Low frequency stimulation modifies receptor binding in rat brain

Directions of Deep Brain Stimulation for Epilepsy and Parkinson's Disease

BACKGROUND

Deep brain stimulation (DBS) is an effective treatment for movement disorders and neurological/psychiatric disorders. DBS has been approved for the control of Parkinson disease (PD) and epilepsy.

OBJECTIVES

A systematic review and possible future direction of DBS system studies is performed in the open loop and closed-loop configuration on PD and epilepsy.

METHODS

We searched Google Scholar database for DBS system and development. DBS search results were categorized into clinical device and research system from the open-loop and closed-loop perspectives.

RESULTS

We performed literature review for DBS on PD and epilepsy in terms of system development by the open loop and closed-loop configuration. This study described development and trends for DBS in terms of electrode, recording, stimulation, and signal processing. The closed-loop DBS system raised a more attention in recent researches.

CONCLUSION

We overviewed development and progress of DBS. Our results suggest that the closed-loop DBS is important for PD and epilepsy.

Interaction of Sodium Valproate With Low-Frequency Electrical Stimulation During Kindlingn

Introduction

The interaction between antiepileptic drugs and brain electrical stimulation is a potential therapy to control seizures in patients with pharmacoresistance to drugs. So, the present study aimed to design to determine the effect of a subeffective dose of sodium valproate combined with low-frequency electrical stimulation during kindling.

Methods

One tripolar electrode was implanted stereotactically in the CA1 hippocampus of male Wistar rats. One week after surgery, the rats were kindled by electrical stimulation of hippocampus in a rapid manner (12 stimulations/day) for 6 days with sodium valproate alone or combined with low-frequency electrical stimulation (four packages contained 200 monophasic square wave pulses of 0.1-ms duration at 1 Hz, immediately after kindling stimulations). The duration of afterdischarge, maximum latency to stages 4 and 5, and the maximum duration of these stages were recorded by electromadule during kindling.

Results

Application of sodium valproate with low-frequency electrical stimulation caused a reduction in cumulative afterdischarge duration. The maximum latency to the onset of stage 5 seizure increased after sodium valproate application alone, without having a significant effect on the fourth stage. Our findings showed reductions in the seizures duration and increasing in the latency times of both stages after the application of sodium valproate with low-frequency electrical stimulation.

Conclusion

It seems that usage of sodium valproate with low-frequency electrical stimulation during kindling was more effective to suppress the epileptic activity than its administration alone and may have a critical role on the antiepileptic effects of sodium valproate.

Electrical stimulation of the endopiriform nucleus attenuates epilepsy in rats by network modulation

OBJECTIVE

Neuromodulatory anterior thalamic deep brain stimulation (DBS) is an effective therapy for intractable epilepsy, but few patients achieve complete seizure control with thalamic DBS. Other stimulation sites may be considered for anti-seizure DBS. We investigated bilateral low-frequency stimulation of the endopiriform nuclei (LFS-EPN) to control seizures induced by intracortically implanted cobalt wire in rats.

METHODS

Chronic epilepsy was induced by cobalt wire implantation in the motor cortex unilaterally. Bipolar-stimulating electrodes were implanted into the EPN bilaterally. Continuous electroencephalography (EEG) was recorded using electrodes placed into bilateral motor cortex and hippocampus CA1 areas. Spontaneous seizures were monitored by long-term video-EEG, and behavioral seizures were classified based on the Racine scale. Continuous 1-Hz LFS-EPN began on the third day after electrode implantation and was controlled by a multi-channel stimulator. Stimulation continued until the rats had no seizures for three consecutive days.

RESULTS

Compared with the control and sham stimulation groups, the LFS-EPN group experienced significantly fewer seizures per day and the mean Racine score of seizures was lower due to fewer generalized seizures. Ictal discharges at the epileptogenic site had significantly reduced theta band power in the LFS-EPN group compared to the other groups.

INTERPRETATION

Bilateral LFS-EPN attenuates cobalt wire-induced seizures in rats by modulating epileptic networks. Reduced ictal theta power of the EEG broadband spectrum at the lesion site may be associated with the anti-epileptogenic mechanism of LFS-EPN. Bilateral EPN DBS may have therapeutic applications in human partial epilepsies.

Electrical cortical stimulations modulate spike and post-spike slow-related high-frequency activities in human epileptic foci

OBJECTIVE

Using interictal epileptiform discharges (IEDs), consisting of spikes and post-spike slow waves (PSSs), and IED-related high-frequency activities (HFAs), we elucidated inhibitory effects of electrical cortical stimulation (ECS) on human epileptic foci.

METHODS

We recruited 8 patients with intractable focal epilepsy, and 50-Hz ECS was applied to the seizure-onset zone (SOZ) and non-SOZ. Before (5-min) and after (20-min) ECS, we evaluated the number of IED, the amplitudes of spikes and PSSs, spike-related HFA power, and PSS-related low gamma (30-50 Hz) activities.

RESULTS

SOZ stimulation significantly decreased the number of IEDs and amplitude of spikes. Spike-related HFA power values in fast ripple (200-300 Hz) and ripple (80-150 Hz) bands were significantly suppressed only by SOZ stimulation in 4 and 3 patients, respectively. Among 4 patients with discrete PSSs, the amplitude ratio of spike/PSS decreased and the PSS-related low gamma activity power increased significantly in 2 patients and marginally in 1 patient.

CONCLUSIONS

ECS potentially modulates cortical excitability by reducing excitation and increasing inhibition, and monitoring IED-related HFAs may help achieve the optimal effects of ECS.

SIGNIFICANCE

IED and IED-related HFAs are dynamic, potential surrogate markers for epileptic excitability during the interictal period.

Influence of hippocampal low-frequency stimulation on GABAA R α1, ICER and BNDF expression level in brain tissues of amygdala-kindled drug-resistant temporal lobe epileptic rats

This study investigated the therapeutic effect of hippocampal low-frequency stimulation (Hip-LFS) and its influence on the type A γ-aminobutyric acid receptor α1 subunit (GABA_A R α1 subunit), inducible cAMP early repressor (ICER) and brain-derived neurotrophic factors (BNDF). The model of epilepsy was induced by chronic electrical stimulation in amygdala. Drug-resistant and drug-sensitive epileptic rats were selected by testing their seizure response to phenytoin and phenobarbital. The changes of GABA_A R α1 subunit, ICER and BDNF expression were detected via immunohistochemistry and western blot. The expression levels of ICER and BDNF were increased remarkably but the GABA_A R α1 subunit decreased significantly in the drug-resistant epileptic rats. However, the expression levels of ICER, BDNF were decreased and the expression of the GABA_A R α1 subunit increased significantly in the drug-resistant epileptic rats after two weeks of Hip-LFS. Meanwhile, the seizure degree was reduced and the electroencephalograms were improved. The present study demonstrated thatincreased ICER and BDNF might be associated with the development of drug-resistance. The effect of Hip-LFS in the treatment of drug-resistant epileptic rats might be associated with increasing the levels of the ICER and the BDNF.

Effects of Low Frequency Stimulation on Spontaneous Inhibitory and Excitatory Post-Synaptic Currents in Hippocampal CA1 Pyramidal Cells of Kindled Rats

OBJECTIVE

Low-frequency stimulation (LFS) exerts suppressive effects in kindled animals. It is believed that overstimulated glutamatergic and decreased GABAergic transmission have long been associated with seizure activity. In this study, we investigated the effect of electrical LFS on different parameters of spontaneous excitatory and inhibitory post-synaptic currents (sEPSCs and sIPSCs) in hippocampal CA1 pyramidal cells in kindled animals.

MATERIALS AND METHODS

In this experimental study, rats were kindled by electrical stimulation of the hippocampal CA1 area in a semi-rapid manner (12 stimulations/day). The animals were considered fully kindled when they showed stage 5 seizures on three consecutive days. One group of animals received LFS 4 times at 30 seconds, 6 hours, 18 and 24 hours following the last kindling stimulation. Each LFS consisted of 4 packages at 5 minutes intervals. Each package of LFS consisted of 200 pulses at 1 Hz and each monophasic square wave pulse duration was 0.1 millisecond. At 2-3 hours post-LFS, acute hippocampal slices were prepared and a whole cell patch clamp recording was performed in all animals to measure the different parameters of sEPSCs and sIPSCs.

RESULTS

In kindled animals, the inter-event interval (as an index of occurrence) of sEPSCs decreased, whereas sIPSC increased. In addition, the decay time constant of sIPSCs as an index of the duration of its activity decreased compared to the control group. There was no significant difference in other parameters between the kindled and control groups. Application of LFS in kindled animals prevented the observed changes. There was no significant difference between the measured parameters in kindled+LFS and control groups.

CONCLUSION

LFS application may prevent seizure-induced increase in the occurrence of sEPSCs and seizure-induced decrease in occurrence and activity duration of sIPSCs.

Entorhinal Principal Neurons Mediate Brain-stimulation Treatments for Epilepsy

Brain stimulation is an alternative treatment for epilepsy. However, the neuronal circuits underlying its mechanisms remain obscure. We found that optogenetic activation (1Hz) of entorhinal calcium/calmodulin-dependent protein kinase II α (CaMKIIα)-positive neurons, but not GABAergic neurons, retarded hippocampal epileptogenesis and reduced hippocampal seizure severity, similar to that of entorhinal low-frequency electrical stimulation (LFES). Optogenetic inhibition of entorhinal CaMKIIα-positive neurons blocked the antiepileptic effect of LFES. The channelrhodopsin-2-eYFP labeled entorhinal CaMKIIα-positive neurons primarily targeted the hippocampus, and the activation of these fibers reduced hippocampal seizure severity. By combining extracellular recording and pharmacological methods, we found that activating entorhinal CaMKIIα-positive neurons induced the GABA-mediated inhibition of hippocampal neurons. Optogenetic activation of focal hippocampal GABAergic neurons mimicked this neuronal modulatory effect and reduced hippocampal seizure severity, but the anti-epileptic effect is weaker than that of entorhinal LFES, which may be due to the limited spatial neuronal modulatory effect of focal photo-stimulation. Our results demonstrate a glutamatergic-GABAergic neuronal circuit for LFES treatment of epilepsy, which is mediated by entorhinal principal neurons.

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.

Synaptic vesicle protein2A decreases in amygdaloid-kindling pharmcoresistant epileptic rats

Synaptic vesicle protein 2A (SV2A) involvement has been reported in the animal models of epilepsy and in human intractable epilepsy. The difference between pharmacosensitive epilepsy and pharmacoresistant epilepsy remains poorly understood. The present study aimed to observe the hippocampus SV2A protein expression in amygdale-kindling pharmacoresistant epileptic rats. The pharmacosensitive epileptic rats served as control. Amygdaloid-kindling model of epilepsy was established in 100 healthy adult male Sprague-Dawley rats. The kindled rat model of epilepsy was used to select pharmacoresistance by testing their seizure response to phenytoin and phenobarbital. The selected pharmacoresistant rats were assigned to a pharmacoresistant epileptic group (PRE group). Another 12 pharmacosensitive epileptic rats (PSE group) served as control. Immunohistochemistry, real-time PCR and Western blotting were used to determine SV2A expression in the hippocampus tissue samples from both the PRE and the PSE rats. Immunohistochemistry staining showed that SV2A was mainly accumulated in the cytoplasm of the neurons, as well as along their dendrites throughout all subfields of the hippocampus. Immunoreactive staining level of SV2A-positive cells was 0.483 ± 0.304 in the PRE group and 0.866 ± 0.090 in the PSE group (P < 0.05). Real-time PCR analysis demonstrated that 2(-ΔΔCt) value of SV2A mRNA was 0.30 ± 0.43 in the PRE group and 0.76 ± 0.18 in the PSE group (P < 0.05). Western blotting analysis obtained the similar findings (0.27 ± 0.21 versus 1.12 ± 0.21, P < 0.05). PRE rats displayed a significant decrease of SV2A in the brain. SV2A may be associated with the pathogenesis of intractable epilepsy of the amygdaloid-kindling rats.

Effect of low-frequency stimulation on kindling induced changes in rat dentate gyrus: an ultrastructural study

It has been shown that low-frequency stimulation (LFS) can induce anticonvulsant effects. In this study, the effect of different LFS frequencies on kindling induced behavioral and ultrastructural changes was investigated. For induction of kindled seizures in rats, stimulating and recording electrodes were implanted in perforant path and dentate gyrus, respectively. Animals were stimulated in a rapid kindling manner. Different groups of animals received LFS at different frequencies (0.5, 1 and 5 Hz) following kindling stimulations and their effects on kindling rate were determined using behavioral and ultrastructural studies. Kindling stimulations were applied for 7 days. Then, the animals were sacrificed and their dentate gyrus was sampled for ultrastructural studies under electron microscopy. All three used LFS frequencies (0.5, 1 and 5 Hz) had a significant inhibitory effect on kindling rate and decreased afterdischarge duration and the number of stimulations to achieve stage 4 and 5 seizures significantly. In addition, application of LFS prevented the increase in the post-synaptic density and induction of concave synaptic vesicles following kindling. There was no significant change between anticonvulsant effects of LFS at different frequencies. Obtained results show that LFS application can prevent the neuronal hyperexcitability by preventing the ultrastructural changes during kindling and this may be one of the mechanisms of LFS anticonvulsant effects.

Effect of low frequency electrical stimulation on spike and wave discharges of perioral somatosensory cortex in WAG/Rij rats

Low frequency electrical stimulation has been revealed that as a potential cure in patient with drug resistant to epilepsy. This study tries to evaluate the effect of low frequency electrical stimulation (LFS) on absence seizure of perioral region primary somatosensory cortex (S1po). Eighteen male WAG/Rij rats were received LFS (3Hz, square wave, monophasic, 200μs, and 400μA) for 25min into S1po for a period of five days. There is 6 animals per group .The stimulating electrodes were implanted according to stereotaxic landmarks and EEG recording was obtained 30min before and after LFS to analyse frequency, number and duration of spike-wave discharges (SWD). The results showed that in animals with unilateral stimulating electrodes (Exp1) in first and second days and also in animals with bilateral stimulating electrodes (Exp2) in days 3rd and 4th. LFS had significant decrease effects (p<0.05) on mean number of SWD between pre-LFS. In comparison pre-LFS to post-LFS, mean of duration in Exp2 decreased significantly. In continuous application of LFS (5 days) only the data of first day was differently significant (p<0.05) but data of other days had no difference. Comparison of data between Exp1, Exp2 and control groups showed that the mean number of Exp1 was significantly different (p<0.05) and mean pick frequency in Exp2 was significantly decreased in comparison with Exp1 group (p<0.05). The LFS of S1po produces significant antiepileptic effect on absence seizure but it was not persistent till the next day and shows a short time effect.

Modulation of excitability by continuous low- and high-frequency stimulation in fully hippocampal kindled rats

BACKGROUND

Low- and high-frequency stimulation (LFS and HFS, respectively) have been, reported to modify seizure characteristics in rats. We here report effects of hippocampal LFS and HFS, applied at two or four sites in fully kindled rats.

METHODS

Rats were kindled through a hippocampal tetrode until the fully kindled state. Animals with, stable afterdischarge (AD) threshold were randomly assigned to 5 groups; stimulation at 1Hz (LFS) or, 130Hz (HFS) was continuously applied for 7 days at 2 or 4 intrahippocampal sites; a control, group received no stimulation. Four-contact stimulation was performed in a rotating fashion. Stimulation effects on AD threshold, AD duration and behavioral seizures were assessed.

KEY FINDINGS

Four-contact LFS consistently increased AD threshold for a period of 2 days to 2 weeks, whereas 4-contact HFS significantly decreased AD duration 24hours following the stimulation period. No significant AD modification was observed with either 2-contact stimulation paradigms. No, behavioral alteration occurred in any group.

SIGNIFICANCE

These findings suggest that effects of hippocampal stimulation depend on frequency and topography of stimulus application. LFS and HFS had anti-epileptic effect on afterdischarges when applied in a rotating pattern. This supports concepts on patterned stimulation to result in desynchronization and anti-kindling effects.

Long-lasting hyperpolarization underlies seizure reduction by low frequency deep brain electrical stimulation

Mesial temporal lobe epilepsy (MTLE) is a common medically refractory neurological disease. Deep brain electrical stimulation (DBS) of grey matter has been used for MTLE with limited success. However, stimulation of a white matter tract connecting the hippocampi, the ventral hippocampal commissure (VHC), with low frequencies that simulate interictal discharges has shown promising results, with seizure reduction greater than 98% in bilateral hippocampi during stimulation and greater than 50% seizure reduction in bilateral hippocampi after treatment. A major hurdle to the implementation and optimization of this treatment is that the mechanisms of seizure reduction by low frequency electrical stimulation (LFS) are not known. The goal of this study is to understand how commissural fibre tract stimulation reduces bilateral hippocampal epileptic activity in an in vitro slice preparation containing bilateral hippocampi connected by the VHC. It is our hypothesis that electrical stimuli induce hyperpolarization lasting hundreds of milliseconds following each pulse which reduces spontaneous epileptic activity during each inter-stimulus interval (ISI). Stimulus-induced long-lasting-hyperpolarization (LLH) can be mediated by GABA(B) inhibitory post-synaptic potentials (IPSPs) or slow after-hyperpolarization (sAHP). To test the role of LLH in effective bilateral seizure reduction by fibre tract stimulation, we measured stimulus-induced hyperpolarization during LFS of the VHC using electrophysiology techniques. Antagonism of the GABA(B) IPSP and/or sAHP diminished stimulus-induced hyperpolarization concurrently with LFS efficacy (greater than 50% reduction). Blocking both the GABA(B) IPSP and sAHP simultaneously eliminated the effect of electrical stimulation on seizure reduction entirely. These data show that LFS of the VHC is an effective protocol for bilateral hippocampal seizure reduction and that its efficacy relies on the induction of long-lasting hyperpolarization mediated through GABA(B) IPSPs and sAHP. Based on this study, optimization of the timing of LFS and LFS-induced-LLH may lead to improved outcomes from DBS treatments for human epilepsy.

Effects of low-frequency hippocampal stimulation on gamma-amino butyric acid type B receptor expression in pharmacoresistant amygdaloid kindling epileptic rats

OBJECTIVE

To observe the effect of low-frequency hippocampal stimulation on gamma-amino butyric acid type B (GABA-B) receptor expression in hippocampus pharmacoresistant epileptic rats.

MATERIALS AND METHODS

Sixteen pharmacoresistant epileptic rats were selected by testing their seizure response to phenytoin and phenobarbital, and they were randomly divided into a pharmacoresistant control group (PRC group, eight rats) and a pharmacoresistant stimulation group (PRS group, eight rats). Another 16 pharmacosensitive epileptic rats were served as control, also divided randomly into a pharmacosensitive control group (PSC group) and a pharmacosensitive stimulation group (PSS group). A stimulation electrode was implanted into the rats' hippocampus in the four groups. Low-frequency hippocampal stimulation was administered twice per day for two weeks. Following these weeks of stimulation, GABA-B receptor-positive neurons were counted and the gray values of GABA-B receptor expression in the rats' hippocampal tissues were measured.

RESULTS

The amygdale stimulus-induced epileptic seizures were decreased significantly in the PRS group compared with the PRC group. The parameters of the amygdale after discharge also were improved after hippocampal stimulation. Simultaneously, the GABA-B receptor-positive neurons increased and the GABA-B expression gray values decreased markedly in the PRS group compared with the PRC group. The same phenomenon also was observed between the PSS group and the PSC group. However, no significant difference was found in the GABA-B receptor-positive neurons and the gray values of GABA-B between the PRS group and the PSC group.

CONCLUSIONS

The low-frequency hippocampal stimulation may inhibit the amygdale stimulus-induced epileptic seizures and the after discharges. The antiepileptic effects of the hippocampal stimulation may be achieved partly by increasing the expression of the GABA-B receptor.

Responsive electrical stimulation suppresses epileptic seizures in rats

Background

A responsive electrical stimulation pattern based on our recently developed novel seizure prediction method was designed to suppress the penicillin-induced epileptic seizures.

Methodology

Seizures were induced by Penicillin injection at rat cortex. A responsive electrical stimulation system was triggered prior to seizures predicted with phase synchronisation. Rats with induced seizures were stimulated by the electrical pulses at a responsive or 1 Hz periodic pattern of an open system. The effectiveness of stimulation on seizures suppression was assessed by measuring the average number and duration of seizures per hour.

Results

The prediction algorithm reliably identified seizures in real time and triggered the responsive stimulation. This type of electrical stimulation dramatically suppressed seizure activity and the performance was better than the open stimulation system with fewer and shorter seizures.

Conclusions

A responsive electrical stimulation system triggered by the phase synchronisation prediction is able to significantly suppress seizures.

Significance

Responsive electrical stimulation could achieve superior treatment performance and reduce power consumption and side effects.

Polarity-dependent effect of low-frequency stimulation on amygdaloid kindling in rats

BACKGROUND

Low-frequency stimulation (LFS, <5 Hz) has been proposed as an alternative option for the treatment of epilepsy. The stimulation pole, anode and cathode, may make different contributions to the anti-epileptic effect of LFS.

OBJECTIVE

To determine whether electrode polarity influences the anti-epileptic effect of LFS at the kindling focus in amygdaloid kindling rats.

METHODS

The effect of bipolar and monopolar (or unipolar) LFS at the amygdala in different polarity directions on amygdaloid kindling acquisition, kindled seizures and electroencephalogram (EEG) were tested.

RESULTS

Bipolar LFS in the same direction of polarity as the kindling stimulation but not in the reverse direction retarded kindling acquisition. Anodal rather than cathodal monopolar LFS attenuated kindling acquisition and kindled seizures. Bipolar LFS showed a stronger anti-epileptic effect than monopolar LFS. Furthermore, anodal LFS (both bipolar and monopolar) decreased, while cathodal LFS increased the power of the EEG from the amygdala; the main changes in power were in the delta (0.5-4 Hz) band, which was specifically increased during kindling acquisition.

CONCLUSIONS

Our results provide the first evidence that the effect of LFS at the kindling focus on amygdaloid kindling in rats is polarity-dependent, and this may be due to the different effects of anodal and cathodal LFS on the activity in the amygdala, especially on the delta band activity. So, It is likely that the electrode polarity, especially that for anodal current, is a key factor affecting the clinical effects of LFS on epilepsy.

Low frequency stimulation of ventral hippocampal commissures reduces seizures in a rat model of chronic temporal lobe epilepsy

PURPOSE

To investigate the effects of low frequency stimulation (LFS) of a fiber tract for the suppression of spontaneous seizures in a rat model of human temporal lobe epilepsy.

METHODS

Stimulation electrodes were implanted into the ventral hippocampal commissure (VHC) in a rat post-status epilepticus (SE) model of human temporal lobe epilepsy (n = 7). Two recording electrodes were placed in the CA3 regions bilaterally and neural data were recorded for a minimum of 6 weeks. LFS (60 min train of 1 Hz biphasic square wave pulses, each 0.1 ms in duration and 200 μA in amplitude, followed by 15 min of rest) was applied to the VHC for 2 weeks, 24 h a day.

KEY FINDINGS

The baseline mean seizure frequency of the study animals was 3.7 seizures per day. The seizures were significantly reduced by the application of LFS in every animal (n = 7). By the end of the 2-week period of stimulation, there was a significant, 90% (<1 seizure/day) reduction of seizure frequencies (p < 0.05) and a 57% reduction during the period following LFS (p < 0.05) when compared to baseline. LFS also resulted in a significant reduction of hippocampal interictal spike frequency (71%, p < 0.05), during 2 weeks of LFS session. The hippocampal histologic analysis showed no significant difference between rats that received LFS and SE induction and those that had received only SE-induction. None of the animals showed any symptomatic hemorrhage, infection, or complication.

SIGNIFICANCE

Low frequency stimulation applied at a frequency of 1 Hz significantly reduced both the excitability of the neural tissue as well as the seizure frequency in a rat model of human temporal lobe epilepsy. The results support the hypothesis that LFS of fiber tracts can be an effective method for the suppression of spontaneous seizures in a temporal lobe model of epilepsy in rats and could lead to the development of a new therapeutic modality for human patients with temporal lobe epilepsy.

Anticonvulsant effect of unilateral anterior thalamic high frequency electrical stimulation on amygdala-kindled seizures in rat

Deep brain stimulation (DBS) is an emerging treatment of epilepsy. Anterior nucleus of the thalamus (ANT) is considered to be an attractive target due to its close connection to the limbic structures and wide regions of neocortex. In this study, we examined the effect of unilateral high frequency stimulation (HFS) of the ANT on amygdala-kindled seizures in Wistar rats. When fully-kindled seizures were achieved by daily amygdala kindling, HFS (15 min train of 100 μs pulses at 200 Hz and 450-800 μA) was delivered to the ipsilateral or contralateral ANT immediately before the kindling stimulation for 15 days. HFS of the ipsilateral ANT significantly decreased the incidence of generalized seizures and the mean behavioral seizure stage and afterdischarge duration (ADD), and shortened cumulative ADD and cumulative generalized seizure duration. Furthermore, HFS of the ipsilateral ANT significantly increased the afterdischarge threshold (ADT). Our data suggest that unilateral HFS of the ANT may be an effective method of inhibiting kindled seizures by suppressing the susceptibility to seizures and generating long lasting anti-epileptic effect preventing the recurrence of kindled seizures, providing an alternative to bilateral ANT DBS for refractory epilepsy.

Low-frequency stimulation of bilateral anterior nucleus of thalamus inhibits amygdale-kindled seizures in rats

Brain stimulation with low-frequency is emerging as an alternative treatment for refractory epilepsy. The anterior nucleus thalamus (ANT) is thought to be a key structure in the circuits of seizure generation and propagation. The present study aimed to investigate the effects of low frequency stimulation (LFS) targeting ANT on amygdala-kindled seizures in Sprague-Dawley rats. Electrodes were implanted into the right basolateral amygdala and the right or bilateral ANT of Sprague-Dawley rats. When fully kindled seizures were achieved by daily electrical stimulation of the amygdala, LFS (15 min train of 0.1 ms pulses at 1 Hz and 200-500 μA) was applied to the unilateral or bilateral ANT immediately before the kindling stimulation (pre-treatment). Our study showed that LFS of the bilateral ANT significantly decreased the incidence of generalized seizures (GS) and seizure stage, as well as shortened duration of afterdischarge and GS demonstrating an inhibition of the severity of seizures. Moreover, LFS elevated the afterdischarge threshold (ADT) and GS threshold indicating an inhibition of susceptibility to seizures. On the other hand, LFS of the unilateral ANT failed to show any significance in inhibiting seizures. Our study demonstrated that bilateral LFS in ANT could significantly inhibit amygdala-kindled seizures by preventing both afterdischarge generation and propagation. It provided further evidence for clinical use of LFS in ANT.

Comparison of hippocampal Deep Brain Stimulation with high (130Hz) and low frequency (5Hz) on afterdischarges in kindled rats

Hippocampal Deep Brain Stimulation (DBS) is proposed as an experimental treatment for refractory epilepsy, but the optimal stimulation parameters are undetermined. High frequency hippocampal DBS at 130Hz is effective in both animals and patients with epilepsy. Low frequency stimulation (approximately 5Hz) is assumed to have anti-epileptic properties but the efficacy is highly debated. This animal study compares the effects of both stimulation modalities in kindled rats. Sprague Dawley rats (n=20) were fully kindled according to the Alternate Day Rapid Kindling-protocol. After a baseline kindling period, rats were divided into a high frequency group (HFS, 130Hz, n=11) and a low frequency group (LFS, 5Hz, n=9), both receiving 10 days of continuous DBS. During and after DBS, the seizure susceptibility of all rats was tested and the characteristics of the afterdischarges (ADs) were compared between both treatments. During HFS, AD threshold was higher (p<0.05) and at the stimulated site, AD latency was longer (p<0.01) than during baseline period. During LFS, a similar but smaller change was observed, but did not reach significance. The duration of the AD was not affected by either HFS or LFS. After termination of HFS, the effects on AD latency and AD threshold recovered to baseline. In conclusion, high frequency stimulation at 130Hz is more effective than LFS (5Hz) in affecting excitability in epileptic rats. This is reflected in a higher AD threshold and longer AD latency during application of stimulation.

Inhibitory transmission in locus coeruleus neurons expressing GABAA receptor epsilon subunit has a number of unique properties

Fast inhibitory synaptic transmission in the brain relies on ionotropic GABA(A) receptors (GABA(A)R). Eighteen genes code for GABA(A)R subunits, but little is known about the epsilon subunit. Our aim was to identify the synaptic transmission properties displayed by native receptors incorporating epsilon. Immunogold localization detected epsilon at synaptic sites on locus coeruleus (LC) neurons. In situ hybridization revealed prominent signals from epsilon, and mRNAs, some low beta1 and beta3 signals, and no gamma signal. Using in vivo extracellular and in vitro patch-clamp recordings in LC, we established that neuron firing rates, GABA-activated currents, and mIPSC charge were insensitive to the benzodiazepine flunitrazepam (FLU), in agreement with the characteristics of recombinant receptors including an epsilon subunit. Surprisingly, LC provided binding sites for benzodiazepines, and GABA-induced currents were potentiated by diazepam (DZP) in the micromolar range. A number of GABA(A)R ligands significantly potentiated GABA-induced currents, and zinc ions were only active at concentrations above 1 muM, further indicating that receptors were not composed of only alpha and beta subunits, but included an epsilon subunit. In contrast to recombinant receptors including an epsilon subunit, GABA(A)R in LC showed no agonist-independent opening. Finally, we determined that mIPSCs, as well as ensemble currents induced by ultra-fast GABA application, exhibited surprisingly slow rise times. Our work thus defines the signature of native GABA(A)R with a subunit composition including epsilon: differential sensitivity to FLU and DZP and slow rise time of currents. We further propose that alpha(3,) beta(1/3,) and epsilon subunits compose GABA(A)R in LC.

Low-frequency stimulation of the tuberomammillary nucleus facilitates electrical amygdaloid-kindling acquisition in Sprague-Dawley rats

Histamine plays a suppressive role in seizure. The tuberomammillary nucleus (TM) is the only locus of histaminergic neurons in the brain. To determine whether deep brain stimulation (DBS) of the TM provides protection against seizures, we tested the effects of low-frequency stimulation (LFS, 1 Hz), high frequency stimulation (HFS, 100 Hz), and electrolytic lesions of the TM on seizures generated by amygdaloid kindling, pentylenetetrazol (PTZ) and maximal electroshock (MES) in rats. LFS of TM accelerated the progression of behavioral seizure stage and increased the mean afterdischarge duration (ADD) during acquisition of amygdaloid-kindling seizures, but had no considerable anticonvulsive effect in fully kindled animals. It augmented the MES-induced seizures as well, but had no appreciable effects on PTZ-kindled seizures. In addition, both HFS and bilateral lesions of the TM exacerbated the progression of amygdaloid-kindling seizures. These results suggest that specific negative sites for DBS exist in the brain, such as the TM. This study indicates that it is crucial to choose a suitable target for DBS in the clinical treatment of epilepsy.

Low-frequency stimulation reverses kindling-induced neocortical motor map expansion

Repeated application of low-frequency stimulation can interrupt the development and progression of seizures. Low-frequency stimulation applied to the corpus callosum can also induce long-term depression in the neocortex of awake freely moving rats as well as reduce the size of neocortical movement representations (motor maps). We have previously shown that seizures induced through electrical stimulation of the corpus callosum, amygdala or hippocampus can expand the topographical expression of neocortical motor maps. The purpose of the present study was to determine if low-frequency stimulation administered to the corpus callosum could reverse the expansion of neocortical motor maps induced by seizures propagating from the hippocampus. Adult Long-Evans hooded rats were electrically stimulated in the right ventral hippocampus, twice daily until 30 neocortical seizures were recorded. Subsequently, low-frequency stimulation was administered to the corpus callosum once daily for 20 sessions. High-resolution intracortical microstimulation was then utilized to derive forelimb-movement representations in the left (un-implanted) sensorimotor neocortex. Our results show that hippocampal seizures result in expanded motor maps and that subsequent low-frequency application can reduce the size of the expanded motor maps. Low-frequency stimulation may be an effective treatment for reversing seizure-induced reorganization of brain function.

Low-frequency stimulation of cerebellar fastigial nucleus inhibits amygdaloid kindling acquisition in Sprague–Dawley rats

Low-frequency stimulation (LFS) of the kindling focus or the piriform cortex inhibits kindling epileptogenesis, but whether LFS of brain targets outside the limbic system has anticonvulsive actions remain unknown. The current study was designed to investigate the effect of LFS of the cerebellar fastigial nucleus (FN) on seizure progression induced by amygdaloid kindling. Stimulation at 1 Hz (15-min train of 0.1-ms pulses, 100 muA), but not at 3 Hz, in the ipsilateral FN immediately after the daily kindling stimulus (1-s train of 1-ms pulses at 60 Hz and 100-300 muA) significantly inhibited the seizure stage and afterdischarge duration in kindling acquisition. Neither 1 Hz nor 3 Hz stimulation of the contralateral FH had any significant effect. It is interesting that delaying delivery (immediately after the cessation of afterdischarge) of LFS in the ipsilateral FN accelerated the rate of kindling acquisition compared to controls. Our study suggests that LFS of targets outside the limbic system, such as the FN, may have a significant anti-epileptogenic action, and the effects of LFS depend on the frequency and timing of stimulation.

Low- and high-frequency electric cortical stimulation suppress the ferric chloride-induced seizures in rats

The clinic treatment of epilepsy with epileptic foci overlapped with eloquent cortex is not satisfactory. In this study we investigated the direct effects of low- and high-frequency electric cortical stimulation (ECS) on ferric chloride-induced seizures in the experimental rats. Results showed that spontaneous seizures were observed in all rats during the EEG recording after the intracortical injection of ferric chloride solution into left sensorimotor cortex. One-hertz or 100-Hz ECS with 0.3 ms duration and 0.1 mA amplitude square pulses in 1h on the cortical lesioned area significantly decreased the number of seizures compared with that of the non-stimulation control group. The mean duration time of seizures in 1-Hz or 100-Hz groups was apparently shorter than that in the control group. In brief, this study showed that both low- and high-frequency ECS suppressed the seizures induced by ferric chloride in rats, indicating their potential treatment effects on epilepsy in clinic.

Effect of low frequency stimulation of perforant path on kindling rate and synaptic transmission in the dentate gyrus during kindling acquisition in rats

Low frequency stimulation (LFS) has an inhibitory effect on kindling acquisition. In the present study the effect of the perforant path LFS on induction of rapid perforant path kindled seizures and synaptic transmission in the dentate gyrus was investigated. Animals were kindled by perforant path stimulation in a rapid kindling manner (12 stimulations per day). In one group of animals LFS (0.1 ms pulse duration at 1 Hz, 200 pulses, and 50-150 microA) was applied to perforant path, immediately after termination of each rapid kindling stimulation. Application of LFS significantly retarded the kindling acquisition and increased the number of stimulations to achieved different kindled seizure stages. LFS also prevented an increment in the slope of field excitatory postsynaptic potentials and population spike amplitude during kindling. In addition, LFS significantly reduced the marked increase in early (10-50 ms intervals) and late (300-1000 ms intervals) paired-pulse depression induced by kindling. According to obtained results, it may be suggested that LFS of perforant path has a significant antiepileptogenic effect through inhibition of synaptic transmission in dentate gyrus. Meanwhile, LFS prevents an increase in the paired-pulse depression during kindling acquisition.

Effect of focal low-frequency stimulation on amygdala-kindled afterdischarge thresholds and seizure profiles in fast- and slow-kindling rat strains

PURPOSE

To determine whether low-frequency, 1-Hz sine-wave stimulation (LFS) applied to a fully kindled amygdala focus would show antiepileptic properties in rats that were either naturally seizure prone (Fast) or seizure resistant (Slow).

METHODS

Normal twisted and/or "spanning" bipolar electrode configurations were implanted in the amygdalae of adult male Fast and Slow rats. In experiment one, rats were kindled daily to stage-5 levels through one electrode type until stable afterdischarge thresholds (ADTs) were obtained. Next, LFS was applied through the kindled electrode, and ADTs were redetermined 1 min later, and daily for a week, without reapplying the LFS. In experiment two, a single, normal bipolar kindling electrode was implanted in the amygdala and centered between two poles of a spanning electrode. After stable kindled ADTs were obtained, LFS was applied to the amygdala "area" through the spanning electrode. ADTs were redetermined at the kindled electrode as earlier.

RESULTS

LFS through the kindling electrode had no effect on ADTs 1 min later, but the ADTs increased dramatically 24 h later and then slowly returned to baseline over days. In experiment two, LFS applied through the nonkindled spanning electrode also showed a small but significant threshold elevation at the interposing kindled electrode. Importantly, no obvious neuropathology was associated with these LFS treatments.

CONCLUSIONS

LFS applied directly to the kindled network has significant threshold-elevating properties that are less evident when applied to the "general area"; here LFS must be delivered through a larger surface area and/or at higher intensity.

Behavioral effects of high frequency electrical stimulation of the hippocampus on electrical kindling in rats

Experiments were designed to evaluate the effects of high frequency electrical stimulation (HFS) applied in ventral hippocampus during the hippocampal kindling process, as well as on the expression of fully kindled seizures and the refractoriness for subsequent convulsions during their postictal period. Male Wistar rats, stereotactically implanted in both ventral hippocampus, received daily bilateral HFS (pulses of 60 micros width at 130 Hz at subthreshold current intensity) during 1h immediately after each kindling stimulation (1s train of 60 Hz biphasic square waves, each 1 ms) during 40 days or until the kindled state was achieved. Rats were classified as follows: (a) Responder animals, who required low current intensity for HFS (208+/-38.2 microA), did not show progress of the kindling process and remained in stages II and III seizures. (b) Nonresponders rats, in which the current intensity for HFS was higher (434.5+/-51.7 microA), developed the kindling process as the kindling control group. When HFS was applied before the kindling stimulation in fully kindled rats, animals presented a reduced expression of the fully kindled seizures (nonresponders animals) and an enhanced refractoriness for subsequent seizures during the postictal period (kindling control and nonresponder animals). There was no correlation between the area where the HFS was applied and the effects induced. It was concluded that HFS at 130 Hz in ventral hippocampus is able to modify the epileptogenesis induced by the hippocampal kindling process and the refractoriness to subsequent seizures during the postictal period in rats.

Unilateral low-frequency stimulation of central piriform cortex delays seizure development induced by amygdaloid kindling in rats

Low-frequency stimulation of the kindling site interferes with the course of kindling epileptogenesis. The present study examined the effect of unilateral low-frequency stimulation of the central piriform cortex on seizure development induced by amygdaloid kindling in rats. The ipsilateral or contralateral central piriform cortex received low-frequency stimulation (15 min train of 0.1 ms pulses at 1 Hz and 50-150 muA) immediately after termination of once daily kindling stimulation (2 s train of 1 ms pulses at 60 Hz and 150-300 microA) in the right amygdala for 30 days. Low-frequency stimulation of either the ipsilateral or contralateral central piriform cortex significantly suppressed the progression of seizure stages and reduced afterdischarge duration throughout the course of amygdaloid kindling. The marked suppression induced by low-frequency stimulation of the central piriform cortex on either side was predominantly due to the significant retardation of progression from stage 0 to stage 1 and stage 3 to stage 4 seizures. In addition, the suppressive effect of low-frequency stimulation did not disappear when the stimulation was stopped; it could persist for at least 10 days. These findings indicate that brain areas other than the kindling focus, such as the central piriform cortex on both sides, can also be used as reasonable targets for low-frequency stimulation to retard seizure development induced by amygdaloid kindling. Secondly, like the ipsilateral central piriform cortex, the contralateral central piriform cortex may also participate in the progression and secondary generalization of focal seizures. The study suggests that unilateral low-frequency stimulation of the central piriform cortex may have a significant antiepileptogenic effect, and may be helpful for exploring effective and long-lasting therapies for human temporal lobe epilepsy.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.