Consecutive 15min is necessary for focal low frequency stimulation to inhibit amygdaloid-kindling seizures in rats

Low-frequency Stimulation at the Subiculum Prevents Extensive Secondary Epileptogenesis in Temporal Lobe Epilepsy

Secondary epileptogenesis is characterized by increased epileptic susceptibility and a tendency to generate epileptiform activities outside the primary focus. It is one of the major resultants of pharmacoresistance and failure of surgical outcomes in epilepsy, but still lacks effective treatments. Here, we aimed to test the effects of low-frequency stimulation (LFS) at the subiculum for secondary epileptogenesis in a mouse model. Here, secondary epileptogenesis was simulated at regions both contralateral and ipsilateral to the primary focus by applying successive kindling stimuli. Mice kindled at the right CA3 showed higher seizure susceptibilities at both the contralateral CA3 and the ipsilateral entorhinal cortex and had accelerated kindling processes compared with naive mice. LFS at the ipsilateral subiculum during the primary kindling progress at the right CA3 effectively prevented secondary epileptogenesis at both the contralateral CA3 and the ipsilateral entorhinal cortex, characterized by decreased seizure susceptibilities and a retarded kindling process at those secondary foci. Only application along with the primary epileptogenesis was effective. Notably, the effects of LFS on secondary epileptogenesis were associated with its inhibitory effect at the secondary focus through interfering with the enhancement of synaptic connections between the primary and secondary foci. These results imply that LFS at the subiculum is an effective preventive strategy for extensive secondary epileptogenesis in temporal lobe epilepsy and present the subiculum as a target with potential translational importance.

Transcranial Focal Electric Stimulation Avoids P-Glycoprotein Over-Expression during Electrical Amygdala Kindling and Delays Epileptogenesis in Rats

Recent evidence suggests that P-glycoprotein (P-gp) overexpression mediates hyperexcitability and is associated with epileptogenesis. Transcranial focal electrical stimulation (TFS) delays epileptogenesis and inhibits P-gp overexpression after a generalized seizure. Here, first we measured P-gp expression during epileptogenesis and second, we assessed if TFS antiepileptogenic effect was related with P-gp overexpression avoidance. Male Wistar rats were implanted in right basolateral amygdala and stimulated daily for electrical amygdala kindling (EAK), P-gp expression was assessed during epileptogenesis in relevant brain areas. Stage I group showed 85% increase in P-gp in ipsilateral hippocampus (p < 0.001). Stage III group presented 58% and 57% increase in P-gp in both hippocampi (p < 0.05). Kindled group had 92% and 90% increase in P-gp in both hippocampi (p < 0.01), and 93% and 143% increase in both neocortices (p < 0.01). For the second experiment, TFS was administrated daily after each EAK stimulation for 20 days and P-gp concentration was assessed. No changes were found in the TFS group (p > 0.05). Kindled group showed 132% and 138% increase in P-gp in both hippocampi (p < 0.001) and 51% and 92% increase in both cortices (p < 0.001). Kindled + TFS group presented no changes (p > 0.05). Our experiments revealed that progression of EAK is associated with increased P-gp expression. These changes are structure-specific and dependent on seizure severity. EAK-induced P-gp overexpression would be associated with neuronal hyperexcitability and thus, epileptogenesis. P-gp could be a novel therapeutical target to avoid epileptogenesis. In accordance with this, TFS inhibited P-gp overexpression and interfered with EAK. An important limitation of the present study is that P-gp neuronal expression was not evaluated under the different experimental conditions. Future studies should be carried out to determine P-gp neuronal overexpression in hyperexcitable networks during epileptogenesis. The TFS-induced lessening of P-gp overexpression could be a novel therapeutical strategy to avoid epileptogenesis in high-risk patients.

Electrical stimulation in animal models of epilepsy: A review on cellular and electrophysiological aspects

Epilepsy is a debilitating condition, primarily refractory individuals, leading to the search for new efficient therapies. Electrical stimulation is an important method used for years to treat several neurological disorders. Currently, electrical stimulation is used to reduce epileptic crisis in patients and shows promising results. Even though the use of electricity to treat neurological disorders has grown worldwide, there are still many caveats that must be clarified, such as action mechanisms and more efficient stimulation treatment parameters. Thus, this review aimed to explore the comprehension of the main stimulation methods in animal models of epilepsy using rodents to develop new experimental protocols and therapeutic approaches.

Subicular pyramidal neurons gate drug resistance in temporal lobe epilepsy

OBJECTIVE

Drug-resistant epilepsy causes great clinical danger and still lacks effective treatments.

METHODS

Here, we used multifaceted approaches combining electrophysiology, optogenetics, and chemogenetics in a classic phenytoin-resistant epilepsy model to reveal the key target of subicular pyramidal neurons in phenytoin resistance.

RESULTS

In vivo neural recording showed that the firing rate of pyramidal neurons in the subiculum, but not other hippocampal subregions, could not be inhibited by phenytoin in phenytoin-resistant rats. Selective inhibition of subicular pyramidal neurons by optogenetics or chemogenetics reversed phenytoin resistance, whereas selective activation of subicular pyramidal neurons induced phenytoin resistance. Moreover, long-term low-frequency stimulation at the subiculum, which is clinically feasible, significantly inhibited the subicular pyramidal neurons and reversed phenytoin resistance. Furthermore, in vitro electrophysiology revealed that off-target use of phenytoin on sodium channels of subicular pyramidal neurons was involved in the phenytoin resistance, and clinical neuroimaging data suggested the volume of the subiculum in drug-resistant patients was related to the usage of sodium channel inhibitors.

INTERPRETATION

These results highlight that the subicular pyramidal neurons may be a key switch control of drug-resistant epilepsy and represent a new potential target for precise treatments. ANN NEUROL 2019;86:626-640.

Temporally irregular electrical stimulation to the epileptogenic focus delays epileptogenesis in rats

BACKGROUND

Variation in the temporal patterns of electrical pulses in stimulation trains has opened a new field of opportunity for the treatment of neurological disorders, such as pharmacoresistant temporal lobe epilepsy. Whether this novel type of stimulation affects epileptogenesis remains to be investigated.

OBJECTIVE

The purpose of this study was to analyze the effects of temporally irregular deep brain stimulation on kindling-induced epileptogenesis in rats.

METHODS

Temporally irregular deep brain stimulation was delivered at different times with respect to the kindling stimulation. Behavioral and electrographic changes on kindling acquisition were compared with a control group and a temporally regular deep brain stimulation-treated group. The propagation of epileptiform activity was analyzed with wavelet cross-correlation analysis, and interictal epileptiform discharge ratios were obtained.

RESULTS

Temporally irregular deep brain stimulation delivered in the epileptogenic focus during the interictal period shortened the daily afterdischarge duration, slowed the progression of seizure stages, diminished the generalized seizure duration and interfered with the propagation of epileptiform activity from the seizure onset zone to the ipsi- and contralateral motor cortex. We also found a negative correlation between seizure severity and interictal epileptiform discharges in rats stimulated with temporally irregular deep brain stimulation.

CONCLUSION

These results provide evidence that temporally irregular deep brain stimulation interferes with the establishment of epilepsy by delaying epileptogenesis by almost twice as long in kindling animals. Thus, temporally irregular deep brain stimulation could be a preventive approach against epilepsy.

An update for epilepsy research and antiepileptic drug development: Toward precise circuit therapy

Epilepsy involves neuronal dysfunction at molecular, cellular, and circuit levels. The understanding of the mechanism of the epilepsies has advanced greatly in the last three decades, especially in terms of their cellular and molecular basis. However, despite the availability of ~30 anti-epileptic drugs (AEDs) with diverse molecular targets, there are still many challenges (e.g. drug resistance, side effects) in pharmacological treatment of epilepsies today. Because molecular mechanisms are integrated at the level of neuronal circuits, we suggest a shift in epilepsy treatment and research strategies from the "molecular" level to the "circuit" level. Recent technological advances have facilitated circuit mechanistic discovery at each level and have paved the way for many opportunities of novel therapeutic strategies and AED development toward precise circuit therapy.

Low Frequency Electrical Stimulation Attenuated The Epileptiform Activity-Induced Changes in Action Potential Features in Hippocampal CA1 Pyramidal Neurons

Objective

Electrical low frequency stimulation (LFS) is a new therapeutic method that moderates hyperexcitability during epileptic states. Seizure occurrence is accompanied by some changes in action potential (AP) features. In this study, we investigated the inhibitory action of LFS on epileptiform activity (EA) induced-changes in AP features in hippocampal CA1 pyramidal neurons.

Materials and Methods

In this experimental study, we induced EA in hippocampal slices by increasing the extracellular potassium (K+) concentration to 12 mM. LFS (1 Hz) was applied to the Schaffer collaterals at different pulse numbers (600 and 900) at the beginning of the EA. Changes in AP features recorded by whole-cell patch clamp recording were compared using phase plot analysis.

Results

Induction of EA depolarized membrane potential, decreased peak amplitude, as well as the maximum rise and decay slopes of APs. Administration of 1 Hz LFS at the beginning of EA prevented the above mentioned changes in AP features. This suppressive effect of LFS depended on the LFS pulse number, such that application of 900 pulses of LFS had a stronger recovery effect on AP features that changed during EA compared to 600 pulses of LFS. The constructed phase plots of APs revealed that LFS at 900 pulses significantly decreased the changes in resting membrane potential (RMP), peak amplitude, and maximum rise and decay slopes that appeared during EA.

Conclusion

Increasing the numbers of LFS pulses can magnify its inhibitory effects on EA-induced changes in AP features.

The epileptic amygdala: Toward the development of a neural prosthesis by temporally coded electrical stimulation

Many patients with epilepsy do not obtain proper control of their seizures through conventional treatment. We review aspects of the pathophysiology underlying epileptic phenomena, with a special interest in the role of the amygdala, stressing the importance of hypersynchronism in both ictogenesis and epileptogenesis. We then review experimental studies on electrical stimulation of mesiotemporal epileptogenic areas, the amygdala included, as a means to treat medically refractory epilepsy. Regular high-frequency stimulation (HFS) commonly has anticonvulsant effects and sparse antiepileptogenic properties. On the other hand, HFS is related to acute and long-term increases in excitability related to direct neuronal activation, long-term potentiation, and kindling, raising concerns regarding its safety and jeopardizing in-depth understanding of its mechanisms. In turn, the safer regular low-frequency stimulation (LFS) has a robust antiepileptogenic effect, but its pro- or anticonvulsant effect seems to vary at random among studies. As an alternative, studies by our group on the development and investigation of temporally unstructured electrical stimulation applied to the amygdala have shown that nonperiodic stimulation (NPS), which is a nonstandard form of LFS, is capable of suppressing both acute and chronic spontaneous seizures. We hypothesize two noncompetitive mechanisms for the therapeutic role of amygdala in NPS, 1) a direct desynchronization of epileptic circuitry in the forebrain and brainstem and 2) an indirect desynchronization/inhibition through nucleus accumbens activation. We conclude by reintroducing the idea that hypersynchronism, rather than hyperexcitability, may be the key for epileptic phenomena and epilepsy treatment.

Low-frequency electrical stimulation enhances the effectiveness of phenobarbital on GABAergic currents in hippocampal slices of kindled rats

Low frequency stimulation (LFS) has been proposed as a new approach in the treatment of epilepsy. The anticonvulsant mechanism of LFS may be through its effect on GABAA receptors, which are the main target of phenobarbital anticonvulsant action. We supposed that co-application of LFS and phenobarbital may increase the efficacy of phenobarbital. Therefore, the interaction of LFS and phenobarbital on GABAergic inhibitory post-synaptic currents (IPSCs) in kindled and control rats was investigated. Animals were kindled by electrical stimulation of basolateral amygdala in a semi rapid manner (12 stimulations/day). The effect of phenobarbital, LFS and phenobarbital+LFS was investigated on GABAA-mediated evoked and miniature IPSCs in the hippocampal brain slices in control and fully kindled animals. Phenobarbital and LFS had positive interaction on GABAergic currents. In vitro co-application of an ineffective pattern of LFS (100 pulses at afterdischarge threshold intensity) and a sub-threshold dose of phenobarbital (100μM) which had no significant effect on GABAergic currents alone, increased the amplitude and area under curve of GABAergic currents in CA1 pyramidal neurons of hippocampal slices significantly. Interestingly, the sub-threshold dose of phenobarbital potentiated the GABAergic currents when applied on the hippocampal slices of kindled animals which received LFS in vivo. Post-synaptic mechanisms may be involved in observed interactions. Obtained results implied a positive interaction between LFS and phenobarbital through GABAA currents. It may be suggested that a combined therapy of phenobarbital and LFS may be a useful manner for reinforcing the anticonvulsant action of phenobarbital.

Low-frequency stimulation in anterior nucleus of thalamus alleviates kainate-induced chronic epilepsy and modulates the hippocampal EEG rhythm

High-frequency stimulation (HFS) of the anterior nucleus of thalamus (ANT) is a new and alternative option for the treatment of intractable epilepsy. However, the responder rate is relatively low. The present study was designed to determine the effect of low-frequency stimulation (LFS) in ANT on chronic spontaneous recurrent seizures and related pathological pattern in intra-hippocampal kainate mouse model. We found that LFS (1 Hz, 100 μs, 300 μA), but not HFS (100 Hz, 100 μs, 30 μA), in bilateral ANT significantly decreased the frequency of spontaneous recurrent seizures, either non-convulsive focal seizures or tonic-clonic generalized seizures. The anti-epileptic effect persisted for one week after LFS cessation, which manifested as a long-term inhibition of the frequency of seizures with short (20-60 s) and intermediate duration (60-120 s). Meanwhile, LFS decreased the frequency of high-frequency oscillations (HFOs) and interictal spikes, two indicators of seizure severity, whereas HFS increased the HFO frequency. Furthermore, LFS decreased the power of the delta band and increased the power of the gamma band of hippocampal background EEG. In addition, LFS, but not HFS, improved the performance of chronic epileptic mice in objection-location task, novel objection recognition and freezing test. These results provide the first evidence that LFS in ANT alleviates kainate-induced chronic epilepsy and cognitive impairment, which may be related to the modulation of the hippocampal EEG rhythm. This may be of great therapeutic significance for clinical treatment of epilepsy with deep brain stimulation.