Anticonvulsant effects after grafting of rat, porcine, and human mesencephalic neural progenitor cells into the rat subthalamic nucleus.

Cell transplantation based therapy is a promising strategy for treating intractable epilepsies. Inhibition of the subthalamic nucleus (STN) or substantia nigra pars reticulata (SNr) is a powerful experimental approach for remote control of different partial seizure types, when targeting the seizure focus is not amenable. Here, we tested the hypothesis that grafting of embryonic/fetal neural precursor cells (NPCs) from various species (rat, human, pig) into STN or SNr of adult rats induces anticonvulsant effects. To rationally refine this approach, we included NPCs derived from the medial ganglionic eminence (MGE) and ventral mesencephalon (VM), both of which are able to develop a GABAergic phenotype. All VM- and MGE-derived cells showed intense migration behavior after grafting into adult rats, developed characteristics of inhibitory interneurons, and survived at least up to 4 months after transplantation. By using the intravenous pentylenetetrazole (PTZ) seizure threshold test in adult rats, transient anticonvulsant effects were observed after bilateral grafting of NPCs derived from human and porcine VM into STN, but not after SNr injection (site-specificity). In contrast, MGE-derived NPCs did not cause anticonvulsant effects after grafting into STN or SNr (cell-specificity). Neither induction of status epilepticus by lithium-pilocarpine to induce neuronal damage prior to the PTZ test nor pretreatment of MGE cells with retinoic acid and potassium chloride to increase differentiation into GABAergic neurons could enhance anticonvulsant effectiveness of MGE cells. This is the first proof-of-principle study showing anticonvulsant effects by bilateral xenotransplantation of NPCs into the STN. Our study highlights the value of VM-derived NPCs for interneuron-based cell grafting targeting the STN.

Continuous bilateral infusion of vigabatrin into the subthalamic nucleus: Effects on seizure threshold and GABA metabolism in two rat models.

The subthalamic nucleus (STN) plays a crucial role as a regulator of basal ganglia outflow but also influences the activity of cortical and limbic structures, so that it is widely used as a therapeutic target in different brain diseases, including epilepsy. In addition to electrical stimulation of the STN, targeted delivery of anti-seizure drugs to the STN may constitute an alternative treatment approach in patients with pharmacoresistant epilepsy. In the present experimental study, we investigated the anti-seizure and adverse effects of chronic infusion of vigabatrin into the STN of rats. Vigabatrin is a clinically approved anti-seizure drug, which acts by increasing brain GABA levels by irreversibly inhibiting GABA-aminotransferase (GABA-T). Based on functional and neurochemical effects of acute STN microinjection, doses for continuous infusion were calculated and administered, using an innovative drug infusion technology. Bilateral infusion of only 10µg/day vigabatrin over 3weeks into the STN resulted in an almost complete inhibition of GABA-T and 4-fold increase in GABA in the target region, which was associated with a significant increase in seizure threshold, determined once weekly by i.v. infusion of pentylenetetrazole (PTZ). Lower doses or unilateral infusion were less effective, both on PTZ seizures and on kindled seizures. Bilateral infusion into substantia nigra pars reticulata was less effective and more toxic than STN infusion. In part of the rats, tolerance to the anti-seizure effect developed. The data demonstrate that chronic administration of very low, nontoxic doses of vigabatrin into STN is an effective means of increasing local GABA concentrations and seizure threshold.

Different preparations, doses, and treatment regimens of cyclosporine A cause adverse effects but no robust changes in seizure thresholds in rats.

UNLABELLED: Neuronal transplantation is a promising experimental treatment approach for intractable epilepsies, but rejection of porcine or human cells in rodent epilepsy models requires adequate immunosuppression to enable long-term survival of xenografts. The commonly used immunosuppressive drug cyclosporine A (CsA) itself was suggested to affect seizure thresholds. However, putative pro- or anticonvulsant effects of CsA have not yet been sufficiently explored in a direct comparison study involving different preparations, dosages, and application routes. We therefore comprehensively investigated the effects of acute versus chronic treatment using different dosages (5mg/kg, 10mg/kg), application routes (i.p., s.c.), and preparations of CsA (pure substance solved in polyethoxylated castor oil and a ready-to-use drug additionally containing ethanol) on acute seizure thresholds in rats in the pentylenetetrazole seizure threshold test and verified the most harmless protocol in the chronic amygdala-kindling model for temporal lobe epilepsy. None of the CsA treatment regimens induced acute changes of seizure thresholds. Chronic CsA treatment also did not robustly change seizure thresholds. As evaluated by whole blood analyses, bioavailability of CsA was significantly higher after i.p. application of the ready-to-use preparation compared to the pure substance and compared to s.c. APPLICATION: Observed adverse effects differed between CsA treatment regimens and included reversible diarrhea, lowered body temperature, and tremor, the latter two of which were also induced by vehicle injections containing ethanol and/or polyethoxylated castor oil. Our data suggest that chronic treatment (2 weeks) with 10mg/kg CsA injected i.p. in the ready-to-use preparation is an appropriate protocol for use in neural transplantation in epilepsy research applying the presently used rat models. Transplantation studies in experimental epilepsy research require a careful assessment of putative CsA effects on seizure thresholds in the specific experimental settings to be used.

Vigabatrin for focal drug delivery in epilepsy: bilateral microinfusion into the subthalamic nucleus is more effective than intranigral or systemic administration in a rat seizure model.

Vigabatrin is a rationally developed antiepileptic drug, which acts by increasing GABA levels in the brain by irreversibly inhibiting GABA degradation. However, its clinical use in epilepsy is restricted by severe side effects, including vision loss, which is thought to be a consequence of drug exposure of the retina and nonepileptic brain regions. Targeted delivery into brain regions involved in seizure generation and propagation would overcome this problem. Previous studies in rat models of seizures or epilepsy have shown that anticonvulsant effects can be achieved by bilateral microinjection of vigabatrin into the substantia nigra pars reticulata (SNr), a basal ganglia output structure that plays an important role in the modulation of seizures. In the present study, we compared the anticonvulsant efficacy of vigabatrin after systemic and intranigral administration in a rat model, in which seizure susceptibility can be determined by timed intravenous infusion of pentylenetetrazol (PTZ) before and after drug injection in individual animals. Furthermore, because the subthalamic nucleus (STN) plays a crucial role as a regulator of basal ganglia outflow by providing excitatory glutamatergic input into the two output nuclei of the basal ganglia, SNr and entopeduncular nucleus, we evaluated the effects of bilateral focal delivery of vigabatrin into the STN on PTZ seizure threshold. A significant increase in seizure threshold was observed following systemic (i.p.) administration of high (600 or 1200 mg/kg) doses of vigabatrin. Bilateral microinjection of vigabatrin (10 µg) into either the anterior or posterior SNr also increased seizure threshold, but less markedly than systemic treatment. In contrast, focal delivery into the STN increased seizure threshold more markedly than either intranigral or systemic administration of vigabatrin. Furthermore, focal inhibition of STN was not associated with the severe adverse effects associated with systemic treatment. The data demonstrate that vigabatrin is an interesting substance for focal drug delivery in epilepsy and may be advantageous compared to more commonly evaluated compounds such as muscimol.