Increased hippocampal T2 in a rat model of pentylenetetrazol-induced kindling correlates with seizure scores

Insights into the development of pentylenetetrazole-induced epileptic seizures from dynamic metabolomic changes

Epilepsy is often considered to be a progressive neurological disease, and the nature of this progression remains unclear. Understanding the overall and common metabolic changes of epileptic seizures can provide novel clues for their control and prevention. Herein, a chronic kindling animal model was established to obtain generalized tonic-clonic seizures via the repeated injections of pentylenetetrazole (PTZ) at subconvulsive dose. Dynamic metabolomic changes in plasma and urine from PTZ-kindled rats at the different kindling phases were explored using NMR-based metabolomics, in combination with behavioral assessment, brain neurotransmitter measurement, electroencephalography and histopathology. The increased levels of glucose, lactate, glutamate, creatine and creatinine, together with the decreased levels of pyruvate, citrate and succinate, ketone bodies, asparagine, alanine, leucine, valine and isoleucine in plasma and/or urine were involved in the development and progression of seizures. These altered metabolites reflected the pathophysiological processes including the compromised energy metabolism, the disturbed amino acid metabolism, the peripheral inflammation and changes in gut microbiota functions. NMR-based metabolomics could provide brain disease information by the dynamic plasma and urinary metabolic changes during chronic epileptic seizures, yielding classification of seizure stages and profound insights into controlling epilepsy via targeting deficient energy metabolism.

Behavioral and Brain Structural Changes in Kindled Rats Induced by Coriaria Lactone/Pentylenetetrazol

Epilepsy is a common chronic neurological disease that is characterized by spontaneous seizures. It is commonly comorbid with behavioral and mood disorders. No studies have yet examined the behavioral or structural brain changes associated with coriaria lactone (CL)-induced and pentylenetetrazol (PTZ)-induced kindlings. This study examined whether the increased seizure susceptibility induced by CL/PTZ is accompanied by behavioral impairments and aimed to identify associated structural brain changes. Kindling models were induced using CL and PTZ, with 10 rats in each group. After successful kindling, rats were subjected to brain structural imaging using T2-weighted imaging and underwent behavioral tests, namely, the open field test, water maze tasks, and contextual fear conditioning. Voxel-based morphometry was then used to identify possible brain structural changes associated with kindling and/or behaviors. Support-vector machine learning was also applied for the integrative analysis of behavioral changes and structural brain imaging. In the open field test, both the CL (P = 0.04) and PTZ groups (P = 0.002) spent more time in the central area than the control group. Only the PTZ group (50.29 ± 29.56 s) showed a freezing time that was significantly less than that of the control group (94.8 ± 41.04 s; P = 0.024, Tukey's HSD-corrected) in contextual fear conditioning, which is suggestive of impaired fear-associated learning ability. Furthermore, brain imaging analysis revealed that the gray matter volume (GMV) of the hippocampus changed in both the CL and PTZ groups when compared to control. The support-vector machine learning model indicated that the retrosplenial dysgranular and primary somatosensory cortices were associated with both of the mentioned kindling models. Furthermore, the support-vector regression model results indicated that kindling-associated GMV changes can be used to predict general exploratory activity in the open field test. In conclusion, this is the first study to report greater general exploratory activity in a CL-induced kindling model. Moreover, the general exploratory activity in the open field test can be predicted by the GMV of brain regions associated with kindling.

Investigation of Cerebral O-(2-[18F]Fluoroethyl)-L-Tyrosine Uptake in Rat Epilepsy Models

PURPOSE

A recent study reported on high, longer lasting and finally reversible cerebral uptake of O-(2-[¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET) induced by epileptic activity. Therefore, we examined cerebral [¹⁸F]FET uptake in two chemically induced rat epilepsy models and in patients with focal epilepsy to further investigate whether this phenomenon represents a major pitfall in brain tumor diagnostics and whether [¹⁸F]FET may be a potential marker to localize epileptic foci.

PROCEDURES

Five rats underwent kainic acid titration to exhibit 3 to 3.5 h of class IV-V motor seizures (status epilepticus, SE). Rats underwent 4× [¹⁸F]FET PET and 4× MRI on the following 25 days. Six rats underwent kindling with pentylenetetrazol (PTZ) 3 to 8×/week over 10 weeks, and hence, seizures increased from class I to class IV. [¹⁸F]FET PET and MRI were performed regularly on days with and without seizures. Four rats served as healthy controls. Additionally, five patients with focal epilepsy underwent [¹⁸F]FET PET within 12 days after the last documented seizure.

RESULTS

No abnormalities in [¹⁸F]FET PET or MRI were detected in the kindling model. The SE model showed significantly decreased [¹⁸F]FET uptake 3 days after SE in all examined brain regions, and especially in the amygdala region, which normalized within 2 weeks. Corresponding signal alterations in T₂-weighted MRI were noted in the amygdala and hippocampus, which recovered 24 days post-SE. No abnormality of cerebral [¹⁸F]FET uptake was noted in the epilepsy patients.

CONCLUSIONS

There was no evidence for increased cerebral [¹⁸F]FET uptake after epileptic seizures neither in the rat models nor in patients. The SE model even showed decreased [¹⁸F]FET uptake throughout the brain. We conclude that epileptic seizures per se do not cause a longer lasting increased [¹⁸F]FET accumulation and are unlikely to be a major cause of pitfall for brain tumor diagnostics.

Deep Brain Stimulation Increases Seizure Threshold by Altering REM Sleep and Delta Powers During NREM Sleep

We previously demonstrated that seizure occurrences at different zeitgeber times alter sleep and circadian rhythm differently. On the other hand, the synchronized delta wave of electroencephalogram (EEG) during non-rapid eye movement (NREM) sleep facilitates seizure, while the desynchronized EEG of rapid eye movement (REM) sleep suppresses it. We also elucidated that unilateral deep brain stimulation (DBS) of the anterior nucleus of thalamus (ANT) suppresses seizure recurrence. In the present study, we intraperitoneally injected pentylenetetrazol (PTZ, 40 mg/kg) for 14 consecutive days (PTZ kindling) to induce spontaneous seizure in rats, and a 30-min (delivered 10 min before each PTZ injection) or a 3-h DBS of unilateral ANT (delivered 1 h before each PTZ injection) was applied to suppress seizure. The frequency of DBS stimulation was 200 Hz and the electrical current consisted of biphasic square pulses with 50-μA intensity, 100-μs pulse width, and 4.1-ms stimulation interval. Our results found that PTZ-induced spontaneous seizure did not cause a significant change in the quantity of NREM sleep but suppressed the amount of REM sleep. Unilateral ANT DBS prolonged the onset latency of ictal seizure, decreased the spontaneous seizure duration, and increased the survival rate but did not change the amplitude of epileptiform EEGs during ictal period. Unilateral ANT DBS did not significantly alter NREM sleep but increased the amount of REM sleep. An analysis of the spectrograms of fast Fourier transform indicated that the intensities of all frequencies were enhanced during the PTZ-induced ictal period and the subsequent spontaneous seizure. Thirty minutes of unilateral ANT DBS suppressed the augmentation of low-frequency (<10 Hz) intensities during the spontaneous seizure induced by PTZ kindling. We further found that consecutive injections of PTZ progressively increased the enhancement of the delta powers during NREM sleep, whereas unilateral ANT DBS inhibited this progressive enhancement. It was also noticed that 30 min of ANT DBS exhibited a better efficacy in epilepsy suppression than 3 h of ANT DBS. These results elucidated that unilateral ANT DBS enhanced the seizure threshold by increasing the amount of REM sleep and decreasing the progressive enhancement of delta power during NREM sleep to suppress spontaneous seizure recurrences in PTZ kindling-induced epileptic rats.

Comparison of behavioral, neuroprotective, and proinflammatory cytokine modulating effects exercised by (+)-cis-EC and (-)-cis-EC stereoisomers in a PTZ-induced kindling test in mice

Epoxy-carvone (EC) has chiral centers that allow generation of stereoisomers, including (+)-cis-EC and (-)-cis-EC, whose effects in the kindling tests have never been studied. Accordingly, this study aims to comparatively investigate the effect of stereoisomers (+)-cis-epoxy-carvone and (-)-cis-epoxy-carvone on behavioral changes measured in scores, in the levels of cytokines (IL-1β, IL-6, and TNFα) and neuronal protection in the face of continuous treatment with pentylenetetrazol. Swiss mice were divided into five groups (n = 10), receiving vehicle, (+) - cis-EC, (-) - cis-EC (both at the dose of 30 mg/kg), and diazepam (4 mg/kg). Thirty minutes after the respective treatment was administered to the animals one subconvulsive dose of PTZ (35 mg/kg). Seven subconvulsives treatments were made on alternate days, in which each treatment several parameters were recorded. In the eighth treatment, the animals receiving the highest dose of PTZ (75 mg/kg) and were sacrificed for quantification of cytokines and histopathologic analysis. All drugs were administered by intraperitoneal route. In the kindling test, (+)-cis-EC and (-)-cis-EC reduced the average scores. The stereoisomer (+)-cis-EC decreased levels of proinflammatory cytokines IL-1β, IL-6, and TNFα, whereas comparatively (-)-cis-EC did not reduce IL-1β levels. Histopathological analysis of the mice hippocampi undergoing this methodology showed neural protection for treated with (+)-cis-EC. The results suggest that the anticonvulsant effect of (+)-cis-EC possibly takes place due to reduction of proinflammatory cytokines involved in the epileptogenic process, besides neuronal protection, yet further investigation of the mechanisms involved is required.

[The influence of growing seizure readiness on the autonomic regulation of the heart]

AIM

To study the functional state of the heart in a progressive increase of seizure readiness (SR) due to pentylenetetrazole kindling.

MATERIAL AND METHODS

The study was carried out on male rats of the Wistar line. Simultaneous telemetric monitoring of electrocardiogram and electroencephalogram on-line was used. Individual SR of animals in 7- and 27 day pentylenetetrazole kindling was determined.

RESULTS

The decrease in the index of LF/HF after 7 days of kindling reflects a compensatory reaction of the autonomic nervous system. However, the increase in SI indicates that the result obtained at the price of considerable stress regulation mechanisms. The increase in QTc, Tpeak Tend and reduced SDNN and TP suggest that compensatory mechanisms cannot prevent the high risk of life-threatening arrhythmias. High SR after 27 days of kindling is accompanied by a shift of autonomic balance towards the growth of tone of the sympathetic system which may lead to decompensation and prenosological state.

CONCLUSION

The characteristics of autonomic regulation of the heart in progressive SR are important for fundamental and clinical cardioneurology.

TNP-ATP is Beneficial for Treatment of Neonatal Hypoxia-Induced Hypomyelination and Cognitive Decline

Our previous study together with other investigations have reported that neonatal hypoxia or ischemia induces long-term cognitive impairment, at least in part through brain inflammation and hypomyelination. However, the detailed mechanisms are not fully understood. Here, we used a rodent model of neonatal hypoxia by subjecting postnatal day 0 (P0) rat pups to systemic hypoxia (3.5 h). We found that neonatal hypoxia increased the glutamate content and initiated inflammatory responses at 4 h and 1 day after hypoxia, caused hypomyelination in the corpus callosum, and impaired hippocampus-dependent learning and memory when assessed 30-60 days after hypoxia. Interestingly, much of the hypoxia-induced brain damage was ameliorated by treatment with the ATP analogue 2',3'-0-(2,4,6-trinitrophenyl)-adenosine 5'-triphosphate (TNP-ATP; blocks all ionotropic P2X1-7 receptors), whereas treatment with pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; inhibits P2X1-3 and P2X5-7 receptors) was less neuroprotective. Our data indicated that activation of ionotropic ATP receptors might be partially, if not fully, involved in glutamate deregulation, neuroinflammation, hypomyelination, and cognitive dysfunction after neonatal hypoxia.

Changes in Hippocampal Volume are Correlated with Cell Loss but Not with Seizure Frequency in Two Chronic Models of Temporal Lobe Epilepsy

Kainic acid (KA) or pilocarpine (PILO) have been used in rats to model human temporal lobe epilepsy (TLE) but the distribution and severity of structural lesions between these two models may differ. Magnetic resonance imaging (MRI) studies have used quantitative measurements of hippocampal T₂ (T₂HP) relaxation time and volume, but simultaneous comparative results have not been reported yet. The aim of this study was to compare the MRI T₂HP and volume with histological data and frequency of seizures in both models. KA- and PILO-treated rats were imaged with a 2 T MRI scanner. T₂HP and volume values were correlated with the number of cells, mossy fiber sprouting, and spontaneous recurrent seizures (SRS) frequency over the 9 months following status epilepticus (SE). Compared to controls, KA-treated rats had unaltered T₂HP, pronounced reduction in hippocampal volume and concomitant cell reduction in granule cell layer, CA1 and CA3 at 3 months post SE. In contrast, hippocampal volume was unchanged in PILO-treated animals despite detectable increased T₂HP and cell loss in granule cell layer, CA1 and CA3. In the following 6 months, MRI hippocampal volume remained stable with increase of T₂HP signal in the KA-treated group. The number of CA1 and CA3 cells was smaller than age-matched CTL group. In contrast, PILO group had MRI volumetric reduction accompanied by reduction in the number of CA1 and CA3 cells. In this group, T₂HP signal was unaltered at 6 or 9 months after status. Reductions in the number of cells were not progressive in both models. Notably, the SRS frequency was higher in PILO than in the KA model. The volumetry data correlated well with tissue damage in the epileptic brain, suggesting that MRI may be useful for tracking longitudinal hippocampal changes, allowing the assessment of individual variability and disease progression. Our results indicate that the temporal changes in hippocampal morphology are distinct for both models of TLE and that these are not significantly correlated to the frequency of SRS.

Neuroimaging biomarkers for epilepsy: advances and relevance to glial cells

Glial cells play an important role in normal brain function and emerging evidence would suggest that their dysfunction may be responsible for some epileptic disease states. Neuroimaging of glial cells is desirable, but there are no clear methods to assess neither their function nor localization. Magnetic resonance imaging (MRI) is now part of a standardized epilepsy imaging protocol to assess patients. Structural volumetric and T2-weighted imaging changes can assist in making a positive diagnosis in a majority of patients. The alterations reported in structural and T2 imaging is predominantly thought to reflect early neuronal loss followed by glial hypertrophy. MR spectroscopy for myo-inositol is a being pursued to identify glial alterations along with neuronal markers. Diffusion weighted imaging (DWI) is ideal for acute epileptiform events, but is not sensitive to either glial cells or neuronal long-term changes found in epilepsy. However, DWI variants such as diffusion tensor imaging or q-space imaging may shed additional light on aberrant glial function in the future. The sensitivity and specificity of PET radioligands, including those targeting glial cells (translocator protein) hold promise in being able to image glial cells. As the role of glial function/dysfunction in epilepsy becomes more apparent neuroimaging methods will evolve to assist the clinician and researcher in visualizing their location and function.