Indian Jou rnal of Experimental Biology Vol. 38, February 2000, pp. I 05-! 12

Motor and electro graphic response of refractory experimental status epilepticus 1 n rats and effect of calcium channel blockers

B George & S K Kulkarni *

Pharmacol ogy Division, Uni versity Institute of Pharmaceutical Sciences . Pan jab Universi ty. Chandigarh I (J() () 1-1. lmli;1

and

R Mathur

Department of Ph ysiology, All India Institute of Medi cal Sciences, New Delhi I I 0 02!J . Indi a

Received 28 September / 998; revised I November / 999

Effects of various calcium channel inhibitors have been studied in lithium-pil ocarpi ne mode l of status epilepticus. Status ep ilepti cus was induced by administrat ion of lithium chloride (3 meq/kg) foll owed 2 1 hr later by pilocarp ine-(30 mg/kg). Diltiazem (5 and 10 mg/kg) was not effec ti ve in delaying onset of co nvul sions. Yerapamil (20 mg/kg) showed protecti on ag inst lithium-pilocarpine-induced convulsions. The dih ydropv ri dine nifidepine (2.5 and 5 mg/kg) did not show any protecti on in thi s model. Aml odipine (5 and I 0 mg/kg J as partially protecti ve. Flunar izi ne ( I 0 and 20 mg/kg) delayed the onset of forelimb clonus and rea rin g and on I y 60% of the rats underwent status in the 20 mg/kg group. Pre-treatment of MK-801 led to a poten ti ation o l· th L· anti seri zure acti vity of calc ium channel inhibitors. The percent increase in amp litude at various time po int s wit h amlodip ine pretreatment was significant onl y at the 30th min recording, and at the res t nf the time franH.:s was practically simil ar as the controls. It can be concluded that the anti convulsant action of M K-XO I can he enhanced by centrally acting calcium channel inhibitors.

Accumulating experimental evidence suggest that abnormalit ies in calcium-regulated ion channels or enzymatic processes may underlie alterations in neuronal excitabi lity and result in seizure activity. Increased Ca2

+ influx in epileptogenesis is well established, and it is assumed that both receptor­operated and vo ltage-sensitive Ca2

+ channel s take active part in these processes. Desmedt et a /.1

demonstrated that two piperazine derivatives, flunarazine and cinnarizine antagoni zed PTZ and electroshock-induced seizures. These observations were confirmed and extended for calcium channel inhibitors (CCis) from two other classes, dihydropyridine and benzothi azep ines. Consi stent with these findings, BAY K 8644, an L-type C}+ channel agonist, can elicit seizures by itself and potentiate audiogenic, PTZ- or NMDA-induced convulsions . CCis are the onl y effecti ve drugs for BAY K 8644-induced seizures . Representati ves of the class I CCis (verapamil, gallopamil) do not appear to exhibit significant anticonvul sant activity in any of the above mentioned models, with the notable

*Correspondent author

exception of BAY K 8644-induced se izures2. BAY K

8644 augments NMDA-induced seizures whereas CCis such as diltiazem, nifidepine or verapami l antagonize NMDA- and kainate- ind uced co nvul sions in mice. Convulsions e li cited with intrahippocampal injections of quin.olinic ac id. an endogenous agonist act ing preferenti all y at NM DA-typc , receptors are suppressed by flunari zine or verapami I. · hut not hy nifedipine3

.

The development and evaluati on of dru gs which block Ca2

+ channels has therefore been an important rational strategy for anticonvulsant dru g desi g n ~. Most selective CCTs which ha ve been evaluated for anticonvul sant effect s primaril y bl ock the L-typc channel. Ev idence suggest that dihydropyridines (nifidepine) may act on T-type channe ls at hi gher doses, and some CCis may ac t at other non -calc iu m binding sites as well -'- Flunari zinc is ab le ro bl ock T­type as well as L-type c./+ channels in seve ral ti ssues including brain membranes. Nifed ipinc and flunarizine, partiall y protects the kind led rats from subsequent kindling ·stimuli ' . CC I nimoclipine. has been shown to block amygdalar and hippocampal kindling6

.

106 I DIAN J. EXP. BIOL., FEB RUARY 2000

The metabolic demands and ph ys iological changes to epileptogenesis. CCis acting at C 1S si tes m;ty he associated with SE indicate a major role of Ca2+ in use ful in treating epilepsy. modulating continued excitabi lity and cytotoxicit / and thi s hi gh [C}+] has been repeatedly shown to M t . ·I d M tl d

II I I s G ·rr·· l ; 'J 1 r· aenasan e 10 s cause ce c eat 1 . n 1t 1s et {/ . were t 1e trst to suggest thi s to be the mechanism of status- induced Animo/s-Wistar rats of either sex. ~ 00-2 .'i0 g from ce llular damage. They showed th at during 2 hr of Centra l Anima l house facilit y. Panjah Uni ve rsit y \\'ere statu s induced by bicuculline or L-all ylglyc ine in rat s, used. Anima ls were housed in cages <t nd rece i1·cd Ca2+ accumul ates in the swo llen and di srupted standard I<.Jborat ory chow and W<tt et. f\n itll<ti s we re mitochondria in basal dendrites and se lected neuronal acclimatized to the la boratory cond:r ions and all ce ll bodies within the hippocampus. In vitro studi es experiment s were ca rri ed out betwee n 1).00 and 17.00

indicate that hippocampal bursting acti vity is Ca2+ hrs . dependent and dihydropyridine channe ls are locali zed Drugs-The follow ing dru gs (vvith the ir respec ti ve in regions such as the hippocampus which are relatt J source) were used during the entire study: lithium

Li -Pilocarpine : Control

Con ox D. Hippocampus

~ ( M~l~l'vl~t«\MtiMAt\1~\\IIJ i I ~1)!~,~~~~~~#\lihNi~NII'1\\»il·/r~;ill~\\1;11 ' N

,

0 l1 ~~~~~~~ ~'{~~~,{~\~~~~~ ~~~~~~~~~~~~~(Jif/l/~~{~~~f~/t~(~(i~' ~ . r ~~lf!~l\!~~~j\~~ f~ > ~ ~~~

. \ . ~ \\\\ 1\ ~ • , \\ 8L 6L N N

, 1s 1s

Fig. 1- Rcp rcscn talivc conical and dorsal hippocampal (DI-Ic) EEG in Li -pil ocarpinc control ra ts slHlll'ln,!.! tile d c ~c· i<lp111Cill nr Sl ·: .11 different time intervals. A: Basa l recording: B. c. D. E: 0 .5. I . 1.5 and 4 hr post pi locarpine no mg) ch ;tllcngL· I JJ ==Il ). T he cortJ c. tl amplitude corresponding to A ( 100 p V): B---7E (200 pV) and Dl-lc amplitude corresponding to A (200 pV >: l l ~ r. I ~IH ) pV 1. IL' ' JlLTtl\ el l arc indicated.

GEORGE cl a/.: MOTOR AND ELECTROGRAP HI C RESPO SE OF REFRACTORY EX PER IMENTAL STA J" l JS I 07

chl oride (Merck, Germany), atropine sulphate, pilo­carpine nitrate, (Boenringer Ingelheim, Germany), ketamine (Themis, India) , MK-80 1 (Merck Sharp and Dohme, UK), ni fed ip ine (Torrent Labs, Ahemeda­bad), diltiazem (Torrent Labs, Ahemedabad), verapamil (Torrent Labs, Ahemedabad), aml odipine (Sys topic Laboratories Ltd ., Faridabad, Indi a), flun ari zine (Torrent Pharmaceutica l Ltd , Baroda, India). The doses used in the present study are based upon the prev tous studies carri ed out tn our laboratory.

Experimental procedure-SE was induced by the method of Honchar and co lleagues 10 by admini stering lithium chl oride (3 meq/kg, ip) followed 2 1 hr later by pilocarpine (30 mg/kg, sc), fo llowing which rats were

70

60 ~ ~ ~ ~ ~

c 50 E c 40

~

a; 30 (/)

c 20 0 10

0

c ii) 0 0 0 (.) ~ T"' N

iS iS c: c: > >

~

ii)

g. z

obse rved continuously fo r occu rrence of behavioura l and electroencephalographic (EEG) se izures (Fig. I ). In the interacti on studi es, the dru gs we re admini stered 30 min prior to pil oca rpine challenge . The latency to attain forelimb clonu s with re~1 r in g was noted and seizu res were monitored till 90 min post pil ocarpine behav iourall y.

For electrophys iologic stud y. under ketamine anaesthesi a (80 mg/kg, im ) ra t .~ were s t en:: o t a x i ca ll y 1 ~ (Dav id Kopff, Model- 1404, SA) imp lanted wi th both corti cal bil ateral watch sc rew electrodes ~111d

unilatera l uni po lar electrode in . the right dorsa l hippocampus (-2.8 mm posteri or. 2 mm la te ral and 3.5 mm ventral). Prior to keta mine at rop ine sulphate (7 mg/kg, ip ) was give n to rats to reduce resp iratory

120

~set J ~ Mortal itY.. ~

100

80 >-

60 ~ 0 2

40 ~ 0

~ 20

0

·e ii) 0 0 0

;- e N z E 'E <( u. u.. <(

Fi g. 2-EITect or different calcium chan nel blockers di lt iazem (Dt : 5 and 10 mg/kg) . vcrapami l (Vp: 10 ;lild :w me!/ke! ) ni k dipinc tNL 2.5 and 5 mg/kg), ;11nlodipine (A md: 5 and 10 mg/kg), and flun arizine (FI: 10 and 20 mg/kg) admi ni stered :10 min hdo1·c piloc:11·pinc (1 ()

mg/kg) chall enge in Li-pretreated rats. Severity was assessed as onset or F.C+R and percent morta li ty. Each v;du e rcprc:-.c nt s 1nc; 11 l±S.L (n=7-9). *P<O.OS !compared w.r.t. contro l (Cnt). Kruskal Walli s test fo ll owed by Student's t-testj.

100

90 lf • • .. ,. ~ Jl( k *

120

80

70 c

·----\ D Onset ... ~ % M-~~ali ty_

100

80 c .E 60

50 -CIJ (/) 40 c 0 30 ,.....-

60 ~ 0 2 , o

40 0

20 20

10 ~ ~ ~

0 • 0

c +~ +N' +~

+ ~ + N' N 0 N

~o ~ o 0 ~ o ~a 0 ~

§: ~ 0 ~ LO~ LO .,._.. ~ :.:: ~:.:: C'i :.:: ~ :l&::

0 ::1: C::::E :;:' ::!E E ::E rf::i: > z <1:

Fig. 3-Effect of combi nation of MK-801 (0.3 mg/kg) with di ffe rent calcium channel blockers ad m i ni st~rcd -15 ;tml 30 min hclorc pil ocarpine (30 mg/kg), respective ly in Li-pretreated rats. Di lt iazem (Dt: 5 mg/kg) , verapamil (Vp: 10 mg/kg ). ni kd ipinc tN L 2.5 mg/kg ). aml odipi ne (A md: 5 mg/kg). and tl una ri zine (FI: I 0 mg/kg). Severity was assessed as onset or F.C+R and p~ rce nt monalit y. F~tch value represents mean±S.E. (n=7-9). *P<O.OS, ** P<O.O I J:co mpared w.r.t. cont ro l (Cnt), Kru skal Wal lis tes t folio w~d hy Student s t-le, tl .

108 INDIAN J. EXP. BIOL., FEBRUARY 2000

secreti ons. After 5 days recovery each animal was allowed atleast 30 min for habituati on to the transparent recording cage (mod ified skinner box, 25x25x29 em) permitting free movement with the experimental set up foll ow ing which SE was induced6

. Onset of seizures was characterised electrographically by the occurrence of generali zed spikes and polyspikes for longer than 20 s associated with sniffing, chew ing, eye blinking and head nodding as reported by Hirsch et al 1 1

• SE was defined as continuous convul sions for a peri od longer than 30 min assoc iated with continuous spikes of high l:lmp litude. EEG signals were recorded on the ch:' :l paper of Grass Model 70 pol ygraph (Grass In struments Co. , Quincy, Mass, USA) . Prior to

recording, ca libration of EEG signals was clone by determining the height of signal having vo ltage of 50 11 v. Frequency was determined by ca lculating the average number of peaks recurring per second taken up from three 5 s intervals. similar ly for amplitude. determined by measurin g peak to pe; tk vo lt age manuall y. The changes in EEG we re recorded alternately for cortex and hi ppocampu ~ ~() min hcl'on~ lithium (basa l), 30 min aft er amlocl tpine (~0 .) hr post lithium), and after administering pil oc;trpinc (~ I hr post lithium) at 30 min interva ls up to YO th min. and finally after 4 hr of pilocarpi ne.

Statistical wwlvsis- ln beha v i our;.~! studi es data on onset of fo re limb c lonu s with reari ng was subj ected to Kruskal -Walli s one-way anal ys is of va ri ance output -

ll - Amlodlplno • Pllocarplno

Cortox D. Hlppocampu'

f(llil~~~~~.il'\ll'tlil~~~~·l'~

/W;~1ft~llf\\ll~jl~~~~l;1 1\~~~ i lc A~h~\\)JwrvV~IWJ~~~\(V > J !\~ AI AI, j 1 i I 1'11 1 ~~~~~~~~~M~v~j~lf\A(,~

0 \ . ~~~~~~~~ I r~ ~~ ~ ~{\1 E

: ~ t~tttfcffN : Lfrffl~~~f 1s 1s

Fig. 4--Represen tative cortical and dorsal hippocampal (DHc) EEG. showing the development ot' SE in .nnlndip111c 11 (I 111).'/ k).'l

. pretreated rats at di fferent time intervals. A: Basa l recording; B. C, D , E: 0.5. I . 1 .. '5 <llld 4 hr post pil ocarp111c t30 111 .~/ ~ ).'l ch:dlcn)!c. The cortical amplitude co rresponding to A-~C (200 pV ), D~E (400 pV), F (200 pY ). respccJivcly. arc indi cat ed.

GEORGE el a /.: MOTOR A 1D ELECTROGR APHIC RESPONSE OF REFRACTOR Y EXPERIM ENTAL ST i\T l iS I 09

test foll owed by Student' s t-test. Descriptive statistics for amp litude and frequency in the cortex and hippocampus at vari ous time points was ca lculated by mean and standard dev iation for all the groups separately. Frcidmans tes t (non-parametric test) was app li ed to find out at what time fro m the basal value changes become signifi cant. Thi s was done for borh the parameters in the cortex and hippocampus group wise. Area under the curve (AUC) was compared among the groups by Kru skal Walli s tes t. In case of overall signi ficance, multiple range test was app li ed. The data on the percent change in amplitude and frequency was analyzed by one way analysis of variance (ANOV A) amongst the groups . Further application of least signifi cant difference procedure was performed for testin g significance of each group. P < 0.05 was considered stati stica ll y signifi cant.

Results Behavioural studies-Among the CC!s , diltiazem

(5 and 10 mg/kg) was not effec ti ve in de laying onset

350

300

~ 250 > :::!

-;;;- 200 "0 :::! = 150 0.. E <( 100

50

of status . Representati ves of the class I CC!s. verapamil ( I 0 and 20 mg/kg) whi ch is cllccrivc against kindling was effec ti ve onl y at the hi gher Jose. The dih ydropyridine nif"idepine (2.5 and 5 mg/kg) did not show any protecti on in thi s mode l. Amlod ipine ( 5

and 10 mg/kg) was partiall y protec ti ve. Flunari zinc ( 10 and 20 mg/kg, po), a diphenylalky lamine ;tnd a potent CCI, able to block T-type as we ll as L-typc Ca2

+ channels in several ti ssues inc luding brai n membranes was successful in dela ying the onse t or F.C+R, and only 60% of the rats underwent statu s in the 20 mg/kg group (Fig. 2).

MK-80 I when given 15 min before the sub­effec ti ve doses of" CC is studied rd ilti a7.e l11 (5 ti1g/kg). verapamil ( 10 mg/kg), ni fcd ipine () mg/kg). am lod ipine (5 mg/kg), and flunari zine ( I 0 mg/kg. p(l) I Jed tO a potentiati on Of" the anti sc i/.Urt' activ it y (Fig. 3).

EEG studies- However, aml odipine ( 10 mg/kg) neither reduced the severit y o f" SE nor the subseque nt mortality apart from the fact that it dc l;tyed the onse t

6

5.8

5.6 N

5.4 I

>-5.2 g

<ll ::J

5 CT <ll

4.8 u: 4.6

0 +--'----'---t---L----'---t----'-----'--+--L---'--+ 4.4

8 (Ctx) Am (Ctx) B (DHc) Am (DHc)

Fi g. 5-EITecl of amlodipine (A md : I 0 mg/kg) pretreatment in Li -pretreated rats on con ical (C!x ) and dor,al hi p poL-~IIn p~ d 1 Dl iL l

amp litude and frequ ency, compa red wi th respec t to hasa l (B ) va lues. Each va lue represent s mean±S. D. ( n=4 ). ( Fri edm:111s tc' t ).

I_.._ Cnt (Ctx) T 1 --o-- Amd (Ctx) • . .

1 ~ 2000 l .. . . ·Cnt (DHc) • • X ••• • -> • ·X - Amd (DHc) • • • • , 1 " " .. . . - · - .

; 1500 . --- --- ~-- - ~- • , , .. .. J< ' -,- .

~ '

2500

- . - - ii

~1000 ~~ S',, :1 500 ' ', / ~ I

1

>-----------<

oe~ 8 30, p 60, p 90 , p 240, p

TIME (min)

Fig. 6----Ti me course changes in the con ic tl (Ct x) and dorsal hippoca mpal (D Hc) EEG amplitude in ~lln l udipinc 1!\md: 10 m~ i k ~J

pretreated rat s as compared to the cont ruls in Li -piloq1rpine model. Eac h va lue represent s mc~m±S . D. (n=-1 -6 ). TilL· At IC ul Cnt tCtx 1 ,./, Amd (Ctx ) and Cnt (DHcl v/s Amd tD I !c) showed no signil"i cant difference (Kruskal Wal li s test).

110 I DIAN J. EXP. BIOL. , FEBRUARY 2000

of status (Figs 4-6). The % increase in amplitude (wit h reference to the basa l value) at va ri ous time points with amlodipine pretreatment was sign ifi cant only at the 30th min recording, and at the res t of the time frames was practica ll y similar as the control s (Fig. 7A). The hippocampa l frequency in am lod ipine group remained more or less at the basal value till 60th min. record, whereas in the contro l rats the DHc frequency increased right from the 30th min . record till the 90th min post pilocarpine. Recording taken at the 4th hr (240 min ) showed a drop in frequency (Fig. 7B).

Discussion Intracellul ar Ca2

+ plays a crucial ro le in the initiation and regulati on of a variety of physio logica l c~ llul ar processes, which include release of neurotransmitters and hormones , neuronal electrica l activity, muscle contraction, ge ne ex press ion, ce ll growth and eli fferentiatio n and cell death 11

.

This potentiation of the antiseizure activity cou ld be the result of simultaneous bl ockade of exc itatory

1 100 Q)

-g 1200 .... a. 1000 E ro 800 c Q)

Ol c ro .!: u ;!!. 0

600

400

200

!O Cnt(Ctx) · :m Amd(Ctx) I lo cnt(DHc))

·D Amd(DHc) i L -----·

events and vo ltage-dependent calc tutn channe ls. Because of the reported role of neuronal Ca 2

+

channels in seizure disorders. \'a ri ou..; CC is we re exam ined for anticonvu lsa nt acti vit y in Li-pilocarpine model of SE.

The CC I, dilt iazem (5 and I 0 tll ):!/ k ~). a putent coronary dilator, was not protec ti ve: in the prese nt model of SE. Yerapami I and D-hOO ( meth ox y­verapamil ) are known to reduce the amp litude or Ca2

+

sp ikes induced by iontophoreti c pulses or NMDA in hippocampal sli ce preparation. Vn<tp<tmil also part iall y protects the kincl lccl rat s rrom subsequent kind ling sti muli 3

. In the present study ve rapamil ( I 0 and 20 mg/kg) was protec ti ve onl y at the hi gher dose. The dihydropy ridine CC L niridepiliL: (2.5 and 5 mg/kg) was also inerfective and di d not show an y respite from the se izures. Aml odipinc (5 and I 0 mg/kg), another dihydropyridine CCI. with a long durat ion of act ion was found to be partia lly efkcti vc at 10 mg/kg dose in de laying the onset uf seizures . In the EEG studies, the percent increase in amp li tude at va ri ous time points with aml odipin c ( I 0 mg/kg)

0+---------~~~~~-L~~~~~

50

40

> 30 u ~ 20 :J

g- 10 .... -

30, D

D Cnt(Ctx) . D Amd (Ctx)

I D Cnt(DHc)

30,P

i D Amd (DHcL

60,P

TIME ( min

90,P 240,P

B

c 0+---r-r-r-.;-L-+-+-L-L;-~+-+-A-~~~~~~-r.-.-.-.-~ Q)

g' -10 90,P ro t3 -20

<f. -30

-40

-50 TIME (min)

Fig. 7-A. The percent change in amplitude observed afte r amlodipine (A mcl : 10 mg/kg) pretre;ttnlcnt on curt ll',d tCt xJ <IIlli dm~:d

hippocampa l (D Hc) EEG acti vit y. 13 . Similarly, fur percent change in frequency in Li- pilocarpine mode l. Each \';il uc n.:prc~c n1 ~

mean±S.D. (n=4-6). P<O.OS [co mpared with res pect to control values. one way ANOY A foll owed by Student · s t - t c~ l l

GEORGE el a/.: MOTOR AND ELECTROGRAPHIC RESPONSE OF REFRACTORY EXPER IME0!T1\L ST ;\ Tt S I I I

pretreatment was practica ll y similar as th at of control s.

Flunarizine (d ifluoro deri vat ive of cinnari zi ne), a diphenylalkylamine, has a wide spectrum of pharmaco logical activ ity. Among these, ac ti ons which may account for its an ticonvulsant properti es are suppression of N- and T-type c}+ channel conductance, phenytoin-like effects on sod ium channels , and inhibition of adenos ine reuptake. Flumirizine ( I 0 and 20 mg/kg) dose dependentl y delayed the onset of F.C+R. The 20 mg/kg dose also brought down the mortality rate significantl y.

The mechan ism of act ion of CCis in epilepsy is not well understood. The anti epileptic effects may be by either decreas ing neuronal recruitment or abo li shing the paroxysmal depolarizati on shift (PDS) , an excitatory fi eld potential recorded in groups of neurons during the process of seizure initiation. The PDS is believed to be the underl ying generator of burst fir ing of neuronal groups that synch roni ze firin g in discrete areas of the brai n. CC!s , such as verapami l have been reported to reduce the amplitude of the PDS or poss ibl y to decrease generati on of such spikes in hippocampal slice preparation14

. Ca2+ entry into

neurons· is in vo lved in initiation of epileptiform activ ity by activating C}+ and calmodu lin-dependent protein kinases. The subsequent ce ll damage is mediated largely through second messenger mechani sms.

Ca2+ ions also play a pivotal role in EAA-mediated 1' C b. . I events · . om tnatt on t 1erapy, opens new

possibi lities for some of the EAA receptor antagonists in the treatment of epil epsy 11

'. In the present stu dy, MK-80 I (0.2 mg/kg) adm ini stered before the subeffec ti ve doses of CCis in Li -pil ocarpine model [di ltiazem (5 mg/kg), verapamil ( I 0 mg/kg), ni fedip ine (5 mg/kg), am lodipine (5 mg/kg), and flunari zine ( I 0 mg/kg)] led to a potentiati on of the antiseizure activity. The exact nature of the interacti on between vo ltage-dependent calcium channels and EAA receptors remains to be determined. NMDA and non-NMDA receptors differ substant ia ll y in ion selectivit y17 It is know n that the

MDA receptor-medi ated effects are ca lcium .dependent due to the hi gh permeab ility of the NMDA -· c '+ . IK CCI h f' reooptor to a· tons . s, t ere ore, may synergist icall y tncrease the protective ac ti on of competiti ve NMDA receptor an tagonists aga inst convulsions. It can be conc luded th at the anticonvul sant acti on of M K-80 I ca n be enhanced by centrall y acting CCis. Such combinations may prove

use ful in ratio ncdi zin g polyphannaco logical approaches in the treatment of epil epsy.

Dynamic regul ati on of C} + signal tran sduct ion system may provide in sight into the molecu lar mechani sms of altered neuronal exci tabilit y whi ch arc important not onl y in the de ve lopment or bcttn therapeutic strategies in pathologic pmccsscs such a:-­epilepsy, but also in understandin g ti ll' ph ys JPiug ica l deve lopment of neuronal pl ~ J s ti c it y.

References I Desmcd t LKC. i c nu;~cc r> C.I F & .l:tn"..:n l 'i\.1.

An ti convul sant propertic> or cinnari;inc :111d rlun aril.llle in rats aml mice. Dmg Ncs. 25 ( J<J76) I.+OX- 141 .1.

2 Czuczwar SJ. M alek U & K leinrok Z. lnlluencc or calcium channel inhibitors upon the ant iconl ·ul s; tlll clli can· ol· common antiepileptic a~enl s a~ain > l I'TZ-indun:d convulsions in mice. NeumJJ!unw£1<'!1/ogr. 2<) 1 I <J'JO) 'J-+3 -948.

3 Vezzani A. Wu Q. Stasi tvl A. A n~e l iL·" I' & Saman1 n R. Errect or various calciu m channe l blockers Oil three dilkrcnl models limbic seizures 111 ra ~>. iVI'll/'rljJ/unwur!l!o~\. 27 ( 19SX) 45 I -45X.

4 Porter RJ & Rogawski M /\. Ncll' :lllt icpi lcl'li c dm~>: l rom serendipit y to rati onal disco ve ry. l :'eif,·t"iu . . ~ . \ I Supp l. I l ( 1992 ) S I -S6.

5 Faingold CL, Overvicw or ion ch:lllnci >. :tnti cpilcplic dru~'· and scizures. in: Dmgs .fin· conlml of <p il<'i' ·'L ~\t'tions on 11 1'11 /'0IIa l 11 1'1\\'orks inmliw l in sei~nu · di.wnlns. Edited h1 Fangold CL. Fromm GH. (CRC' l'rc". lloc:1 R:llon ) I 'J'J2 . 57-68.

6 Wurpel JN & lyer SN. C il ciu m channel hllll'kcrs IHap;t lnil and nimodipine inhibit kind l in ~ in :Jdul l :llld 1111111:11u rc r;lts. t / JiletJs ia. 35 ( 1994) 44:1-44X.

7 Dob le A & Martin IL. Mullip lc hcn;od i:lll.: pill L' rcL'l'pitll ·s: llP

reason ror anxiety. Trends J.>fuuwucol. s, ·i . I 3 1 I 'J'J2 l 7Cl -X I . X Meldrum 13 S. Excit :llory :Imino :IL·ids 111 ep i lepsy :111d

potellli al novel therapies. 1:/Ji fq,sr l<n. I 2 t I 'J'J 2) I X'J- I 1!!1.

9 Grifrith s T. Evan s C & M eld rum ns. Si ;tlll\ epilcp i lLW< Th e· reversibilit y or calci u1n lo ad in~ ;~ 11 d :tL'l li L' ncuron:il pathological changes in the rat hi ppoc.Jlll JHls. N<·umsci<'l l<'<'. 12 ( 1984) 557 -5 67 .

10 Hunchar MP. Olney .JW & Shmmn WR. SyslL'l1lir cholinergi c agents induce sc i1.urcs :tnd hr:1i 11 lbm : l ~c· in l ithiu m treated ra ts. Sciencl'. 2201 I 'JX:ll 32 .\-325.

II Hirsch E. Snead OC. Vcr~ncs i\ 1 & Cilk.s 1:. Corpus ca llusotomy in the lithium-piloc: lrpinc ll ll>lkl ''I sc11urcs :111d st:llus epil cpticu s. l~i,il<'/ l.l' l ' l<l's. II t J<J'J2J JX.>- I'Jl .

12 Pax inos G & Wa1son C. Tlw mt hmin iu ,,,,.,·,·ntll\ir·

coordi11mes. (Academic Prc>s. Sydnn· 1 I 'JX2 13 Tsicn RW. Lipscombc D. i\!l:Jdi>on \l V . llk1 KR 8: h> \ AI'.

Mullip lc types or neuron:1l c:tlciu 1n L'li:t llll l'is :111d lh,· it se lect i ve modula1ion. Trl'llds N<·um.lf·i. II 1 I'JXX : 431--l 3X .

14 Dinglcdinc R. J. NMDA aclil';ll c> l ' oila~c dcpcndcnl c;~lctum conductance in r:ll hippoc:unp:tl I'~ r:t lllid:tl n: l ls . .I 1'/n ·.\/ld. 343 ( 1915:1 ) 3X5-405 .

I." Gasior M . Klei nrok Z & Czuczw:tr S.l. lniluclll'C ol \3 .-\Y K-86444 , a calcium channel a~oni s1. tlll ihL· ;Jnlll'lllll'llls;llll acti vity or convcnl iona l :lllllcpilcpil rs ;~~:unsl

eleclroconvul sions in mi l·c. N,·ur"tdwmJu, ·o/ug\ . . ~-+! I'J'I~I

433-438.

11 2 INDI AN J. EX P. BIOL., FEBR UA RY 2000

16 Rogawski MA, in: CNS neumtran.1m iners and neuro111odulators. Edited by Stone TW. (CRC Press. Boca Raton), 1995 , 219.

17 Kullmann DM , Perkel DJ, Manabe T & Nico ll RA. Calcium entry via postsynapt ic voltage-sensitive calci um channels can

transientl y potentiate excit atory synaptic tran~m i ss in n in the hi ppocampu s. Neuron. lJ ( l lJlJ2 ) 1175- 11 X.\.

18 Wroblewski JT & Danys7. W. Modul ;lli<lll oi' )! lu tamatc receptors: Molecular mechani sms and i'unctiu na l implications. Ann Rev Pham wcol To.ricol. 2lJ ( l lJXlJ ) 44 1--+7-1.