Susceptibility to epilepsy after traumatic brain injury is associated with preexistent gut microbiome profile.

OBJECTIVE: We examined whether posttraumatic epilepsy (PTE) is associated with measurable perturbations in gut microbiome. METHODS: Adult Sprague Dawley rats were subjected to lateral fluid percussion injury (LFPI). PTE was examined 7 months after LFPI, during 4-week continuous video-electroencephalographic monitoring. 16S ribosomal RNA gene sequencing was performed in fecal samples collected before LFPI/sham-LFPI and 1 week, 1 month, and 7 months thereafter. Longitudinal analyses of alpha diversity, beta diversity, and differential microbial abundance were performed. Short-chain fatty acids (SCFAs) were measured in fecal samples collected before LFPI by liquid chromatography with tandem mass spectrometry. RESULTS: Alpha diversity changed over time in both LFPI and sham-LFPI subjects; no association was observed between alpha diversity and LFPI, the severity of post-LFPI neuromotor impairments, and PTE. LFPI produced significant changes in beta diversity and selective changes in microbial abundances associated with the severity of neuromotor impairments. No association between LFPI-dependent microbial perturbations and PTE was detected. PTE was associated with beta diversity irrespective of timepoint vis-à-vis LFPI, including at baseline. Preexistent fecal microbial abundances of four amplicon sequence variants belonging to the Lachnospiraceae family (three enriched and one depleted) predicted the risk of PTE, with area under the curve (AUC) of .73. Global SCFA content was associated with the increased risk of PTE, with AUC of .722, and with 2-methylbutyric (depleted), valeric (depleted), isobutyric (enriched), and isovaleric (enriched) acids being the most important factors (AUC = .717). When the analyses of baseline microbial and SCFA compositions were combined, AUC to predict PTE increased to .78. SIGNIFICANCE: Whereas LFPI produces no perturbations in the gut microbiome that are associated with PTE, the risk of PTE can be stratified based on preexistent microbial abundances and SCFA content.

Modification of post-traumatic epilepsy by fecal microbiota transfer.

It has been well established that traumatic brain injury (TBI) modifies the composition of gut microbiome. Epilepsy, which represents one of the common sequelae of TBI, has been associated with dysbiosis. Earlier study showed that the risk of post-traumatic epilepsy (PTE) after lateral fluid percussion injury (LFPI) in rats can be stratified based on pre-existing (i.e., pre-TBI) gut microbiome profile. In the present study, we examined whether fecal microbiota transfer (FMT) from naïve rats with different prospective histories of PTE would affect the trajectory of PTE in recipients. Fecal samples were collected from naïve adult male Sprague-Dawley rats, followed by LFPI. Seven months later, upon four weeks of vide-EEG monitoring (vEEG), the rats were categorized as those with and without PTE. Recipients were subjected to LFPI, followed by FMT from donors with and without impending PTE. Control groups included auto-FMT and no-FMT subjects. Seven month after LFPI, recipients underwent four-week vEEG to detect spontaneous seizures. After completing vEEG, rats of all groups underwent kindling of basolateral amygdala. Fecal microbiota transfer from donors with impending PTE exerted mild-to-moderate pro-epileptic effects in recipients, evident as marginal increase in multiple spontaneous seizure incidence, and facilitation of kindling. Analysis of fecal samples in selected recipients and their respective donors confirmed that FMT modified microbiota in recipients along the donors' lines, albeit without full microbiome conversion. The findings provide further evidence that gut microbiome may actively modulate the susceptibility to epilepsy.

Disruption of intestinal barrier and endotoxemia after traumatic brain injury: Implications for post-traumatic epilepsy.

OBJECTIVE: Traumatic brain injury (TBI) may lead to the disruption of the intestinal barrier (IB), and to the escape of products of commensal gut bacteria, including lipopolysaccharide (LPS), into the bloodstream. We examined whether lateral fluid percussion injury (LFPI) and post-traumatic epilepsy (PTE) are associated with the increased intestinal permeability and endotoxemia, and whether these events in turn are associated with PTE. METHODS: LFPI was delivered to adult male Sprague-Dawley rats. Before, 1 week, and 7 months after LFPI, the IB permeability was examined by measuring plasma concentration of fluorescein isothiocyanate-labeled dextran (FD4) upon its enteral administration. Plasma LPS concentration was measured in the same animals, using enzyme-linked immunosorbent assay. PTE was examined 7 months after LFPI, with use of video-EEG (electroencephalography) monitoring. RESULTS: One week after LFPI, the IB disruption was detected in 14 of 17 and endotoxemia - in 10 of 17 rats, with a strong positive correlation between FD4 and LPS levels, and between plasma levels of each of the analytes and the severity of neuromotor deficit. Seven months after LFPI, IB disruption was detected in 13 of 15 and endotoxemia in 8 of 15 rats, with a strong positive correlation between plasma levels of the two analytes. Five of 15 LFPI rats developed PTE. Plasma levels of both FD4 and LPS were significantly higher in animals with PTE than among the animals without PTE. The analysis of seven rats, which were examined repeatedly at 1 week and at 7 months, confirmed that late IB disruption and endotoxemia were not due to lingering of impairments occurring shortly after LFPI. SIGNIFICANCE: LFPI leads to early and remote disruption of IB and a secondary endotoxemia. Early and late perturbations may occur in different subjects. Early changes reflect the severity of acute post-traumatic motor dysfunction, whereas late changes are associated with PTE.

Inherent vulnerabilities in monoaminergic pathways predict the emergence of depressive impairments in an animal model of chronic epilepsy.

The objective was to determine whether the depression comorbid with epilepsy could be predicted based on inherent premorbid patterns of monoaminergic transmission. In male Wistar rats, despair-like and anhedonia-like behaviors were examined using forced swimming and taste preference tests, respectively. Serotonergic raphe nucleus (RN)-prefrontal cortex (PFC) and dopaminergic ventral tegmental area (VTA)-nucleus accumbens (NAcc) pathways were interrogated by fast scan cyclic voltammetry (FSCV). The assays were performed before and 2 months after pilocarpine status epilepticus. In a subset of naive rats, FSCV, coupled with the intensity-dependent stimulation paradigm, detected specific deviations in each pathway (six rats for RN-PFC and seven rats for VTA-NAcc, with overlap in two, of 19 total subjects) in the absence of behavioral impairments. During epilepsy, animals with preexisting deviations in RN-PFC invariably developed despair, and rats with deviations in VTA-NAcc developed anhedonia. Serotonergic and dopaminergic pathways, respectively, showed signs of explicit deterioration. We suggest that epilepsy triggers decompensations in the already vulnerable depression-relevant neuronal circuits, which culminate in depression. The established connection between the identified specific signatures in monoamine transmission in naive rats and specific symptoms of epilepsy-associated depression may help in understanding causes of comorbidity and in developing its early biomarkers.

Regulation of kindling epileptogenesis by hippocampal Toll-like receptors 2.

This study examined whether Toll-like receptors 2 (TLR2) contribute to rapid kindling epileptogenesis. A TLR2 agonist, lipoteichoic acid (LTA), LTA antibody (LTA-A), or normal saline (control) was administered daily over 3 consecutive days, unilaterally into ventral hippocampus of adult male Wistar rats. Thirty minutes after the last injection, the animals were subjected to a rapid kindling procedure. The ictogenesis was gauged by comparing afterdischarge threshold (ADT) and afterdischarge duration (ADD) before the treatments, after the treatments prior to kindling, and 24 h after kindling. Kindling progression and retention were analyzed using video recording. The results showed that before kindling, LTA produced an ADT reduction. Neither LTA nor LTA-A affected baseline ADD. On kindling progression, LTA accelerated occurrence of generalized seizures, whereas LTA-A delayed this effect. Treatment with LTA-A reduced the number of secondary generalized complex partial seizures. Twenty-four hours after kindling, the rats of both the saline and LTA groups showed increased hippocampal excitability as compared with prekindling parameters. Administration of LTA-A prevented kindling-induced increase of hippocampal excitability. Immunostaining revealed that LTA-A attenuated the inflammatory response produced by seizures. These findings suggest that the activation of TLR2 in the hippocampus may facilitate limbic epileptogenesis.

Kindling epileptogenesis and panic-like behavior: Their bidirectional connection and contribution to epilepsy-associated depression.

Anxiety is one of the most common comorbidities of epilepsy, which has major detrimental effects on the quality of life. Generalized anxiety disorder (GAD) associated with epilepsy has been receiving most attention. However, several other forms of anxiety reportedly present in patients with epilepsy, including panic disorder (PD). In this study, using an animal model of limbic epilepsy, we examined the interplay between epilepsy and panic-like behavior (PLB). Further, considering the high degree of comorbidity between depression on the one hand, and both epilepsy and PD on the other hand, we studied whether and how the presence of PLB in animals with epilepsy would affect their performance in depression-relevant tests. Fifty-day-old male Wistar rats were subjected to repeated alternating electrical stimulations of the basolateral amygdala (BLA) to induce kindling of limbic seizures, and the dorsal periaqueductal gray (DPAG) to induce panic-like episodes. Seizure susceptibility and panic reaction threshold were examined before the first and 24h after the last stimulation. At the end of the stimulations, the rats were examined in depression-relevant tests: saccharin preference test (SPT) for anhedonia and forced swimming test (FST) for despair/hopelessness. With regard to kindling, BLA+DPAG stimulation induced more profound increase of seizure susceptibility than BLA stimulation alone (evident as the reduction of the afterdischarge threshold and the increase of the afterdischarge duration). With regard to PLB, the BLA+DPAG stimulation exacerbated the severity of panic-like episodes, as compared with the DPAG stimulation alone. Basolateral amygdala stimulation alone had no effects on panic-like reactions, and DPAG stimulation alone did not modify kindling epileptogenesis. Combined stimulation of BLA and DPAG induced depressive-like behavioral impairments. This is the first experimental study showing bidirectional, mutually exacerbating effect of epilepsy and PLB, and the precipitation of depressive-like state by the epilepsy-PLB comorbidity.

Effects of selective serotonin and norepinephrine reuptake inhibitors on depressive- and impulsive-like behaviors and on monoamine transmission in experimental temporal lobe epilepsy.

OBJECTIVE: Examine therapeutic potential of a selective serotonin reuptake inhibitor (SSRI) and a norepinephrine reuptake inhibitor (NERI) in an animal model of comorbidity between epilepsy, depression-like, and impulsive-like impairments. METHODS: Epilepsy was induced in male Wistar rats by LiCl and pilocarpine. An SSRI fluoxetine (FLX), and an NERI reboxetine (RBX) were administered either alone or as a combination over 1 week. Depressive-like and impulsive-like behaviors were examined using the forced swim test. Fast scan cyclic voltammetry was used to analyze serotonergic transmission in the raphe nucleus (RN)-prefrontal cortex (PFC) pathway, and noradrenergic transmission in locus coeruleus (LC)-PFC, and LC-RN projections. Monoamine levels in PFC were measured using high-performance liquid chromatography (HPLC). Functional capacities of 5-HT1A receptors and α2A adrenoreceptors in PFC were analyzed by autoradiography. RESULTS: Epileptic rats showed behavioral signs of depression and hyperimpulsivity, suppressed serotonergic and noradrenergic tones, decreased levels of serotonin (5-HT), and norepinephrine (NE); 5-HT1A receptor and α2A adrenoreceptors functions remained intact. FLX failed to improve behavioral deficits, but effectively raised 5-HT level and marginally improved RN-PFC serotonergic transmission. RBX reversed impulsive-like behavior, normalized content of NE and noradrenergic tone in LC-PFC and LC-RN. FLX-RBX combination fully reversed depressive-like behavior, and normalized RN-PFC serotonergic transmission. None of the treatment modified the function of 5-HT and NE receptors. SIGNIFICANCE: Depressive- and impulsive-like behaviors in the pilocarpine model of epilepsy stem respectively from dysfunctions of serotonergic and noradrenergic ascending pathways. At the same time, epilepsy-associated depression is SSRI resistant. The finding that an SSRI-NERI combination exerts antidepressant effect, along with RBX-induced improvement of LC-RN noradrenergic transmission point toward the involvement of LC-RN noradrenergic input in enabling therapeutic potential of FLX. Medications that improve serotonergic and noradrenergic transmission, such as serotonin-norepinephrine reuptake inhibitors may be effective in treating epilepsy-associated SSRI-resistant depression, as well as concurrent depression and attention-deficit/hyperactivity disorder (ADHD).

Cytokine-dependent bidirectional connection between impaired social behavior and susceptibility to seizures associated with maternal immune activation in mice.

Maternal immune activation (MIA) results in the development of autism in the offspring via hyperactivation of IL-6 signaling. Furthermore, experimental studies showed that the MIA-associated activation of interleukin-1ß (IL-1ß) concurrently with IL-6 increases the rate and the severity of hippocampal kindling in mice, thus, offering an explanation for autism-epilepsy comorbidity. We examined whether epileptic phenotype triggered by prenatal exposure to IL-6 and IL-1ß combination is restricted to kindling or whether it is reproducible in another model of epilepsy, whereby spontaneous seizures develop following kainic acid (KA)-induced status epilepticus. We also examined whether in mice prenatally exposed to IL-6 and IL-6+IL-1ß, the presence of spontaneous seizures would exacerbate autism-like features. Between days 12 and 16 of pregnancy, C57BL/6J mice received daily injections of IL-6, IL-1ß, or IL-6+IL-1ß combination. At postnatal day 40, male offspring were examined for the presence of social behavioral deficit, and status epilepticus was induced by intrahippocampal KA injection. After 6weeks of monitoring for spontaneous seizures, sociability was tested again. Both IL-6 and IL-6+IL-1ß offspring presented with social behavioral deficit. Prenatal exposure to IL-6 alleviated, while such exposure to IL-6+IL-1ß exacerbated, the severity of KA-induced epilepsy. Increased severity of epilepsy in the IL-6+IL-1ß mice correlated with the improvement of autism-like behavior. We conclude that complex and not necessarily agonistic relationships exist between epileptic and autism-like phenotypes in an animal model of MIA coupled with KA-induced epilepsy and that the nature of these relationships depends on components of MIA involved.

Maternal immune activation promotes hippocampal kindling epileptogenesis in mice.

OBJECTIVE: Maternal immune activation (MIA) triggered by infections has been identified as a cause of autism in offspring. Considering the involvement of perturbations in innate immunity in epilepsy, we examined whether MIA represents a risk factor for epilepsy as well. The role of specific MIA components interleukin (IL)-6 and IL-1ß was also addressed. METHODS: MIA was induced in C57BL/6 mice by polyinosinic-polycytidylic acid (PIC) injected during embryonic days 12 to 16. Beginning from postnatal day 40, the propensity of the offspring to epilepsy was examined using hippocampal kindling; autismlike behavior was studied using the sociability test. The involvement of IL-6 and IL-1ß in PIC-induced effects was studied by the coadministration of the cytokine antibodies with PIC, and by delivering recombinant cytokines in lieu of PIC. RESULTS: The offspring of PIC-exposed mice exhibited increased hippocampal excitability, accelerated kindling rate, prolonged increase of seizure susceptibility after kindling, and diminished sociability. Epileptic impairments were abolished by antibodies to IL-6 or IL-1ß. Neither of the recombinant cytokines alone increased the propensity to seizures; however, when combined, they produced effects similar to those induced by PIC. PIC-induced behavioral deficits were abolished by IL-6 antibodies and were mimicked by recombinant IL-6; IL-1ß was not involved. INTERPRETATION: In addition to confirming the previously established critical role of IL-6 in the development of autismlike behavior following MIA, the present study shows that concurrent involvement of IL-6 and IL-1ß is required for priming the offspring for epilepsy. These data shed light on mechanisms of comorbidity between autism and epilepsy.

Behavioral impairments in rats with chronic epilepsy suggest comorbidity between epilepsy and attention deficit/hyperactivity disorder.

Attention deficit/hyperactivity disorder (ADHD) is encountered among patients with epilepsy at a significantly higher rate than in the general population. Mechanisms of epilepsy-ADHD comorbidity remain largely unknown. We investigated whether a model of chronic epilepsy in rats produces signs of ADHD, and thus, whether it can be used for studying mechanisms of this comorbidity. Epilepsy was induced in male Wistar rats via pilocarpine status epilepticus. Half of the animals exhibited chronic ADHD-like abnormalities, particularly increased impulsivity and diminished attention in the lateralized reaction-time task. These impairments correlated with the suppressed noradrenergic transmission in locus coeruleus outputs. The other half of animals exhibited depressive behavior in the forced swimming test congruently with the diminished serotonergic transmission in raphe nucleus outputs. Attention deficit/hyperactivity disorder and depressive behavior appeared mutually exclusive. Therefore, the pilocarpine model of epilepsy affords a system for reproducing and studying mechanisms of comorbidity between epilepsy and both ADHD and/or depression.

Structural basis for substrate specificity and mechanism of N-acetyl-D-neuraminic acid lyase from Pasteurella multocida.

N-Acetylneuraminate lyases (NALs) or sialic acid aldolases catalyze the reversible aldol cleavage of N-acetylneuraminic acid (Neu5Ac, the most common form of sialic acid) to form pyruvate and N-acetyl-d-mannosamine. Although equilibrium favors sialic acid cleavage, these enzymes can be used for high-yield chemoenzymatic synthesis of structurally diverse sialic acids in the presence of excess pyruvate. Engineering these enzymes to synthesize structurally modified natural sialic acids and their non-natural derivatives holds promise in creating novel therapeutic agents. Atomic-resolution structures of these enzymes will greatly assist in guiding mutagenic and modeling studies to engineer enzymes with altered substrate specificity. We report here the crystal structures of wild-type Pasteurella multocida N-acetylneuraminate lyase and its K164A mutant. Like other bacterial lyases, it assembles into a homotetramer with each monomer folding into a classic (ß/α)8 TIM barrel. Two wild-type structures were determined, in the absence of substrates, and trapped in a Schiff base intermediate between Lys164 and pyruvate, respectively. Three structures of the K164A variant were determined: one in the absence of substrates and two binary complexes with N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). Both sialic acids bind to the active site in the open-chain ketone form of the monosaccharide. The structures reveal that every hydroxyl group of the linear sugars makes hydrogen bond interactions with the enzyme, and the residues that determine specificity were identified. Additionally, the structures provide some clues for explaining the natural discrimination of sialic acid substrates between the P. multocida and Escherichia coli NALs.

Neuroprotective and antiepileptogenic effects of combination of anti-inflammatory drugs in the immature brain.

BACKGROUND: Inflammatory signaling elicited by prolonged seizures can be contributory to neuronal injury as well as adverse plasticity leading to the development of spontaneous recurrent seizures (epilepsy) and associated co-morbidities. In this study, developing rat pups were subjected to lithium-pilocarpine status epilepticus (SE) at 2 and 3 weeks of age to study the effect of anti-inflammatory drugs (AID) on SE-induced hippocampal injury and the development of spontaneous seizures. FINDINGS: We selected AIDs directed against interleukin-1 receptors (IL-1ra), a cyclooxygenase-2 (COX-2) inhibitor (CAY 10404), and an antagonist of microglia activation of caspase-1 (minocycline). Acute injury after SE was studied in the 2-week-old rats 24 h after SE. Development of recurrent spontaneous seizures was studied in 3-week-old rats subjected to SE 4 months after the initial insult.None of those AIDs were effective in attenuating CA1 injury in the 2-week-old pups or in limiting the development of spontaneous seizures in 3-week-old pups when administered individually. When empiric binary combinations of these drugs were tried, the combined targeting of IL-1r and COX-2 resulted in attenuation of acute CA1 injury, as determined 24 h after SE, in those animals. The same combination administered for 10 days following SE in 3-week-old rats, reduced the development of spontaneous recurrent seizures and limited the extent of mossy fiber sprouting. CONCLUSIONS: Deployment of an empirically designed 'drug cocktail' targeting multiple inflammatory signaling pathways for a limited duration after an initial insult like SE may provide a practical approach to neuroprotection and anti-epileptogenic therapy.

Diversity of kindling of limbic seizures after lateral fluid percussion injury in the rat.

Lateral fluid percussion injury (LFPI) in rats is used to model post-traumatic epilepsy (PTE), with spontaneous seizures occurring in up to ½ of the subjects. Using the kindling paradigm, we examined whether animals without detectable seizures had an altered seizure susceptibility. Male Sprague Dawley rats were subjected to LFPI. Seven-nine months later, spontaneous seizures were monitored for two weeks. Afterward, the animals underwent kindling of basolateral amygdala. For kindling outcomes, the animals were categorized based on the 95% confidence intervals of mean number trials to kindling (ie 3 consecutive stage 4-5 seizures). Spontaneous seizures were detected in 7 out of 24 rats. There was no correlation between the severity of LFPI and either baseline afterdischarge properties, or kindling rates. Six LFPI rats kindled at a rate comparable to those in sham-LFPI (n = 10) and in naïve (n = 7) subjects. Ten LFPI rats kindled faster and 8-slower than controls. None of slow-kindling rats had spontaneous seizures during the prekindling monitoring. During the same period, six fast-kindling and three normal-kindling rats had been seizure-free. Thus, kindling reveals a diversity to seizure susceptibility after LFPI beyond an overt seizure symptomatology, ranging from the increased susceptibility to the increased resistance.

Inflammation enhances epileptogenesis in the developing rat brain.

In many experimental systems, proinflammatory stimuli exhibit proconvulsant properties. There are also accumulating data suggesting that inflammation may contribute to epileptogenesis in experimental models as well as in humans. Using two different models (Lithium-pilocarpine induced-status epilepticus (SE) and rapid kindling), we address this issue in the developing brain. Using P14 Wistar rat pups, we showed that inflammation induced by LPS results, after SE, into a more severe disease in adulthood. The main histological feature was an active gliosis that was observed only when inflammation and SE was combined. The use of a kindling model at P14, a model where seizure progress without any neurodegeneration, permits to show that systemic inflammation is responsible of an enhancement of epileptogenesis. The role of inflammation should be further explored in immature brain to identify therapeutic targets that may be relevant to clinical practice where the association of inflammation and epileptic events is common.

Comorbidity between epilepsy and depression: role of hippocampal interleukin-1beta.

Depression is a frequent comorbidity of temporal lobe epilepsy (TLE); however, its mechanisms remain poorly understood and effective therapies are lacking. Augmentation of hippocampal interleukin-1beta (IL-1beta) signaling may be a mechanistic factor of both TLE and clinical depression. We examined whether pharmacological blockade of hippocampal interleukin-1 receptor exerts antidepressant effects in an animal model of comorbidity between TLE and depression, which developed in Wistar rats following pilocarpine status epilepticus (SE). In post-SE animals, depression-like state was characterized by behavioral equivalents of anhedonia and despair; dysregulation of the hypothalamo-pituitary-adrenocortical axis; compromised raphe-hippocampal serotonergic transmission. Two-week long bilateral intrahippocampal infusion of human recombinant Interleukin-1 receptor antagonist (IL-1ra) improved all of the examined depressive impairments, without modifying spontaneous seizure frequency and without affecting normal parameters in naïve rats. These findings implicate hippocampal IL-1beta in epilepsy-associated depression and provide a rationale for the introduction of IL-1beta blockers in the treatment of depression in TLE.

Hypoxic-ischemic brain injury exacerbates neuronal apoptosis and precipitates spontaneous seizures in glucose transporter isoform 3 heterozygous null mice.

We examined the effects of 45-min hypoxia (FiO(2) 0.08; Hx) vs. normoxia (FiO(2) 0.21; Nx) on the ipsilateral (Ipsi) and contralateral (Ctrl) sides of the brain in neuronal glucose transporter isoform 3 (Glut3) heterozygous null mice (glut3(+/-)) and their wild-type littermates (WT), undergoing unilateral carotid artery ligation. Glut3(+/-) mice, under Nx, demonstrated a compensatory increase in blood-brain barrier/glial Glut1 protein concentration and a concomitant increase in neuronal nitric oxide synthase (nNOS) enzyme activity and Bax protein, with a decrease in procaspase 3 protein (P < 0.05 each). After Hx, reoxygenation in FiO(2) of 0.21 led to no comparable adaptive up-regulation of the ipsilateral brain Glut3 or Glut1 protein at 4 hr and Glut1 at 24 hr in glut3(+/-) vs. WT. These brain Glut changes in glut3(+/-) but not WT mice were associated with an increase in proapoptotic Bax protein and caspase-3 enzyme activity (P < 0.01 each) and a decline in the antiapoptotic Bcl-2 and procaspase-3 proteins (P < 0.05 each). Glut3(+/-) mice after Hx demonstrated TUNEL-positive neurons with nuclear pyknosis in most ipsilateral (hypoxic-ischemia) brain regions. A subset (∼55%) of glut3(+/-) mice developed spontaneous seizures after hypoxic-ischemia, confirmed by electroencephalography, but the WT mice remained seizure-free. Pentylenetetrazole testing demonstrated an increased occurrence of longer lasting clinical seizures at a lower threshold in glut3(+/-) vs. WT mice, with no detectable differences in monamine neurotransmitters. We conclude that hypoxic-ischemic brain injury in glut3(+/-) mice exacerbates cellular apoptosis and necrosis and precipitates spontaneous seizures.

Inflammation induced by LPS enhances epileptogenesis in immature rat and may be partially reversed by IL1RA.

Inflammatory signaling in the central nervous system (CNS) has been shown to exacerbate both seizure activity and seizure-induced neuronal injury. However, it has not been firmly established whether neurodegeneration is a prerequisite of proconvulsant effect of neuroinflammation, or whether the latter may facilitate seizures without involving neuronal injury. We examined effects of inflammation in the rapid kindling model, where seizure progression occurs in the absence of neurodegeneration. P14 male Wistar rats were subjected to a rapid kindling procedure: 60 electrical stimulations of the hippocampus delivered every 5 min at the current that had been established to induce afterdischarge. Lipopolysaccharide (LPS) was injected (50 microg/kg, i.p., 2 h prior to the rapid kindling protocol [RKP]); IL-1Ra was injected (25 mg/kg, i.p., 2 h prior to the RKP). The effects of treatments were examined on baseline hippocampal excitability, on the progression of rapid kindling, and on the retention of rapid kindling. LPS increased baseline hippocampal excitability, evident as the decrease of hippocampal ADT. LPS also increased kindling progression. Twenty-four hours after the completion of kindling procedure, LPS-treated animals exhibited increased excitability as compared with saline-treated kindling controls. The kindling progression was blocked by IL1RA when given in combination with LPS. IL1RA was able to reverse the effect of LPS on afterdischarge duration (ADD) while IL1RA alone decreased ADT. We showed that inflammation provoked by LPS enhanced rapid kindling epileptogenesis in immature rat brains. IL1RA was also able to mitigate this augmentation of epileptogenesis enhanced by LPS.

Comorbidity between epilepsy and depression: experimental evidence for the involvement of serotonergic, glucocorticoid, and neuroinflammatory mechanisms.

Depression represents one of the most common comorbidities of temporal lobe epilepsy (TLE), and has profound negative impact on the quality of life of patients with TLE. However, causes and mechanisms of depression in TLE remain poorly understood, and effective therapies are lacking. We examined whether a commonly used model of TLE in rats could be used as a model of comorbidity between epilepsy and depression suitable for both mechanistic studies and for the development of mechanism-based antidepressant therapies. We established that animals that had been subjected to lithium chloride and pilocarpine status epilepticus (SE) and developed spontaneous recurrent seizures, exhibited a set of impairments congruent with a depressive state: behavioral equivalents of anhedonia and despair, dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis, and compromised raphe-hippocampal serotonergic transmission. Pharmacologic studies have suggested that depressive impairments following SE develop as a result of enhanced interleukin-1beta signaling in the hippocampus, which leads to depression via inducing perturbations in the HPA axis and subsequent deficit in the raphe-hippocampal serotonergic transmission.

Evaluation of development-specific targets for antiepileptogenic therapy using rapid kindling.

We used the method of rapid hippocampal kindling to assess the potential antiepileptogenic efficacy of a number of anticonvulsant medications. This method afforded a higher throughput than methods based on traditional kindling or post-status epilepticus models of epileptogenesis. This "compressed epileptogenesis" model also permitted the study of age-dependent pharmacologic targets, and distinguished among antiepileptic drugs (AEDs) on the basis of their age-specific antiepileptogenic efficacy. We found retigabine to be the most effective anticonvulsant therapy during early development. Topiramate seemed most effective further along development, whereas some drugs did not demonstrate an age-specific effect. The method also reproduced some of the paradoxical pharmacologic findings previously shown with lamotrigine. Although the utility of this model for screening the antiepileptogenic therapies requires further validation, it introduces the ability to undertake development-specific testing and a more rapid throughput than conventional methods.

Elevated plasma corticosterone level and depressive behavior in experimental temporal lobe epilepsy.

Depression is frequently reported in epilepsy patients; however, mechanisms of co-morbidity between epilepsy and depression are poorly understood. An important mechanism of depression is disinhibition within the hypothalamo-pituitary-adrenocortical (HPA) axis. We examined the functional state of the HPA axis in a rat model of co-morbidity between temporal lobe epilepsy and depression. Epilepsy was accompanied by the interictal elevation of plasma corticosterone, and by the positively combined dexamethasone/corticotropin releasing hormone test. The extent of the HPA hyperactivity was independent of recurrent seizures, but positively correlated with the severity of depressive behavior. We suggest that the observed hyperactivity of the HPA axis may underlie co-morbidity between epilepsy and depression.