The effect of lifarizine (RS-87476), a novel sodium and calcium channel modulator, on ischaemic dopamine depletion in the corpus striatum of the gerbil

AM-36, a novel neuroprotective agent, profoundly reduces reactive oxygen species formation and dopamine release in the striatum of conscious rats after endothelin-1-induced middle cerebral artery occlusion

Elevated generation of reactive oxygen species (ROS) has been demonstrated during ischemia and reperfusion. Dopamine (DA) autooxidation may contribute to increased ROS generation. The novel neuroprotective agent AM-36 has antioxidant and Na(+) channel blocking activity and reduces neuronal damage in both cortex and striatum after middle cerebral artery (MCA) occlusion. Here we sought in vivo evidence of the ability of AM-36 to inhibit intrastriatal ROS generation and DA release after ischemia. Salicylate hydroxylation coupled with in vivo microdialysis in the striatum of conscious Long Evans rats was performed during MCA occlusion by perivascular microinjection of endothelin-1 (ET-1). AM-36 (6 mg/kg) was administered intraperitoneally 30 min after MCA occlusion. Dialysates were analysed using high performance liquid chromatography with electrochemical detection for the salicylate hydroxylation product, 2,3-dihydroxybenzoic acid (2,3 DHBA) and for DA and metabolites. MCA occlusion resulted in a marked increase in 2,3 DHBA and a secondary increase in all analytes, 180-300 min later. Increased DA release coincided with 2,3 DHBA formation. AM-36 significantly reduced ischemia induced increases in 2,3 DHBA and DA, and infarct volume in the striatum. Significant improvements in a battery of behavioural tests was also found in AM-36 treated rats. This study has demonstrated profound inhibition of ROS generation by a novel compound with antioxidant activity, administered post-ischemia in conscious rats.

Synthesis and biological evaluation of new 4-arylpiperidines and 4-aryl-4-piperidinols: dual Na(+) and Ca(2+) channel blockers with reduced affinity for dopamine D(2) receptors

A series of novel 4-arylpiperidines and 4-aryl-4-piperidinols (2a-f, 3a-f and 4a-f) was synthesized and evaluated for blocking effects on both neuronal Na(+) and T-type Ca(2+) channels and binding affinity for dopamine D(2) receptors. Most of the compounds blockaded both ion channels with potency greater than or equal to flunarizine 1a which was adopted as a reference standard. In addition, these compounds had significantly reduced affinity for dopamine D(2) receptors which is common in this class of structure. Compounds 2a-f, 3a-f and 4a-f exhibited potent anticonvulsant effects following systemic (ip) administration on audiogenic seizures in DBA/2 mice, indicating their excellent brain permeability. The neuroprotective activity of 2a, 3a and 4a was also assessed in a transient middle cerebral artery occlusion (MCAO) model. These compounds significantly reduced neuronal damage without affecting ischemic hyperthemia, while flunarizine 1a produced only minor reductions. In particular, 4a had 1.7-fold the potency in this MCAO model but only 1/20 the affinity for dopamine D(2) receptors of 1a. The superposition of 2a, 3a and 4a on the basis of analyses of systematic conformation and similar structure has revealed that the cinnamyl, phenacyl and phenoxypropanol groups are likely to be structurally and biologically equivalent. Moreover, the superposition of 2a and 2f shows that diphenyl ether and biphenyl groups occupy a similar space, suggesting that both groups act as a bioisostere for the blockade of ion channels; however, this is not the case for dopamine D(2) receptors since only biphenyl compounds such as 2f had high affinity similar to flunarizine 1a. Compound 4a (SUN N5030) has a good pharmacological profile and may be useful in the alleviation and treatment of ischemic diseases.

Cerebral ischemia-reperfusion injury: a novel therapeutic approach with TAK-218

The goal of the present study was to evaluate the potential neuroprotective effect of TAK-218 in an in vivo rat focal cerebral ischemia/reperfusion model. TAK-218 is a novel compound with multiple antiischemic properties, including suppression of aberrant dopamine release, modulation of sodium channels, and inhibition of lipid peroxidation. The study was a blinded, randomized, placebo-controlled study of TAK-218 in a three-vessel focal ischemic rat model. A total of 22 rats were randomly assigned to the treatment or placebo group. Animals were injected intrapertoneally with either a 2 mg/kg dose of drug or saline at 2 hours after reperfusion. Infarction volume was measured with use of 2,3,5-triphenyltetrazolium chloride. Total adjusted infarction volume in treated animals decreased by 10%. With use of a statistical analysis requiring 80% power with a 20% reduction desired effect, there was no statistically significant difference in the end-point of infarction volume between drug and placebo treatment groups. In light of the proven efficacy of thrombolytic therapy for acute stroke, it is now desirable to test neuroprotective agents during the 3-hour therapeutic window after ischemia. Further research is necessary to discern if a therapeutic agent with multiple antiischemic properties may provide a more robust neuroprotective effect than an agent with a single neuroprotective action.

A novel class of Na+ and Ca2+ channel dual blockers with highly potent anti-ischemic effects

A series of novel arylpiperidines (4a-d) which have highly potent blocking effects for both neuronal Na+ and T-type Ca2+ channels with extremely low affinity for dopamine D2 receptors were synthesized. Among these compounds, 1-(2-hydroxy-3-phenoxy)propyl-4-(4-phenoxyphenyl)-piperidine hydrochloride (4c; SUN N5030) exhibited remarkable neuroprotective activity in a transient middle cerebral artery occlusion (MCAO) model.

Blockade by NS-7, a neuroprotective compound, of both L-type and P/Q-type Ca2+ channels involving depolarization-stimulated nitric oxide synthase activity in primary neuronal culture

The effect of 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride (NS-7), a neuroprotective compound, on Ca2+ channels involving the activation of nitric oxide synthase (NOS) was investigated in primary neuronal culture. The NOS activity was estimated from the cyclic GMP formation. The KCl (25 mM)-stimulated cyclic GMP formation was totally abolished by a combined treatment with nifedipine and omega-agatoxin IVA (omega-Aga), whereas spontaneous cyclic GMP formation was partially but significantly reduced by nifedipine. In contrast to nifedipine, NS-7 blocked KCl-stimulated cyclic GMP formation without affecting spontaneous cyclic GMP formation. Subsequently, the effects of nifedipine and NS-7 on L-type Ca2+ channels were compared. Nifedipine blocked equally the cyclic GMP formation stimulated by various concentrations of (+/-)-Bay K 8644, whereas NS-7 inhibited the maximal response without affecting the responses induced by low concentrations of (+/-)-Bay K 8644. The effects of NS-7 on L-type and P/Q-type Ca2+ channels involving KCl-stimulated cyclic GMP formation were subsequently examined. NS-7 suppressed the KCl-stimulated cyclic GMP formation measured in the presence of omega-Aga to almost the same extent as that determined in the presence of nifedipine. In contrast, NS-7 had no influence on ionomycin-induced enhancement of cyclic GMP formation. Finally, NS-7 reversed KCl-induced elevation of the intracellular free Ca2+ concentration. These findings suggest that NS-7 inhibits NOS activation in primary neuronal culture by reducing Ca2+ entry through L-type and P/Q-type Ca2+ channels, in which the inhibition is largely dependent on Ca2+ channel activity.

Focal cerebral ischemia in the mouse: hypothermia and rapid screening of drugs

1. We have investigated the ability of several compounds to diminish both infarct area and volume induced by middle cerebral artery occlusion in the mouse. 2. Lifarizine, ipsapirone and N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine HCl (DPPE) all reduced both infarct area and volume. Ifenprodil diminished the infarct area, but the effect on total infarct volume was much less pronounced. 3. In addition, we tested the protective effects of some other drugs on infarct area only. Nimodipine, verapamil, diltiazem, N-[1-[4-(4-fluorophenoxy)butyl]-4-piperidinyl]-N-methyl-2-benzothiazo lamine (R56865) and sabeluzole had no effect on infarct area. (S)-Emopamil significantly diminished infarct area. 2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) also diminished infarct area significantly. 4. In some brain ischemia models hypothermia protects against ischemic damage. Mild hypothermia had no effect on infarct area in the present mouse model of focal ischemia.

Na+ and high-voltage-activated Ca2+ channel blocking actions of NS-7, a novel neuroprotective agent, in NG108-15 cells

The actions of a novel neuroprotective compound, 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride (NS-7), on voltage-gated Na+, Ca2+ and K+ channels were investigated in a mouse neuroblastoma and rat glioma hybrid cell line, NG108-15, using a whole-cell voltage clamp technique. NG108-15 cells have a tetrodotoxin-sensitive Na+ channel, three types of Ca2+ channel (L, N and T) and voltage-gated K+ channels, all of which were inhibited by NS-7 in a concentration-dependent manner. However, there was a considerable difference in its potency: the IC50 values for the tetrodotoxin-sensitive Na+ channel, L-type Ca2+ channel and N-type Ca2+ channel were similar (7.8, 4.5 and 7.3 microM, respectively), lower than the IC50 value for the T-type Ca2+ channel (17.1 microM), and much lower than the IC50 value for the voltage-gated K+ channel (160.5 microM). NS-7 altered neither the shape nor the reversal potential of the current-voltage curves for Na+, L-type or N-type Ca2+ channels, although the currents were reduced at every potential tested. These results indicate that NS-7 is a Na+ and high-voltage-activated (L- and N-type) Ca2+ channel blocker, and its channel-blocking properties may contribute to its neuroprotective action.

Inhibition by lifarizine of intracellular Ca2+ rises and glutamate exocytosis in depolarized rat cerebrocortical synaptosomes and cultured neurones

1. The effects of lifarizine (RS-87476) on intracellular Ca2+ rises and the release of glutamate from rat cerebrocortical synaptosomes depolarized with 30 mM KCl were investigated by use of entrapped fura 2 and exogenous glutamate dehydrogenase. 2. Prior (1 min) addition of lifarizine decreased 30 mM KCl-induced total glutamate release, with 3 microM and 10 microM causing 39% and 72% averaged decreases from controls. The calcium-dependent component of glutamate release (approx. 40% of total) was similarly decreased by 47% and 74%, whereas the calcium-independent component was decreased by only 32% and 43% respectively. 3. In parallel experiments with fura-2-loaded synaptosomes, lifarizine reduced the depolarization-induced increases in intracellular [Ca2+], suggesting that this is the means by which the decreases in glutamate release are brought about. Lifarizine inhibited both the plateau and the spike phases of the Ca2+ increases suggesting that, in addition to its known sodium channel blocking properties, it may also inhibit more than one class of calcium channel in the synaptosomes. 4. Lifarizine at 1 microM and 3 microM also inhibited the rises in intracellular [Ca2+] in rat cultured cortical neurons depolarized with 60 mM KCl. 5. These effects of lifarizine on intracellular Ca2+ and glutamate exocytosis may contribute to its neuroprotective action.

Neuroprotective efficacy of lifarizine (RS-87476) in a simplified rat survival model of 2 vessel occlusion

1. A new, modified rat two vessel occlusion model (with hypotension) was established and the neuroprotective efficacy of the novel agent lifarizine (RS-87476) was examined. 2. The two vessel occlusion model used in the study was a modification of the model described in the literature, whereby we have obviated the need to use a muscle relaxant and intubate the trachea to provide ventilatory support by providing a tight fitting face mask attached to the ventilator. Furthermore, the need to combine exsanguination and additional pharmacological means of inducing the mandatory hypotension (50 mmHg), required to decrease brain blood perfusion pressure, has been removed by simply manipulating the concentration of the already present halothane anaesthetic. 3. The appropriate level of hypotension having been reached, microvascular clips were applied to bilaterally occlude the common carotid arteries for 12 min. This resulted in a loss of the cortical EEG activity. Local cerebral blood flow was measured 6 min into the occlusion period, using the fully quantitative [14C]-iodoantipyrine autoradiographic technique, in a separate group of rats (n = 5). This illustrated the lack of any blood flow, in the areas under study, during the period when there was an isoelectric cortical EEG pattern. 4. The high grade global ischaemic lesion which occurred gave quantifiable neuronal damage in several vulnerable regions of the brain, namely, the hippocampal CA1 sub-field, cortex, thalamus, striatum, and cerebellar brain stem (Purkinje cells). 5. Following the global ischaemic insult the rats were allowed to recover for 72 h before assessment of the damage, during which time one group of rats (n = 11) received 100 micrograms kg-1 lifarizine i.a. 5 min post-occlusion, 500 micrograms kg-1 lifarizine i.p. 15 min post-occlusion, and 500 micrograms kg-1 lifarizine i.p. twice daily for 72 h. A second group of rats (n = 12) was treated with appropriate volumes of vehicle (0.4 ml kg-1 i.a. and 2 ml kg-1 i.p.) at identical time points. 6. Histopathological damage was assessed, from cresyl violet and haematoxyline/eosin stained sections, using a scoring system of 0-6 (no damage-complete neuronal death). The dosing regimen of lifarizine gave reduced damage in the hippocampal CA1 sub-field (4.1 +/- 0.3 to 2.8 +/- 0.6) and striatum (1.7 +/- 0.3 to 1.2 +/- 0.3) and significant neuroprotection in the anterior cortex (2.0 +/- 0.2 to 1.2 +/- 0.2; p < 0.05), thalamus (1.5 +/- 0.2 to 0.8 +/- 0.2; p < 0.01), posterior cortex (1.5 +/- 0.2 to 1.0 +/- 0.2; p < 0.05) and cerebellar brain stem (0.9 +/- 0.2 to 0.4 +/- 0.1; p < 0.01). The overall mean brain score was significantly reduced (from 1.5 +/- 0.1 to 0.9 +/- 0.2). 7. These data show that the newly modified 2 vessel occlusion model produced a quantifiable level of ischaemic damage and that the novel agent lifarizine is neuroprotective in the model.

Reduction by lifarizine of the neuronal damage induced by cerebral ischaemia in rodents

1. The objective of this study was to evaluate the broad neurocytoprotective potential of the novel sodium-calcium ion channel modulator, lifarizine (RS-87476), in two rodent 72 h survival models of forebrain ischaemia. 2. Under fluothane anaesthesia, rats were subjected to 10 min four vessel occlusion and gerbils to either (i) 5 or (ii) 10 min bilateral carotid artery occlusion. 3. Rats were dosed parenterally solely post-ischaemia (reperfusion) in a series of five studies covering a range of intra-arterial/intraperitoneal (i.a./i.p.) combination doses from 2/10, 5/20, 20/100, 50/200 and 100/500 micrograms kg-1, where the initial loading dose was injected i.a. at 5 min. An i.p. dose was given at 15 min and repeated twice daily. In a sixth study, treatment at 50/200 micrograms kg-1 was deferred for 1 h. 4. Gerbils were treated (i) 15 min pre-ischaemia with either (a) 250, (b) 500 micrograms kg-1 i.p., or (c) 5 mg kg-1 by gavage (p.o.) for 3 days then at 1 h pre-ischaemia. Animals treated as (ii) received 500 micrograms kg-1 i.p. 15 min pre-ischaemia. The above doses were repeated twice daily for 3 days post-ischaemia for the respective groups. 5. In rats, the protective effect of lifarizine was regionally and cumulatively assessed in six brain regions (anterior and posterior neocortex, hippocampal CA1 subfield, thalamus, striatum, cerebellar Purkinje cells-brain stem) at each dose level. Cumulative (total) means +/-s.e.mean neurohistopathological scores(0-4) of 1.16+/-0.09 (n=5), 1.02+/-0.10 (n=5), 0.93+/-0.06 (n=6), 0.79+/-0.09 (n=9) and 0.45+/-0.16(n = 7), respectively, were obtained for the above treatment groups compared to the control (2.01 +/- 0.17,n = 16) group (P<0.0035). The score for the 1 h deferred treatment group was also significant at 0.77 +/- 0.10, n =5 (P< 0.0035). The normal group without ischaemia showed a score of 0.52 +/- 0.09 (n = 6).6. In gerbils, (i) percentage delayed neuronal death (DND) of hippocampal pyramidal cells in the CA1subfield was prevented at 250 (a) and 500 microg kg-' i.p. (b) (27.2+/- 14.6, n=6 and 26.9+/- 10.4%, n= 10 respectively, P<0.02) compared to controls (78.3+/-8.5%, n= 12) and by 5 mg kg-1 p.o. (c) (2.9+/-0.8%,n =l1, P <0.002). Mean +/- s.e.mean total brain scores (0-4) for each of 4 different features denoting cerebral 'oedema' were lower for normal brains (1.60 +/-0.34, n =6) and reduced in animals dosed at 250(a) (3.00+/-0.79, n=6) and 500 microg kg-1 i.p. (b) (3.75 0.36, n= 10) compared to controls (6.58+/-1.00,n = 12) (P< 0.02 -0.03). There was a linear relationship (r = 0.97) between the 'oedema' scores and percentage CA1 DND. Percentage CA1 DND in response to 10 min ischaemia (ii) was reduced(53.0+/-21.0%, n=6, P<0.05) compared to controls (100.0+/-0.0%, n=7).7 The significant neuroprotection shown by lifarizine in rodents substantiates findings in other species.These observations, together with its effect on ion channels and efficacy at extremely low doses offers novelty and suggests a broad spectrum of activity in ischaemia.

[3H]-lifarizine, a high affinity probe for inactivated sodium channels

1. [3H]-lifarizine bound saturably and reversibly to an apparently homogeneous class of high affinity sites in rat cerebrocortical membranes (Kd = 10.7 +/- 2.9 nM; Bmax = 5.10 +/- 1.43 pmol mg-1 protein). 2. The binding of [3H]-lifarizine was unaffected by sodium channel toxins binding to site 1 (tetrodotoxin), site 3 (alpha-scorpion venom) or site 5 (brevetoxin), Furthermore, lifarizine at concentrations up to 10 microM had no effect on [3H]-saxitoxin (STX) binding to toxin site 1. Lifarizine displaced [3H]-batrachotoxinin-A 20-alpha-benzoate (BTX) binding with moderate affinity (pIC50 7.31 +/- 0.24) indicating an interaction with toxin site 2. However, lifarizine accelerated the dissociation of [3H]-BTX and decreased both the affinity and density of sites labelled by [3H]-BTX, suggesting an allosteric interaction with toxin site 2. 3. The binding of [3H]-lifarizine was voltage-sensitive, binding to membranes with higher affinity than to synaptosomes (pIC50 for cold lifarizine = 7.99 +/- 0.09 in membranes and 6.68 +/- 0.14 in synaptosomes). Depolarization of synaptosomes with 130 mM KCl increased the affinity of lifarizine almost 10 fold (pIC50 = 7.86 +/- 0.25). This suggests that lifarizine binds selectively to inactivated sodium channels which predominate both in the membrane preparation and in the depolarized synaptosomal preparation. 4. There was negligible [3H]-lifarizine and [3H]-BTX binding to solubilized sodium channels, although [3H]-STX binding was retained under these conditions. 5. The potencies of a series of compounds in displacing [3H]-lifarizine from rat cerebrocortical membranes correlated well with their affinities for inactivated sodium channels estimated from whole-cell voltage clamp studies in the mouse neuroblastoma cell line, NIE-115 (r=0.96).6. These results show that [3H]-lifarizine is a high affinity ligand for neuronal sodium channels which potently and selectively labels a site, allosterically linked to toxin binding site 2, associated within activated sodium channels.

New drug binding sites in Ca2+ channels

New classes of drugs modifying Ca2+ channel activity have become available, this may enlarge the clinical utilities that have been associated with established Ca2+ channel antagonists such as the dihydropyridines (for example, nifedipine). Two such classes are reviewed by Michael Spedding, Barry Kenny and Pierre Chatelain. Fantofarone is a non-dihydropyridine with a novel site of action in the L-type Ca2+ channel that appears to yield a distinct cardiovascular profile. In contrast, fluspirilene and related Na+ and Ca2+ channel inhibitors have a distinct site of action in Ca2+ channels, which is not specific for one channel type. The utility of Na+ and Ca2+ channel inhibitors in ischaemic stroke is compared with new and more selective Na+ channel inhibitors.

Actions of the novel neuroprotective agent, lifarizine (RS-87476), on voltage-dependent sodium currents in the neuroblastoma cell line, N1E-115

1. The actions of the neuroprotective agent, lifarizine (RS-87476-190), on voltage-dependent Na+ currents have been examined in the neuroblastoma cell line, N1E-115, using the whole-cell variant of the patch clamp technique. 2. At a holding potential of -80 mV, lifarizine reduced the peak Na+ current evoked by a 10 ms depolarizing step with an IC50 of 1.3 microM. At holding potentials of -100 and -60 mV the IC50 concentrations of lifarizine were 7.3 microM and 0.3 microM, respectively. 3. At a holding potential of -100 mV, most channels were in the resting state and the IC50 value for inhibition of Na+ current should correspond to the dissociation constant of lifarizine for resting channels (KR). KR was therefore estimated to be 7.3 microM. 4. In the absence of lifarizine, recovery from inactivation following a 20 s depolarization from -100 mV to 0 mV was complete within 2 s. However, in the presence of 3 microM lifarizine recovery took place in a biexponential fashion with time constants of 7 s and 79 s. 5. Lifarizine (1 microM) had no effect on steady-state inactivation curves when conditioning pre-pulses of 1 s duration were used. However, when pre-pulse durations of 1 min were used the curves were shifted to the left by lifarizine by about 10 mV. Analysis of the shifts induced by a range of lifarizine concentrations revealed that the apparent affinity of lifarizine for the inactivated state of the channel (K1) was 0.19 microM. 6. Lifarizine (1 microM) had no effect on chloramine-T-modified Na+ currents, suggesting no significant open channel interaction. 7. Taken together, these data show that lifarizine is a potent voltage-dependent inhibitor of Na+currents in NIE-115 cells and that the voltage-dependence arises from an interaction of the compound with the inactivated state of the channel. The possible contribution of Na+ current inhibition to the neuroprotective actions of lifarizine is discussed.

Neuroprotective profile of lifarizine (RS-87476) in rat cerebrocortical neurones in culture

1. The ability of the neuroprotective agent, lifarizine (RS-87476), to mitigate veratridine-, cyanide- and glutamate-induced toxicity in rat embryonic cerebrocortical neurones in primary culture has been compared with that of tetrodotoxin (TTX), nitrendipine, (+)-MK-801 and (-)-MK-801. Lactate dehydrogenase (LDH) released into the culture medium was used as the indicator of cell viability. 2. Incubation of cultures for 16 h in a medium containing veratridine (10(-4) M), sodium glutamate (10(-3) M) or sodium cyanide (10(-3) M) resulted in consistent elevations of LDH activity in the culture medium. The ability of compounds to attenuate these elevations was expressed as the concentration required to inhibit the increases in LDH release by 50% (IC50). 3. Neurotoxicity induced by veratridine was inhibited by lifarizine (IC50 = 4 x 10(-7) M), TTX (IC50 = 3 x 10(-8) M) and nitrendipine (IC50 = 3 x 10(-5) M). In contrast, (+)-MK-801 (up to 3 x 10(-5) M) was ineffective against this insult. 4. Glutamate-induced neurotoxicity was inhibited by (+)-MK-801 (IC50 = 1.4 x 10(-8) M) and to a lesser extent by (-)-MK-801 (IC50 = 1 x 10(-7) M), but was unaffected by lifarizine, TTX or nitrendipine (up to 10(-6) M). 5. (+)-MK-801 was effective against sodium cyanide-induced neurotoxicity (IC50 = 1.9 x 10(-8) M), whereas lifarizine and TTX (up to 10(-6) M) and nitrendipine (up to 3 x 10(-6) M) were without protective activity against this insult. 6. The results demonstrate that lifarizine potently protects rat cortical neurones in vitro against a neurotoxic insult that requires activation of sodium channels for its expression, and that the compound is ineffective against insults mediated by N-methyl-D-aspartate receptor activation. The weak efficacy of nitrendipine against veratridine-induced cell death argues against the involvement of L-type calcium channels in this insult. These data are consistent with the notion that the neuroprotective activity oflifarizine observed in vivo may be mediated by inhibition of neuronal sodium currents.

Endothelin-1 induced middle cerebral artery occlusion: pathological consequences and neuroprotective effects of MK801

In the present study we utilise the potent vasoconstrictor properties of endothelin-1 (Et-1) in a new model of middle cerebral artery occlusion in the anaesthetized rat. We evaluate the reproducibility of the model and examine the neuroprotective efficacy of the potent anti-ischaemic agent, MK801. Adult male SD rats received MK801 (5 mg/kg, n = 7) or saline vehicle (n = 7) 30 mins prior to the microinjection of Et-1 (60 pmol in 3 microliters) via a 31-g cannula stereotaxically positioned 0.5 mm above the middle cerebral artery. Three days after the injection of Et-1, rats were perfusion fixed, the brain removed, cryostat sectioned and processed for histological staining. Sections at eight predetermined levels were examined by light microscopy and the volume of infarction calculated. Following administration of Et-1, saline-pretreated rats exhibited a pattern of ischaemic damage similar to that previously reported following permanent occlusion of the rat middle cerebral artery. This pattern was characterised by a large volume of infarction covering the dorsal and lateral neocortex (98 +/- 12 mm3) and striatum (32 +/- 3 mm3) ipsilateral to the insult. Power analysis predicted a group size of 7 would be required for a 50% reduction in ischaemic damage to be recorded as statistically significant at the 5% level. Pretreatment with MK801 reduced cortical tissue damage by 51% (P = 0.026) but did not significantly alter either the pattern or volume of infarction (33 +/- 4 mm3; P = 0.95) in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study of voltage-sensitive sodium channel blockers in focal ischaemia and electric convulsions in rodents

This study evaluates the neuroprotective properties of some voltage-sensitive sodium channel blockers in a model of focal ischaemia. After curative treatment (0.5 and 24.5 h after insult), well known voltage-sensitive sodium channel blockers, phenytoin (2 x 100 mg/kg i.p.), carbamazepine (2 x 50 mg/kg i.p.), lamotrigine (2 x 50 mg/kg i.p.) and RP 66055 (2 x 8 mg/kg i.p.) were found to protect rats against brain damage induced by occlusion of the middle cerebral artery, by 40%, 24%, 28% and 44% respectively. These compounds were also active in protecting both mice and rats against tonic convulsions induced by electroshock, Intraperitoneal ED50 values in mice and rats respectively were of 5.2 and 12.5 mg/kg for phenytoin, 8.4 and 3.6 mg/kg for carbamazepine, 4.4 and 3.1 mg/kg for lamotrigine, 3.9 and 0.22 mg/kg for RP 66055. In contrast, lifarizine was totally devoid of activity in these three tests. This study extends an accumulation of data in the literature pointing to a therapeutic potential for voltage-dependent sodium channel blockers which penetrate the blood brain barrier. Such compounds as phenytoin, carbamazepine, lamotrigine or RP 66055 may act at sodium channels to prevent depolarization, inhibit release of neurotransmitters such as glutamate and thus protects the cortex against cellular damage induced by focal ischaemia by both pre- and post-synaptic inhibition of abnormal neurotransmission.