Behavioral and electrographic effects of opioids on kindled seizures in rats

The origin of the substance P-like immunoreactivity in the rat submandibular gland and its major duct was investigated. Lesions severing the sympathetic, pre- and postganglionic parasympathetic and sensory innervation of the submandibular gland, or treatment with the neurotoxin capsaicin produced only a small non-significant decrease in the substance P-like immunoreactivity content of the gland. In contrast both sensory denervation and capsaicin treatment produced a substantial decrease in the content of substance P-like immunoreactivity in the major duct of the submandibular gland. These observations indicate that the duct innervation is clearly of sensory origin, whilst the substance P-like immunoreactivity of the gland itself appears to be intrinsic.     

Anticonvulsant action of amino acid antagonists against kindled hippocampal seizures

Single unit recordings were made from neurons of the subfornical organ (SFO) in hemispherectomized cats following electrical stimulation in the paraventricular nucleus (PVN) of the hypothalamus. Of 132 neurons tested, 48 (36%) were inhibited, 3 (2.3%) excited and two (1.5%) antidromically activated. In separate experiments the wall of the third ventricle near the PVN was locally perfused with glutamate solution using a concentric push-pull cannula. Of 35 SFO neurons tested, 6 were inhibited, 5 were facilitated and 24 unaffected. The results indicate that one-third of SFO neurons receive synaptic inputs from cells in or near the PVN.     

Comparing the anticonvulsive effects of dapsone on amygdala-kindled seizures and hippocampal-kindled seizures in rats

Dapsone, an antileprosy drug, was administered to rats with amygdala (AM)-kindled seizures or hippocampal (HIPP)-kindled seizures to elucidate its anticonvulsive efficacy. Adult male Wistar rats were subjected to kindling stimulations 2 weeks after electrode-implantation. The subjects were tested once a day for 7 successive days after inducing three generalized (stage 5) seizures to study the effects of dapsone. Dapsone had an inhibitory effect on stage 5 seizures at 12.50 mg/kg in the AM-kindled rats and at 6.25 mg/kg and 9.375 mg/kg in the HIPP-kindled rats. Thus, there was a distinct difference in the effective dose for generalized seizures between the AM-kindled rats and the HIPP-kindled rats. The inhibitory action of dapsone on stage 5 seizures may be due mainly to the elevation of the afterdischarge-triggering threshold at the stimulation site of the AM or HIPP. Such inhibitory action appears prominently at serum concentrations of about 13 micrograms/ml in AM-kindled rats and about 6 micrograms/ml in HIPP-kindled rats. The level of 6 micrograms/ml almost equals the therapeutic serum concentration of dapsone used in the treatment of leprosy.     

Activating endogenous opioid systems by electroconvulsive shock or footshock stress inhibits recurrent kindled seizures in rats

Electroconvulsive shock (ECS) significantly decreased the behavioral manifestations of seizures elicited by amygdaloid stimulation in kindled rats. This anticonvulsant effect was significantly reduced by the opiate antagonist, naloxone, and by the development of morphine tolerance. A form of footshock stress known to cause opioid-mediated analgesia had a similar anticonvulsant effect, whereas another form causing non-opioid analgesia did not. These results suggest that the anticonvulsant effects of ECS and stress are mediated by the release of endogenous opioids.     

Test-specific analgesia elicited by kindled seizures in rats

Analgesia following kindled seizures in rats was studied using a test thought to measure pain integration at 3 levels of the CNS. Seizures caused an elevation of the threshold at which tail shocks elicited multiple squeaks, without affecting single squeak or tail withdrawal thresholds. Opioid involvement was indicated by naloxone's partial blockade of this effect.     

Antiepileptic effect and serum levels of clorazepate on children with refractory seizures

Clorazepate dipotassium is rapidly decarboxylated to yield desmethyl diazepam. The antiepileptic effect of clorazepate was studied in 29 epileptic children with refractory seizures. Their ages were ranged from one year 9 months to 20 years (mean 11 years 6 months). Serum clorazepate levels were also determined in 16 patients. The mean initial dose was 0.91 mg/kg/day, and the dose was increased up to 3 mg/kg/day. Within several days after initiation of clorazepate therapy, a decrease in seizure frequency was seen in patients in whom clorazepate was effective. Excellent results (decrease in seizure frequency by more than 80%) were obtained in 7 patients (24.1%), a moderate improvement with a 50 to 80% decrease was seen in 7 patients (24.1%), and a partial improvement with less than 50% decrease was seen in 7 patients (24.1%). No benefit was seen in 8 patients (27.7%). Serum clorazepate levels in patients with excellent results were 31 to 77 ng/ml (mean 55 ng/ml), those in patients with a moderate improvement were 130 to 225 ng/ml (mean 163 ng/ml), and those in patients with a partial improvement were 142 to 518 ng/ml (mean 273 ng/ml). Serum clorazepate levels in patients with no benefit were 34 to 97 ng/ml (mean 56 ng/ml). There was no direct relationship between serum clorazepate levels and clinical response. The results of this study indicate the efficacy of clorazepate for epileptic children with refractory seizures.     

Combined treatment with muscarinic and nicotinic cholinergic antagonists slows development of kindled seizures

Rats were given daily injections of atropine, mecamylamine or both drigs in combination, 1 h prior to daily electrical amygdaloid kindling stimulation. Neither drug was effective alone, but the two drugs in combination significantly increased the latency to develop stage 5 kindled seizures.     

Anticonvulsant effect of sodium cyclamate and propylparaben on pentylenetetrazol‐induced seizures in zebrafish

Screening for novel anticonvulsant drugs requires appropriate animal seizure models. Zebrafish provide small, accessible, and cost‐efficient preclinical models applicable to high‐throughput small molecule screening. Based on previous results in rodents, we have here examined the effects of artificial sweetener sodium cyclamate and antimicrobial agent sodium propylparaben on a model of pentylenetetrazole (PTZ)‐induced seizures in zebrafish. Sodium cyclamate reduced the bursts of hyperactivity, the spasms, increased the latency to spasms, and the latency to seizure, while propylparaben increased the latency to spasms. The results show the potential of zebrafish to detect novel anticonvulsant compounds while they also demonstrate the ability of two commonly ingested chemical compounds to modify the seizure threshold when were administrated at low concentration.     

戊四氮点燃癫(癎)大鼠海马巢蛋白和骨形成蛋白-4的表达研究

目的观察巢蛋白(nestin)和骨形成蛋白4(BMP4)基因在戊四氮(PTZ)点燃癫大鼠海马中的表达,并探讨两者与癫发病机制的关系。方法将81只成年雄性SD大鼠随机分为实验组(n=54)和对照组(n=27)。实验组采用PTZ点燃癫大鼠,按点燃中的不同时相点,又随机分为9组。用免疫组化技术、地高辛标记特异性寡核苷酸探针原位杂交组织化学技术,观察海马nestin和BMP4表达的变化。结果nestin阳性细胞在PTZ注射后3d开始出现在齿状回、CA3区和CA1区,到7d达到高峰,以后逐渐减少。BMP4在PTZ注射后7d开始增多,在点燃后1d达到高峰,以后逐渐减少,主要分布在齿状回、CA3区和CA1区。结论PTZ点燃可引起海马内星形胶质细胞增生、活化和神经发生,这可能是癫海马组织胶质化、神经元可塑性的病理基础;BMP4可能在PTZ癫形成过程中起重要作用。     

Benzodiazepine receptor declines in hippocampal formation following limbic seizures

Electrolytic lesions of entorhinal cortex have previously been shown to consistently produce limbic seizures. We report a bilateral and symmetrical decline in benzodiazepine receptor number in dentate gyrus of the hippocampal formation in unilateral entorhinal cortex-lesioned animals. We think this decline is caused by seizures since phenobarbital pretreatment prevented the appearance of limbic seizures and blocked the receptor decline. We postulate that these receptor declines may contribute to decreased endogenous recurrent inhibition (a presumed GABAergic synapse) of dentate granule cells which could lead to their repetitive firing. Thus these benzodiazepine receptor declines may be a consequence of limbic seizures yet increase the likelihood of subsequent seizures.     

The effects of ACTH and adrenocorticosteroids on seizure susceptibility in 15-day-old male rats

Infantile spasms are generalized convulsive seizures seen in the first year of life. They respond poorly to conventional anticonvulsants, but are often controlled by adrenocorticotropic hormone (ACTH) therapy. Other childhood seizures are also responsive to ACTH. The present study tested the effects of ACTH and related adrenocorticosteroids in prepubertal, 15-day-old rats. Compounds were tested against minimal (scMET) and maximal (MMT) pentylenetetrazol seizures, maximal electroconvulsive shock (MES) seizures, and hippocampal kindled seizures. ACTH had no significant anticonvulsant effects against any type of seizure. Several of the adrenocorticoid hormones, however, had strong anticonvulsant effects. Deoxycorticosterone (DOC) and progesterone (P4) both significantly suppressed scMET, MMT, and MES seizures 15 min after s.c. injection. DOC and P4 also shortened hippocampal discharge duration in the kindling model, and DOC, but not P4, suppressed the kindled convulsion. Aldosterone and corticosterone were effective against scMET seizures, and aldosterone was effective against MMT seizures. Dexamethasone and dihydroepiandrosterone had no anticonvulsant activity. These findings indicate that the adrenal steroid precursors, DOC and P4, have a broad spectrum of anticonvulsant activity in animal seizure models. They may play a role in mediating the anticonvulsant effects of ACTH in human infants.     

Changes in physostigmine-induced hippocampal seizures during ethanol withdrawal

Hippocampal cholinergic neurons are sensitive to acute ethanol administration, and specific alterations are seen in the functioning of these neurons following chronic ethanol. The present study examined the effects of chronic ethanol exposure and withdrawal on the sensitivity of the hippocampus to local injection of physostigmine, an inhibitor of acetylcholine metabolism. While intrahippocampal physostigmine elicited hippocampal seizure activity in 80% of the animals tested during withdrawal from chronic exposure to low levels of ethanol, seizure activity was elicited in only 30% of ethanol-naive subjects. These results suggest that chronic ethanol exposure may increase the sensitivity of hippocampal neurons to cholinergic stimulation, and that some of the symptoms of ethanol withdrawal may be related to this change.     

NAP prevents hippocampal oxidative damage in neonatal rats subjected to hypoxia-induced seizures

Neonatal seizures in which hypoxic-ischemic encephalopathy is the main triggering etiology have a challenging diagnosis and limited efficacy of treatment. NAP (NAPVSIPQ) has shown extensive neuroprotective and antioxidant capacity in vitro and in vivo. To evaluate its neuroprotective role in the context of seizures associated with perinatal hypoxia, we assessed the integrity of DNA and lipid membranes as well as the redox status in the hippocampus of 10-day-old rats exposed to hypoxia-induced seizures (HS) with and without NAP treatment. Rats were exposed to transient global hypoxia (12 min exposure to 5–7% O₂ was able to induce electrographic seizures) or room air with subsequent intraperitoneal NAP (0.03, 0.3 or 3 μg/g) or vehicle administration. Results showed elevated DNA damage immediately after the insult until 72 h post-HS, while oxidized bases were only detected 3, 6 and 24 h later. In addition, thiobarbituric acid reactive species peaked at 6 h in parallel with decreased levels of reduced glutathione between 3 and 72 h post-HS insult. Our findings expand on the knowledge about the time course of HS-induced oxidative damage and demonstrate for the first time that a single NAP injection dose-dependently prevents HS-induced oxidative damage to DNA and lipid membranes, in correlation with modulation of the glutathione system. Hence, NAP may represent a promising therapeutic strategy for avoiding HS-induced oxidative damage.     

Effects of age on kindling and kindled seizure-induced increase of benzodiazepine receptor binding

We examined the effects of age on kindled seizure development, benzodiazepine receptor binding, and kindled seizure-induced increases of benzodiazepine receptor binding. The results disclosed that: (1) development of kindling required greater numbers of stimulations in middle-aged than in young-adult animals; (2) in comparison to young-adult animals, middle-aged animals exhibited increased benzodiazepine receptor binding in the dentate gyrus of hippocampal formation: and (3) no age-related differences existed in the effects of seizures on benzodiazepine receptor binding. We suggest that senescence-related impairment of kindling development is due at least in part to alterations in the hippocampus, and that the increased benzodiazepine receptor binding in dentate gyrus may be one of the factors responsible for this impairment.     

Anticonvulsant action of topiramate against motor seizures in developing rats

PURPOSE: To study the anticonvulsant action of topiramate (TPM) in developing rats. METHODS: Motor seizures were elicited by administering pentylenetetrazol (100 mg/kg subcutaneously) in five age groups of Wistar rats (7, 12, 18, 25, and 90 days old). TPM was administered intraperitoneally in doses from 10 to 640 mg/kg 2 hours before pentylenetetrazol. The time course of TPM action was studied in 12- and 25-day-old rats up to 24 hours after the 160-mg/kg dose, and the incidence and pattern of seizures were evaluated. RESULTS: TPM did not influence minimal seizures (clonus of forelimb and head muscles with preserved righting ability). Generalized tonic-clonic seizures, however, were reliably changed at all developmental stages studied. The tonic phase was suppressed so that the majority of animals exhibited generalized clonic seizures (with a loss of righting reflexes). In addition, the incidence of generalized seizures was decreased after the 20-, 40-, and 80-mg/kg doses in the 7-day-old rat pups. The specific suppression of the tonic phase of generalized seizures was observed up to 12 hours in the 12-day-old rat pups. The same result was obtained over 6 hours after TPM administration in the 25-day-old animals, and with longer intervals the incidence of generalized seizures decreased in this age group. CONCLUSIONS: TPM exhibits stable anticonvulsant action against the tonic phase of generalized tonic-clonic seizures throughout development. In addition, it suppresses all phases of generalized seizures in 7-day-old rats. The anticonvulsant action of TPM lasted longer in 25-day-old than in 12-day-old rats. The two actions of TPM might be ascribed to two different mechanisms of action.     

Anticonvulsant activity of PNU-151774E in the amygdala kindled model of complex partial seizures

PURPOSE: PNU-151774E [(S)-(+)-2-(4-(3-fluorobenzyloxy) benzylamino) propanamide, methanesulfonate] is a novel antiepileptic drug (AED) with a broad spectrum of activity in a variety of chemically and mechanically induced seizures. The objective of this study was to evaluate the activity of PNU-151774E in the amygdala fully kindled rat model of complex partial seizures, and to compare its effects with those of carbamazepine (CBZ), phenytoin (PHT), lamotrigine (LTG), and gabapentin (GBP), drugs used to treat this disease state. METHODS: Male Wistar rats were stimulated daily through electrodes implanted in the amygdala with a threshold current until fully generalized seizures developed. The rats were then treated with various doses of a single compound. Control values for each rat and drug dose were determined after vehicle administration followed by electrical stimulation 1 day before drug treatment. RESULTS: PNU-151774E (1, 10, 30 mg/kg; i.p.) reduced the duration of behavioral seizures significantly and dose-dependently at doses starting from 1 mg/kg. Higher doses significantly reduced seizure severity and afterdischarge duration. In contrast, no dose-related effects were noted after administration of PHT, whereas after CBZ treatment, a plateau of activity was noted from the intermediate to higher doses. The effects of PNU-151774E were comparable to those of LTG and GBP. CONCLUSIONS: The activity shown by PNU-151774E at doses similar to those that are active in models of generalized seizures indicates that PNU-151774E would also have potential efficacy in the treatment of complex partial seizures.     

The effects of histamine H3-receptor antagonists on amygdaloid kindled seizures in rats

The effects of histamine H₃-receptor antagonists, thioperamide, and clobenpropit on amygdaloid kindled seizures were investigated in rats. Both intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) injections of H₃-antagonists resulted in a dose-related inhibition of amygdaloid kindled seizures. An inhibition induced by thioperamide was antagonized by an H₃-agonist [(R)-α-methylhistamine] and H₁-antagonists (diphenhydramine and chlorpheniramine). On the other hand, an H₂-antagonist (cimetidine and ranitidine) caused no antagonistic effect. Metoprine, an inhibitor of N-methyltransferase was also effective in inhibiting amygdaloid kindled seizure, and this effect was augmented by thioperamide treatment.     

Induction and suppression of seizures by cysteamine in hippocampal kindled rats

An increase in the concentration of ascorbate in the extracellular fluid of the rat striatum following systemic amphetamine administration previously has been demonstrated with the use of in vivo electrochemistry, push-pull cannula and in vivo dialysis. In this report, the effect of infusions of amphetamine into the substantia nigra on extracellular ascorbate levels in the striatum is further investigated by in vivo electrochemistry. Electrolytic lesions in the crus cerebri of the striatonigral pathway abolish this effect. Furthermore, these lesions abolish the effect of systemic amphetamine in the striatum ipsilateral to the lesion but not on the contralateral side. This phenomenon is independent of neostriatal dopamine or γ-aminobutyric acid since levels were shown to be unchanged relative to the intact side. These results lend further support to the hypothesis that ascorbate secretion in the striatum after amphetamine is mediated in the central nervous system, and indicate that a pathway that courses through the crus cerebri is necessary for this release.     

Effects of phenobarbital and SC-13504 on partially kindled hippocampal seizures in rats

The effects of three doses of SC-13504 were determined on prekindled and partially kindled hippocampal seizures in rats. A dose of phenobarbital previously shown to be anticonvulsant in rats was used for comparison. The drugs were tested for effectiveness twice during the 12 sessions, once during session 2 to determine the prekindling effectiveness and once during the last session to determine the effectiveness against kindled seizures. After 11 stimulations, the seizures showed a significant increase in afterdischarge duration, clinical seizure severity, and time to return to normal EEG and the stimulus threshold showed a nonsignificant decrease compared to the first stimulation. These results indicate that the development of progressively more severe hippocampal seizures (kindling) can occur with just 11 days of stimulation. When stimulated at the control day threshold, 3 and 300 mg/kg SC-13504 provided anticonvulsant protection against both prekindled and kindled seizures, whereas 30 mg/kg SC-13504 was less effective. Animals stimulated until seizures occurred on drug days showed a dose-dependent decrease in afterdischarge duration and an increase in voltage threshold with all three doses of SC-13504. Phenobarital provided no protection against prekindled seizures but was very effective against kindled seizures. These results may indicate that phenobarbital is a more effective anticonvulsant against developing or developed limbic system seizures than against prekindled seizures. This paradigm may provide a model for testing the effectiveness of anticonvulsants during the progressive development of epileptic seizures.     

Inhibitory effect of iodophenpropit, a selective histamine H3 antagonist, on amygdaloid kindled seizures

The effect of histamine H₃ antagonist, iodophenpropit on amygdaloid kindled seizures in rats was studied in comparison with those of other H₃ antagonists. Under pentobarbital anesthesia, the rats were fixed to a stereotaxic apparatus and bipolar electrodes were implanted into the amygdala. Electrodes were connected to a miniature receptacle, which was embedded in the skull with dental cement. To cause kindled seizures, electrical stimulation was applied to the amygdala bipolarly every day by a constant current stimulator, and electroencephalogram and convulsive behavior were observed. Drug effects were estimated in rats showing generalized kindled seizures. Intraperitoneal injection of H₃ antagonists, iodophenpropit, thioperamide, AQ0145 and clobenpropit, resulted in a dose-related inhibition of amygdaloid kindled seizures. The effect of iodophenpropit on amygdaloid kindled seizures was more potent than those of thioperamide, AQ0145 and clobenpropit. In conclusion, iodophenpropit may be useful for the treatment of partial epilepsy and/or secondary generalized seizures in humans.