Maternal sevoflurane exposure increases the epilepsy susceptibility of adolescent offspring by interrupting interneuron development.

BACKGROUND: Exposure to general anesthesia influences neuronal functions during brain development. Recently, interneurons were found to be involved in developmental neurotoxicity by anesthetic exposure. But the underlying mechanism and long-term consequences remain elusive. METHODS: Pregnant mice received 2.5% sevoflurane for 6-h on gestational day 14.5. Pentylenetetrazole (PTZ)-induced seizure, anxiety- and depression-like behavior tests were performed in 30- and 60-day-old male offspring. Cortical interneurons were labeled using Rosa26-EYFP/-; Nkx2.1-Cre mice. Immunofluorescence and electrophysiology were performed to determine the cortical interneuron properties. Q-PCR and in situ hybridization (ISH) were performed for the potential mechanism, and the finding was further validated by in utero electroporation (IUE). RESULTS: In this study, we found that maternal sevoflurane exposure increased epilepsy susceptibility by using pentylenetetrazole (PTZ) induced-kindling models and enhanced anxiety- and depression-like behaviors in adolescent offspring. After sevoflurane exposure, the highly ordered cortical interneuron migration was disrupted in the fetal cortex. In addition, the resting membrane potentials of fast-spiking interneurons in the sevoflurane-treated group were more hyperpolarized in adolescence accompanied by an increase in inhibitory synapses. Both q-PCR and ISH indicated that CXCL12/CXCR4 signaling pathway downregulation might be a potential mechanism under sevoflurane developmental neurotoxicity which was further confirmed by IUE and behavioral tests. Although the above effects were obvious in adolescence, they did not persist into adulthood. CONCLUSIONS: Our findings demonstrate that maternal anesthesia impairs interneuron migration through the CXCL12/CXCR4 signaling pathway, and influences the interneuron properties, leading to the increased epilepsy susceptibility in adolescent offspring. Our study provides a novel perspective on the developmental neurotoxicity of the mechanistic link between maternal use of general anesthesia and increased susceptibility to epilepsy.

TC-G 1008 facilitates epileptogenesis by acting selectively at the GPR39 receptor but non-selectively activates CREB in the hippocampus of pentylenetetrazole-kindled mice.

The pharmacological activation of the GPR39 receptor has been proposed as a novel strategy for treating seizures; however, this hypothesis has not been verified experimentally. TC-G 1008 is a small molecule agonist increasingly used to study GPR39 receptor function but has not been validated using gene knockout. Our aim was to assess whether TC-G 1008 produces anti-seizure/anti-epileptogenic effects in vivo and whether the effects are mediated by GPR39. To obtain this goal we utilized various animal models of seizures/epileptogenesis and GPR39 knockout mice model. Generally, TC-G 1008 exacerbated behavioral seizures. Furthermore, it increased the mean duration of local field potential recordings in response to pentylenetetrazole (PTZ) in zebrafish larvae. It facilitated the development of epileptogenesis in the PTZ-induced kindling model of epilepsy in mice. We demonstrated that TC-G 1008 aggravated PTZ-epileptogenesis by selectively acting at GPR39. However, a concomitant analysis of the downstream effects on the cyclic-AMP-response element binding protein in the hippocampus of GPR39 knockout mice suggested that the molecule also acts via other targets. Our data argue against GPR39 activation being a viable therapeutic strategy for treating epilepsy and suggest investigating whether TC-G 1008 is a selective agonist of the GPR39 receptor.

Kalirin is involved in epileptogenesis by modulating the activity of the Rac1 signaling pathway.

BACKGROUND AND OBJECTIVE: Epilepsy is a common chronic brain disease. Despite the availability of various anti-seizure drugs, approximately 30 % of patients do not respond to treatment. Recent research suggests that Kalirin plays a role in regulating neurological function. However, the pathogenesis of Kalirin in epileptic seizures remains unclear. This study aims to investigate the role and mechanism of Kalirin in epileptogenesis. MATERIALS AND METHODS: An epileptic model was induced by intraperitoneal injection of pentylenetetrazole (PTZ). Endogenous Kalirin was inhibited using shRNA. The expression of Kalirin, Rac1, and Cdc42 in the hippocampal CA1 region was measured using Western blotting. Spine and synaptic structures were examined using Golgi staining and electron microscopy. Moreover, the necrotic neurons in CA1 were examined using HE staining. RESULTS: The results indicated that the epileptic score increased in epileptic animals, while inhibition of Kalirin decreased the epileptic scores and increased the latent period of the first seizure attack. Inhibition of Kalirin attenuated the increases in Rac1 expression, dendritic spine density, and synaptic vesicle number in the CA1 region induced by PTZ. However, the increase in Cdc42 expression was not affected by the inhibition of Kalirin. CONCLUSION: This study suggests that Kalirin is involved in the development of seizures by modulating the activity of Rac1, providing a novel anti-epileptic target.

Downregulatory effect of miR-342-3p on epileptogenesis in the PTZ-kindling model.

BACKGROUND: Epileptogenesis is a process that results in neurons firing abnormally, causing seizures. Increasing evidence has shown that miRNAs expressed in the epileptic hippocampus are involved in epileptogenesis. We demonstrated the expression changes of miRNAs that may be effective in epileptogenesis in silico analysis in the kindling model created with Pentylenetetrazole (PTZ). Thus, we aimed to identify the target genes responsible for epileptogenesis. METHODS AND RESULTS: Fifteen male Wistar-albino rats (200-230 g) were randomly divided into two groups control (n = 6) and PTZ (n = 9). The control group received 0.5 ml saline, and the PTZ group (35 mg/kg i.p.) intraperitoneally (i.p.) (11 times, every other day) to induce tonic-clonic seizures. Seizures were observed and scored 30 min after PTZ injection. After the last dose of PTZ (75 mg/kg) administration, the hippocampus tissues of the rats were removed by anesthesia. Analysis of miRNAs was performed with the Affymetrix gene chip miRNA sequence (728 miRNA) and confirmed by the Real-Time Polymerase Chain Reaction (Real-Time PCR) method (29 miRNAs). We evaluated the expression change of the target gene of miRNA, whose expression change was detected using in silico analysis, by q-RT PCR. Eight miRNAs with changes in expression were detected. Of these miRNAs, miR-342-p was downregulated in the PTZ group and was statistically significant (p < 0.005). Ultimately, we determined that the target gene of miR-342-p is a metabotropic glutamate receptor 2 (GRM2) and that GRM2 expression is upregulated. CONCLUSIONS: Downregulation of miR-342-3p in the PTZ kindling model may result in the upregulation of GRM2.

Gene Expression Analysis Identifies Cholesterol Metabolism Dysregulation in Hippocampus of Phenytoin-Resistant Pentylenetetrazol-Kindled Epileptic Mice.

Pharmaco-resistant Epilepsy has been a major challenge for medical interventions in controlling seizures. To date, up to 33% of the patients with epilepsy do not show adequate response to anti-epileptic drugs even after prolonged combinatorial drug usage. Using microarray, this study explores the changes in hippocampal gene expression in the phenytoin-resistant pentylenetetrazol (PTZ)-kindled mouse model of epilepsy. Our results from mRNA microarray analysis show distinct gene expression profiles in the hippocampus of phenytoin-resistant and sensitive mice. Pathway enrichment analysis showed differential expression of genes involved in cholesterol biosynthesis in phenytoin-resistant and sensitive mice.

Anti-Epileptic Effects of FABP3 Ligand MF1 through the Benzodiazepine Recognition Site of the GABAA Receptor.

Recently, we developed the fatty acid-binding protein 3 (FABP3) ligand MF1 (4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid) as a therapeutic candidate for α-synucleinopathies. MF1 shows affinity towards γ-aminobutyric acid type-A (GABAA) receptor, but its effect on the receptor remains unclear. Here, we investigate the pharmacological properties of MF1 on the GABAA receptor overexpressed in Neuro2A cells. While MF1 (1-100 µm) alone failed to evoke GABA currents, MF1 (1 µm) promoted GABA currents during GABA exposure (1 and 10 µm). MF1-promoted GABA currents were blocked by flumazenil (10 µm) treatment, suggesting that MF1 enhances receptor function via the benzodiazepine recognition site. Acute and chronic administration of MF1 (0.1, 0.3 and 1.0 mg/kg, p.o.) significantly attenuated status epilepticus (SE) and the mortality rate in pilocarpine (PILO: 300 mg/kg, i.p.)-treated mice, similar to diazepam (DZP: 5.0 mg/kg, i.p.). The anti-epileptic effects of DZP (5.0 mg/kg, i.p.) and MF1 (0.3 mg/kg, p.o.) were completely abolished by flumazenil (25 mg/kg, i.p.) treatment. Pentylenetetrazol (PTZ: 90 mg/kg, i.p.)-induced seizures in mice were suppressed by DZP (5.0 mg/kg, i.p.), but not MF1. Collectively, this suggests that MF1 is a mild enhancer of the GABAA receptor and exercises anti-epileptic effects through the receptor's benzodiazepine recognition site in PILO-induced SE models.

Inhibition of NMDA Receptors Downregulates Astrocytic AQP4 to Suppress Seizures.

Aquaporin 4 (AQP4), a water-specific channel protein locating on the astrocyte membrane, has been found to be antagonist, agonist and undergone closely related to epilepsy. Our previous study showed that inhibition of an N-methyl-D-aspartate receptor (NMDAR) subunit NR2A can suppress epileptic seizures, suggesting that AQP4 is potentially involved in NR2A-mediated epilepsy treatment. In this study, we aimed to explore the relevance of AQP4 in NR2A-mediated seizures treatment in pentylenetetrazol (PTZ)-induced rat models. We performed electroencephalogram (EEG) recording and examined AQP4 expression at mRNA and protein levels, and the downstream molecules of AQP4 as well. It showed that AQP4 expression was increased after the induction of seizures. Lateral ventricle pretreatment of NR2A inhibitor could mitigate the PTZ-induced seizures severity and counterbalance the increase of AQP4 expression. In contrast, NR2A activator that resulted in seizures aggravation could further augment the seizure-related elevations of AQP4 expression. Pharmacological inhibition of AQP4 alone could also suppress the PTZ-induced seizure activities, with decreased expressions of NF-κB p65, interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)-α in the brain. The results indicated that increased expression of AQP4 might be an important mechanism involved in NR2A of NMDAR-mediated treatment for epileptic seizures, enlightening a potentially new target for seizures treatment.

Spatial exploration induced expression of immediate early genes Fos and Zif268 in adult-born neurons Is reduced after pentylenetetrazole kindling.

Seizure activity stimulates adult neurogenesis, the birth of new neurons, in the hippocampus. Many new neurons that develop in the presence of repeatedly induced seizures acquire abnormal morphological and functional characteristics that can promote network hyperexcitability and hippocampal dysfunction. However, the impact of seizure induced neurogenesis on behaviour remains poorly understood. In this study, we investigated whether adult-born neurons generated immediately before and during chronic seizures were capable of integration into behaviorally relevant hippocampal networks. Adult rats underwent pentylenetetrazole (PTZ) kindling for either 1 or 2 weeks. Proliferating cells were labelled with BrdU immediately before kindling commenced. Twenty-four hours after receiving their last kindling treatment, rats were placed in a novel environment and allowed to freely explore for 30 min. The rats were euthanized 90 min later to examine for behaviourally-induced immediate early gene expression (c-fos, Zif268). Using this approach, we found that PTZ kindled rats did not differ from control rats in regards to exploratory behaviour, but there was a marked attenuation in behaviour-induced expression of Fos and Zif268 for rats that received 2 weeks of PTZ kindling. Further examination revealed that PTZ kindled rats showed reduced colocalization of Fos and Zif268 in 2.5 week old BrdU + cells. The proportion of immature granule cells (doublecortin-positive) expressing behaviorally induced Zif268 was also significantly lower for PTZ kindled rats than control rats. These results suggest that chronic seizures can potentially disrupt the ability of adult-born cells to functionally integrate into hippocampal circuits important for the processing of spatial information.

Menthone aryl acid hydrazones: a new class of anticonvulsants.

A series of ten compounds (Compounds J(1)-J(10)) of (±) 3-menthone aryl acid hydrazone was synthesized and characterized by thin layer chromatography and spectral analysis. Synthesized compounds were evaluated for anticonvulsant activity after intraperitoneal (i.p) administration to mice by maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) induced seizure method and minimal clonic seizure test. Minimal motor impairment was also determined for these compounds. Results obtained showed that four compounds out of ten afforded significant protection in the minimal clonic seizure screen at 6 Hz. Compound J(6), 4-Chloro-N-(2-isopropyl-5-methylcyclohexylidene) benzohydrazide was found to be the most active compound with MES ED(50) of 16.1 mg/kg and protective index (pI) of greater than 20, indicating that (±) 3-menthone aryl acid hydrazone possesses better and safer anticonvulsant properties than other reported menthone derivatives viz. menthone Schiff bases, menthone semicarbazides and thiosemicarbazides.

Effect of Brewer's yeast-induced pyrexia on aminophylline-elicited convulsions in mice.

Theophylline-associated convulsions have been observed most frequently in children with fever, but the mechanism is not fully understood. In this study, we investigated the basic mechanism of aminophylline [theophylline-2-ethylenediamine]-induced convulsions and the effects of Brewer's yeast-induced pyrexia in mice. Diazepam (5-10mg/kg, i.p.), a benzodiazepine receptor agonist, significantly prolonged the onset and significantly decreased the incidence of convulsions induced by aminophylline (350 mg/kg, i.p.). However, the gamma aminobutyric acid (GABA)A receptor agonist muscimol (1-4 mg/kg, i.p.), the GABAB receptor agonist baclofen (2-4 mg/kg, i.p.) and the N-methyl-D-aspartic acid receptor antagonist dizocilpine (0.1-0.3 mg/kg, i.p.) failed to protect against the convulsions. 20% Brewer's yeast (0.02 ml/g, s.c.) increased body temperature by 1.03, and also significantly shortened the onset and significantly increased the incidence of convulsions induced by aminophylline. The anticonvulsant action of diazepam (2.5-10mg/kg, i.p.) on the convulsions induced by aminophylline was reduced by Brewer's yeast-induced pyrexia. The proconvulsant actions of the GABAA receptor antagonists picrotoxin (3-4 mg/kg, i.p.) and pentylenetetrazol (40-60 mg/kg, i.p.) were enhanced by Brewer's yeast. These results suggest that the anticonvulsant action of diazepam against aminophylline is reduced by Brewer's yeast-induced pyrexia, and that GABAA receptors are involved in the aggravation of the convulsions by Brewer's yeast in mice.

The pentylenetetrazole-induced activity in the hippocampus can be inhibited by the conversion of L-kynurenine to kynurenic acid: an in vitro study.

The kynurenine pathway converts tryptophan into various compounds, including L-kynurenine, which in turn can be converted into the excitatory amino acid receptor antagonist kynurenic acid. The ionotropic glutamate receptors have been considered to be attractive targets for new anticonvulsants in neurological disorders such as epileptic seizure. This study was designed to examine the conversion of L-kynurenine to kynurenic acid and to investigate the effects of kynurenic acid on pentylenetetrazole-treated rat brain slices, and in parallel to draw attention to the fact that a well-designed in vitro model has many advantages in pharmacological screening. Schaffer collateral stimulation-evoked field EPSPs were recorded from area CA1 of rat hippocampal slices in vitro; drugs were bath-applied. Pretreatment with the kynurenic acid precursor L-kynurenine led to the elimination of the effect of pentylenetetrazole on hippocampal slices in vitro. N-Omega-nitro-L-arginine, which inhibits kynurenine aminotransferase I and II, abolished this neuroprotective effect. This study has furnished the first in vitro electrophysiological evidence that rat brain slices have the enzymatic capacity to convert exogenously administered L-kynurenine (16 microM) to kynurenic acid in an amount sufficient to protect them against pentylenetetrazole (1 mM)-induced hyperexcitability.

Gender difference in the influence of antioxidants on the blood-brain barrier permeability during pentylenetetrazol-induced seizures in hyperthermic rat pups.

Our purpose in this study was to investigate the protective effects of selenium and vitamin E on the blood-brain barrier (BBB) permeability in rats with convulsion under hyperthermic conditions. To eliminate the effect of sex on BBB, we performed our study on 4- to 5-week-old prepubertal rat pups. Evans-blue was used as a BBB tracer. Convulsions were induced by administration of i.p. pentylenetetrazol. In the selenium group, 4 ppm selenium was added to the drinking water for 4-5 weeks. Vitamin E was administered at 700 mg/kg ip. It was shown that the convulsions, both under normothermic and hyperthermic conditions, caused widespread increase in the BBB permeability (p < 0.05). In addition, a significant difference was observed among female and male rats (f [1, 102] = 6.387, p < 0.05). In convulsions under normothermic conditions, there was a further increase in the BBB permeability (F[3, 102] = 43.534, p < 0.001) and a greater increase of permeability in males compared to females (F[1, 102] = 6.387, p < 0.05). Selenium and vitamin E significantly decreased the BBB destruction caused by convulsions under hyperthermic conditions in males (p < 0.05). Treatment with selenium or vitamin E has beneficial effects on the BBB breakdown during convulsions. But gender differences are very important in BBB permeability under pathological conditions and antioxidant treatments.

Epileptogenic drugs in a model nervous system: electrophysiological effects and incorporation into a phospholipid layer.

Mechanisms of epileptiform activity in a model nervous system (buccal ganglia of Helix pomatia) are presented. The ganglia contain the identified giant neurons B1 through B4. For epileptiform activity, pentylenetetrazol (1 mmol/L to 40 mmol/L) or etomidate (12.5 micromol/L to 500 micromol/L) were applied. Membrane pressure was measured using a Wilhelmy film balance. In electrophysiological experiments, both drugs induced several effects in all studied neurons: membrane resistance increased, down-stroke of action potentials declined, and all types of chemical synaptic potentials decreased (the latter concerns pentylenetetrazol only). The threshold was 1 mmol/L of pentylenetetrazol and 12.5 micromol/L of etomidate. Epileptiform potentials developed in neurons that had expressed the membrane mechanisms underlying pacemaker potentials. The threshold of this development was again 1 mmol/L of pentylenetetrazol and 12.5 micromol/L of etomidate. Epileptiform depolarizations appeared with 40 mmol/L of pentylenetetrazol and 500 micromol/L of etomidate. In biochemical experiments, both drugs incorporated into an artificial phospholipids membrane and increased pressure in the membrane. The threshold of pressure increase was 1 mmol/L of pentylenetetrazol and 12.5 micromol/L of etomidate. Pressure increased dose-dependently and was 69% and 63% above starting pressure of 10 mN/m with epileptogenic concentrations of pentylenetetrazol (40 mmol/L) and of etomidate (500 micromol/L), respectively. It is postulated that amphiphilic substances incorporate into cell membranes and increase intramembranous pressure, and that this disturbs several membrane processes mechanically and leads to epileptic depolarizations in pacemaker neurons.

Cloning and characterization of pentylenetetrazol-related cDNA, PTZ-17.

cDNAs related to pentylenetetrazol-induced bursting activity in neurons were screened by a differential hybridization method using normal and pentylenetetrazol-treated primary cultured neurons from the cerebral cortex of mice. Twenty clones of candidate cDNA with expression increased or decreased by treatment with pentylenetetrazol were obtained. One of them, PTZ-17, was sequenced. Injection of PTZ-17 derived RNA into Xenopus oocytes showed a large calcium inward current with extracellular application of pentylenetetrazol.

Lack of tolerance to anticonvulsant effects of clonazepam in a rat pentylenetetrazol (PTZ) induced kindled seizure model.

The development of tolerance to the anticonvulsant effects of clonazepam (CZP) was investigated using a pentylenetetrazol (PTZ)-induced kindled rat seizure model. PTZ kindled rats received twice daily injections, either 0.3 mg/kg of CZP for 3 weeks, 2.0 mg/kg of CZP for 2 weeks or vehicle (propylene glycol) as maintenance doses. PTZ injections (30 mg/kg) were given once weekly both prior to and after the initiation of maintenance doses. The protective effect of CZP against PTZ-induced seizures was examined by determining the protective effect of a single dose of CZP (0.1 or 0.3 mg/kg) given once weekly 30 min prior to 30 mg/kg PTZ injection. CZP treatment continued to protect the rats from kindled seizures during the CZP maintenance period in both experiments. No significant differences were found in seizure responses between rats receiving either dose of CZP maintenance and the vehicle maintenance control group (p > 0.05). We were unable to demonstrate tolerance to the protective effects of CZP against PTZ-induced kindled seizures in this rat seizure model.

Blockade of N-methyl-D-aspartate induced convulsions by 1-aminocyclopropanecarboxylates.

1-Aminocyclopropanecarboxylic acid is a potent and selective ligand for the glycine modulatory site on the N-methyl-D-aspartate receptor complex. This compound blocks (ED50 234 mg/kg) the convulsions and deaths produced by N-methyl-D-aspartate (125 mg/kg) in a dose dependent fashion. In contrast, 1-aminocyclopropanecarboxylic acid does not protect mice against convulsions induced by pentylenetetrazole (80 mg/kg), strychnine (2 mg/kg), bicuculline (6 mg/kg), or maximal electroshock (50 mA, 0.2 s), and does not impair motor performance on either a rotarod or horizontal wire at doses of up to 2 g/kg. The methyl- and ethyl- esters of 1-aminocyclopropanecarboxylic acid are 5- and 2.3-fold more potent, respectively, than the parent compound in blocking the convulsant and lethal effects of N-methyl-D-aspartate. However, these esters are several orders of magnitude less potent (IC50 greater than 40 microM) than 1-aminocyclopropanecarboxylic acid as inhibitors of strychnine-insensitive [3H] glycine binding, indicating that conversion to the parent compound may be required to elicit an anticonvulsant action. These findings suggest that 1-aminocyclopropanecarboxylates may be useful in the treatment of neuropathologies associated with excessive activation of N-methyl-D-aspartate receptor coupled cation channels.

Effect of aspartame on seizures in various models of experimental epilepsy.

We investigated in rats whether aspartame intake affected the susceptibility to seizures induced chemically (metrazol, quinolinic acid) or electrically (electroshock). Aspartame (0.75-1.0 g/kg), given orally as a single bolus to 16-hr fasted animals 60 min before metrazol, significantly increased the number of animals showing clonic-tonic seizures. At 1.0 g/kg the ED50 for clonic-tonic convulsions was lowered by 23%. A similar increase in seizure susceptibility was observed with 0.25-0.5 g/kg of the aspartame's metabolite phenylalanine. When aspartame was administered to fasted rats in three divided doses (0.33 g/kg) over 120 min or to fed animals after a meal, or overnight with the diet, no significant changes in the incidence of animals showing seizures was observed. One gram per kilogram aspartame and 0.5 g/kg phenylalanine did not modify the CC50 (mA) for tonic hindlimb extension induced by electroshock and the electroencephalographic seizures caused by intrahippocampal injection of 120 nmol quinolinic acid. Plasma and brain levels of phenylalanine and tyrosine significantly raised after both 1 g/kg aspartame as a single bolus (plasma: Phe 285%, Tyr 288%; brain: Phe 146%, Tyr 192%; above controls) or in three divided doses (plasma: Phe 207%, Tyr 315%; brain Phe 103%, Tyr 211%; above controls) and 0.5 g/kg phenylalanine (plasma: Phe 339%, Tyr 410%; brain: Phe 219%, Tyr 192%; above controls), but the ratio Phe/Tyr was not modified. Our data indicate that aspartame cannot be regarded as a general proconvulsant agent. The mechanisms of potentiation of seizures induced by metrazol after the administration of the sweetner in a single rapid intake will be discussed.

Seizure susceptibility in DBA and C57 mice: the effects of various convulsants.

Convulsive dose 50s (CD50s) for various convulsive drugs and minimal and maximal electroshock seizure thresholds were determined in DBA and C57 mice. DBA mice had lower maximal electroshock seizure thresholds (MESTs, 15%) and CD50s for homocysteine thiolactone (HTL, 23%) and bicuculline (69%), and a higher CD50 for pentylenetetrazol (PTZ) at 3 weeks of age, the age of maximal audiogenic seizure (AGS) susceptibility. At 8 weeks, when DBA mice are not susceptible to AGSs, significant differences were a lower minimal electroshock seizure threshold (mEST, 37%) and maximal EST (MEST) (19%), lower CD50s for N-methyl-D-aspartate (NMDA) (39%), kainic acid (KA, 50%), HTL (32%), strychnine (37%), and a higher CD50 for nicotine (55%) in DBA mice. Based on these data it is suggested that pathways involving NMDA and KA receptors are responsible for increased susceptibility to seizure initiation (mEST), and are opposed by glycine pathways, and that opposing GABA and cholinergic systems at higher CNS levels are involved in seizure spread (AGSs and MEST) in these mice. Latency patterns indicate that nicotine, strychnine, PTZ and bicuculline have high blood-brain barrier (BBB) penetrability. Picrotoxin and the excitatory amino acid receptor agonists had longer latencies, suggesting low BBB penetrability. Age-related changes in latency, however, give evidence that difficulty in drug penetration of the BBB is not responsible for differences observed in CD50s between strains.

Age-dependent decrease in the lethal threshold of pentylenetetrazole in mice.

We previously reported that the minimal effective concentrations in plasma and brain for inducing the maximal seizure after intraperitoneal injection of pentylenetetrazole (PTZ) significantly increased with age in mice. We also observed that some old mice died without the maximal seizure during the observation period of 15 min. To examine how the lethal dose changes with age in the mouse, in the present study we employed a continuous intravenous infusion of PTZ that enabled us to control the dose, either stopping the infusion after the maximal seizure or continuing it until the lethal dose was reached. This study has demonstrated that the lethal threshold of PTZ in the oldest mice (27 months for males and 30 months for females) was significantly lower than that for the respective younger groups. We conclude that our observation in old mice of death occurring before the appearance of maximal seizure is due to a decrease in the lethal threshold combined with an increase in the threshold for maximal seizure.