Low-frequency stimulation of the external globus palladium produces anti-epileptogenic and anti-ictogenic actions in rats

The therapeutic mechanism of epilepsy seizures in different target areas: Research on a theoretical model

BACKGROUND

The selection of optimal target areas in the surgical treatment of epilepsy is always a difficult problem in medicine.

OBJECTIVE

We employed a theoretical calculation model to explore the control mechanism of seizures by an external voltage stimulus acting in different nerve nuclei.

METHODS

Theoretical analysis and numerical simulation were combined.

RESULTS

The globus pallidus, excitatory pyramidal neurons, striatal D1 neurons, thalamic reticular nucleus and specific relay nuclei were selected, we analyzed that the electrical stimulation has different effects in these target areas.

CONCLUSIONS

The data selected were reasonable in study, the results may give a theoretical support for similar studies in clinical.

Regulation and control roles of the basal ganglia in the development of absence epileptiform activities

Absence epileptiform activities are traditionally considered to be primarily induced by abnormal interactions between the cortical and thalamic neurons, which form the thalamocortical circuit in the brain. The basal ganglia, as an organizational unit in the brain, has close input and output relationships with the thalamocortical circuit. Although several studies report that the basal ganglia may participate in controlling and regulating absence epileptiform activities, to date, there have been no studies regarding whether the basal ganglia directly cause absence epileptiform activities. In this paper, we built a basal ganglia-corticothalamic network model to determine the role of basal ganglia in this disease. We determined that absence epileptiform activities might be directly induced by abnormal coupling strengths on certain pivotal pathways in the basal ganglia. These epileptiform activities can be well controlled by the coupling strengths of three major pathways that project from the thalamocortical network to the basal ganglia. The results implied that the substantia nigra pars compacta (SNc) can be considered to be the effective treatment target area for inhibiting epileptiform activities, which supports the observations of previous studies. Particularly, as a major contribution of this paper, we determined that the final presentation position of the epileptic slow spike waves is not limited to the cerebral cortex; these waves may additionally appear in the thalamus, striatal medium spiny neurons, striatal fast spiking interneuron, the SNc, subthalamic nucleus, substantia nigra pars reticulata and globus pallidus pars externa. In addition, consistent with several previous studies, the delay in the network was observed to be a critical factor for inducing transitions between different types of absence epileptiform activities. Our new model not only explains the onset and control mechanism but also provides a unified framework to study similar problems in neuron systems.

Mode of seizure inhibition by sodium channel blockers, an SV2A ligand, and an AMPA receptor antagonist in a rat amygdala kindling model

PURPOSE

A number of antiepileptic drugs (AEDs) with a variety of modes of action, are effective in treating focal seizures. Several AEDs, such as perampanel (PER), levetiracetam (LEV), lacosamide (LCM), lamotrigine (LTG), and carbamazepine (CBZ), have been shown to elevate the seizure threshold in kindling models. These AEDs are clinically effective, but differences exist in the anti-seizure profiles of drugs with similar modes of action. Therefore, we hypothesized that there are differences in how these AEDs affect seizures. Here, we evaluated the effects of AEDs on various seizure parameters in a rat amygdala kindling model upon stimulation at the after-discharge threshold (ADT) and at three-times the ADT (3xADT) to characterize the differences in the effects of these AEDs.

METHODS

PER, LEV, LCM, LTG, CBZ, or vehicle was administered intraperitoneally to fully kindled rats. Changes in Racine seizure score, after-discharge duration (ADD), and latency to Racine score 4 generalized seizure (S₄L) were measured to assess differences in the modes of seizure inhibition among the AEDs. Stimulation at 3xADT was used to eliminate the influence of any AED-induced elevation of the seizure threshold on these parameters.

RESULTS

PER, LEV, LCM, LTG, and CBZ significantly reduced the seizure score from Racine score 5 after stimulation at the ADT; this effect was lost with LEV and LTG after stimulation at 3xADT. PER and LEV significantly shortened the ADD when the seizure focus was stimulated at the ADT, whereas LCM, LTG, and CBZ did not. LEV, LCM, LTG, and CBZ failed to shorten the ADD upon stimulation at 3xADT. PER dose-dependently and significantly increased S₄L, even at doses that were ineffective for seizure score reduction, after stimulation at both the ADT and 3xADT. LEV and LTG significantly increased S₄L after stimulation at the ADT, whereas LCM and CBZ did not significantly increase S₄L at any of the doses tested.

CONCLUSIONS

The sodium channel blockers (LCM, LTG, and CBZ) appeared to act by elevation of the seizure threshold via reduction of neuronal excitability, whereas the AMPA receptor antagonist (PER) and the SV2A ligand (LEV), as well as LTG, exerted their effects through the weakening of synaptic transmission in neuronal networks at the seizure focus. Maintenance of the effect of PER even at 3xADT suggests direct and strong modulation of excitatory synaptic transmission by PER, both at the focus and along the seizure propagation route. These findings may provide further rationale for usage of AEDs beyond their respective modes of action.

The role of the basal ganglia in the control of seizure

Epilepsy is a network disorder and each type of seizure involves distinct cortical and subcortical network, differently implicated in the control and propagation of the ictal activity. The role of the basal ganglia has been revealed in several cases of focal and generalized seizures. Here, we review the data that show the implication of the basal ganglia in absence, temporal lobe, and neocortical seizures in animal models (rodent, cat, and non-human primate) and in human. Based on these results and the advancement of deep brain stimulation for Parkinson's disease, basal ganglia neuromodulation has been tested with some success that can be equally seen as promising or disappointing. The effect of deep brain stimulation can be considered promising with a 76% in seizure reduction in temporal lobe epilepsy patients, but also disappointing, since only few patients have become seizure free and the antiepileptic effects have been highly variable among patients. This variability could probably be explained by the heterogeneity among the patients included in these clinical studies. To illustrate the importance of specific network identification, electrophysiological activity of the putamen and caudate nucleus has been recorded during penicillin-induced pre-frontal and motor seizures in one monkey. While an increase of the firing rate was found in putamen and caudate nucleus during pre-frontal seizures, only the activity of the putamen cells was increased during motor seizures. These preliminary results demonstrate the implication of the basal ganglia in two types of neocortical seizures and the necessity of studying the network to identify the important nodes implicated in the propagation and control of each type of seizure.

Low-frequency stimulation of the primary focus retards positive transfer of secondary focus

Positive transfer of secondary focus (PTS) refers to new epileptogenesis outside the primary focus and is minimally controlled by existing treatments. Low-frequency stimulation (LFS) has benefits on the onset of epilepsy and epileptogenesis. However, it's unclear whether LFS can retard the PTS in epilepsy. Here we found that PTS at both contralateral amygdala and ipsilateral hippocampus were promoted after the primary focus was fully kindled in rat kindling model. The promotion of PTS at the mirror focus started when the primary kindling acquisition reached focal seizures. LFS retarded the promotion of PTS when it was applied at the primary focus during its kindling acquisition, while it only slightly retarded the promotion of PTS when applied after generalized seizures. Meanwhile, we found the expression of potassium chloride cotransporter 2 (KCC2) decreased during PTS, and LFS reversed this. Further, the decreased expression of KCC2 was verified in patients with PTS. These findings suggest that LFS may be a potential therapeutic approach for PTS in epilepsy.