Neuromodulatory role of serotonin in the anticonvulsant activity of 2-phenylbenzoate of 3-diethylamino-1-propanol.HCl (JAW-669)

The role of serotonin in the mediation of the anticonvulsant activity of JAW-669 was investigated against maximal electric shock (MES)-induced seizures in mice. A dose-dependent protection against seizures was provided by JAW-669 (4, 6 and 8 mg/kg, IP) and the calculated ED50 value was 6.01 mg/kg, IP. Pretreatment of mice with 5-hydroxytryptophan (50 mg/kg, IP) 2 hr before the administration of JAW-669 (6.01 mg/kg, IP) was found to cause a 40% increase in the ability of JAW-669 to provide protection against MES-induced seizures. Similar pretreatment with tryptophan (100 mg/kg, IP, 1 hr) caused a 30% decrease in the anticonvulsant activity of JAW-669. Prior administration of p-chlorophenylalanine (300 mg/kg, IP, 48 hr) and methysergide (10 mg/kg, IP; 0.5 hr) before administration of JAW-699 caused a 66% and 74% decrease, respectively, in the ability of JAW-669 to provide protection against MES-induced seizures. These results suggest a facilitatory role of serotonin in the anticonvulsant activity of JAW-669.     

On the anticonvulsant activity of kaurenic acid

Kaurenic acid [(-)-kaur-16-en-19-oic acid] is a diterpene isolated from the aerial parts of Espeletia semiglobulata, one of 85 species of Espeletiinae found in Venezuela. Its anticonvulsive activity was studied using two different models of experimental seizures: spinal seizures induced by sudden cooling (SSSC) in amphibians and seizures induced by pentylenetetrazol (PTZ) in mice. In SSSC, kaurenic acid (KA) inhibited the tonic hind-limb extension with an ED50 of 2.5 mg/kg. It was 4-fold more potent than known anticonvulsant drugs such as carbamazepine and phenytoin and 100-fold more potent than valproic acid. However, KA as well as valproic acid were ineffective against the clonic phase of SSSC. In the PTZ-induced seizures, KA at doses of 0.625 and 1.25 mg/kg increased the latency of seizure onset and protected against generalized clonic-tonic seizures by 45% and 65%, respectively. The sedative effects of KA had an ED50 of 8.5 mg/kg in mice and 75 mg/kg in amphibians. This work provides experimental evidence supporting the potential value of kaurenic acid as an anticonvulsive drug.     

Antiepileptic action of excitatory amino acid antagonists in the photosensitive baboon, Papio papio

Antagonists of excitation induced by dicarboxylic amino acids have been evaluated for acute anticonvulsant activity in baboons, Papio papio, with photosensitive epilepsy. 2-Amino-7-phosphonoheptanoic acid, 1 mmol/kg, i.v., abolishes myoclonic responses for 5 h. Less prolonged protection is seen after cis-2,3-piperidine-dicarboxylic acid, 1-3.3 mmol/kg; 2-amino-5-phosphonovaleric acid, 1-3.3 mmol/kg; or glutamic acid diethyl ester, 1-3.3 mmol/kg. Toxic side-effects are prominent after the latter two compounds. Antagonists of excitation due to N-methyl-D-aspartate possess acute anticonvulsant activity in a wider range of models epilepsy.     

Carnosine, a precursor of histidine, ameliorates pentylenetetrazole-induced kindled seizures in rat

Carnosine (beta-alanyl-l-histidine) has been characterized as a putative neurotransmitter. However, so far, understanding of the role of carnosine in the brain is very limited. The objective of this study was to examine the effects of carnosine on the development of pentylenetetrazol (PTZ) kindling seizures and protection against the PTZ kindled seizures in rats. Chemical kindling was elicited by repeated intraperitoneal injection of PTZ (35 mg/kg) once every 48 h until the occurrence of Stage 4-5 seizures, and the seizure activity of kindling was recorded for 30 min. In an acute PTZ challenge study, 60 mg/kg PTZ was used to induce kindled seizure. Injection of carnosine (200, 500 mg/kg, i.p.) significantly decreased seizure stage, and prolonged the latencies for myoclonic jerks, in a dose- and time-dependent manner. In the seizure development process, 500 mg/kg carnosine also significantly delayed the onset of PTZ kindled seizures. In addition, carnosine significantly reversed decreased histamine levels induced by PTZ kindled seizure in the hippocampus. These results indicate that carnosine can protect against PTZ-induced seizures in both the development of kindling and the challenge process in rats. The results suggest that carnosine might be an endogenous anticonvulsant factor in the brain and can be used as a new antiepileptic drug in future.     

Evidences of cannabinoids-induced modulation of paroxysmal events in an experimental model of partial epilepsy in the rat

The anticonvulsant effect of cannabinoids (CB) has been shown to be mediated by the activation of the CB₁ receptor. This study evaluates the anticonvulsant activity of (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-Yl]-1-naphthalenylmethanone (WIN55,212-2, CB agonist) alone or preceded by the administration of N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251, selective CB₁ antagonist) in an experimental in vivo model of complex partial seizures (maximal dentate gyrus activation – MDA) in the rat. WIN55,212-2 (21 mg kg⁻¹) exerted an anticonvulsant effect, significantly reduced by the pre-treatment with AM251 (1 mg kg⁻¹, 30 min interval). Surprisingly, AM251, administered alone at the same dose, failed to induce any modification in MDA responses. Our data suggest the involvement of the CB system in the inhibitory control of hyperexcitability phenomena in a model of acute partial epilepsy. Although the MDA model per se does not induce a basal activation of CB₁ receptors, as suggested by the lack of efficacy of AM251 when administered alone, the partial suppression of WIN55,212-2-induced effects in rats pre-treated with AM251 allows to hypothesise that the WIN55,212-2-induced antiepileptic effect is strictly linked to an increased CB₁ receptor activation or to the involvement of further receptor subtypes.     

癫痫发作的大鼠延髓内脏带神经元的FOS表达

为研究大鼠"延髓内脏带"神经元在红藻氨酸诱导癫痫发作时的反应,本文用抗FOS蛋白和抗酪氨酸羟化酶双重免疫组织化学方法,对下列三组实验动物进行了观察：（1）红藻氨酸（10mg／kg）腹膜腔注射组;（2）L－精氨酸慢性腹膜腔注射给药（40mg／kg,2次／d,共4d）后,再注射红藻氨酸组;（3）L－硝基精氨酸慢性腹膜腔注射给药（50mg／kg,2次／1d,4d）后,再注射红藻氨酸组。所有动物均在红藻氨酸注射3h后处死,制片,染色。结果：红藻氨酸注射组动物出现癫痫发作,"延髓内脏带"内显示密集的FOS阳性神经元,其中FOS／酪氨酸羟化酶神经元占酪氨酸羟化酶神经元总数的85％,占FOS阳性神经元总数的15％;酪氨酸羟化酶神经元出现胞体变形,胞浆内有空泡,突起短缺等现象。L－精氨酸＋酪氨酸羟化酶组癫痫发作较轻,"延髓内脏带"内FOS阳性神经元较少;L-硝基精氨酸＋酪氨酸羟化酶组癫痫发作加重,死亡率增高,"延髓内脏带"内FOS阳性神经元极多。以上结果表明,"延髓内脏带"内神经元在癫痫发作时反应强烈;一氧化氮介质可能有抗惊厥作用。     

Anticonvulsant effect of celecoxib on pentylenetetrazole-induced convulsion: Modulation by NO pathway

This study aimed to examine whether celecoxib influences clonic seizure thresholds through modulation of nitric oxidergic (NO) pathway. The effect of celecoxib (1-5 mg per kg, p.o.) was investigated on clonic seizures induced by pentylenetetrazole (PTZ, 50 and 80 mg per kg, i.p.) in male Swiss mice. The interaction of celecoxib-induced effects with NO pathway was examined using a NO synthase (NOS) inhibitor, N(G)-omega-nitro-L-arginine methyl ester (L-NAME, 20 and 50 mg per kg, i.p.) and a NOS substrate, L-arginine (100 and 200 mg per kg, i.p.). The criteria for the development of seizure activity were the possibility for appearance of generalized clonus and prolongation of latency to the onset of convulsions following administration of 50 and 80 mg per kg of PTZ, respectively. Pretreatment with celecoxib (2.5 and 5 mg per kg) or L-NAME (50 mg per kg) induced anticonvulsant effect on the PTZ-induced clonic seizures. L-arginine at the dose of 200 mg per kg had proconvulsant effect. A sub-effective dose of celecoxib (1 mg per kg) induced an additive anticonvulsant effect when co-administered with L-NAME (20 mg per kg). Although L-arginine (100 mg per kg) per se did not influence PTZ-induced convulsion, it could attenuate the anticonvulsant effect of celecoxib (5 mg per kg). Our results indicate that celecoxib induces an anticonvulsant effect on clonic seizure threshold that may involve NO pathway.     

Anticonvulsant doses of ganaxolone do not compromise motor performance in immature rats

Neuroactive steroids that function as positive modulators of GABA-A receptors are potential anticonvulsant drugs. We previously demonstrated that ganaxolone is effective against pentetrazol-induced motor seizures in immature rats. In the present study, we examined the effects of ganaxolone in another model, cortical epileptic afterdischarges (ADs). The possible side effects of ganaxolone were studied in rats 12, 18, and 25 days of age following the implantation of epidural electrodes. Low-frequency stimulation of the sensorimotor cortical area elicited ADs characterized by a spike-and-wave rhythm and clonic seizures. Ganaxolone (5, 10, 20, or 40 mg/kg) was administered intraperitoneally after the first AD and stimulation was repeated five more times. The highest dose of ganaxolone (40 mg/kg) suppressed progressive prolongation of ADs in 25-day-old rats and postponed it in 12-day-old rats. No significant effect was observed in 18-day-old animals. Movements during stimulation and clonic seizures accompanying ADs were not affected by ganaxolone. Ganaxolone at doses of 20 and 40 mg/kg had no significant effect on motor function, such as surface righting, negative geotaxis, wire mesh ascending, and bar holding. After administration of 40 mg/kg ganaxolone to 18- and 25-day-old rats, spontaneous locomotion in the open field tended to decrease. Doses of ganaxolone with a moderate anticonvulsant effect in the present model did not seriously compromise motor performance.     

合成红藻氨酸诱发大鼠癫痫作用的研究

目的: 观察合成红藻氨酸(SKA) 诱发大鼠癫痫的作用及其作用特点。方法: Wistar大鼠40只,随机分为正常对照组、SKA 12 mg/kg、SKA 10 mg/kg 和 SKA 5 mg/kg 剂量组及红藻氨酸 (KA)10 mg/kg阳性对照组。腹腔注射给药,连续8 h观察大鼠癫痫发作的行为学变化及连续3.5 h记录其脑电图变化。结果: 合成红藻氨酸5、10、12 mg/kg 腹腔注射,可诱发大鼠癫痫发作,其行为学及脑电改变与KA对照组无明显差异。但合成红藻氨酸诱发动物癫痫呈现规律、稳定及阶段性明显的特征,且大鼠的死亡率较天然红藻氨酸低。结论: 合成红藻氨酸腹腔注射可诱发大鼠癫痫发作,以10 mg/kg为较合适剂量。     

Effects of leukotriene B4 receptor antagonist, LY293111Na, on antigen-induced bronchial hyperresponsiveness and leukocyte infiltration in sensitized guinea pigs

OBJECTIVE AND DESIGN: LY29311 Na, 2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxyphenoxy] propoxy] -phenoxy]-benzoic acid sodium salt, is a novel leukotriene B4 (LTB4) receptor antagonist. Its effects on guinea pig models of asthma were compared with those of dexamethasone. METHODS: Effects of LY293111Na were tested in antigen (ovalbumin, OA)-induced bronchial hyperresponsiveness (BHR) and leukocyte accumulation in actively sensitized guinea pigs. Its effects on antigen-induced acute bronchoconstriction in passively sensitized guinea pigs were also studied. RESULTS: LY293111 Na (10 to 30 mg/kg p.o., 1 h before and 6 h after OA challenge) inhibited BHR to acetylcholine. LY293111 Na (3 mg/kg p. o.) significantly inhibited accumulation of neutrophils in bronchoalveolar lavage (BAL) fluid 24 h after antigen challenge but it did not inhibit accumulation of eosinophils and macrophages at any doses used. In contrast, dexamethasone (30 mg/kg p.o., 4 h before OA challenge) not only inhibited BHR but also reduced the infiltration of all three types of leukocytes. A significant increase of LTB4 levels in BAL fluid was noted at 3 and 15 min after the antigen challenge. LY293111Na did not inhibit antigen-induced acute bronchoconstriction in passively sensitized guinea pigs. CONCLUSION: These results indicate that LTB4 may participate in antigen-induced BHR but not in eosinophil infiltration and acute bronchoconstriction in guinea pigs.     

Castration alters susceptibility of male rats to specific seizures

Studies in female rats indicate that estrogen reduction has both pro- and anticonvulsant effects on seizures, but that the respective effects are limited to specific types of seizures at selected doses of picrotoxin. This study was conducted to see if testosterone reduction had parallel effects on seizure susceptibility in males. Male rats were given castration or sham operations and allowed 3 weeks to recover. The latencies to myoclonic, focal, akinetic, and generalized tonic-clonic (GTC) seizures were scored in independent groups of sham-operated or castrated males after injection with picrotoxin (3.5-7.5 mg/kg). The results showed that castrated males had significantly shorter latencies to GTC seizures than sham-operated males at the 3.5 mg/kg and 5.5 mg/kg doses of picrotoxin. There were no significant differences in the latencies to myoclonic, focal, or akinetic seizures between the two surgical groups. The findings suggest that, unlike endogenous estrogen, endogenous testosterone exerts only an anticonvulsant effect and that the effect is limited to GTC seizures.     

Carnosine inhibits pentylenetetrazol-induced seizures by histaminergic mechanisms in histidine decarboxylase knock-out mice

In the present study, we used both histidine decarboxylase-deficient (HDC-KO) mice and wild-type (WT) mice to elucidate the possible role of carnosine in pentylenetetrazol (PTZ)-induced seizures. In the acute PTZ challenge study, PTZ (75 mg/kg) was injected intraperitoneally (i.p.) to induce seizures. Carnosine (200, 500 or 1000 mg/kg, i.p.) significantly decreased seizure stage, and prolonged the latency for myoclonic jerks in WT mice in a dose-dependent manner. The effects of carnosine (500 mg/kg) were time-dependent and reached a peak at 1 h. However, it had no significant effect on HDC-KO mice. Carnosine (500 mg/kg) also significantly elevated the thresholds in WT mice but not HDC-KO mice following intravenous (tail vein) administration of PTZ. We also found that α-fluoromethylhistidine substantially reversed the protective effects of carnosine in WT mice. In addition, carnosine pretreatment reduced the cortical EEG activity induced by PTZ (75 mg/kg, i.p.). These results indicate that carnosine can protect against PTZ-induced seizures and its action is mainly through the carnosine–histidine–histamine metabolic pathway. This suggests that carnosine may be an endogenous anticonvulsant factor in the brain and may be used as a new antiepileptic drug in the future.     

Anticonvulsant role of nigrotectal projection in the maximal electroshock model of epilepsy--I. Mapping of dorsal midbrain with bicuculline.

Previous work has indicated that the anticonvulsant effect of nigral inactivation on the maximal electroshock model of generalized seizures is mediated by the projection from substantia nigra to superior colliculus. In accordance with this idea, and with the GABAergic nature of the nigrotectal pathway, microinjections of the GABAA antagonist bicuculline methiodide into the superior colliculus have been reported to block tonic hindlimb extension induced by maximal electroshock. To characterize the relevant circuitry more precisely, the present study sought to determine which region of the superior colliculus was important for the anticonvulsant effect of bicuculline by systematic mapping in the rat. Bilateral injections of bicuculline methiodide (50 pmol in 400 nl/side) were most effective in the caudal deep layers of the superior colliculus and adjoining midbrain reticular formation. These results suggest that the well-known projection from substantia nigra pars reticulata to the superior colliculus may not be involved in the anticonvulsant effect of nigral inactivation in the electroshock model, because this pathway terminates primarily in the intermediate layers of the superior colliculus throughout its rostrocaudal extent. Instead, some other pathway from ventral midbrain to a dorsal midbrain anticonvulsant zone appears to be part of the brain's anticonvulsant circuitry. The following paper [Redgrave et al. (1991) Neuroscience 46, 391-406] describes an anatomical study to characterize this pathway.     

Effects of carnosine on amygdaloid-kindled seizures in Sprague-Dawley rats

The effects of carnosine (beta-alanyl-L-histidine) on amygdaloid-kindled seizures were investigated in rats. I.p. injection of carnosine (500, 1000, 1500 mg/kg, i.p.) significantly decreased seizure stage, afterdischarge duration and generalized seizure duration, and significantly prolonged generalized seizure latency of amygdaloid-kindled seizures, in a dose-dependent, and time-related manner. The protective effect of carnosine (1500 mg/kg) was completely antagonized by histamine H1-antagonists pyrilamine (2, 5 mg/kg, i.p.) and diphenhydramine (5, 10 mg/kg, i.p.), but not by histamine H2-antagonist zolantidine even at a high dose of 10 mg/kg. Carnosine (1500 mg/kg, i.p.) caused a significant increase of carnosine and histidine levels in the hypothalamus, thalamus, hippocampus, amygdala and cortex, as well as histamine levels in the hippocampus and amygdala. I.c.v. injection of alpha-fluoromethylhistidine (50 microg, i.c.v.), a selective and irreversible histidine decarboxylase inhibitor, only partially reversed the inhibition of amygdaloid-kindled seizures induced by carnosine. In addition, carnosine significantly decreased glutamate contents in the amygdala and hippocampus. These results indicate that carnosine could protect against amygdaloid-kindled seizures in rats, and its action may be due to the activation of histamine postsynaptic H1-receptors via two different mechanisms, one being carnosine's direct action, and the other being indirectly mediated by histaminergic pathway. The study suggests that carnosine may be an endogenous anticonvulsant factor in the brain and could be used as a new antiepileptic drug in the future.     

Phosphonic analogues of excitatory amino acids raise the threshold for maximal electroconvulsions in mice

2-Amino-5-phosphonopentanoic acid (100 and 200 mg/kg) and 2-amino-7-phosphonoheptanoic acid (50-200 mg/kg i.p.) significantly elevated the threshold for maximal electroconvulsions in mice, the latter being more effective in this respect. In contrast, neither alpha-aminoadipic acid nor L-glutamic acid diethyl ester (up to 200 and 400 mg/kg, respectively) offered any protection. The present results add further evidence to support the importance of the blockade of N-methyl-D-aspartic acid receptor-mediated events in the suppression of seizure activity.     

Synthesis and anticonvulsant activity of 7-alkoxy-triazolo-[3, 4-b]benzo[d]thiazoles

The present study describes the chemical synthesis and anticonvulsant activity evaluation of a series of 7-alkoxy-triazolo-[3, 4-b]benzo[d]thiazoles. Most compounds exhibited good anticonvulsant activity in the Maximal electroshock (MES) test. And the structure-activity relationships (SAR) were analyzed. Among the compounds studied, 7-octyloxy-triazolo-[3, 4-b]benzo[d]thiazole (5g) was found to be the most potent compound with a median effective dose (ED(50)) value of 8.0 mg/kg and a protective index (PI) value of 15.0, possessing better anticonvulsant activity and higher safety than marketed drugs carbamazepine and phenytoin. The mechanism study of compound 5g showed that it displayed broad spectrum activity in several models, and it is likely to have several mechanisms of action (including inhibiting voltage-gated ion channels and GABAergic activity).     

5-HT2 modulation of AY-9944 induced atypical absence seizures

We investigated the role of 5-HT(2A) and 5-HT(2C) receptors in atypical absence seizures (AAS) induced by trans-1,4-bis[2-chloro-benzylaminomethyl] cyclohexane, dihydrocholoride (AY-9944). The total duration and number and mean duration of the spontaneous bursts of slow spike-and-wave discharges (SSWD) that characterize the AY model were measured using electrocorticographic (ECoG) recordings in freely moving animals. In a randomized counterbalanced dose response design, rats were treated with either the 5-HT(2A) agonist 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI, 0.5, 1 or 2 mg/kg), the 5-HT(2C) preferring agonist m-chlorophenylpiperazine (mCPP, 1, 2, or 4 mg/kg), the 5-HT(2A) antagonist ketanserin (2.5 or 5 mg/kg), or vehicle. DOI significantly reduced the total duration and number of SSWD. In contrast, mCPP had no effect on total duration or number of SSWD. Ketanserin exacerbated the number of SSWD at 2.5 mg/kg but produced mixed results at 5.0 mg/kg. However, none of the treatments affected the mean SSWD duration. These data support the hypothesis that 5HT(2A) receptors are involved in the pathology of experimental atypical absence seizures.     

Anti-inflammatory planar chiral [2.2]paracyclophaneacetic acid enantiomers

OBJECTIVE AND DESIGN: To elucidate if the planar chiral paracyclophane moiety conveys pharmacological activity to arylacetic acid analogs in two animal models. MATERIAL OR SUBJECTS: Female NMRI mice (6 mice/group); female Wistar rats (8 rats/group); thrombocytes from human blood. TREATMENT: The enantiomers of [2.2]paracyclophaneacetic acid were applied locally (10(-7) and 10(-6) mol/ear) and orally (10-100 mg/kg). METHODS: (a) Phorbol myristyl acetate model of acute inflammation of the inner auricle. (b) Oxazolone model of allergic contact dermatitis. (c) Carrageenan model of acute inflammation. (d) Inhibition of cyclooxygenase-1 and 12-lipoxygenase (in vitro). RESULTS: (a) PMA model: pR-(-)-[2.2]paracyclophaneacetic acid (10(-6) mmol/ear): 58% inhibition after 24 h (p < 0.05). (b) Oxazolone model: pR-(-)-[2.2]paracyclophaneacetic acid (10(-6) mmol/ear): 42% inhibition after 24 h (p < 0.05). (c) Carrageenan model: pR-(-)-[2.2]paracyclophaneacetic acid (10 mg/kg): 31.4% inhibition (paw volume 0.48 +/- 0.13 ml). (d) Cyclooxygenase-1 and 12-lipoxygenase: no inhibition at concentrations up to 10 microM. CONCLUSIONS: The easily accessible [2.2]paracyclophane moiety should find its use in medicinal chemistry as it is a pharmacophoric substituent with the interesting feature of planar chirality.     

Time-course and dose-response relationships of imperatorin in the mouse maximal electroshock seizure threshold model

This study was designed to evaluate the anticonvulsant effects of imperatorin (a furanocoumarin isolated from fruits of Angelica archangelica) in the mouse maximal electroshock seizure threshold model. The threshold for electroconvulsions in mice was determined at several times: 15, 30, 60 and 120 min after i.p. administration of imperatorin at increasing doses of 10, 20, 30, 40, 50 and 100 mg/kg. The evaluation of time-course relationship for imperatorin in the maximal electroshock seizure threshold test revealed that the agent produced its maximum antielectroshock action at 30 min after its i.p. administration. In this case, imperatorin at doses of 50 and 100 mg/kg significantly raised the threshold for electroconvulsions in mice by 38 and 68% (P<0.05 and P<0.001), respectively. The antiseizure effects produced by imperatorin at 15, 60 and 120 min after its systemic (i.p.) administration were less expressed than those observed for imperatorin injected 30 min before the maximal electroshock seizure threshold test. Based on this study, one can conclude that imperatorin produces the anticonvulsant effect in the maximal electroshock seizure threshold test in a dose-dependent manner.     

Convulsant action of morphine, [D-Ala2, D-Leu5]-enkephalin and naloxone in the rat amygdala: electroencephalographic, morphological and behavioural sequelae

Morphine hydrochloride (25-200 nmol), [D-Ala2, D-Leu5]enkephalin (10-200 nmol) and naloxone hydrochloride (100-1000 nmol) were injected unilaterally into the rat amygdala and the following electrographic, behavioural and neuropathological responses were studied. Microinjections of low doses of morphine (25-50 nmol) resulted in behavioural alterations characterized by staring, gustatory automatisms and wet shakes, whereas higher doses additionally produced motor limbic seizures and status epilepticus. The first changes in the electroencephalogram appeared in the amygdala immediately after the administration of morphine and rapidly spread to hippocampal and cortical areas. Electrographic alterations consisted of high voltage fast activity, spiking, bursts of polyspiking, electrographic seizures and periods of postictal depression. Neuropathological analysis of frontal forebrain sections by means of light microscopy revealed widespread, seizure-related damage confined to amygdala, olfactory cortex, thalamus, hippocampal formation, neocortex and substantia nigra. Pretreatment of animals with naloxone, 2-20 mg/kg s.c., as well as simultaneous microinjection of the non-convulsant dose of naloxone, 100 nmol, with morphine, 100 nmol, into the amygdala failed to block the development of convulsant activity and seizure-related brain damage produced by the opiate. In contrast, diazepam, 10 mg/kg i.p., when administered prior to the microinjection of morphine into the amygdala, abolished the epileptogenic effects of the drug. [D-Ala2, D-Leu5]Enkephalin, 10-200 nmol, elicited electrographic and behavioural responses similar to those seen after low doses of morphine, when administered into the amygdala. High voltage fast activity, single spikes, bursts of polyspiking, electrographic seizures and periods of postictal depression were seen in the electroencephalogram, but no behavioural signs of motor limbic seizures could be detected. The only behavioural correlates of epileptiform electrographic activity were wet shakes, myoclonic head twiches and gustatory automatisms. The examination of frontal forebrain sections from rats receiving [D-Ala2, D-Leu5]enkephalin revealed no morphological changes. Pretreatment of rats with either naloxone, 2 mg/kg, or diazepam, 10 mg/kg, blocked the development of behavioural and electrographic sequelae of the peptide. Naloxone, 100-1000 nmol, when microinjected into the amygdala, produced electrographic, behavioural and morphological alterations resembling those seen after high doses of morphine.(ABSTRACT TRUNCATED AT 400 WORDS)