Changes In Seizure Threshold Research Articles

Factors Predicting Ictal Quality in Bilateral Electroconvulsive Therapy Sessions.

In electroconvulsive therapy (ECT), ictal characteristics predict treatment response and can be modified by changes in seizure threshold and in the ECT technique. We aimed to study the impact of ECT procedure-related variables that interact during each session and might influence the seizure results. Two hundred and fifty sessions of bilateral ECT in forty-seven subjects were included. Seizure results were evaluated by two different scales of combined ictal EEG parameters (seizure quality index (SQI) and seizure adequacy markers sum (SAMS) scores) and postictal suppression rating. Repeated measurement regression analyses were performed to identify predictors of each session’s three outcome variables. Univariate models identified age, physical status, hyperventilation, basal oxygen saturation, days between sessions, benzodiazepines, lithium, and tricyclic antidepressants as predictors of seizure quality. Days elapsed between sessions, higher oxygen saturation and protocolized hyperventilation application were significant predictors of better seizure quality in both scales used in multivariate models. Additionally, lower ASA classification influenced SQI scores as well as benzodiazepine use and lithium daily doses were predictors of SAMS scores. Higher muscle relaxant doses and lower applied stimulus intensities significantly influenced the postictal suppression rating. The study found several modifiable procedural factors that impacted the obtained seizure characteristics; they could be adjusted to optimize ECT session results.

Protective effect of minocycline on LPS-induced mitochondrial dysfunction and decreased seizure threshold through nitric oxide pathway

Lipopolysaccharide (LPS) increases inflammatory cytokines of the brain and deregulates the mitochondrial function, thus could increase the seizure susceptibility. Studies have shown that minocycline has neuroprotective and antioxidant properties. In this study, we aimed to evaluate the anticonvulsant properties of minocycline in LPS-treated animals and the possible involvement of nitric oxide and mitochondrial pathways. In a PTZ model of seizure in mice, minocycline was administrated to LPS-treated mice. Then followed by co-injection of its sub-effective dose and NOS inhibitors including 7-Nitroindazole (7-NI), aminoguanidine (AG) and L-NG-Nitroarginine methyl ester (L-NAME) to evaluate the changes in seizure threshold and the possible involvement of nitrergic system. Molecular assessments were used to evaluate the effects of each treatment on inflammation and mitochondrial function in the brain. LPS-treated animals had lower seizure threshold compared to intact animals; injection of minocycline (80 mg/kg) to LPS-treated mice reversed this effect. Co-injection of sub-effective doses of minocycline (40 mg/kg) and L-NAME to LPS-treated animals significantly increased seizure threshold. We observed that co-treatment of minocycline and AG dissimilar to 7-NI could increase the seizure threshold of LPS-treated animals. L-arginine reversed the anticonvulsant effect of minocycline. Also, molecular evaluations showed that LPS could increase the ATP levels, GSH levels, and reactive oxygen species formation. However, minocycline at both doses significantly reversed the effect of LPS. Minocycline counteracts the proconvulsant effects of LPS through regulating of mitochondrial function and decreasing of neuro-inflammation. Also, co-administration of minocycline and i-NOS inhibitors could intensify anticonvulsant effects of minocycline.

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TRPV1 deletion exacerbates hyperthermic seizures in an age-dependent manner in mice

Febrile seizures (FS) are the most common seizure disorder to affect children. Although there is mounting evidence to support that FS occur when children have fever-induced hyperventilation leading to respiratory alkalosis, the underlying mechanisms of hyperthermia-induced hyperventilation and links to FS remain poorly understood. As transient receptor potential vanilloid-1 (TRPV1) receptors are heat-sensitive, play an important role in adult thermoregulation and modulate respiratory chemoreceptors, we hypothesize that TRPV1 activation is important for hyperthermia-induced hyperventilation leading to respiratory alkalosis and decreased FS thresholds, and consequently, TRPV1 KO mice will be relatively protected from hyperthermic seizures. To test our hypothesis we subjected postnatal (P) day 8–20 TRPV1 KO and C57BL/6 control mice to heated dry air. Seizure threshold temperature, latency and the rate of rise of body temperature during hyperthermia were assessed. At ages where differences in seizure thresholds were identified, head-out plethysmography was used to assess breathing and the rate of expired CO2 in response to hyperthermia, to determine if the changes in seizure thresholds were related to respiratory alkalosis. Paradoxically, we observed a pro-convulsant effect of TRPV1 deletion (∼4min decrease in seizure latency), and increased ventilation in response to hyperthermia in TRPV1 KO compared to control mice at P20. This pro-convulsant effect of TRPV1 absence was not associated with an increased rate of expired CO2, however, these mice had a more rapid rise in body temperature following exposure to hyperthermia than controls, and the expected linear relationship between body weight and seizure latency was absent. Based on these findings, we conclude that deletion of the TRPV1 receptor prevents reduction in hyperthermic seizure susceptibility in older mouse pups, via a mechanism that is independent of hyperthermia-induced respiratory alkalosis, but possibly involves impaired development of thermoregulatory mechanisms, although at present the mechanism remain unknown.

Anticonvulsant Mechanisms of Electroconvulsive Therapy and Relation to Therapeutic Efficacy.

Electroconvulsive therapy (ECT) is held to confer anticonvulsant effects, although the role of rise in seizure threshold upon clinical effect is uncertain. This study investigated the relationship in a large, consecutive, retrospective sample of patients receiving ECT in Aberdeen. We have tested the hypotheses of previous authors to further examine the relationship between seizure and therapeutic effect as well as discuss the potential underlying neurobiological mechanisms. All patients receiving ECT at the Royal Cornhill Hospital between 2000 and the end of 2008 were identified from the Scottish ECT Accreditation Network. Electroconvulsive therapy was administered twice weekly with a bifrontotemporal electrode placement using routine dosage schedules. Data were gathered from the Scottish ECT Accreditation Network and case notes regarding ECT course and clinical effect. The seizure threshold increased in 219 (94.4%) patients, stayed the same in 13 (5.6%) patients, and decreased in 0 patient (n = 232). No significant relationship was present between change in seizure threshold and change in Montgomery-Asberg Depression Rating Scale score (P = 0.39; Kendall τ b r = 0.047; n = 182), although responders did display greater increase in seizure threshold than nonresponders. Electroconvulsive therapy confers anticonvulsant effects in a consecutive sample of real-life patients. Neither initial seizure threshold nor magnitude of seizure threshold increase is a predictor of clinical response to ECT. A rise in seizure threshold is not essential for therapeutic effect but may represent an important marker of underlying neuronal state. The evidence reviewed in this article supports a link between neuroplastic effects of ECT and the evidenced rise in seizure threshold.

Different preparations, doses, and treatment regimens of cyclosporine A cause adverse effects but no robust changes in seizure thresholds in rats

Neuronal transplantation is a promising experimental treatment approach for intractable epilepsies, but rejection of porcine or human cells in rodent epilepsy models requires adequate immunosuppression to enable long-term survival of xenografts. The commonly used immunosuppressive drug cyclosporine A (CsA) itself was suggested to affect seizure thresholds. However, putative pro- or anticonvulsant effects of CsA have not yet been sufficiently explored in a direct comparison study involving different preparations, dosages, and application routes. We therefore comprehensively investigated the effects of acute versus chronic treatment using different dosages (5mg/kg, 10mg/kg), application routes (i.p., s.c.), and preparations of CsA (pure substance solved in polyethoxylated castor oil and a ready-to-use drug additionally containing ethanol) on acute seizure thresholds in rats in the pentylenetetrazole seizure threshold test and verified the most harmless protocol in the chronic amygdala-kindling model for temporal lobe epilepsy. None of the CsA treatment regimens induced acute changes of seizure thresholds. Chronic CsA treatment also did not robustly change seizure thresholds. As evaluated by whole blood analyses, bioavailability of CsA was significantly higher after i.p. application of the ready-to-use preparation compared to the pure substance and compared to s.c. Observed adverse effects differed between CsA treatment regimens and included reversible diarrhea, lowered body temperature, and tremor, the latter two of which were also induced by vehicle injections containing ethanol and/or polyethoxylated castor oil. Our data suggest that chronic treatment (2 weeks) with 10mg/kg CsA injected i.p. in the ready-to-use preparation is an appropriate protocol for use in neural transplantation in epilepsy research applying the presently used rat models. Transplantation studies in experimental epilepsy research require a careful assessment of putative CsA effects on seizure thresholds in the specific experimental settings to be used.

Evaluation of Anticonvulsant, Antidepressant-, and Anxiolytic-like Effects of an Aqueous Extract from Cultured Mycelia of the Lingzhi or Reishi Medicinal Mushroom Ganoderma lucidum (Higher Basidiomycetes) in Mice

Ganoderma lucidum is a well-known medicinal mushroom with a long history of use. This study was designed to assess the anticonvulsant potential of an aqueous extract from cultured G. lucidum mycelium in 3 acute seizure models: timed intravenous pentylenetetrazole infusion, maximal electroshock seizure threshold, and 6-Hz-induced psychomotor seizure tests in mice. Moreover, antidepressant-like and anxiolytic-like effects of G. lucidum were evaluated using the forced swim test and the elevated plus maze test in mice, respectively. No changes in seizure thresholds in the intravenous pentylenetetrazole and maximal electroshock seizure threshold tests after acute treatment with G. lucidum extract (200-600 mg/kg) was observed. However, the studied extract (100-400 mg/kg) significantly increased the threshold for psychomotor seizures in the 6-Hz seizure test. In the forced swim test, G. lucidum (100-400 mg/kg) significantly reduced the duration of immobility. No anxiolytic-like or sedative effects were reported in mice pretreated with the extract (400-600 mg/kg). G. lucidum extract (50-2400 mg/kg) did not produce toxic effects in the chimney test (motor coordination) or grip-strength test (neuromuscular strength). Further studies are required to explain the neuropharmacological effects of G. lucidum and to identify its active ingredients that may affect seizure threshold, mood, or anxiety.

Involvement of the nitrergic system in the proconvulsant effect of social isolation stress in male mice

Social isolation stress (SIS) in adolescence is accompanied by neurobehavioral disturbances and pathophysiological changes in certain regions of the CNS such as the hippocampus. In this study, we tested whether SIS impacts seizure susceptibility in postnatal male mice due to a role of hippocampal nitric oxide (NO). To do this, we used the pentylenetetrazole (PTZ) model of clonic seizures, open-field test, hole-board test, forced swimming test, and plasma corticosterone assay. We aimed to evaluate if 4weeks of SIS is capable of decreasing seizure threshold along with altering affective and neuroendocrine responses in isolated conditioned (IC) animals in comparison with socially conditioned (SC) animals. In addition, we applied subeffective doses of NO precursor l-arginine (25, 50, and 100mg/kg) and NOS inhibitors 7-NI (15 and 40mg/kg), aminoguanidine (50 and 100mg/kg), and l-NAME (10 and 15mg/kg) to both IC and SC groups prior to the determination of seizure threshold. Injection of a single dose of all mentioned drugs did not induce changes in seizure threshold of SC mice. On the other hand, l-NAME and 7-NI, but not aminoguanidine, modulated the proconvulsant effect of SIS, while l-arginine augmented the latter effect. We also measured the hippocampal nitrite levels after the administration of the aforementioned drugs. Social isolation stress increased the nitrite levels in comparison with those in SC mice, whereas 7-NI and l-NAME, unlike aminoguanidine, mitigated the effect of SIS. Additionally, l-arginine boosted the effects of SIS on nitrite production. In summary, we showed that SIS enhanced seizure susceptibility in the PTZ model of clonic seizures through the activation of the nitrergic system in the hippocampus. Also, we proved that nNOS, but not iNOS, accounts for these changes following SIS.

Esters of valerenic acid as potential prodrugs

Valerenic acid (VA) is a β2/3 subunit-specific modulator of γ-aminobutyric acid (GABA) type A (GABAA) receptors inducing anxiolysis. Here we analyze if VA-esters can serve as prodrugs and if different ester structures have different in vitro/in vivo effects. Modulation of GABAA receptors expressed in Xenopus oocytes was studied with 2-microelectrode-voltage-clamp. Anxiolytic effects of the VA-esters were studied on male C57BL/6N mice by means of the elevated plus maze-test; anticonvulsant properties were deduced from changes in seizure threshold upon pentylenetetrazole infusion. VA was detected in plasma confirming hydrolysis of the esters and release of VA in vivo. Esterification significantly reduced the positive allosteric modulation of GABAA (α1β3γ2S) receptors in vitro. in vivo, the studied VA-ester derivatives induced similar or even stronger anxiolytic and anticonvulsant action than VA. While methylation and propylation of VA resulted in faster onset of anxiolysis, the action of VA-ethylester was longer lasting, but occurred with a significant delay. The later finding is in line with the longer lasting anticonvulsant effects of this compound. The estimated VA plasma concentrations provided first insight into the release kinetics from different VA-esters. This might be an important step for its future clinical application as a potential non-sedative anxiolytic and anticonvulsant.

Intraperitoneal administration of docosahexaenoic acid for 14 days increases serum unesterified DHA and seizure latency in the maximal pentylenetetrazol model

Docosahexaenoic acid (DHA) is an omega-3 polyunsaturated fatty acid (n−3 PUFA) which has been shown to raise seizure thresholds following acute administration in rats. The aims of the present experiment were the following: 1) to test whether subchronic DHA administration raises seizure threshold in the maximal pentylenetetrazol (PTZ) model 24h following the last injection and 2) to determine whether the increase in seizure threshold is correlated with an increase in serum and/or brain DHA.Animals received daily intraperitoneal (i.p.) injections of 50mg/kg of DHA, DHA ethyl ester (DHA EE), or volume-matched vehicle (albumin/saline) for 14days. On day 15, one subset of animals was seizure tested in the maximal PTZ model (Experiment 1). In a separate (non-seizure tested) subset of animals, blood was collected, and brains were excised following high-energy, head-focused microwave fixation. Lipid analysis was performed on serum and brain (Experiment 2). For data analysis, the DHA and DHA EE groups were combined since they did not differ significantly from each other.In the maximal PTZ model, DHA significantly increased seizure latency by approximately 3-fold as compared to vehicle-injected animals. This increase in seizure latency was associated with an increase in serum unesterified DHA. Total brain DHA and brain unesterified DHA concentrations, however, did not differ significantly in the treatment and control groups. An increase in serum unesterified DHA concentration reflecting increased flux of DHA to the brain appears to explain changes in seizure threshold, independent of changes in brain DHA concentrations.

Stress during first pregnancy increases seizure threshold in adult male offspring.

Stress induces many homeostatic aberrations which are followed by lifelong allostatic responses. Epilepsy is developed or influenced by different environmental factors, i.e. prenatal stress which makes many contradictory developmental changes in seizure threshold and intensity. We investigated the potential seizure response of the rat offspring to prenatal stress; the stress which was applied to their mothers. Nine day heterogeneous sequential stress (HSS) model was used before and during the first and before the second pregnancy. The kindling was induced using 13 IP injections of pentylenetetrazol (PTZ) every 48 hr to adult male Wistar rat's offspring. The results of the present study demonstrated that, before pregnancy stress decreased the rate of kindling (P<0.05) in the offspring, while stress which was applied during pregnancy completely prevented kindling (P <0.001). Further, their convulsive latency was increased and tonic clonic seizure duration was decreased. In contrast, previous pregnancy and between pregnancies stress could not change kindling process. Although maternal separation stress did not change kindling development, it could increase convulsive intensities by elongating the duration of seizures (P<0.05) and reducing convulsion latency (P <0.05). It is concluded that stress detrimental effects could be prevented by stress which was applied around first pregnancy; however this beneficial effect is weakened by before second pregnancy stress.

English

Pharmacognosy studies have shown that&nbsp;Valeriana officinalis&nbsp;L. roots containing significant amounts of free amino acids such as GABA and other substances like valeric acid and isovalerate. In this study, anticonvulsant effects of&nbsp;V. officinalis&nbsp;(VO) roots aqueous extract, using standard methods of chemical seizure caused by pentylenetetrazole (PTZ) in mice was assessed. To evaluate mechanisms involved in VO anticonvulsant effects, diazepam and flumazenil were used. After determining the seizure threshold in the control group, different doses of VO (0.25, 0.5 and 1 g/kg) were intraperitoneally (IP) administered and their effects on the threshold of PTZ-induced seizure were studied. Diazepam (1, 2 and 3 mg/kg) and flumazenil (1, 2 and 4 mg/kg) were injected intraperitoneally and the seizure threshold was determined, after which the different doses of the VO drugs were evaluated. The results showed that PTZ-induced seizure threshold in control mice was 35.52 &plusmn; 0.87 mg/kg. VO and diazepam were increased and flumazenil were decreased the threshold of PTZ-induced seizure. Also results showed that diazepam and flumazenil, respectively increase and decrease the effect of VO on PTZ-induced seizure. Changes in seizure threshold in this study indicate that probably the mechanism of VO anticonvulsant effects is due to the inhibitory GABA system, but this issue needs further investigations. &nbsp; Key words:&nbsp;Valeriana officinalis, root, diazepam, flumazenil, PTZ, clonic seizure threshold.

Commentary: A Skeptical View of Experimental Gene Therapy to Block Epileptogenesis

Gene therapy offers exciting new options for treating epileptic seizures, and even for blocking the development of epilepsy (i.e., epileptogenesis) after a brain insult. Although the available studies provide interesting new data, the experiments discussed in this issue also have limitations and raise concerns. The criticisms offered in this commentary center around the nature of the experimental testing (e.g., changes in seizure threshold), the animal models (e.g., kindling), and the measures of epileptogenesis in those animal models with spontaneous seizures (e.g., the latent period after pilocarpine-induced status epilepticus). Another set of criticisms relate to the relative lack of positive controls showing that the actual mechanism purported to be activated via the gene-therapeutic approach has in fact been upregulated in the specific animals that show the hypothetical antiepileptic result. This commentary takes the con side in the debate, to generate constructive criticism to help direct future studies to provide increasingly stronger data to support the view that gene therapy approaches may be useful in the treatment of epilepsy.

Microglial activation and TNFα production mediate altered CNS excitability following peripheral inflammation

Peripheral inflammation leads to a number of centrally mediated physiological and behavioral changes. The underlying mechanisms and the signaling pathways involved in these phenomena are not yet well understood. We hypothesized that peripheral inflammation leads to increased neuronal excitability arising from a CNS immune response. We induced inflammation in the gut by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) to adult male rats. To examine the excitability of the brain in vivo, we administered pentylenetetrazole (PTZ; a GABAergic antagonist) intravenously to evoke clonic seizures. Rats treated with TNBS showed increased susceptibility to PTZ seizures that was strongly correlated with the severity and progression of intestinal inflammation. In vitro hippocampal slices from inflamed, TNBS-treated rats showed increased spontaneous interictal burst firing following application of 4-aminopyridine, indicating increased intrinsic excitability. The TNBS-treated rats exhibited a marked, reversible inflammatory response within the hippocampus, characterized by microglial activation and increases in tumor necrosis factor alpha (TNFalpha) levels. Central antagonism of TNFalpha using a monoclonal antibody or inhibition of microglial activation by i.c.v. injection of minocycline prevented the increase in seizure susceptibility. Moreover, i.c.v. infusion of TNFalpha in untreated rats for 4 days also increased seizure susceptibility and thus mimicked the changes in seizure threshold observed with intestinal inflammation. Our finding of a microglia-dependent TNFalpha-mediated increase in CNS excitability provides insight into potential mechanisms underlying the disparate neurological and behavioral changes associated with chronic inflammation.

Alcohol significantly lowers the seizure threshold in mice when co-administered with bupropion hydrochloride

BackgroundBupropion HCl is a widely used antidepressant that is known to cause seizures in a dose-dependent manner. Many patients taking antidepressants will consume alcohol, even when advised not to. Previous studies have not shown any interactions between bupropion HCl and alcohol. However, there have been no previous studies examining possible changes in seizure threshold induced by a combination of alcohol and bupropion HCl.MethodsExperimentally naïve female Swiss albino mice (10 per group) received either single doses of bupropion HCl (ranging from 100 mg/kg to 120 mg/kg) or vehicle (0.9% NaCl) by intraperitoneal (IP) injection in a dose volume of 10 ml/kg, and single-dose ethanol alone (2.5 g/kg), or vehicle, 5 min prior to bupropion dosing. The presence or absence of seizures, the number of seizures, the onset, duration and the intensity of seizures were all recorded for 5 h following the administration of ethanol.ResultsThe results show that administration of IP bupropion HCl alone induced seizures in mice in a dose-dependent manner, with the 120 mg/kg dose having the largest effect. The percentage of convulsing mice were 0%, 20%, 30% and 60% in the 0 (vehicle), 100, 110, and 120 mg/kg dose groups, respectively. Pretreatment with ethanol produced a larger bupropion HCl-induced convulsive effect at all the doses (70% each at 100, 110 and 120 mg/kg) and a 10% effect in the ethanol + vehicle only group. The convulsive dose of bupropion HCl required to induce seizures in 50% of mice (CD50), was 116.72 mg/kg for bupropion HCl alone (CI: 107.95, 126.20) and 89.40 mg/kg for ethanol/bupropion HCl (CI: 64.92, 123.10).ConclusionThese results show that in mice alcohol lowers the seizure threshold for bupropion-induced seizures. Clinical implications are firstly that there may be an increased risk of seizures in patients consuming alcohol, and secondly that formulations that can release bupropion more readily in alcohol may present additional risks to patients.

Change in Seizure Threshold During Electroconvulsive Therapy

The seizure threshold (ST) is a measure of the minimum electrical energy necessary to induce a grand mal seizure. Dose titration of the ST has been suggested to optimize stimulus dosing in electroconvulsive therapy (ECT). The change in ST with remission is examined in a large sample of unipolar depressed patients. In a study of continuation treatments after successful ECT, the ST was determined at the first treatment and again 1 week after remission using a conventional ST measurement protocol. Patients were treated with bilateral electrode placement at 150% above the measured ST. In 80 subjects, the ST measured the same in 70%, increased in 21%, and decreased in 9% at remission. In a study of bilateral ECT, the ST did not rise conclusively with remission.

Intestinal inflammation alters the susceptibility to pentylenetetrazole-induced seizure in mice.

Inflammatory bowel disorders are associated with increased incidence of seizures. Alteration in the endogenous opioid system and overproduction of nitric oxide have been implicated in colitis. The possible contribution of opioid receptors and nitric oxide to increased seizure susceptibility was examined in a putative model of intestinal inflammation. The alterations in clonic seizure threshold, induced by pentylenetetrazole, following the induction of intestinal inflammation by the administration of two consecutive daily oral doses of croton oil, was evaluated in mice. This model was used to evaluate the effects of pretreatment with opioid receptor antagonist naltrexone (10 mg/kg, once daily for 4 days or a single dose on the test day), non-specific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (10 mg/kg, once daily), and specific inducible nitric oxide synthase inhibitor aminoguanidine (100 mg/kg, once daily) on seizure threshold in intestinal inflammation. A significant decrease in clonic seizure threshold was observed in mice with intestinal inflammation compared to the control group. Chronic pretreatment with naltrexone per se did not cause any significant change in seizure threshold, but it significantly restored the threshold in croton oil-treated mice to that of the control animals. However, acute naltrexone pretreatment (on the test day) could not restore the decreased seizure threshold to control level. Chronic pretreatment with neither NG-nitro-L-arginine methyl ester nor aminoguanidine altered the seizure threshold in the control animals and in mice treated with croton oil. Experimental croton oil-induced intestinal inflammation leads to a proconvulsant effect, which may have clinical relevance. Chronic alterations mediated by endogenous opioids may be involved in this process, though a direct opioid-receptor-mediated effect is unlikely. Nitric oxide synthesis, via constitutive or inducible pathways, is not involved in this increased susceptibility.

The Effects of Brain-Irradiation-Induced Decreases in Hippocampal Mitotic Activity on Flurothyl-Induced Epileptogenesis in Adult C57BL/6J Mice

Previous studies have demonstrated that seizures are potent inducers of mitotic activity in the rodent hippocampus. The role of this mitotic activity in epileptogenesis currently remains unknown. In the present study, we investigated the effect of alterations in hippocampal mitotic activity on changes in seizure threshold and phenotype using flurothyl kindling. In flurothyl kindling, eight repeated flurothyl-induced generalized forebrain (clonic) seizures result in a rapid, progressive, and permanent lowering of the generalized seizure threshold in mice and in a slowly evolving increase in the percentage of animals expressing forebrain–brain stem (clonic–tonic) seizures when reexposed to flurothyl following a 2- to 4-week stimulation-free period. Therefore, flurothyl kindling serves as an excellent model for evaluating mechanisms of generalized seizure threshold and seizure propagation. To investigate this relationship between hippocampal mitotic activity and epileptogenesis, mice were given brain irradiation, focused mainly on the hippocampus, bilaterally, and were exposed to the flurothyl kindling model of epileptogenesis. Brain irradiation virtually eliminated all basal and seizure-induced mitotic activity in the hippocampal dentate gyrus of mice. In addition, animals that underwent irradiation and flurothyl kindling did not differ from control mice on measures of seizure threshold (threshold induction and maintenance) and seizure phenotype. Overall, these results suggest that seizure-induced increases in mitotic activity in the hippocampal dentate gyrus are not directly related to the processes that underlie the shift in behavioral seizure phenotype or in either the induction or the maintenance of lowered seizure threshold that is observed in this flurothyl model of epileptogenesis.

Increased mitotic activity in the dentate gyrus of the hippocampus of adult C57BL/6J mice exposed to the flurothyl kindling model of epileptogenesis

Repeated flurothyl-induced generalized forebrain seizures result in a progressive and permanent lowering of the generalized seizure threshold in mice and an increase in the percentage of animals expressing forebrain–brainstem seizures, when rechallenged with flurothyl, after a stimulation-free period. Since this seizure paradigm serves as an excellent model for examining changes in seizure threshold and seizure propagation, we were interested in examining mitotic activity in hippocampal progenitors following flurothyl-induced epileptogenesis. In the present studies, we investigated (1) the effect of one or eight flurothyl-induced seizures on mitotic activity in the hippocampal dentate gyrus of adult mice measured by 5-bromo-2′-deoxyuridine incorporation, (2) the time course of change in hippocampal mitotic activity, (3) the cellular phenotype of these mitotically active cells, and (4) the relationship of changes in mitotic activity to changes in seizure threshold and phenotype. Significant increases in hippocampal mitotic activity were observed in mice exposed to either one or eight flurothyl-induced seizures. Increases were observed at 1 and 3 days following one seizure, and at 0, 1, 3, and 7 days following eight seizures. Confocal analyses, using neuronal and glial markers, suggest that the majority of these mitotic cells are neurons. In addition, no correlation was observed between hippocampal mitotic activity and the final seizure type that animals expressed following incubation and flurothyl retest. A significant correlation was observed between hippocampal mitotic activity and seizure threshold in flurothyl-kindled mice. Overall, these results indicate that both one and eight flurothyl-induced seizures are potent inducers of hippocampal neurogenesis in adult mice. Results further suggest that the increases in hippocampal neurogenesis are not directly related to the processes that underlie the shift in behavioral seizure phenotype, but may be involved in either the establishment or the maintenance of seizure threshold in this flurothyl model of epileptogenesis.

Behavioral and metabolic features of repetitive seizures in immature and mature rats

Seizure incidence varies significantly with age, with seizure susceptibility particularly high during the first few years of life. Of significant concern is what effects do brief, repetitive seizures have on the developing brain. We approached this issue by examining the change in seizure threshold, and related markers of neuronal activity and metabolic activity (c-fos mRNA and 2-deoxyglucose [2DG]), as a function of repetitive seizure episodes in immature and mature rats. Starting on postnatal day 15 (P15) (immature) or P60 (adult) rats were given two flurothyl seizures a day for 5 days (nine or ten seizures). The seizure latency profile, our measure of threshold, in immature versus adult rats across the 5-day testing period was different. In immature rats, threshold for the second seizure on each day was significantly lower than for the first seizure, suggesting that there was little refractoriness after the first seizure of the day. In contrast, the mature animal had a significantly longer threshold latency to the second seizure for the first 3 days of testing. The immature animal was also more likely than the adult to exhibit tonic extension as a feature of the first seizure of the day. Following repetitive seizures, more regions of the CNS showed c-fos mRNA expression in the immature animal than adults, suggesting that repetitive seizures in the immature animal activated a greater percentage of the brain. Compared with the effects of a single seizure, repetitive seizures resulted in less 2DG labeling in most regions of the brain (except the hippocampus); in the immature brain this difference was more distinct than in adults. The consequences of repetitive seizures in the immature animal results in distinctly different seizure behavior and neuronal activity pattern (c-fos expression) than that observed in the mature animal.