Research reportEffect of zonisamide on molecular regulation of glutamate and GABA transporter proteins during epileptogenesis in rats with hippocampal seizures
Introduction
Zonisamide (ZNS), 1,2-benzisoxazole-3-methanesulfonamide, is an antiepileptic drug known to be effective in treating patients with partial seizures or secondary generalized tonic clonic seizures [6], [9], [25]. Mechanisms for the anticonvulsant effects of ZNS include (a) blocking voltage-sensitive Na+ and T-type Ca2+ channels [10], [20], [27], [31], (b) modulating the dopaminergic system [17], [18], (c) reducing epileptiform events by inhibiting excitatory glutamatergic transmission [19], (d) inhibiting lipid peroxidation in a rat model of epilepsy [11], and (e) scavenging hydroxyl radical and nitric oxide radicals in a dose-dependent manner by increasing reducing ability in the brain [10], [16], [32].
Prior work has shown that epileptogenesis with collapse of glutamate regulation leading to glutamatergic excitatory synaptic transmission and reduced γ-aminobutyric acid (GABA)-ergic inhibitory synaptic transmission is associated with changes in the molecular expression of amino acid transporters [34].
Some antiepiletic drugs are known to have molecular effects on amino acid transporter proteins. Valproic acid is associated with increased expression [36] or up-regulation [4] of excitatory amino acid transporters in the hippocampus, suggesting that valproic acid may have unique mechanisms of action by affecting the removal of glutamate by up-regulating EAATs of excitatory amino acid transporters.
To study the molecular effects of the antiepileptic drug zonisamide (ZNS), albino rats with chronic, spontaneous, recurrent seizures induced by amygdalar injection of FeCl3 were treated for 14 days with either ZNS, or with saline used as an injection control. Regions of the hippocampus and the frontal cortex were assayed with Western blots for glutamate and GABA transporters.
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Materials and methods
Twenty male Wistar rats weighing between 200 and 250 g were used. The animals were kept in hanging cages; they had unlimited access to food and water and were exposed to 12-h light–dark cycles. Surgical procedures were performed with pentobarbital sodium anesthesia (37.5 mg/kg, i.p. ). The experimental design was reviewed and approved by the Committee for the Ethics on Animal Experiments in Miyazaki Medical College. The experiments were carried out under the control of the guideline for Animal
Results
Spontaneous stage 4 kindled behavioral seizures [22] were observed 5 days after FeCl3 was injected into the amygdala in control rats treated with saline, as previously reported [37]. Seizures were not observed in rats treated with ZNS whether they had an amygdalar FeCl3 injection or saline injection.
GLAST protein immunoreactivity in the hippocampus of FS animals was reduced by 30% of that of the control group (SS; see Fig. 1). Expression of GLAST was not effected by ZNS treatment (SZ, FZ).
Discussion
Treatment of animals with ZNS prevented seizures and resulted in increased production of EAAC-1 in both the hippocampal region and in frontal cortex. Further, ZNS-treated animals had down-regulation of GABA transporter (GAT-1) production in hippocampus and frontal cortex. EAAC-1, a neuronal glutamate transporter, provides re-uptake of glutamate for GABA synthesis [14], [28] as opposed to acting as a protective mechanism for attenuating glutamate excitotoxicity [7]. As reported by Sepkuty et al.
Acknowledgements
This study was partially supported by a Grant-in-Aid for Encouragement of Young Scientists (08770777 and 10770490) from the Ministry of Education, Science, Sport and Culture, Japan (to Y.U.).
References (37)
- et al.
Production of specific antibodies against GABA transporter subtypes (GAT1, GAT2, GAT3) and their application to immunocytochemistry
Mol. Brain Res.
(1994) Family of neural and acidic amino acid transporters: molecular biology, physiology and medical implications
Curr. Opin. Cell Biol.
(1997)- et al.
Increasing anticonvulsant effect of AD-810 (zonisamide) in aging BDF1 mice
Life Sci.
(1987) - et al.
Mechanisms of T-type calcium channel blockade by zonisamide
Seizure
(1996) - et al.
Efficacy and safety of zonisamide: results of a multicenter study
Epilepsy Res.
(1993) - et al.
Alterations in neurotransmitter amino acids in hippocampal kindled seizures
Epilepsy Res.
(1987) - et al.
The anticonvulsant zonisamide scavenges free radicals
Epilepsy Res.
(1998) - et al.
Effects of zonisamide on extracellular levels of monoamine and its metabolite, and on Ca2+ dependent dopamine release
Epilepsy Res.
(1992) - et al.
Effects of zonisamide on dopaminergic system
Epilepsy Res.
(1995) Modification of seizure activity by electrical stimulation. II. Motor seizure
Electroencephalogr. Clin. Neurophysiol.
(1972)
Blockade of sustained repetitive action potentials in cultured spinal cord neurons by zonisamide (AD 810, CI 912), a novel anticonvulsant
Epilepsy Res.
Knockout of glutamate transporters reveals a major role for astroglial transport in excitotoxicity and clearance of glutamate
Neuron
Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the separation of proteins in the range from 1 to 100 kDa
Anal. Biochem.
Zonisamide enhances slow sodium inactivation in Myxicola
Brain Res.
Zonisamide blocks T-type calcium channel in cultured neurons of rat cerebral cortex
Epilepsy Res.
Simultaneous monitoring of the seizure-related changes in extracellular glutamate and gamma-aminobutyric acid concentration in bilateral hippocampi following development of amygdaloid kindling
Epilepsy Res.
Hippocampal gamma-aminobutyric acid transporter alterations following focal epileptogenesis induced in rat amygdala [In Process Citation]
Brain Res. Bull.
Amygdalar injection of FeCl3 causes spontaneous recurrent seizures
Exp. Neurol.
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