PDF hosted at the Radboud Repository of the Radboud University Nijmegen The following full text is a publisher's version. For additional information about this publication click this link. http://hdl.handle.net/2066/28624 Please be advised that this information was generated on 2021-09-30 and may be subject to change. Epilepsia, 36(1):8&92, 1995 Raven Press, Ltd., New York 0 International League Against Epilepsy Role of L-Type Calcium Channel Modulation in Nonconvulsive Epilepsy in Rats E. L. J. M. van Luijtelaar, N. Ates, and A. M. L. Coenen NZCZ, Department of Psychology, University of Nijmegen, Nijmegen, The Netherlands Summary: Old male Wistar rats spontaneously showing est dose of BAY K 8644 also induced fatal convulsions in hundreds of spike-wave discharges daily were used to 3 animals. Our results demonstrate that the L-type cal- investigate the role of calcium ions in nonconvulsive ep- cium antagonist nimodipine facilitates spike-wave dis- ilepsy. The effects of the L-type calcium channel blocker charges and that the L-type calcium agonist BAY K 8644 nimodipine and the L-type channel opener BAY K 8644 protects against these discharges, in contrast to previous on number and duration of these spike-wave discharges results suggesting that calcium channel blockers act as were investigated. In rats aged 84-94 weeks standard antiepileptic drugs (AEDs) and that calcium channel EEG electrodes were chronically implanted; animals openers act as convulsants. Our results are a further ex- were allowed to recover for 10 days. After a baseline ample of the different pharmacologic profile of convulsive registration, nimodipine 2.2, 8.8, and 35.2 mgkg or BAY and nonconvulsive epilepsy and are also in contrast to K 8644 in dosages of 0.12, 0.47, and 1.88 mg/kg was ad- what has been described for T-type calcium channel mod- ministered. A control group received the solvent. EEG ulation. We therefore propose that modulation of L-type recordings were made to evaluate drug effects. The high- and T-type calcium channels have opposite effects in non- est dose of nimodipine increased the number of spike- convulsive epilepsy. Key Words: Absence epilepsy- wave discharges, whereas BAY K 8644 reduced the num- Nimodipine-Bay K 8644-L-type calcium channels- ber of spike-wave discharges dose dependently. The high- Spike-wave discharges-Aged rats. There are several indications that calcium plays a The role of calcium ions in genetic epilepsy rat role in epileptogenesis. During a seizure, the con- models was confirmed by De Sarro et al. (1990), centration of intracellular calcium ions increases who showed that the calcium channel opener Bay K and the extracellular concentration of calcium ions 8644 facilitates convulsions in sound-induced epi- decreases (Heinemann et al., 1977). Crowder and lepsy in genetically epilepsy-prone rats (GEPR). Bradford (1987) and Yaari et al. (1987) also demon- Bay K 8644, a dihydropyridine derivative, increases strated involvement of calcium, reporting that anti- the opening probability of a particular subclass of epileptic drugs (AEDs) such as phenytoin (PHT) calcium channels, the L-type channel, thereby pro- and carbamazepine (CBZ) inhibit influx of calcium moting voltage-dependent calcium influx (Bernath, ions. Finally, the specific antiabsence drugs etho- 1992). On the other hand, nimodipine also belongs suximide (ESM) and a-methyl-a-phenylsuccinimide to the class of dihydropyridines, but this centrally block a subtype of calcium channel, the T-type, in active drug acts as a calcium antagonist by blocking thalamic neurons (Coulter et al., 1990). Therefore, the voltage-dependent L-type calcium channels drugs that block influx of calcium ions into the cells (Meyer et al., 1987; Suzuki and Rogawski, 1989). by blocking calcium channels, calcium antagonists, Spedding and Paoletti (1992) suggest that BAY K probably have antiepileptic properties (Ashton and 8644 and nimodipine are rather selective for the Wauquier, 1979; Hoffmeister et al., 1982; Heine- L-type calcium channels. mann and Hamon, 1986; Meyer et al., 1987; De Among the many epilepsy models used to evalu- Sarro et al., 1988; Speckmann and Walden, 1989; ate calcium channel modulation, models for gener- Sills et al., 1994). alized absence epilepsy are lacking. We investi- gated the effects of acute administration of nimo- Received December 1993; revision accepted March 1994. dipine and Bay K 8644 on number and mean Address correspondence and reprint requests to Dr. E. L. J. M. van Luijtelaar at NICI, Department of Psychology, duration of spontaneously occurring spike-wave P.O. Box 9104, 6500 HE Nijmegen, The Netherlands. discharges in old Wistar rats. Several inbred rat 86 L-TYPE CALCIUM MODULATION AND ABSENCE EPILEPSY 87 strains such as the WAG/Rij strain (van Luijtelaar were connected to the recording leads 16 h before and Coenen, 1986), but also selection lines such as EEG recordings were made. Nimodipine was in- Strasbourg rats (Vergnes et al., 1982) and outbred jected in dosages of 2.2, 8.8 and 35.2 mg/kg; Bay K strains such as the Wistar and the Sprague Dawley 8644 was administered in dosages of 0.12, 0.47 and strains, show an age-dependent increase in both the 1.88 mg/kg. In addition, we established a control amount of spontaneously occurring spike-wave dis- group by injecting rats with solvent. After a 1-h charges and in number of affected animals (Coenen baseline EEG recording, animals were injected i.p. et al., 1992). These genetically determined spike- with drugs or solvent. Subsequently, the EEG was wave discharges are accompanied by minor clinical recorded for 2 consecutive h. signs (van Luijtelaar and Coenen, 1986) and occur The EEG signal was amplified and filtered by an predominantly during passive wakefulness and light Elema-Schonander polygraph and frequencies be- slow-wave sleep (SWS) and less during deep SWS tween 1 and 70 Hz were allowed to pass. The EEG and REM sleep (Coenen et al., 1991; Drinkenburg was subsequently stored in digitized form on a mag- et al., 1991). The spike-wave discharges can be netooptical disk (DATA Instruments, AT-CODAS). blocked by broad spectrum AEDs such as diazepam Spike-wave discharges were visually scored ac- (DZP) and valproate (VPA) and also by ESM and cording to criteria described previously (van Luijte- trimethadion, but not by AEDs such as CBZ and laar and Coenen, 1986). The number of spike-wave PHT (Peeters et al., 1988). We report the effects of discharges and total duration of individual episodes acute administration of nimodipine and BAY K of spike-wave discharges were determined by one 8644 in old Wistar rats, which exhibit several hun- of us (N.A.). Examples of spike-wave discharges dred spontaneously occurring spike-wave dis- are shown in Fig. 1. The number and duration of the charges daily (van Luijtelaar et al., 1994). spike-wave discharges were calculated for the base- line hour and for the four postinjection 30-min pe- METHODS riods. Spontaneous behavior of the rats in their cages Old male random-bred Wistar rats donated by was closely observed through a window from an Troponwerke (Cologne, Germany) and originally adjacent room. We quantified duration of the fol- purchased from Winkelmann (Borchen, Germany) lowing behavioral categories for 30 min, beginning 5 were studied. The rats had no previous drug his- min after injection: exploratory behavior (walking, tory. Preoperatively , they were housed in groups rearing, sniffing, digging), automatic behavior and then were singly housed. At operation, they (grooming, eating, drinking), and immobile behav- were aged 84-94 weeks and weighed 389-528 g. An- ior (sitting, lying, and standing still) (Coenen and imals were maintained on a 12/12-h light/dark re- van Luijtelaar, 1989). Data were recorded and ana- gime, with white lights on at 2000 h. lyzed with a PC registration software package (The EEG electrodes in the frontal and parietooccipital Observer, Wageningen, NL) (Noldus, 1991). All cortical region with coordinates A 2.0, L 3.5 and data were statistically verified by analysis of vari- A-6.0, L 4.0 respectively, with skull surface flat and ance (ANOVA), followed by Duncan’s post hoc bregma zero zero, were permanently implanted un- test for multiple comparisons. der pentobarbital anaesthesia (60 mg/kg). The ground electrode was placed over the cerebellum. RESULTS Postoperatively, subjects were allowed to recover for 10 days. All rats showed predrug spontaneously occurring The experiment was performed in freely moving spike-wave discharges in their cortical EEG, and animals during the dark phase of the day and drugs most of the spike-wave discharges occurred during were always administered at 1100 h. In this period passive behavior. Sample records of EEGs contain- of the lighddark cycle, rats have the highest amount ing spike-wave discharges made before and after of spike-wave discharges (van Luijtelaar and Coe- nimodipine and BAY K 8644 administration are nen, 1988). shown in Fig. la and b. The effects of nimodipine Nimodipine and Bay K 8644 (Bayer, Germany) on spike-wave discharges are shown in Fig. 2. were given intraperitoneally (i.p.) in a volume of 2 There were no differences between the four groups mYkg body weight as a freshly ultrasonicated solu- before injection. Nimodipine induced an increase in tion in a mixture of solutol/ethanol/0.9% NaCl number of spike-wave discharges in the first and (5:5:90). The solution was prepared in a dark room fourth 30-min period after injection (F = 4.02, p < and shielded from light. Animals were divided into 0.05 and F = 5.20, p < 0.01 respectively; both df seven groups, each consisting of 7-10 rats. They 3,28): post hoc tests showed that at 0-30 min after- Epilepsia, Vol.