Lack of effect of intranigral transplants of a GABAergic cell line on absence seizures

Not Part of the Temporal Lobe, but Still of Importance? Substantia Nigra and Subthalamic Nucleus in Epilepsy

The most researched brain region in epilepsy research is the temporal lobe, and more specifically, the hippocampus. However, numerous other brain regions play a pivotal role in seizure circuitry and secondary generalization of epileptic activity: The substantia nigra pars reticulata (SNr) and its direct input structure, the subthalamic nucleus (STN), are considered seizure gating nuclei. There is ample evidence that direct inhibition of the SNr is capable of suppressing various seizure types in experimental models. Similarly, inhibition via its monosynaptic glutamatergic input, the STN, can decrease seizure susceptibility as well. This review will focus on therapeutic interventions such as electrical stimulation and targeted drug delivery to SNr and STN in human patients and experimental animal models of epilepsy, highlighting the opportunities for overcoming pharmacoresistance in epilepsy by investigating these promising target structures.

Ultrastructural GABA immunogold labeling in the substantia nigra pars reticulata of kindled genetic absence epilepsy rats

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is a well-known animal model of absence epilepsy and they are resistant to electrical kindling stimulations. The present study aimed to examine possible differences in gamma-aminobutyric acid (GABA) levels and synapse counts in the substantia nigra pars reticulata anterior (SNRa) and posterior (SNRp) regions between GAERS and Wistar rats receiving kindling stimulations. Animals in the kindling group either received six stimulations in the amygdala and had grade 2 seizures or they were kindled, having grade five seizures. Rats were decapitated one hour after the last stimulation. SNR regions were obtained after vibratome sectioning of the brain tissue. GABA immunoreactivity was detected by immunogold method and synapses were counted. Sections were observed by transmission electron microscope and analyzed by Image J program. GABA density in the SNRa region of fully kindled GAERS and Wistar groups increased significantly compared to that of their corresponding grade 2 groups. The number of synapses increased significantly in kindled and grade 2 GAERS groups, compared to kindled and grade 2 Wistar groups, respectively, in the SNRa region. GABA density in the SNRp region of kindled GAERS group increased significantly compared to that of GAERS grade 2 group. In the SNRp region, both kindled and grade 2 GAERS groups were found to have increased number of synapses compared to that of GAERS control group. We concluded that both SNRa and SNRp regions may be important in modulating resistance of GAERS to kindling stimulations.

The neurotoxic effects of prenatal gabapentin and oxcarbazepine exposure on newborn rats

AIM

Teratogenicity is a problematic issue for pregnant women because of X-ray radiation, drugs, and genetic and unknown variables. First-generation antiepileptic drugs (AED) like valproic acid are well-known teratogens for developing fetuses. However, their usage is necessary in order to prevent maternal seizures. The underlying mechanism of birth defects associated with AED exposure remains unclear and information about the neurotoxic effects of prenatal exposure to AED is still limited. Oxcarbazepine (OXC) and gabapentin (GBP) are second-generation AED. It still remains unclear how much these drugs are safe during pregnancy. This study aimed to investigate whether any neurotoxic effect of OXC and GBP in utero exposure on the developing brain.

METHODS

Eighteen pregnant Wistar albino rats were divided into six groups. The first group was exposed to OXC at 100 mg/kg/day, the second to GBP at 50 mg/kg/day, and third to saline (0.9% NaCl) at 1.5 ml/day between the first and the fifth days of gestation. The same procedure was applied at the same dosages between the 6th and the 15th days of gestation for the 2nd three groups. Five female offspring (total n = 30, 45 days old) were taken from each group and stereological methods were applied in order to analyze the total and dopaminergic neuron number of the substantia nigra pars compacta (SNc).

CONCLUSION

The result is that the OXC and GBP exposure at different gestational periods may not give rise to congenital malformation and it appears that the GBP exposure during the organogenesis period proliferatively affects the total number of neurons.

A Molecular Approach to Epilepsy Management: from Current Therapeutic Methods to Preconditioning Efforts

Epilepsy is the most common and chronic neurological disorder characterized by recurrent unprovoked seizures. The key aim in treating patients with epilepsy is the suppression of seizures. An understanding of focal changes that are involved in epileptogenesis may therefore provide novel approaches for optimal treatment of the seizure. Although the actual pathogenesis of epilepsy is still uncertain, recently growing lines of evidence declare that microglia and astrocyte activation, oxidative stress and reactive oxygen species (ROS) production, mitochondria dysfunction, and damage of blood-brain barrier (BBB) are involved in its pathogenesis. Impaired GABAergic function in the brain is probably the most accepted hypothesis regarding the pathogenesis of epilepsy. Clinical neuroimaging of patients and experimental modeling have demonstrated that seizures may induce neuronal apoptosis. Apoptosis signaling pathways are involved in the pathogenesis of several types of epilepsy such as temporal lobe epilepsy (TLE). The quality of life of patients is seriously affected by treatment-related problems and also by unpredictability of epileptic seizures. Moreover, the available antiepileptic drugs (AED) are not significantly effective to prevent epileptogenesis. Thus, novel therapies that are proficient to control seizure in people who are suffering from epilepsy are needed. The preconditioning method promises to serve as an alternative therapeutic approach because this strategy has demonstrated the capability to curtail epileptogenesis. For this reason, understanding of molecular mechanisms underlying brain tolerance induced by preconditioning is crucial to delineate new neuroprotective ways against seizure damage and epileptogenesis. In this review, we summarize the work to date on the pathogenesis of epilepsy and discuss recent therapeutic strategies in the treatment of epilepsy. We will highlight that novel therapy targeting such as preconditioning process holds great promise. In addition, we will also highlight the role of gene reprogramming and mitochondrial biogenesis in the preconditioning-mediated neuroprotective events.

Glutamatergic Excitation and GABA Release from a Transplantable Cell Line

The cell line M213-2O CL-4 was derived from cell line M213-2O and further modified to express human glutamate decarboxylase (hGAD-67), the enzyme that synthesizes GABA. Brain transplants of this cell line in animal models of epilepsy have been shown to modulate seizures. However, the mechanisms that underlie such actions are unknown. The purpose of the present study was to characterize this cell line and its responsiveness to several depolarizing conditions, in order to better understand how these cells exert their effects. Intracellular GABA levels were 34-fold higher and GAD activity was 16-fold higher in clone M213-2O CL-4 than in M213-2O. Both cell lines could take up [3H]GABA in vitro, and this uptake was prevented by nipecotic acid. By combining GABA release measurements and calcium imaging in vitro, we found that high extracellular K+, zero Mg2+, or glutamate activated M213-2O CL-4 cells and resulted in GABA release. The response to glutamate appeared to be mediated by AMPA/NMDA-like receptors. High KCl-induced GABA release was prevented when a Ca2+-free Krebs solution was used, suggesting an exocytotic-like mechanism. These results indicate that the cell line M213-2O CL-4 synthesizes, releases, and takes up GABA in vitro, and can be activated by depolarizing stimuli.