the entire ZNS administration period were used to assess tolerability.

RESULTS

Fifty-six dogs were included in our study. Of the dogs, 53 were assessed for efficacy; 40 (76%) had a ≥ 50% reduction in seizure frequency, and 29 (55%) achieved seizure freedom. For 90% of the dogs with ≥50% reduction in seizure frequency, the mean ZNS dose was 4.8 (range, 2.7-8.6) mg/kg q12h and the mean trough plasma ZNS concentration was 18.9 (range, 8.0-48.0) μg/mL. In 7 of the 56 dogs (13%), reduced activity, decreased appetite, vomiting, hindlimb weakness, soft stools, or constipation was observed, albeit mild and temporary. Laboratory tests revealed no relevant changes.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our study suggests that ZNS monotherapy is effective and well-tolerated in dogs with newly diagnosed IE.

Adverse effects of antiepileptic drugs on hormones of the hypothalamic-pituitary-gonadal axis in males: A review

The HPG axis is critical in the maintenance of spermatogenesis and sexual function in males. The GnRH-releasing neurons of the hypothalamus are the axis's main hierarchical element. These neurons make connections with different areas of the brain to regulate the release of GnRH. Neurotransmitters have a critical in the connections between these neurons. So, neurotransmitters can inhibit or stimulate the release of GnRH by affecting GnRH-releasing neurons. In neurological disorders, neurotransmitter's activities inevitably change; therefore, these changes can affect the HPG axis via affecting GnRH-releasing neurons, just like in epilepsy. Many investigations have attracted attention to be decreased fertility potential in males with epilepsy. It has been stated that changes in the HPG axis hormone levels have been found in these patients. Moreover, it has also been observed that sperm quality decreased in patients. It has been emphasized that a decrease in sperm quality may be related to both epilepsy and AEDs. It has been shown that AEDs caused decreased sperm quality by impairing the HPG axis, so they act like endocrine-disrupting chemicals. AEDs can affect fertility and cause additive adverse effects in terms of sperm quality together with epilepsy. Therefore, it is crucial to investigate the adverse reproductive effects of AEDs, which are frequently used during reproductive ages, and determine the role of the HPG axis on potential reproductive pathologies.

Anticonvulsant Effects of Carbonic Anhydrase Inhibitors: The Enigmatic Link Between Carbonic Anhydrases and Electrical Activity of the Brain

Acetazolamide (ACZ), a sulfonamide carbonic anhydrase (CA) inhibitor, was first introduced into medical use as a diuretic in the1950s. Shortly after its introduction, its antiglaucoma and anticonvulsant properties came to light. Subsequently, studies of ACZ have explored a plethora of neurophysiological functions of CAs in the CNS. In addition, topiramate (TPM) and zonisamide (ZNS), which were developed as antiepileptic drugs (AEDs) in the1990s, were found to have the ability to inhibit CAs. How CA inhibition prevents seizures is elusive. CA expression and activity are extensively detected in neurons, the choroid plexus, oligodendrocytes and astrocytes. TPM and ZNS appear to produce multimodal actions in the CNS as well as CA inhibition unlike ACZ. Nonetheless, CA inhibitors share some common denominators. They do not only affect the fine equilibrium among CO₂, H⁺ and HCO₃^- in the extraneuronal and intraneuronal milieu, but also modulate the activity of ligand gated ion channels at the neuronal level such as GABA-A signaling through inhibiting CA-replenished HCO₃^- efflux. In addition, there are studies reporting their ability to alter Ca²⁺ kinetics through modulation of ligand gated Ca²⁺ channels, voltage gated Ca²⁺ channels (VGCC) or Ca²⁺-induced Ca²⁺ release channels (CICRC). The present study will review the involvement of CAs in the formation of epileptogenesis, and likely mechanisms by which CA inhibitors suppress the electrical activity of the brain. The common properties of CA inhibitors provide some clues for a possible link among metabolism, CAs, Ca²⁺ and GABA signaling.

Chronic Administrations of Guanfacine on Mesocortical Catecholaminergic and Thalamocortical Glutamatergic Transmissions

It has been established that the selective α2A adrenoceptor agonist guanfacine reduces hyperactivity and improves cognitive impairment in patients with attention-deficit/hyperactivity disorder (ADHD). The major mechanisms of guanfacine are considered to involve the activation of the postsynaptic α2A adrenoceptor of glutamatergic pyramidal neurons in the frontal cortex, but the effects of chronic guanfacine administration on catecholaminergic and glutamatergic transmissions associated with the orbitofrontal cortex (OFC) are yet to be clarified. The actions of guanfacine on catecholaminergic transmission, the effects of acutely local and systemically chronic (for 7 days) administrations of guanfacine on catecholamine release in pathways from the locus coeruleus (LC) to OFC, the ventral tegmental area (VTA) and reticular thalamic-nucleus (RTN), from VTA to OFC, from RTN to the mediodorsal thalamic-nucleus (MDTN), and from MDTN to OFC were determined using multi-probe microdialysis with ultra-high performance liquid chromatography. Additionally, the effects of chronic guanfacine administration on the expression of the α2A adrenoceptor in the plasma membrane fraction of OFC, VTA and LC were examined using a capillary immunoblotting system. The acute local administration of therapeutically relevant concentrations of guanfacine into the LC decreased norepinephrine release in the OFC, VTA and RTN without affecting dopamine release in the OFC. Systemically, chronic administration of therapeutically relevant doses of guanfacine for 14 days increased the basal release of norepinephrine in the OFC, VTA, RTN, and dopamine release in the OFC via the downregulation of the α2A adrenoceptor in the LC, OFC and VTA. Furthermore, systemically, chronic guanfacine administration did not affect intrathalamic GABAergic transmission, but it phasically enhanced thalamocortical glutamatergic transmission. The present study demonstrated the dual actions of guanfacine on catecholaminergic transmission-acute attenuation of noradrenergic transmission and chronic enhancement of noradrenergic transmission and thalamocortical glutamatergic transmission. These dual actions of guanfacine probably contribute to the clinical effects of guanfacine against ADHD.

Pharmacological management of dementia with Lewy bodies with a focus on zonisamide for treating parkinsonism

INTRODUCTION

Dementia with Lewy bodies (DLB) has no approved symptomatic or disease-modifying treatments in the US and Europe, despite being the second most common cause of neurodegenerative dementia.

AREAS COVERED

Herein, the authors briefly review the DLB drug development pipeline, providing a summary of the current pharmacological intervention studies. They then focus on the anticonvulsant zonisamide, a benzisoxazole derivative with a sulfonamide group and look at its value for treating parkinsonism in DLB.

EXPERT OPINION

Several new compounds are being tested in DLB, the most innovative being those aimed at decreasing brain accumulation of α-synuclein. Unfortunately, new drug testing is challenging in terms of consistent diagnostic criteria and lack of reliable biomarkers. Few randomized controlled trials (RCTs) are well-designed, with enough power to detect significant drug effects. Levodopa monotherapy can treat the parkinsonism in DLB, but it can cause agitation or visual hallucination worsening. Two Phase II/III RCTs of DLB patients recently reported a statistically significant improvement in motor function in those receiving zonisamide as an adjunctive treatment to levodopa. New biomarker strategies and validated outcome measures for DLB or prodromal DLB may enhance clinical trial design for the development of specific disease-modifying treatments.

A Novel Sulfonamide, 4-FS, Reduces Ethanol Drinking and Physical Withdrawal Associated With Ethanol Dependence

Carbonic anhydrase (CA) is abundant in glial cells in the brain and CA type II isoform (CA II) activity in the hippocampus plays an important role in buffering extracellular pH transients produced by neural activity. Chronic ethanol exposure results in respiratory and metabolic acidosis, producing shifts in extracellular pH in the brain and body. These neurophysiological changes by ethanol are hypothesized to contribute to the continued drinking behavior and physical withdrawal behavior in subjects consuming ethanol chronically. We explored whether chronic ethanol self-administration (ethanol drinking, 10% v/v; ED) without or under the influence of chronic intermittent ethanol vapor (CIE-ED) experience alters the expression of CA II in the hippocampus. Postmortem hippocampal tissue analyses demonstrated that CA II levels were enhanced in the hilus region of the hippocampus in ED and CIE-ED rats. We used a novel molecule-4-fluoro-N-(4-sulfamoylphenyl) benzenesulfonamide (4-FS)-a selective CA II inhibitor, to determine whether CA II plays a role in ethanol self-administration in ED and CIE-ED rats and physical withdrawal behavior in CIE-ED rats. 4-FS (20 mg/kg, i.p.) reduced ethanol self-administration in ED rats and physical withdrawal behavior in CIE-ED rats. Postmortem hippocampal tissue analyses demonstrated that 4-FS reduced CA II expression in ED and CIE-ED rats to control levels. In parallel, 4-FS enhanced GABAA receptor expression, reduced ratio of glutamatergic GluN2A/2B receptors and enhanced the expression of Fos, a marker of neuronal activation in the ventral hippocampus in ED rats. These findings suggest that 4-FS enhanced GABAergic transmission and increased activity of neurons of inhibitory phenotypes. Taken together, these findings support the role of CA II in assisting with negative affective behaviors associated with moderate to severe alcohol use disorders (AUD) and that CA II inhibitors are a potential therapeutic target to reduce continued drinking and somatic withdrawal symptoms associated with moderate to severe AUD.

Effects of Carbamazepine, Lacosamide and Zonisamide on Gliotransmitter Release Associated with Activated Astroglial Hemichannels

Recent studies using the genetic partial epilepsy model have demonstrated that hyperfunction of astroglial hemichannels contributes to pathomechanism of epileptic seizure. Therefore, to explore the novel anticonvulsive mechanisms, the present study determined the effects of voltage-dependent Na⁺ channel (VDSC)-inhibiting anticonvulsants, carbamazepine (CBZ), lacosamide (LCM), and zonisamide (ZNS) on the astroglial release of l-glutamate and adenosine triphosphate (ATP). The effects of subchronic administration of therapeutic-relevant dose of three anticonvulsants on the release of l-glutamate and ATP in the orbitofrontal cortex (OFC) were determined using microdialysis. The concentration-dependent effects of acute and subchronic administrations of anticonvulsants on astroglial gliotransmitter release were determined using primary cultured astrocytes. The concentration-dependent effects of subchronic administrations of anticonvulsants on connexin43 (Cx43) expression in the plasma membrane of primary cultured astrocytes were determined using the Simple Western system. An increase in the levels of extracellular K⁺ resulted in a concentration-dependent increase in the astroglial release of l-glutamate and ATP. The depleted levels of extracellular Ca²⁺ alone did not affect astroglial gliotransmitter release but did accelerate K⁺-evoked gliotransmitter release via activation of astroglial hemichannels. Both non-selective hemichannel inhibitor carbenoxolone (CBX) and selective Cx43 inhibitor GAP19 prevented both gliotransmitter release through activated astroglial hemichannels and the hemichannel-activating process induced by elevation of the levels of extracellular K⁺ with depletion of the levels of extracellular Ca²⁺. ZNS subchronically decreased Cx43 expression and acutely/subchronically inhibited Cx43 hemichannel activity. LCM acutely inhibited hemichannel activity but did not subchronically affect Cx43 expression. Therapeutic-relevant concentration of CBZ did not affect hemichannel activity or Cx43 expression, but supratherapeutic concentration of CBZ decreased Cx43 expression and hemichannel activity. Therefore, the present study demonstrated the distinct effects of CBZ, LCM, and ZNS on gliotransmitter release via modulation of astroglial hemichannel function. The different features of the effects of three VDSC-inhibiting anticonvulsants on astroglial transmission associated with hemichannels, at least partially, possibly contributing to the formation of the properties of these three anticonvulsants, including the antiepileptic spectrum and adverse effects regarding mood and cognitive disturbance.

Upregulated and Hyperactivated Thalamic Connexin 43 Plays Important Roles in Pathomechanisms of Cognitive Impairment and Seizure of Autosomal Dominant Sleep-Related Hypermotor Epilepsy with S284L-Mutant α4 Subunit of Nicotinic ACh Receptor

To understand the pathomechanism and pathophysiology of autosomal dominant sleep-related hypermotor epilepsy (ADSHE), we studied functional abnormalities of glutamatergic transmission in thalamocortical pathway from reticular thalamic nucleus (RTN), mediodorsal thalamic nucleus (MDTN) to orbitofrontal cortex (OFC) associated with S286L-mutant α4β2-nicotinic acetylcholine receptor (nAChR), and connexin43 (Cx43) hemichannel of transgenic rats bearing rat S286L-mutant Chrna4 gene (S286L-TG), corresponding to the human S284L-mutant CHRNA4 gene using simple Western analysis and multiprobe microdialysis. Cx43 expression in the thalamic plasma membrane fraction of S286L-TG was upregulated compared with that of wild-type. Subchronic administrations of therapeutic-relevant doses of zonisamide (ZNS) and carbamazepine (CBZ) decreased and did not affect Cx43 expression of S286L-TG, respectively. Upregulated Cx43 enhanced glutamatergic transmission during both resting and hyperexcitable stages in S286L-TG. Furthermore, activation of GABAergic transmission RTN-MDTN pathway conversely enhanced, but not inhibited, l-glutamate release in the MDTN via upregulated/activated Cx43. Local administration of therapeutic-relevant concentration of ZNS and CBZ acutely supressed and did not affect glutamatergic transmission in the thalamocortical pathway, respectively. These results suggest that pathomechanisms of ADSHE seizure and its cognitive deficit comorbidity, as well as pathophysiology of CBZ-resistant/ZNS-sensitive ADSHE seizures of patients with S284L-mutation.

Pathogenesis and pathophysiology of autosomal dominant sleep-related hypermotor epilepsy with S284L-mutant α4 subunit of nicotinic ACh receptor

BACKGROUND AND PURPOSE

The mechanisms causing spontaneous epileptic seizures, including carbamazepine-resistant/zonisamide -sensitive seizures and comorbidity in autosomal dominant sleep-related hypermotor epilepsy (ADSHE) are unclear. This study investigated functional abnormalities in thalamocortical transmission in transgenic rats bearing rat S286L-mutant Chrna4 (S286L-TG) of α4 subunit of the nicotinic ACh receptor (nAChR) that corresponds to the human S284L-mutant CHRNA4.

EXPERIMENTAL APPROACH

Effects of carbamazepine and zonisamide on epileptic discharges of S286L-TG rat were measured using telemetry electrocorticogram. Transmission abnormalities of L-glutamate and GABA in thalamocortical pathway of S286L-TG rats were investigated using multiprobe microdialysis and ultra-high-performance liquid-chromatography.

KEY RESULTS

Epileptic discharges in S286L-TG rats were reduced by zonisamide but not by carbamazepine, similar to that of S284L-ADSHE patients. Carbamazepine unaffected functional abnormality in transmission of S286L-TG rats. However, zonisamide was able to compensate for the attenuated S286L-mutant nAChR induced GABA release in frontal-cortex, without affecting attenuated thalamocortical glutamatergic transmission. Excitatory effects of S286L-mutant nAChR on thalamocortical transmission were attenuated compared with those of wild-type nAChR. Loss-of-function of S286L-nAChR enhanced transmission in thalamocortical motor pathway by predominantly attenuating GABAergic transmission. However, it attenuated transmission in thalamocortical cognitive pathway by reducing inhibitory GABAergic and excitatory glutamatergic transmission.

CONCLUSION AND IMPLICATIONS

Our results suggest that functional abnormalities of S286L-nAChR are associated with intra-frontal and thalamocortical transmission, possibly contributing to the pathogenesis of ADSHE-seizure and comorbidity of S284L-ADSHE. Selective compensation of impaired GABAergic transmission by zonisamide (but not by carbamazepine) in frontal cortex may be involved, at least partially, in carbamazepine-resistant ADSHE-seizure of S284L-ADSHE patients.

The adverse effects of psychotropic drugs as an endocrine disrupting chemicals on the hypothalamic-pituitary regulation in male

Adverse effects of drugs on male reproductive system can be categorized as pre-testicular, testicular, and post-testicular. Pre-testicular adverse effects disrupt the hypothalamic-pituitary-gonadal (HPG) axis, generally by interfering with endocrine function. It is known that the HPG axis has roles in the maintenance of spermatogenesis and sexual function. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) which enters the hypophyseal portal system to stimulate the anterior pituitary. The anterior pituitary secretes gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) which are vital for spermatogenesis, into the blood. The FSH stimulates the Sertoli cells for the production of regulatory molecules and nutrients needed for the maintenance of spermatogenesis, while the LH stimulates the Leydig cells to produce and secrete testosterone. Many neurotransmitters influence the hypothalamic-pituitary regulation, consequently the HPG axis, and can consequently affect spermatogenesis and sexual function. Psychotropic drugs including antipsychotics, antidepressants, and mood stabilizers that all commonly modulate dopamine, serotonin, and GABA, can affect male spermatogenesis and sexual function by impairment of the hypothalamic-pituitary regulation, act like endocrine-disrupting chemicals. Otherwise, studies have shown the relationship between decreased sperm quality and psychotropic drugs treatment. Therefore, it is important to investigate the adverse reproductive effects of psychotropic drugs which are frequently used during reproductive ages in males and to determine the role of the hypothalamic-pituitary regulation axis on possible pathologies.

Upregulated Connexin 43 Induced by Loss-of-Functional S284L-Mutant α4 Subunit of Nicotinic ACh Receptor Contributes to Pathomechanisms of Autosomal Dominant Sleep-Related Hypermotor Epilepsy

To study the pathomechanism and pathophysiology of autosomal dominant sleep-related hypermotor epilepsy (ADSHE), this study determined functional abnormalities of glutamatergic transmission in the thalamocortical motor pathway, from the reticular thalamic nucleus (RTN), motor thalamic nuclei (MoTN) tosecondary motor cortex (M2C) associated with the S286L-mutant α4β2-nicotinic acetylcholine receptor (nAChR) and the connexin43 (Cx43) hemichannel of transgenic rats bearing the rat S286L-mutant Chrna4 gene (S286L-TG), which corresponds to the human S284L-mutant CHRNA4 gene using multiprobe microdialysis, primary cultured astrocytes and a Simple Western system. Expression of Cx43 in the M2C plasma membrane fraction of S286L-TG was upregulated compared with wild-type rats. Subchronic nicotine administration decreased Cx43 expression of wild-type, but did not affect that of S286L-TG; however, zonisamide (ZNS) decreased Cx43 in both wild-type and S286L-TG. Primary cultured astrocytes of wild-type were not affected by subchronic administration of nicotine but was decreased by ZNS. Upregulated Cx43 enhanced glutamatergic transmission during both resting and hyperexcitable stages in S286L-TG. Furthermore, activation of glutamatergic transmission associated with upregulated Cx43 reinforced the prolonged Cx43 hemichannel activation. Subchronic administration of therapeutic-relevant doses of ZNS compensated the upregulation of Cx43 and prolonged reinforced activation of Cx43 hemichannel induced by physiological hyperexcitability during the non-rapid eye movement phase of sleep. The present results support the primary pathomechanisms and secondary pathophysiology of ADSHE seizures of patients with S284L-mutation.

Pathomechanism of nocturnal paroxysmal dystonia in autosomal dominant sleep-related hypermotor epilepsy with S284L-mutant α4 subunit of nicotinic ACh receptor

To study the pathomechanism and pathophysiology of nocturnal paroxysmal dystonia of autosomal dominant sleep-related hypermotor epilepsy (ADSHE), this study determined functional abnormalities in thalamic hyperdirect pathway from reticular thalamic nucleus (RTN), motor thalamic nuclei (MoTN), subthalamic nucleus (STN) to substantia nigra pars reticulata (SNr) of transgenic rats (S286L-TG) bearing S286 L missense mutation of rat Chrna4 gene, which corresponds to the S284 L mutation in the human CHRNA4 gene. The activation of α4β2-nAChR in the RTN increased GABA release in MoTN resulting in reduced glutamatergic transmission in thalamic hyperdirect pathway of wild-type. Contrary to wild-type, activation of S286L-mutant α4β2-nAChR (loss-of-function) in the RTN relatively enhanced glutamatergic transmission in thalamic hyperdirect pathway of S286L-TG via impaired GABAergic inhibition in intra-thalamic (RTN-MoTN) pathway. These functional abnormalities in glutamatergic transmission in hyperdirect pathway contribute to the pathomechanism of electrophysiologically negative nocturnal paroxysmal dystonia of S286L-TG. Therapeutic-relevant concentration of zonisamide (ZNS) inhibited the glutamatergic transmission in the hyperdirect pathway via activation of group II metabotropic glutamate receptor (II-mGluR) in MoTN and STN. The present results suggest that S286L-mutant α4β2-nAChR induces GABAergic disinhibition in intra-thalamic (RTN-MoTN) pathway and hyperactivation of glutamatergic transmission in thalamic hyperdirect pathway (MoTN-STN-SNr), possibly contributing to the pathomechanism of nocturnal paroxysmal dystonia of ADSHE patients with S284L mutant CHRNA4. Inhibition of glutamatergic transmission in thalamic hyperdirect pathway induced by ZNS via activation of II-mGluR may be involved, at least partially, in ZNS-sensitive nocturnal paroxysmal dystonia of ADSHE patients with S284L mutation.

Reproductive toxic effects and possible mechanisms of zonisamide in male rats

Zonisamide (ZNS) is an anticonvulsant which is used to treat the symptoms of epilepsy. Although it is frequently used during reproductive ages, studies that investigated the effects of ZNS on reproductive system are limited. Therefore, we aimed to assess the effects of ZNS on male reproductive system by oral administration to rats in 25, 50, and 100 mg/kg doses for 28 days. After the exposure period, sperm concentration, motility, morphology, and DNA damage, as biomarkers of reproductive toxic effects, were determined, and histopathological examination of testis was performed. In addition, levels of the hormones that play a role in the regulation of reproductive functions, such as follicle-stimulating hormone, luteinizing hormone (LH), and testosterone were measured and the levels of oxidative stress biomarkers that take part in the reproductive pathologies such as catalase, superoxide dismutase, glutathione, and malondialdehyde, were determined. Reproductive toxic effects related to ZNS administration were shown by the significant decrease of sperm concentration and normal sperm morphology in ZNS groups. Additionally, pathological findings were observed in the testicular tissues of ZNS-administered groups dose dependently. In addition, serum LH and testosterone levels were significantly decreased in the ZNS groups. Decreased catalase activities and increased malondialdehyde levels in ZNS groups were evaluated as oxidative stress findings in the testis tissue. It could be expressed that ZNS administration induced dose-dependent reproductive toxic effects in rats, and pathological findings associated with the reproductive system could be the result of that hormonal changes and testicular oxidative stress, which in turn might be considered as possible mechanisms of male reproductive toxicity.

Amantadine Combines Astroglial System Xc- Activation with Glutamate/NMDA Receptor Inhibition

A glutamate/NMDA receptor (NMDA-R) antagonist, amantadine (AMA) exhibits a broad spectrum of clinically important properties, including antiviral, antiparkinsonian, neuroprotective, neuro-reparative and cognitive-enhancing effects. However, both clinical and pre-clinical studies have demonstrated that noncompetitive NMDA-R antagonists induce severe schizophrenia-like cognitive deficits. Therefore, this study aims to clarify the clinical discrepancy between AMA and noncompetitive NMDA-R antagonists by comparing the effects of AMA with those of a noncompetitive NMDA-R antagonist, MK801, on rat tripartite glutamatergic synaptic transmission using microdialysis and primary cultured astrocytes. Microdialysis study demonstrated that the stimulatory effects of AMA on L-glutamate release differed from those of MK801 in the globus pallidus, entorhinal cortex and entopeduncular nucleus. The stimulatory effect of AMA on L-glutamate release was modulated by activation of cystine/glutamate antiporter (Sxc). Primary cultured astrocytes study demonstrated that AMA also enhanced glutathione synthesis via Sxc activation. Furthermore, carbon-monoxide induced damage of the astroglial glutathione synthesis system was repaired by AMA but not MK801. Additionally, glutamate/AMPA receptor (AMPA-R) antagonist, perampanel enhanced the protective effects of AMA. The findings of microdialysis and cultured astrocyte studies suggest that a combination of Sxc activation with inhibitions of ionotropic glutamate receptors contributes to neuroprotective, neuro-reparative and cognitive-enhancing activities that can mitigate several neuropsychiatric disorders.

Effects of acute and sub-chronic administrations of guanfacine on catecholaminergic transmissions in the orbitofrontal cortex

The selective α2A adrenoceptor agonist guanfacine reduces hyperactivity and improves cognitive impairment in patients with attention-deficit/hyperactivity disorder (ADHD). The major mechanisms of guanfacine have been considered to involve activation of postsynaptic α2A adrenoceptor in frontal pyramidal neurons. However, the effects of chronic guanfacine administration on catecholaminergic transmissions associated with the orbitofrontal cortex (OFC) remain unclear. To explore the mechanisms of action of guanfacine on catecholaminergic transmission, the effects of its acute local or sub-chronic systemic administration on catecholamine release within pathways from locus coeruleus (LC) to OFC and reticular thalamic nucleus (RTN), from RTN to mediodorsal thalamic nucleus (MDTN), and from MDTN to OFC were determined using multi-probe microdialysis with ultra-high performance liquid chromatography. Acute OFC local administration of guanfacine did not affect catecholamine release in OFC. Acute LC local and sub-chronic systemic administrations of guanfacine reduced norepinephrine release in LC, OFC and RTN, and also reduced GABA release in MDTN, whereas AMPA-induced (perfusion with AMPA into NDTN) releases of l-glutamate, norepinephrine and dopamine in OFC were enhanced by sub-chronic systemic guanfacine administration. This study identified that catecholaminergic transmission is composed of three pathways: direct noradrenergic and co-releasing catecholaminergic LC-OFC pathways and intermediate LC-OFC (LC-RTN-MDTN-OFC) pathway. We demonstrated the dual actions of guanfacine on catecholaminergic transmission: attenuation of direct noradrenergic LC-OFC transmission at the resting stage and enhancement of direct co-releasing catecholaminergic LC-OFC transmission via GABAergic disinhibition in the intermediate LC-OFC pathway. These dual actions of guanfacine probably contribute to clinical actions of guanfacine against ADHD and its comorbid symptoms. This article is part of the Special Issue entitled 'Current status of the neurobiology of aggression and impulsivity'.

Topiramate for essential tremor

BACKGROUND

Essential tremor (ET) is one of the most common movement disorders. The management is primarily based on pharmacological agents and in clinical practice propranolol and primidone are considered the first-line therapy. However, these treatments can be ineffective in 25% to 55% of people and are frequently associated with serious adverse events (AEs). For these reasons, it is worthwhile evaluating other treatments for ET. Topiramate has been suggested as a potentially useful agent for the treatment of ET but there is uncertainty about its efficacy and safety.

OBJECTIVES

To assess the efficacy and safety of topiramate in the treatment of ET.

SEARCH METHODS

We carried out a systematic search without language restrictions to identify all relevant trials in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (January 1966 to January 2017), Embase (January 1988 to January 2017), National Institute for Health and Care Excellence (1999 to January 2017), ClinicalTrials.gov (1997 to January 2017) and World Health Organization International Clinical Trials Registry Platform (ICTRP; 2004 to January 2017). We searched BIOSIS Citation Index (2000 to January 2017) for conference proceedings. We handsearched grey literature and the reference lists of identified studies and reviews.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) of topiramate versus placebo/open control or any other treatments. We included studies in which the diagnosis of ET was made according to accepted and validated diagnostic criteria. We excluded studies conducted in people presenting with secondary forms of tremor or reporting only neurophysiological parameters to assess outcomes.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected and extracted data using a data collection form. We assessed the risk of bias and the quality of evidence. We used a fixed-effect meta-analysis for data synthesis.

MAIN RESULTS

This review included three trials comparing topiramate to placebo (309 participants). They were all at high overall risk of bias. The quality of evidence ranged from very low to low. Compared to placebo, participants treated with topiramate showed a significant improvement in functional disability and an increased risk of withdrawal (risk ratio (RR) 1.78, 95% confidence interval (CI) 1.23 to 2.60). There were more AEs for topiramate-treated participants, particularly paraesthesia, weight loss, appetite decrease and memory difficulty.

AUTHORS' CONCLUSIONS

This systematic review highlighted the presence of limited data and very low to low quality evidence to support the apparent efficacy and the occurrence of treatment-limiting AEs in people with ET treated with topiramate. Further research to assess topiramate efficacy and safety on ET is needed.

Zonisamide Enhances Neurite Elongation of Primary Motor Neurons and Facilitates Peripheral Nerve Regeneration In Vitro and in a Mouse Model

No clinically applicable drug is currently available to enhance neurite elongation after nerve injury. To identify a clinically applicable drug, we screened pre-approved drugs for neurite elongation in the motor neuron-like NSC34 cells. We found that zonisamide, an anti-epileptic and anti-Parkinson’s disease drug, promoted neurite elongation in cultured primary motor neurons and NSC34 cells in a concentration-dependent manner. The neurite-scratch assay revealed that zonisamide enhanced neurite regeneration. Zonisamide was also protective against oxidative stress-induced cell death of primary motor neurons. Zonisamide induced mRNA expression of nerve growth factors (BDNF, NGF, and neurotrophin-4/5), and their receptors (tropomyosin receptor kinase A and B). In a mouse model of sciatic nerve autograft, intragastric administration of zonisamide for 1 week increased the size of axons distal to the transected site 3.9-fold. Zonisamide also improved the sciatic function index, a marker for motor function of hindlimbs after sciatic nerve autograft, from 6 weeks after surgery. At 8 weeks after surgery, zonisamide was protective against denervation-induced muscle degeneration in tibialis anterior, and increased gene expression of Chrne, Colq, and Rapsn, which are specifically expressed at the neuromuscular junction. We propose that zonisamide is a potential therapeutic agent for peripheral nerve injuries as well as for neuropathies due to other etiologies.

Zonisamide regulates basal ganglia transmission via astroglial kynurenine pathway

To clarify the anti-parkinsonian mechanisms of action of zonisamide (ZNS), we determined the effects of ZNS on tripartite synaptic transmission associated with kynurenine (KYN) pathway (KP) in cultured astrocytes, and transmission in both direct and indirect pathways of basal ganglia using microdialysis. Interactions between cytokines [interferon-γ (IFNγ) and tumor-necrosis factor-α (TNFα)] and ZNS on astroglial releases of KP metabolites, KYN, kynurenic-acid (KYNA), xanthurenic-acid (XTRA), cinnabarinic-acid (CNBA) and quinolinic-acid (QUNA), were determined by extreme liquid-chromatography with mass-spectrometry. Interaction among metabotropic glutamate-receptor (mGluR), KP metabolites and ZNS on striato-nigral, striato-pallidal GABAergic and subthalamo-nigral glutamatergic transmission was examined by microdialysis with extreme liquid-chromatography fluorescence resonance-energy transfer detection. Acute and chronic ZNS administration increased astroglial release of KYN, KYNA, XTRA and CNBA, but not QUNA. Chronic IFNγ administration increased the release of KYN, KYNA, CNBA and QUNA, but had minimal inhibitory effect on XTRA release. Chronic TNFα administration increased CNBA and QUNA, but not KYN, KYNA or XTRA. ZNS inhibited IFNγ-induced elevation of KYN, KYNA and QUNA, but enhanced IFNγ-induced that of CNBA. TNFα-induced rises in CNBA and QUNA were inhibited by ZNS. ZNS inhibited striato-nigral GABAergic, striato-pallidal GABAergic and subthalamo-nigral glutamatergic transmission via activation of groups II and III mGluRs. ZNS enhanced astroglial release of endogenous agonists of group II mGluR, XTRA and group III mGluR, CNBA. Activated endogenous mGluR agonists inhibited transmission in direct and indirect pathways of basal ganglia. These mechanisms contribute to effectiveness and well tolerability of ZNS as an adjunct treatment for Parkinson's disease during l-DOPA monotherapy. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

The role of intracellular calcium stores in synaptic plasticity and memory consolidation

Memory processing requires tightly controlled signalling cascades, many of which are dependent upon intracellular calcium (Ca(2+)). Despite this, most work investigating calcium signalling in memory formation has focused on plasma membrane channels and extracellular sources of Ca(2+). The intracellular Ca(2+) release channels, ryanodine receptors (RyRs) and inositol (1,4,5)-trisphosphate receptors (IP3Rs) have a significant capacity to regulate intracellular Ca(2+) signalling. Evidence at both cellular and behavioural levels implicates both RyRs and IP3Rs in synaptic plasticity and memory formation. Pharmacobehavioural experiments using young chicks trained on a single-trial discrimination avoidance task have been particularly useful by demonstrating that RyRs and IP3Rs have distinct roles in memory formation. RyR-dependent Ca(2+) release appears to aid the consolidation of labile memory into a persistent long-term memory trace. In contrast, IP3Rs are required during long-term memory. This review discusses various functions for RyRs and IP3Rs in memory processing, including neuro- and glio-transmitter release, dendritic spine remodelling, facilitating vasodilation, and the regulation of gene transcription and dendritic excitability. Altered Ca(2+) release from intracellular stores also has significant implications for neurodegenerative conditions.

Effects of valproate on neurotransmission associated with ryanodine receptors

To clarify the antiepileptic mechanisms of valproate (VPA), we determined the effects of acute and sub-acute administrations of VPA on ryanodine receptor (RyR)-associated hippocampal releases of GABA and glutamate using microdialysis, as well expression of mRNA and protein of RyR subtypes in the rat hippocampus. Acute administration of therapeutic-relevant VPA did not affect the hippocampal extracellular levels of GABA or glutamate, whereas sub-acute administration increased GABA level without affecting that of glutamate. Perfusion with ryanodine increased the hippocampal extracellular level of glutamate (ryanodine concentration range: 1-1000μM) concentration-dependently; however, that of GABA was increased by 1-100μM ryanodine concentration-dependently but the stimulatory effects of 1000μM ryanodine on GABA release was not observed. Both acute and sub-acute administrations of therapeutic-relevant VPA inhibited ryanodine-induced responses of hippocampal extracellular glutamate level without affecting that of GABA. Especially, both acute and sub-acute administrations of VPA prevented the breakdown of GABA release induced by 1000μM ryanodine. Sub-acute administration of therapeutically-relevant dose VPA weakly increased RyR mRNA expression but we could not detect the changes of RyR protein expression in rat hippocampus. These results suggest that VPA inhibited the neurotransmitter release associated with RyR without affecting the expression of RyR protein. Therefore, the antiepileptic action of VPA seems to be mediated, at least in part, by an increase in basal GABA release and inhibition of RyR-associated glutamate release.

Placebo-controlled trial of zonisamide for the treatment of alcohol dependence

INTRODUCTION

Zonisamide is an anticonvulsant medication with GABAergic, glutamatergic, and monoaminergic effects. Zonisamide has also been shown to reduce alcohol intake in rodents and in risky drinkers in the context of a laboratory study. This pilot clinical trial evaluated the safety, tolerability, and efficacy of zonisamide for the treatment of alcohol dependence.

METHODS

Forty alcohol-dependent subjects (23 men) were randomly assigned to receive treatment with either placebo or zonisamide in a 12-week double-blind trial. Zonisamide was initiated at a dosage of 100 mg/d, which was increased by 100 mg/d every 2 weeks for 8 weeks to a maximum dosage of 500 mg/d. The medication was continued for 4 weeks at the target dosage and then tapered and discontinued. The primary outcomes were drinks per week, heavy drinking days per week, and abstinent days per week, which were measured using the Timeline Follow-Back method.

RESULTS

There was a significant medication by treatment week interaction effect favoring the zonisamide group for heavy drinking days (HDD; P = 0.012), drinks per week (P = 0.004), and alcohol urge scores (P = 0.006). There was not a significant effect on the number or rate of increase in abstinent days. There were no serious adverse events reported and zonisamide treatment was well tolerated.

CONCLUSION

The findings provide preliminary support for the use of zonisamide to treat alcohol dependence. Efforts to replicate and extend these findings are warranted.

Idiopathic hemifacial spasm responsive to zonisamide: a case report

AIM

We describe a patient with idiopathic hemifacial spasm (HFS) that was responsive to zonisamide treatment.

METHODS AND RESULTS

A 65-year-old woman presented with a 4-year history of left-sided HFS developing gradually, starting from the upper facial muscles. After several analyses, the diagnosis of idiopathic HFS was made, and the clonazepam treatment (0.5 mg every 8 hours) was started, without a complete remission of symptoms. Therefore, zonisamide (150 mg twice a day for a 6-week period) was added, with a complete resolution. The rechallenge with zonisamide after its dechallenge confirmed its effectiveness. During follow-up, the patient remained symptom-free, with no adverse drug reactions.

CONCLUSIONS

We suggest that zonisamide could represent a useful therapeutic option in the treatment of idiopathic HFS.

Rats harboring S284L Chrna4 mutation show attenuation of synaptic and extrasynaptic GABAergic transmission and exhibit the nocturnal frontal lobe epilepsy phenotype

Mutations of genes encoding alpha4, beta2, or alpha2 subunits (CHRNA4, CHRNB2, or CHRNA2, respectively) of nAChR [neuronal nicotinic ACh (acetylcholine) receptor] cause nocturnal frontal lobe epilepsy (NFLE) in human. NFLE-related seizures are seen exclusively during sleep and are characterized by three distinct seizure phenotypes: "paroxysmal arousals," "paroxysmal dystonia," and "episodic wandering." We generated transgenic rat strains that harbor a missense mutation S284L, which had been identified in CHRNA4 in NFLE. The transgenic rats were free of biological abnormalities, such as dysmorphology in the CNS, and behavioral abnormalities. The mRNA level of the transgene (mutant Chrna4) was similar to the wild type, and no distorted expression was detected in the brain. However, the transgenic rats showed epileptic seizure phenotypes during slow-wave sleep (SWS) similar to those in NFLE exhibiting three characteristic seizure phenotypes and thus fulfilled the diagnostic criteria of human NFLE. The therapeutic response of these rats to conventional antiepileptic drugs also resembled that of NFLE patients with the S284L mutation. The rats exhibited two major abnormalities in neurotransmission: (1) attenuation of synaptic and extrasynaptic GABAergic transmission and (2) abnormal glutamate release during SWS. The currently available genetically engineered animal models of epilepsy are limited to mice; thus, our transgenic rats offer another dimension to the epilepsy research field.

Zonisamide enhances delta receptor-associated neurotransmitter release in striato-pallidal pathway

A recent randomized control study demonstrated that zonisamide (ZNS), an antiepileptic drug, is effective in Parkinson's disease at the lower than the therapeutic doses against epilepsy (25-50 mg/day); however, the detailed mechanism of antiparkinsonian effects of ZNS remains to be clarified. To determine the mechanism of antiparkinsonian effect of ZNS, we investigated the effects of ZNS on extracellular levels of dopamine in the striatum (STR), glutamate in substantia nigra pars reticulata (SNr), GABA in globus pallidus (GP), subthalamic nucleus (STN) and SNr, using multiple microdialysis probes. Striatal perfusion of 1000 microM ZNS (within therapeutic-relevant concentration against epilepsy) increased extracellular levels of dopamine in STR, whereas 100 microM ZNS (lower than the therapeutic-relevant concentration against epilepsy but within the therapeutic rage against Parkinson's disease) did not affect it. Striatal perfusion of ZNS (100 and 1000 microM) decreased the extracellular levels of GABA in STN and glutamate in SNr, but decreased extracellular GABA level in GP without affecting GABA level in SNr. These concentration-dependent effects of ZNS on extracellular neurotransmitter levels were independent of dopamine and delta(2) receptors; however, blockade of delta(1) receptor inhibited the effects of ZNS. Furthermore, activation of delta(1) receptor enhanced the effects of ZNS on neurotransmitter level. These results suggest that ZNS does not affect the direct pathway but inhibits the indirect pathway, which is mediated by delta(1) receptor. Therefore, the antiparkinsonian effects of ZNS seem to be mediated through the interaction between lower than therapeutically-relevant concentration against epilepsy of ZNS (100 microM) and delta(1) receptor.

Topiramate and zonisamide prevent paradoxical intoxication induced by carbamazepine and phenytoin

The mechanisms of paradoxical aggravation of epileptic seizures induced by selected antiepileptic drugs (AEDs) remain unclear. The present study addressed this issue by determining the seizure-threshold doses of carbamazepine (CBZ) and phenytoin (PHT), as well the dose-dependent effects of CBZ, PHT, and carbonic anhydrase-inhibiting AEDs, acetazolamide (AZM), topiramate (TPM), and zonisamide (ZNS), on neurotransmitter release in rat hippocampus. The dose-dependent effects of AEDs on hippocampal extracellular levels of glutamate (Glu), GABA, norepinephrine (NE), dopamine (DA), and serotonin (5-HT) were determined by microdialysis with high-speed and high-sensitive extreme liquid chromatography. Proconvulsive effects of AEDs were determined by telemetric-electrocorticography. Therapeutically relevant doses of AZM, CBZ, TPM, and ZNS increased hippocampal extracellular levels of GABA, NE, DA, and 5-HT, while PHT had no effect. Supratherapeutic doses of AZM, CBZ, PHT, TPM, and ZNS decreased extracellular levels of GABA, NE, DA, and 5-HT, without affecting Glu levels. Toxic doses of CBZ and PHT produced seizures (paradoxical intoxication), markedly increasing all transmitter levels, but TPM and ZNS even at toxic doses did not produce seizure. Co-administration experiments showed that therapeutically relevant doses of CBZ or PHT reduced the seizure-threshold doses of PHT or CBZ, respectively. In contrast, therapeutically relevant doses of AZM, TPM, and ZNS elevated the seizure-threshold doses of CBZ and PHT. These results suggested that blockade of high percentage of the population of voltage-dependent sodium channels by CBZ and PHT might be important in inducing paradoxical intoxication/reaction, and that inhibition of carbonic anhydrase inhibits this effect. TPM and ZNS are candidate first-choice agents in treatment of epilepsy when first-line AEDs are ineffective.

Antiepileptic drugs in non-epilepsy disorders: relations between mechanisms of action and clinical efficacy

Antiepileptic drugs (AEDs) are used extensively to treat multiple non-epilepsy disorders, both in neurology and psychiatry. This article provides a review of the clinical efficacy of AEDs in non-epilepsy disorders based on recently published preclinical and clinical studies, and attempts to relate this efficacy to the mechanism of action of AEDs and pathophysiological processes associated with the disorders. Some newer indications for AEDs have been established, while others are under investigation. The disorders where AEDs have been demonstrated to be of clinical importance include neurological disorders, such as essential tremor, neuropathic pain and migraine, and psychiatric disorders, including anxiety, schizophrenia and bipolar disorder. Many of the AEDs have various targets of action in the synapse and have several proposed relevant mechanisms of action in epilepsy and in other disorders. Pathophysiological processes disturb neuronal excitability by modulating ion channels, receptors and intracellular signalling pathways, and these are targets for the pharmacological action of various AEDs. Attention is focused on the glutamatergic and GABAergic synapses. In psychiatric conditions such as schizophrenia and bipolar disorder, AEDs such as valproate, carbamazepine and lamotrigine appear to have clear roles based on their effect on intracellular pathways. On the other hand, some AEDs, e.g. topiramate, have efficacy for nonpsychiatric disorders including migraine, possibly by enhancing GABAergic and reducing glutamatergic neurotransmission. AEDs that seem to enhance GABAergic neurotransmission, e.g. tiagabine, valproate, gabapentin and possibly levetiracetam, may have a role in treating neurological disorders such as essential tremor, or anxiety disorders. AEDs with effects on voltage-gated sodium or calcium channels may be advantageous in treating neuropathic pain, e.g. gabapentin, pregabalin, carbamazepine, oxcarbazepine, lamotrigine and valproate. Co-morbid conditions associated with epilepsy, such as mood disorders and migraine, may often respond to treatment with AEDs. Other possible disorders where AEDs may be of clinical importance include cancer, HIV infection, drug and alcohol abuse, and also in neuroprotection. A future challenge is to evaluate the second-generation AEDs in non-epilepsy disorders and to design clinical trials to study their effects in such disorders in paediatric patients. Differentiation between the main mechanisms of action of the AEDs needs more consideration in drug selection for tailored treatment of the various non-epilepsy disorders.

Pharmacological treatment of Parkinson's disease: life beyond dopamine D2/D3 receptors?

Parkinson's disease (PD) is a multisystemic disorder in which several neurotransmitters other than dopamine are affected. Drugs acting on non-dopaminergic systems are envisaged as promising agents to treat PD and levodopa-induced dyskinesias (LID). However, compounds targeting glutamate, adenosine, noradrenaline, 5-hydroxytryptamine, cannabinoid, and opioid transmitter systems have been assessed in human studies showing negative, inconsistent or unsatisfactory results. Most of these drugs had been tested previously in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned monkeys, as well as in the classic 6-hydroxydopamine-lesioned rat model. These failures raise several questions and concerns about the true reliability of animal studies, the adequacy of the working hypotheses and design of clinical trials, the validity of tools in current use to evaluate a particular effect, and the selectivity of the drugs used. More importantly, observed discrepancies between the results in models and patients, could challenge the validity of current ideas about the pathophysiology of parkinsonism and LID.

Serotonin but not zonisamide inhibits theophylline-induced epileptiform activity in guinea pig hippocampal CA3 neurons

To test the putative serotonin (5-HT)-like effect of zonisamide (ZNS) we employed xanthine-induced epileptiform activity in the hippocampus slice preparation from guinea pigs. In this model Na(+)- and T-type Ca(2+) channel blockers are hardly effective while 5-HT should be inhibitory. Bath application of 5-HT hyperpolarized neurons and abolished theophylline-induced epileptiform activity. In contrast, ZNS failed to alter epileptiform bursting. We conclude that 5-HT augmenting effects of ZNS are missing or are not sufficient to inhibit epileptiform activity in hippocampal slice preparations.

Carbamazepine prevents breakdown of neurotransmitter release induced by hyperactivation of ryanodine receptor

To clarify the mechanisms of the pharmacological action of carbamazepine (CBZ), we determined the effect of CBZ on GABA and glutamate release associated with the ryanodine receptor (Ryr)-sensitive Ca(2+)-induced Ca(2+)-releasing system (CICR) in the rat hippocampus using microdialysis. The therapeutically relevant concentration of CBZ increased basal GABA release without affecting basal glutamate release; however, K(+)-evoked releases were concentration-dependently reduced by CBZ. Lower-concentration ryanodine increased basal and K(+)-evoked releases of GABA and glutamate in a concentration dependent manner, whereas higher-concentration ryanodine reduced them. These inflection points in the concentration-response curves of ryanodine for neurotransmitter release (critical concentrations) were shifted to the left by K(+)-evoked stimulation. The critical concentration of ryanodine in GABA release was lower than that in glutamate release. During the resting stage, the critical concentrations of ryanodine were unaffected by inhibition of L-type, N-type and P-type voltage-sensitive Ca(2+) channels (VSCCs) but were prevented by CBZ; however, during the neuronal hyperexcitable stage, the critical concentration was increased by CBZ, L-type and P-type VSCC inhibitors but not the N-type VSCC inhibitor. Therefore, a therapeutically relevant concentration of CBZ protects against the breakdown of the neurotransmitter release mechanism induced by hyperactivation of Ryr via inhibition of L-type and P-type VSCCs as well as inhibition of Ryr-sensitive CICR. These actions of CBZ appear to be involved, at least partially, in its anti-seizure mechanisms.

Activation by zonisamide, a newer antiepileptic drug, of large-conductance calcium-activated potassium channel in differentiated hippocampal neuron-derived H19-7 cells

Zonisamide (ZNS; 3-sulfamoylmethyl-1,2-benzisoxazole), as one of the newer antiepileptic drugs, has been demonstrated its broad-spectrum clinical efficacy on various neuropsychiatric disorders. However, little is known regarding the mechanism of ZNS actions on ion currents in neurons. We thus investigated its effect on ion currents in differentiated hippocampal 19-7 cells. In whole-cell configuration of patch-clamp technology, the ZNS (30 microM) reversibly increased the amplitude of K+ outward currents, and paxilline (1 microM) was effective in suppressing the ZNS-induced increase of K+ outward currents. In inside-out configuration, ZNS (30 microM) applied to the intracellular face of the membrane did not alter single-channel conductance; however, it did enhance the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels primarily by decreasing mean closed time. In addition, the EC50 value for ZNS-stimulated BK(Ca) channels was 34 microM. This drug caused a left shift in the activation curve of BK(Ca) channels, with no change in the gating charge of these channels. Moreover, ZNS at a concentration greater than 100 microM also reduced the amplitude of A-type K+ current in these cells. A simulation modeling based on hippocampal CA3 pyramidal neurons (Pinsky-Rinzel model) was also analyzed to investigate the inhibitory effect of ZNS on the firing of simulated action potentials. Taken together, this study suggests that, in hippocampal neurons during the exposure to ZNS, the ZNS-mediated effects on BK(Ca) channels and A-type K+ current could be potential mechanisms through which it affects neuronal excitability.

Novel anticonvulsant drugs

Principles of complex mechanisms of action of anticonvulsants including latest reports concerning new antiepileptic drugs (AED) are considered. Different aspects of new anticonvulsant drugs (2nd generation) from preclinical and clinical testing, pharmacokinetics, and mono or combination therapy in children and adults are summarized. In the following condensed synopsis pharmacological and clinical characteristics of gabapentin (GBP), lamotrigine (LTG), levetiracetam (LEV), oxcarbazepine (OXC), pregabalin (PGB) and tiagabine (TGB) as well as topiramate (TPM) and zonisamide (ZNS) are discussed. In addition to the mechanisms of action, pharmacokinetics, interactions, indications and dosages as well as side effects are considered. Important data concerning the effect and tolerability of anticonvulsant drugs can be obtained from controlled studies. In comparison to drugs of the first generation (phenobarbital [PB], primidon [PRD], phenytoin [PHT], carbamazepine [CBZ] and valproic acid [VPA]) the potential for interactions and side effects due to enzyme induction or inhibition is reduced by most of the anticonvulsant drugs of the second generation. New anticonvulsant drugs increase the spectrum of treatment and represent further steps with regard to the optimization of an individual therapy of the epilepsies.

Effects of interleukin-1beta on hippocampal glutamate and GABA releases associated with Ca2+-induced Ca2+ releasing systems

Recent clinical and basic studies have demonstrated that hyperactivation of interleukin-1beta (IL-1beta) plays important roles in generation of febrile and epileptic seizures. To clarify this mechanism, the present study determined the effects of IL-1beta on Ca2+-associated releases of glutamate and GABA in mouse hippocampus. Both basal and K+-evoked GABA releases were regulated by Ca2+ influx and Ca2+-induced Ca2+ releasing system (CICR). The K+-evoked glutamate release was also regulated by Ca2+ influx and CICR, whereas basal glutamate release was not affected by them. IL-1beta increased basal releases of glutamate and GABA depending on the activation of Ca2+ influx and ryanodine receptor (RyR)-sensitive CICR, but reduced K+-evoked releases depending on Ca2+ influx, RyR-sensitive and inositol 1,4,5-trisphosphate receptor (IP3R)-sensitive CICRs. During neuronal hyperexcitability, the effect of IL-1beta on GABA release was more predominantly modulated by Ca2+ influx and RyR-sensitive CICR than that on glutamate. These results indicate that hyperactivation of IL-1beta leads to imbalance between glutamatergic and GABAergic transmission via toxic overload response of Ca2+ influx and CICR.