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N-[1-(2-Thienyl)cyclohexyl]-piperidine (TCP) does not block kainic acid-induced status epilepticus but reduces secondary hippocampal damage
174
Neuroscience Letters, 122 (1991) 174-178 Elsevier Scientific Publishers Ireland Ltd.
NSL 07495
N-[1-(2-Thienyl)cyclohexyl]-piperidine (TCP) does not block kainic acid-induced status epilepticus but reduces secondary hippocampal damage Mireille L e r n e r - N a t o l i 1, G 6 r a r d R o n d o u i n 1, M h a m m e d Belaidi 1, Michel B a l d y - M o u l i n i e r 1 and J.M. Kamenka 2 ~CNRS UPR41. INSERM U249, Laboratoire de Mbdecine ExpOrimentale, Institut de Biologie and ZEcole Nationale Supkrieure de Chimie, Montpellier (France)
(Received 25 July 1990; Revisedversion received 10 October 1990; Accepted 17 October 1990) Key words: Statusepilepticus; Kainic acid; Hippocampus; NMDA; Neuroprotection; TCP
Distant damage, localized in the CA3 and CA 1 areas, was observedin the hippocampus of rats as a consequence of status epilepticus (SE) induced by the injection of 2.5 nmol of kainic acid (KA) into the amygdala. In animals pretreated with an intraperitoneal injection of the non-competitive antagonist of the N-methyl-D-aspartatereceptor, N-[l-(2-thienyl)cyclohexyl]-piperidine(TCP) (20 mg/kg), distant neuronal damage was reduced (CAI neurons were always spared) whereas the rats still developed SE with an earlier onset. These results demonstrate the protective effectof TCP and confirm that epileptic activity and brain damage may be dissociated by NMDA receptor antagonists.
Hippocampal damage is frequently observed after various acute pathologies, and particularly sustained epileptic seizures [4, 11, 17, 19]. It was proposed that these lesional processes are due to an excessive release of endogenous excitatory amino acids (EAAs) which massively activate the EAA receptors [14]. Indeed, the implication of N-methyl-D-aspartate ( N M D A ) receptors in damage localized in the hippocampal CA1 area following ischaemia, epilepsy or direct application of EAA was pharmacologically demonstrated (e.g. refs. 1, 5, 6, 8, 9, 18). Therefore, the search for new molecules, antagonists of the EAA receptors, currently constitutes an exciting pharmacological challenge. The systemic or intracerebral injection of kainic acid (KA) provides an appropriate animal model of status epilepticus (SE). This powerful neurotoxin triggers severe limbic seizures, associated with neuronal damage in specific brain areas, particularly the limbic system [13]. Intraamygdaloid injections of K A (1.5-2.5 nmol) induced SE and two kinds of lesions: direct amygdaloid lesions and distant neuronal loss in other structures. In the hippocampus ipsilateral to the injection site, the areas C A 3 - C A 4 and CA1 were reported to be comple-
Correspondence." M. Lerner-Natoli, CNRS UPR41, INSERM U249,
Laboratoire de M~decine Exp~rimentale, Institut de Biologie, Bd. Henri IV, 34060 Montpellier, France. 0304-3940/91/$ 03.50 © 1991 ElsevierScientific Publishers Ireland Ltd.
tely lesioned, while CA2 and the dentate gyrus were spared [2]. The present experiment was designed to study the effects of a non-competitive antagonist of N M D A receptors N-[1-(2-thienyl)cyclohexyl]-piperidine (TCP) [20], which displayed a protective action against in vitro glutamate neurotoxicity [15], on the electro-behavioural parameters and histological consequences of SE induced by intraamygdaloid injections of KA. Surgery: 18 male, adult Sprague-Dawley rats, weighing 230-300 g were prepared as follows: 10 rats (control group) were anaesthetized with 0.35 ml/100 g of Equithesine. A stainless-steel cannula was stereotaxically positioned in the right basolateral amygdala. One/~1 of a solution containing 2.5 nmol of K A dissolved in phosphate buffer was injected at the rate of 0.1/zl/min. Five screws were placed on the skull and linked to a microconnector with dental acrylic cement. Thirty min before anaesthesia, 8 rats (TCP-treated group) received an intraperitoneal injection of TCP (20 mg/kg, dissolved in NaC1 0.9%). In a previous study [1], we demonstrated that this dose was able to protect CAI neurons against the toxicity of N M D A (20 nmol) injected into the hippocampus. Since we observed that TCP potentiated Equithesine anaesthesia, the dose of Equithesine was limited to 0.17 ml! 100 g. Then these rats were submitted to the same protocol as controls. Recording and behavioural observation." After surgery, the rats were placed in recording chambers, linked to an
175
(b) TCP group: For the 8 animals examined, in which the right amygdala was also massively injured, the hippocampal lesions were selectively limited to the right (ipsilateral to the injection) CA3/CA4 area (see Fig. 2 and Table I). In both groups, the dentate granular cells were always intact. We did not observe any lesions in other brain regions. Behavioural observation and EEG monitoring: During a period of approximately 2 h following the injection of KA, all the animals showed numerous wet dog shakes, followed by a stereotypic circling behaviour, head nodding, mastication, forelimb, then hindlimb clonus and generalized convulsions. During the WDS period, a first electrical discharge appeared on the EEG, followed by others, until the beginning of the electrical SE, characterized by a constant epileptic discharge. All along SE, the rats continuously displayed either partial or generalized seizures. The end of SE was characterized by a gradual lowering of EEG amplitude and frequency, with a fast spiking activity, concomitant to numerous WDS, which progressively disappeared. The latency of the first discharge and the onset of SE were strongly shortened in TCP rats compared with the control group, while the total duration of electrical and behavioural SE was not significantly modified (Table I). The present study indicates that: (1) neuronal damage in area CA1 following KA-induced SE can be prevented by a systemically administered non-competitive NMDA antagonist and thus likely depends on the activation of NMDA receptors; (2) this protective effect is not related to an antiepileptic effect of TCP, since the treated rats still developed SE, earlier than controls; (3) CA3 lesions, which cannot be avoided by TCP treatment, probably involve KA receptors. The hippocampal CA3 area, ipsilateral to the KAinjected amygdala, was always injured in both groups.
EEG monitor (ALVAR) and observed during 24 h by 3 successive experimenters. They noted, for each animal, the latency of the first epileptic discharge recorded on cortical leads, the onset and the end of the electrical status epilepticus. The behavioural manifestations were scored and classified into partial seizures (wet dog shakes (WDSs), stereotyped circling, head nodding, facial clonus and mastication) and convulsive seizures (forelimb clonus, hindlimb clonus, generalized convulsions). The total duration of behavioural and electrical seizures was computed. Histology: 10 days later, the rats were anaesthetized with ether and intracardially perfused with buffered formaline. Brains were removed and frontal serial sections (50/tm) were performed with a vibratome, mounted on slides and stained with Cresyl violet for light microscopy observation. Data analysis: The extent of hippocampal CA3 and CA1 damage was measured bilaterally on all sections, using a camera lucida and a digitizing tablet, with the help of a computer assisted semi-quantitative method. Both amygdalae were directly observed on the light microscope and the presence or absence of lesions was noted. The electro-clinical parameters (latency of the first discharge, onset and total duration of electrical SE, duration of behavioural seizures), were compared with a Student's t-test. Histology. (a) Control group: All rats had a massive lesion in the right amygdala, extending to the pyriform cortex, and two of them showed picnotic neurons in the homotypic contralateral structures. On the injected side, the CA3 area was always strongly injured, and both CA1 and the contralateral CA3/CA4 areas showed various degrees of lesion, ranging from restricted cell loss to extended neuronal death and gliosis (see Table I for quantification and Fig. 1).
TABLE I HISTOLOGICAL CONSEQUENCES AND ELECTROBEHAVIOURAL PARAMETERS OF KA-INDUCED STATUS EPILEPTiCUS Comparison of control and TCP treated rats (mean + S.E.M.). Lesions are expressed in arbitrary units of area. 1st D; first epileptic discharge. Rats
Lesions
Electrobehavioural seizures
Right
Control
Left
Latency (min)
Duration (min)
CA3
CA I
CA3
CA 1
1st D
SE
EEG
Seizures
95+15
53+21
52+__21
52_+22
108+6
149_+7
841+53
832+58
743+18
728-+24
(n= 10) TCP
72__+17
(n= 8) *P < 0.001 Student's t-test
0
0
0
52_+8*
66-+8*
176
Fig. 1. Hippocampallesions in a control rat after limbic status epilepticus induced by an intraamygdaloidinjection of 2.5 nmol of kainic acid (Cresyl violet stain). A: the pyramidal neurons of CA1 and CA3 area are lesioned. Note the gliosissurrounding the stratum pyramidale. B: higher magnification of the marked (*) zone in A: picnotic neurons and glial cells of CA1.
Control rats also presented distant lesions in the ipsilateral CA1 and contralateral CA1 and CA3 areas, with a high variability in their extent. Although there is a general agreement on the relationship between the seizure severity and the spread of neuronal damage, some authors already described various degrees of hippocampal lesions, with different routes of K A administration (e.g. ref. 9). In contrast, in TCP-treated rats, CA1 neurons were always spared while the lesions of CA3
remained strictly unilateral. The absence of lesion in the contralateral CA3 area of these animals suggests that the propagation of seizure activity to this side through excitatory pathways is mediated by N M D A receptor activation. An intriguing observation was the shorter onset of electrical discharges and SE in the TCP group. Even if this effect may be partially related to the lower dose of Equithesine received by these rats, this result completely
177
ii ¸ il¸ ,i~ii~i?ii!!ii~!!ii~¸¸¸ i~i i
!B
i~
i| I0 i
Fig. 2. Hippocampal lesions in a rat treated by TCP (20 mg/kg) 1 h before the injection of 2.5 nmol of kainic acid into the amygdala inducing a limbic status epilepticus (Cresyl violet stain). A: lesions affect only CA3 area while the pyramidal neurons of CA1 are protected. B: higher magnification of the marked (*) zone in A: CA1 neurons are intact.
agrees with that of Fariello et al. [5] who also reported an earlier appearance of KA-induced EEG seizures and • SE in rats pretreated with MK-801. As suggested by these authors, this potentiation could, between other hypotheses, be a consequence of the use-dependent antagonistic effect of TCP or MK-801. This is in accordance with the relative inefficacy of phencyclidines and MK801 to block kindled seizures in contrast with their ability to inhibit the development" of kindling [2, 7, 16]. How-
ever in KA-induced SE, an anticonvulsant effect of PCP and ketamine was reported by Labruyere et al. [8]. Likewise, Fariello et al. [5] showed that MK-801 abolished KA-induced convulsions. In keeping with our present resuits, Lason et al. [9] demonstrated that an intracerebroventricular injection of the competitive antagonist of NMDA receptors, 2-amino-5-phosphonova!erate (APV), failed to inhibit convulsions. Despite the relative discrepancy about the antiepileptic properties of these
178
drugs, there is a general consensus that they effectively protect CA1 but not CA3 neurons against seizure related damage. The topography of 'protected' areas and remaining damage in TCP-treated rats versus controls is in accordance with the distribution of EAA receptors and TCP binding sites within the hippocampus [10, 12]. Therefore, our results support the hypothesis that the distant lesions provoked by the injection of KA into the amygdala depend on excitatory mechanisms involving principally N M D A receptors. Moreover, they emphasize that the neuroprotective effect of a drug may be dissociated from its antiepileptic activity. The authors gratefully thank J.R. Teilhac for his technical assistance. This work was supported by grants from the Ministrre de la Recherche et de l'Enseignement Suprrieur (88.C.0562).
1 Belaidi M., Rondouin, G., Lerner-Natoli, M., N'Gouemo, P. and Kamenka, J.M., Lrsions excitotoxiques de l'hippocampe chez le rat: implication des rrcepteurs au N-mrthyl-D-aspartate, C.R. Soc. Biol., 183 (1989) 256-262. 2 Ben Ari, Y., Ottersen, O.P., Tremblay, E. and Naquet, R., Epileptic phenomena following intraamygdaloid injection of KA: an electroencephalographic, behavioral, and neuropathologic study. In R. Canger, F. Angeleri and J.K. Penry (Eds.), Advances in Epileptology: Xlth Epilepsy International Symposium, Raven, New York, 1980, pp. 25-38. 3 Bowyer, J.F., Phencyclidine inhibition of the rate of development of amygdaloid kindled seizures, Exp. Neurol., 75 (1982) 173-183. 4 Epstein, M.H. and O'Connors, J.S., Destructive effects of prolonged status epilepticus, J. Neurol. Neurosurg. Psychiatr., 29 (1966) 251-254. 5 Fariello, R.G., Golden, C.T., Smith, G.G. and Reyes, P.F., Potentiation of kainic acid epileptogenicity and sparing from neuronal damage by an NMDA receptor antagonist, Epilepsy Res., 3 (1989) 206-213. 6 Foster, A.C., Gill, R., Kemp, J.A. and Woodruff, G.N., Systemic administration of MK 801 prevents NMDA-induced neuronal degeneration in rat brain, Neurosci. Lett., 76 (1987) 307 311. 7 Gilbert, M.E., The NMDA receptor antagonist, MK801, suppresses limbic kindling and kindled seizures, Brain Res., 463 (1988) 90-99.
8 Labruyere, J., Fuller, T.A., Olney, J.W., Price, M.T., Zorumsky, C. and Clifford, D., PCP and ketamine protect against KA-induced seizures and seizures related brain damage, Soc. Neurosci. Abstr., 12 (1986) 344. 9 Lason, W., Simpson, J.N., and McGinty, J.F., Effect of D-(--)APV on behavioural and histological changes induced by systemic KA, Neurosci. Lett., 87 (1988) 23-28. 10 Maragos, W.F., Chu, D.C.M., Greenamyre, J.T., Penney, J.B. and Young, A.B., High correlation between the localization of pH]TCP binding and NMDA receptors, Eur. J. Pharmacol., 123 (1986) 173174. 11 Meldrum, B.S. and Briefly, J.B., Prolonged epileptic seizures in primates. Ischemic cell change and its relation to ictal physiological events, Arch. Neurol,, 28 (1973) 10-17. 12 Monaghan, D.T. and Cotman, C.W., The distribution of pH]kainic acid binding sites in the rat CNS as determined by autoradiography, Brain Res., 252 (1982) 91-100. 13 Nadler, J.V., Kainic acid as a tool for the study of temporal lobe epilepsy, Life Sci., 29 (1981) 2031-2042. 14 Olney, J.W., Excitotoxic amino acids, News Physiol. Sci., 1 (1986) 19-23. 15 Rondouin, G., Drian, M.J., Chicheportiche, R., Kamenka, J.M. and Privat, A., Non-competitive antagonists of N-methyl-D-asparrate receptors protect cortical and hippocampal cell cultures against glutamate neurotoxicity, Neurosci. Lett., 9l (1988) 19% 203. 16 Rondouin, G., Chaudieu, I., Belaidi, M., Allaoua, H., N'Gouemo, P., Kamenka, J.M. and Chicheportiche, R., The effects of thienylphencyclidine (TCP) on kindling in the rat: putative role of TCPPCP receptors in the kindling model. In E.F. Domino and J.M. Kamenka (Eds.), Sigma and Phencyclidine-like Compounds as Molecular Probes in Biology, NPP Books, Ann Arbor 1988, pp. 215-222. 17 Sagar, H.J. and Oxbury, J.M., Hippocampal neuron loss in temporal lobe epilepsy: correlation with early childhood convulsions, Ann. Neurol., 22 (1987) 334-430. 18 Simon, R.P., Swan, J.H. and Meldrum, B.S., Blockade of Nmethyl-D- aspartate receptors may protect against ischemic damage in the brain, Science, 226 (1984) 850-852. 19 Sommer, W., Erkrankung des Ammons' Hornes als aetiologisches Moment der Epilepsie, Arch. Psychiatr. Nervenkrank., 10 (1980) 631~75. 20 Vignon, J., Chicheportiche, R., Chicheportiche, M., Kamenka, J.M., Geneste, P. and Lazdunski, M., [3H]TCP: a new tool with high affinity for the PCP receptor in rat brain, Brain Res., 280 (1983) 194-197.
Neuroscience Letters, 122 (1991) 174-178 Elsevier Scientific Publishers Ireland Ltd.
NSL 07495
N-[1-(2-Thienyl)cyclohexyl]-piperidine (TCP) does not block kainic acid-induced status epilepticus but reduces secondary hippocampal damage Mireille L e r n e r - N a t o l i 1, G 6 r a r d R o n d o u i n 1, M h a m m e d Belaidi 1, Michel B a l d y - M o u l i n i e r 1 and J.M. Kamenka 2 ~CNRS UPR41. INSERM U249, Laboratoire de Mbdecine ExpOrimentale, Institut de Biologie and ZEcole Nationale Supkrieure de Chimie, Montpellier (France)
(Received 25 July 1990; Revisedversion received 10 October 1990; Accepted 17 October 1990) Key words: Statusepilepticus; Kainic acid; Hippocampus; NMDA; Neuroprotection; TCP
Distant damage, localized in the CA3 and CA 1 areas, was observedin the hippocampus of rats as a consequence of status epilepticus (SE) induced by the injection of 2.5 nmol of kainic acid (KA) into the amygdala. In animals pretreated with an intraperitoneal injection of the non-competitive antagonist of the N-methyl-D-aspartatereceptor, N-[l-(2-thienyl)cyclohexyl]-piperidine(TCP) (20 mg/kg), distant neuronal damage was reduced (CAI neurons were always spared) whereas the rats still developed SE with an earlier onset. These results demonstrate the protective effectof TCP and confirm that epileptic activity and brain damage may be dissociated by NMDA receptor antagonists.
Hippocampal damage is frequently observed after various acute pathologies, and particularly sustained epileptic seizures [4, 11, 17, 19]. It was proposed that these lesional processes are due to an excessive release of endogenous excitatory amino acids (EAAs) which massively activate the EAA receptors [14]. Indeed, the implication of N-methyl-D-aspartate ( N M D A ) receptors in damage localized in the hippocampal CA1 area following ischaemia, epilepsy or direct application of EAA was pharmacologically demonstrated (e.g. refs. 1, 5, 6, 8, 9, 18). Therefore, the search for new molecules, antagonists of the EAA receptors, currently constitutes an exciting pharmacological challenge. The systemic or intracerebral injection of kainic acid (KA) provides an appropriate animal model of status epilepticus (SE). This powerful neurotoxin triggers severe limbic seizures, associated with neuronal damage in specific brain areas, particularly the limbic system [13]. Intraamygdaloid injections of K A (1.5-2.5 nmol) induced SE and two kinds of lesions: direct amygdaloid lesions and distant neuronal loss in other structures. In the hippocampus ipsilateral to the injection site, the areas C A 3 - C A 4 and CA1 were reported to be comple-
Correspondence." M. Lerner-Natoli, CNRS UPR41, INSERM U249,
Laboratoire de M~decine Exp~rimentale, Institut de Biologie, Bd. Henri IV, 34060 Montpellier, France. 0304-3940/91/$ 03.50 © 1991 ElsevierScientific Publishers Ireland Ltd.
tely lesioned, while CA2 and the dentate gyrus were spared [2]. The present experiment was designed to study the effects of a non-competitive antagonist of N M D A receptors N-[1-(2-thienyl)cyclohexyl]-piperidine (TCP) [20], which displayed a protective action against in vitro glutamate neurotoxicity [15], on the electro-behavioural parameters and histological consequences of SE induced by intraamygdaloid injections of KA. Surgery: 18 male, adult Sprague-Dawley rats, weighing 230-300 g were prepared as follows: 10 rats (control group) were anaesthetized with 0.35 ml/100 g of Equithesine. A stainless-steel cannula was stereotaxically positioned in the right basolateral amygdala. One/~1 of a solution containing 2.5 nmol of K A dissolved in phosphate buffer was injected at the rate of 0.1/zl/min. Five screws were placed on the skull and linked to a microconnector with dental acrylic cement. Thirty min before anaesthesia, 8 rats (TCP-treated group) received an intraperitoneal injection of TCP (20 mg/kg, dissolved in NaC1 0.9%). In a previous study [1], we demonstrated that this dose was able to protect CAI neurons against the toxicity of N M D A (20 nmol) injected into the hippocampus. Since we observed that TCP potentiated Equithesine anaesthesia, the dose of Equithesine was limited to 0.17 ml! 100 g. Then these rats were submitted to the same protocol as controls. Recording and behavioural observation." After surgery, the rats were placed in recording chambers, linked to an
175
(b) TCP group: For the 8 animals examined, in which the right amygdala was also massively injured, the hippocampal lesions were selectively limited to the right (ipsilateral to the injection) CA3/CA4 area (see Fig. 2 and Table I). In both groups, the dentate granular cells were always intact. We did not observe any lesions in other brain regions. Behavioural observation and EEG monitoring: During a period of approximately 2 h following the injection of KA, all the animals showed numerous wet dog shakes, followed by a stereotypic circling behaviour, head nodding, mastication, forelimb, then hindlimb clonus and generalized convulsions. During the WDS period, a first electrical discharge appeared on the EEG, followed by others, until the beginning of the electrical SE, characterized by a constant epileptic discharge. All along SE, the rats continuously displayed either partial or generalized seizures. The end of SE was characterized by a gradual lowering of EEG amplitude and frequency, with a fast spiking activity, concomitant to numerous WDS, which progressively disappeared. The latency of the first discharge and the onset of SE were strongly shortened in TCP rats compared with the control group, while the total duration of electrical and behavioural SE was not significantly modified (Table I). The present study indicates that: (1) neuronal damage in area CA1 following KA-induced SE can be prevented by a systemically administered non-competitive NMDA antagonist and thus likely depends on the activation of NMDA receptors; (2) this protective effect is not related to an antiepileptic effect of TCP, since the treated rats still developed SE, earlier than controls; (3) CA3 lesions, which cannot be avoided by TCP treatment, probably involve KA receptors. The hippocampal CA3 area, ipsilateral to the KAinjected amygdala, was always injured in both groups.
EEG monitor (ALVAR) and observed during 24 h by 3 successive experimenters. They noted, for each animal, the latency of the first epileptic discharge recorded on cortical leads, the onset and the end of the electrical status epilepticus. The behavioural manifestations were scored and classified into partial seizures (wet dog shakes (WDSs), stereotyped circling, head nodding, facial clonus and mastication) and convulsive seizures (forelimb clonus, hindlimb clonus, generalized convulsions). The total duration of behavioural and electrical seizures was computed. Histology: 10 days later, the rats were anaesthetized with ether and intracardially perfused with buffered formaline. Brains were removed and frontal serial sections (50/tm) were performed with a vibratome, mounted on slides and stained with Cresyl violet for light microscopy observation. Data analysis: The extent of hippocampal CA3 and CA1 damage was measured bilaterally on all sections, using a camera lucida and a digitizing tablet, with the help of a computer assisted semi-quantitative method. Both amygdalae were directly observed on the light microscope and the presence or absence of lesions was noted. The electro-clinical parameters (latency of the first discharge, onset and total duration of electrical SE, duration of behavioural seizures), were compared with a Student's t-test. Histology. (a) Control group: All rats had a massive lesion in the right amygdala, extending to the pyriform cortex, and two of them showed picnotic neurons in the homotypic contralateral structures. On the injected side, the CA3 area was always strongly injured, and both CA1 and the contralateral CA3/CA4 areas showed various degrees of lesion, ranging from restricted cell loss to extended neuronal death and gliosis (see Table I for quantification and Fig. 1).
TABLE I HISTOLOGICAL CONSEQUENCES AND ELECTROBEHAVIOURAL PARAMETERS OF KA-INDUCED STATUS EPILEPTiCUS Comparison of control and TCP treated rats (mean + S.E.M.). Lesions are expressed in arbitrary units of area. 1st D; first epileptic discharge. Rats
Lesions
Electrobehavioural seizures
Right
Control
Left
Latency (min)
Duration (min)
CA3
CA I
CA3
CA 1
1st D
SE
EEG
Seizures
95+15
53+21
52+__21
52_+22
108+6
149_+7
841+53
832+58
743+18
728-+24
(n= 10) TCP
72__+17
(n= 8) *P < 0.001 Student's t-test
0
0
0
52_+8*
66-+8*
176
Fig. 1. Hippocampallesions in a control rat after limbic status epilepticus induced by an intraamygdaloidinjection of 2.5 nmol of kainic acid (Cresyl violet stain). A: the pyramidal neurons of CA1 and CA3 area are lesioned. Note the gliosissurrounding the stratum pyramidale. B: higher magnification of the marked (*) zone in A: picnotic neurons and glial cells of CA1.
Control rats also presented distant lesions in the ipsilateral CA1 and contralateral CA1 and CA3 areas, with a high variability in their extent. Although there is a general agreement on the relationship between the seizure severity and the spread of neuronal damage, some authors already described various degrees of hippocampal lesions, with different routes of K A administration (e.g. ref. 9). In contrast, in TCP-treated rats, CA1 neurons were always spared while the lesions of CA3
remained strictly unilateral. The absence of lesion in the contralateral CA3 area of these animals suggests that the propagation of seizure activity to this side through excitatory pathways is mediated by N M D A receptor activation. An intriguing observation was the shorter onset of electrical discharges and SE in the TCP group. Even if this effect may be partially related to the lower dose of Equithesine received by these rats, this result completely
177
ii ¸ il¸ ,i~ii~i?ii!!ii~!!ii~¸¸¸ i~i i
!B
i~
i| I0 i
Fig. 2. Hippocampal lesions in a rat treated by TCP (20 mg/kg) 1 h before the injection of 2.5 nmol of kainic acid into the amygdala inducing a limbic status epilepticus (Cresyl violet stain). A: lesions affect only CA3 area while the pyramidal neurons of CA1 are protected. B: higher magnification of the marked (*) zone in A: CA1 neurons are intact.
agrees with that of Fariello et al. [5] who also reported an earlier appearance of KA-induced EEG seizures and • SE in rats pretreated with MK-801. As suggested by these authors, this potentiation could, between other hypotheses, be a consequence of the use-dependent antagonistic effect of TCP or MK-801. This is in accordance with the relative inefficacy of phencyclidines and MK801 to block kindled seizures in contrast with their ability to inhibit the development" of kindling [2, 7, 16]. How-
ever in KA-induced SE, an anticonvulsant effect of PCP and ketamine was reported by Labruyere et al. [8]. Likewise, Fariello et al. [5] showed that MK-801 abolished KA-induced convulsions. In keeping with our present resuits, Lason et al. [9] demonstrated that an intracerebroventricular injection of the competitive antagonist of NMDA receptors, 2-amino-5-phosphonova!erate (APV), failed to inhibit convulsions. Despite the relative discrepancy about the antiepileptic properties of these
178
drugs, there is a general consensus that they effectively protect CA1 but not CA3 neurons against seizure related damage. The topography of 'protected' areas and remaining damage in TCP-treated rats versus controls is in accordance with the distribution of EAA receptors and TCP binding sites within the hippocampus [10, 12]. Therefore, our results support the hypothesis that the distant lesions provoked by the injection of KA into the amygdala depend on excitatory mechanisms involving principally N M D A receptors. Moreover, they emphasize that the neuroprotective effect of a drug may be dissociated from its antiepileptic activity. The authors gratefully thank J.R. Teilhac for his technical assistance. This work was supported by grants from the Ministrre de la Recherche et de l'Enseignement Suprrieur (88.C.0562).
1 Belaidi M., Rondouin, G., Lerner-Natoli, M., N'Gouemo, P. and Kamenka, J.M., Lrsions excitotoxiques de l'hippocampe chez le rat: implication des rrcepteurs au N-mrthyl-D-aspartate, C.R. Soc. Biol., 183 (1989) 256-262. 2 Ben Ari, Y., Ottersen, O.P., Tremblay, E. and Naquet, R., Epileptic phenomena following intraamygdaloid injection of KA: an electroencephalographic, behavioral, and neuropathologic study. In R. Canger, F. Angeleri and J.K. Penry (Eds.), Advances in Epileptology: Xlth Epilepsy International Symposium, Raven, New York, 1980, pp. 25-38. 3 Bowyer, J.F., Phencyclidine inhibition of the rate of development of amygdaloid kindled seizures, Exp. Neurol., 75 (1982) 173-183. 4 Epstein, M.H. and O'Connors, J.S., Destructive effects of prolonged status epilepticus, J. Neurol. Neurosurg. Psychiatr., 29 (1966) 251-254. 5 Fariello, R.G., Golden, C.T., Smith, G.G. and Reyes, P.F., Potentiation of kainic acid epileptogenicity and sparing from neuronal damage by an NMDA receptor antagonist, Epilepsy Res., 3 (1989) 206-213. 6 Foster, A.C., Gill, R., Kemp, J.A. and Woodruff, G.N., Systemic administration of MK 801 prevents NMDA-induced neuronal degeneration in rat brain, Neurosci. Lett., 76 (1987) 307 311. 7 Gilbert, M.E., The NMDA receptor antagonist, MK801, suppresses limbic kindling and kindled seizures, Brain Res., 463 (1988) 90-99.
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